University of Vermont

About: University of Vermont is a education organization based out in Burlington, Vermont, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 17592 authors who have published 38251 publications receiving 1609874 citations. The organization is also known as: UVM & University of Vermont and State Agricultural College.

Neighborhood Analyses Of Canopy Tree Competition Along Environmental Gradients In New England Forests

Abstract: We use permanent-plot data from the USDA Forest Service's Forest Inventory and Analysis (FIA) program for an analysis of the effects of competition on tree growth along environmental gradients for the 14 most abundant tree species in forests of northern New England, USA. Our analysis estimates actual growth for each individual tree of a given species as a function of average potential diameter growth modified by three sets of scalars that quantify the effects on growth of (1) initial target tree size (dbh), (2) local environmental conditions, and (3) crowding by neighboring trees. Potential growth of seven of the 14 species varied along at least one of the two environmental axes identified by an ordination of relative abundance of species in plots. The relative abundances of a number of species were significantly displaced from sites where they showed maximum potential growth. In all of these cases, abundance was displaced to the more resource-poor end of the environmental gradient (either low fertility or low moisture). The pattern was most pronounced among early successional species, whereas late-successional species reached their greatest abundance on sites where they also showed the highest growth in the absence of competition. The analysis also provides empirical estimates of the strength of intraspecific and interspecific competitive effects of neighbors. For all but one of the species, our results led us to reject the hypothesis that all species of competitors have equivalent effects on a target species. Most of the individual pairwise interactions were strongly asymmetric. There was a clear competitive hierarchy among the four most shade-tolerant species, and a separate competitive hierarchy among the shade-intolerant species. Our results suggest that timber yield following selective logging will vary dramatically depending on the configuration of the residual canopy, because of interspecific variation in the magnitude of both the competitive effects of different species of neighbors and the competitive responses of different species of target trees to neighbors. The matrix of competition coefficients suggests that there may be clear benefits in managing for specific mixtures of species within local neighborhoods within stands.

Photosynthesis-nitrogen relations in Amazonian tree species : I. Patterns among species and communities.

Abstract: Among species, photosynthetic capacity (Amax) is usually related to leaf nitrogen content (N), but variation in the species-specific relationship is not well understood. To address this issue, we studied Amax-N relationships in 23 species in adjacent Amazonian com- munities differentially limited by nitrogen (N), phospho- rus (P), and/or other mineral nutrients. Five species were studied in each of three late successional forest types (Tierra Firme, Caatinga and Bana) and eight species were studied on disturbed sites (cultivated and early sec- ondary successional Tierra Firme plots). Area x expressed on a mass basis (Amass) was correlated (p < 0.05) with N.... in 17 of 23 species, and Area x on an area basis (Aarea) was correlated (p<0.05) with N.... in 21 of 23 species. The slopes of Amax-N relationships were greater and intercepts lower for disturbance adapted early suc- cessional species than for late successional species. On a mass basis, the Amax-N slope averaged g 15 gmol CO2 (g N) -~ s -1 for 7 early secondary successional species and ~4 pmol CO2 (g N) -1 s -1 for 15 late successional species, respectively. Species from disturbed sites had shorter leaf life-span and greater specific leaf area (SLA) than late successional species. Across all 23 species, the slope of the Amass-N.... relationship was related (p < 0.001) positively to SLA (r 2 = 0.70) and negatively to leaf life-span (r 2= 0.78) and temporal niche during sec- ondary succession (years since cutting-and-burning, r2= 0.90). Thus, disturbance adapted early successional species display a set of traits (short leaf life-span, high SLA and Amax and a steep slope of Amax-N) conducive to resource acquisition and rapid growth in their high resource regeneration niches. The significance and form of the Amax-N relationship were associated with the rela- tive nutrient limitations in the three late successional communities. At species and community levels, Amax was more highly dependent on N in the N-limited Caatinga than in the P- and N-limited Bana and least in the P- and Ca-limited Tierra Firme on oxisol- and dif- ferences among these three communities in their mass- based Ama slope reflects this pattern (6.0, 2.4, and 0.7 pmol CO2 (g N)- 1 s-1, respectively). Among all 23 spe- cies, the estimated leaf N.... needed to reach compensa- tion (net photosynthesis ~ zero) was positively related to the A.... -N.... slope and to dark respiration rates and negatively related to leaf life-span. Variation among species in the Amax-N slope was well correlated with potential photosynthetic N use efficiency, Ama x per unit leaf N. The dependence of Ama x on N and the form of the relationship vary among Amazonian species and com- munities, consistent with both relative availabilities of N, P, and other mineral nutrients, and with intrinsic ecophysiological characteristics of species adapted to habitats of varying resource availability.

Predicting opportunities for greening and patterns of vegetation on private urban lands

Abstract: This paper examines predictors of vegetative cover on private lands in Baltimore, Maryland. Using high- resolution spatial data, we generated two measures: ''pos- sible stewardship,'' which is the proportion of private land that does not have built structures on it and hence has the possibility of supporting vegetation, and ''realized stew- ardship,'' which is the proportion of possible stewardship land upon which vegetation is growing. These measures were calculated at the parcel level and averaged by US Census block group. Realized stewardship was further de- fined by proportion of tree canopy and grass. Expenditures on yard supplies and services, available by block group, were used to help understand where vegetation condition appears to be the result of current activity, past legacies, or abandonment. PRIZM TM market segmentation data were tested as categorical predictors of possible and realized stewardship and yard expenditures. PRIZM TM segmenta- tions are hierarchically clustered into 5, 15, and 62 cate- gories, which correspond to population density, social stratification (income and education), and lifestyle clusters, respectively. We found that PRIZM 15 best predicted var- iation in possible stewardship and PRIZM 62 best predicted variation in realized stewardship. These results were further analyzed by regressing each dependent variable against a set of continuous variables reflective of each of the three PRIZM groupings. Housing age, vacancy, and population density were found to be critical determinants of both stewardship metrics. A number of lifestyle factors, such as average family size, marriage rates, and percentage of sin- gle-family detached homes, were strongly related to real- ized stewardship. The percentage of African Americans by block group was positively related to realized stewardship but negatively related to yard expenditures.

Improving the Glasgow Coma Scale score: motor score alone is a better predictor.

Abstract: Background The Glasgow Coma Scale (GCS) has served as an assessment tool in head trauma and as a measure of physiologic derangement in outcome models (e.g., TRISS and Acute Physiology and Chronic Health Evaluation), but it has not been rigorously examined as a predictor of outcome.Methods Using a la

Functional roles of KATP channels in vascular smooth muscle.

Abstract: 1. ATP-sensitive potassium channels (K(ATP)) are present in vascular smooth muscle cells and play important roles in the vascular responses to a variety of pharmacological and endogenous vasodilators. 2. The K(ATP) channels are composed of four inwardly rectifying K+ channel subunits and four regulatory sulphonylurea receptors. The K(ATP) channels are inhibited by intracellular ATP and by sulphonylurea agents. 3. Pharmacological vasodilators such as cromakalim, pinacidil and diazoxide directly activate K(ATP) channels. The associated membrane hyperpolarization closes voltage-dependent Ca2+ channels, which leads to a reduction in intracellular Ca2+ and vasodilation. 4. Endogenous vasodilators such as calcitonin gene-related peptide, vasoactive intestinal polypeptide, prostacylin and adenosine activate K(ATP) by stimulating the formation of cAMP and increasing the activity of protein kinase A. Part of the mechanism of contraction of endogenous vasoconstrictors is due to inhibition of K(ATP) channels. 5. The K(ATP) channels appear to be tonically active in some vascular beds and contribute to the physiological regulation of vascular tone and blood flow. These channels also are activated under pathophysiological conditions, such as hypoxia, ischaemia, acidosis and septic shock, and, in these disease states, may play an important role in the regulation of tissue perfusion.