Exploring relationships of spring green-up to moisture and temperature across Wyoming, U.S.A

Vegetation green-up signals the timing of available nutritious plants and shrubs providing high-quality forage for ungulates. In this study, we characterized spatial and temporal patterns of spring phenology and explored how they were related to preceding temperature and moisture conditions. We tested correlations between late winter weather and indicators of the onset and the length of the spring growing period with 250-m resolution time-series satellite data (2001 – 2013) for Wyoming, USA. In western Wyoming mountains, drier and warmer conditions during late winter were associated with earlier spring green-up onset of growth in forests, shrubs, and grasses. In the northeast mountains, onset of spring correlated positively with preceding warmer temperatures, but not with precipitation. In most basin and plains shrublands and grasslands, spring onset was not correlated with temperature, although earlier onset of spring was correlated with drier conditions in 25% of shrub/scrub areas. Results about the length of spring were less definitive, with warmer temperatures related to longer green-up time for 12–30% of the land cover in western mountains but to shorter green-up time periods for 10–20% of the grasses and shrubs in basins and plains. Complex phenological patterns are likely to affect ungulate foraging behaviour on a local scale.

植被返青（vegetation green-up）标志着可为有蹄类动物（ungulates）提供优质饲草的草本与灌木的可利用时间节点。本研究聚焦春季物候（spring phenology）的时空分布格局，探讨其与前期气温及水分条件的关联。我们基于美国怀俄明州2001—2013年的250米分辨率时间序列卫星数据，检验了冬末气象条件与春季生长季起始时间及长度的相关性。怀俄明州西部山地中，冬末暖干的气象条件与森林、灌木及草本的春季返青提前显著相关。怀俄明州东北部山地的春季物候起始时间与前期升温呈正相关，但与降水量无显著关联。在多数盆地与平原的灌丛地和草原中，春季返青起始时间与气温无显著关联；仅25%的灌丛区域的春季返青提前与更干燥的环境条件相关。关于春季生长季长度的研究结果则相对缺乏确定性：怀俄明州西部山地中12%—30%的土地覆被类型的返青时长随升温而延长，但盆地与平原地区10%—20%的草本与灌木的返青时长则随升温而缩短。复杂的物候格局可能在局地尺度上影响有蹄类动物的觅食行为。