Empirical analysis of the influence of forest extent on annual and seasonal surface temperatures for the continental United States

Abstract

Aim Because of the low albedo of forests and other biophysical factors, most scenario‐based climate modelling studies indicate that removal of temperate forest will promote cooling, indicating that temperate forests are a source of heat relative to other classes of land cover. Our objective was to test the hypothesis that US temperate forests reduce surface temperatures. Location The continental United States. Methods Ordinary least squares regression was used to develop relationships between forest extent and surface temperature. Forest extent was derived from the 900 m2 2001 National Land Cover Database (NLCD 2001) and surface temperature data were from the MODIS 1 km2 8‐day composite (MYD11A2). Forest–surface temperature relationships were developed for winter, spring, summer, autumn and annually using 5 years of MODIS land surface temperature data (2007–11) across six spatial scales (1, 4, 9, 16, 25 and 36 km2). Regression models controlled for the effects of elevation, aspect and latitude (by constraining the regressions within a 1° range). Results We did not find any significant positive slopes in regressions of average annual surface temperatures versus the proportion of forest, indicating that forests are not a source of heat relative to other types of land cover. We found that surface temperatures declined as the proportion of forest increased for spring, summer, autumn and annually. The forest–surface temperature relationship was also scale dependent in that spatially extensive forests produced cooler surface temperatures than forests that were dominant only locally. Main conclusions Our results are not consistent with most scenario‐based climate modelling studies. Because of their warming potential, the value of temperate afforestation as a potential climate change mitigation strategy is unclear. Our results indicate that temperate afforestation is a climate change mitigation strategy that should be implemented to promote spatially extensive forests.

Atmospheric, radiative, and hydrologic effects of future land use and land cover changes: A global and multimodel climate picture

“…It is widely accepted that the impact of removing forests for agriculture depends on the spatial scale of the change [ Lawrence and Vandecar , ; Pitman and Lorenz , ]. However, to our knowledge, few global studies addressed the linearity and strength of the relationship between BPH changes and LULCC intensity [e.g., D'Almeida et al , ; de Noblet‐Ducoudré et al , ; Wickham et al , ; Badger and Dirmeyer , ].…”

Community Earth System Model Simulations Reveal the Relative Importance of Afforestation and Forest Management to Surface Temperature in Eastern North America

“…Remote sensing has been used to compare satellite-derived estimates of air temperature between pixels of different land-cover and forest types [6,15,16]. However, comparing the relative influence of location, species, and intensity of management requires detectable differences in these factors within a relatively small spatial domain in which background climate is assumed to be homogeneous.…”

Synergistic effects of climate and land cover: grassland birds are more vulnerable to climate change

“…Such weak responses across a suite of different species suggest that forests might provide a modulating effect from changing climatic conditions across the range of variability in this study. This modulating effect could be due to the cooler microclimatic conditions created by the forest canopy closure, which decreases summer ground-level temperatures via increased shading and reduction in movement of air masses (Wickham et al 2012;De Frenne et al 2013;von Arx et al 2013). Indeed, studies on plant ecosystems have shown that forest canopies moderate the sensitivity of juvenile trees to climatic variation .…”

“…Research suggests that forest canopies moderate the impact of climate warming on understory plants by creating cooler microclimatic conditions during the summer months (Bonan 2008;De Frenne et al 2013). Reduced solar radiation, decreased movement of air masses, and increased transpiration tend to decrease temperature variation and lower daily thermal minima in forested areas (Murcia 1995;Chen et al 1999;Wickham et al 2012). On the other hand, open habitats, such as old fields, agricultural, and pasture land (hereafter grasslands), generally create warmer, drier, and more variable microclimates than forests (Geiger et al 2009) and are therefore less likely to provide a similar buffering effect (Villegas et al 2010).…”