Soil climate underpins year effects driving divergent outcomes in semi-arid cropland to grassland restoration

Authors: Mahood, Adam; Barnard, David; Green, Timothy; MACDONALD, JACOB - Colorado State University; Erskine, Robert - Rob

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2024
Publication Date: 10/25/2024
Citation: Mahood, A.L., Barnard, D.M., Green, T.R., Macdonald, J., Erskine, R.H. 2024. Soil climate underpins year effects driving divergent outcomes in semi-arid cropland to grassland restoration. Ecosphere. 15. e70042. https://doi.org/10.1002/ecs2.70042.
DOI: https://doi.org/10.1002/ecs2.70042

Interpretive Summary: Restoration from cropland to native perennial plant cover is difficult, and outcomes in plant community composition can be unpredictable. We took a wheatfield out of agricultural production and seeded it with a mix of perennial native grasses along with an alfalfa cover crop, with half the field being seeded in a dry year, and the other half in a wet year. We found that tempetature and water availability in the soil before treatment was predictive of the community composition 10 years after seeding. This work suggests that land managers can use pre-treatment soil moisture and temperature to tailor their restoration strategies.

Technical Abstract: Problem: The vast majority of the Great Plains Shortgrass Prairie has been converted to cropland since European colonization. Land managers are incentivized by various programs such as the Conservation Reserve Program to restore croplands back to perennial shortgrass prairie in order to achieve ecosystem service benefits like erosion control, belowground carbon storage and ecohydrologic connectivity. But there is much uncertainty about how to conduct restoration treatments that result in long-term cover of native perennials, rather than non-native annuals. In particular, how can pre-treatemnt temperature and moisture conditions inform land managers when selecting species for seeding treatments? Methods: We seeded a 120 ha field in North Central Colorado with a mix of perennial grasses, one shrub species, and a non-native cover crop. Before treatment, the field was managed for many years in two sets of alternating wheat/fallow strips, and entered into the CRP in 2013. The first set of strips seeded in mid-May 2013, a dry year, and the other in mid-May 2014, a wet year. Results: The restoration outcomes were quite different. The set of strips that was seeded in the drier 2013 had lower diversity and species richness, with establishment of Atriplex canescens, a drought-tolerant shrub, and Pascopyrum smithii, a native rhizomatous grass. The strips seeded in 2014 had more native perennial grasses from the seed mix. Non-native annual grasses and forbs were the dominant surface fuels, except where P. smithii was abundant and appeared to competitively exclude the non-native annuals. Analysis: Non-metric multidimensional scaling indicated that the two strips had distinct species compositions, but were dominated by the same four species. A joint species distribution model with soil temperature and moisture surfaces as predictors (measured on site and modeled using high resolution topography data) found clear patterns of pre-treatment climatic conditions that may be informative for predicting long-term success of restoration treatments. In particular, soil moisture in the months immediately preceding seed application was beneficial for most caespitose native perennials, while rhizomatous native grasses and drought-tolerant native shrubs were less sensitive to soil moisture. We also found evidence of facilitatory interactions between non-native annual grasses and forbs, and antagonistic interactions between rhizomatous perennial grasses and non-native annuals. Synthesis: 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. This can inform restoration practitioners in developing restoration strategies. Increasing the quantity of seeds for functional groups that have a favorable outlook for establishment may be an effective strategy to maximize resources. However, still including the full suite of functional groups in seed mixes can be a key bet-hedging strategy to allow for uncertainty around post-fire conditions.