Performing Department
School of Forest Resources
Non Technical Summary
Climate change is expected to increase the likelihood of drought and extreme heat events that candamage the water transport system in trees leading to tree mortality and subsequent shifts in forestcommunity composition. Much of ourunderstanding of drought impacts in forests is from arid systems such as the western United States(US) where drought has been implicated in large scale forest community changeand tree mortality. In contrast to the western US, droughtshave been rare in the relatively mesic forests of the northeastern US. The lack of drought in thenortheastern US, however, has resulted in forests composed of drought intolerant species that may not be adapted to future climate conditions.To predict how northeastern US forests willrespond to future climate conditions, this project willuse experimental manipulation of environmentalconditions to reflect future climates and direct measurements of plant physiological responses to those changes. Experimental manipulations will includelimiting moisture for sapling and canopy sized trees and measuring their physiological responses and survival. In addition, to understand how the anatomyof different species can make some species more or less resilient to climate change, I will measure fine-scale aspects of their water transport systemsand how they function during drought. Finally, to better predict drought responses at whole-forest scales, I will collect data linking leaf and tree level metrics of photosynthesis and water transportto large-scale ecosystem level metrics.This research will improve our knowledge of how forests of the northeastern US will respond to future climate conditions benefitingforest managersand resulting in moreresilient forestecosystems.
Animal Health Component
0%
Research Effort Categories
Basic
75%
Applied
25%
Developmental
(N/A)
Goals / Objectives
1. Determine how forest trees will respond to future novel climate conditions.2. Test xylem structure-function relationships for woody plants in the northeastern US.3. Develop a framework for understanding and predicting drought responses of forestecosystems from small (cell, organ) to large (tree, forest) scales.
Project Methods
Approach: This research will use a combination of experimental and observational field studies as well as lab physiological and anatomical measurements of xylem structure and function.1. Forest tree responses to novel future climates and changing environments. To test tree responses to novel climate conditions, this research will manipulate environmental conditions at important tree life stages: 1) germination, 2) seedling/sapling growth, and 3) mature canopy trees. We will establish a greenhouse germination and field drought experiment where water availability can be controlled and monitored with rainout shelters and supplemental irrigation. This initial study will include a mix of regionally important tree species including those with more southerly and more northerly distributions that will be monitored for germination and growth under differentwatering regimes in the greenhouse. At least 50 seeds from each species will be included in the germination trials. A second set of seedlings will be germinated under well-watered conditions for transplantation to the field experiment that will have elevated clear plastic sheeting to exclude all rainfall from three treatment blocks. Each block will be split into drought and irrigated treatments that will be irrigated with collected rainfall and supplemented with other water as needed. Five individuals per species of five species will be planted in 6×6 ft treatment areas. This research will also inform other longer-term objectives to establish common garden trials with sapling treesplanted across elevational and/or latitudinal gradients.We will also run a pilot test of canopy tree responses to manipulated environmental conditions using elevated rainout shelters (tarps suspended ~1.5 meters above the soil surface) in canopy forests (D'Orangeville et al., 2013). We will locate three forest locations where rainout shelters can be installed in ~10×10 m areas similar to D'Orangeville et al. (2013). In both drought experiments we will monitor environmental conditions (e.g., temperature, rainfall, soil moisture), plant growth (e.g., height, diameter, increment growth, root and shoot biomass), xylem anatomy (e.g., vessel size and number, cross-ring connection frequency), and physiological responses (e.g.,water potential, conductance, photosynthesis, water use efficiency, embolism resistance).2. Xylem structure and function. To determine the relationships between xylem structure and function in woody plants, we will start with a broad survey of cross-ring xylem connections in woody plants of the northeastern United States. We will use a combination of dye-staining, light microscopy, and X-ray microtomography measurements to determine which species and tissues use previous growth rings for axial sap transport. After developing a database of species traits related to cross-ring xylem transport, we will measure the impact of cross-ring connections on drought resistance such as the ability to access stored water reserves in older growth rings(Mcculloh et al., 2014) and how drought resistance may change across growth rings (Melcher et al., 2003). Samples for these measurements will be collected locally at the Demeritt Forest and Penobscot Experimental Forest. Extensions of this research will be explored with the forest products industry to better understand how xylem structure, water transport, and storage differences between species and at different times of the year may impact harvest time and cost.3. Multi-scale drought responses. To explore the drought response of canopy forest trees and the relationship to stand level metrics of water use, we will take advantage of the long-term eddy-covariance measurements at Howland Cooperating Experimental Forest. Measurements of leaf-level gas exchange and whole-tree sap flow on canopy trees will be used to compare leaf, tree, and stand level estimates of water use efficiency during different environmental conditions (Medlyn et al., 2017). Sampling will be conducted on multiple days during the growing season selected to represent moist and dry soil conditions by periodically tracking soil moisture and tree water potential. During a sampling day, stomatal conductance will be measured on multiple species and leaves every two hours. In addition, a sap flow sensor will be installed in at least one test tree for the duration of the growing season. Other cross-scale comparisons will be explored including comparing temperature and moisture conditions of a species' current range with tree growth and photosynthesis requirements to determine if physiological limitations match growth and distributions. These experiments will be exploratory and preliminary to help leverage external funding.