Abstract
Forest resources have a high economic value in the State of Georgia (USA) and the landscape is frequently disturbed as a part of forest management activities, such as plantation forest management activities. Thus, tracking the stand-clearing disturbance history in a spatially referenced manner might be pivotal in discussions of forest resource sustainability within the State. The two major objectives of this research are (i) to develop and test a reliable methodology for statewide tracking of forest disturbances in Georgia, (ii) to consider and discuss the use and implications of the information derived from the forest disturbance map. Two primary disturbance detection methods, a threshold algorithm and a statistical boundary method, were combined to develop a robust estimation of recent forest disturbance history. The developed model was used to create a forest disturbance record for the years 1987–2016, through the use of all available Landsat Thematic Mapper (TM)/Enhanced Thematic Mapper (ETM+) data. The final product was a raster database, where each pixel was assigned a value corresponding to the last disturbance year. The overall accuracy of the forest disturbance map was 87%, and it indicated that 4,503,253 ha, equivalent to 29.2% of the total land area in Georgia, experienced disturbances between 1987 and 2016. The estimated disturbed area in each year was highly variable and ranged between 84,651 ha (±36,354 ha) to 211,780 ha (±49,504 ha). By combining the use of the disturbance map along with the 2016 database from the National Land Cover Database (NLCD), we also analyzed the regional variation in the disturbance history. This analysis indicated that disturbed forests in urban areas were more likely to be converted to other land-uses. The forest disturbance record created in this research provides the necessary spatial data and address forest resource sustainability in Georgia. Additionally, the methodology used has application in the analysis of other resources, such as the estimation of the aboveground forest biomass.
Highlights
As forest disturbances are a primary factor in the dynamics of a forest ecosystem, the history of disturbances helps keeps track of the condition and development of a forest [1]
The overall accuracy of the forest disturbance map was 87%, and it indicated that 4,503,253 ha, equivalent to 29.2% of the total land area in Georgia, experienced disturbances between 1987 and 2016
Google Earth Engine was used to process all available images from the time series of Landsat Thematic Mapper (TM)/ETM+ imagery
Summary
As forest disturbances are a primary factor in the dynamics of a forest ecosystem, the history of disturbances helps keeps track of the condition and development of a forest [1]. Forest disturbances may affect the forest species composition and stand structure depending on the disturbance agent, magnitude, and other complex factors such as soil type, water and nutrient availability, and ecosystem biodiversity [2]. In Europe, disturbances caused by wind, bark beetles, and wildfires have increased over the last century [8]. As spatially referenced forest disturbance tracking provides fundamental information in describing the current state of a forest, accurate knowledge of it facilitates the accurate prediction of future conditions and outcomes
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