SPECIES, ROTATION-LENGTH, AND LIFE-FORM-DIVERSITY EFFECTS ON SOIL CARBON IN EXPERIMENTAL TROPICAL ECOSYSTEMS

Authors: Russell, Ann; Cambardella, Cynthia; EWEL, J - USDA FOREST SERVICE; Parkin, Timothy

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2003
Publication Date: 1/5/2004
Citation: RUSSELL, A.E., CAMBARDELLA, C.A., EWEL, J.J., PARKIN, T.B. SPECIES, ROTATION-LENGTH, AND LIFE-FORM-DIVERSITY EFFECTS ON SOIL CARBON IN EXPERIMENTAL TROPICAL ECOSYSTEMS. ECOLOGICAL APPLICATIONS. 2004. V. 14(1). P. 47-60.

Interpretive Summary: Extensive areas of species-rich forests in the tropics have been replaced by tree plantations over the last two decades. The effects on soil fertility and carbon storage, hence the global carbon cycle, however, are poorly known. In an experimental tropical site, we characterized the effects that three different tree species had on soil organic matter quantity and quality, when grown under different rotation lengths in single-species stands, and in mixed-species polycultures. The three native, non-N-fixing tree species were Spanish cedar (Cedrela odorata), laurel (Cordia alliodora), and pilon (Hyeronima alchorneoides) and the polycultures contained a palm and a banana-like plant. We found that after 10 years, the amount of soil organic matter, and of a biologically active soil carbon fraction, differed beneath the three species. Rotation-length had an even stronger effect under Cedrela and Cordia, with soil carbon stocks higher under 4-yr rotations than under uncut stands. Increased biodiversity tended to result in greater soil nutrient-supply capacity and carbon storage. We also found that differences in root traits, especially their chemistry, best accounted for the differences in effects of individual species and diversity on soil carbon storage and nutrient availability. These results increase our understanding of human impacts on the biosphere, especially with regards to loss of biodiversity. These data can be used to improve models of tropical forest nutrient cycling and to help guide selection of species for ecosystem management purposes. Scientists in this specialization, tropical foresters and land-use managers will benefit from this information.

Technical Abstract: Extensive areas of species-rich forests in the tropics have been replaced by tree monocultures over the last two decades, and the impact on biogeochemical cycles is unclear. In lowland Costa Rica, we characterized effects on soil carbon of species identity, rotation frequency, and life-form diversity in model ecosystems containing three non-N-fixing tree species, Hyeronima alchoreoides, Cedrela odorata, and Cordia alliodora, grown in monocultures and polycultures with two additional life forms. Over all treatments, change in total soil organic carbon (TSOC, 0-15 cm) after 10 yr ranged from a loss of 24% (0.9 Mg/ha in 1-yr rotations) to an increase of 14% (0.6 Mg/ha in Hyeronima polycultures). Species differed in effects on TSOC stocks, but light particulate organic matter, a biologically active soil C fraction, was a more sensitive indicator of species effects. Effects of rotation frequency were strong; in Cedrela and Cordia, 4-yr rotations had higher soil C stocks than did uncut, long-term monocultures. Effect of life-form diversity differed among species: polycultures had higher soil C stocks than monocultures only in Cedrela and Cordia . In polycultures, Hyeronima dominated detrital inputs, contributing 88% of litterfall and fine root growth, whereas Cedrela and Cordia contributed <34%. Root C:N ratio and fine root growth accounted for the majority of variability in changes in soil C stocks after 10 yr in long-term cultures (partial r**2 = 0.70 and 0.14, respectively). This suggested that roots drove soil carbon accrual in these systems and that over the long term, mechanisms involving root litter chemistry better explained effects of species and biodiversity on soil C sequestration and nutrient availability, than did quantity of detrital inputs.