Ecosystem health and sustainability of an indigenous agroforestry system in Chiapas, Mexico

1. Ecosystem health and sustainability of an indigenous agroforestry system in Chiapas, Mexico Stewart A.W. Diemont and Jay F. Martin; Ecological Engineering Group; Department of Food, Agricultural, and Biological Engineering; The Ohio State University Abstract The Lacandon Maya of Chiapas, Mexico practice a system of agroforestry that mimics the surrounding ecosystem and its successional stages. Their fields rotate through grass (milpa), and shrub (acahual) and forest fallow sages that regenerate soil, nutrients, and seed banks. Each successional stage, including the fallow stages, produces over 25 types of crops, raw materials, and medicines. Lacandon traditionally do not use fertilizers, pesticides, or herbicides. Emergy, plant community, nematode and soil chemistry analyses were used to evaluate the system. Emergy calculations resulted in high emergy sustainability indices (ESI) ranging from 31 to 4356. ESI was found to be a function of fallow area and did not relate to management practice. In contrast, nematodes were found to be a function of management practice. In milpas where weeds were removed and applied to the field, plant parasites were reduced by 44% and fungivorous nematode concentrations were cut in half. In these same fields, bacterivorous nematodes were found to be a function of soil organic matter (P< 0.05). These results indicate that Lacandon management practices delayed the nematode successional processes. Lacandon Maya land management, although limited by land pressures, offers insights into pest reduction and fertility maintenance in agroecosystems. Methods Sampling was conducted during July and August 2003 in six Lacandon Maya agroforestry systems in Lacanja Chansayab, Mexico. Soil and plant community sampling was performed in each successional stage from each system in three traditional Lacandon systems and three non-traditional systems. In addition to the three field stages, milpa, acahual, and secondary forest, one primary forest was also sampled. Only one non-traditional acahual was sampled. Sampling locations were determined in each field stage using a transect method. Soil samples were collected within a circular 1-m2 quadrat at each sampling location. Soil samples were partitioned for organic matter, inorganic nitrogen, total nitrogen and nematode analysis. Using the Baermann wet funnel technique, nematodes were extracted into water from 20-g soil samples for 72 hours. The nematodes were then identified to trophic level using a 45x stereoscopic dissecting microscope. Plant cover assessment was conducted at each sampling location. In the milpa, all plants in the quadrat were recorded based on percent cover. In the acahuals, secondary and primary forests, plants with a stem or trunk diameter greater than 1-cm were counted in the quadrat, and all plants with a diameter greater than 5-cm were counted within a 20 m2 circular area. Interviews for emergy evaluations were conducted during July and August 2003 with six Lacandon Maya farmers in Lacanja Chansayab, Mexico. The six farmers included three who fallow traditional methods (Manuel Castellanos, Kin Bor, and Jorge Paneagua) and three non-traditional (Vicente Paneagua, Enrique Paneagua, and Kin Paneagua). The ratio of cultivated area to total land area spanned a broad range across the six systems. Figure 4. Nematode fungivore concentration as a function of nematode plant parasite concentration. Results 1. The agroforestry system is highly sustainable. The emergy sustainability index (ESI) was greater than 30 (Table 1). These results are due to a large proportion of renewable resources utilized. ESI was not dependent upon adherence to traditional practice, but was proportional (on a log-log scale) to the land area occupied by the system (or the amount of area in fallow) (Figure 3). 2. Nematode population, soil chemistry, and plant community was dependent upon successional stage and adherence to traditional practice. a. Plant parasite nematode concentrations were proportional to fungivorous nematode concentrations (Figure 4). b. Plant parasite concentrations were greater in non-traditional than traditional systems. Weedy species were greater in non-traditional systems. c. Weedy species management affected both plant parasites and the successional conversion of the degradation pathway of a field from bacterivorous to fungivorous (Figure 5). d. Soil organic matter and total nitrogen increased with successional stage and also differed between traditional and non-traditional systems. Figure 1. Lacanja Chansayab is the home to 400 Lacandon Maya who practice swidden agroforestry • Introduction • The Lacandon rainforest of Chiapas, Mexico is losing 7% of the remaining forest each year. Erosion has moderately degraded 10% to 25% of the arable soil and severely degraded 5% of the arable soil in the coffee-producing lowlands of Chiapas (Howard and Homer-Dixon 1996). These problems are endemic throughout the tropics, as increasing population densities stress the environment through demands on agricultural land (Lal 1995, Alvarez and Naughton-Treves 2003). These demands result in diminished fallow time, which leads to deforestation and soil erosion (Drechsel et al. 2001). • Numerous researchers recognize the importance of recording indigenous knowledge to better understand sustainable methods of land management (De Clerk and Negreros-Castillo 2000, Fox et al. 2000, Long and Zhou 2001, Hardwick et. al. 2004). Swidden agroforestry systems can be productive (Long and Nair 1999) while maintaining ecological integrity (Zhijun and Young 2003). The indigenous knowledge in southern Mexico is quickly disappearing as younger members of the community seek work in urban centers and in ecotourism (Trujillo 1998, McGee 2002, Gillespie et al. 2004). This makes it vital to understand how indigenous knowledge is used to design agroforestry systems. • The Lacandon Maya are an indigenous group living in Lacanja Chansayab, Mexico (Figure 1) who have supported themselves for centuries through effective use of their surrounding environment. They practice a unique method of swidden agroforestry in which they manage the fallow period for production and soil regeneration (Nations and Nigh 1980, Levy 2000, McGee 2002). Their system cycles through three field stages of production starting with the milpa, progressing to the acahual, and then to the secondary forest, before returning to the milpa (Figure 2). Components of their agroforestry could serve as a model to farmers in Chiapas and in similar ecological regions throughout the tropics. • In order to better understand the Lacandon agroforestry system, research was conducted during 2003 that evaluated: • Emergy • Plant community • Soil chemistry • Soil nematodes • It was hypothesized that traditional management of Lacandon systems would impact the system differently than systems where traditional management was no longer being practiced. Figure 2. Systems diagram of Lacandon Maya swidden agroforestry system Figure 5. Nematode concentration as affected by weed management in traditional Lacandon agroecosystems Conclusions The Lacandon agroforestry swidden system offers insight into how sustainable land management can be conducted in tropical regions. Emergy analysis determined that the system is highly sustainable, although the sustainability is dependent upon land area devoted to the system. System management that adheres to traditional practices results in fewer live weeds, reduced plant parasite pests, and a slower conversion of the degradation pathways in the field from bacterivorous to fungivorous. These results indicate that pests can be reduced and fertility maintained if the traditional management is utilized and adequate land is available for the swidden system. R2 = 0.90 y = 1.4x + 1.1 P = 0.005 Table 1. Emergy indices of the Lacandon agroforestry systems. References Alvarez, NL, Naughton-Treves L, 2003. Linking national agrarian policy to deforestation in the Peruvian Amazon: a case study of Tambopata, 1986-1997. Ambio 32 (4), 269-274. Drechsel, P, Gyiele, L., Kunze, D, Cofie, O, 2001. Population density, soil nutrient depletion, and economic growth in sub-Saharan Africa. Ecological Economics 38 (2), 251-258. DeClerk, FAJ, Negreros-Castillo, P, 2000,Plant species oftraditional Mayan homegardens of Mexico as analogs for mulitstrata agroforests. 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Sucesión causada por roza-tumba-quema en las selvas de Lacanhá, Chiapas. Doctoral Dissertation, Institution de Ensenanza e Investigacion en Ciencias Agricolas, Instituto de Recursos Naturales. Montecillo, Texcoco, Mexico. Long CL, Zhou YL, 2001. Indigenous community forest management of Jinuo people's swidden agroecosystems in southwest China. Biodiversity and Conservation, 10 (5): 753-767. McGee, RJ, 2002. Watching Lacandon Maya. Allyn and Bacon, Boston. Nations, JD, Nigh, R, 1980. Evolutionary potential of Lacandon Maya sustained-yield tropical forest agriculture. Journal of Anthropological Research 36, 1-30. Trujillo, HAG 1998. Sustainability of Ecotourism and Traditional Agricultural Practices in Chiapas, Mexico. Ph.D. dissertation. Environmental Engineering Sciences. University of Florida, Gainesville. Figure 3. Log of the Emergy Sustainability Index (ESI) as a function of Log of the land area devoted to Lacandon agroforestry system