Climate before and after planting drive divergent outcomes ten years after restoration of a wheat field to grassland

Abstract

Converting croplands to grasslands can restore ecosystem functions and services, but there is uncertainty about why some restoration treatments succeed and others do not. Existing restoration strategies tailor species compositions of seed mixes according to long-term climate means and hardiness zones. However, individual years typically deviate from average climate norms such that restoration activities may be better informed by recent conditions than with climate averages. We monitored a field in eastern Colorado that was converted from winter wheat-fallow to native perennial grassland via seeding. The same seed mix was used to seed half of the strips in 2013 (drier) and the other half in 2014 (wetter). In the strips seeded in 2013, only one native grass and one shrub species from the seed mix established widely, whereas in 2014 all native grasses established. Higher soil moisture preceding seed application was positively associated with perennial grasses, while rhizomatous grasses, shrubs and introduced annuals were associated with other variables. After seeding, high summer soil moisture was positively associated with a rhizomatous C3 grass, while the planted C4 bunchgrasses were negatively associated with high summer soil moisture and positively associated with high fall soil temperatures. We found evidence of facilitatory interactions between grasses and forbs, and antagonistic interactions between native perennial grasses and introduced annuals. These findings highlight the potential for land managers to improve upon current approaches by considering antecedent and forecasted conditions during restoration planning.