Natural regeneration and species diversification after seed-tree method cutting in a maritime pine reforestation

Abstract

Forest adaptation to global change has become one of the main objectives of forest management in recent years. Species and structural diversification by thinning is a well-known adaptation measure, often applied by managers in monospecific even-aged stands. However, regeneration fellings may be more efficient for enhancing naturalization and resilience of monospecific reforested pine stands, widely distributed throughout the Mediterranean basin. This work focuses on the evaluation of natural regeneration after seed-tree method cuttings, adopted as a diversification strategy in a 60-year old P. pinaster reforestation with varying presence of broad-leaved species (mainly Quercus spp.) in mountains of Southern Spain. A trial consisting of 78 circular plots (1 m radius) was installed to monitor annual tree-species regeneration over seven years, classified into seedlings (0-10 cm height) and saplings (10-130 cm). Scrub coverage and other ecological variables were also measured. Sampling was carried out in three stand types (Pure, Mixed 1 and Mixed 2, in order of increasing presence of broad-leaved species), according to forest species composition before the felling. Maritime pine regeneration was successfully achieved by the end of the study period (over 2000 trees ha-1 widely distributed throughout the stand), whereas Quercus spp. seedlings even colonised plots in which there were no seed trees. Pine seedling density was positively affected by summer precipitation and the presence of conspecific adult pines, and negatively influenced by scrub coverage. High temperatures during the mid-summer months (especially August) negatively affected the seedling to sapling change ratio as well as sapling survival during the study period. Our results point to regeneration fellings with retention of pine and broadleaf species as a suitable method for diversifying species composition in Pinus pinaster reforestations in the Mediterranean region.

Keywords

• Adaptation
• Global Change
• Mixed Forests
• Naturalization
• Regeneration Fellings