Creating a Hydraulic Vulnerability Curve for Two-Year Old Ponderosa Pine Seedlings

Abstract

Anthropogenic driven climate change and subsequent drought conditions have negatively affected limber pine and ponderosa pine forests through mass mortality events, jeopardizing the future of these species and the overall health of montane and subalpine ecosystems. Hydraulic failure is pervasive in tree mortality caused by drought, and results in the loss of conductivity of the xylem through embolism. Complete hydraulic failure is likely not necessary for tree mortality; therefore, quantifying the levels of xylem percent loss of conductivity (PLC) associated with tree death is important for understanding and predicting landscape scale patterns of tree mortality. Hydraulic vulnerability curves can be utilized to quantify the percent loss of conductivity in the xylem at a given water potential, which can then be used to predict the lethal threshold for the species. We’ve created three hydraulic vulnerability curves, one found from limber pine leaves, one from limber pine stems, and one from ponderosa pine stems. These were created by measuring the water potential and PLC of 30 two-year old seedlings having undergone different levels of water stress, ranging from no stress to severe water stress. The lethal threshold for hydraulic failure on the curves were determined using logistic regression. These curves can be utilized to predict landscape scale mortality events of limber pine and ponderosa pine colonies due to ongoing water stress, and ultimately help to conserve and protect these species from future drought conditions.