Grassy biomes such as savannas are maintained by a suite of ecosystem processes from herbivory to rainfall and fire. Many studies have examined the impacts of large mammalian herbivores on herbaceous plant communities but few of these studies have been conducted in humid, fertile savannas. We present the findings of a short-term experiment that investigated the effects of herbivory in one such savanna. We erected large-herbivore exclosures in Alas Purwo National Park, Java where rainfall is high and fire is suppressed to test how herbivores impact plant community development during and in response to the wet season. When large mammalian herbivores were excluded, herbaceous plant communities in Alas Purwo were less grassy and less similar; diverging in their composition as the growing season progressed. Notably, weedy plant species (Imperata cylindrica and Senna cf. tora) appeared to benefit most from herbivore release. Our results suggest that heavy grazing pressure by native large herbivores controlled the composition of the herbaceous layer and prevented strong light competitors from becoming dominant. At the end of the growing season, herbivore exclusion plots showed higher beta diversity than plots exposed to herbivores. Our findings suggest that, at our high-rainfall site, large mammalian herbivores constrain the developmental trajectory of plant communities through the growing season.

See Methods section of Potter et al. 2021 PLOS ONE.