Colonization history, the order of plant species arrival, is increasingly being recognized as a fundamental determinant of community structure, which can alter biotic and abiotic environmental conditions and ecosystem services, such as productivity. Invasive plant species can intensify changes to the productivity of a community and can alter the success of native species. We were interested in understanding how colonization history, including the arrival history of an invasive grass, influences productivity. Using a greenhouse experiment, we explored the effects of colonization history on productivity of communities consisting of four species, including a highly competitive invasive species, Bromus tectorum (BT), and three native perennial grasses, Pseudoroegneria spicata (PS), Festuca campestris (FC), and Poa sandbergii (POA).
Seedlings of each species were introduced to a pot at an interval of one species per planting interval (every two weeks) without repeating a species, resulting in 24 possible combinations of arrival orders. Four individuals of the same species were also planted at the same planting intervals to serve as a control. All treatments were replicated six times. Biomass of the roots and shoots were collected from each individual and were used to represent the productivity of each plant community.
Results/Conclusions
Productivity in this system was heavily influenced by the order of arrival of the invasive species, BT. Treatments that included BT as the first species to colonize, including the control for BT, had the greatest productivity (p < 0.001) with BT contributing to the majority of the biomass (>80%; p < 0.001 ). Productivity was similar to these treatments in two other combinations (POA/BT/FC/PS and PS/BT/POA/FC; p < 0.001), and BT contributed to the majority of the biomass (>60%; p < 0.001). Generally, productivity was higher when BT was the first or second species to arrive and was lowest when BT was planted third or last (p < 0.001). The treatments where BT was planted last had the lowest proportion of BT (<25%; p < 0.001). Productivity was lowest in controls for POA and FC (p < 0.001).
This work illustrates the necessity to explore the impacts that species arrival has on ecosystem function and structure, particularly when an exotic species is a threat to altering productivity and dominance within a system. Restoration efforts where invasive species are of concern should consider these impacts to ensure exotic species do not disrupt succession or ecosystem structure and function.