Recipient Organization
RUTGERS, THE STATE UNIVERSITY OF NEW JERSEY
3 RUTGERS PLZA
NEW BRUNSWICK,NJ 08901-8559
Performing Department
Ecology, Evolution & Natural Resources
Non Technical Summary
Regeneration failure of canopy trees due to overabundance of white-tailed deer and invasive non-native plant species is a critical issue defining the future of Northeastern forests. These stressors affect current and future populations of economically important tree species by impeding plant regeneration. In a test site, Rutgers' Hutcheson Memorial Forest (HMF), a unique old growth forest of this region, we have recently discovered detailed forest structure data sheets and field plots from 1950. These give us the opportunity to compare the historic structure from 66 years ago to four more recent data intervals. These 1950 detailed data sets also provide a foundation for putting future forest dynamics into a very long-term ecological perspective. Additionally, a 3-meter tall deer-proof fence was installed around HMF in the fall of 2015; we now can study precisely the dynamics of forest regeneration after the substantial removal of the main herbivore stressor.However, even without deer herbivory, the fate of this forest and others in the region is uncertain. Future climate change, particularly more severe summer droughts, is expected to increase tree mortality and decrease rate of recruitment, resulting in a loss of habitat and wood products. Understanding how the future of woodlots (important for both forest products and ecosystem services such as groundwater protection and air quality) can be made sustainable requires detailed understanding of the impact of these stresses and pragmatic treatments to ameliorate them. The results of this study will inform regional forest health and sustainability management protocols. We will study the old plots and see what has changed. We will compare areas with and without deer. We will record growth of the wildflower populations now that dense deer herds are gone.
Animal Health Component
25%
Research Effort Categories
Basic
75%
Applied
25%
Developmental
(N/A)
Goals / Objectives
Four complementary studies are proposed:What is the trajectory of forest change over the past 6 decades? We now have available detailed quantitative data sets from 1950, 1969, and 1979 which can be appended to our previously known data set from 2003. The historic data are from 25 experimental plots, each 10x10m, which we can now revisit. We have already located the old 1950 plots in the field. This integrates 66 years of stressors: deer, invasive plant and insect damage, as well as climate change that has already occurred. This is a rare opportunity to build off this long-term data set to characterize successional trajectories of this forest type that has been impacted by climate change, urbanization, and biotic invasion (plants and insects). We believe this represents the longest continual data set for a woodlot in an urbanized landscape. (Harvard Forest in Massachusetts is a longer data set, but in a rural setting.) With additional sampling in 2016, we will have extensive data from the five investigative moments during this 66 year interval. This will be a foundation upon which to interpret future forest structure change, as it unfolds, during the increasingly rapid climate regime expected in coming decades. We have found 7 of the 8 transect markers from the 1950 plots and we have re-marked and GPS-mapped them. This will allow us to investigate very long-term forest dynamics at these locations after sixty-six years of stand development. Future investigators can then add to this record, as research needs evolve. This will also set the baseline for an NSF Long-Term Research in Environmental Biology proposal which requires 5 data points for funding.2. What is the outcome of a forest released from deer herbivory in the presence and absence of the current suite of invasive plant species?Many studies have shown that forest structure and composition can recover after being released from deer herbivory, but this recovery varies spatially. Recovery may be contingent upon how long the forest has been degraded (propagules unavailable, for example) and the impact of presence and abundance of invasive plant and insect species. In 2013, we reestablished 20 plots that M. Aronson had established in the old growth and an adjacent old secondary forest. In 5 plots in each forest type, we removed all invasive plant species. In the fall of 2015, a 3-meter fence was installed around only the old growth stand. We now can assess how the forest responds to both deer and invasive species removal. These first years after fence installation are critical to examine the impact of the seed bank, regrowth from cropped stems, and seedling establishment. This will allow us to determine which specific canopy tree species will "return" and which species must be considered for proactive re-planting. Results from this data set will inform many other woodlot managers where deer management actions are occurring as to the need for (expensive) replanting of past species diversity or whether no planting actions are needed.3. In a post-herbivory condition, what are other potential ecological barriers to recruitment of canopy trees? At HMF we observe a forest community in which many of the old growth oaks have begun to senesce or fall during major storms while smaller size classes of oak species are underrepresented. The failure of oak species to regenerate and recruit has been reported across manydeciduousforests of eastern North America (McEwan et al., 2011). Recent research suggests multiple driving forces limiting oak recruitment, including fire suppression, seed/seedling predation, anthropogenic disturbances, and changing climate. With the removal of high density of deer from HMF, we have the opportunity to measure the recruitment limitation in the old growth forest and identify some critical ecological barriers for native tree recruitment.More broadly, what is the potential for the oak-hickory forest to persist at HMF? Does the limited disturbance to soils make HMF more resilient when compared to other regional sites that are on previously plowed land? We seek to measure recruitment limitation in closed canopy and gap conditions to determine how the mosaic of recruiting tree species may shift over time following deer exclusion. This experiment will run concurrently with similarly designed studies from our lab (led by M. Piana) in other urban andruraloak-hickory forests across the region, allowing for comparison of the processes at HMF with sites across the mid-Atlantic.4. Can the critical spring flora recover after severe herbivory?This stratum of the forest plant community has been heavily damaged by deer herbivory, regionally (Aronson and Handel, 2011). These herbs are important species for ecological function and well as cultural interest. Spring ephemerals bind the soil during spring rains, and provide resources for forest animal species (bees, ants, ground foraging mammals, and birds) early in the growing season when few other living plant resources are available. Moreover, these plant species are important for nutrient retention in forest systems: the "vernal dam" hypothesis, as the plants and their associated microbes are active when canopy trees and shrubs are still substantially dormant (Muller, 2003; Gerken et al., 2010). The spring plants have been shown to retain N in watersheds, keeping these nutrients away from drainage waters. The Hutcheson Memorial Forest lies in the Raritan River watershed and contains a headwater stream, Spooky Brook.These species have very small populations at HMF due to deer and invasive species. They once were abundant, according to our older records. To understand the potential for regeneration of small remnant populations, we will monitor clonal expansion and seedling recruitment of individual ramets and genets of four representative native spring herb populations. Mayapple (Podophyllum peltatum), blue stemless violet (Viola sororia), wild leek (Allium tricoccum), and jack-in-the-pulpit (Arisaema triphyllum) are all present in small population numbers inside the deer fence. These represent a guild of herbaceous species with different life history expansion strategies (exploratory clonal growth and mammal-dispersed fruit, ant-mediated and explosive seed dispersal, cespitose clonal expansion and bird-dispersal fruit, and small-mammal-dispersed seed clusters), and have well-known natural histories (e.g. Ruhren and Handel, 2000, 2011; Nault and Gagnon, 1993; Sohn and Policansky, 1977; Culver and Beattie, 1978). By recording growth of numbers and mode of expansion of these remnant populations, we can model the speed and extent of population expansion after removal of the deer herbivores, and project the speed with which these species can cover the ground, restoring the history density of these species in this habitat type.
Project Methods
1. What is the trajectory of forest change over the past 6 decades? In the 25 original plots established in 1950 by Buell (see above), we will sample canopy tree seedling species and abundance, sapling and tree species and growth, shrub species and cover, and herbaceous species identity and cover in all plots. All trees >10 cm dbh will be tagged with permanent tree tags and their location mapped with GPS. These plots will be sampled in the exact methods outlined in Sulser (1971) and Davison and Forman (1982). We will sample the plots in Year 1 to capture the present condition and in Year 3 to see performance two years after deer removal. Data will be analyzed to examine the change in the flora from Year 1 to 3, and the change over 69 years, comparing to the 1950, 1969, and 1979 data. Using a database on plant traits, developed by M. Aronson, we will also examine the phylogenetic and plant functional trait changes over time. Most importantly, we will use this data to examine the changes in canopy seedling and sapling species composition and abundance over time. This will allow us not only to report on how the forest has changed, but also to make predictions of how the forest may change with future stressors.2. What is the outcome of a forest released from deer herbivory in the presence and absence of invasive species?Twenty 100 m2 experimental plots were established in 2013 at HMF to examine the impact of invasive plant species on canopy tree regeneration and forest vegetation structure and composition. Ten plots were established in the old growth forest and 10 plots in an adjacent old (~150 years) secondary forest. In each forest type, invasive species were removed from five plots continuously from 2013-2015. We also measured canopy tree seedling species and abundance, sapling and tree species and growth, shrub species and cover, and herbaceous species identity and cover in all plots. The old growth forest plots were recently fenced to exclude deer but not small mammal predators. In this current research, we will continue to eliminate invasive species from the removal plots. We will also sample the above listed variables in all 20 plots. We will compare recruitment of seedlings and forest vegetation composition and structure in the two nested conditions (with and without deer; with and without invasive removals).3. In a post-herbivory condition, what are other potential ecological barriers to recruitment of canopy trees?The proposed experiment will use a combination of seed traps, seed bank samples, and seed addition plots to quantify recruitment limitation in two forest conditions: full canopy and canopy gaps.Three plots will be established in each forest condition. These methods will test seed bank and sourceavailability,seed and seedling predation, and establishment dynamics for native trees species in each forest condition.Seed DispersalTen seed traps(0.14m2)will be installed within each experimental plot (n=6) to measure seed rain. Seed traps will be installed at 5 m intervals in two parallel transects (5 traps/transect) spaced 20 m apart. All captured seeds are to be collected from each trap monthly and identified to the species level.We will determine seed limitation and dispersalkernelsbygeo-spatially locating and identifying to species all trees with dbh >10 cm within a 38.85 fixed radius (3600 m2) derived from plot center (methods adapted from Clark et al. 1998).Seed BankWe use seed emergence techniques to determine the abundance and diversity of woody plant species available in the two forest conditions. At each seed trap station, two 5x5x5 cm soil samples will be extracted using a soil core (20 samples per plot). Soil samples will be layered on 4.0 cm of seedling soil mix in plastic flats in a Rutgers greenhouse. Seedling emergence will be monitored for 18 months, with all emergentsidentified to species and then removed from theflat.Recruitment and PredationSeed addition plots will be used to test recruitment limitation and the impact of both seed/seedling predation and leaf litter on recruitment. Using a nested design, we will add native tree seed and observe establishment in a two treatment design: caged/un-caged and ambient leaf-litter/leaf litter removed treatments. In each plot, two seed addition plots (3.5 x 2.5 m) will be installed to quantify recruitment limitation. Each 3.5 x 2.5 m station will be divided into 12 0.5 x 0.5 m quadrats, with 0.5 m between each quadrat to provide access for data collection. To measure the impact of predation on recruitment, seed addition quadrats will be either caged or uncaged. Predation cages are to be constructed with 13 mm hardware cloth and garden stakes. To record the impact of leaf litter on establishment, leaf litter from one half of each quadrat will be removed, but the other half will not be altered. This design will test recruitment in ambient leaf litter and in bare ground conditions.Five species will be included in the caged/un-caged treatment, including Quercus rubra, Carya spp., Acerrubrum, Prunus serotina, and Betula lenta. Augmentationdensity will be determined from the natural species-specific seed rain density observed from seed traps and seed bank sampling. In each treatment, seeds from a single species will be added to the surface. Following seed addition, we will monitor seedling emergence and survival for two years. At each observation we will map seedling location, measure height, and record condition (methods adapted from Poulsen et al. 2013).Microsite conditions or niche-based mechanisms may limit establishment. We will quantify climatic and biotic factors that could impact germination and early seedling establishment, including light availability, leaf litter depth, temperature, soil moisture, and soil nutrient availability (N, P, K, Ca, Mg, and Al), SOM, pH, and bulk density/compaction.4. Can the critical spring flora recover after severe herbivory?For herbaceous species, we will identify five replicate stands of each of the four test species, map and mark location of individual ramets during the 2016 growing season, then remap ramets and genets (seedlings) during the next two years. Most population expansion by asexual (clonal) and sexual (seedling) recruitment is within 3 m of existing plants, and we will search this area for new recruits. (This will underestimate the uncommon long-distance dispersal events. However, space occupation and the bulk of population expansion will occur within this closer zone.) These data will allow us to estimate population growth rate over this initial short period. These mapped populations can be revisited over the longer term for more data, as will be our data sets for the woody species in the forest.