Symptoms of forest decline, apparently due to climate change, have become evident in the last 10 years on the Trans-Mexican Volcanic Belt and northwestern temperate forest of Mexico, particularly at the xeric (low elevational) limit of several forest tree species. We review and provide recent evidence of massive infestation of timberline Pinus hartwegii Lindl. by the mistletoes Arceuthobium globosum Hawksw. & Wiens and Arceuthobium vaginatum (Humb. & Bonpl. ex Willd.) J.Presl; insufficient Abies religiosa (Kunth) Schltdl. & Cham. seedling recruitment at the Monarch Butterfly Biosphere Reserve; indications of inbreeding and defoliation in endangered Picea chihuahuana Martínez, Picea martinezii T.F. Patt., Picea mexicana Martínez, and extreme southern populations of Pseudotsuga menziesii (Mirb.) Franco; and the incidence of unusual pest and disease outbreaks (e.g., Dendroctonus Erichson, 1836 spp., Neodiprion autumnalis Smith, and Phytophthora cinnamomi Rands) in several conifer and oak species. We also discuss a difficult question: Is natural genetic variation sufficient to provide populations with the adaptive variation necessary to survive the natural selection imposed by projected climate change scenarios, or will phenotypic plasticity be exhausted and populations decline? Controversial ex situ conservation within natural protected areas, assisted migration, and translocation of species ensembles are discussed as options by which to accommodate projected climatic change impacts on the management and conservation practices of the megadiverse Mexican temperate forest.
Sample plots were established in the principal forest types in the the Nevado de Toluca National Park, Mexico including those dominated by Pinus hartwegii, Abies religiosa, Quercus laurina and Alnus jorullensis. The vertical structure was defined by three strata in the coniferous forests and two strata in the broadleaved forests. Timber harvesting in Abies religiosa and Quercus laurina forests and fires generated by humans in Pinus hartwegii forests impeded the recruitment of saplings. Mature trees were also heavily impacted by logging in Pinus hartwegii forests. On the contrary, Alnus jorullensis forests were increasing due to the disturbance of Pinus and Quercus forests, as well abandoned crop lands within the park. A combination of logging, uncontrolled fire, and grazing appears to be compromising the recruitment of important tree species in this national park. These factors, together with human settlements, have also increased the proportion of early successional species. Changes in forest structure from human disturbance indicate a need to control these activities if conservation goals are not to be compromised.
Key message Under climate warming the presence of key microsite facilitators modify soil moisture levels associated with successful tree recruitment at the treeline ecotone of Pinus hartwegii.
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.
En el presente estudio se hace una evaluación forestal asociada a la cantidad y calidad de combustibles muertos en bosques de P. hartwegii para señalar condiciones de vulnerabilidad y propensión a incendios. Con interpretación de imágenes de satélite multiespectrales del 2010, se determinaron tres densidades de cobertura para 23 685 ha de bosque de P. hartwegii del Estado de México. Se realizó un inventario forestal, presencia de actividad humana, carga de combustibles y parámetros físicos en 30 sitios de muestreo de 1000 m2. La estimación de la cantidad y tipo de combustible se realizó bajo la técnica de intersecciones planares. Se calculó el área basal, biomasa forestal y la estructura vertical, por sitio y clase de cobertura. Los resultados señalan que existen diferencias entre las tres categorías relativas a densidad arbórea (ind ha-1) área basal (m2) y cantidad de biomasa (t ha-1) así como de la estructura vertical de los bosques. Se presenta mayor cantidad de combustibles en los bosques fragmentados con 33.81 t ha-1, principalmente de clases diamétricas grandes (de 2.5 cm a 7.5 cm, así como ≥ 7.5 cm de diámetro); donde el fuego reside más tiempo en momentos de una conflagración. Las actividades antrópicas desarrolladas en estas áreas desencadenaron esta situación, que se presenta como un riesgo que debe ser atendido en la zona. La metodología empleada es propicia para el análisis de grandes áreas forestales, permitiendo determinar las características del entorno vivo y del combustible muerto, brindando elementos útiles para declarar áreas vulnerables a incendios en el marco de un Programa de Manejo Integral del Fuego.
La mayor diversidad florística de los bosques templados se encuentra en el componente herbáceo y arbustivo del sotobosque, en estos, la flora adquiere gran importancia ecológica y funcional. Los procesos esenciales del ciclo de nutrientes y la trayectoria sucesional, dependen directamente de la vegetación del sotobosque. Por ello, es necesario realizar la caracterización florística de estas comunidades y conocer su diversidad. En este estudio se determinó la composición y estructura de las especies herbáceas y arbustivas en bosques densos de Pinus hartwegii (Lindl) y Abies religiosa (Kunth Schltdl. et Cham.) del Nevado de Toluca y se cuantificó la abundancia de regeneración arbórea en 10 cuadrantes continuos de 10 m × 10 m. En las especies menores a 50 cm de altura se estimó la cobertura y abundancia con base en la escala Braun-Blanquet. En las especies mayores a 50 cm se obtuvo el valor relativo en cobertura, frecuencia y densidad, además del valor de importancia. De acuerdo con los resultados obtenidos, la flora del sotobosque de Abies religiosa posee una mayor riqueza y está compuesta por 33 especies, 25 géneros y 14 familias, donde Asteraceae es la familia dominante. El sotobosque de Pinus hartwegii registró un total de 18 especies, 16 géneros y 10 familias, con dominancia en cobertura y abundancia de la familia Poaceae. En ambas comunidades vegetales la abundancia de la regeneración es mayor en plántulas y menor en brinzales y latizales.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.