Fractional Woody Cover Mapping of Texas Savanna at Landsat Scale

Xuebin Yang,Kelley A Crews

doi:10.3390/land8010009

Abstract

Texas savanna experienced substantial woody plant encroachment during the past several decades, resulting in habitat fragmentation and species loss. A detailed map of woody plant abundance and distribution in this area is critically needed for management purpose. This study endeavors to map the fractional woody cover of Texas savanna at Landsat scale (30 m) in an affordable way. The top of atmosphere reflectance, thermal bands, and NDVI layer of Web-Enabled Landsat Data (WELD) of 2012 were used as predictors, together with mean annual precipitation. Classification and Regression Trees (CART) were calibrated against training data of a whole range of fractional woody cover, which were derived from 1-m resolution digital orthophotos of 2012. Validation indicates a reasonable pixel level accuracy of the result fractional woody cover map, with a R-squared value of 0.45. Moreover, the result map clearly depicts the distribution of woody plants across the study area, as reflected by the orthophotos. Furthermore, this new map proves an improvement over the existing Landsat Vegetation Continuous Fields (VCF) tree cover product. The method developed here, combining remote sensing and statistical techniques, can contribute to savanna management through revealing the abundance and distribution of woody plants.

Highlights

Savanna ecosystems feature the coexistence of woody plant and herbaceous vegetation, and the balance between these two different life forms is crucial for the structure and function of the ecosystems [1,2,3]
The color ramp of light green to dark green illustrates the range of fractional woody cover from 0.09 to 0.77, while the light green to dark green illustrates the range of fractional woody cover from 0.09 to 0.77, while the white inside the map indicates non-woody areas such as developed land and water body, according white inside the map indicates non-woody areas such as developed land and water body, according to the National Land Cover Database 2011
This map shows a high spatial coherency, to the National Land Cover Database 2011. This map shows a high spatial coherency, an an increasing trend of woody plant density along the precipitation gradient, which agrees with our increasing trend of woody plant density along the precipitation gradient, which agrees with our reconnaissance fieldwork from roadside and state park across the study area

Summary

Introduction

Savanna ecosystems feature the coexistence of woody plant and herbaceous vegetation, and the balance between these two different life forms is crucial for the structure and function of the ecosystems [1,2,3]. The increasing availability of remote sensing data provides us an opportunity to map woody plant cover over large areas in savanna ecosystems. Very high spatial resolution imagery can recognize individual woody plants, but such imagery is characterized by small extent and low temporal frequency and is vulnerable to cloud contamination. These characteristics limit their application in regional woody cover mapping. While the medium to coarse resolution reduces data volume required to cover large areas, the high temporal frequency can offset the effect of possible cloud contamination [10]

Methods

Results

Discussion

Conclusion