Comparative Dynamics of Above-Ground Litter Production and Decomposition from Eucalyptus grandis Hill ex Maiden and Pinus taeda L., and Their Contribution to Soil Organic Carbon

Abstract

The replacement of native pasture by exotic commercial forest species is an infrequent situation worldwide. In these systems, a new component is introduced, forest litter, which constitutes one of the main ways of incorporating carbon into the soil–plant system. The present work seeks to establish a methodological approach to study the dynamics of litter production and decomposition in an integrated way. The general objective was to characterize and compare the litter production dynamics in 14-year-old Eucalyptus grandis Hill ex Maiden and Pinus taeda L. commercial plantations. During two years, seasonal evaluations of fall, decomposition and accumulation of litter were carried out in stands of both species. In turn, the contribution of carbon from forest species to the soil through isotopic analysis techniques was quantified. Litterfall in E. grandis showed maximums during the spring of the first year and in the spring and summer of the second. In P. taeda, the maximums occurred in summer of the first year and in autumn of the second. In relation to the decomposition rate, the results based on short periods of evaluation between 15 and 21 months did not show differences between species, nor for the different moments of beginning of the evaluation, obtaining average values of 0.0369 month−1 for E. grandis and 0.0357 month−1 for P. taeda. In turn, both the decomposition rate of the material as a whole and the estimates of accumulated biomass in equilibrium state did not show significant differences between the species. Additionally, there was a relevant incorporation of carbon into the soil by forest species, fundamentally in the first few centimeters, substituting an important proportion of the carbon inherited by the original cover of native pastures. Finally, it is necessary to specify that the scope of the findings obtained is greatly limited by the sample size used in this study.

Comparative Dynamics of Nutrient Release through Litter Decomposition in Eucalyptus grandis Hill ex Maiden and Pinus taeda L. Stands

“…According to the results from a previous study, there were not significant differences in the litter decomposition rate obtained from exponential decay models between the considered species and layers [5]. In this context, this study found that the nutrient dynamics differs enough to alter the average trend evidenced for biomass loss.…”

“…This situation allows to verify a more consistent trend, which is characterized by a greater enrichment of this metal in E. grandis. This context would explain the Zn immobilization processes identified in E. grandis and the oscillations between release and immobilization periods obtained in P. taeda, since there were no significant differences in the decomposition rate between species [5].…”

“…The obtained decomposition rate from the model for each layer was compared between species and layers by each species individually. A detailed explanation of the sampling methodology and the results of the decomposition dynamics are available in a related previous work [5].…”

“…The soils under the experiment correspond to thermic Humic Hapludults [27]. A detailed soil characterization is available in previous studies [2,5]. The climate in the area is temperate, with an average annual temperature around 18.6 • C and an average annual rainfall of 1605 mm which distribution presents a main maximum during autumn and a main minimum in winter, showing high interannual variation [28].…”

“…Normally, these systems are designed for pulp or wood production, in relatively short rotations, with immediate replanting, usually on soils with low natural fertility [3,4]. This change in coverage implies the incorporation of a new component to the soil-plant system, the forest litter [5]. In this sense, the nutrient leaching and forest litter decomposition constitute fundamental processes in nutrient recycling, acquiring relevance in this productive context [4,[6][7][8][9].…”