Post-fire recovery of vegetation and diversity patterns in semiarid pinus halepensis mill. Habitats after salvage logging

Abstract

After wildfires, emergency actions and post-fire management are implemented to mitigate fire damage. Salvage logging is a tool often applied to burned stands, but despite being a post-fire forest management tool to restore ecosystem functions, its ecological effects remain poorly understood. In the Mediterranean Basin, where land use and land-use change are bringing about changes in drought periods and fire regimes, optimal treatments should be included in adaptive management in order to increase resilience and reduce vulnerability. In July 2012, a mid-to high-burn severity fire burned almost 7000 ha of an Aleppo pine forest (Pinus halepensis Mill.) in southeastern Spain. Five years later (late spring 2017), we designed an experimental study to monitor four stand categories on a burn severity basis (unburned mature stands, low-burn severity stands, and high-burn severity stands) and a salvage logging operation carried out 6 months after the fire in high-burn severity areas. We set 60 circular plots (15 in each treatment scenario) and 180 linear transects (3 per plot, 45 per scenario) to check the ecological facilitation of pine trees and snags (canopy size and/or perch effect). We estimated plant alpha diversity (floristic richness, abundance and dominance indices) and post-fire plant recovery (pine recruitment and adaptive traits). Fire depleted the system’s diversity, but in low-severity burning areas some basic functions remained intact (e.g., soil protection). We found that high-burn severity very negatively impacted ecosystem functions through the removal of duff and litter leaving unprotected soil. Collecting wood reduced pine regeneration and growth, which was considerable in the areas that suffered high-burn severity. The burned snags did not appear to act as perches resulting in seed dispersal. Obligate seeders were determined to be an efficient strategy for facing high-severity fires, whereas resprouters response showed no clear burn severity pattern despite being present in all the scenarios. Therefore, salvage logging did not affect the recovery of some ecosystem properties/features (such as plant total cover or litter cover), although retaining dead pines facilitated pine regeneration. Thus, leaving snags in areas affected by high-burn severity in ecosystems mainly modelled by fires is proposed. However, the ecosystem response could be widely variable and influenced by local abiotic factors, so restoration might not be as effective as in the current proposal.