Vegetation dynamics of managed Mediterranean forests 16 yr after large fires in southeastern Spain

Question: Adaptive forest management requires scientific knowledge about post-fire vegetation dynamics, mainly on initial and transitional stages. We hypothesized that management practices are as important as the timing of the operations themselves, with respect to diversity and species composition of the understorey post-fire regenerated Pious halepensis forests. Location: Two post-fire regenerated P. halepensis stands burned in 1994 under contrasting climatic conditions (Dry -595 mm.yr(-1)- and Semi-arid - 340 mm.yr(-1) - sites) in southeast Spain. Methods: At both sites, we set experimental plots to test early treatments, including removal of the understorey vegetation (scrubbing, at post-fire year 5), thinning (at post-fire years 5 and 10) and control plots. Alpha diversity indices, including species richness, Shannon diversity index and plant cover, as a measure of vegetation abundance, and beta diversity indices, such as Jaccard index and non-metric multidimensional scaling were diachronically analysed at post-fire years 5 (before the treatments) and 16. Results: At both sites, the most abundant species were obligate seeders or grass resprouters. Low overlap in the occurrence of species was also found between sites on both dates, but the number of shared species increased by the end of the study period. Significant differences in the diversity indices were detected between sites. Despite the silvicultural treatments, the species richness and Shannon diversity index values at the Dry site were similar in the treated and control plots at 16 yr. Conversely, at the Semi-arid site, the species richness and Sh.annon diversity index values were enhanced by the thinning treatments carried out 10 yr after the fire. Plant cover increased despite the treatments (scrubbing and thinning) on both the pine and understorey layers in every treated plot. Conclusion: Our forest management trials eshanced the diversity indices when applied to very high tree density post-fire regenerated stands, even applied to areas with very limited resources (nutrients, water, such as semi-arid ecosystems. Thus, scrubbing at post-fire year 5 plus thinning carried out at post-fire year 10 proved to be a suitable option to reduce fire hazards in the short term at both sites and to enhance plant diversity at the Semi-arid site.