Changes in the canopy strncture and species composition as part of the agricultural management in traditional and rustic coffee plantations affect the nutrient cycling through the alteration in the litter quality and production deposited in the forest floor.
The use of endemic canopy tree species of the subperennial medium forest in the coffee plantations can be an important component for the leaf litter production in terms of quality and quantity and can be as well, imp01tant for the nutrient storage, litter decomposition and the general physical-chemical characteristics of the soil.
The objetives of this research was to study the changes in the tree canopy species composition and the effect in the quality of the leaf litter and the effect of it in the decomposition rates of the litter deposited in the forest floor. A study about the contribution and quality of representative species litterfall in traditional (TCS) and rustic coffee systems (RCS) and subperennial medium forest (Spmf) was performed with the objective to analyze the effect of the litter qualities in the forest floor decomposition processes. The study was carried out in the community of San Miguel in the Mountain range of Atoyac in Veracruz, Mexico. Nine plots (20 x 50 m), were randomly established, three in each of traditional (TCS), rustic coffee plantations (RCS) and disturbed sub-perennial medium forest (Spmf). All plot vegetation inventoried and Shannon diversity index (H') and Jaccard similarity index (Jee) calculated per system. In each plot, four littertraps (lm2) were placed to collect leaf litter from the trees. The leaf-litter collection was carried out every 15 days for 12 months.
Organic matter decomposition process was evaluated using the litterbag method, 252 litterbags were placed in the nine plots and sampling was perfo1med at interva ls of: 0,22, 44, 88, 176 and 352 days. Soil analyses were perfom1ed on the same dates and sites of collection of litterbags and included total N, P, K, Ca, pH and organic matter content. Differences in tree canopy species composition and litter production influenced the litter quality deposited on the forest floor and decomposition and nutrient cycling on the systems studied.
Nutrient analyses of the litterbags contents (Robinsonella mirandae, Co_ffea arnbico, Mastichodendron capirii, Piper hispidum, Croton officinalis and a representati ve tree species general mixture per system) were pe1fom1ed at each litterbag collection to determine best quality and predict the changes in the leaf litter quality over time.
Analyses were for total N, P, K, Ca, hemicelluloses, celluloses and lignin contents
were also detennined. The decomposition rate was calculated by developing the ·'k'" constant from the weight loss of the litterbags. Results indicated that litter quality and climate influenced decomposition rates and decomposition probably follows two distinctive phases that ocour with the start of the rainy season and the dry season.
The parameters that most influenced the decomposition process were lignin:N and C:N ratios followed by the initial rates of N and P. Quality species with the highest content of N and the lowest initial lignin:N and C:N ratios were Robinsonella mirandae/Coffea arabica in Spmf, Mastichodendron capirii and Piper hispidwn and these showed the highest rates of decomposition which increased continuously with time. Low quality litter represented by Croton officinalis had the lowest rates of decomposition and the lowest N, lignin:N and C:N ratios and progressive declines in cellulose and hemicelluloses which were approximately linear over time.
Increasing N and P soil concentration are coffelated with S.O.M. at different times of
the year, but probably do not have any effect on decomposition rates of litter. In
general it was concluded that the changes in the tree canopy species composition does have an effect on the litter quality deposited in the forest floor of coffee plantations and disturbed forest and consequently in the nutrient cycling in the ecosystems.