Life at the interface: above- and below-ground responses of a grazed pasture soil to reforestation

Abstract

Conversion of agricultural lands to mixed species woody plantings is increasingly being undertaken as ameans of sequestering C and increasing biodiversity. The implications of such changes in land use for soilcommunities, and the ecosystem services they provide (e.g., nutrient and C cycling), are relatively littleunderstood. Results of a detailed study of vegetation, soil physicochemical properties and soilcommunities (primarily microbial) to reforestation of a pasture (15 years post reforestation), and itsimmediately adjacent un-restored pasture, are presented. Whereas the reforested portion of the site hadsignificantly higher levels of tree canopy cover and a well-developed litter layer than the immediatelyadjacent pasture, the reverse was true for grass biomass. Although there were no differences in total rootbiomass between the sampling zones, the pasture zone was dominated by fine roots and the reforestedzone by coarse roots. Reforestation had a significant impact on soil physicochemical properties, with soilC, C:N and mineral N being higher than in the pasture. The reforestation also supported a greatermicrobial PLFA, a higher Fungal:Bacterial PLFA ratio and a different microbial community (based on PLFAprofiles) from that of the adjacent pasture. There were also differences in earthworm abundance, withearthworms present and absent in soils from the pasture and reforested zones, respectively. All of thechanges in vegetation, soil physicochemical properties and biotic communities occurred abruptly at theinterface between the land-use types, with no evidence of an interaction between side of fence(reforested versus pasture zones) and distance from the fence. Results are discussed in the context ofchanges in land-use on soil ecology and their potential functional significance.