Assessing Allowable Take of Migratory Birds

ABSTRACT Legal removal of migratory birds from the wild occurs for several reasons, including subsistence, sport harvest, damage control, and the pet trade. We argue that harvest theory provides the basis for assessing the impact of authorized take, advance a simplified rendering of harvest theory known as potential biological removal as a useful starting point for assessing take, and demonstrate this approach with a case study of depredation control of black vultures (Coragyps atratus) in Virginia, USA. Based on data from the North American Breeding Bird Survey and other sources, we estimated that the black vulture population in Virginia was 91,190 (95% credible interval = 44,520-212,100) in 2006. Using a simple population model and available estimates of life-history parameters, we estimated the intrinsic rate of growth (r_max) to be in the range 7–14%, with 10.6% a plausible point estimate. For a take program to seek an equilibrium population size on the conservative side of the yield curve, the rate of take needs to be less than that which achieves a maximum sustained yield (0.5 × r_max). Based on the point estimate for r_max and using the lower 60% credible interval for population size to account for uncertainty, these conditions would be met if the take of black vultures in Virginia in 2006 was <3,533 birds. Based on regular monitoring data, allowable harvest should be adjusted annually to reflect changes in population size. To initiate discussion about how this assessment framework could be related to the laws and regulations that govern authorization of such take, we suggest that the Migratory Bird Treaty Act requires only that take of native migratory birds be sustainable in the long-term, that is, sustained harvest rate should be <r_max. Further, the ratio of desired harvest rate to 0.5 X r_max may be a useful metric for ascertaining the applicability of specific requirements of the National Environmental Protection Act.     

Deer Forage Response to Herbicide and Fire in Mid-Rotation Pine Plantations

ABSTRACT Mid-rotation management practices for pine (Pinus spp.) plantations enrolled in cost-share programs have not been widely evaluated for wildlife. Mid-rotation pine plantations often have a substantial hardwood mid-story that limits growth of desirable understory forage species important to white-tailed deer (Odocoileus virginianus; deer). We treated with imazapyr herbicide and prescribed burning (HB) 11 thinned, 13–22-year-old loblolly pine (P. taeda) plantations in the Upper Coastal Plain (UCP; n = 5) and the Lower Coastal Plain (LCP; n = 6) of Mississippi, USA, enrolled in cost-share programs. We then sampled these plantations for production of important deer forages during July of 2003 and 2004, years 1 and 2 posttreatment. Deer foraging habitat was clearly improved by the HB treatment in both regions by year 2. Forb species of annual importance to deer increased in percent cover and biomass in the UCP and in biomass in the LCP. We estimated nutritional carrying capacity using a target diet quality of 14% crude protein; estimates in HB plots were 3 times greater than controls in the UCP and 19 times greater in the LCP. Although UCP sites had baseline carrying capacities nearly 8 times greater than LCP sites, the greater relative response to HB in the LCP eliminated the regional difference. Our results indicate that imazapyr herbicide treatment followed by prescribed fire is a beneficial tool for deer management in mid-rotation pine plantations.     

Plant controls on Late Quaternary whole ecosystem structure and function

Plants and animals influence biomass production and nutrient cycling in terrestrial ecosystems; however, their relative importance remains unclear. We assessed the extent to which mega‐herbivore species controlled plant community composition and nutrient cycling, relative to other factors during and after the Late Quaternary extinction event in Britain and Ireland, when two‐thirds of the region's mega‐herbivore species went extinct. Warmer temperatures, plant–soil and plant–plant interactions, and reduced burning contributed to the expansion of woody plants and declining nitrogen availability in our five study ecosystems. Shrub biomass was consistently one of the strongest predictors of ecosystem change, equalling or exceeding the effects of other biotic and abiotic factors. In contrast, there was relatively little evidence for mega‐herbivore control on plant community composition and nitrogen availability. The ability of plants to determine the fate of terrestrial ecosystems during periods of global environmental change may therefore be greater than previously thought.     

Fire in the Brazilian Amazon: 1. Biomass,nutrient pools,and losses in slashed primary forests

Deforestation in the Brazilian Amazon has resulted in the conversion of >230,000 km² of tropical forest, yet little is known on the quantities of biomass consumed or the losses of nutrients from the ecosystem. We quantified the above-ground biomass, nutrient pools and the effects of biomass burning in four slashed primary tropical moist forests in the Brazilian Amazon. Total above-ground biomass (TAGB) ranged from 292 Mg ha^-1 to 436 Mg ha^-1. Coarse wood debris (>20.5 cm diameter) was the dominant fuel component. However, structure of the four sites were variable. Coarse wood debris comprised from 44% to 69% of the TAGB, while the forest floor (litter and rootmat) comprised from 3.7 to 8.0% of the TAGB. Total biomass consumption ranged from 42% to 57%. Fires resulted in the consumption of >99% of the litter and rootmat, yet <50% of the coarse wood debirs. Dramatic losses in C, N, and S were quantified. Lesser quantities of P, K, and Ca were lost by combustion processes. Carbon losses from the ecosystem were 58–112 Mg ha^-1. Nitrogen losses ranged from 817 to 1605 kg ha^-1 and S losses ranged from 92 to 122 kg ha^-1. This represents losses that are as high as 56%, 68%, and 49% of the total above-ground pools of these nutrients, respectively. Losses of P were as high as 20 kg ha^-1 or 32% of the above-ground pool. Losses to the atmosphere arising from primary slash fires were variable among sites due to site differences in concentration, fuel biomass, and fuel structure, climatic fluctuations, and anthropogenic influences. Compared to fires in other forest ecosystems, fires in slashed primary tropical evergreen forests result in among the highest total losses of nutrients ever measured. In addition, the proportion of the total nutrient pool lost from slash fires is higher in this ecosystem compared to other ecosystems due to a higher percentage of nutrients stored in above-ground biomass.     

Ecological aspects of soil seed-banks in relation to bauxite mining. II. Twelve year old rehabilitated mines

Abstract Germinable seed stores were estimated for 12–13 year old rehabilitation sites in the jarrah forest over two seasons (autumn and spring). Collected soils were subjected to combinations of smoking and heating treatments before the germination procedure was commenced. The mean topsoil seed reserve to a depth of 10 cm was 1938 seeds m^?2. Of this total reserve, more than 80% was found in the upper 5 cm of soil. The topsoil seed reserve of these rehabilitation areas was almost seven times that of the adjacent native jarrah forest (292 seeds m^?2; Ward et al. 1997). There was a seasonal effect with autumn-collected soils having significantly more germinable seeds (2723 seeds m^?2) than soils collected in spring (1153 seeds m^?2). More than half (53%) of the topsoil seed reserve in rehabilitated areas was composed of annual weed species, dominated by Aira caryophyllea, Centaurium erythraea and the native Levenhookia pusilla. Of the total of 70 species identified, 13 species showed significantly higher germination in smoked trays while 11 species exhibited significantly higher germination in heated trays. Species responding to the smoking treatment tended to be annuals while those responding to the heating treatment were typically legume shrub species. Examination of the topsoil seed reserve and the vegetation present in these areas showed that while the species composition was similar between the seed store and the vegetation, there was a large difference in densities, with species occurring at much higher densities in the topsoil than in the vegetation. However, the rankings of species were significantly correlated between the topsoil seed reserve and the vegetation present at the site. The implications of these results to prescribed burning of these rehabilitated areas is discussed.     

The Holocene Prehistory of a coastal wetland system: Discovery Bay,Southeastern Australia

Recent theories of socio-economic change in hunter-gatherer societies have referred to associated changes in intensity and mode of resource exploitation. These ideas are examined in the light of pollen and charcoal analyses of an Australian coastal wetland system which allow, at the local scale, (1) documentation of resource availability, (2) identification of resource use, particularly where fire technology is involved, and (3) examination of the effect of environmental change on the archeological record. Evidence of plant food management through fire around 6800 BP suggests a longer history of deliberate swamp exploitation than indicated by the archeological record, and lends support to models which propose long-term gradual change in zones of high productivity.     

Using carbon isotope analysis of the diet of two introduced Australian megaherbivores to understand Pleistocene megafaunal extinctions

Aim Australia lost a diverse assemblage of large marsupial herbivores in the late Pleistocene, with suggestions that the extinctions were biased towards browsers. In modern times two bovines, the Asian water buffalo (Bubalus bubalis) and banteng (Bos javanicus), have established feral populations in the Northern Territory, Australia. Buffalo have aggressively expanded throughout the savanna landscape, yet banteng remain near their point of introduction on the Cobourg Peninsula. We hypothesized that this difference is related to feeding ecology, possibly reflecting a legacy of the Pleistocene extinctions. Location Western Arnhem Land, Northern Territory, Australia. Methods Analysing a previously published dataset of body mass and feeding ecology of extinct and extant marsupial herbivores, we evaluated whether browsers were at greater risk of extinction than grazers. We compared the carbon isotope composition and nitrogen content of banteng and buffalo dung in order to evaluate the hypotheses that the differences in invasion success are related to feeding ecology, and that seasonal variation in browse consumption is linked to changing nutritional quality of grass. Results Controlling for body mass, the Pleistocene extinctions were clearly biased towards browsers. Introduced banteng appear to be primarily browsers, with their diets comprising 40% grass in the wet season and 15% in the late dry season. Buffalo have a more variable diet, with an increasing proportion of browse from the wet (30%) to the late dry season (75%), and can therefore be described as switching from grazer to browser. The decline of grass in the diet of both species appears to reflect the decline in the nutritional value of grass through the dry season, an inference supported by the negative relationship between δ¹³C values and the nitrogen content of dung. Main conclusions Banteng and buffalo are much larger than extant native herbivores, of which browsers are restricted to isolated rocky habitats. This suggests that banteng and buffalo have filled niches made vacant following the Pleistocene extinctions. The success of buffalo appears to be related to their greater dietary breadth, which enables them to graze and browse in eucalypt savannas, whilst the browsing banteng remain tethered to a mosaic of rain forest patches. The restriction of browsers may be a long‐range consequence of habitat transformations associated with Aboriginal landscape burning.