Reliable ecological restoration outcomes are of paramount importance in today’s era of extensive environmental degradation, yet restoration outcomes are notoriously variable. One commonly assumed source of this variation is weather conditions during the planting year, though empirical evidence for these effects are scarce. In addition to implications for restoration practice, evidence for these “year effects” would provide support for historically contingent assembly models, in which early community dynamics impact long-term community trajectories. Despite experimental evidence for short-term year effects in restoration, their long-term persistence and importance compared to other factors is unclear. Our research sheds light on the implications of year effects over the longer term and across a broader geographic gradient. In 2016, we visited 90 restored tallgrass prairies in Illinois, Indiana, and Michigan that had been planted between 1998 and 2015 by different managers. We compiled management histories, surveyed current community compositions, and downloaded data on the temperature and precipitation in each planting year. We asked whether there is a measurable signature of planting year conditions on present-day plant communities and, if so, which conditions are influential? How do these year effects compare in impact to other known drivers of restored communities (e.g. seed mix richness, fire frequency)?
Results/Conclusions
We found a signature of conditions in the first growing season on the present-day communities at 90 restored tallgrass prairie sites, ranging in age from 2 to 20 years. There was a significant negative effect of the amount of precipitation accumulated by June 1 of the planting year (χ 2=4.39, p=0.036) on the present-day richness of sown species. Although the effect was relatively small—accounting for 5.5% of the variation in our model predicting the richness of sown species—it is remarkable that this signature has persisted alongside other predictors known to influence restoration outcomes, such as the richness of the seed mix (χ2=9.40, p=0.002, partial-R2=0.24). Other metrics that related to temperature in the planting year had no significant effect on the present-day community. Overall, we conclude that planting conditions can leave measurable impacts on the communities that assemble during ecological restoration.