Planting designs in ecological restoration: Insights from the Button Wrinklewort

Summary  The re-establishment of threatened (and common) plant species populations is an important conservation activity in the agricultural landscapes of Australia where habitat fragmentation has destroyed much of their former range. The initial design of restoration plantings, including the number of individuals planted and their spatial configuration, is likely to affect long-term persistence of the re-introduced populations because of its potential effects on pollination and gene flow, but this topic has received little attention in the restoration literature. This study examined how population size and population density of experimental arrays of the grassland daisy Button Wrinklewort affected percentage seed set, a measure of reproductive success. We found strong evidence that population density, but not population size, affected seed set in this species. Seed set increased by, on average, 275% when plants were placed at high-density relative to low-density populations. The low seed set observed may occur because pollinator visitation rates decline in sparse populations or, alternatively, because pollinators are less efficient at pollen transfer when individuals are at low density. Hence, planting designs appear to be an important facet of restoration works that deserve far greater theoretical and practical attention than they have previously received.