Agriculture and development have made the temperate forests the most heavily fragmented forest biome in the world. Landscapes with fragmented forests are typically characterized by abrupt transitions between forest and non-forest land covers (e.g., meadows, agricultural land, development). These abrupt transitions between forest and non-forest land covers induce large gradients in environmental conditions (e.g., light, temperature, humidity, and soil moisture) between the forest edge and interior. For example, forest edges are typically hotter, drier, and have greater exposure to wind and light than the forest interior (Smith et al. 2018). Gradients in environmental conditions across the non-forest-to-forest interior ecotone can be large and create gradients in carbon and water cycling and forest structure (e.g., above and belowground biomass, rooting behavior, and canopy architecture) (Reinmann and Hutyra 2017; Harper et al. 2005; Herbst et al. 2007). At the same time, forest edge effects can exacerbate the negative impacts of climate stress (e.g., excessive heat, drought) on ecosystem processes (Reinmann et al. 2020; Reinmann and Hutyra 2017). This summer, we will use the Climate Interactions with Forest Fragmentation (CLIFF) experiment–a new forest fragmentation x precipitation manipulation experiment–as a model system to study how carbon and water cycling, tree growth, leaf ecophysiology, and litter decomposition/detritivores respond to changes in important resources and stressors related to temperature and availability of light and water. Through this new experiment we are also manipulating precipitation to better understand how edge effects, water availability, and air temperatures all interact to mediate ecosystem processes.
SUBPROJECT 1 - Living on the edge: Tree growth in fragmented forests
Forest fragmentation creates abrupt transitions (i.e., forest edges) which induce large gradients in key environmental drivers of tree growth (e.g., light, temperature, and soil moisture) between the forest edge and interior. However, we are only beginning to learn how these changes in environmental conditions alter tree architecture and wood production dynamics. The higher light conditions at the edge likely trigger a cascade of ecophysiological responses that, over time, result in a vegetative “walling off” of the forest edge. During this walling off period, tree canopy architecture likely becomes more complex from epicormic branching–lateral growth of tree limbs–and a proliferation of new leaves taking advantage of higher light conditions at the edge. As the walling off process matures, the influence of excess light and elevated temperatures on the forest interior likely subsides. We know that trees along mature forest edges can grow twice as fast or faster than trees in the interior, but these trees are also more adversely impacted by heat stress. This REU project will use measurements at CLIFF to address three key remaining areas of uncertainty. First, how do tree growth dynamics evolve over time as forest canopy structure changes following the creation a new forest edge? Second, how does water availability modulate the magnitude of heat sensitivity of trees near a forest edge versus the forest interior? Third, does the response of tree growth respond before or after changes in leaf area (e.g., walling off)? Field work will center around using dendrometer bands and automated point dendrometers to quantify the magnitude and temporal patterns of tree stem wood production along transects between the forest edge and interior. Additional measurements will include quantifying leaf area index and possibly tree sap flow. A typical week will entail: field work to measure dendrometer bands and download data from point dendrometers and microenvironment sensors, compile/review literature on forest edge effects, curating and analyzing datasets, and preparation for a final presentation. We expect this project will fill important knowledge gaps on environmental controls tree growth that support broader research goals of linking tree ecophysiology to ecosystem carbon sequestration across human-altered landscapes.
SUBPROJECT 2 - Impacts of forest fragmentation and climate on CO2 fluxes from soils
Forest soil fluxes of CO2 are largely driven by biological metabolic processes of roots and microbes. These metabolic processes are heavily mediated by microenvironmental conditions such as temperature, soil moisture, and substrate availability, all of which vary considerably between the forest interior and edge. Prevailing climate conditions can also influence biological fluxes of CO2. Recent research has indicated that forest edge effects can stimulate rates of soil respiration in rural landscapes but suppress soil respiration in urban landscapes (Smith et al. 2019; Garvey et al. 2022). In this subproject, we will conduct weekly or bi-weekly soil respiration measurements along transects from the cleared area adjacent to the forest to the forest edge and through the forest interior across precipitation treatments at CLIFF to better understand the environmental controls and influences of forest fragmentation on forest CO2 fluxes. Through measurements of soils with and without roots, we will also quantify the separate contributions of roots + rhizosphere and heterotrophs (i.e., microbes) to soil respiration. A typical week will entail: field work to quantify rates of soil respiration via measurements of CO2 fluxes from PVC collars we have placed in the soil, download data from microenvironment sensors, compile/review literature on forest edges and forest carbon fluxes, curating and analyzing datasets, and preparation for a final presentation. This work may also include quantification of leaf litter mass on the forest floor to explain spatial variations in soil respiration. We expect this project will fill important knowledge gaps on environmental controls on carbon fluxes in temperate forests that support broader research goals of linking above and belowground processes to ecosystem carbon sequestration across human-altered landscapes.
SUBPROJECT 3 - Soil Invertebrate Communities and Litter decomposition
Soil invertebrates are essential for ecosystem functioning, contributing to decomposition and nutrient cycling, as well as numerous trophic interactions below and above ground. Invertebrates are impacted by numerous interacting stressors, including habitat loss and climate change, yet disentangling factors at a large spatial scale has been logistically challenging and limits our ability to forecast future impacts of climate change. Previous work in this system has shown that warming can affect both abundance, diversity, and composition of soil invertebrates, as well as decomposition rates (Figueroa et al. 2021), yet how edge effects and water availability influence patterns is much less known. In this project we will evaluate how edge effects and water availability influence invertebrate abundance, diversity, functional role, and ecosystem service provisioning. The students will collect weekly leaf litter samples, and using Berlese funnels, will evaluate the soil invertebrates present in the six different treatments: forest interior low water, forest interior high water, forest interior water control, forest edge low water, forest edge high water, and forest edge water control. The student will also evaluate maple leaf decomposition from previous years.The students will learn to analyze the patterns in R, evaluating the effects of forest edge and water availability on invertebrate abundance, diversity, and functional role (namely predators vs not), as well as evaluate consequences for leaf litter loss at the end of the field season. This project will expand our understanding of how interacting anthropogenic stressors, namely climate change and habitat alteration, influence invertebrate communities and ecosystem service provisioning.
SUBPROJECT 4 - Tree sway dynamics and wind resistance
The interacting impacts of climate change and anthropogenic forest fragmentation on forest microclimates pose unknown ramifications for forest composition, structure, and function. Storm damage, drought, and fragmentation are all increasing forest health concerns in regions such as Southern New England where both storm and drought frequency and intensity are increasing under global climate change. Trees in edge forests experience greater wind and water stress than interior forest. Individual trees, especially in edge habitats, develop wind resistant structural features through the process of thigmomorphogenesis. Wind-driven thigmomorphogenesis is the process through which the movement of tree structures triggers the development of stouter, wind firm growth patterns. The characteristics of tree sway are an indicator of this process and can serve as a biomechanical link between climate and tree growth signaling that can provide quantifiable insight into how efficiently an individual is coping with its wind load. This study focuses on Quercus rubra (anisohydric) and Acer rubrum (isohydric) individuals across the edge to interior spectrum. Anisohydric trees such as red oak allow their leaf water potential to decrease by leaving their stomata open under water stress and isohydric species such as red maple close their stomata to conserve leaf water potential under water stress conditions. Anisohydric behavior is considered a higher risk, higher reward drought management strategy than isohydric behavior. By understanding patterns of tree sway within the CLIFF experimental context, we hope to better understand the interactive relationship between edge, climate, and structure for these two ecologically important species. We utilize biaxial inclinometers to capture tree sway for twelve Q. rubra and eight A. rubrum individuals. Half of the study population is in the CLIFF reference area and half are in the throughfall exclusion area to facilitate comparison.
This summer, we will deploy field cameras to measure vegetation reflectance, phenology, and tree sway videos. The objective is to assess leaf health and density using vegetation indices such as NDVI, track leaf emergence and senescence, and develop proof of concept for video-based tree sway measurement. Students will also assist with maintenance of all sensors, including the ~1 mile long wire network for the biaxial inclinometer sensors, and deploying new meteorological instruments.
General requirements for all overall project, regardless of sub-project:
1. Depending on the subproject, students can expect to spend ~50% of their time in the field. The ideal candidate has a positive attitude in group environments and is comfortable working under a range of conditions (e.g., hot and humid, cool and rainy, buggy, etc.)
2. An inquisitive nature and comfortable asking questions
3. Experience using R or the motivation to learn. This will be the primary software used for data analysis and visualization
4. Capable of walking 2+ miles (in a day) on and off trails to visit field sites
1. Reinmann AB and Hutyra LR. 2017. Edge effects enhance carbon uptake and its vulnerability to climate change in temperate broadleaf forests. Proceedings of the National Academy of Sciences 114(1): 107-112. DOI: 10.1073/pnas.1612369114
2. Smith et al. 2018. Piecing together the fragments: elucidating edge effects on forest carbon dynamics. Frontiers in Ecology and the Environment 16: 213-221.
3. Reinmann, A. B., Smith, I. A., Thompson, J. R., & Hutyra, L. R. (2020). Urbanization and fragmentation mediate temperate forest carbon cycle response to climate. Environmental Research Letters, 15, 114036–114036.
4. Mourelle, C., Kellman, M., & Kwon, L. (2001). Light occlusion at forest edges: An analysis of tree architectural characteristics. Forest Ecology and Management, 154(1–2), 179–192.
5. Herbst, M., Roberts, J. M., Rosier, P. T. W., Taylor, M. E., & Gowing, D. J. (2007). Edge effects and forest water use: A field study in a mixed deciduous woodland. Forest Ecology and Management, 250(3), 176–186. https://doi.org/10.1016/j.foreco.2007.05.013
6. Smith, I. A., Hutyra, L. R., Reinmann, A. B., & Thompson, J. R. (2019). Evidence for Edge Enhancements of Soil Respiration in Temperate Forests Geophysical Research Letters. Geophysical Research Letters, 46, 1–10. https://doi.org/10.1029/2019GL082459
7. Garvey SM, Templer PH, Pierce EA, Reinmann AB, and Hutyra LR. 2022. Diverging patterns at the forest edge: soil respiration dynamics of fragmented forests in urban and rural areas. Global Change Biology. 28:3094-3109. DOI: 10.1111/gcb.16099
8. Barker-Plotkin A, Blumstein M, Laflower D, Pasquarella VJ, Chandler JL, Elkinton JS, and Thompson JR. 2021. Defoliated trees die below a critical threshold of stored carbon. Functional Ecology. 34(10): 2156-2167.
9. Richardson AD, Carbone MS, Keenan TF, Czimczik CI, Hollinger DY, Murakami P, Schaberg PG, and Xu X. 2013. Seasonal dynamics and age of stemwood nonstructural carbohydrates in temperate forest trees. New Phytologist. 197: 850-861.