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.
Highlights
Worldwide, high-mountain forests represent one of the main sources of local and regional environmental services
This study defines high-mountain forests in Mexico as the forest ecosystem developed above the 3500 masl
Even though the forests are located above the superior limits of communities and crop fields, they are in severe pressure due to anthropic activities, leading to a local fragmentation of the pine forest
Summary
High-mountain forests represent one of the main sources of local and regional environmental services. They are important habitats of an extensive rank of endemic species associated; are environments threatened by over-exploitation and practices of land management. The deterioration of the high-mountain forests is characterized by its scarcity of data and lack of empirical analyses. In the case of Mexico, high-mountain forests are intimately related to the provision of environmental services that fulfil the needs of the largest urban conglomeration in Latin America. Mexico City and its metropolitan area depend directly of the environmental services provided the only zone of high-mountain forests in the country, the transversal volcanic system. The transversal volcanic system includes three of the highest volcanic buildings of the country: Popocatépetl, Iztaccihuatl and the Nevado de Toluca
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