Impacts of barley (Hordeum vulgare L.) straw mulch on post-fire soil erosion and ground vegetation recovery in a strawberry tree (Arbutus unedo L.) stand

Abstract

Rural fires are now a major societal concern across the world, especially where fire regimes have (apparently) intensified in terms of burnt area, intensity and recurrency. Among the indirect fire effects, fire-enhanced runoff and erosion have been an important focus of post-fire land and water management, in particular through emergency stabilization of hillslopes using a range of erosion mitigation measures. The most widely applied and – scientifically tested – measure is that of mulching with agricultural straw, in spite of concerns of introducing exogenous organic material and especially seeds of non-native higher plant species, including the straw species it- or themselves. So far, field studies in the present study region of north-central Portugal have preferred using endogenous forest residues but these studies concerned forest types for which such residues are easily available. The latter, however, is not the case for strawberry tree stands, so that straw mulch was selected in this study as a cheaper alternative to eucalypt or pine residues. This - apparently, first – post-fire erosion mitigation study in a strawberry tree (Arbutus unedo L.) stand aimed to compare post-fire sediment and organic matter losses as well as ground vegetation recovery without and with applying barley (Hordeum vulgare L.) straw mulch at a low rate of 2 Mg ha−1. The experimental set-up involved a randomized block design with a total of six geotextile-bounded erosion plots of 2 m by 5 m that were organized in three blocks, were installed and mulched roughly one month after the 17-October-2017 M-fire in inland Central Portugal, and monitored at 12 irregular intervals during the first two post-fire years. The principal findings were that: (i) especially the specific sediment losses without mulching over the first post-fire year were notably higher than those reported by the prior field studies in the region, in eucalypt and maritime pine plantations; and that the - low - mulching rate: (ii) was extremely effective in reducing these first-post-fire-year losses; but (iii) did not result in changes in the cover or floristic composition of the ground vegetation cover that were noteworthy and longer-lived than the first post-fire year.