Cotler H.,Intituto Nacional de Ecologia y Cambio Climatico INECC |
Cram S.,National Autonomous University of Mexico |
Martinez Trinidad S.,National Autonomous University of Mexico |
Bunge V.,Intituto Nacional de Ecologia y Cambio Climatico INECC
Investigaciones Geograficas | Year: 2015
Given the intense soil degradation that spans almost half of Mexico, the Mexican government has establis-hed various public policies in which soil conservation practices are carried out by the owners in return for a subsidy. The main practices promoted on forest soils by these programs are mechanical, in particular, the construction of ditches. Nowadays this practice is the main soil conservation practice held in Mexico and carried out in various geo-graphical and ecological conditions; however its impact is not assessed. The international literature specifies that the goal of this practice is to facilitate the storage of rainwater in arid and semi-arid ecosystems, to reduce the length of water flow, to conserve water and promote the afforestation in degraded environments and to regúlate water runoff in urban áreas. Unlike the international experience, in Mexico this practice seeks to preserve and restore forest soils. This work aims to assess the ditches from the perspective of a practice that allows the forest soil conservation and to identify environ-mental and social conditions under which this practice may be appropriate in Mexico. The evaluation of ditches as a soil conservation practice was performed in 28 sites in seven states (Baja California Sur, Guanajuato, Hidalgo, Querétaro, Michoacán, Tlaxcala and Veracruz), addressing different ecosystems, from arid to humid tropical, expressed in a wide variability of soils and vegetation (scrub, pine, oak forest, grassland and maize). In each site we characterize the physical environment, with an emphasis on soil analysis, erosión features, infiltra-tion measures as well as interviews with landowners. Measu-rements were made in sites with and without (control sites) ditches. Infiltration was measured on the pile of excavated soil where the trees for reforestation are planted. The main findings indícate that the construction of the ditches result in a large number of negative impacts. Among them, the removal of soils as a result of the excavation of 250 ditches per hectare (recommendation of the policy pro-gram), which can mobilize 60-123 ton/ha. Given the depth of the ditch (40 cm), the removal also causes the exposition of 0.4-6.3 ton/ha of soil organic carbon, which is susceptible to mineralization. In terms of hydrologic regulation, this practice does not improve the conditions of moisture retention, which is necessary for a successful reforestation. Nowadays this practice is not adopted by the landowners. The biggest single benefit received for performing these work, either in private property or common use areas is the economic resource that the program provides. In any case was observed willingness of people to increase the area of trenches, reflecting the weak appropriation around this practice. The results and the literature review helped to identify certain environmental conditions under which the construction of ditches may be adequate: arid or semi-arid climate (aprox. 300 mm average rainfall), slope range up to 40%, shallow soils (less than 20 cm) without a clay horizon and sparse and discontinuous vegetation. These recommenda-tions were presented and discussed with decision makers and were subsequently introduced into the National Forest Program (PRONAFOR). © 2015 Universidad Nacional Autonóma de México.