UNDERSTANDING THE ECOHYDROLOGICAL IMPACTS AND MANAGEMENTS IMPLICATIONS OF CLIMATE CHANGE IN NORTHERN HARDWOOD FOREST ECOSYSTEMS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: TERMINATED
• Funding Source: MCINTIRE-STENNIS
• Reporting Frequency: Annual
• Accession No.: 1013351
• Project No.: NH00091-M
• Project Start Date: Oct 1, 2017
• Project End Date: Sep 30, 2020

Project Director
Asbjornsen, H.

Recipient Organization
UNIVERSITY OF NEW HAMPSHIRE
51 COLLEGE RD SERVICE BLDG 107
DURHAM,NH 03824

Performing Department
Natural Resources and the Environment

Non Technical Summary
Water is expected to become an ever-increasing critical resource in the northeastern U.S., as the frequency and intensity of extreme precipitation events (both extreme droughts and wet spells) has already increased and this trend is expected to continue under future climate change projections. This project will substantially enhance scientific understanding the impacts of climate change on forest ecosystems, the degree of resilience and vulnerability of different tree species, and interactions with other critical drivers of environmental change (e.g., pests and pathogens, nutrient availability). Additionally, alternative agroforesty (e.g., silvopasture) and forest farming (e.g., diversified syrup production) practices will be evaluated for their potential to optimize trade-offs among multiple ecosystem services (e.g., water supply, flood control, flow regulation, carbon sequestration), while enhancing resilience to environmental change. The findings will provide a basis for making policy and management recommendations for how society can best mitigate, adapt, and prepare for such changes, particular in terms of sustainable management of natural resources and ecosystem service provisioning. The following outcomes are expected from the proposed work: (1) improved understanding by managers and policy makers about the potential impacts of environmental change on New Hampshire's forests and alternative strategies for mitigating these impacts through management and policy interventions; (2) increased adoption by managers and landowners of sustainable land use practices that offer greater resilience to environmental change while maintaining diverse ecological, social, and economic values; (3) generation of a cadre of young professionals and scientists in the natural resource fields capable of effectively tackling the challenges of managing New Hampshire's landscapes for healthy forests and sustainable water resources; and (4) increased awareness among members of the general public about the importance of changing climate, droughts, pathogens, and other environmental drivers for the state's forests and people, and possible strategies for adapting to these changes.

Animal Health Component

0%

Research Effort Categories

Basic

50%

Applied

50%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
123	0320	1070	100%

Knowledge Area
123 - Management and Sustainability of Forest Resources;

Subject Of Investigation
0320 - Watersheds;

Field Of Science
1070 - Ecology;

Keywords

climate change

ecosystem services

drought

non-timber forest products

resilence

Goals / Objectives
The overarching long-term goal for this new NHAES project is to further enhance understanding of the long-term trends, drivers, and ecological consequences of climate change impacts on the ecohydrology and health of natural and managed northern forest ecosystems.There are four specific objectives that will contribute to achieving this long-term goal:Identify the underlying biological and physical controls explaining observed trends in evapotranspiration and water yield, and assess the implications for key ecosystem services and climate change impacts.Assess how interactions between climate and pathogens influence forest productivity, water use dynamics, and forest health, and evaluate the potential for using silvicultural thinnings to enhance the resilience of forests to pathogens.Assess the impacts of extreme droughts and wet spells on the health and ecohydrological function of northern forests and simulate future impacts of altered precipitation regimes.Evaluate the ecohydrological impacts, resilience to climate variability, and ecosystem service trade-offs of diverse agroforestry and forest farming systems (e.g., silvopasture, syrup production) as a basis for developing sustainable management strategies.

Project Methods
Objective #1. We are using dendrochronology and stable isotope techniques to assess the effects of climate variability and changing atmospheric [CO2] on plant growth and water use efficiency (WUE) in relation to evapotranspiration trends. Tree cores were collected with increment borers from 10-20 individuals (3 cores per tree) of three dominant tree species at each of the 7 study sites. Ring widths were measured to the nearest 0.01 mm, cross-dated, and converted to basal area increment (BAI) for total, earlywood, and latewood ring width. Individual rings from each core were cut into earlywood and latewood segments under a stereozoom boom arm microscope (10-40X), and the three samples from each tree pooled into a single sample for stable isotope analysis. Cellulose was be extracted from each bulk wood sample and analyzed for δ13C and δ18O on aFinningan delta-V isotope ratio mass spectrometer at the UNH Stable Isotope Laboratory UNH. Regression analysis will be used to examine the relationship between iWUE and meteorological variables (precipitation, temperature, evapotranspiration (ET), vapor pressure (VPD), solar radiation) and increasing atmospheric [CO2]. Data generated from the above analyses will be integrated to examine the relationship between ET trends, BAI, water use efficiency, and regional distribution of nitrogen deposition across the study sites.Objective #2. This work is being conducted at two white pine stands located at the Fox State Forest in Hillsborough, NH and the UNH Bearcamp property in Ossipee, NH. The plots within these two sites are each composed of 6 acres dominated by eastern white pine, and uses a blocked experimental design (n=2) consisting of three experimental plots: a low thinning targeting a residual basal area of 60 ft2/ac, a high thinning targeting a residual basal area of 100 ft2/ac, and a paired control plot (no tree removal). During June 2015 while White Pine Needle Damage (WPND) symptoms were present we conducted a pre-treatment forest inventory and established a permanent network of variable-point sampling subplots using a BAF 20 angle gauge prism. At each inventory subplot we measured tree diameter, height, live crown ratio, crown diameter, crown light exposure, crown transparency, crown dieback, and WPND severity. Both treatment sites were thinned in February 2016. Dendrometer bands are used to obtain high-resolution diameter growth measurements on a subset of trees, and all pre-treatment measurements will be continued. Quantitative measure of defoliation caused by WPND will be obtained with leaf area index measurements using a LAI-2200 Plant Canopy Analyzer. Rainfall, soil moisture, and within-canopy temperature and relative humidity will also be monitored. Leaf gas exchange measurements will be collected using a Li-Cor Portable Photosynthesis System.Objective #3. Drought experiments (50% throughfall removal) have been established at two sites: UNH's Thompson Farm (Durham, NH) and the Hubbard Brook Experimental Forest (Woodstock, NH). The following field measurements are being conducted: leaf-level physiological responses (e.g., gas exchange, pre-dawn moisture potential, composition of δ13C and δ18O stable isotopes, foliar concentration of N, P, and Ca), sapflow, tree growth and productivity, litter decomposition, and root biomass and growth (sequential root cores). We will collect 8-10 branches from each sample tree at midday and the next morning to determine xylem-specific hydraulic conductivity (Ks), percent loss of conductivity (PLC), and PLC-recovery. Vulnerability curves will be determined using the bench dehydration technique, taking care to relax stem xylem tensions prior to excision of the measurement sample. Pre-dawn and mid-day plant water potential of leaves (YL-pd, YL-md) will be measured every three weeks on excised leaves from sample trees being monitored for sapflow (n=3) using a pressure chamber. Non-structural carbohydrates (NSCs) will be determined for the same three sample trees to assess patterns of carbon allocation in response to drought. Briefly, leaves, branches, and roots will be collected three times each year and brought back to UNH. Plant samples will be ground, incubated with amyloglucosidase to break down total NSC to glucose, and NSC concentration determined photometrically with a spectrophotometer. An additional aliquot will be centrifuged and used to determine the concentration of soluble sugars. Starch will be calculated as total NSC minus soluble sugars. We will use the data to parameterize the "Multi-Array Evaporation Soil-Plant-Atmosphere" model (MAESPA) to examine linkages between photosynthesis, transpiration, and tree growth.Objective #4.Silvopasture agroforestry systems. Three experimental treatments were conducted on one hectare plots at UNH's Organic Dairy Research Farm: (1) forest conversion to open pasture, and (2) to silvopasture, and (3) reference (unmanaged) forest, to assess impacts on hydrologic services (e.g., water supply, hydrologic regulation). Water yield is being determined using ecophysiological and hydrological measurements collected over a three-week period at each site during the peak growing season (July-August), as follows: Tree transpiration (T) is measured using the heat ratio (HRM) sapflow method, for dominant species at each site (~12 trees/site) across a range of diameters. Interception (I) will be determined as the difference between P and net P (throughfall, TF plus stemflow, SF). TF is measured daily using 30 funnel gauges in each site. SF will be measured on 6-8 individuals of the dominant species, using collar-type gauges. For the open pasture sites, soil evaporation (E) will be determined gravimetrically using soil lysimeters. Surface soil water content, meteorological conditions, and below-canopy climate measurements will be measured continuously. Soil hydraulic properties at the plot scale will be assessed by quantifying soil infiltration, hydraulic conductivity (Ksat), and soil penetration resistance using direct field measurements. Surface soil infiltration will be measured with tension infiltrometers at 20 locations within each site. Ksat profiles will be obtained at 10 locations within each site, using Guelph permeameters at three soil depths (0-15, 15-30, 30-50 cm). Soil penetration resistance will be measured with a Penetrometer (< 100 cm; SoilMoisture Equipment Corp.).Syrup production forest farming systems. We will select at least 6 actively managed sugar bush stands in NH and VT, each matched with a nearby unmanaged sugar maple stand. Additionally, we will identify 6 single- or mixed-species stands dominated by alternative syrup-producing species (e.g. red maple, black birch, yellow birch). For the latter sites, at least 10 trees per stand will be tapped, and paired with 10 untapped reference trees within the same stand. For each study tree, we will conduct the following measurements: Historical patterns in stem increment growth will be assessed using dendrochronology techniques to determine differences among species' sensitivity to historical climate variability (especially drought) and impacts of sap extraction on growth. Sapflow will be measured in five trees per species per stand using the heat ratio method and scaled to water use at the stand level based on site- and species-specific measurements of sapwood area and density. Additionally, phenological patterns (e.g. bud burst, flowering, fruiting, leaf abscission) will be recorded visually on a weekly basis to correlate with sapflow measurements. Vulnerability to embolism and NSCs will be assessed using the methods described above. The results will be used to establish key characteristics for each species related to development of sap extraction management practices (e.g. patterns of sapflow in relation to climate and phenology) and to assess each species' resilience and sensitivity to climate variability.

Progress 10/01/17 to 09/30/20

Outputs
Target Audience: The target audiences served by this project included scientists, post-docs, and graduate and undergraduate students, in addition to land managers and policy-makers in both the private and public sectors who make decisions related to managing forests for multiple ecosystem services. For example, several undergraduate and graduate students participated in courses (e.g., Silviculture) where project information was presented and conducted research related to this project as part of their honors theses, practicum experience, and MS and Ph.D. degrees. As part of this research, participants gained skills in field and laboratory techniques, as well as experience with all aspects of scientific research. Professional organizations and annual meetings are also targeted as part of dissemination activities, including NH Farm & Forestry, Society of American Foresters, NH and VT Maple Producers Association), field days (e.g., Hubbard Brook, Dairy Farmers), and New England Society of American Foresters. Finally, opportunities to reach broader public audiences via diverse media outlets are also pursued, including NHPR, UNH, and various newspapers and newsletters. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Over the past three years, this project has contributed to the training of one postdoctoral scientist (Adam Coble), three PhD students (Samuel Zuckerman, David Moore, Cameron McIntire), and two MSc students (Anthony Stewart, Ayhan Yener). Additionally, a total of 15 undergraduate students were employed in my lab on projects partially funded by NHAES and were trained in a variety of lab and field techniques. Two of these students received SURF fellowships for independent summer research related to NHAES projects, two received URA assistantships for such research, and one received a Weeks Fellowship for such research.Alumni from my lab have been successful at securing high-quality professional or educational opportunities. For example, McIntire was recently hired by the US Forest Service's Northern Research Station in Durham, NH as their Forest Pathologist with State and Private Forestry, after completing a two-year post-doctoral position working with a long-term experimental drought project at the University of New Mexico. Stewart recently started a position as a PhD student at the University of Washington, following two years of working as a research technician at Cornell University. Coble is currently working as a Research Scientist for the Oregon State Department of Forestry. During the most recent project year, current Ph.D. student Moore has continued his dissertation research focused on understanding winter sap flow dynamics in potential sap-producing northern hardwood species and increasing the sustainability and resilience of the maple syrup industry through sugarbush diversification. His first year of preliminary data yielded promising results for several non-maple tree species and also contributed to our ability to attract new grant funding from four different sources (USDA-SARE, USDA-Acer Access and Development Program, North American Maple Council, and the USDA Forest Service Ecological Monitoring Program), as well as a seed grant from UNH's CoRE program which is supporting new interdisciplinary collaboration across UNH and with the University of Rhode Island. As part of these efforts, Moore is also working with UNH-Innovations to establish a patent for an anticipated new tap design for improving sap extraction. A relatively new Ph.D. student in my lab, Sam Zuckerman, completed his first field season of data collection focused on assessing the acclimation potential of functional traits to extreme drought in two dominant northeastern species, White Pine and Red Oak. Zuckerman's dissertation research is being conducted as part of our long-term experimental drought research at UNH's Thompson Farm. Final, a MS student in my lab, Ayhan Yener, took a leave of absence and is planning to return to UNH in Fall 2021 to continue his studies focused on understanding the effects of experimental drought and fog reduction on tropical cloud forest dynamics and resilience. My lab is continuing to provide technical support and training for two international drought experiments, one in Jalisco, Mexico (to Assistant Professor Karolina Riano Ospina) and the other at the Wayqecha Field Station in Peru (to Professor Dan Metcalfe), as well as one drought experiment in Maine (to Assistant Professor Jay Wason). This year, we also graduated three undergraduate assistants: Olivia Fortuna, Samantha Allen, and Emily Beard, who each spent multiple years assisting with lab and field tasks, particularly focused around our two drought experiments. In the fall, our undergrads all participated in a large field work effort associated with seasonal maintenance of Thompson Farm drought experiment - removing seasonally deployed equipment and putting the drought structure into winter mode. Our spring and summer field plans were reduced in scope this year due to COVID-related, and the majority of work on our ongoing drought experiments was therefore conducted by grad students and full-time staff. Tanner Frost '21 conducted a SURF project analyzing tree cores and dendrometer band data from the Hubbard Brook drought experiment, and when rules allowed, Tanner also assisted with the collection of twig and leaf samples from both tapped and untapped trees in sugarbushes statewide (for analysis or starch and sugar content), as well as from our Thompson Farm drought experiment (for analysis of mid-day and pre-dawn water potential, nutrient content, and leaf anatomy). Throughout the year, Chloe Gordner, Emily Chen, and Casey. This fall, Steph Petrovick '21 started a URA project examining tree cores from the Thompson Farm drought experiment for changes in wood anatomy (e.g. vessel number and diameter) that are expected to respond to drought stress.Additionally, Tanner Frost presented the preliminary findings from his research at the Hubbard Brook Long-term Experimental Research Annual Meeting in July 2020, entitled "Tree growth and response to the Drought-Net experiment at Hubbard Brook", supporting his professional development. How have the results been disseminated to communities of interest?Over the past three years, the results from my NHAES research have been disseminated to diverse communities through a variety of different media channels and public fora that focus on reaching a broad audience. Combined, these have included one NH Public Radio feature on climate change and forest fires in NH, four local and regional newspaper articles (e.g., Boston Globe, Concord Monitor, NH Union Leader, Weekly Market Bulletin), and multiple press releases and newsletters, such as UNH NHAES, UNH SPHERES, UNH TODAY, and Granite Geek. My lab group has also contributed presentations at numerous annual meetings by professional societies in NH and the greater New England area, including the following: NIFA Multistate White Pine Health Meeting; Northeastern Forest Pest Council; Climate Smart Land Network Member Gathering; U.S. Forest Service Cooperators' Meeting; New England Society of American Foresters; Northern States Research Cooperative; NH and VT Sugar Maple Producers Association; New Hampshire Farm and Forestry Expo; Lamprey River Symposium. Finally, presentations have also been given at scientific conferences, including the Ecological Society of America, the American Geophysical Union, the Society of American Foresters, the International Union of Forest Research Organization, the Hubbard Brook Research Forest Annual Cooperators' Meeting, and the Long-Term Research Network's All Scientists Meeting. This year, the following media releases were made related to my ongoing drought research: Weekly Market Bulletin, Concord, NH. UNH Scientist: 2020 Severe Drought Likely to Slow Tree Growth Next Year. October 28, 2020. New Hampshire Union Leader. "UNH Researchers say Drought will Affect Future of Red Oaks, White Pines". October 27, 2020. UNH NH Agricultural Experiment Station press release. "Severe Drought Likely to Slow Tree Growth Next Year. October 26, 2020. https://www.colsa.unh.edu/nhaes/article/2020/10/2020drought What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Climate change forecasts predict that NH will become warmer, wetter, and more variable--including more frequent extreme droughts. Because droughts have historically been rare in the region, their effects on northern forest tree species, ecosystems, and forest-dependent industries are largely unknown. This project seeks to enhance understanding about the impacts of drought on NH's forests and evaluate management strategies for improving ecosystem resilience and sustaining provisioning of societal benefits. Results from this NHAES-funded project show differences among dominant tree species in their sensitivity to and recovery from drought, providing insights into potential long-term responses of NH's forests to future climate change. The impact of this work is that it has increased awareness and understanding among natural resource managers and private citizens about the potential consequences of drought for the sustainability of the region's forests. In particular, insight into which species may be more drought-adapted provides information to guide decisions regarding silvicultural treatments for promoting future resilient forests. Given that the region experienced two of the most extreme droughts within the past 5 years in the modern record and that this trend will likely only continue, increasing the knowledge among diverse stakeholders about forest-drought interactions and the potential consequences for the multiple services provided by forests is a critical first step in identifying (and motivating) effective mitigation and adaptive strategies. Silvicultural thinning treatments were found to enhance the resilience of white pine stands impacted by White Pine Needle Damage. This work has important relevance for the development of effective management strategies to ensure the health and sustainability of white pine dominated forests in the face of increasing pressures by pests and pathogens, which are expected to be exacerbated by future climate change. White pine is the most dominant and one of the most valuable tree species in New Hampshire, comprising approximately 2,175 million cubic feet, with an estimated value of almost $1.5 billion dollars (FIA 2018). Most of these forest lands are owned by private landowners, who are often eligible for financial support from Timber Stand Improvement programs to conduct thinnings. Thus, the results from this study provide a strong rationale and incentive to encourage landowners in NH to implement thinnings as a management strategy to improve the health and resilience of white pine stands, especially in regions experiencing pest and pathogen outbreaks such as White Pine Needle Damage. Additionally, silvopasture systems showed high potential as a sustainable land use practice for maintaining greater hydrologic functions than open pastures, while also enhancing the resilience of trees to droughts. Given that NH is approximately 88.9% forested, and that 65% of NH's total farmland is classified as woodland (USDA NASS 2014), any expansion of agricultural land in the State to meet the growing demand for local food will likely require the conversion of forest land to agriculture. There already exists a growing number of farmers throughout the Northeast who have expressed interest in establishing silvopasture (over conventional open pasture) because of the perceived environmental and agricultural benefits; however, lack of information on best practices is frequently cited as one of the greatest barriers (e.g., Orefice et al. 2017). Thus, this results from this study are an important step towards filling this knowledge gap, as it provides farmers with science-based evidence for the potential advantages for adopting silvopasture systems and has the potential to impact over half of the State's agricultural lands that currently support forest cover. Research on chaga harvesting (an important forest farming system in NH) in the White Mountain National Forest (WMNF) found that the chaga resource is currently stable, providing valuable information to managers regarding the need for regulations to ensure sustainable harvesting practices.The wide-spread harvesting of Chaga in the northeastern U.S. is a relatively new phenomenon, spurred largely by growing public awareness of the potential health benefits and increasing access to the resource at farmers markets and natural food stores. As forest managers begin to grapple with the question of whether or not to impose stricter harvesting rules and enforcement, they now have access to scientific data to guide their decisions. At least in the short term, there does not appear to be an urgent need to reduce harvesting pressure, which allows managers to 'buy more time' to continue to monitor the state of the Chaga resource before taking definitive action. Another contribution of this work is that it provides a protocol for monitoring Chaga using ecologically and statistically sound methods, something which previously was unavailable. Finally, this project also led to a smaller experimental study currently ongoing that is assessing the impacts of different harvesting techniques on birch tree health, which will help inform guidelines for sustainable Chaga harvesting. Finally, research on a second forest farming system--syrup production--is generating new knowledge about the potential for using non-maple species in sugarbush management to promote the ecological and economic diversification and sustainability of the syrup industry. Monocultures - whether of annual crops or tree plantations - are widely known to be more vulnerable to diverse stressors, such as pests and pathogens and extreme weather events, and sugarbushes comprised predominantly of sugar maple are no exception. Also notable is the importance of the maple syrup industry to local economies in the Northeast--estimated at $47.2 million annually and, contribution up to $8 billion annually when including tourism and cultural activities connected to the industry (USDA NASS 2017). Many NH sugarmakers own forest lands that support other potential syrup producing species; however, scientific and technical information needed to develop harvesting and processing guidelines for these other species is lacking. This study is generating information to fill this knowledge gap, which could potentially provide industry-expanding opportunities for most of the State's syrup producers. Combined, these results are informing management decisions by landowners and natural resource managers for climate change adaptation and sustainable forest management. ?

Publications

• Type: Journal Articles Status: Submitted Year Published: 2020 Citation: Asbjornsen, H., C.D. McIntire, M. Vadeboncoeur, Z.C. Berry, K. Jennings, A. Coble. Sensitivity and threshold dynamics of two northern temperate forest trees (Pinus strobus and Quercus spp.) in response to experimental and naturally-occurring severe droughts. Tree Physiology. In review.
• Type: Journal Articles Status: Awaiting Publication Year Published: 2020 Citation: Brydon-Williams, R., I. Munck, H. Asbjornsen. 2020. Distribution, presence, and tree health impacts of the chaga fungus (Inontus obliquus) in hardwood forests of the northeastern United States. Canadian Journal of Forest Research. In press.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: McIntire, C., B. Huggett, I. Munck, M. Vadeboncoeur, H. Asbjornsen. 2020. Pathogen-induced defoliation impacts on transpiration, leaf gas exchange, and non-structural carbohydrate allocation in eastern white pine (Pinus strobus). Trees. https://doi.org/10.1007/s00468-020-02037-z
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Coble, A.P., A.R. Contosta, R.G. Smith, N.W. Siegert, M. Vadeboncoeur, K.A. Jennings, A. Stewart, H. Asbjornsen. 2020. Influence of forest-to-silvopasture conversion and drought on components of evapotranspiration. Agriculture, Ecosystems, & Environment. https://doi.org/10.1016/j.agee.2020.106916
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Vadeboncoeur, M.A., K.A. Jennings, A.P. Ouimette, H. Asbjornsen. 2020. Correcting tree-ring ?13C time series for tree-size effects in eight temperate tree species. Tree Physiology. 40:333-349. DOI:10.1093/treephys/tpz138
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Stewart*, A., A. Coble, A.R. Contosta, J.N. Orefice, R.G. Smith, H. Asbjornsen. 2020. Forest conversion to silvopasture and open pasture: effects on soil hydraulic properties. Agroforestry Systems. DOI:10.1007/s10457-019-00454-9
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Yang, Y., L. Meng, R.D. Yanai, C.T. Driscoll, M. Montesdeoca, P.H. Templer, L.E. Rustad, H. Asbjornsen. 2019. Climate change may worsen mercury pollution in northern hardwood forests. Environmental Science and Technology. DOI:10.1007/s10533-019-00605-1
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Guerrieri**, R., S. Belmecheri, S. Ollinger, H. Asbjornsen, K. Jennings, J. Xiao, B.D. Stocker, Martin, D. Hollinger, R. Bracho-Garrillo, K. Clark, S. Dore, T. Kolb, J.W. Mungers, K. Novick, A.D. Richardson. 2019. Disentangling the role of photosynthesis and stomatal conductance on rising forest water-use efficiency. Proceedings of the National Academy of Science. DOI:https://doi.org/10.1073.pnas.1905912116
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Gutierrez Lopez*, J., H. Asbjornsen, T. Pypker, J. Licata. 2019. Effects of heater wattage on sap flux density estimates using an improved tree-cut experiment. Tree Physiology. 39(4):679-696. DOI:org/10.1093/treephys/tpy137.

Progress 10/01/18 to 09/30/19

Outputs
Target Audience:The target audiences served by this project included scientists, post-docs, and graduate and undergraduate students, in addition to land managers and policy-makers in both the private and public sectors who make decisions related to managing forests for multiple ecosystem services. For example, several undergraduate and graduate students participated in courses (e.g., Silviculture) where project information was presented and conducted research related to this project as part of their honors theses, practicum experience, and MS and Ph.D. degrees. As part of this research, participants gained skills in field and laboratory techniques, as well as experience with all aspects of scientific research. Professional organizations and annual meetings are also targeted as part of dissemination activities, including NH Farm & Forestry, Society of American Foresters, NH and VT Maple Producers Association), field days (e.g., Hubbard Brook, Dairy Farmers), and New England Society of American Foresters. Finally, opportunities to reach broader public audiences via diverse media outlets are also pursued, including NHPR, UNH, and various newspapers and newsletters. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?A current Ph.D. student in my lab, David Moore, has continued his dissertation research related to resilience and adaptation of syrup producing species to climate change, which included increasing mastery of field application and data analysis, including sensor design modifications to make the sensors more durable and to allow the measurement of sapflow at a wider range of sapwood depths. I also recently recruited a new Ph.D. student, Sam Zuckerman, who has been assisting with project management at the Thompson Farm drought experiment during the fall semester and is currently developing dissertation research ideas based in part on this experiment. In July, my lab co-hosted (along with the Ollinger Lab) Stanford Ph.D. student (and UNH alumnus) Shersingh "Joe" Tumber-Dávila, who collected soil core samples to help us characterize variation in rooting depth and soil properties at our experiment and also near the eddy-flux tower at Thompson Farm, as part of his dissertation on resource competition across forest functional types. NHAES funding has allowed my lab to consistently employ and train a large number of undergraduate students from Natural Resources and the Environment (NREN) majors, with an eye towards gaining experience and building a resume for graduate school applications. During FY19, we employed ten undergraduate students in the Ecohydrology Lab, all of whom worked primarily on NHAES-related projects. We graduated three seniors this spring: Taylor Lindsay '19, Robert Lafreneiere '19, Kensley Hammond '19, a cohort of students that was well trained on fieldwork (e.g. dendrometer and soil respiration measurements) and lab work (e.g. dendrochronology, sapflow sensor construction, processing litter, and root samples, etc) at the Thompson Farm and Hubbard Brook drought experiments. Taylor Lindsay '19 worked throughout the academic year on processing tree core samples collected from fertilized forest stands in the White Mountain National Forest and used these data for a project in her Biogeochemistry course. Emily Beard '20, whose SURF project was conducted during summer 2017, continued analyzing sap flow data from red maples at Thompson Farm and presented at theundergraduate research conference (URC) this spring. Along with David Moore and Robert Lafreniere, she trained a new cohort of undergraduates on the construction of sapflow sensors (Chloe Gordner '21, Olivia Fortuna'20, Emily Johnson '21, Stephanie Petrovick '21, and Ayhan Yener '20). Emily Johnson is currently working on an Undergraduate Research Award (URA) investigating allocation to ectomycorrhizal fungi in the Thompson Farm drought experiment. Stephanie Petrovick recently started developing ideas for a URA based at Thompson Farm next fall. We employed two full-time summer field assistants (Tanner Frost '20.5 and Ayhan Yener) who worked at both drought experiments, maintaining infrastructure, deploying equipment, and collecting samples and data. Tanner is currently developing ideas for a SURF project to be conducted at Thompson Farm. Ayhan was admitted to the accelerated M.S. program and recently submitted an NSF GRFP proposal with the hope of applying his experience gained at Thompson Farm to a similar project in Peru (which is led by a close collaborator of mine at the Lund University, Sweden). The Thompson Farm field experiment also allowed us to recruit two new sophomores as lab and field assistants this fall - Casey Devanney '22 and Emily Chen '22. These students along with most of the others assisted with end-of-summer collection and processing of samples and maintenance of experimental infrastructure. In summary, we are excited about the high quality and diversity of undergraduate and graduate student research projects, the new collaborations with UNH and non-UNH scientists being developed, and the opportunities for building both a publication record and high-quality baseline datasets that will raise the profile of Thompson Farm as a research site and attract additional students and collaborators in the future. How have the results been disseminated to communities of interest?This research has been disseminated to diverse communities through a variety of different media channels and public fora that focus on reaching a broad audience, including radio, local and regional newspapers, and stakeholder meetings. Below is a list of these outreach activities conducted during this reporting period: Brydon-Williams*, R., I. Munck, H. Asbjornsen. 2019. The ecology and management of the Chaga resource in the White Mountain National Forest. White Mountain National Forest Headquarters, North Conway, NH, May 14, 2019. McIntire, C.A., M. Vadeboncoeur, H. Asbjornsen. U.S. Forest Service Cooperators' Meeting: Drought impacts on tree health in the northeast; November 8, 2018, Portsmouth, NH Falling into autumn: Experts weigh in on peak color.Conway Daily Sun, September 20, 2019. We also have numerous opportunities to share information about the ongoing climate change/drought experiment at Thompson Farm with the general public through informal conversations with a wide range of recreational users. What do you plan to do during the next reporting period to accomplish the goals?The following activities are planned for each objective during the next reporting period: Objective 1. Focus on completing the final publication from this project, which seeks to characterize the underlying mechanisms explaining long-term trends in evapotranspiration over the northeastern U.S. region. Objective 2. Participate in a region-wide effort to secure long-term support (from USDA AFRI) for continued research on the impacts of pathogen-climate change interactions on the health of white pine forests throughout the eastern and midwestern U.S., led by Dr. William Livingston (UofMaine). Pursue other relevant funding opportunities as they emerge. Objective 3. Continue long-term monitoring efforts on both drought experiments (Thompson Farm and Hubbard Brook), with an emphasis on understanding the physiological mechanisms controlling responses in growth, health, and vitality among dominant tree species. This work comprises the focus of current Ph.D. student Sam Zuckerman's dissertation research. Complete at least two publications from this work, and submit at least one major grant proposal (to NSF-Ecosystems) to secure long-term funding. Objective 4. Continue research on the ecology and resilience of traditional (e.g., sugar maple, red maple, birch) and novel (sycamore, hickory, basswood, American beech, aspen, hophornbeam) syrup-producing species to inform management for alternative sugarbush industries and climate change adaptation. Expand this research to include other agroforestry systems, such as harvesting of the non-timber product "Chaga" mushrooms. Complete at least one publication and submit at least one major grant proposal for continued funding to support this work. For all projects, we will continue to engage in a wide variety of outreach opportunities to disseminate information about research activities and results to broad and diverse audiences.

Impacts
What was accomplished under these goals? Climate change forecasts predict that NH will become warmer, wetter, and more variable--including more frequent and severe extreme climate events such as drought. Because droughts have historically been rare in the region, their effects on northern forest tree species, ecosystems, and forest-dependent industries are largely unknown. This project seeks to improve understanding about the impacts of drought on New Hampshire's forests and evaluate management strategies for improving ecosystem resilience and sustaining provisioning of societal benefits. Results this year show differences among dominant tree species in their sensitivity to and recovery from drought, providing insights into potential long-term responses of NH's forests to future climate change. Silvicultural thinning treatments were found to enhance the resilience of white pine stands impacted by pathogens. Additionally, silvopasture systems showed high potential as a sustainable land use practice for maintaining greater hydrologic functions than open pastures, while also enhancing the resilience of trees to droughts. Combined, these results are informing management decisions by landowners and natural resource managers for climate change adaptation. Objective 1. Long-term data from 7 small watersheds and 11 larger watersheds across the Northeast were analyzed to assess trends in annual evapotranspiration (AET) in relation to climate change. We found a trend of increasing AET in the cooler northern part of the region and decreasing AET in warmer regions to the southwest, with temperature and summer precipitation as the strongest controls underlying these differences. This past year we completed research to resolve a controversial topic related to assumptions used in constructing time-series from stable carbon isotopes (δ13C) in tree rings to derive estimates of Water Use Efficiency ( WUE). Specifically, we found strong tree-size effects on δ13C; however, open-grown seedlings were usually more similar to large dominant trees than to shade-grown seedlings, indicating that light exposure can outweigh the direct effects of height. We also developed a relatively simple procedure to correct tree- or stand-scale δ13C-based WUE chronologies for changing tree diameter over the period of record. A manuscript presenting these findings was recently accepted for publication in Tree Physiology (Vadeconboeur et al. in press), and we are currently preparing a third manuscript on the underlying physiological mechanisms explaining landscape scale AET trends. Objective 2. The effects of the emerging fungal disease White Pine Needle Disease (WPND) on white pine tree and forest health were assessed in permanent plots established in 7 sites throughout NH, ME, MA, VT. A thinning experiment was conducted in two white pine stands to assess the potential for reducing negative impacts of WPND. We found that WPND-infected trees lost approximately 50% of their annual litterfall in June and July and had significantly greater N loss from needles. WPND-diseased stands experienced a 41% decline in wood growth relative to pre-outbreak growth trends, equivalent to an 11 cm2 yr-1 basal area reduction. Thinning treatments improved tree health and reduced WPND severity ratings; however, tree diameter growth was not affected within the first two years of the study. We also found that trees experiencing a high-severity defoliation had 20% lower water use compared to low-severity individuals. Further, residual current-year foliage of defoliated trees compensated for the loss of mature second- and third-year foliage by upregulating photosynthesis. Soluble sugars and starches varied significantly over time and by tissue type, but defoliation severity had little effect on carbohydrate concentrations. Together with reduced basal area increment in high-severity trees, this indicates that WPND-affected trees are prioritizing carbohydrate storage over secondary growth. These findings are presented in a manuscript recently accepted for publication by TREES (McIntire et al. 2019), adding to the previous five papers published from this work. Our group also participated in a multi-state AFRI proposal (led by Dr. William Livingston, UofMaine); although not invited to the full proposal stage, we plan to continue these efforts next year. Objective 3. Drought experiments were initiated at Hubbard Brook in 2015 and at UNH's Thompson Farm in 2016 to simulate a 1-in-a-century year drought, coinciding with the 2016 natural drought. Data were collected on diameter growth, litterfall, soil moisture, leaf gas exchange, sapflow, soil nutrients, decomposition, temperature, relative humidity, fine root production, and soil and stem respiration. Overall, pine was more sensitive than the oaks to the severe 2016 drought, showing greater reductions in water use and stem growth than the oaks. However, once soil moisture thresholds were reached, oak's water use declined rapidly, suggesting that its physiological capacity to adjust to the drought was surpassed. Post-drought recovery of growth occurred more quickly in white pine than in the oaks. Combined, these results support our main hypothesis that that red oak's ecological strategy may be well-suited to surviving moderate droughts yet may make this species exceptionally vulnerable to extreme drought due to its inability to protect tissues from extensive damage from hydraulic dysfunction. The more conservative strategy of white pine may make it less competitive under moderate drought, but confers advantages for withstanding severe drought. After the surprising lack of response of red maple trees to 4 years of 50% throughfall removal at Hubbard Brook, we increased the removal around to ~90% during the 2019 growing season. Preliminary data suggest strong responses in several key variables, including soil respiration and stem growth. Objective 4. During this past year, data analysis was completed for a project assessing the effects of forest conversion to silvopasture vs. open pasture on soil hydraulic properties at two sites: the UNH ODRF and North Branch Farm, NY. Results showed that saturated hydraulic conductivity was significantly greater for forest compared to silvopasture and open pasture, while silvopasture maintained intermediate levels. Although long-term monitoring is needed, these early findings suggest a strong potential for silvopasture to serve as a more environmentally sustainable land-use system for cattle grazing. Results from the first year of a Northeast-SARE-funded project entitled 'Harvesting Sap and Producing Syrup From Trees Other Than Maples, Birches, and Walnuts' (and part of PhD student David Moore's dissertation research) showed that winter-dormant-season sap flow occurs regularly in several different deciduous, woody tree species, including white ash (Fraxinus americana), American basswood (Tilia americana), quaking aspen (Populus tremuloides), American hophornbeam (Ostrya virginiana), American beech (Fagus grandifolia), shagbark hickory (Carya ovata), and London planetree (Platanusx acerifolia). Interestingly, none of these species exhibited winter-dormant-season sap flows as prolific as those in maples (Acerspp.), birches (Betulaspp.), or walnuts (Juglansspp.), but all study species did nonetheless exhibit regular patterns of winter-dormant-season sap flow. Sap flow was largely limited to the outermost sapwood depths (< 1" below the cambium), unlike in maples and birches, where winter-dormant-season sap flow often occurs abundantly to depths >4". Atmospheric temperature was the most important factor driving winter-dormant-season sap flow, followed by solar radiation and precipitation. Sap from white ash and shagbark hickory were especially sweet and worthy of consideration for syrup production.

Publications

• Type: Other Status: Published Year Published: 2019 Citation: Asbjornsen, H., J.L. Campbell, A.W. DAmato, J. Garnas, J.S. Gunn, L.R. Iverson, T.A. Ontl, N. Pederson, M.P. Peters, P. Shannon. 2019. Forest management options for addressing drought in the Midwest and Northeast U.S. In: Vose, James M.; Peterson, David L.; Luce, Charles H.; Patel-Weynand, Toral., eds. Effects of drought on forests and rangelands in the United States: translating science into management responses. Gen. Tech. Rep. WO-98. Washington, DC: U.S. Department of Agriculture Forest Service, Washington Office. 227 p. https://doi.org/10.2737/WO-GTR-98.
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Guerrieri, R., S. Belmecheri, S. Ollinger, H. Asbjornsen, K. Jennings, J. Xiao, B.D. Stocker, Martin, D. Hollinger, R. Bracho-Garrillo, K. Clark, S. Dore, T. Kolb, J.W. Mungers, K. Novick, A.D. Richardson. 2019. Disentangling the role of photosynthesis and stomatal conductance on rising forest water-use efficiency. Proceedings of the National Science Academy. https://doi.org/10.1073.pnas.1905912116
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Yang, Y., L. Meng, R.D. Yanai, C.T. Driscoll, M. Montesdeoca, P.H. Templer, L.E. Rustad, H. Asbjornsen. 2019. Climate change may worsen mercury pollution in northern hardwood forests. Environmental Science and Technology. DOI 10.1007/s10533-019-00605-1
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Stewart, A., A. Coble, A.R. Contosta, J.N. Orefice, R.G. Smith, H. Asbjornsen. Forest conversion to silvopasture and open pasture: effects on soil hydraulic properties. Agroforestry Systems. DOI: 10.1007/s10457-019-00454-9.
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Vadeboncoeur, M.A., K.A. Jennings, A.P. Ouimette, H. Asbjornsen. Correcting tree-ring ?13C time series for tree-size effects in eight temperate tree species. Tree Physiology. DOI:10.1093/treephys/tpz138
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Djukic, I., et al. (59 authors), 2018. Early stage litter decomposition across biomes. Science of the Total Environment. 628629, 13691394. https://doi.org/10.1016/j.scitotenv.2018.01.012.

Progress 10/01/17 to 09/30/18

Outputs
Target Audience:The target audiences served by this project included scientists, post-docs, and graduate and undergraduate students, in addition to land managers and policy-makers in both the private and public sectors who make decisions related to managing forests for multiple ecosystem services. For example, several undergraduate and graduate students participated in courses (e.g., Silviculture) where project information was presented and conducted research related to this project as part of their honors theses, practicum experience, and MS and Ph.D. degrees. As part of this research, participants gained skills in field and laboratory techniques, as well as experience with all aspects of scientific research. Professional organizations and annual meetings are also targeted as part of dissemination activities, including NH Farm & Forestry, Society of American Foresters, NH and VT Maple Producers Association), field days (e.g., Hubbard Brook, Dairy Farmers), and New England Society of American Foresters. Finally, opportunities to reach broader public audiences via diverse media outlets are also pursued, including NHPR, UNH, and various newspapers and newsletters. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?As part of this project, one PhD student (Cameron McIntire) successfully defended his dissertation, and was able to secure a prestigious post-doctoral researcher position at the University of New Mexico. Former MSc student Anthony Steward completed his degree focused on the impacts of forest conversion to silvopasture and pasture on soil hydraulic properties, and secured a position as a research technician at Cornell University. A post-doctoral researcher, Adam Coble, who worked on the silvopasture and drought experiments, received training in sap flow and carbohydrate extraction techniques, and has moved on to a researcher position with the Oregon Forest Service. A new Ph.D. student, David Moore, initiated his dissertation research related to resilience and adaptation of syrup producing species to climate change, which included extensive training in sap flow and dendrochronology techniques. During FY18, we employed seven undergraduate students in the Ecohydrology Lab, and all worked on NHAES-related projects.Five of these students are seniors who have worked with us for 2-3 years, and we have mentored three of these students through the process of applying to graduate programs.Robert Lafreneiere '19 and Zach Shemenski '21 were responsible for field work (dendrometer and soil respiration measurements, as well as infrastructure maintenance) at the Thompson Farm drought experiment.Taylor Lindsay '19, Kensley Hammond '19, Samantha Allen '19, and Emily Perry '18.5 processed decomposition bag samples, root ingrowth samples, and tree-ring samples from both drought experiments, as well as other research sites in New Hampshire.Emily Beard '20 received a SURF this summer to conduct sap flow measurements in red maples at Thompson Farm, and she is currently our resident expert on the improved (more durable) sap flow sensor design that we recently started using.Zach Shemenski received a Weeks Fellowship to test and implement a new method for measuring xylem vulnerability to embolism, which had previously not been extensively tested in temperate hardwood species.We strive to create a collaborative environment in our lab where students have the opportunity to participate in a variety of projects, but also to eventually become an expert in one particular method. How have the results been disseminated to communities of interest?This research has been disseminated to diverse communities through a variety of different media channels and public fora that focus on reaching a broad audience, including radio, local and regional newspapers, and stakeholder meetings. Below is a list of these outreach activities conducted during this reporting period: NH Public Radio: The Exchange: Could it Happen Here? Fighting Forest Fires in NH. Oct 25, 2017 Climate Smart Land Network, 2nd Annual Gathering, Woodstock, NH. May 23, 2018. Boston Globe: It's shaping up to be a good year for foliage in New England. November 11, 2018 Concord Monitor: Peak foliage to be seen throughout New Hampshire this weekend. Oct 12, 2018 U.S. Forest Service Cooperators' Meeting: Drought impacts on tree health in the northeast; Nov 8, 2018, Portsmouth, NH Granite Geek Newsletter: In warmer climates, a native fungus becomes a threat to white pine. April 2, 2018. Additionally, my research group has given presentations at various scientific conferences aimed at disseminating the results to diverse communities interested in both the fundamental science and practical applications of the work. A list of these presentations is provided below: Vadeboncoeur MA., Asbjornsen H. Droughts and Deluges - effects in forest ecosystems. Workshop talk presented at the 2018 LTER All Scientists' Meeting. Pacific Grove, CA. Vadeboncoeur MA, Jennings KA, Ouimette AP, Asbjornsen H. Understanding and removing height and canopy-position artifacts in tree-ring 13C chronologies. Talk at the Dynamics of Forest Growth and Resource Use Symposium, University of Virginia, Charlottesville, VA, February 2018. McIntire, C.D., Munck, I.A., Broders, K., Wyka, S., Livingston, W., Vadeboncoeur, M.A., Ducey, M.J., and Asbjornsen, H. 2018. Impacts and management of White Pine Needle Damage in the Northeastern US. NIFA Multistate White Pine Health Meeting. February 6-9. Athens, GA. McIntire, C.D., Jennings, K.A., Vadeboncoeur, M.A., Coble, A.P., Asbjornsen, H. Northern Forest DroughtNet: Understanding impacts of precipitation change on northern forest ecosystems. The International Drought Experiment (IDE) Meeting. May 16-18, 2018. Fort Collins, CO. Munck, I.A., Constanza K., McIntire, C.D. 2018. White Pine Health: Updates on pests and diseases affecting white pine in the Northeast. Managing Our Changing Forests: A Monthly Webinar Series by UVM Extension, UVM Forestry, & VT Department of Forests, Parks and Recreation. February 15. What do you plan to do during the next reporting period to accomplish the goals?The following activities are planned for each objective during the next reporting period: Objective 1. Focus on publishing at least two additional papers related to this research: the first will validate the relationship between carbon isotopes, water use efficiency, and tree size to address recent concerns raised by the Brienen et al. (2017) paper in Nature Communications. The second will present the results from our research in the Northeastern U.S. documenting the effects of historical climate variability on tree species' growth and water use efficiency. Objective 2. We will continue to monitory the impacts of the thinning treatments on the fungal disease WPND on white pine trees, including collecting data on needle shedding, tree growth, and tree health. We will also continue to participate in region-wide collaborative research efforts to address this issue. Objective 3. At Hubbard Brook, we will increase the severity of the drought treatment to a near-100% throughfall exclusion in order to push the red maple trees to their ecological threshold and generate new knowledge about this species' ability to tolerate and adapt to moisture stress. At Thompson Farm, we will continue to assess the response of the dominant tree species to the drought treatment. Contingent upon future funding, we also plan to include new measurements to assess non-structural carbohydrates and hydraulic conductivity as a means of identifying the underlying physiological mechanisms that explain differences in drought response between red oak and white pine. Objective 4. Research will be initiated by Ph.D. student David Moore to assess the resilience and adaptation of different syrup producing species to climate change and to develop effective methods for syrup production for alternative species besides sugar maple, including white birch, yellow birch, walnut, and sycamore. This work is being funded by a new grant to Moore from the Northeast Sustainable Agriculture, Research, and Education (SARE).

Impacts
What was accomplished under these goals? Climate change forecasts predict that NH will become warmer, wetter, and more variable--including more frequent and severe extreme climate events such as drought. Because droughts have historically been rare in the region, their effects northern forest tree species, ecosystems, and forest-dependent industries is largely unknown. This project seeks to improve understanding about the impacts of climate change on New Hampshire's forests and evaluate management strategies for improving ecosystem resilience while sustainably producing key goods and services for society. Results this year show differences in species' sensitivities to drought and provide evidence that thinning treatments enhance resilience and silvopastures maintain greater hydrologic functions than open pastures. New methods development related to stable isotope and sapflow techniques provide a strong foundation for future work. Objective 1. Long-term data from 7 small watersheds and 11 larger watersheds across the Northeast were analyzed to assess trends in evapotranspiration (ET) in relation to climate change. Increment cores were collected from major tree species to assess tree age, growth, and water use efficiency (WUE). We found a trend of increasing ET, which contrasts with declining ET to the south and west over the past 50 years, suggesting that climate change impacts on ET are complex. Key outcomes include 10 presentations at professional conferences and a paper. Publication of future manuscripts on WUE requires addressing a recent paper (Brienen et al. 2017, Nature Communications) that calls into question assumptions used in constructing time-series from stable carbon isotopes (δ13C) in tree rings. With new supplemental funding from NSF, we conducted additional sampling of over 300 trees and analyzed δ13C in the most recent 5 years of growth to develop the dataset needed to quantify the effects of tree size and canopy position on δ13C, and to correct time-series of WUE. We found strong tree-size effects on δ13C; however, open-grown seedlings were usually more similar to large dominant trees than to shade-grown seedlings, indicating that light exposure can outweigh the direct effects of height. We also developed a relatively simple procedure to correct tree- or stand-scale δ13C-based WUEchronologies for changing tree diameter over the period of record.We are currently preparing a manuscript reporting these results and using this approach to correct and interpret previously unpublished multi-decadal composite isotope chronologies at sites across the northeast. A third manuscript focused on identifying the underlying physiological mechanisms explaining landscape scale ET trends will also be prepared based on these results. Objective 2. The effects of the emerging fungal disease WPND on white pine tree and forest health were assessed in permanent plots established in 7 sites throughout NH, ME, MA, VT. We measured monthly litterfall to quantify defoliation severity, foliar nitrogen (N) content, and collected stem increment cores to determine annual growth. A thinning experiment was conducted in two white pine stands to assess the potential for reducing negative impacts of WPND, with three treatments: low thinning (residual basal area = 60 ft2 /ac), high thinning (100 ft2 /ac), and control. We found that mid-season defoliations occurring in the months of June and July accounted for ~50% of the total annual litterfall biomass (g m-2), and that WPND-induced litterfall matched or exceeded the amount of litterfall cast in October (when white pine typically sheds older needles). Further, infected white pines had significantly greater N loss from needles. Tree ring analyses showed that WPND-diseased stands experienced a 41% decline in wood growth relative to pre-outbreak growth trends, equivalent to an 11 cm2 yr-1 basal area reduction. Both thinning treatments resulted in positive (healthier) index scores and reduced WPND severity ratings; however, tree diameter growth was not affected within the first two years of the study. Five papers were published from this work. Objective 3. Drought experiments were initiated at Hubbard Brook in 2015 and at UNH's Thompson Farm in 2016 to simulate an extreme drought event by removing 50% of the throughfall over a 4-year period. Data were collected for diameter growth, litterfall, soil moisture, leaf gas exchange, sapflow, soil nutrients, decomposition, temperature, relative humidity, fine root production, and soil and stem respiration. Since our experiment coincided with the 2016 extreme drought, conditions in the drought treatment were likely the greatest moisture stress ever experienced by these trees. Results suggest that red oak was more negatively impacted by the drought (i.e. had more profound reductions in water use and growth) than white pine, challenging the current ecological theory that considers red oak to be the more drought tolerant species. Post-drought recovery appeared to occur more quickly in white pine, evidenced by greater post-drought rates of water uptake and stem increment growth. We hypothesize that red oak's ecological strategy may be well-suited to surviving moderate droughts yet may make this species more vulnerable to extreme drought due to its inability to protect tissues from extensive damage due to 'hydraulic failure', 'carbon starvation', or a combination. The more conservative strategy of white pine may make it less competitive under moderate drought, while conferring advantages for growth and survival following severe drought. We are currently exploring the role of these two mechanisms in explaining differences in white pine and red oak drought response. Surprisingly, red maple trees at Hubbard Brook did not respond to drought, which may be related to study design limitations or greater drought tolerance. We will explore these questions conducting a 100% throughfall exclusion in 2019. Objective 4. During this past year, data analysis was completed for a project focused on assessing the effects of forest conversion to silvopasture vs. open pasture on soil hydraulic properties at two sites: the UNH ODRF and North Branch Farm, NY. Results showed that saturated hydraulic conductivity was significantly greater for forest compared to silvopasture and open pasture, and a trend that silvopasture maintained intermediate levels of soil hydraulic conductivity between forest and open pasture. Although long-term monitoring is needed, these early findings suggest a strong potential for silvopasture to serve as a more environmentally sustainable land use system for cattle grazing. A new project is assessing the resilience and adaptation of syrup production from diverse tree species to climate variability. The first step has been to develop reliable methods for measuring sap flow, as traditional sap flow sensors have design flaws that limit their durability and longevity in the field, resulting in broken sensors, lost data, and high costs. This year we successfully designed and produced improved sensors that will greatly enhance future data collection efforts. Another effort focused validating winter data collection of sap yield. Maple syrup production relies on sap flow during the winter dormant period when trees are leafless, yet sap flow sensors have never been used to measure winter sap flow, which is critical to generating practical guidelines for the sugaring industry. Our experiments showed that that freezing temperatures do not adversely affect sap flow data, while sensors positioned above the tap exhibited the strongest relationship with sap yield. These findings are being used to develop the study design for the 2019 field season.

Publications

• Type: Journal Articles Status: Published Year Published: 2018 Citation: Vadeboncoeur, M., M.B. Green, H. Asbjornsen, J.L. Campbell, M.B. Adams, E.W. Boyer, D.A. Burns, I.J. Fernandez, M.J. Mitchell, J.B. Shanley. 2018. Systematic variation in evapotranspiration trends and drivers across the northeastern United States. Hydrological Processes. DOI: 10.1002/hyp.13278.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Asbjornsen, H., Rustad, L., K. Jennings, P. Templer, et al. 2018. Challenges and opportunities for coordinated approaches to precipitation manipulation experiments in forest ecosystems. Methods in Ecology and Evolution. doi:10.1111/2041-210X.13094
• Type: Other Status: Awaiting Publication Year Published: 2018 Citation: Asbjornsen, H., J.L. Campbell, A.W. D⿿Amato, J. Garnas, J.S. Gunn, L.R. Iverson, T.A. Ontl, N. Pederson, M.P. Peters, P. Shannon. 2018. Forest management options for addressing drought in the Midwest and Northeast U.S. Vose, J. (ed). USDA Forest Service Technical Report. In Press.
• Type: Journal Articles Status: Under Review Year Published: 2018 Citation: Stewart, A., A. Coble, A.R. Contosta, J.N. Orefice, R.G. Smith, H. Asbjornsen. Effects of forest conversion to silvopasture on soil hydraulic properties. Agroforestry Systems. In review.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: McIntire, C.D., I.A. Munck, M.J. Ducey, H. Asbjornsen. 2018. Thinning treatments reduce severity of foliar pathogens in eastern white pine. Forest Ecology and Management. 423:106-113.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: McIntire, C.D., I.A. Munck, M. Vadeboncoeur, H. Asbjornsen. 2018. Impacts of White Pine Needle Damage on seasonal litterfall dynamics and wood growth of eastern white pine (Pinus strobus) in New England. Forest Ecology and Management. 423:27-36.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Wyka, S.A., McIntire, C.D., Smith, C., Munck, I.A., Rock, B.N., Asbjornsen, H., Broders, K.D. 2018. Effect of climatic variables on abundance and dispersal of Lecanosticta acicola spores and impact of defoliation on eastern white pine (Pinus strobus). Phytopathology. 108:374-383. https//doi.org/10.1094/PHYTO-02-17-0065-R.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Orefice, J., Smith, R.G., Carroll, J., Asbjornsen, H., and D. Kelting. 2017. Soil and understory plant dynamics during conversion of forest to silvopasture, open pasture, and heavily thinned woodlot. Agroforestry Systems. 91(4):729-739.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Costanza, K.K.L., Whitney, T.D., McIntire, C.D., Livingston, W.H., and Gandhi, KJK. 2018 A synthesis of emerging health issues of eastern white pine (Pinus strobus) in eastern North America. Forest Ecology and Management. 423: 3-17. DOI: 10.1016/j.foreco.2018.02.049
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Crowley, M.A., Shannon, K.E., Leslie, I.S., Jilling, A., McIntire, C.D., Kyker-Snowman, E. 2018. Sustainable beef production in New England: policy and value-chain challenges and opportunities. Agroecology and Sustainable Food Systems. In press. DOI: 10.1080/21683565.2018.1492494
• Type: Other Status: Published Year Published: 2017 Citation: McIntire, C.D. 2017. White Pine Needle Damage Report. Landscape Message: UMass Amherst Center for Agriculture, Food, and the Environment. Issue 8. 6 p.