Fire, anthropogenic influence, and habitat factors affect grassland persistence in the face of woody encroachment in a Terai-Duars savanna and grasslands habitat.

Grasslands in wet tropical climates are unique ecosystems because water availability does not limit the establishment of trees. The Terai Duars Savanna and Grasslands ecoregion (hereafter, Terai) is a heterogeneous woodland-grassland mosaic where pure grasslands occur despite relatively high rainfall. The factors that maintain grasslands under such conditions are poorly understood. We studied grassland persistence in a Terai ecosystem in northeastern India by deriving land use land cover (LULC) classification from Landsat images (30 m) and examining vegetation transitions over a 34-year period. Overall, we found high dynamism, with balanced interchange between grasslands and woodlands even over brief time intervals. However, in the last 15 years, the changes have favored woodland formation, resulting in a 24% decline in grassland area. We tested the influence of several environmental, anthropogenic, and topographic factors on grassland persistence at fine spatial scales over seven time intervals (~ 5 years each). We used non-spatial generalized linear mixed models and spatial regression models in a Bayesian framework with conditional autoregressive priors. Both models revealed that grassland persistence was favored by fire and anthropogenic influences (quantified as distance from human habitation), whereas a greater extent of the grass-woodland ecotone and proximity to water bodies reduced persistence. We expected topography to affect grassland persistence because of seasonal flooding, but elevation had no consistent influence. The influence of fire and anthropogenic activities has weakened in recent years, resulting in a decline in grassland area. Our results highlight widespread concerns of woody encroachment in grassland habitats that may erode biodiversity and ecosystem functioning.