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We analyzed the effect of intensifying the traditional slash-and-burn system on floristic diversity in order to determine the threshold of frequency and duration of cultivation below which native woody species can be maintained.A total of 39 floristic inventories were conducted in the Northern Region of the Selva Lacandona of secondary vegetation with different ages (AE) and use history. We constructed an integrity index (II) that combines agricultural use intensity (number of years under cultivation) and frequency of slash-and-burn agriculture.We applied a canonical correspondence analysis to group the species according to AE and II. We found that fallows originated from slash-and-burn systems with low use intensity and low frequency can act as a reservoir of species of mature tropical forests. However, if the intensification trend of slash-and-burn continues toward longer periods of cultivation and higher frequencies of slash-and-burn, this will create a more homogeneous landscape with a very high contrast with the remaining forest patches, which will limit the dispersal, establishment and sustainability of the portion of  primary species that could survive under conditions of low-intensive slash-and-burn agriculture.

Energy flows were studied for the [2002][2003] agricultural cycle in four households for which agriculture is part of a diversified survival strategy and four that practice agriculture as a business. Home garden inputs and outputs were measured monthly. Quantified inputs were: household labour, household agro-system production, and purchased external renewable and non-renewable energy. Outputs measured were: sales, family and animal foods. While both strategies had similar indicators in biomass and energy production, vegetable richness, and soil quality, household garden function and sustainability differed between subsistence and commercial householders. Subsistence gardens complemented family diet and contributed to household system resiliency. They relied heavily on renewable energy sources from within their agro-system. Gardens in commercial households reduced fruit tree area and increased animal husbandry for the market. They depended more on purchased nonrenewable energy sources and were less sustainable and much less energy efficient than traditional gardens.

Revista Mexicana de Biodiversidad www.ib.unam.mx/revista/ Revista Mexicana de Biodiversidad 88 (2017) 141-149 Resiliencia, vulnerabilidad y sustentabilidad de sistemas socioecológicos en México Resilience, vulnerability and sustainability of socioecological systems in Mexico

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