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Awareness of environmental heterogeneity in ecosystems is critical for management and conservation. We used the Xochimilco freshwater system to describe the relationship between heterogeneity and human activities. This tropical aquatic ecosystem south of Mexico City is comprised of a network of interconnected canals and lakes that are influenced by agricultural and urban activities. Environmental heterogeneity was characterized by spatially extensive surveys within four regions of Xochimilco during rainy and dry seasons over 2 years. These surveys revealed a heterogeneous system that was shallow (1.1 m, SD=0.4 ), warm (17 degrees C, SD=2.9), well oxygenated (5.0 mg l(-1), SD=3), turbid (45.7 NTU SD = 26.96), and extremely nutrient-rich (NO(3)-N=15.9 mg l(-1), SD=13.7; NH(4)-N=2.88 mg l(-1), SD=4.24; and PO(4)-P=8.3 mg l(-1), SD=2.4). Most of the variables were not significantly different between years, but did differ between seasons, suggesting a dynamic system within a span of a year but with a high resilience over longer periods of time. Maps were produced using interpolations to describe distributions of all variables. There was no correlation between individual variables and land use. Consequently, we searched for relationships using all variables together by generating a combined water quality index. Significant differences in the index were apparent among the four regions. Index values also differed within individual region and individual water bodies (e.g., within canals), indicating that Xochimilco has high local heterogeneity. Using this index on a map helped to relate water quality to human activities and provides a simple and clear tool for managers and policymakers.

In spite of widely documented studies of deforestation rates and land use/cover changes in tropical dry forests in Mexico, relatively little is known about fragmentation patterns in such forests. This study defines the spatial distribution of landforms and land use/cover types the lower Papagayo River basin and examines their influence on fragmentation patterns and biological diversity in a tropical dry forest in that southern Pacific region. The land use/cover map was constructed from aerial photographs, Landsat TM imagery (2000) and fieldwork. Landform units were defined based on altitude, slope, lithology and morphology. Landscape fragmentation parameters were obtained using FRAGSTATS (version 3.3) considering the numbers of patches, mean, minimum and maximum patch size, edge density, total edge and connectivity. Results show tropical dry forest to be remnant vegetation (~11 per cent), characterized by isolation and low connectivity. Land use/cover types have different effects on fragmentation patterns. Agriculture and cattle raising produce similar numbers of patches, but with a different mean size; and human settlements have a scattered distribution pattern. The abandonment of rural agricultural livelihoods has favoured the expansion of secondary tropical dry forest characterized by continuity and high connectivity, which suggests a high regeneration potential from land abandonment. It can be concluded that tropical dry forest fragmentation and recovery at regional scales depend on such landscape attributes as lithology, slope, geomorphology and management.

Identification of the ecosystem services provided by Mexican temperate forests is a prerequisite in ensuring their conservation and sustainable management. This study aimed (1) to describe ecosystem services provided by Mexican temperate forests (provisioning, regulating and cultural services); and (2) to identify possible trade-offs and synergies based on the types of ecosystem services available in Mexican temperate forests. We synthesized relevant literature from scientific articles, government statistics and grey literature covering the years 1985-2012. Timber extraction is the main beneficial ecosystem service of temperate forests recognized by public policy as shown by the high income from this activity; but it has trade-offs of greater magnitude with other provisioning services (water, bioenergy and non-timber forest resources), and with other supporting, regulating and cultural ecosystem services. For example, it causes the loss of other forest resources, extinction of commercially important species and loss of the system's structural complexity. Water capture and extraction of non-timber forest resources have lesser effects on support and regulation services, and in the case of water capture, the magnitude of the effect depends on the type and reversibility of the modification of the ecosystem. The synergies between ecosystem services have mutual benefits; for example, a decision to enhance the scenic beauty in temperate forests potentially improves water cycling and provision of non-timber forest resources, and has a positive effect on cultural and regulation services. In Mexican temperate forests the recognition of ecosystem services is limited and is based largely on grey literature. More robust scientific information is needed on the role of these forests in maintaining biodiversity and provision of ecosystem services essential to the welfare of the population. Also, monitoring of ecosystem processes of highland temperate forests in tropical regions is very limited, so it is necessary to generate research to develop a paradigm shift from forest management based strictly on logging to one based on ecosystem management.