Regional dynamics of forest canopy change and underlying causal processes in the contiguous U.S.

Abstract

[1] The history of forest change processes is written into forest age and distribution and affects earth systems at many scales. No one data set has been able to capture the full forest disturbance and land use record through time, so in this study, we combined multiple lines of evidence to examine trends, for six US regions, in forest area affected by harvest, fire, wind, insects, and forest conversion to urban/surburban use. We built an integrated geodatabase for the contiguous U.S. (CONUS) with data spanning the nation and decades, from remote sensing observations of forest canopy dynamics, geospatial data sets on disturbance and conversion, and statistical inventories, to evaluate relationships between canopy change observations and casual processes at multiple scales. Results show the variability of major change processes through regions across decades. Harvest affected more forest area than any other major change processes in the North East, North Central, Southeast, and South central regions. In the Pacific Coast and Intermountain West, more forest area was affected by harvest than forest fires. Canopy change rates at regional scales confounded the trends of individual forest change processes, showing the importance of landscape scale data. Local spikes in observed canopy change rates were attributed to wind and fire events, as well as volatile harvest regimes. This study improves the geographic model of forest change processes by updating regional trends for major disturbance and conversion processes and combining data on the dynamics of fire, wind, insects, harvest, and conversion into one integrated geodatabase for the CONUS.

Disturbance and the carbon balance of US forests: A quantitative review of impacts from harvests, fires, insects, and droughts

“…This attribution is likely to over-attribute VCT disturbances to beetle impacts but under-attributes VCT events to windthrow with a likely aggregate effect of underestimating harvest rates based on our use of the NAFD product. Results are consistent with a similar but more detailed disturbance attribution effort by Schleeweis et al (2013). Nonetheless, the wall-to-wall, nationwide data product offers a major leap forward so we include it here.…”

“…In the US, disturbance rates have generally been stable in the east since the 1980s, but the west has seen trends toward elevated tree mortality and stand scale disturbances in response to warming and drought, more frequent and larger fires as well as outbreaks of bark beetles and other pests (Masek et al, 2013;Raffa et al, 2008;Schleeweis et al, 2013;van Mantgem et al, 2009;Westerling et al, 2006). Nationwide rates of forest disturbance measured at a stand scale with remote sensing (order 1000 m 2 ) average about 1.1% per year, but regions with intensive forestry such as the southeast experience 1.5% per year, rising even higher in the mountain West (N2%) where drought, fire and bark beetle disturbances have hastened (Masek et al, 2013;Schleeweis et al, 2013;Williams et al, 2014a). These rates place US forest cover change as high as anywhere in the world (Hansen et al, 2013).…”

How Similar Are Forest Disturbance Maps Derived from Different Landsat Time Series Algorithms?

“…The Canadian portion of scene 12/28 was excluded from the study, as was the significant section of the Atlantic Ocean in 16/37. These scenes were selected to represent a wide range of forest ecosystems, which ensured that a diversity of forest type groups (Table 2) and forest change processes (e.g., harvest, fire, insects, and urbanization as depicted in Figure 5 of [23]) were available for comparing map products. …”

The legacy of episodic climatic events in shaping temperate, broadleaf forests

“…And, unlike semiarid or coniferous systems, fire in this region is typically fine-scaled, spatially heterogeneous (Clark and Royall 1996, Parshall and Foster 2002, Guyette et al 2006, McEwan et al 2007 and less likely to occur at regional scales (though see McMurry et al [2007] for an exception). Thus, dynamics in broadleaf-dominated forests are often characterized as asynchronous in space and time and not seen as strongly influenced by climatic variation like other forest types (Schleeweis et al 2013, Vanderwel et al 2013. Given future climate forecasts, it is imperative that we understand how broadleaf forests in humid regions might respond to climate change at large spatial scales.…”