Changes in Agroecosystem Structure and Function Along a Chronosequence of Taungya System in Chiapas, Mexico

The shifting cultivation system was widely used in the past; however in recent times it is no longer sustainable. In Mexico, a group of Mayan farmers established Taungya system (Ixim’te) as alternative to shifting cultivation. The system consists of the rotational association of crops with cultivated and spontaneous timber trees. The aim was to evaluate the changes in ecological structure and functions, and economic value along a chronosequence of 2 to 13 years. Twenty farmer’s plots were selected. In each plot, structure, function and economic indicators were evaluated. Along the chronosequence cultivated trees (Cedrela odorata, Swietenia macrophyla, Tabebuia rosea, Cordia alliodora and Enterolobium cyclocarpum) mixed with crops and spontaneous trees, forming a sort of diverse garden containing 75 plant species. Tree diameter, tree height, total biomass, carbon stock, timber volume, timber value and present value significantly increased along the chronosequence. Two harvests of maize and beans were obtained yearly. According to interviews in the early years maize and beans yielded about 2400 kg and 600 kg ha-1, respectively, maize was reduced with each crop cycle at a rate of approximately 280 kg ha-1 yr-1, no reductions for bean yield were reported. The number of woody species per 500 m2-sampling area showed a minimum of 4 species on the first years and a maximum of 34 species on the last years. At years 11-13 carbon aboveground stock averaged 45.4 Mg C ha-1 and stored 3.9 Mg C ha-1 Year-1. The timber volume reached 110.7 m3 ha-1; the timber value was estimated in 4261.7 USD ha-1 and the present value in 5665.7 USD ha-1. Most of the plots presented low levels of soil nitrogen and phosphorus. The studied system increased in complexity, productivity, carbon stocks, and economic value. However, this system may require inputs in organic matter in order to restore soil nitrogen and phosphorus.