Deforestation and cultivation mobilize mercury from topsoil.

Terrestrial biomass and soils are a primary global reservoir of mercury (Hg) derived from natural and anthropogenic sources; however, relatively little is known about the fate and stability of Hg in the surface soil reservoir and its susceptibility to change as a result of deforestation and cultivation. In southwest Ohio, we measured Hg concentrations in soils of deciduous old- and new-growth forests, as well as fallow grassland and agricultural soils that had once been forested to examine how, over decadal to century time scales, man-made deforestation and cultivation influence Hg mobility from temperate surface soils. Mercury concentrations in surficial soils were significantly greater in the old-growth than new-growth forest, and both forest soils had greater Hg concentrations than cultivated and fallow fields. Differences in Hg:lead ratios between old-growth forest and agricultural topsoils suggest that about half of the Hg lost from deforested and cultivated Ohio soils may have been volatilized and the other half eroded. The estimated mobilization potential of Hg as a result of deforestation was 4.1 mg m(-2), which was proportional to mobilization potentials measured at multiple locations in the Amazon relative to concentrations in forested surface soils. Based on this relationship and an estimate of the global average of Hg concentrations in forested soils, we approximate that about 550 M mol of Hg has been mobilized globally from soil as a result of deforestation during the past two centuries. This estimate is comparable to, if not greater than, the amount of anthropogenic Hg hypothesized by others to have been sequestered by the soil reservoir since Industrialization. Our results suggest that deforestation and soil cultivation are significant anthropogenic processes that exacerbate Hg mobilization from soil and its cycling in the environment.

Thirty-two years of change in an old-growth Ohio beech-maple forest.

Old-growth forests dominated by understory-tolerant tree species are among forest types most likely to be in equilibrium. However, documentation of the degree to which they are in equilibrium over decades-long time periods is lacking. Changes in climate, pathogens, and land use all are likely to impact stand characteristics and species composition, even in these forests. Here, 32 years of vegetation changes in an old-growth beech (Fagus grandifolia)-sugar maple (Acer saccharum) forest in Hueston Woods, southwest Ohio, USA, are summarized. These changes involve canopy composition and structure, turnover in snags, and development of vegetation in treefall gaps. Stand basal area and canopy density have changed little in 32 years. However, beech has decreased in canopy importance (49% to 32%) while sugar maple has increased (32% to 47%). Annual mortality was about 1.3% throughout the study period. Mortality rates increased with stem size, but the fraction of larger stems increased due to ingrowth from smaller size classes. Beech was represented by more very large stems than small canopy stems: over time, death of those larger stems with inadequate replacement has caused the decrease in beech importance. Sugar maple was represented by more small canopy stems whose growth has increased its importance. The changes in beech and sugar maple relative importance are hypothesized to be due to forest fragmentation mostly from the early 1800s with some possible additional effects associated with the formation of the state park. Snag densities (12-16 snags/ha) and formation rates (1-3 snags.ha(-1).yr(-1)) remained consistent. The treefall gaps previously studied are closing, with a few, large stems remaining. Death of gap border trees occurs consistently enough to favor species able to combine growth in gaps and survival in the understory.

Influence of climate on butterfly community and population dynamics in Western Ohio.

Climate influences butterflies both directly and through impacts on their food plants and habitat. We look at the relationship between climate and butterflies in the Aullwood Audubon Center, west central Ohio, using the weekly Long-Term Butterfly Monitoring (LTBM) surveys (April through October 2000-2006) and the annual fourth of July counts (1989-2006). The 18 annual Fourth of July surveys yielded 20,709 butterflies and 59 species. The number of individuals though not species decreased over time. Most but not all of that decrease was from a large drop in Pieris rapae L. (Pieridae). The number of individuals was greatest when the previous and current growing seasons were cool and winter precipitation high. Individual species varied in their response to climate. Recent years have been warmer (all seasons) and have had drier winters than earlier years. The 7 yr of weekly LTBM surveys recorded 5,784 butterflies and 58 species. The total number of individuals has not changed significantly over time. The weather of the day of sampling had some effect: the total number of species was highest on clear days with some wind. The results over the 18 yr are compatible with the hypothesis that global warming has led to a decrease in the number of butterflies. Habitat changes cannot be excluded as an alternate hypothesis, but these effects seem minor. The value of a large, environmentally heterogeneous natural area like Aullwood is that it buffers short-term climatic and weather conditions to provide long-term stability for a diverse butterfly community.