Impacts of post-fire straw mulching on plant diversity dynamics and mid-term persistence of introduced weed species in a Mediterranean chronosequence

Post-fire straw mulching is widely used to reduce soil erosion and facilitate vegetation recovery in fire-affected ecosystems. However, straw mulch may introduce agricultural weedy species, raising concerns about their persistence and potential effects on post-fire plant community assembly. This study evaluated the medium-term ecological implications of straw mulch application using a post-fire chronosequence in semi-arid Mediterranean ecosystems of southeastern Spain. Vegetation was surveyed in 54 plots (27 mulched and 27 untreated) distributed across sites representing 1, 2 and 6 years after fire (YAF). Species richness, diversity, composition and the abundance of agricultural weedy species were analysed to assess treatment effects across the chronosequence. Straw mulching increased species richness and diversity during the early post-fire stages, through the introduction of agricultural weedy species. Community composition differed significantly among post-fire stages and between treatments, although post-fire stage explained a substantially larger proportion of the variation than mulching treatment. The abundance of agricultural weedy species declined markedly along the chronosequence, and these species showed very low abundance at the site representing 6 YAF. Plant communities in mulched and untreated plots became more similar at the latest stage represented in the chronosequence. Overall, the results suggest that straw mulching can temporarily enhance plant diversity during early post-fire recovery without evidence of negative medium-term effects on vegetation recovery under the environmental conditions evaluated in this study. These findings support the use of straw mulching as a post-fire restoration measure in semi-arid Mediterranean ecosystems while highlighting the importance of considering straw provenance when assessing early community responses.