Distribution of biomass dynamics in relation to tree size in forests across the world.

Tree size shapes forest carbon dynamics and determines how trees interact with their environment, including a changing climate. Here, we conduct the first global analysis of among-site differences in how aboveground biomass stocks and fluxes are distributed with tree size. We analyzed repeat tree censuses from 25 large-scale (4-52 ha) forest plots spanning a broad climatic range over five continents to characterize how aboveground biomass, woody productivity, and woody mortality vary with tree diameter. We examined how the median, dispersion, and skewness of these size-related distributions vary with mean annual temperature and precipitation. In warmer forests, aboveground biomass, woody productivity, and woody mortality were more broadly distributed with respect to tree size. In warmer and wetter forests, aboveground biomass and woody productivity were more right skewed, with a long tail towards large trees. Small trees (1-10 cm diameter) contributed more to productivity and mortality than to biomass, highlighting the importance of including these trees in analyses of forest dynamics. Our findings provide an improved characterization of climate-driven forest differences in the size structure of aboveground biomass and dynamics of that biomass, as well as refined benchmarks for capturing climate influences in vegetation demographic models.

Physical Maturity and Concussion Symptom Duration among Adolescent Ice Hockey Players.

OBJECTIVE: To investigate the association between physical maturity and risk of prolonged concussion symptoms in adolescent ice hockey players. STUDY DESIGN: Prospective cohort study of 145 patients ages 13-18 years with concussion referred to 3 hospital-affiliated sports medicine clinics between September 1, 2012 and March 31, 2015. Concussion evaluations included Post Concussive Symptom Score, neurologic examination, and postinjury computerized neurocognitive testing. Pubertal development at initial visit was assessed by the Pubertal Developmental Scale. Duration of concussion symptoms (days) was the main outcome. Statistical comparisons were conducted using Student t test, Wilcoxon rank sum, and logistic regression. RESULTS: Mean symptom duration was 44.5 ± 48.7 days. Nearly one-half (48.3%) of all players enrolled had prolonged concussion symptoms (≥ 28 days); most (86.9%) had symptom resolution by 90 days. Among males, less physically mature adolescents took longer to recover than more physically mature players (54.5 days vs 33.4 days; P = .004). "Early" Pubertal Category Score was the strongest predictor of prolonged symptoms (OR = 4.29, 95% CI 1.24-14.85; P = .021) among males. Among females, heavier weight increased the odds of experiencing prolonged symptoms (OR 1.07, 95% CI 1.00-1.14; P = .039). CONCLUSIONS: Among adolescent ice hockey players, early-pubertal stage is independently associated with longer recovery from concussion in males, and heavier weight is associated with longer concussion recovery in females. Until further studies determine valid physical maturity indicators, peripubertal collision sport athletes should compete in leagues grouped by relative age and be discouraged from "playing up" on varsity teams.