Climate warming can have many effects on plant growth, potentially altering growth rates, phenology, and fecundity. Together, these changes are anticipated to enhance the performance of some weed species, perhaps necessitating increased control efforts. Plants’ responses to management efforts may also be altered by warming, adding another layer of uncertainty with which land managers must cope. We investigated temperature’s impact on the invasive thistle Carduus nutans’ response to mowing in a two-cohort field experiment. We crossed treatments controlling the seasonal timing of a single mowing event (early, late, and an unmowed control) with temperature treatments (ambient and warmed using fiberglass open top chambers) in a split-plot design. In addition to observing differences in plant fecundity and plant height resulting from these treatments, we also investigated the demographic consequences of delayed flowering after mowing using integral projection models.
Results/Conclusions:
As expected, mowing had a significant impact on C. nutans fecundity, height and phenology. Plants mowed early in the season reached end-of-season heights 31.5 cm shorter, on average, than unmowed controls and flowered 20.2 days later in the season. Plants mowed later in the season reached end-of-season heights 64.7 cm shorter than unmowed controls and flowered 30.2 days later. Warming speeded growth after mowing. Warmed plants grew taller by an average of 0.22 cm/day greater than plants grown under ambient conditions. Our demographic model integrates these impacts, along with changes in vital rates due to altered phenology, to project warming’s effect on mowed and unmowed populations of musk thistle. Taken together, warming’s impacts on recovery after mowing are expected to result in reduced efficacy of mowing as a means to control thistle population growth and spread. This finding suggests that existing successful weed management strategies may not continue to function as effectively as global temperatures rise.