In the Great Basin of the western United States, expansion of Pinus monophylla (singleleaf piñyon) and Juniperus osteosperma (Utah juniper) out of historic woodlands and into Artemisia spp. (sagebrush) shrubland communities can facilitate the invasion of exotic downy brome (Bromus tectorum) and lead to decreases in ecological and economic values of shrublands. This expansion has, therefore, been the focus of management efforts, including the thinning or removal of trees in areas that were historically shrubland. Our study examined the effects of tree thinning at two sites located in eastern Nevada, near the center of the Great Basin. Such projects can be controversial, so our goal was to estimate and document the ecological effects of low-disturbance tree thinning at these two sites. Both sites were mechanically thinned using a feller-buncher and were aerially seeded with native grasses. Aerial seeding had no apparent effect at either site. The site that had lower tree cover before treatment (Ely, NV) showed an increase in native forbs and a small increase in invasives. The site that initially had very high tree cover and low shrub cover (Mt. Wilson, NV) showed increases in native forbs and species diversity and a substantial increase in invasives. We conclude that low-disturbance methods for thinning encroaching trees can have positive ecological effects in shrublands but that the initial cover of both trees and native herbaceous species should be considered to determine the potential of the site to recover naturally from the seedbank and the risk of invasion by downy brome.

This discussion is a review and critique of the three papers in the 2012Southern Agricultural Economics Association invited paper session titledCauses of Agricultural and Food Price Inflation and Volatility.

Conversion to permanent agriculture is rapidly occurring over vast areas of the 1.8 million km2; Brazilian Cerrado; a region that is naturally a mosaic of grasslands, savannas and evergreen tropical woodlands. Yet, few studies have quantified total biomass of plant communities in this ecosystem, particularly the belowground component; a C pool of potential global significance. Total biomass (aboveground and belowground), and the quantity of biomass consumed by fires were measured in four plant communities comprising a vegetation gradient from pure grassland (campo limpo) to a woodland with a closed canopy of tall shrubs and scattered trees (cerrado denso) near Brasilia, DF, Brazil. Total aboveground biomass (TAGB) increased along this gradient from 5.5 Mg ha-1 in campo limpo to 29.4 Mg ha-1 in cerrado denso. Vegetation structure varied among communities; trees were nonexistent in campo limpo, but were at a density of 1000 ha-1 and a biomass of 12.9 Mg ha-1 in cerrado denso. Fires consumed 92 and 84% of the TAGB in campo limpo (pure grassland) and campo sujo (savanna), respectively. In cerrado aberto and cerrado denso, trees and tall shrubs were little affected by fire. Combustion factors of the TAGB in these communities was 54 and 33%, respectively. The total biomass consumed by fire ranged from 5.0 Mg ha-1 in campo limpo to 13.5 Mg ha-1 in cerrado aberto. Compared to other widespread Brazilian ecosystems (tropical dry forest and evergreen forest), the Cerrado has a lower aboveground biomass. The TAGB of cerrado denso is > 9% of that of Amazonian tropical evergreen forest. The total quantity of biomass consumed by fire, and hence emissions to the atmosphere is lower in intact Cerrado communities compared to fires in slashed tropical forest.