Post-wildfire straw mulching and salvage logging affects initial pine seedling density and growth in two Mediterranean contrasting climatic areas in Spain

Abstract

Mulching application and salvage logging are often performed in forests after wildfire to avoid soil erosion and recover timber values, respectively. Mulch may increase soil moisture and decrease contrasted temperatures, which thus promotes seedling recruitment, whereas logging operations may destroy seedlings or generate soil compaction, which may enhance soil erosion and to cause plant seedling damage. We investigated whether and to what extent postfire mulching application and logging initially altered some mineral soil properties and pine seedling density and growth in contrasting Mediterranean climate sites (Liétor, in SE. Spain, in semiarid climate and A Gudiña in NW Spain, in subhumid climate). Twelve plots were set up among four different experimental conditions (mulching + salvage logging, mulching + no salvage logging, no mulching + salvage logging, and no mulching + no salvage logging) in the two sites (semiarid and. subhumid climates). The subhumid site was affected by fire in autumn and the semiarid site was affected by fire in summer. Mulching was applied one and three months after wildfire in A Gudiña and Liétor, respectively, whereas logging was applied three months after mulching in Liétor and immediately after mulching in A Gudiña. One year after wildfire in A Gudiña (Pinus pinaster Ait. stands) and two years after wildfire in Liétor (Pinus halepensis M. stands), all surviving seedlings in each plot were counted. Our results suggest that soil organic matter content and total nitrogen were significantly affected by treatments at Liétor (semiarid climate), whereas no differences were detected at the A Gudiña site (subhumid climate). Results confirmed that regardless of whether tree felling took place, mulch treatment improved seedling density (over 40% higher when mulching was applied) and seedling height in the short term in a semiarid climate. The limited water availability and the light demands of pine species could be decisive for understanding the effect of mulching and logging operations for initial seedling recruitment in Liétor. The mulching + logging combination showed the highest seedling density at A Gudiña (subhumid climate), which could be related to increased light availability after tree felling. Seedling height, stem dry weight, root length, leave-covered shoot length and leave-covered shoot dry weight were always higher in mulching + salvage logging plots at A Gudiña. Our results generally suggest the compatibility between mulching and logging, which enhance initial seeding recruitment in burned semiarid and subhumid Mediterranean pine forests.