Environmental controls on sap flow in a northern hardwood forest

Abstract

Our objective was to gain a detailed understanding of how photosynthetically active radiation (PAR), vapor pressure deficit (D) and soil water interact to control transpiration in the dominant canopy species of a mixed hardwood forest in northern Lower Michigan. An improved understanding of how these environmental factors affect whole-tree water use in unmanaged ecosystems is necessary in assessing the consequences of climate change on the terrestrial water cycle. We used continuously heated sap flow sensors to measure transpiration in mature trees of four species during two successive drought events. The measurements were scaled to the stand level for comparison with eddy covariance estimates of ecosystem water flux (Fw). Photosynthetically active radiation and D together explained 82% of the daytime hourly variation in plot-level transpiration, and low soil water content generally resulted in increased stomatal sensitivity to increasing D. There were also species-specific responses to drought. Quercus rubra L. showed low water use during both dry and wet conditions, and during periods of high D. Among the study species, Acer rubrum L. showed the greatest degree of stomatal closure in response to low soil water availability. Moderate increases in stomatal sensitivity to D during dry periods were observed in Populus grandidentata Michx. and Betula papyrifera Marsh. Sap flow scaled to the plot level and Fw demonstrated similar temporal patterns of water loss suggesting that the mechanisms controlling sap flow of an individual tree also control ecosystem evapotranspiration. However, the absolute magnitude of scaled sap flow estimates was consistently lower than Fw. We conclude that species-specific responses to PAR, D and soil water content are key elements to understanding current and future water fluxes in this ecosystem.

Species‐specific transpiration responses to intermediate disturbance in a northern hardwood forest

“…Allometric equations relating diameter at breast height to sapwood area were developed for the main species (aspen, birch, and maple) at our site by Bovard et al [2005]. An expansion of the Bovard et al [2005] study was conducted during summer 2014 to determine allometric scaling relationships for red oak, white pine, and American beech.…”

“…An expansion of the Bovard et al [2005] study was conducted during summer 2014 to determine allometric scaling relationships for red oak, white pine, and American beech. To develop these relationships, tree cores were taken at breast height and stained using a 2% solution of tetrazolium chloride (TTC) to determine the depth of hydroactive xylem.…”

Leaf water status and stem xylem flux in relation to soil drought in five temperate broad-leaved tree species with contrasting water use strategies

“…An expected rise in air temperature in temperate regions would increase the evaporative demand and should decrease available soil water relative to current conditions. The consequences of these changes for European temperate tree species and forests are still not sufficiently understood (Bovard et al, 2005).…”

Assessing the environmental controls on Scots pine transpiration and the implications for water partitioning in a boreal headwater catchment

“…32 T is regulated by stomata behavior constrained by both atmospheric conditions and soil water 49 availability (Whitehead, 1998;Buckley et al, 2003;Wang et al, 2014). The mechanisms have 50 been extensively explored at multiple scales from stomata and leaf to whole tree and ecosystem 51 levels (Jarvis and McNaughton, 1986;Schulze et al, 1994;Bovard et al, 2005). Among the 52 constraining variables, atmospheric vapor pressure deficit (VPD) and solar radiation (Rs) are 53 the two major dominant controlling factors (Bovard et al, 2005).…”

“…The mechanisms have 50 been extensively explored at multiple scales from stomata and leaf to whole tree and ecosystem 51 levels (Jarvis and McNaughton, 1986;Schulze et al, 1994;Bovard et al, 2005). Among the 52 constraining variables, atmospheric vapor pressure deficit (VPD) and solar radiation (Rs) are 53 the two major dominant controlling factors (Bovard et al, 2005). However, secondary 54 controlling factors (such as temperature, Ta, soil water content, θ) vary with climates and 55 species (Guo et al, 2010;Chen et al, 2014).…”