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Climate Regimes

Climate plays a significant role in plant community dynamics, whether they are normal conditions (30-year averages), extreme highs/lows in precipitation and temperature, duration of extreme conditions, and rising atmospheric CO2 concentrations. Extremes in weather affect plants. Over the past decade, the increasingly large fluctuation from long-term average conditions has resulted in extreme high and low temperature and precipitation levels. During a normal year, drought or flooding may still negatively impact plants because of altered frequency and duration of precipitation. Increasing CO2 concentrations in the atmosphere are having a positive effect on the growth of certain plants (e.g., C3 plants), which could provide non-native plants with an advantage in the invasion process.

Case in point – In 2012, much of the US Midwest was gripped in one of the most severe droughts on record. While conducting experimental fieldwork at a site in Nebraska during June of that year, a single musk thistle (Carduus nutans) appeared to be in the bolt or early flowering stage, which is typical for the species at that time. Here, however, two things were unusual: this plant was less than 1 meter tall (with adequate moisture and light, musk thistle typically grows to heights of 1–2.5 meters before flowering), and was only 3 months old (the bolt stage, when it would produce a flowering stem and set seed typically occurs during the thistle’s second year). Interestingly, this plant died less than 3 weeks later, without producing flowers or seeds. Apparently, this particular plant was unable to successfully spearhead an invasion in this field because it could not complete its normal life cycle during a period of drought.

 musk thistle

In temperate climates, episodes of heavy rainfall, summer flooding, and severe droughts are already occurring along with what some are suggesting will be a concomitant increase in the impacts from invasive plants, partly due to their more widespread distribution. Certainly, the effects of increased extreme weather patterns on facilitating or limiting plant invasions have not been studied extensively and will be a focus of the Invasive Plant Science Lab.