Can surface treatments and climate matching enhance restoration success in the Sonoran Desert?

Introduction

Restoring native plant communities in arid ecosystems through seeding is a critical yet often unsuccessful strategy due to severe environmental stressors, including degraded soils, low and variable rainfall, and seed predation.

Objectives

To improve restoration outcomes, we examined the influence of seed mix types and soil surface treatments on seeded and unseeded plant establishment across three Sonoran Desert sites, Arizona, United States.

Methods

Using a factorial design, we tested two seed mix types (cool versus warm adapted species) and four soil surface treatments (pits, mulch, connectivity modifiers or ConMods, and controls) on plant establishment. We examined if patterns of plant establishment could be predicted by whether the climate envelope of species in the seed mix types was similar to the site climate where they were seeded (climate matching). We monitored seeded and unseeded species establishment for 3 years and analyzed these effects using generalized linear mixed models and Tukey-adjusted multiple comparisons.

Results

Pit treatments significantly enhanced seeded species density by nearly 3× and cover by 2× compared with ConMods and increased unseeded plant density by 2× to 4× times during post-drought springs. During these same seasons, species suited to cooler temperatures (e.g. Salvia columbariae and Lupinus sparsiflorus) had higher cover at the site receiving the highest precipitation, and species suited to warmer temperatures (e.g. Sphaeralcea ambigua and Senna covesii) established better at the drier two sites.

Conclusions

In arid systems, surface treatments like pits that retain soil moisture were most promising for supporting seed-based restoration, and matching species that have high temperature tolerance with hotter, drier sites may enhance restoration success.