Wind dispersal and 1-year survival of Vataireopsis iglesiasii (Fabaceae) seedlings in a Neotropical lowland rain forest
Queenborough, Simon; Valencia, Renato; Alvia, Pablo (2022), Wind dispersal and 1-year survival of Vataireopsis iglesiasii (Fabaceae) seedlings in a Neotropical lowland rain forest, Dryad, Dataset, https://doi.org/10.5061/dryad.h44j0zpnh
Populations of many tropical tree species are regulated by negative distance- and density-dependent processes (NDD), yet most studies on the effects of conspecific seedling and adult neighbours on seedling survival have focused on animal-dispersed species. Species with seeds dispersed by wind may not be moved as far on average as seeds dispersed by animals, but some seeds may be dispersed a lot further, suggesting that knowledge of dispersal mechanism may help in our understanding of NDD. In this study, we took advantage of a high-fecundity reproductive event that occurred for an individual isolated canopy tree of Vataireopsis iglesiasii in a tropical lowland rain forest site in Amazonian Ecuador to document seed dispersal and seedling survival to 1-year post-dispersal. Most seeds did not disperse far: 86% of germinated seedlings were found within 100 m. Mortality was high: only 49 of the 1732 monitored seedlings survived one year and only five survived a further four years. We found a significant negative effect of conspecific seedling density (but no effect of distance from the parent tree) on 1-year survival. Rare long-distance dispersal events may increase the probability of a seed reaching specific habitats, such as high-light patches, and surviving beyond one year, thereby shifting the population recruitment curve outwards away from adult trees and maintaining diversity in species-rich forests.
The 50-ha Yasuni Forest Dynamics Plot (FDP, 0°41’ S, 76°24’ W) is situated in tropical lowland rain forest, Amazonian Ecuador, wherein all trees >1 cm diameter at breast height (DBH, 1.3m) have been marked, mapped, and identified regularly since 1994 (Valencia et al. 2004). The dominant vegetation type is evergreen terra firme forest with a canopy height of 10–30 m. Emergent trees can reach 50 m in height. The climate has is aseasonal with a mean annual rainfall of 2800 mm and no month’s rainfall averages less than 100 mm (Pérez et al. 2014). Mean monthly temperature is 25–27°C (Valencia et al. 2004).
Vataireopsis iglesiasii Ducke (Fabaceae, Faboideae) is a large emergent tree that occurs in lowland rain forest from Colombia to Brazil. It has large single-seeded samara fruits that are wind dispersed (Figure 1). The species is locally rare in western Amazonian forests. In the Yasuni 50-ha plot, it is represented by only two individuals >1 cm DBH; a mature adult tree of 84.4 cm DBH and a juvenile tree of 4.3 cm DBH located about 170 m away (Figure 2).
In early March 2016, the adult tree (tag = #400565, DBH = 84.4 cm in 2015, x = 807.2, y = 464.1) released fruit during a period of strong wind. Many fruit were dispersed widely across the 50-ha plot. In 22–26 May 2016, we censused transects of 20×20m quadrats running in each of the 8 cardinal and ordinal directions from the base of the fruiting tree to the edges of the plot, corresponding to the FDP gridlines. Transects running NW, N, NE, and E were extended outside the FDP boundaries until no more seedlings were found. Several additional 20×20 m plots were also surveyed following the prevailing direction of the wind (Figure 2). Within each 20×20 m section of the transects (or 20×20 m plot), we counted the number of newly emerged Vataireopsis iglesiasii seedlings and the number of leaves on each seedling. In 5–9 December 2017, we censused the same transects for Vataireopsis iglesiasii seedlings again, recording the number of surviving seedlings and the number of leaves on each one. On 7 November 2021, we checked these few surviving seedlings again.