Investigating Water Sources and Survival Strategies of Conifer Trees Growing on Cliffs.
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2024-02-12
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Abstract
Vertical limestone cliffs in the Canadian Rockies are often heavily fractured. These fractures can collect soil and organic matter and provide a substrate for tree growth on these otherwise inhospitable bedrock cliffs. Trees growing in this environment face several constraints, the most significant of which is limited water availability, yet often live to be well over 150 years old. With the increasing potential for tree mortality due to climate-induced drought in forests worldwide, insight from these already chronically water-stressed trees is invaluable. Here I investigate the source and quantity of water for two species of trees, Douglas Fir (Pseudostuga mensiesii) and Engelmann spruce (Picea engelmannii), growing on a south facing limestone cliff in the Canadian Rockies. I explore the role of the fracture contributing area and fracture soil characteristics in the volume of infiltrated water. Additionally, I look at adaptations of the two species to long-term water stress in this harsh environment. I found that: 1) Both species of trees get water from recent rainfall and evaporated soil water. 2) Overland flow may be a significant additional water input for trees growing on cliffs (2x the volume of direct rainfall). The volume of this input depends on contributing area and soil hydraulic characteristics, with larger contributing areas generating more overland flow and more overland flow infiltrating in soils with higher hydraulic conductivity. 3) Trees growing on the limestone cliff have access to limited amounts of water, moving max daily volumes of sapflow less than 50 L/day in 2021 and 80 L/day in 2022, while trees at nearby glacial till site are moving up to 619 L/day and 418 L/day. 4) Both species cope with chronic water stress by growing slowly and maintaining consistently small sapwood areas. Douglas Fir growing on the cliff maintain higher levels of transpiration during periods with low water availability, which may be attributed to their more cavitation resistant tracheid cells. Although these trees are extremely water limited, they have survived long periods of time, and provide some insight into how chronically water stressed trees are better adapted to deal with water limitation.
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Ives, M. A. (2024). Investigating water sources and survival strategies of conifer trees growing on cliffs (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.