Responses of soil, herbaceous vegetation and ants to woody debris
additions in restored old fields in a multi-site
Before-After-Control-Impact experiment
Abstract
Ecological restoration of former agricultural land can improve soil
condition, recover native vegetation, and provide fauna habitat.
However, restoration benefits are often associated with time lags, as
many attributes, such as leaf litter and coarse woody debris, need time
to accumulate. Here we experimentally tested whether adding fine and
coarse woody debris to a decade-old restoration sites can accelerate
restoration benefits. We used a Multi-site Before-After / Control-Impact
design to test the effects on 30 response variables over a period of two
years, including those describing soil physical and biochemical
properties, herbaceous vegetation and ant communities. We analysed the
data using linear mixed-effect models and perMANOVAs. Of the 30 response
variables, a significant effect of mulch or log additions was found for
just four variables: volumetric water content, decomposition of tea
leaves, native herbaceous species cover and species richness of
opportunistic ants. Mulch addition had a positive effect on soil
moisture when compared to controls but suppressed growth of native (but
not exotic) herbaceous plants. Whilst other soil properties such as
organic matter and dissolved organic carbon showed a positive response
to mulch addition, the effect was not statistically significant. On
plots with log additions, decomposition rates of tea leaves decreased,
and species richness of opportunistic ants increased. However, we found
no effect on total species richness and abundance of other ant
functional groups. The benefit of mulch to soil moisture was offset by
its disbenefit to native herbs in our study. Logs increased species
richness of opportunistic ants, but given time, may provide habitat for
cryptic species. Indeed, benefits to other soil biophysical properties,
vegetation and ant fauna may require longer timeframes to be detected.
Further research is needed to determine whether the type, quantity and
context of mulch and log additions may improve restoration outcomes.