Interannual variation in precipitation and other planting conditions impacts seedling establishment in sown plant communities

Abstract

Ecological restoration can reverse biodiversity loss worldwide, yet restoration goals and outcomes vary widely, which limits this potential. Divergent restoration outcomes may stem from variation in conditions at the outset of restoration, but empirical evidence is lacking and typically confounded with site differences. Additionally, precipitation is usually cited as the source of this variation, although a wide range of conditions can vary annually. We tested for effects of planting year on seedling establishment by installing identical restorations in three different years. Within those years, we manipulated rainfall with rain‐out shelters to disentangle the effects of precipitation from other annually variable conditions. Additionally, we tested whether increasing seed mix richness buffers against adverse planting conditions. For the first growing season after planting, we followed emergence and survival of sown prairie species and nonsown weed species to determine how planting year conditions influence an establishing plant community, if at all. We found that seedling establishment differed across planting years and precipitation treatments, and that varying emergence patterns by species led to differences in the composition of the first‐year community. We also found significant variation in sown species establishment across years when precipitation was held constant, illustrating the previously overlooked role of nonprecipitation drivers on planting year effects. Higher seed mix richness did not consistently improve establishment of sown species under different planting conditions. This research provides important experimental evidence for effects of interannual variation in planting conditions on first‐year establishment. Future work will examine how these initial changes affect longer‐term assembly dynamics.

Grassland restoration characteristics influence phylogenetic and taxonomic structure of plant communities and suggest assembly mechanisms

“…We expected that the first growing season's precipitation would predict community composition because low rainfall can act as a strong environmental filter, limiting establishment and survival of some plant species (Groves & Brudvig, ). Because drought tolerance can be phylogenetically conserved (Engelbrecht et al, ; Niinemets & Valladares, ; Rueda, Godoy, & Hawkins, ), we anticipated that phylogenetic community patterns would correspond to taxonomic patterns.…”

“…Precipitation in the first year of a restoration can be an important environmental filter. In a replicated precipitation manipulation experiment across 3 years, first‐year precipitation during community establishment significantly affected plant composition (Groves & Brudvig, ). Low precipitation may reduce PD because response to drought (susceptible or tolerant) often is conserved (Niinemets & Valladares, ; but see Cavender‐Bares & Reich, ).…”

Year effects: Interannual variation as a driver of community assembly dynamics

“…However, the authors note that other unconsidered interannual variation—such as solar radiation or herbivore abundance—might still be important. The potential for multiple mechanisms as drivers of year effects is echoed in the Groves and Brudvig (2019) manipulative study of prairie restoration, which did find significant effects of planting year even after holding precipitation constant.…”

The Limits to Adaptation in Restored Ecosystems and How Management Can Help Overcome Them

“…The benefits of sowing a high density of seeds for resulting population genetic diversity may increase if seeds were collected from many environmentally well-matched donor locations (McKay et al, 2005). Moreover, sowing under conditions that maximize plant establishment, such as after fire that exposes mineral soil or during rainy years (Maret & Wilson, 2005;Groves & Brudvig, 2019) or introducing soil microorganisms including those necessary for later successional species (Wubs et al, 2016;Koziol et al, 2018), potentially will enhance the genetic diversity resulting from sowing by increasing the resulting population size and increasing the number of genotypes that might establish. For species that do not establish well Volume 104, Number 3 from seed (e.g., owing to low seed viability or exacting germination requirements), propagation and outplanting of seedlings may be an additional method to promote genetically diverse plantings, as transplanted seedling survival can be very high compared to establishment from seed (Gallagher & Wagenius, 2016).…”