Establishment of Quercus marilandica Muenchh. and Juniperus virginiana L. in the tallgrass prairie of Oklahoma, USA increases litter inputs and soil organic carbon

Abstract

The establishment of trees in grasslands alters ecosystem processes and services. Litter inputs shift from herbaceous to tree-derived, which affects the litter quantity and quality and may in turn alter soil carbon dynamics and ecosystem-level carbon sequestration. This study determined changes in the quantity of organic matter inputs following encroachment by two native tree species (Quercus marilandica Muenchh. and Juniperus virginiana L.) into a tallgrass prairie in northcentral Oklahoma, and related it to spatial heterogeneity in soil carbon by measuring variables near the stem, under the tree canopy, at the outer edge of the tree canopy, and beyond the tree canopy. Presence of trees increased aboveground litter inputs (dominated by foliage for J. virginiana and acorns for Q. marilandica) and increased the duff and litter layer. Regardless of leaf litter source, decomposition of foliage was slower under the tree canopy than beyond the tree canopy (7% slower) and this change was associated with cooler and potentially drier conditions. However, the foliage of trees decomposed more quickly than grass foliage when measured both beneath and beyond the tree canopy (25% faster). Coarse root biomass was greater under tree canopies than beyond, which increased total root biomass in the deeper soil layer (10-30 cm). The net effect was an approximately 15% increase in soil carbon stock under the trees as compared to areas beyond the tree canopy. Therefore, in addition to greater carbon storage in the aboveground biomass, tree encroachment increases carbon sequestration by increasing soil carbon.