Burning season effects on the short-term post-fire vegetation dynamics of a Mediterranean heathland.

摘要

Question: What are the short-term (first 4 yrs) dynamics of a Mediterranean heathland following burning during the early- vs the late-fire season? Location: Serra da Lousa, Central Portugal. Methods: The vegetation studied was a 16-year old heathland with Erica australis (resprouter), Pterospartum tridentatum (resprouter/seeder) and Erica umbellata (seeder) among the dominant species. Four blocks, each with three 50 m x 40 m plots, were established. One plot per block was burned during the early season (ES) and one during the late season (LS), and the third remained unburned. Prior to, and during the first 4 yrs after burning, each burned plot was sampled for species abundance, vigour and richness. The effects of fire through time were tested using random blocks repeated measures ANOVA. Recruitment was modelled as a function of percentage of post-fire soil covered by litter (%). MANOVA was used to test changes in the relative dominance of the woody species due to fire. Community dynamics were assessed by NMDS ordination analysis. Results: Fire severity was higher and the percentage of post-fire soil covered by litter lower in ES than LS burns. The post-fire plant dynamics were dominated by the resprouting response. Resprouting was not affected by burning season, but ES fires resulted in higher seedling recruitment than LS fires, particularly in the dominant seeder E. umbellata. Seedling recruitment was negatively related to post-fire soil covered by litter. Additionally, seedling emergence was delayed by nearly 1 yr in LS fires with respect to ES fires. Species richness was higher in ES than LS fires. Fire did not globally affect the relative abundance of the dominant species, although the seeder E. umbellata decreased its relative cover with respect to the other dominant species. Ordination analysis showed that the post-fire dynamics of the vegetation were on a track of convergence with the community existing before fire. Conclusion: Burning season differentially affected regeneration, mainly by its effect on seeding, with little effect on resprouting. Burning season and associated changes in fire severity and soil covered by litter could alter the short-term regeneration dynamics, which can have important implications for managing this highly flammable vegetation.