Warming shortens flowering seasons of tundra plant communities

Advancing phenology is one of the most visible effects of climate change on plant communities, and has been especially pronounced in temperature-limited tundra ecosystems. However, phenological responses have been shown to differ greatly between species, with some species shifting phenology more than others. We analysed a database of 42,689 tundra plant phenological observations to show that warmer temperatures are leading to a contraction of community-level flowering seasons in tundra ecosystems due to a greater advancement in the flowering times of late-flowering species than early-flowering species. Shorter flowering seasons with a changing climate have the potential to alter trophic interactions in tundra ecosystems. Interestingly, these findings differ from those of warmer ecosystems, where early-flowering species have been found to be more sensitive to temperature change, suggesting that community-level phenological responses to warming can vary greatly between biomes

3-d finite element model development for biomechanics: a software demonstration

Finite element analysis is becoming an increasingly important part of biomechanics and orthopedic research, as computational resources become more powerful, and data handling algorithms become more sophisticated. Until recently, tools with sufficient power did not exist or were not accessible to adequately model complicated, three-dimensional, nonlinear biomechanical systems. In the past, finite element analyses in biomechanics have often been limited to two-dimensional approaches, linear analyses, or simulations of single tissue types. Today, we have the resources to model fully three-dimensional, nonlinear, multi-tissue, and even multi-joint systems. The authors will present the process of developing these kinds of finite element models, using human hand and knee examples, and will demonstrate their software tools

Computational tool for comparison of kinematic mechanisms and commonly used kinematic models

Accurate, reliable, and reproducible methods to measure the movements of human joints have been elusive. Currently, three-dimensional recording methods are used to track the motion of one segment relative to another as the joint moves. Six parameters describe the moving segment`s location and orientation relative to the reference segment: three translations (x, y, and z) and three rotations (yaw, pitch and roll) in the reference frame. The raw data can be difficult to interpret. For this reason, several methods have been developed to measure the motion of human joints and to describe the resulting data. For example, instant helical axes or screw deviation axes (Kinzell et al., 1972), the Joint Coordinate System of Grood and Suntay (1983), and the Euler angle method have been used to describe the movements of bones relative to each other. None of these methods takes into account the physical kinematic mechanism producing the joint motion. More recently, Lupichuk (1995) has developed an algorithm to find, for an arbitrary revolute, the axis` position and orientation in three- dimensional space. Each of these methods has advantages and disadvantages in analyzing joint kinematics. The authors have developed software to provide a means of comparing these methods for arbitrary, single degree of freedom, kinematic mechanisms. Our objective is to demonstrate the software and to show how it can be used to compare the results from the different kinematic models as they are applied to specific kinematic mechanisms

Arctic plants are capable of sustained responses to long-term warming

Previous studies have shown that Arctic plants typically respond to warming with increased growth and reproductive effort and accelerated phenology, and that the magnitude of these responses is likely to change over time. We investigated the effects of long-term experimental warming on plant growth (leaf length) and reproduction (inflorescence height, reproductive phenology and reproductive effort) using 17–19 years of measurements collected as part of the International Tundra Experiment (ITEX) at sites near Barrow and Atqasuk, Alaska. During the study period, linear regressions indicated non-significant tendencies towards warming air temperatures at our study sites. Results of our meta-analyses on the effect size of experimental warming (calculated as Hedges’ d) indicated species generally responded to warming by increasing inflorescence height, increasing leaf length and flowering earlier, while reproductive effort did not respond consistently. Using weighted least-squares regressions on effect sizes, we found a significant trend towards dampened response to experimental warming over time for reproductive phenology. This tendency was consistent, though non-significant, across all traits. A separate analysis revealed significant trends towards reduced responses to experimental warming during warmer summers for all traits. We therefore propose that tendencies towards dampened plant responses to experimental warming over time are the result of regional warming. These results show that Arctic plants are capable of sustained responses to warming over long periods of time but also suggest that, as the region continues to warm, factors such as nutrient availability, competition and herbivory will become more limiting to plant growth and reproduction than temperature