Direct and indirect effects of an invasive ecosystem engineer on a rare herbaceous wetland

Abstract

Feral hogs (Sus scrofa) are invasive, ecosystem engineers and a novel disturbance to rare, fire-dependent, herbaceous wetland ecosystems in Florida, USA. Their feeding activity uproots vegetation, altering plant composition and continuity. Hog rooting can also create linked disturbance by ingesting vegetation critical for fire spread. Herbaceous communities are vulnerable to shrub encroachment when fire return intervals are increased. We examined the impact of hog rooting intensity (% uprooted vegetation) on the resilience of herbaceous, seepage wetland vegetation cover and composition and the effect of hog rooting on fire spread. We hypothesized that (1) vegetation cover and composition would reflect initial intensity of hog rooting and remain altered with and without additional rooting, and (2) reduction of foliar cover by feral hog rooting would reduce fire spread. Total foliar cover, functional group cover, richness, and cover of plant genera were estimated in plots subjected to three intensity levels of hog rooting then appraised inside and outside of exclosures for 7 years. Spatial data was collected to compare areas with and without damage from hogs to areas burned by prescribed fires from 2010–2013. Total foliar cover was reduced for 5 years with high intensity hog rooting compared to no-low intensity rooting. Cover of a keystone, bunchgrass species was reduced with high intensity hog rooting. With repeated rooting, total and graminoid foliar cover were reduced outside exclosures. Fire spread was significantly reduced in areas of hog rooting. These findings have broader implications for conservation of other fire-maintained herbaceous communities impacted by nonindigenous feral hogs.