Print PageEvidence from small-scale experimental investigations suggest that species diversity and introduced species success are negatively correlated and that resident species identity can determine the strength of this interaction. In this study, we assess the applicability of the diversity-invasion hypothesis to restoration. We hypothesize that, following management efforts, richness of restored plots will be a determinant of invasive species re-establishment and, furthermore, that some restored species and species combinations will be more effective than others. Attempts are also made to apply the overlapping-resource-use hypothesis to explain our findings. We employed a two-way factorial experiment in a randomized complete block design where richness and native species composition were manipulated in 1 x 1 m plots. Richness levels include 1, 2, 3, and 4 species. At richness levels 2 and 3, all possible species combinations were established. This resulted in 20 treatment combinations per block and each block was replicated four times. Restored species were plug planted in January 2010 following removal of the target invasive (Bothiochloa ischaemum or KR Bluestem; hereafter referred to as KR) using a prescribed burn in fall 2009. Restored species were native, perennial grasses available commercially and widely used in restoration projects in Central Texas. They include: big bluestem (Andropogon gerardii), indian grass (Sorghastrum nutans), sideoats grama (Bouteloua curtipendula), and little bluestem (Schizachyrium scoparium). Response variables measured to date include cover of KR, resident, and restored species; ellipsoid area of all individuals of restored species; and KR and restored species phenologies.
Results/Conclusions
Restored species established at an overall rate of 60%. Nonetheless, rates of establishment varied greatly among species. Re-establishment of KR was found to be a negative function of restored species establishment success and cover and as well as the average and total restored species ellipsoid basal area. We also found significant differences among species as determinants of KR re-establishment; however, this effect was confounded by species establishment success. We found no significant relationship between assigned or actual richness and KR re-establishment. Future work will focus on restored species richness x species composition effects as well as soil resource measures to assess the mechanism of competition among these species. In addition, we aim to inform local land management efforts in restoration regarding the suppressive effects of native species combinations.
