COS 123-1 - Interannual and seasonal variability in temperature water availability leads to starkly different restoration outcomes in a restored wheat field.

Abstract: Understanding how species diversity develops in novel ecosystems remains an important question in plant science today. One of the most common types of novel ecosystems is post agricultural systems. The vast majority of the Great Plains Shortgrass Prairie has been converted to cropland since European colonization. Land managers are incentivized by programs such as the Conservation Reserve Program (CRP) to restore croplands back to perennial shortgrass prairie in order to achieve ecosystem service benefits. But there is uncertainty about how restoration treatments can achieve long-term cover of native perennials. In particular, how can pre-treatment temperature and moisture conditions inform land managers when selecting species for seeding treatments?

We explored these questions in a 120 ha field in North Central Colorado that was seeded with a mix of perennial grasses, one shrub species, and alfalfa as a cover crop starting in 2013. Before treatment, the field was managed for many years in two sets of alternating wheat/fallow strips. The first set of strips seeded on April 29, 2013, a dry year, and the other on May 1, 2014, a wet year. We conducted botanical surveys in June 2022.

The restoration outcomes were quite different. The two sets of strips had distinct species compositions, but were dominated by the same four species. The strips seeded in the drier 2013 had lower diversity and species richness, with establishment of Atriplex canescens, a drought-tolerant, native shrub, and Pascopyrum smithii, a native, rhizomatous grass. Those seeded in 2014 had more native perennial grasses from the seed mix. Non-native annual grasses and forbs were the dominant plants in most areas, except where P. smithii was abundant and appeared to competitively exclude the non-native annuals. We found that pre-treatment climatic conditions were informative for predicting long-term success of restoration treatments. Soil moisture in the months immediately preceding seed application was beneficial for native perennial bunchgrasses, while rhizomatous native grasses, drought-tolerant native shrubs and introduced annuals were less sensitive to soil moisture.

The particular pre-treatment climatic conditions for a given treatment can favor the establishment of certain functional groups, and this can have a lasting legacy. Existing strategies tailor species compositions of seed mixes according to hardiness zones. Land management agencies may be able to build upon this approach by developing species mixes that are contingent upon antecedent temperature and moisture conditions.