Ecological Restoration and the Water and Carbon Budgets of Ponderosa Pine Forests
Ecological Restoration Institute
Collaborators: Oleg Menyailo, Tom Kolb, George Koch, Mario Montes-Helu
Project Summary: Assessing the effects of restoration on water and carbon budgets of ponderosa pine forests is critical to predicting the long-term impacts of restoration on forest productivity and water use, ecosystem level processes with clear implications for wildlife, diversity, and links to critical aquatic habitats in the arid Southwest. If forest productivity increases with forest restoration, one might expect water use to increase in concert, as the two are often tightly correlated. Alternatively, because C4 grasses inhabit the understory in restored stands, we might expect that the greater water-use efficiency conferred by this photosynthetic pathway could allow greater forest productivity with less total stand water use. However, understanding the mechanisms altering water-use in restored and control stands requires sophisticated techniques that enable one to partition water use accurately between trees and understory vegetation, and between plants capable of more water-use-efficient C4 photosynthesis versus plants that utilize C3 photosynthesis. In a companion proposal, Kolb, Koch, and Montes-Helú propose to use sap-flow techniques to measure tree water use, and understory removal treatments to assess water use by the understory vegetation. Here, we propose to complement these efforts by: 1) measuring the source of water taken up by trees and understory vegetation; 2) determining the relative contributions of trees and understory vegetation to total stand water flux, and 3) determine the relative contributions of trees and understory vegetation to total forest productivity and respiration. Novel, stable isotope techniques offer a powerful tool for addressing these questions non-intrusively in restored and control forest stands. This research will help managers assess the mechanisms through which forest restoration alters productivity and water use, and will demonstrate a tool for assessing these impacts that could be applied in other restoration efforts.