Analysis of Fragmentation Processes in High-Mountain Forests of the Centre of Mexico

Abstract

High-mountain forests (>3500 masl) are the main supplier of environmental services to Mexico City and its metropolitan area. Taking as a study case the Nevado de Toluca National Park, this article focuses on the considerable reduction on the density of its forest cover, characterised by disturbances in the structure and dynamics of Pinus hartwegii. This specie is located towards the upper limits of the altitudinal gradient (3500 - 4100 masl) constituting the only pine species in the world capable to be established in those extreme environmental conditions. The information was collected through the implementation of 30 Sampling Plots (SP) of 20 × 50 mts (1000 m2) in three forest density categories: dense, semi-dense and fragmented. For each forest category, all trees ≥2.5 cm DBH were measured in 10 SPs. The measurement variables were DBH, total and commercial height, forest health and forest extraction. The results show the abundance of dense, semi-dense and fragmented forest (336, 202 and 150 trees/Ha-1), with extraction percentages of 11%, 20% and 33% respectively. The horizontal structure distribution shows the shape of an inverted J for the three conditions. However, the phytosanitary conditions of the semi-dense forests (83% infested trees) and fragmented (63% infested trees), do not guaranties the survival of the adult trees, implying an intensification of the fragmentation process for the next decade; given the reduction of the regeneration patterns due to the lack of healthy tree breeding.