Geomorphic responses to post-grazing recovery and stream restoration in semiarid grassland streams

Semiarid grassland streams are sensitive to land use, climate, extreme
discharges, and internal geomorphic thresholds that drive episodic
erosion. Rooted in a process-based philosophy and commonly applied to
historically wood-rich, beaver-modified systems, low-tech process-based
restoration using structures is increasingly being extended to other
geomorphic settings, including grasslands. In these wood-poor systems with
fine-grained substrate, channel adjustment depends primarily on subsurface
soil piping and asynchronous responses to changing boundary conditions. We
evaluate post-grazing recovery and structural restoration outcomes at
transect-to-landscape scales in southeastern Colorado. Following grazing
cessation, soil compaction decreased after roughly a decade of rest, as
indicated by a multivariate linear regression analysis of 238 bulk density
samples. In contrast, visible above-ground upland vegetation recovers on
timescales longer than the observation window (>10 years), based on
analyses of growing-season composite Landsat imagery from 2013–2024.
Logistic regression models indicate that the performance of restoration
structures depends strongly on drainage area, slope, local vegetation
cover, and the recency of large-scale commercial grazing. In total, only
~30% of the 92 in-channel structures evaluated (mostly ≤4 years old) were
both intact and produced visible geomorphic change. Structures in
piping-dominated headwaters remained intact but rarely trapped sediment,
whereas those in larger catchments were more likely to initiate local
geomorphic change, despite having higher odds of destruction during peak
flows. These findings highlight the need to match restoration strategies
with the geomorphic processes driving channel adjustment and call into
question the extent to which commonly implemented structure-based
interventions in grassland systems are truly process-based.