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Resource pulses are rare events with a short duration and high magnitude that drive the dynamics of both plant and animal populations and communities1. Mast seeding is perhaps the most common type of resource pulse that occurs in terrestrial ecosystems2, is characterized by the synchronous and highly variable production of seed crops by a population of perennial plants3,4, is widespread both taxonomically and geographically5, and is often associated with nutrient scarcity6. The rare production of abundant seed crops (mast events) that are orders of magnitude greater than crops during low seed years leads to high reproductive success in seed consumers and has cascading impacts in ecosystems2,7. Although it has been suggested that mast seeding is potentially synchronized at continental scales8, studies are largely constrained to local areas covering tens to hundreds of kilometres. Furthermore, summer temperature, which acts as a cue for mast seeding9, shows patterns at continental scales manifested as a juxtaposition of positive and negative anomalies that have been linked to irruptive movements of boreal seed-eating birds10,11. Here, we show a breakdown in synchrony of mast seeding patterns across space, leading to asynchrony at the continental scale. In an analysis of synchrony for a transcontinental North America tree species spanning distances of greater than 5,200 km, we found that mast seeding patterns were significantly asynchronous at distances of greater than 2,000 km apart (all P < 0.05). Other studies have shown declines in synchrony across distance, but not asynchrony. Spatiotemporal variation in summer temperatures at the continental scale drives patterns of synchrony in mast seeding, and we anticipate that this affects the spatial dynamics of numerous seed-eating communities, from insects to small mammals to the large-scale migration patterns of boreal seed-eating birds. Previous studies showing that mast seeding was synchronized at large scales were constrained to hundreds of kilometres, but this continental-scale study shows that such events are asynchronous, driving spatial and temporal impacts for a wide range of species.

Kelly's commentary regarding our paper1, claiming that nutrient scarcity cannot select for masting behaviour in plants, initiated a fruitful discussion on traditionally settled hypotheses about the evolution of reproductive behaviour in plants. In his commentary, Prof. Kelly raises support for a contrasting hypothesis explaining our observation that temporally variable seed production is more pronounced under nutrient scarcity, namely that nutrient scarcity does not directly cause seed production variability, but instead increases variability induced by economies of scale. The commentary hinges mainly on the argument that an economy of scale (EOS) is necessary to select for highly variable seed production. It also points out that there are no mechanisms by which nutrient scarcity would select for that particular trait over generations. In reply to the stimulating comment, we 1) propose a mechanism by which nutrient scarcity may select for highly variable seed production, with larger-scale weather patterns inducing masting synchrony across populations; 2) we further discuss why wind-pollination and predator satiation, the EOS suggested by Kelly, cannot be the only selective pressures that select for highly variable reproduction.

Seed distribution and deposition patterns around parent trees are strongly affected by functional traits and therefore influence the development of plant communities. To assess the limitations of seed dispersal and the extent to which diaspore and neighbouring parental traits explain seed rain, we used a 9-year seed data set based on 150 seed traps in a 25-ha area of a temperate forest in the Changbai Mountain. Among 480,598 seeds belonging to 12 families, 17 genera, and 26 species were identified, only 54% of the species with mature trees in the community were represented in seeds collected over the 9 years, indicating a limitation in seed dispersal. Understory species were most limited; overstory species were least limited. Species with wind-dispersed seed had the least limitation, while the lowest similarity in species richness was for animal-dispersed species followed by gravity-dispersed species; fleshy-fruited species had stronger dispersal limitations than dry-fruited species. Generalized linear mixed models showed that relative basal area had a significant positive effect on seed abundance in traps, while the contribution of diaspore traits was low for nearly all groups. These results suggest that tree traits had the strongest contribution to seed dispersal and deposition for all functional groups examined here. These findings strengthen the knowledge that tree traits are key in explaining seed deposition patterns, at least at the primary dispersal stage. This improved knowledge of sources of seeds that are dispersed could facilitate greater understanding of seedling and community dynamics in temperate forests.

Forest habitat is important for a variety of woodpecker species, and is under pressure from urbanization. Red-headed Woodpeckers (Melanerpes erythrocephalus; RHWO) were once abundant across Eastern North America, and their populations have been declining since the 1960s. Their distribution encompasses urban centers, and since urban habitats differ from natural forest areas, our goal was to understand RHWO nest-site selection in an urban context. We addressed two main questions 1) what are the characteristics of RHWO nest selection across multiple spatial scales and 2) how do RHWO nest tree characteristics in city parks compare to those in forest preserves? This work was done in Cook County, IL, which includes Chicago, the third-largest city in the USA by population. We examined 34 RHWO nest trees used between 2010 and 2013, their surrounding habitat, and the landscape within a 1 km radius. Used trees and habitats were compared to paired unused trees and habitats, and landscape-scale characteristics were compared to random locations. Advanced decay of the nest tree, low canopy cover and increased presence of fungus on trees in the surrounding habitat were the best predictors of RHWO nesting in the area. Nests were most commonly found in forested areas outside of dense urban areas. However, we did not detect significant differences in the characteristics of the nest trees located in forest preserves and city parks. Our findings are consistent with nest selection studies in rural and natural areas, suggesting that forest habitats in metropolitan landscapes can support RHWO nesting.

Tree cavities are used by a wide variety of species for nesting, food storage, and cover. Most studies on cavity availability have been conducted in forests, and little is known about urban areas. With urbanization, species that excavate cavities may be less abundant, natural tree-decay processes are managed, and tree densities are reduced, all of which may influence tree-cavity availability. We investigated three questions: 1) What is the prevalence of tree cavities in different habitats in the Chicago area? 2) How do the characteristics of natural and woodpecker-excavated cavities and cavity-trees differ across habitats? 3) How does the urban landscape influence the prevalence of tree cavities? We tested the capacity for large urban parks and residential areas to provide tree cavities at levels similar to forested areas. We surveyed 1,545 trees in these three habitats for excavated and natural (caused by decay) cavities. Cavities were most available in forests, where the density of trees was highest. We found that a similar proportion of trees in forests and parks had excavated cavities, but excavated cavities were rare in residential areas. Trees containing cavities were larger than control trees and had more decay, and excavated cavities were in larger trees with more decay than natural cavity trees. Canopy cover was the main landscape variable influencing excavated cavity availability. Our results suggest that the prevalence of tree cavities may not be a limiting factor for urban wildlife, however that is contingent on the levels of use of natural cavities, which is currently unknown.