Climate change increases threat to plant diversity in tropical forests of Central America and southern Mexico.

Global biodiversity is negatively affected by anthropogenic climate change. As species distributions shift due to increasing temperatures and precipitation fluctuations, many species face the risk of extinction. In this study, we explore the expected trend for plant species distributions in Central America and southern Mexico under two alternative Representative Concentration Pathways (RCPs) portraying moderate (RCP4.5) and severe (RCP8.5) increases in greenhouse gas emissions, combined with two species dispersal assumptions (limited and unlimited), for the 2061-2080 climate forecast. Using an ensemble approach employing three techniques to generate species distribution models, we classified 1924 plant species from the region's (sub)tropical forests according to IUCN Red List categories. To infer the spatial and taxonomic distribution of species' vulnerability under each scenario, we calculated the proportion of species in a threat category (Vulnerable, Endangered, Critically Endangered) at a pixel resolution of 30 arc seconds and by family. Our results show a high proportion (58-67%) of threatened species among the four experimental scenarios, with the highest proportion under RCP8.5 and limited dispersal. Threatened species were concentrated in montane areas and avoided lowland areas where conditions are likely to be increasingly inhospitable. Annual precipitation and diurnal temperature range were the main drivers of species' relative vulnerability. Our approach identifies strategic montane areas and taxa of conservation concern that merit urgent inclusion in management plans to improve climatic resilience in the Mesoamerican biodiversity hotspot. Such information is necessary to develop policies that prioritize vulnerable elements and mitigate threats to biodiversity under climate change.

Environment-driven changes in diversity of riparian plant communities along a mountain river.

The study of changes in species richness and composition along rivers has focused on large spatial scales. It has been ignored that in different sections of the river (high mountain area, middle zone, and mouth of the river) the specific environmental conditions can generate different longitudinal patterns of the species richness and composition. In this study, we determine whether species richness and composition of the riparian plant communities change along a mountain river and whether these changes are related to environmental variables. We expect an increase in species richness and turnover along the river, that the upstream communities would be a subset of the downstream communities, and that such would be related to edaphic and hydrologic conditions. To test this, we sampled three strata of the riparian vegetation (upper: individuals with <1 cm of ND, middle: individuals with >1 cm of ND, low: individuals with >1 m tall) in a set of 15 sites that we place along a mountain river. Additionally, we recorded topographic, hydrological, morphological, and soil variables. We performed correlation analyzes to determine whether changes in species richness and turnover were related to increased distance to the origin of the river. Also, we obtained the nestedness and evaluated the importance of environmental variables with GLM, LASSO regression, and CCA. With the increase in distance, the species richness decreases in the upper stratum, but not in the middle and the low stratum (although the highest values were observed near the origin of the river), the turnover increase in all strata and the upstream communities were not a subset of the downstream communities. The changes in species richness and composition were related to topographic (altitude), hydrological (flow), and edaphic (conductivity and pH) variables. Our results indicate that at small spatial scales the patterns of richness and composition differ from what has been found at larger spatial scales and that these patterns are associated with environmental changes in the strong altitude gradients of mountain rivers.

Are Mayan community forest reserves effective in fulfilling people's needs and preserving tree species?

Mayan community forest reserves (MCFR) play an important role in agricultural landscapes in Mexico, as they provide forest products and a broad variety of benefits that contribute to improving local people's livelihoods. Nevertheless, academia has generally considered conservation and use of forest resources to be incompatible. We describe the spatial configuration of MCFR, evaluate floristic and structural characteristics of woody vegetation present in selected reserves, and identify social norms that govern use and conservation of MCFR. These reserves largely consist of mature vegetation (80% of total cover); their plant structure is similar to that of the surrounding tropical sub-deciduous forest; and they house a large number of endemic species. The MCFR studied contain a total of 146 tree species and cover 11% of the study area, which includes at least 140 villages in the north-central part of the Yucatan Peninsula. These reserves are collectively managed and conserved by Mayan peasants in the interest of the common good. The communities in our study area combine conservation and use of forest resources, and we recommend that in public policy, government agencies and NGOs incorporate MCFR as a model of biological conservation and sustainable natural resource use, taking into account traditional knowledge and local norms that allow these reserves to function in a sustainable manner.

Assessment of browsed plants in a sub-tropical forest frontier by means of fuzzy inference.

Browsing of forest frontiers by cattle in sub-tropical landscapes is detrimental to ecosystem health, but essential to smallholder livelihoods. We described a silvopastoral landscape, searching for browsed plants to assess how much of the forest is actually used for this end, and also searching for potential new useful species for silvopastoral purposes. The first objective was accomplished through a floristic description, making observations of individuals with browsing marks. Information from interviews, bromatological analyses and vegetative propagation tests further complemented this information to achieve the second objective. We classified the results using Fuzzy Inference Systems (FISs). A great variety of nutritious browsed plants was found, distributed across various types of vegetation, growth habits and taxonomic groups: forest frontiers already are like silvopastoral systems. Various plants like Acalypha leptopoda, Montanoa tomentosa and Verbesina perymenioides are interesting prospects for further intensification of silvopastoral systems.

Efecto del manejo sobre la diversidad de árboles en vegetación secundaria en la Reserva de la Biosfera de Calakmul, Campeche, México / Effect of management on tree diversity in secondary vegetation in the Biosphere Reserve of Calakmul, Campeche, Mexico

ResumenEl bosque tropical seco (BTS) de la Península de Yucatán ha sido manejado por siglos, pero la relación del efecto del manejo sobre la diversidad de árboles no ha sido completamente entendida. El objetivo de este estudio fue evaluar el efecto del manejo forestal (aclareos, aprovechamiento y enriquecimiento de especies) en la estructura de la vegetación secundaria derivada de bosques tropicales secos, en dos comunidades en Calakmul, Campeche, Sureste de México. Se analizaron cambios en la composición, riqueza de especies, diversidad de especies y estructura en vegetación secundaria sujetas a los siguientes tipos de manejo: 1) vegetación secundaria con manejo apícola (MA), 2) vegetación secundaria con manejo forestal (MF), 3) vegetación secundaria sin manejo (SM) y bosque tropical seco (BTS). La composición de especies fue similar entre vegetación secundaria manejada y no manejada. Por otro lado, entre vegetación secundaria manejada y el BTS hubo diferencias en la composición de especies. La riqueza de especies no fue diferente entre todas las condiciones. La MA mostró la más baja diversidad de especies y presentó la mayor densidad promedio (5 413 ± 770.26 ind./ha). La MF tuvo la menor densidad promedio (3 289 ± 1 183.60 ind./ ha). El BTS mostró la mayor área basal promedio (24.89 ± 1.56 m2/ha) respecto a las demás condiciones. Se concluye que es necesario mantener el monitoreo de las áreas manejadas, para detectar efectos del manejo que pueden ser adversos o favorables para la conservación de la diversidad florística de los BTS.

Abstract:The tropical dry forest (BTS) of Yucatan Peninsula has been managed for centuries, but the relationship between these management efforts and their effects on trees diversity has not been fully understood. The aim of this study was to evaluate the effect of forest management (thinning, harvesting and enrichment of species), in the structure of secondary vegetation derived from dry tropical forests, in two communities in Calakmul, Campeche, Southeast Mexico. We analyzed changes in the composition, species richness, species diversity, and structure in secondary vegetation subject to following types of management: (1) secondary vegetation with beekeeping management (MA), secondary vegetation with forest management (MF), natural secondary vegetation (SM) and tropical dry forest (BTS). The species composition was similar between secondary vegetation managed and unmanaged. On the other hand, between managed secondary vegetation and BTS there were differences in species composition. Species richness was not different between all conditions. MA showed the lowest species diversity and presented higher average density (5 413±770.26 ind.ha-1).MF had lowest average density (3 289 ± 1 183.60 ind.ha-1). BTS showed the highest average basal area (24.89 ± 1.56 m2.ha-1) regarding the other conditions. We concluded that is necessary to keep monitoring the managed areas to detect effects of management that may be adverse or favorable to conservation of floristic diversity of BTS. Rev. Biol. Trop. 65 (1): 41-53. Epub 2017 March 01.

[Effect of management on tree diversity in secondary vegetation in the Biosphere Reserve of Calakmul, Campeche, Mexico]. / Efecto del manejo sobre la diversidad de árboles en vegetación secundaria en la Reserva de la Biosfera de Calakmul, Campeche, México.

The tropical dry forest (BTS) of Yucatan Peninsula has been managed for centuries, but the relationship between these management efforts and their effects on trees diversity has not been fully understood. The aim of this study was to evaluate the effect of forest management (thinning, harvesting and enrichment of species), in the structure of secondary vegetation derived from dry tropical forests, in two communities in Calakmul, Campeche, Southeast Mexico. We analyzed changes in the composition, species richness, species diversity, and structure in secondary vegetation subject to following types of management: (1) secondary vegetation with beekeeping management (MA), secondary vegetation with forest management (MF), natural secondary vegetation (SM) and tropical dry forest (BTS). The species composition was similar between secondary vegetation managed and unmanaged. On the other hand, between managed secondary vegetation and BTS there were differences in species composition. Species richness was not different between all conditions. MA showed the lowest species diversity and presented higher average density (5 413±770.26 ind.ha-1).MF had lowest average density (3 289 ± 1 183.60 ind.ha-1). BTS showed the highest average basal area (24.89 ± 1.56 m2.ha-1) regarding the other conditions. We concluded that is necessary to keep monitoring the managed areas to detect effects of management that may be adverse or favorable to conservation of floristic diversity of BTS.

Tropical montane cloud forests: current threats and opportunities for their conservation and sustainable management in Mexico.

Tropical montane cloud forests (TMCF) are among the most threatened ecosystems globally in spite of their high strategic value for sustainable development due to the key role played by these forests in hydrological cycle maintenance and as reservoirs of endemic biodiversity. Resources for effective conservation and management programs are rarely sufficient, and criteria must be applied to prioritize TMCF for conservation action. This paper reports a priority analysis of the 13 main regions of TMCF distribution in Mexico, based on four criteria: (1) forest quality, (2) threats to forest permanence, (3) threats to forest integrity, and (4) opportunities for conservation. Due to the diverse socio-environmental conditions of the local communities living in Mexican TMCF regions, their associated social characteristics were also evaluated to provide a background for the planning of conservation actions. A set of indicators was defined for the measurement of each criterion. To assign priority values for subregions within each main region, an international team of 40 participants evaluated all the indicators using multicriteria decision-making analysis. This procedure enabled the identification of 15 subregions of critical priority, 17 of high priority, and 10 of medium priority; three more were not analysed due to lack of information. The evaluation revealed a number of subjects that had hitherto been undetected and that may prove useful for prioritization efforts in other regions where TMCF is similarly documented and faces equally severe threats. Based on this analysis, key recommendations are outlined to advance conservation objectives in those TMCF areas that are subjected to high pressure on forest resources.

Sistemas agroforestales y almacenamiento de carbono en comunidades indígenas de Chiapas México / Agroforestry systems and carbon stocks in indigenous communities from Chiapas México

Una consecuencia de la agricultura de roza-tumba-quema (r-t-q) es la conversión de áreas boscosas a sistemas agrícolas. Esta práctica contribuye a la deforestación, el deterioro de los suelos, a las emisiones de carbono (C) y, por lo tanto, al efecto invernadero. El objetivo de este estudio fue evaluar los reservorios de C en cultivos de maíz tradicionales y en sistemas agroforestales (taungya, barbechos o acahuales naturales y enriquecidos), y explorar su relación con la edad y su complejidad funcional y estructural. En el marco del proyecto Scolel’te se realizaron inventarios en 25 parcelas circulares en cuatro comunidades indígenas del municipio de Chilón, Chiapas, México, usando métodos destructivos para la estimación de C, a excepción de árboles, juveniles y raíces gruesas, para los cuales se emplearon fórmulas alométricas. Una mayor complejidad de los sistemas derivó en mayor acumulación de carbono. Taungya, milpa, barbecho enriquecido y natural presentaron 109,4; 127,9; 150,1 y 177,6Mg C·ha-¹, respectivamente. La materia orgánica del suelo fue el mayor reservorio (70% del C total en todos los sistemas); la biomasa viva y materia orgánica muerta aportaron un tercio del C total. El C total mostró incremento con la edad del sistema en taungya y barbecho natural, mientras que en la milpa se encontró una relación negativa entre materia muerta y edad. Los sistemas taungya y barbecho enriquecido pueden reducir los ciclos de r-t-q, ofrecer el servicio ambiental de captura de C y producir bienes para la población local.

Correlations between precipitation patterns in southern mexico and the El Niño sea surface temperature index

Historical data for regional climate research in the tropics is typified by extreme unevenness in both temporal and spatial coverage. Spatial interpolation techniques were applied in order to fill the gaps in time series of rainfall records for the state of Chiapas. The method involved iterated universal Kriging that combines a spatial covariance function with a polynomial trend surface. Automated outlier removal was used to prevent spurious records distorting the results. The procedure was applied 612 times in order to produce complete monthly time series from 1950 to 2000. In order to trace temporal trends the time series were decomposed into seasonal, trend and irregular components and analyzed using loess smoothing (STL). The seasonal values were removed, and the remainder smoothed to find the trend. An identical procedure was applied to the El Niño3.4 index. The trend component of each data set was analyzed for autocorrelation and cross correlation. The autocorrelation function for the standardized number of days with rainfall shows significant positive correlations between data points around three to four months apart. There is significant negative cross correlation between the standardized El Niño sea surface temperature index and rainfall. The technique thus led to a clear description of a pattern that might be used in order to partly predict precipitation driven events such as floods and wildfire