Winner and losers: examining biotic interactions in forbs and grasses in response to changes in water and temperature in a semi-arid grassland

Warming and changing water amount can alter the outcome of biotic interactions in native and exotic plants between facilitation and competition. Exotic plants may adapt better to changing environmental conditions, such that they may compete better than native plants. We conducted competition trials for four plant species, two exotic forbs (Centaurea stoebe and Linaria vulgaris) and two grasses (exotic Poa compressa and native Pseudoroegneria spicata), commonly found in Southern interior British Columbia. We compared the effects of warming and changing water on target plant shoot and root biomass, and on pair-wise competitive interactions among all four species. We quantified interactions using the Relative Interaction Intensity index, which has values from -1 (complete competition) to +1 (complete facilitation). C. stoebe biomass was highest under low water and no competition. Facilitation of C. stoebe was found under high water and low temperatures but shifted to competition under low water and/or warming. Competition in L. vulgaris decreased due to reduced water and increased due to warming. Grasses were less competitively suppressed by warming but more competitively suppressed by reduced water input. The response of exotic plants to climate change can differ by plant species, moving in opposite directions for both forbs, but grasses appear to respond similarly. This has consequences for grasses and exotic plants in semi-arid grasslands. As climate change continues to be of worldwide concern, interactions between plant functional groups such as grasses and forbs, or native and exotic species are expected to change as plants response to changes in water content and warming. In this greenhouse study, response to elements of climate change was individual, rather than based on plant functional groups. Further studies in field settings, extended to a wider range of competitive interactions may help elucidate the impact of competition on plant species in grasslands.

Automated summary

Warming and changing water amount can have different effects on facilitation and competition between native and exotic plants. Exotic plants may have better adaptability and may outcompete native plants. The study compared the competitive interactions and biomass of four plant species in response to warming and changing water conditions.