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. © SAGE Publications 2011