Effects of aggregated classifications of forest composition on estimates of evapotranspiration in a northern Wisconsin forest

Abstract

Forest management presents challenges to accurate prediction of water and carbon exchange between the land surface and atmosphere, due to its alteration of forest structure and composition. We examined how forest species types in northern Wisconsin affect landscape scale water fluxes predicted from models driven by remotely sensed forest classification. A site‐specific classification was developed for the study site. Using this information and a digital soils database produced for the site we identified four key forest stand types: red pine, northern hardwoods, aspen, and forested wetland. Within these stand types, 64 trees representing 7 species were continuously monitored with sap flux sensors. Scaled stand‐level transpiration from sap flux was combined with a two‐source soil evaporation model and then applied over a 2.5 km × 3.0 km area around the WLEF AmeriFlux tower (Park Falls, Wisconsin) to estimate evapotranspiration. Water flux data at the tower was used as a check against these estimates. Then, experiments were conducted to determine the effects of aggregating vegetation types to International Geosphere– Biosphere Program (IGBP) level on water flux predictions. Taxonomic aggregation resulting in loss of species level information significantly altered landscape water flux predictions. However, daily water fluxes were not significantly affected by spatial aggregation when forested wetland evaporation was included. The results demonstrate the importance of aspen, which has a higher transpiration rate per unit leaf area than other forest species. However, more significant uncertainty results from not including forested wetland with its high rates of evaporation during wet summers.

A satellite‐based biosphere parameterization for net ecosystem CO2 exchange: Vegetation Photosynthesis and Respiration Model (VPRM)

“…Several studies have noted [Desai et al, 2008;Wang et al, 2006] the sharp differences between WLEF fluxes versus WCREEK and LCREEK, which are not as similar to each other, or to Howland, as one would like. Mackay et al [2002] compared WLEF stand types to IGBP classes and suggested that four distinct stand types are needed to characterize the region's evapotranspiration fluxes. Possibly the great tower height affects resolution of surface fluxes, extends the area influencing the tower, or introduces measurement artifacts.…”

The Effect of Atmospheric Water Vapor on Neutron Count in the Cosmic-Ray Soil Moisture Observing System

“…The tower is located in the Chequamegon National Forest, and the surrounding area has elevation between 470 and 500 m and is mainly covered with deciduous broadleaf forest vegetation [International Geosphere-Biosphere Programme (IGBP) classification]. According to MacKay et al (2002), the growing seasons are typically short and the winters are long and cold: mean temperatures in January and July are approximately 2128 and 198C, respectively.…”

Ecosystem CO2/H2O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

“…Using physiological responses of individual plants to predict the response of an ecosystem can be challenging [Jarvis, 1995], requiring intensive field campaigns [Sellers et al, 1997] and modeling efforts [Mackay et al, 2002] to capture the relevant nonlinearities and feedbacks. Though the primary physiological response to disturbance might be obvious on the plant scale, the ultimate forest ecosystem response can be complex and difficult to predict [Gough et al, 2013].…”