Birds in a partly clearfelled dry eucalypt forest on dolerite in southeastern Tasmania

An area of dry eucalypt forest on dolerite in southeastern Tasmania was clearfelled in 1981. A portion of this area was subsequently slash-burnt and aerially sown in 1982, whilst the rest of the area was left unburnt and unsown. A monthly bird census was conducted during 1983-1984 in surrounding uncut, mature forest and also on the clearfelled area. Species were recorded together with the habitat in which they occurred and the particular plant species being utilised. A total of 46 avian species were recorded during the monthly censuses, with most species and individuals being observed in the spring months. The numbers of species and individuals recorded on the burnt and unburnt clearfelled areas were low in comparison with those observed in the uncut forest. In general, those species able to utilise open-ground habitats tended to be the least affected by clearfelling followed by slash-burning. However, the unburnt clearfelled area provided foraging sites for certain species, in preference to the nearby slash-burnt area. Many individuals recorded in the clearfelled areas made use of trees left standing after logging. The use of fire in dry forest management practice and the importance of cull trees are discussed

Effects of Sample Size on Estimates of Population Growth Rates Calculated with Matrix Models

BACKGROUND: Matrix models are widely used to study the dynamics and demography of populations. An important but overlooked issue is how the number of individuals sampled influences estimates of the population growth rate (lambda) calculated with matrix models. Even unbiased estimates of vital rates do not ensure unbiased estimates of lambda-Jensen's Inequality implies that even when the estimates of the vital rates are accurate, small sample sizes lead to biased estimates of lambda due to increased sampling variance. We investigated if sampling variability and the distribution of sampling effort among size classes lead to biases in estimates of lambda. METHODOLOGY/PRINCIPAL FINDINGS: Using data from a long-term field study of plant demography, we simulated the effects of sampling variance by drawing vital rates and calculating lambda for increasingly larger populations drawn from a total population of 3842 plants. We then compared these estimates of lambda with those based on the entire population and calculated the resulting bias. Finally, we conducted a review of the literature to determine the sample sizes typically used when parameterizing matrix models used to study plant demography. CONCLUSIONS/SIGNIFICANCE: We found significant bias at small sample sizes when survival was low (survival = 0.5), and that sampling with a more-realistic inverse J-shaped population structure exacerbated this bias. However our simulations also demonstrate that these biases rapidly become negligible with increasing sample sizes or as survival increases. For many of the sample sizes used in demographic studies, matrix models are probably robust to the biases resulting from sampling variance of vital rates. However, this conclusion may depend on the structure of populations or the distribution of sampling effort in ways that are unexplored. We suggest more intensive sampling of populations when individual survival is low and greater sampling of stages with high elasticities

The short-term effects of clearfelling and slash-burning on the richness, diversity and relative abundance of higher plant species in two types of eucalypt forest on dolerite in Tasmania

The relative impacts of clearfelling followed by slash-burning, clearfelling, and no treatment were monitored for 2 years in two major types of eucalypt forest in south-eastern Tasmania. Rates of change in species cover were significantly greater in the burned area than in both the clearfell and control areas. More than half the species for which suitable data were available increased most in the burned area and least in the control. More higher plant taxa were present in the permanent burned plots 4 months after the burn than before the burn. By the last 8 months of recording, new taxa were invading at a rate of only 0.1 per month. Composites and shrubs constituted most of the late invaders. The behaviour of diversity measures was largely a function of the behaviour of a few of the taxa. Fire intensity, as measured by degree of soil baking, had a pronounced influence on species composition and cover. The species composition of aerially sown seed had little influence on the species composition of the eucalypt regeneration, with species not sown by the Forestry Commission recovering vegetatively, and much of the sown seed not resulting in seedling establishment. The clearfelling and burning, and clearfelling treatments did not result in the loss of any native species but there was substantial invasion by introduced herbs. However, lack of substantial impact in the short term does not guarantee the same in the long term

Mountain fen distribution, types and restoration priorities, San Juan Mountains, Colorado, USA

Mountain fens are vital ecosystems for habitat, biodiversity, water and carbon cycling, but there is little comprehensive information on their distribution, abundance or condition in any region of the western U.S. Our study objectives were to: 1) evaluate fen distribution, abundance and characteristics in the San Juan Mountains of Colorado, 2) quantify disturbances, and 3) prioritize restoration needs of fens. We mapped 624 fens in 37 watersheds and collected field data on 182 of these fens. We estimated that approximately 2,000 fens occur in the San Juan Mountains, primarily in the subalpine zone at an average elevation of 3,288 m. Fens ranged from 0.2 to 20.5 ha in size, peat thickness ranged between 0.40 to \u3e 4.00 m, and surface slope ranged from 0-21%. Groundwater pH ranged from 3.1-7.6 and Ca+2 from 1-341 mg/L, reflecting the diverse geochemistry of watershed parent materials. We identified 188 vascular and 63 bryophyte taxa, and classified the 309 sampled stands into 20 plant communities that formed along complex hydrogeomorphic and geochemical gradients. The majority of fens were in excellent condition; however 10% of our sampled fens had high to very high restoration potential due to impacts from roads, mining, and ditching. © Society of Wetland Scientists 2010