Relative effects of seed mix design, consumer pressure, and edge proximity on community structure in restored prairies

A central goal of ecosystem restoration is to promote diverse,
native-dominated plant communities. However, restoration outcomes can be
highly variable. One cause of this variation may be the decisions made
during the seed mix design process, such as choosing the number of species
to include (sown diversity), or the number of locations each species
should be sourced from (source diversity, manipulated to affect genetic
diversity). The effects that seed mixes have on plant communities may be
further modified by other factors at the restoration site, including edge
proximity and consumer pressure, which are also likely to vary over time.
However, few studies have evaluated these seed mix attributes together,
and none have done so under realistic field conditions. To address this
research need, we conducted a prairie restoration experiment where two
aspects of a seed mix (sown diversity and source diversity), edge
proximity, and vertebrate consumer access were manipulated across 12
replicate fields. We found that when seed mix design impacted plant
community structure, these effects were dependent on consumer access or
edge proximity and were more prominent after one vs. five growing seasons.
Low seed source diversity plots had more sown species than high source
diversity ones, but only when consumers had access. Similarly, low species
diversity plots had higher richness and cover of species included in both
the low and high species diversity mixes, but this effect weakened over
time. Additionally, plots with high species-diversity were buffered from
the typically detrimental effects of edges and consumers, although this
did not always result in greater sown species abundance. Unexpectedly,
plots with the most sown species were those sown with either low source
diversity or low species diversity seed mixes, perhaps due to lower
seeding rates of reliably establishing species. Our results illustrate how
the influences of seed mix design on restored plant communities can be
highly contingent on factors like edges, consumers, and time.