Effects of tree size, crown damage, and tree location on post-fire survival and cone production of Pinus nigra trees

Abstract

Regeneration of non-fire-prone seeder species after large fires has been claimed to depend closely on the arrival of propagules from seed sources, such as isolated surviving trees present within the burned area (“green islands”) or those on the unburned edges. However, scarce information is available on how individual and environmental factors may condition post-fire survival and, particularly, seed production of these trees. In this study we analyse the survival rate and the ability to produce seeds in the early post-fire years in Pinus nigra Arnold, a non-fire-prone pine severely affected by large fires in the 1990s all round the Mediterranean Basin. Survival and seed production have been analysed during 5 years in respect to tree size, crown damage, and tree location (i.e. location in edges or in islands). Survival increased with tree size (dbh > 20 cm) and decreased with crown damage. However, the response of trees with different fire damage varied with location, as less-affected trees showed higher survival in islands, while more affected ones performed better in the perimeter of the burned area. Concerning seed production, the main factor determining cone production after fire was tree size, because large trees produced more cones, and more frequently than small ones. No differences were observed due to crown damage, but cone production varied considerably depending on tree location. Thus, small trees produced cones more frequently in islands than on edges, while both cone production and the proportion of years that each tree produced cones decreased with island size. These results highlight the possible importance of preserving large trees in relation to non-fire-prone species. Their higher survival and higher and regular seed production rates make them the main post-fire seed sources. On the other hand, the fact that trees located in small “green islands” produce more cones and more frequently than those in edges or large islands, stresses the importance of actively protecting and conserving these small groups of surviving trees.