Browsing by Author "Hoy-Skubik, Sean"

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Creating a Hydraulic Vulnerability Curve for Two-Year Old Ponderosa Pine Seedlings
(Montana State University, 2023-11) Kincy, Sarah; Hoy-Skubik, Sean; Ulrich, Danielle E. M.
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.
Functional traits underlie specialist-generalist strategies in whitebark pine and limber pine
(Elsevier BV, 2023-08) Ulrich, Danielle E. M.; Wasteneys, Chloe; Hoy-Skubik, Sean; Alongi, Franklin
Plant species life history strategies are described by functional variation spanning an acquisitive and conservative resource use continuum. Specialist species can exhibit traits promoting one end of the continuum, while generalist species can display traits promoting both acquisitive and conservative resource use. Whitebark pine (Pinus albicaulis, PIAL) and limber pine (Pinus flexilis, PIFL) are two high-elevation pines that have similar growth and morphology, yet contrasting elevational distributions with PIAL viewed as a specialist inhabiting a narrower elevation range, and PIFL as a generalist inhabiting a broader elevation range. We compared the physiological and morphological traits of greenhouse-grown 5-year-old PIAL and PIFL. Our results suggest that PIFL’s acquisitive and conservative resource use traits contribute to its generalist strategy and ability to inhabit a greater range of elevations than PIAL. PIFL had greater acquisitive resource use traits including: high-light tolerance (greater Qsat, greater fascicle density), increased biomass allocation to photosynthetic tissue (higher needle biomass, aboveground:belowground biomass, needle:branch + stem biomass), and higher C and water uptake (greater stomatal density and size, higher C assimilation rate), as well as greater conservative resource use traits including: greater physical stress resistance (shorter height, higher stem and branch diameters, greater branch and stem diameter:length), drought tolerance (higher SWC, leaf starch proportion), and drought avoidance (earlier budburst phenology, smaller hydroscape area) than PIAL. Our results suggest that PIFL may make more efficient use of high-light loads and maximize C and water uptake when moisture is abundant during spring snowmelt before the onset of dry summer conditions. Other conservative resource use traits describing cold tolerance, heat tolerance, and drought tolerance did not differ between species, suggesting that both species exhibit traits that promote similar conservative resource use enabling their overlapping persistence at higher elevations. Comparing the physiology of PIAL and PIFL within the same environment enables us to identify physiological mechanisms that underlie species establishment and survival, and how juvenile physiology contributes to their contrasting distributions and their generalist-specialist strategies.