Head Impact Telemetry System's Video-based Impact Detection and Location Accuracy

Purpose This study aimed to quantify the Head Impact Telemetry (HIT) System's impact detection and location measurement accuracy using an impact biomechanics data set paired with video of high school football special teams plays. Methods The head impact biomechanics data set and video were collected from 22 high school football players, wearing HIT System instrumented helmets, competing in 218 special teams plays over a single high school football season. We used two separate video analysis approaches. To quantify the impact detection accuracy, we evaluated the video for head impacts independently of the impact data collection triggers collected by the HIT System. Video-observed impacts matched to valid and invalid head impacts by the HIT System algorithm were categorized as true positives, false positives, false negatives, and true negatives. To quantify impact location accuracy, we analyzed video-synchronized head impacts for impact location independent of the HIT System's impact location measurement and quantified the estimated percent agreement of impact location between the HIT System recorded impact location and the impact location observed on video. Results The HIT System's impact-filtering algorithm had 69% sensitivity, 72% specificity, and 70% accuracy in categorizing true and non-head impact data collection triggers. The HIT System agreed with video-observed impact locations on 64% of the 129 impacts we analyzed (unweighted k = 0.43, 95% confidence interval = 0.31-0.54). Conclusion This work provides data on the HIT System's impact detection and location accuracy during high school football special teams plays using game video analysis that has not been previously published. Based on our data, we believe that the HIT System is useful for estimating population-based impact location distributions for special teams plays

Quantifying declines in livestock due to land subdivision

In Kajiado District, Kenya, ranches held communally by Maasai are being subdivided into individually owned parcels. Livestock owners know that herds on parcels that are too small cannot be viable, but the decline in the capacity of parcels to support livestock has not been quantified. We used ecosystem modeling to represent the effects of subdivision as Maasai group ranches were divided into 196, 10, 5, 3, and 1 km2 parcels. Within the spatially explicit, process-based Savanna ecosystem model, we used maps that constrained the movements of livestock to be within parcels. We also modeled cooperative grazing associations, giving groups of herders access to parcels composed of dispersed or contiguous 1 km2 parcels. Vegetatively productive areas had higher carrying capacities when isolated because resident animals did not compete with animals moving in seasonally from other areas. In a ranch of low but heterogeneous productivity, we saw a steady decline in capacity under subdivision, until 25% fewer livestock could be supported on the ranch of 1 km2 parcels relative to the intact ranch. On a ranch with both low productivity and heterogeneity, 20% fewer livestock were supported when parcels were still 10 km2. The most productive ranch studied saw small population changes with subdivision. Participation in grazing associations was helpful in the ranch intermediate in productivity and heterogeneity, but not other ranches. Subdivision of Kajiado lands might be inevitable, but our results show the relative benefits to stakeholders if land owners and policy makers act to maintain open or flexible access to individually held parcels

Large-scale movements of large herbivores: livestock following changes in seasonal forage supply

Large-scale movements allow large herbivores to cope with changes in seasonal forage supply. Pastoralists use mobility to convert low-value ephemeral forage into high-value livestock. Transhumant pastoralists may move livestock less than ten to hundreds of kilometres. In semi-arid tropical sites, water and forage shortages in the dry season cause pastoral livestock to move to water or key resource areas. In temperate summers, livestock may be moved to higher-elevation snow-free meadows. In winters, animals may be moved lower to warmer sites, or to mountain valleys protected from steppe winds. Despite the recognised value of mobility, pastoral mobility is being reduced around the world. Changes in the mobility of three pastoral groups are reviewed, the Aymara of the South-American highlands, Mongolians, and the Maasai of Kenya and Tanzania, for which quantitative results are given. The Maasai of Kajiado District, Kenya are subdividing some group ranches into individually owned parcels. In subdivided Osilalei Group Ranch, herders moved an average of 5.6 km per day, whereas in undivided northern Imbirikani, herders moved 12.5 km per day. Residents of northern Imbirikani accessed more green vegetation the more they moved, whereas those in subdivided southern Imbirikani did not. Maasai selected areas with more heterogeneous vegetation during the dry season than found at their permanent households. In modelling, subdividing to 100-ha parcels allowed Eselengei Group Ranch to support 25% fewer livestock by mass, even though the area remained the same. For any pastoralist, the costs of mobility must be weighed against benefits, but pastoralists have demonstrated flexibility in their mobility, if constraints such as human population growth and limitations in land access are not too great. We show that pastoralists have successfully evolved methods of herding livestock to access adequate forage in areas of variable climat

A critical analysis of species selection and high vs. low-input silviculture on establishment success and early productivity of model short-rotation wood-energy cropping systems

Most research on bioenergy short rotation woody crops (SRWC) has been dedicated to the genera Populus and Salix. These species generally require relatively high-input culture, including intensive weed competition control, which increases costs and environmental externalities. Widespread native early successional species, characterized by high productivity and good coppicitig ability, may be better adapted to local environmental stresses and therefore could offer alternative low-input bioenergy production systems. To test this concept, we established a three-year experiment comparing a widely-used hybrid poplar (Populus nigra x P. maximowiczii, clone 'NM6') to two native species, American sycamore (Platanus occidentalis L) and tuliptree (Liriodendron tulipifera L) grown under contrasting weed and pest control at a coastal plain site in eastern North Carolina, USA. Mean cumulative aboveground wood production was significantly greater in sycamore, with yields of 46.6 Mg hat under high-inputs and 32.7 Mg ha (-1) under low-input culture, which rivaled the high-input NM6 yield of 32.9 Mg ha (-1). NM6 under low-input management provided noncompetitive yield of 6.2 Mg ha (-1). Sycamore also showed superiority in survival, biomass increment, weed resistance, treatment convergence, and within-stand uniformity. All are important characteristics for a bioenergy feedstock crop species, leading to reliable establishment and efficient biomass production. Poor performance in all traits was found for tuliptree, with a maximum yield of 1.2 Mg ha (-1), suggesting this native species is a poor choice for SRWC. We conclude that careful species selection beyond the conventionally used genera may enhance reliability and decrease negative environmental impacts of the bioenergy biomass production sector