Phenology and growth response of conifers to drought and heat

Climate change is expected to advance the timing of spring growth and flowering for many plant species, lengthening growing seasons and leading to increased growth; but the interaction between increased temperatures and drought stress may not produce that response. In this project we are investigating the phenology and growth responses of mature, field-grown pinyon pine (Pinus edulis) and one-seed juniper (Juniperus monosperma) at the Los Alamos Survival/Mortality Experiment (SUMO) to a factorial experiment manipulating temperature and precipitation. Results from the 2013 growth season demonstrate the heat can reduce growth and delay needle development, that drought has similar effects, and that heat and drought in combination can have strong effects inhibiting needle emergence in pinyon pine (Adams et al. 2015, Global Change Biology). Additionally, reduced growth and delayed development were linked to tree-level measures of water stress and stored non-structural carbohydrate resources. Future work will examine phenology and growth responses across multiple years at SUMO and other sites to investigate stem and bole growth dynamics, reproductive phenology — including the effects of treatments on pollen production in juniper, branch architecture responses, and to more fully elucidate mechanistic links with physiological variables of photosynthesis, respiration, non-structural carbohydrate stores, and water potential.

Physiological mechanisms of drought-induced
tree mortality

Widespread tree mortality from drought, increased temperatures, and tree pests and pathogens in response to climate change has the potential to reshape forest ecosystems and alter biosphere-earth system feedbacks, including terrestrial C sink strength. Projection of these changes would be likely improved through a mechanistic understanding of the physiological process of tree death from drought. Experimental and observational research spanning multiple life stages from seedling to tree across a wide variety of tree species is needed to push the field beyond the false dichotomy between carbon starvation and hydraulic failure. Planned future research in the Environmental Ecology Lab will investigate the interaction of tree drought stress physiology with defense against insect pests and fungal pathogens, explore mortality thresholds in hydraulic failure and carbon starvation, test physiological hypotheses in unexamined species, and seek links between functional traits and mortality physiology.

Environmental Ecology of the eastern
prairie-forest ecotone

The eastern prairie-forest ecotone is a prominent feature of the North American continent driven by gradients in temperature, moisture, and disturbance by fire. Yet the future position of this boundary between biomes under climate change is uncertain. Some tree species, such as eastern redcedar (Juniperus viriginia) appear to be responding to these changes by widespread expansion, yet inverse temperature-growth relationships in many other tree species suggest a potential for increased forest stress with climate change. Future research will address past, present and future drivers of ecosystem change in these regions, and the potential for management to foster mitigation and adaptation to future disturbances.

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Environmental Ecology Lab
Investigating the Relationships Between Organisms and Their Environment
Dr. Henry Adams and colleagues
Department of Plant Biology, Ecology, and Evolution
Oklahoma State University