Phenological differences between native and invasive plants have the potential to increase the success of invaders. Invasion by non-native plants can drive plant community shifts with strong consequences for ecosystem function. Changes in climate can promote invasion to new regions. Many western states have experienced invasion by annual grasses, commonly Bromus tectorum, resulting in subsequent alterations to fire regimes, plant community composition, and resource availability. Managing B. tectorum relies, in part, on understanding how annual climatic variability affects the timing of phenological events and how they may change with forecasted changes in climate. To explore the effects of warming on Colorado Plateau plant communities invaded by B. tectorum we constructed climate manipulation experiments that altered precipitation regimes and increased temperatures via infrared lamps that warmed experimental plots 2°C above ambient at two sites. Within one of the sites we warmed another set of plots 4°C above ambient, allowing us to explore the effects of different levels of warming on the same communities. Here, we examine nearly a decade’s worth of B. tectorum weekly phenology data to identify changes in B. tectorum patterns driven by interannual climate and experimental warming.
Results/Conclusions
The Colorado Plateau is subject to large spatial and temporal variation of weather patterns and the timing of B. tectorum phenology appears to correspond with these differences. Since 2010, in our control plots, we have seen an advancing of B. tectorum flowering dates and to a lesser extent the timing of senescence. However, the timing of germination was not shifted. Higher experimental temperatures led to a consistent advancement of flowering and senescence and, occasionally, of earlier germination. The early senescence under warmed conditions to an overall shorter growing season for B. tectorum. We found that warming appeared to negatively affect B. tectorum by shortening its growing season and these effects are stronger in dry years. Warming treatments were not detrimental to B. tectorum survival, rather, the plants appeared to adjust their growth strategies and shift the timing of seed production. These data point to strong responses of B. tectorum in the face of change, responses that could alter B. tectorum competitiveness into the future. An improved understanding of the factors that determine the timing of B. tectorum germination and flowering would provide land managers new insight into best practices for further controlling B. tectorum invasion.