Base de données de recherche des TNO

étiquettes: climate change, dendrochronology

Objectif(s): To determine the growth and recruitment responses of trees and shrubs to changing climate conditions near tree line.

Description du projet: The objective of this project is to determine the growth and recruitment responses of trees and shrubs to changing climate conditions near tree line and to study drivers of shrub expansion on the tundra. To accomplish these objectives, researchers will measure long-term tree and shrub growth at Havikpak and Trail Valley Creek using tree/shrub ring analysis. Specifically, at each site, small wood samples (cores) will be taken from each individual to measure the changes in annual ring widths through time. Within each site, black and white spruce, alder and willow will be sampled in 10 different locations. There is a potential other common woody species will be sampled where present. The soil between sampling locations may vary with respect to organic layer thickness, drainage, nutrient availability, and active layer thickness . This changes the response of plants to environmental conditions thus, at each site trees will be sampled from stands spanning the range of conditions. Within each stand, a small core sample will be taken from each of 10 healthy trees or shrub of the species present. These samples will be stored in paper straws for transport back to the lab where cores will be prepared, mounted on wooden boards, and ring widths measured. Using historical weather data from Inuvik, researchers will analyzed the tree rings for patterns of growth with climate conditions, assess how different species respond to these climate conditions and how site differences impact the response. To understand the drivers of shrub distribution and shrub patch expansion on the tundra research will sample shrub patches located in distinct topographic locations (drainage channels, hillslopes, plateaus). Within each topographic category 10 shrub patches ranging in size will be selected, thus a total of at least 30 patches will be included in the study. For each of these shrub patches, two 50x50 m gridded plots will be set, 1 including shrubs of interest and 1 adjacent to the shrubs in a shrub-free area. Shrub measurements will occur at regular 10-m intervals within the plots, following standard international shrub monitoring methods, and include size and location of each patch within the plot, shrub density and species composition within each patch, shrub size, and shrub canopy cover. At each of these measurement points, soil moisture and thaw depth will be measured repeatedly though the growing season. Previous research suggests that soil moisture may be a key constraint on shrub patch expansion. To directly test this possibility, researchers will study shrub growth, water use (measured with sap flow sensors), and water stress (measured with stem psychrometers) in relation to local soil moisture and topographic position. Shrub patch size, composition, distribution, growth and water use will be related to local physical (soil moisture, thaw depth) and biological (ground vegetation composition and structure, organic layer depth) and the role of topographic position assessed. At the end of the field season, the researchers will host a methods-oriented session with a plain language results presentation. Plain language and technical documentation of all results will be provided online at the researchers' website. The fieldwork for this study will be conducted from May 28, 2015 to August 27, 2015.