5 research outputs found
Predicting Whole Forest Structure, Primary Productivity, and Biomass Density From Maximum Tree Size and Resource Limitations
In the face of uncertain biological response to climate change and the many
critiques concerning model complexity it is increasingly important to develop
predictive mechanistic frameworks that capture the dominant features of
ecological communities and their dependencies on environmental factors. This is
particularly important for critical global processes such as biomass changes,
carbon export, and biogenic climate feedback. Past efforts have successfully
understood a broad spectrum of plant and community traits across a range of
biological diversity and body size, including tree size distributions and
maximum tree height, from mechanical, hydrodynamic, and resource constraints.
Recently it was shown that global scaling relationships for net primary
productivity are correlated with local meteorology and the overall biomass
density within a forest. Along with previous efforts, this highlights the
connection between widely observed allometric relationships and predictive
ecology. An emerging goal of ecological theory is to gain maximum predictive
power with the least number of parameters. Here we show that the explicit
dependence of such critical quantities can be systematically predicted knowing
just the size of the largest tree. This is supported by data showing that
forests converge to our predictions as they mature. Since maximum tree size can
be calculated from local meteorology this provides a general framework for
predicting the generic structure of forests from local environmental parameters
thereby addressing a range of critical Earth-system questions.Comment: 26 pages, 4 figures, 1 Tabl
Comparative results of transluminal extraction coronary atherectomy in saphenous vein graft lesions with and without thrombus
AbstractObjectives. The purpose of this retrospective study was to compare the results of transluminal extraction coronary atherectomy in saphenous vein graft lesions with and without angiographic thrombus.Background. Percutaneous interventions in lesions with thrombus are associated with reduced procedural success and increased risk of complications. Use of the transluminal extraction catheter, which cuts and aspirates atheroma and thrombus, has been advocated as a potential revascularization strategy for lesions with thrombus.Methods. Baseline patient characteristics, lesion morphology, immediate angiographic results, in-hospital complications and follow-up were prospectively entered into an interventional cardiology data base. The results of transluminal extraction coronary atherectomy in saphenous vein bypass grafts with angiographic thrombus were compared with results in similar grafts without angiographic thrombus.Results. Transluminal extraction coronary atherectomy was performed in 175 patients with 183 vein graft lesions, including 59 lesions (32%) with thrombus (Group 1) and 124 (68%) without thrombus (Group 2). Compared with lesions in Group 2, lesions in Group 1 were associated with a higher incidence of baseline total occlusion, diffuse disease and abnormal Thrombolysis in Myocardial Infarction (TIMI) grade flow (p < 0.05); more severe diameter stenosis at baseline, after atherectomy and after final angiography (p < 0.05); a lower rate of clinical success (69% vs, 88%, p < 0.01); and more angiographic and clinical complications, including no reflow (p < 0.05), vascular repair (p < 0.05) and Q wave myocardial infarction (p = 0.09).Conclusions. In transluminal extraction coronary atherectomy of saphenous vein bypass grafts, the presence of thrombus is associated with more baseline lesion complexity, reduced clinical success and increased risk of no reflow, Q wave myocardial infarction and vascular repair