CDRRC growing season aridity and grazing season vegetation biomass data

Growing season aridity and livestock grazing seasonality can influence biomass production of perennial grasses in dryland systems. For this study, we used a long-term dataset (1967-2004) to investigate the independent and joint effects of growing season aridity (De Martonne aridity index calculated for the months of June through September) and grazing season (yearlong continuous, fall, winter/spring, or summer season grazing) on the mean annual biomass (kg per hectare) of the perennial grasses Bouteloua eriopoda (black grama), Aristida spp. (threeawn), and Sporobolus spp. (dropseed) in a southwestern United States Chihuahuan Desert rangeland system. Biomass data were collected from 78 permanent sampling transects that were within one mile (1609.34 m) distance to water. Over the 37-year study period, total perennial grass biomass decreased as growing season aridity increased, but the extent of this relationship depended upon season of grazing and specific grass taxon. Aridity-related decreases in total perennial grass biomass were most severe in the summer and fall summer seasonal grazing pastures, primarily due to inherently low black grama levels. Our findings indicate that over time, summer and fall grazing can potentially exacerbate the negative effects of increasing aridity on perennial grass biomass.干旱区生态系统中，生长季干旱程度与家畜放牧的季节模式，可影响多年生草本的生物量生产。本研究采用1967-2004年的长期数据集，旨在探究生长季干旱度（基于6-9月计算的De Martonne干旱指数（De Martonne aridity index））与放牧季节（全年连续放牧、秋季放牧、冬/春季放牧或夏季放牧）对美国西南部奇瓦瓦沙漠（Chihuahuan Desert）牧场生态系统内3种多年生草本——Bouteloua eriopoda（黑格兰马草，black grama）、三芒草属（Aristida spp.，threeawn）以及鼠尾粟属（Sporobolus spp.，dropseed）——的年平均生物量（千克/公顷）的独立与联合效应。生物量数据采集自距水源1英里（1609.34米）范围内的78条永久样带。在长达37年的研究周期内，多年生草本总生物量随生长季干旱度升高而下降，但该关联的强度取决于放牧季节与特定草本类群。生长季干旱引发的多年生草本总生物量下降，在夏季与秋季放牧牧场中最为显著，这主要源于黑格兰马草本底种群水平较低。本研究结果表明，长期来看，夏季与秋季放牧可能会加剧干旱程度升高对多年生草本生物量的负面影响。