DOI: 10.5061/dryad.q2bvq83n0
title: The environmental drivers of tree cover and forest-savanna mosaics in Southeast Asia

description: Forest-savanna mosaics exist across all major tropical regions. Yet, the
 influence of environmental factors on the distribution of these mosaics is
 not well explored, limiting our understanding of the environmental
 constraints on savannas especially in Southeast Asia, where most savannas
 exist in mosaics. Despite clear structural and functional characteristics
 indicative of savannas, most SE Asian savannas continue to be classified
 as forest. This designation is problematic because SE Asian savannas are
 threatened by both fragmentation and forest-centric management practices.
 By studying forest-savanna mosaics across SE Asia, we aimed to parse out
 how landscape mosaics of forest and savanna may be constrained by fire,
 climate, and soil characteristics. We used remotely sensed data to
 characterize the distribution of tree cover and forest-savanna mosaics.
 Using regression models, we quantified the relative effects of
 precipitation, fire frequency, seasonality, and soil characteristics on
 average tree cover and landscape patchiness. We found that low tree cover,
 indicative of savannas, occurs in drier, seasonal subregions that
 experience frequent fire. Further, our results demonstrate that fire and
 precipitation strongly shape landscape patchiness. Landscapes were
 patchiest in subregions with low precipitation and intermediate fire
 frequency. These results demonstrate that the environmental factors
 important in delineating the distribution of savannas globally shape the
 distribution of tree cover and landscape patchiness across SE Asia. Fire
 especially drives patterns of tree cover across scales. In a region where
 fire suppression is a common management strategy, our results suggest that
 further research studying vegetation response to fire and fire suppression
 is needed to improve management and conservation of these mosaic
 landscapes. More broadly, this work demonstrates a useful approach for
 studying the environmental drivers that influence the distribution of
 forest-savanna mosaics.
description: Fire frequency was derived
 from the MCD64A1.006 MODIS Burned Area Monthly Global product
 (500 m resolution) (Giglio et al. 2018) Mean annual
 precipitation (MAP) was derived from both CHIRPS Daily: Climate Hazards
 Group InfraRed Precipitation with Station Data from 1981-2020 (0.05°
 resolution; roughly 5.6 x 5.6 km) (Funk et al. 2015) and TRMM 3B43:
 Monthly Precipitation Estimates (0.25° resolution; roughly 28 x 28 km)
 (Huffman et al. 2007). Precipitation seasonality was
 derived as described by Schwartz et al. (2020) and Feng et al.
 (2013). Soil sand content was extracted from Harmonized
 World Soil Database (30 arc seconds resolution)
 (FAO/IIASA/ISRIC/ISS-CAS/JRC 2012). We characterized
 tree cover using the Global Forest Change (GFC) v1.7 (2000-2019) product
 which contains high resolution (30 m) maps of tree cover (%) from the year
 2000 (Hansen et al. 2013). Aggregated to 0.05 degrees
 resolution. For analysis of within landscape patterns,
 1,000 grid cells or landscapes were randomly subsampled, and 30 m
 resolution tree cover was extracted for each.
 Characterizing landscape mosaics: Within each landscape, raw 30 m
 tree cover data was classified as either forest (tree cover &gt;65%),
 savanna (tree cover &lt;65%), or anthropogenic land cover.
 Landscape metrics: number of patches, mean patch area, Shannon
 evenness, and landscape shape index.