Using a diverse seed mix to establish native plants on a Sonoran Desert burn

Abstract

Revegetating burns is a major challenge facing resource managers in the low- and unpredictable-precipitation deserts of the southwestern US. We monitored the effectiveness of using a diverse, 28-species seed mix for establishing native plants on a 1.5-ha (3.7-ac) burn in the northern Sonoran Desert. Our objective was to compare species performances, which we assessed by measuring species frequencies and cover on 5 sampling dates to capture variation during a 32-mo period following seeding. By 15 mo after seeding, desert senna (Senna covesii (Gray) Irwin & Barneby [Fabaceae]) established best, with a frequency of 91% (based on 22, 10-m² plots) and a relative cover of 19%. Four other seeded species also became established in > 50% of plots by 32 mo after seeding. Several seeded species, including desert senna (which flowered only 7 wk after seeding) and purple threeawn (Aristida purpurea Nutt. [Poaceae]), were observed with seed heads during one or more sampling periods. Although precipitation was only 67% of normal for 21 mo following seeding and 71% of species established in < 10% of plots, we consider the seeding to have met short-term management objectives because of the subset of highly successful species. Our results also illustrate the caution that should be used when evaluating seeding success: conclusions would have differed if the diversity of the seed mix had not included the successful species, and longer term monitoring was needed to detect some species in the seed mix that did not establish until 32 mo after seeding.