Finding Where U.S. Forests Have Been Undisturbed for a Quarter Century

Forest in Yellowstone National Park

Dr. Chengquan Huang is a Research Professor in the University of Maryland’s Geographical Sciences Department. This afternoon at the 2015 AGU Fall Meeting, Dr. Huang presented a poster explaining where to find U.S. forests that have been undisturbed for last 25 years. His research relied on Landsat to both find these forests and understand forest disturbance trends in the U.S.

Figure 1. High concentrations of undisturbed forests are distributed mostly in the northeast, north central, and western U.S., often along ecoregion boundaries. Image credit: Huang et al.

Presentation title:Where are the forests in the United States “not disturbed” over a quarter century?

Figure 2. Percent forest remaining undisturbed (PFUD) within a time interval decreased following an exponential decay function in the conterminous U.S. and each of its four regions as the time interval increased. Image credit: Huang et al.

• About 1.7 million square kilometers, or two thirds of 2.6 million square kilometers of forest in the conterminous U.S. did not experience any detectable natural or anthropogenic disturbance during the quarter century between 1986 and 2010 (see figure 1)
• The northern states in the eastern U.S. have the highest percentage of forest remaining undisturbed, while those in the south have the lowest values
• At any given time interval, the percentage of forest remaining undisturbed decreases following an exponential decay function as the time interval increases (see figure 2)
• If forest disturbance rates remain relatively stable over time, the conterminous U.S. would have less than 20% forest remaining undisturbed in 100 years, which would become less than 4% in 200 years
• Management approaches aimed at reducing timber harvest rates in the south and mitigating fire risks in the west are needed in order to maintain higher levels of undisturbed forests.

What insight did you gain from Landsat that would have been impossible to glean otherwise?

• Without Landsat, we wouldn’t be able quantify the amount of forest undisturbed over multiple decades at local, regional, state, and national scales;
• We wouldn’t be able to reveal that the percentage of forest remaining undisturbed at any given time interval decreases following an exponential decay function as the time interval increases, and therefore wouldn’t be able to estimate how much forest would remain undisturbed over multiple centuries.

What are the major implications of your findings?

• Old growth forests (> 100-200 years): mostly in the north and west, very little in the south, may constrain the distribution of species that favor old growth forests;
• Forest carbon stock: because old growth forests typically have higher carbon density than young forests, the south have more potential to increase its forest carbon stock than other forested regions in conterminous U.S.;
• Management approaches aimed at reducing timber harvest rates in the south and mitigating fire risks in the west are needed in order to increase and maintain higher levels of undisturbed forests.

Source: NASA/Lansat images

Mapping Forest Disturbance with Landsat

BY CAITLIN DEMPSEY MORAIS

The Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS) takes advantage of the30 year Landsat archive to inventory recent disturbances and forest-cover change. Using mid-summer, cloud free Landsat data from the Global Land Survey (GLS) project, LEDAPS first corrects the images to remove atmospheric effects from surface reflectance (source code for LEDAPS) before applying change detection techniques to map out disturbance, regrowth, and permanent forest conversion across the continental United States.

One of the resulting products is a map of the continental United States and Canada showing forest disturbance rates from 1990-2000. Areas on the map that are green indicate the least amount of disturbance during that time period which pink to red areas indicated the highest amount of disturbance.

Data produced from NASA’s project is contribute to the North American Carbon Program (NACP), a component of the USGCRP Carbon Cycle Science Program. The NACP is a coalition of researchers seeking to better understand the carbon cycle such as carbon sources and sinks and changes in carbon stocks.

Disturbance data can be downloaded from North American Forest Dynamics (NAFD) product archive at ORNL DAAC.

LANDSAT-DERIVED FOREST DISTURBANCE RATE (STAND REPLACING), 1990-2000, AGGREGATED TO 500M GRID. SOURCE: NASA.

Reference


Goward, S.N., C. Huang, J.G. Masek, W.B. Cohen, G.G. Moisen and K. Schleeweis. 2012. NACP North American Forest Dynamics Project: Forest Disturbance and Regrowth Data. Available on-line [http://daac.ornl.gov] from ORNL DAAC, Oak Ridge, Tennessee, U.S.A.http://dx.doi.org/10.3334/ORNLDAAC/1077

Source: GIS Lounge - Maps and GIS

Forest disturbance across the conterminous United States from 1985–2012: The emerging dominance of forest decline

Article by: Warren B. Cohena, Zhiqiang Yangb, Stephen V. Stehmanc, Todd A. Schroederd, David M. Bella, Jeffrey G. Maseke, Chengquan Huangf, Garrett W. Meigsg,





Highlights

• We characterized annual rates of forest disturbance between 1985 and 2012.
• Landsat time series were visually interpreted, with support of ancillary data.
• A probability design was used to scale estimates and provide uncertainties.
• Harvest was the most important disturbance agent class prior to the mid-90s.
• Forest decline is now more important than harvest as the dominant agent class.

Abstract
Evidence of shifting dominance among major forest disturbance agent classes regionally to globally has been emerging in the literature. For example, climate-related stress and secondary stressors on forests (e.g., insect and disease, fire) have dramatically increased since the turn of the century globally, while harvest rates in the western US and elsewhere have declined. For shifts to be quantified, accurate historical forest disturbance estimates are required as a baseline for examining current trends. We report annual disturbance rates (with uncertainties) in the aggregate and by major change causal agent class for the conterminous US and five geographic subregions between 1985 and 2012. Results are based on human interpretations of Landsat time series from a probability sample of 7200 plots (30 m) distributed throughout the study area. Forest disturbance information was recorded with a Landsat time series visualization and data collection tool that incorporates ancillary high-resolution data. National rates of disturbance varied between 1.5% and 4.5% of forest area per year, with trends being strongly affected by shifting dominance among specific disturbance agent influences at the regional scale. Throughout the time series, national harvest disturbance rates varied between one and two percent, and were largely a function of harvest in the more heavily forested regions of the US (Mountain West, Northeast, and Southeast). During the first part of the time series, national disturbance rates largely reflected trends in harvest disturbance. Beginning in the mid-90s, forest decline-related disturbances associated with diminishing forest health (e.g., physiological stress leading to tree canopy cover loss, increases in tree mortality above background levels), especially in the Mountain West and Lowland West regions of the US, increased dramatically. Consequently, national disturbance rates greatly increased by 2000, and remained high for much of the decade. Decline-related disturbance rates reached as high as 8% per year in the western regions during the early-2000s. Although low compared to harvest and decline, fire disturbance rates also increased in the early- to mid-2000s. We segmented annual decline-related disturbance rates to distinguish between newly impacted areas and areas undergoing gradual but consistent decline over multiple years. We also translated Landsat reflectance change into tree canopy cover change information for greater relevance to ecosystem modelers and forest managers, who can derive better understanding of forest-climate interactions and better adapt management strategies to changing climate regimes. Similar studies could be carried out for other countries where there are sufficient Landsat data and historic temporal snapshots of high-resolution imagery.

Source: Science direct