Testing transpiration controls by quantifying spatial variability along a boreal black spruce forest drainage gradient

Abstract

One of the biggest challenges in predicting ecohydrologic fluxes is scaling from easily measured variables to more difficult, often emergent patterns and processes. This is especially true in spatially heterogeneous systems such as black spruce (Picea mariana)‐dominated boreal forests containing excessive and low soil moisture conditions. Traditional hypotheses suggest that transpiration is controlled by hydraulic responses to vapor pressure deficit (D) and soil moisture; however, these may potentially be misinformed because of omission of soil drainage gradients. Thus, we predict that 1) spatial heterogeneity in tree transpiration along a soil drainage gradient is positively correlated with D, 2) sap flux (JS) and leaf‐level transpiration (EL) are higher and whole‐tree transpiration (EC) lower in the poorly drained than well‐drained stands, and 3) spatial heterogeneity of EC is regulated primarily by tree‐related covariates such as sapwood and leaf area and secondarily by environmental covariates including peat and moss depth. With the use of 122 black spruce sap flux measurements, the range of autocorrelation (inverse of spatial variation) decreased from 20 m at low D (<0.7 kPa) to 2 m at midday D values (>0.9 kPa). JS and EL were significantly greater and EC less in poorly drained than well‐drained stands; controlled primarily by tree‐related covariates (sapwood and leaf area) representing long‐term growth conditions and secondarily by soil moisture and spatially sampled D reflecting shorter‐term environmental variation. Quantification of spatial heterogeneity informs predictive models of the distance at which homogeneity can no longer be assumed and will improve mechanistic predictions of transpiration at multiple spatial scales. Copyright © 2012 John Wiley & Sons, Ltd.

Minor contribution of overstorey transpiration to landscape evapotranspiration in boreal permafrost peatlands

“…Such low water use is in accordance with the low productivity and slow growth rates of black spruce at the study site (e.g., following Sniderhan & Baltzer, , at Scotty Creek, a black spruce individual with DBH of ~8 cm is expected to have an average age of ~100 years). In addition, comparable values of J S have been reported for black spruce growing in nutrient‐poor peat soils within the southern boreal forest of western Canada (Angstmann, Ewers, Barber, & Kwon, ; Pappas et al, under review). In contrast, J S reported for smaller‐diameter black spruce growing in mineral soils was about 10 times higher (Ewers et al, ; Van Herk et al, ).…”

“…In contrast, J S reported for smaller‐diameter black spruce growing in mineral soils was about 10 times higher (Ewers et al, ; Van Herk et al, ). This difference may be due to a number of environmental factors controlling the magnitude of J S , including tree structure (Angstmann et al, ; Ewers et al, ), moisture gradients (Angstmann et al, ; Bovard, Curtis, Vogel, Su, & Schmid, ; Oren & Pataki, ), soil nutrients, and presence or absence of permafrost (Iijima et al, ; Patankar et al, ). In particular, Scotty Creek has the lowest overstorey LAI and canopy height among the reported studies in Table and is additionally underlain by nutrient‐poor peat soils.…”

Oil Palm and Rubber Tree Water Use Patterns: Effects of Topography and Flooding

“…The present study adds yet another dimension to the plantation landscape by suggesting that topography and flooding are also strong factors influencing the heterogeneity of landscape-level transpiration patterns. Likewise, studies investigating upland-to-wetland gradients in North-America also found pronounced differences in tree transpiration and it was concluded that it is necessary to include sites at different topographic positions for landscape-level analyses or modeling (Loranty et al, 2008; Mackay et al, 2010; Angstmann et al, 2012). In our case, we found only moderate variation in oil palm water use across space and time, whereas rubber responded strongly to topographic position and temporal flooding.…”

“…In North-America, upland-to-wetland gradients were analyzed by means of sap flux measurements in order to evaluate the significance of site conditions for tree and stand transpiration (Loranty et al, 2008; Mackay et al, 2010; Angstmann et al, 2012). Pronounced differences in tree transpiration were observed among sites and it was concluded that it is necessary to include plots at different topographic positions for landscape-level analyses or modeling of transpiration.…”

Riparian forest transpiration under the current and projected Mediterranean climate: Effects on soil water and nitrate uptake

“…Catchment modelling typically considers riparian areas as homogeneous, even though this is not always the case (Ford, Mitchell, & Teskey, 2008;Tromp-van Meerveld & McDonnell, 2006). Little is known about how spatial patterns of soil characteristics (such as θ, soil texture, soil thickness, and groundwater level [GWL]) can regulate the influence of vegetation on water and N fluxes (Angstmann, Ewers, Barber, & Kwon, 2013;Ocampo, Sivapalan, & Oldham, 2006;Thomas, Abbott, Troccaz, Baudry, & Pinay, 2016). For instance, θ in riparian areas in the Mediterranean region has high spatial variability due to shallow groundwater in the near-stream zone and deeper groundwater in the hillslope zone.…”