Validation of North American Forest Disturbance dynamics derived from Landsat time series stacks

Thomas, Nancy E.; Huang, Chengquan; Goward, Samuel N.; Powell, Scott; Rishmawi, Khaldoun; Schleeweis, Karen; Hinds, A.

doi:10.1016/j.rse.2010.07.009

Cited by 105 publications

(71 citation statements)

References 18 publications

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“…In addition, the accuracy of the VCT change detection was hampered by occasional inconsistencies in the acquisition date of images within the time series. Using the bias--adjusted figure derived from Thomas et al (2011) of 3.63 Mha/yr (1.42% forestland/yr) brings the satellite--based disturbance estimates closer to the inventory figure. Finally, there remains the possibility that the NAFD sampling approach introduced some bias into the results compared to geographically comprehensive estimates from forest inventories.…”

Section: Meddens Et Al (2012) Assessed the Actual Tree Mortality Areamentioning

confidence: 89%

“…The results yielded overall per--scene accuracies of 77% to 86% and kappa values of 0.67 to 0.76 (Thomas et al, 2011). Considering only the forest change classes, omission and commission errors varied widely due to small sample sizes for individual year classes.…”

Section: Per--scene Disturbance Product Qualitymentioning

confidence: 98%

“…The creation of scene--level NAFD disturbance products has been described in detail previously (Huang et al, 2009;2010a, 2010b, Thomas et al, 2011. Here we briefly summarize the steps required to map disturbance within each Landsat sample scene and then describe the quality of the products in terms of severity and types of disturbance detected.…”

Section: Deriving the Scene--level Disturbance Productsmentioning

confidence: 99%

“…First, six scenes representative of a range of forest and disturbance classes were selected to evaluate VCT performance (Thomas et al, 2011). These locations included a variety of disturbance types, including forest fire, harvest, thinning, land use conversion, and both storm and insect damage.…”

Section: Per--scene Disturbance Product Qualitymentioning

confidence: 99%

“…Both natural and anthropogenic stand clearing disturbances (principally clear--cut harvest, severe fires, and major storm events) could be detected with high accuracy (75--85% detection accuracy), while non--stand clearing disturbances (including thinning, understory burns, and insect defoliation events) were only detected with 38% accuracy (Thomas et al, 2011). It should be noted that this latter figure increased to 60% accuracy if the allowable temporal window was relaxed to +/--1 year.…”

Section: Per--scene Disturbance Product Qualitymentioning

confidence: 99%

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United States Forest Disturbance Trends Observed Using Landsat Time Series

et al. 2013

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Disturbance events strongly affect the composition, structure, and function of forest ecosystems; however, existing U.S. land management inventories were not designed to monitor disturbance. To begin addressing this gap, the North American Forest Dynamics (NAFD) project has examined a geographic sample of 50 Landsat satellite image time series to assess trends in forest disturbance across the conterminous United States for 1985--2005. The geographic sample design used a probability--based scheme to encompass major forest types and maximize geographic dispersion. For each sample location disturbance was identified in the Landsat series using the Vegetation Change Tracker (VCT) algorithm.The NAFD analysis indicates that, on average, 2.77 Mha/yr of forests were disturbed annually, representing 1.09%/yr of US forestland. These satellite--based national disturbance rates estimates tend to be lower than those derived from land management inventories, reflecting both methodological and definitional differences. In particular the VCT approach used with a biennial time step has limited sensitivity to low--intensity disturbances. Unlike prior satellite studies, our biennial forest disturbance rates vary by nearly a factor of two between high and low years. High western US disturbance rates were associated with active fire years and insect activity, while variability in the east is more strongly related to harvest rates in managed forests. We note that generating a geographic sample based on representing forest type and variability may be problematic since the spatial pattern of disturbance does not necessarily correlate with forest type. We also find that the prevalence of diffuse, non--stand clearing disturbance in US forests makes the application of a biennial geographic sample problematic. Future satellite--based studies of disturbance at regional and national scales should focus on wall--to--wall analyses with annual time step for improved accuracy. IntroductionChange is ubiquitous in forest ecosystems. Forests experience both seasonality as well as long--term growth cycles that can vary in duration between 50 years and 500 or more years (Waring & Running, 2007). These long--term changes are punctuated by mostly short--term disturbances from fire, insects, disease, and harvest which strongly alter the state and functioning of the forest (He & Mlandenoff, 1999). Both climate change and the increasing global demand for wood and fiber products are likely to drive increases in forest disturbance rates Nepstad et al., 2008). These changes in disturbance will alter the water and carbon cycles of forest stands as well as impact the habitat and biodiversity of these ecosystems (Lindenmayer et al., 2006;Gardner et al., 2009). With respect to the carbon cycle, forest disturbance is now recognized as a major driver of non--fossil--fuels--related terrestrial fluxes to the atmosphere (Running, 2008; Amiro et al., 2010).To effectively understand how forest disturbance impacts forest state and functioning, disturbance rates...

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Section: Meddens Et Al (2012) Assessed the Actual Tree Mortality Areamentioning

confidence: 89%

Section: Per--scene Disturbance Product Qualitymentioning

confidence: 98%

Section: Deriving the Scene--level Disturbance Productsmentioning

confidence: 99%

Section: Per--scene Disturbance Product Qualitymentioning

confidence: 99%

Section: Per--scene Disturbance Product Qualitymentioning

confidence: 99%

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United States Forest Disturbance Trends Observed Using Landsat Time Series

et al. 2013

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

et al. 2013

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[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.

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