Abstract: Seed rain, the dispersal and deposition of plant seeds in a habitat, is a key factor shaping establishment, growth, and persistence of plant communities. Seed rain can structure food webs as many species are granivores. Given the difficulty of tracking seeds, seed rain is often estimated indirectly from canopy tree abundance. However, in temperate forests, seed rain exhibits substantial seasonal and interannual variation. As a result, estimates of plant propagules or food availability for granivores may be poorly estimated from canopy abundance data alone. Our goal was to model the relationship between canopy tree abundance and seed rain for common tree species in temperate forests.
We monitored seed rain in a 46-ha mixed deciduous forest in Clinton, NY from August 2022 to December 2022. We established 14 randomly selected 15m radius long-term monitoring plots where we have stationed seed rain traps. Seeds were sorted by species, counted, and weighed. Using R, we calculated summary statistics and linear regressions for each recorded species.
Among our 14 long-term monitoring plots, the 5 most abundant tree species by basal area were Acer saccharum, Pinus strobus, Fraxinus americana, Picea glauca, and Tsuga canadensis. The 5 most abundant seed species in our traps (by count) were Fraxinus spp. (mean ± standard deviation: 104.1 ± 94.5), Malus spp. (11.1 ± 41.7), Picea glauca (6.2 ± 19.1), Rhamnus cathartica (4.6 ± 16.2), and Robinia pseudoacacia (3.7 ± 6.0).
Basal area and seed rain were strongly associated in some species. For example, Fraxinus spp. had an average 2.9 seed increase per 10 cm^2 basal area increase. Other species showed no such pattern. Although Acer saccharum was the most abundant tree in this forest, we rarely found its seeds in our traps; it ranked 8/13 in seed count. By continuing to collect seed rain data, we will explore temporal variation in these relationships, i.e. seasonality and interannual variation in seed production. We will also examine how functional traits, such as dispersal modes, may shape the relationship between seed rain and basal area. By quantifying the relationship between seed rain and tree abundance, we hope to clarify common assumptions about seed availability in temperate forests. Future research will integrate small mammal capture data to understand the relationship between food availability and granivore activity.
