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Increasing Native Plant Abundance and Diversity Through Assisted Succession
Val Anderson and Robert Cox, Brigham Young University, Provo, UT
Given the goals of land managers to restore native plant diversity and curb the ever increasing invasion of exotic annuals, the procedural questions of how to make the conversion is central to current management discussions. One possible solution may be to combine earlier strategies of reclamation using introduced perennials with a subsequent infusion with native plant species. The approach utilizes the seeding of non-native perennial plants to recapture the site away from invasive annual weeds and then requires perturbation of the non-native perennial community to open niches for the insertion of native species. These non-native perennials such as crested wheatgrass have demonstrated their ability to establish and out compete the invasive annuals to their near extirpation on a site. On western rangelands this site recapture represents a shift back to a former perennial ecology of resource utilization and fire frequency. In a pristine ecosystem this would often be accomplished by early seral, weak perennial species that facilitate the subsequent establishment and eventual dominance of long-lived perennials as secondary succession runs its course. The disruption of these natural processes by changes in the disturbance regime and subsequent invasion of exotic annuals arrests the successional process. Early season resource preemption and higher fire frequencies reduce the establishment window. Using more aggressive non-native plants as surrogates for early colonizers creates a fire resistant vegetative cover that can suppress annuals, unfortunately, they also provide resistance to the recovery of native perennials. Once a site is recaptured to a perennial cover, significant perturbations of the stand are required to open niches for the insertion of native species. These perturbations can most effectively be achieved through the use of mechanical or herbicide treatments. The niche opening treatments are designed to weaken the existing community’s hold on site resources by reducing the density and health of these plants while at the same time facilitating the establishment of seeded native species. The greatest risk to this process is the proximity of reinvading populations of annual exotic weeds. Significant buffers should be left in place around restoration treatments to preempt reinvasion by weeds.