FOREST SUSTAINABILITY, ECOSYSTEM SERVICES, AND BIOENERGY DEVELOPMENT IN THE NORTHERN GREAT LAKES REGION, U.S.

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: MCINTIRE-STENNIS
• Reporting Frequency: Annual
• Accession No.: 1002838
• Project Start Date: May 15, 2014
• Project End Date: Sep 30, 2018
• Program Code: [(N/A)]- (N/A)

Recipient Organization
MICHIGAN TECHNOLOGICAL UNIV
1400 Townsend Drive
HOUGHTON,MI 49931

Performing Department
College of Forest Resources and Environmental Science

Non Technical Summary
Biofuel production from forest ecosystems can modify plant production, greenhouse gas emissions, soil biogeochemical cycling, hydrologic cycling, and biodiversity. Changes in any of these processes and systems can greatly alter forest carbon absorbtion or emissions and water quality and quantity and, therefore, the rationale for sustainable biofuels production. Most biofuel feedstock production systems proposed worldwide rely on the intensification of biomass production or the reduction of some carbon stock such as trees or grasslands. Both of these are likely to negatively affect carbon, water, and biodiversity resources. Different biofuel feedstock production systems, associated land use changes, climate conditions, and soil types will all influence carbon cycling, hydrology, and biodiversity differently at the local scale. These factors will determine whether a particular system results in a net source or sink of greenhouse gas emissions. Furthermore, alteration of carbon cycling will have ramifications for nitrogen, phosphorous and other nutrient balances needed to maintain healthy ecosystems for humans and other plants and animals. All of these forces directly affect other critical components of local- and regional-scale forest ecosystem sustainability.

Animal Health Component

25%

Research Effort Categories

Basic

75%

Applied

25%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
102	0699	1070	25%
123	0699	1070	25%
136	0699	1070	50%

Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships; 136 - Conservation of Biological Diversity; 123 - Management and Sustainability of Forest Resources;

Subject Of Investigation
0699 - Trees, forests, and forest products, general;

Field Of Science
1070 - Ecology;

Keywords

bioenergy

plantations

forest

sustainability

birds

pollinators

carbon

soil

wisconsin

Goals / Objectives
Our goal is to quantify how biofuel production alters: 1) GHG emissions (CO2, CH4, and N2O) and the amount and type of soil C sequestered or lost; 2) hydrologic cycling and water quality; and 3) patterns of native species richness among focal taxa including birds. This comparative approach will enable us to: 1) identify broad patterns of ecosystem response to land use change associated with biofuel production systems; 2) identify how local conditions (e.g. climate, soils) either attenuate or exacerbate ecosystem responses to biofuel production; and 3) assess tradeoffs between ecosystem services provisioned by alternative land use systems.

Project Methods
In each case, we will examine a common set of dependent ecological variables across a range of land use intensities: from monocultures that are intensively managed for biofuel feedstock production, to less intensive agroecosystems and natural land cover. Given that some of the field measurements are quite intensive and require significant instrumentation and project personnel time, we will collect data at one case each year, rotating across the four cases. This approach will enable us to continuously monitor cases for a full year to examine patterns both annually and seasonally. As data become available, they will be incorporated into on-going modeling.Task 1 Soil carbon, nutrient cycling and GHG emissions: a) Soil carbon content and compounds. How does soil carbon vary with biofuel feedstocks, management techniques, soil types and other geographic factors? Soil C, N and P contents will be measured, along with textural analyses. To quantify total soil C, bulk density will be calculated every 10 cm by volumetric coring. Fourier transform infrared spectroscopy (FTIR) will be used to quantify carbon compounds (e.g., lignins, carbohydrates, waxes). At certain locations, additional soil analysis will be conducted to take advantage of changes in C3/C4 plant composition as a result of land use conversionb) GHG emissions. How do feedstocks, management techniques, and soil types interact with one another to impact GHG emissions? GHGs will be measured at all sites (biweekly to bimonthly) to provide data for model calibration (see section c below). At each study site, CO2, CH4, and N2O will be measured using static chamber techniques (Vourlitis et al. 1993). CO2 measurements will be made with a portable Infrared Gas Analyzer (IRGA), and CH4 and N2O will be analyzed on a gas chromatograph at MTU.c) Modeling. Many questions cannot be answered by direct field sampling, especially those involving time frames longer than our project length (e.g., will biofuel be sustainable in 50 years under certain scenarios?). Therefore, our field data will be integrated into the DAYCENT ecosystem model (Parton et al. 1998), which simulates daily carbon and nitrogen cycling in plants and soils, as well as GHG's (N2O, CO2, and CH4) and plot-level water cycling (Del Grosso et al. 2001). DAYCENT has proven successful at simulating Miscanthus, switchgrass, and corn-based biofuels (Adler et al. 2007; Robertson et al. 2011; Davis et al. 2011). We will parameterize the model to simulate new feedstock types (e.g. Jatropha curcas and sugarcane) and test it under many different climate and soil type conditions. DAYCENT output will also provide plot-based inputs for Task 2 watershed modeling.Task 2 Water resource impact assessment: It is generally thought that second-generation biofuel crops (e.g. jatropha) are superior to first-generation crops (e.g., corn) because of their higher net energy gain and environmental benefits such as nutrient and carbon sequestration (Gerbens-Leenes et al. 2009; NRC 2010). However, several studies have also noted concerns regarding the impacts of biofuel feedstock cultivation and fuel production on freshwater systems (e.g. Dominguez-Faus et al. 2009; Le et al. 2011). We will enhance understandings of water-related biofuel impacts by answering these questions: How will biofuel production and feedstock type influence patterns of vegetation water use (e.g., total amount, timing, source) relative to the reference pre-production vegetation? Is the trade-off between amount of water used and carbon fixed (e.g., water use efficiency, ratio of CO2 assimilation rate to transpiration rate at the stomata) at the landscape level altered as a result of biofuel production, and if so, what is the direction and magnitude of change? What will watershed modeling reveal about the sensitivity of water quantity and quality to feedstock cultivation intensity and practices?a) Stand-level water use. Sap flow will be measured on three treatment plots (e.g., two biofuel crops and the reference vegetation) using thermal dissipation probes during a one-year period at each study site. Sap flow will be monitored continuously for 5-10 individuals of the dominant plant species within each of the vegetative cover types. For trees, sap flow will be measured using the Heat Ratio Method (HRM) (Burgess et al. 2001); for herbaceous plants with small stems sap flow will be measured using the Heat Balance Method (HBM) (Ham and Heilman 1990). All sensors will be custom designed and constructed in the University of New Hampshire Asbjornsen Lab. Water use efficiency at the plant and stand level will be calculated as the amount of water used divided by the amount of above-ground biomass produced, with biomass estimates obtained from the Resources/Biomass Production section of this proposal. We will monitor rainfall interception using an array of 20 to 25 manual throughfall gauges placed at random locations within each vegetation cover type (e.g. Pypker et al. 2005) because rainfall interception loss can account for up to 40% of gross precipitation (e.g. Horman 1996) and is sensitive to canopy structure changes (Pypker et al. 2011; Asbjornsen et al. 2011; Goldsmith et al. 2011).Task 3 Biodiversity assessment: We will assess avian species richness and abundance and pollinator community characteristics within the gradient of biofuel cropping systems in replicated fields/stands during three breeding seasons in all three Latin American countries. We have five years of existing data from a study of aspen (Populus spp.) forests in northern Wisconsin (Roth 2012; Webster et al. 2010). In much of its range in North America and Europe, aspen are intensively managed as quasi-monocultures that reproduce clonally after clearcutting. Our research has shown that by retaining former canopy trees (hardwoods and conifers), aspen productivity is not reduced and biodiversity value can be greatly enhanced (Roth 2012).In each country and treatment, we will use distance sampling (Bibby et al. 2000) to record all birds seen and heard from points randomly located with each treatment and Program Mark to estimate abundance. We will conduct bird surveys in each treatment per study area and country to describe breeding bird communities and repeat surveys each year to determine how stand development and thinning affect bird community structure and habitat use. Treatments will be compared in terms of species richness, species-area relationships, composition of native versus exotic bird species, as well as feeding and nesting guild patterns of abundance. We will survey for pollinators (bees, butterflies, flies) in each stand twice each year for two years to capture seasonal variation in pollinator community structure. To characterize the pollinator community, we will use the pan trap method (Campbell and Hanula 2007) to sample bees, flies, butterflies and other pollinators in all treatments and in nearby natural habitats. Collected insects will be stored and local experts will be used for identification. We will also collect descriptive vegetation data to characterize variation in composition and structure, and will include landscape variables from remotely sensed data. For each stand in which birds are sampled, we will calculate and compare across treatments the following measures of biodiversity richness and evenness: species richness (S), Simpson Index (D) and Shannon-Wiener Index (H) (Magurran 2004).

Progress 05/15/14 to 09/30/18

Outputs
Target Audience:The target audiences for this project are professional scientists and natural resource managers including state, federal and academic professionals. Some products of this project were also designed to be useful to land owners, and the general public. Changes/Problems:No major changes were involved in this last year of the reporting period. What opportunities for training and professional development has the project provided? This project resulted in training for one MS student, Dan Haskell, and one PhD student, Dr. Amber Roth as well as 9undergraduate students who worked at field sites in Wisconsin and Brazil. Two female students (Nia Becker and Cindy Fiser) were funded on an IREU through NSF to work on a side project related to the larger project in Brazil and two peer-reviewed papers resulted from that as well as the professional development of these two students. Another undergraduate (Gina Testa) receieved some support from this project, and secured a Summer Undergraduate Research Award from MTU and has a paper coming out soon in another peer-reviewed outlet. Personally, this project allowed me to leverage some larger external funding,"fill in the gaps" and extend the impact of the project. How have the results been disseminated to communities of interest? We have published the attached papers and have also given numerous talks to local land owners, forest managers, and professional societies. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? I was responsible for looking at biodiversity questions related to biofuel production in short-rotationforests and commodity plantings. Research funded by this MS funding clarified the relationship between habitat management in production landscapes and bird movement and habitat use. We have compiled some of our most interesting results into a number of publications that are available to scholars and natural resource managers and related audiences. New knowledge related to how aspen forests, oil palm and fast growing eucalyptus monocultures support or fail to support birds and pollinators. This information is now available for agency personnel and policy makers to guide new policy with specific empirical data. The state of Wisconsin had already moved toward a model of aspen management that retained legacy trees but our research was among the first to confirm the general notion that within intensively managed aspen stands, legacy trees really enhance bird diversity, including imperiled species like the Golden-winged Warbler.

Publications

• Type: Journal Articles Status: Under Review Year Published: 2019 Citation: Dunn, J.L., J.L. Knowlton, R.M. Handler, E.C. Pischke, K.E. Halvorsen, M. Azahara Mesa- Jurado, T. Selfa, D. Flaspohler, J. Licata, E. Mata, R. Medeiros, C. Moseley, E. Nielsen, V. Picasso, J.C. Sacramento Rivero, T. Souza, C. Vazquez, N. Basiliko. Lessons from an Interdisciplinary International Bioenergy (BIOPIRE) project. To be included in K.E. Halvorsen, C. Schelly, R. Handler, and J.L. Knowlton, Eds., A Research Agenda for Environmental Management, under contract with Edward Elgar. (in review).�
• Type: Book Chapters Status: Under Review Year Published: 2019 Citation: Knowlton, J., and D. Flaspohler. Ecosystem services and natural capital of the Tizimin region of the Yucatan, Mexico. Ch. XX in: Ecological Services of Yucatan state, Mexico (in review)
• Type: Journal Articles Status: Accepted Year Published: 2019 Citation: Bruckman, V.J., M. Haruthaithanasan, F. Kraxner, R. Miller, T. Terada, A.-K. Brenner, D. F. Kraxner and D. Flaspohler. Sustainable forest bioenergy development strategies in Indochina: Collaborative effort to establish regional policies. Forests (accepted 8 April 2018)
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Jarvi (Testa), G.M., J.L. Knowlton, C.C. Phifer, A.M. Roth, C.R. Webster and D.J. Flaspohler. 2018. Avian community response to short-rotation aspen forest management: Implications for bioenergy development. Northeastern Naturalist 25(2): 308-318.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Brito, T.F., Phifer, C., Knowlton, J.L., Fiser, C.M., Becker, N.M., Barros, F., Contrera, F.A., Mau�s, M.M., Juen, L., Assis-Montag, L, Flaspohler, D., Webster, C.R., Santos, M., Silva, D.F. Likely 2017. Forest reserves and riparian corridors help maintain orchid bee communities in oil palm plantations. Apidologie doi: 10.1007/s13592-017-0500-z
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Knowlton, J., C. Phifer, C. Fiser, N. Becker, D. Flaspohler, C. Webster. 2017. Oil palm plantations affect movement behavior of a key member of mixed-species flocks of forest birds in Amazonia, Brazil. Tropical Conservation Science. 10:1-10. doi: 10.1177/1940082917692800
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Jimenez, M.M., S.S. Soto, E. G. Lopez, J.R. Napoles, J.L. Knowlton, C. Phifer, D. Flaspohler, and A. de J.J. Mendez. 2016. Diversidad y abundancia de abejas (Hymenoptera: Apoidea) en agroecosistemas de palma aceitera y pastos cultivados, en Tabasco, Mexico. Revista Nicaraguense de Entolologia 115:2-20.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Phifer, C., J. Knowlton, C. Webster, D. Flaspohler, and J. Licata. 2016. Bird community response to afforested eucalyptus on the Argentine pampas. Biodiversity and Conservation. doi:10.1007/s10531-016-1126-6

Progress 10/01/16 to 09/30/17

Outputs
Target Audience:Our project-related peer reveiwed publications will continue to reach professionals in the fields of restoration ecology, aquatic ecology, landscape ecology and lakeshore restoration. We continue to provide information to the Wisconsin and other Great Lakes States DNRs on lakeshore conservation and restoration thorough professional and lakeshore owner association meetings. These meetings reach target audiences from professional natural resource managers to the wider public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?One graduate student partly supported by MS funds has defended and will turn in his final PHD dissertationin Dec. 2017. Two undergraduates, Cindy Fiser and Nia Becker also benefitted from some MS funds and were able to be trained in data collection for birds and pollinator sampling in Wisconsin. Nia is an African Amercian woman, so is from an underrepresented group in science and natural resource management. How have the results been disseminated to communities of interest?Peer reviewed papers, discussions with colleagues, professional meetings and additional proposals to puruse follow-up work. What do you plan to do during the next reporting period to accomplish the goals?We will continue to synthesize the data already collected and share it with target communities and will work with collaborators in the U.S. and elsewhere to build new research plans and proposals to further explore the questions related to this reasarch....how land use related to human development and commodity production affect biodiversity.

Impacts
What was accomplished under these goals? We have completed nearly all of our data collection, done most of the analyses and writing of papers from this work and are continuing to submit and revise manuscripts to share results of this research. The work has lead to additional proposals and one additional graduate student, Sam Oliveira, who will be working this winter on migratory bird use of oil palm in Mexico, a project that has spun off the original MS funding.

Publications

• Type: Journal Articles Status: Awaiting Publication Year Published: 2018 Citation: . Haskell, D.E., A.L. Bales, C.R. Webster, D.J. Flaspohler, and M.W. Meyer. Conifer restoration on lakeshores using three planting techniques. Native Plant Journal.
• Type: Journal Articles Status: Awaiting Publication Year Published: 2018 Citation: Haskell, D.E., C.R. Webster, A.L. Bales, D.J. Flaspohler, and M.W. Meyer. In press Assessment of wildlife habitat attributes at restoration projects on northern Wisconsin lakeshores. Northeastern Naturalist.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Haskell, D.E., A. Bales, C.R. Webster, M.W. Meyer, and D.J. Flaspohler. 2017. Restoring hardwood trees to lake riparian areas using multiple planting treatments. Restoration Ecology. (DOI) - 10.1111/rec.12520
• Type: Journal Articles Status: Accepted Year Published: 2017 Citation: Haskell, D.E., A. Bales, C.R. Webster, M.W. Meyer, and D. Flaspohler. Effectiveness of bare-root and gravel culture shrubs used in wildlife habitat restoration on lake riparian areas in Northern Wisconsin. Ecological Restoration, Accepted, pending revision, 6 April 2017.

Progress 10/01/15 to 09/30/16

Outputs
Target Audience:Our target audience continues to be land owners and land management agencies in the upper Great Lakes region as well as scientists and scholars in the disciplines of wildlife ecology and forest management. To reach these audiences, we have given presentations, published papers, and attended meetings to share our findings. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Two undergraduates, Nia Becker and Cindy Fiser, continue to learn new field and data management skills working on the project. PhD student, Colin Phifer, has further developed his supervisory and scientific skills as has Research Scientist, Dr. Jessie Knowton. How have the results been disseminated to communities of interest?We have published peer-reviewed papers, presented talks at professional meetings, and met informally with land owners, land management agencies and the public in relation to our research. What do you plan to do during the next reporting period to accomplish the goals?In the next year, we will continue to analyze our data, produce peer-reviewed and non-peer-reviewed publcations, and present at local, national and international meetings as a means to further share our findings.

Impacts
What was accomplished under these goals? In the last year, we completed data collection in Wisconsin and have been focusing on compliling data, preparing summary tables and figures, manuscripts and presentations and other products. We have addressed the goals of this project through these activities and have used our data to address questions related to how forest management influences habitat quality for birds and bees. The incipient bioenergy economy remains largely undeveloped in northern WI as well as other parts of the forested northern Midwest but the findings of this project are equally relevant to looking at different degrees of intensity of forest management as proxies for managment as a bioenergy resource.

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: Aldinger, K.R., T.M. Terhune, D.A. Buehler, P.B. Wood, M.H. Bakermans, J.L. Confer, D.J. Flaspohler, J.L. Larkin, J.P. Loegering, K.L. Percy, A.M. Roth, and C.G. Smalling. 2015. A range-wide assessment of factors influencing Golden-winged Warbler nesting demographics. Avian Conservation and Ecology 10 (1): 6-15.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Henschell, M., C. Fortin, C. Webster, and D. Flaspohler. Productivity-diversity relationships in planted grasslands: species quality vs. quantity. 2015. PLoS ONE. DOI: 10.1371/journal.pone.0125758. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0125758
• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Third North American Congress for Conservation Biology, July 2016, Madison, WI. Symposium, Socioeconomic perspectives on forest bioenergy project impacts on biodiversity-related ecosystem service values. Effects of aspen forest age on pollinator communities in Northeastern Wisconsin, USA. C. Phifer, C. Webster, D. Flaspohler.
• Type: Journal Articles Status: Submitted Year Published: 2017 Citation: Haskell, D.E., C.R. Webster, M.W. Meyer, and D.J. Flaspohler. Bare-root and gravel culture shrubs used in wildlife habitat restoration on lake riparian areas in Northern Wisconsin. In review, submitted Ecological Restoration.
• Type: Journal Articles Status: Submitted Year Published: 2017 Citation: Haskell, D.E., A. Bales, D.J. Flaspohler., M.W. Meyer, and C.R. Webster. Assessing the Importance of fencing and irrigation when restoring wildlife habitat along northern Wisconsin lakeshores using native plants. Native Plants Journal

Progress 10/01/14 to 09/30/15

Outputs
Target Audience:Our targest audiences include other researchers in the disciplines of ecology, forest growth and yield, and early successional forest and woody plantation silviculture. We also target local forest dependent communities in northern Wisconsin and have worked with local county and state forestry employees, and private individual and industrial forest land owners. Changes/Problems:There are several sources of financial or in-kind support for this research effort including NIFA, NSF, etc. One of the PhD students who has been in charge of soil data collection, Michelle Cisz, was diagnosed with a serious health issue this fall. While she is being treated and recovering, we have worked to continue the work she so capably began and have a recently graduated PhD student being trained to process and analyze some of her data. This may somewhat slow this portion of the project. What opportunities for training and professional development has the project provided?Dr. Jessie Knowlton (Research Scientist), Colin Phifer (PhD student), Cindy Fiser, Nia Becker, and Gina Testa (3 undergraduate field assistants) have all gained experience organizing details of the experimental design and collecting data. In addition, Dr. Knowlton and Colin Phifer have acquired new skills in data analysis including training in the use of InVEST, a tool for quantifying ecosystem services. Cindy, Nia, and Gina also had some of their first field data collection experience, and Cindy and Gina will present posters of some of their work in the next year at the Michigan Technological University Undergraduate Research Symposium. How have the results been disseminated to communities of interest?Peer-reviewed publications, talks at professional meetings, talks at Kemp Natural Resources Station given to colleagues at the University of Wisconsin-Madison and -Stevens Point. We have also proposedthree symposiums to take place in the next year: 1) 2016 North American Meeting of the Society for Conservation Biology in Madison, WI, 2)2016 International Symposium on Society and Resource Management in Houghton, MI,and 3) the International Union of Forest Research Organizations Regional Congress for Asia and Oceana in Beijing, China. Two of these have been accepted, and one is pending. These efforts will involve dozens of speakers and we estimate hundreds of audience members; publications may also stem from these efforts, compouding the dissemination potetial of this NIFA-supported research. What do you plan to do during the next reporting period to accomplish the goals?We plan to continue data analysis, collect remaining data, draft manuscripts, organize talks and symposia, and otherwise work to achieve the goals of this project. We will also be working with graduate studetns to help them complete their theses.

Impacts
What was accomplished under these goals? To quantify the environmental variables included in the project goals, we first had to collect data on biodiversity, soil carbon and other characteristics, and hydrology at the stand and individual tree scale. As of Sept. 2015, we have collected all of the data on birds and pollinator communities in our different treatments in Wisconsin, all of the soil samples, and most of the hydrology data. Some data analysis is complete and other data will be collected and/or analyzed in the next 18 months.

Publications

• Type: Journal Articles Status: Accepted Year Published: 2016 Citation: Phifer, C., J. Knowlton, C. Webster, D. Flaspohler, and J. Licata. 2016. Bird community response to afforested eucalyptus on the Argentine pampas. Biodiversity and Conservation. Accepted pending revision, 12 Nov. 2015.

Progress 05/15/14 to 09/30/14

Outputs
Target Audience: This is the first year of data collection for this project but several talks have been given to professional societies (IUFRO, INRA-France) on the study design, goals, and preliminary data. In addition, we have had an article published in the Michigan Technological University web page reaching students, faculty, community members, and the wider public. We expect this area to grow as more data is collected and products from this work multiply. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? The PhD student, Colin Phifer and Reserch Scientist, Dr. Jessica Knowlton, have received extensive exposure to new data collection methods, have met with private and industrial forest land owners, and have created and presented talks to the general public as well as to local groups including the Audubon Society. In addition, Cindy Fiser, an undergraduate, has aided with pollinator sampling and keying out collected insects. How have the results been disseminated to communities of interest? As reported above, this has begun and will grow in the following year. What do you plan to do during the next reporting period to accomplish the goals? We plan to complete the data collection in Wisconsin, to complete keying out all insect samples and to continue with analyses of bird and bee data.

Impacts
What was accomplished under these goals? To date, we have nearly completed data collection in Wisconsin, with soils, stand hydrology, bird counts, and pollinator sampling nearly complete. Most data has been entered into spreadsheets and some analysis has been done with more planned in 2014-15. Modeling of watershed hydrology will begin in 2015-16 after data has been acquired.

Publications

• Type: Journal Articles Status: Published Year Published: 2014 Citation: Roth, A.M., D.J. Flaspohler, and C.R. Webster. 2014. Legacy tree retention in young aspen forest improves nest habitat quality for Golden-Winged Warbler (Vermivora chrysoptera). Forest Ecology and Management 321:61-70.