Restoration temporarily supports the resilience of sagebrush-steppe ecosystems subjected to repeated fires

Many ecosystems are experiencing increased fire frequencies and species
invasions that can erode their resilience and cause a shift to alternative
states. In the sagebrush-steppe, a semi-arid shrubland ecosystem in North
America, restoration treatments are often implemented following wildfire
to enhance their resilience to invasion. However, little is known about
the long-term effectiveness of these treatments. We investigated whether
repeated restoration efforts provide greater resilience in
sagebrush-steppe communities initially dominated by species with different
post-fire regeneration traits and subjected to compounding wildfires and
invasion by Bromus tectorum over 25 years. We studied 37 permanent
transects (Columbia Basin, Washington, USA) in which species abundance was
recorded multiple times from 1992 to 2017. We quantified community change
and its relationship with fire, restoration, and moisture availability.
Resilience was evaluated by quantifying community resistance and stability
indices. The greatest change occurred in communities where the obligate
seeding shrub Artemisia tridentata was initially common. Repeated fires
led to the extirpation of this shrub and eventual dominance of B.
tectorum. Herbicide applications temporarily suppressed B. tectorum
post-fire. Seeding treatments and above average precipitation initially
increased native cover. Although communities where resprouting species
were common showed the least change, repeated fires did lead to a gradual
but substantial decline (86%) in resprouting shrubs. Synthesis and
applications: Our findings show that repeated restoration efforts,
together with elevated precipitation, can support native species
re-establishment in systems experiencing altered disturbance regimes and
species invasions. Our unique long-term dataset demonstrates, however,
that many such interventions have short-lived effects due to the strong
“unhelpful resilience” of highly invaded systems. This implicitly suggests
that many such systems have experienced fundamental shifts in ecosystem
state. The likelihood of this occurring is strongly associated with the
dominant species post-fire regeneration traits. We predict that community
composition and resilience will continue to degrade in the
sagebrush-steppe unless management prioritizes fire suppression and an
adaptive restoration approach that considers resource availability.