Late-Holocene successional dynamics in a transitional forest of west-central Mexico

The determination of past successional stages, as well as the factors triggering succession, is crucial for the understanding of forest dynamics and the design of current and future management and conservation strategies. Shifts between successional stages can take decades or even centuries to occur because of tree longevity; therefore palaeoecological studies are important tools for their study. The present research involved the palaeoreconstruction of a transitional forest dominated by Pinus-Carpinus-Quercus in west-central Mexico over the last ~1230 years. The proxies employed include fossil pollen, microscopic fossil charcoal, magnetic susceptibility and organic matter content evaluated by multivariate techniques. The findings reveal that an initial cloud forest stage developed from 1230 to 1050 cal. yr BP. This stage was then interrupted for ~400 years (1050-690 cal. yr BP) when a regional climate change event decreased the number of cloud forest taxa and increased herbaceous taxa including Asteraceae, Poaceae, Plantago and Zea. The cloud forest stage recovered at 690 cal. yr BP and the community has persisted to the present time, yet this stage is dominated by human-induced taxa such as Pinus and Acacia. Whilst the dynamics of individual taxa were related to forest fires and soil erosion, changes between community types were related to an interval of regional climate change (greater aridity) that occurred between 1050 and 690 cal. yr BP. Results from this study indicate that, in order to preserve the cloud forest stage, human disturbances such as logging and agriculture should be excluded; a conservation strategy established in the transitional forest in recent years

4200 years of pine-dominated upland forest dynamics in west-central Mexico: human or natural legacy?

The pine-dominated forests of west-central Mexico are internationally recognized for their high biodiversity, and some areas are protected through various conservation measures including prohibition of human activity. In this region, however, there is evidence for human settlement dating back to ca. AD 1200. It is therefore unclear whether the present forest composition and structure are part of a successional stage following use by indigenous human populations during the past, or due to natural processes, such as climate. We present a study reconstructing the vegetation dynamics of pine-dominated forest over the past 4200 years using paleoecological techniques. Results from fossil pollen and charcoal indicate that, in this region, pine-dominated forests are the native vegetation type and not anthropogenically derived secondary succession. The predominant driving mechanism for the expansion of pine-dominated forest appears to be intervals of aridity and naturally induced burning. A close association is noted between pine abundance and longer-term climatic trends, including intervals of aridity between ca. 4200 and 2500, 1200 and 850, and 500 and 200 cal yr BP and shorter-term trends. Evident periodicity occurs in pine and Poaceae abundance every 80 years. These short-term quasi-periodic oscillations have been recorded in a number of lake and ocean sediments in Mexico and are thought to be linked to solar forcing resulting in drought cycles that occur at approximately the same time intervals

La Red Internacional de Inventarios Forestales (BIOTREE-NET) en Mesoamérica: avances, retos y perspectivas futuras

Los esfuerzos de conservación en la región neotropical están limitados por la falta de información disponible sobre las especies, ya que muchas no han sido descritas o se tiene poca información sobre ellas. La Red Internacional de Inventarios Forestales (BIOTREE-NET) concentra y facilita el acceso a la información y el intercambio entre investigadores, gestores y conservacionistas, organizando y estandarizando los datos de especies de árboles procedentes de inventarios forestales en la región mesoamericana en una única base de datos que incluya información espacial. Este artículo explica el ámbito y objetivos de la red, describe la estructura de la base de datos e identifica los principales avances realizados, así como los retos y perspectivas futuras. La base de datos contiene más de 50 000 registros de árboles de unas 5000 especies, distribuidas en más de 2000 parcelas muestreadas desde el suroeste de México hasta Panamá. La información es heterogénea, tanto en su naturaleza y forma como en la cobertura geográfica de los inventarios. La base de datos tiene una estructura relacional, con 12 tablas interconectadas, incluyendo información sobre las parcelas, los nombres de las especies, el diámetro a la altura del pecho de los árboles medidos y sus atributos funcionales. Se ha desarrollado un sistema para la corrección de errores tipográficos y la estandarización taxonómica y nomenclatural utilizando como referencia The Plant List (http://theplantlist.org/). También se han generado modelos de distribución potencial para cerca de 1700 especies utilizando distintos métodos y en el futuro se prevé habilitar también el acceso público a los modelos de distribución de especies a través del portal web (http://portal.biotreenet.com). Aunque BIOTREE-NET ha contribuido al desarrollo de mejores modelos de distribución, su mayor potencial radica, en nuestra opinión, en el estudio a nivel de comunidades. Finalmente, se reconoce la necesidad de expandir la red a través de la participación de más investigadores interesados en colaborar con datos para ampliar el conocimiento sobre la biodiversidad forestal en la región neotropica