Local neighborhood communities in the understory play a critical role by affecting regeneration niches and subsequent community assembly in a montane cloud forest

Abstract

Regeneration niches for tree seedlings are defined as possessing the biotic and abiotic requirements to successfully replace adults. However, two critical discrepancies obscure our understanding of the role of regeneration niches in forest community assembly: a weak association between seedling assemblages and environmental factors, and an uncoupling between seedling and adult‐tree assemblages. However, understory plants, which may interact with microenvironments and seedlings, may be a better spatial descriptor of regeneration habitats. To test this, the spatial variations of seedling assemblages in a montane cloud forest of Taiwan were analyzed in terms of their association with neighborhood assemblages of understory plants, the shrub layer, and overstory trees, as well as environmental variables. We found that the understory plant spatial structure contributed most in explaining spatial variations of the seedling assemblages (especially for widespread Lauraceae and patchy Fagaceae) and facilitated the identification of patches of different regeneration habitats for specific seedling assemblages. Moreover, among these regeneration patches, tall herbs affected seedling density and diversity differently. We found segregation between tall herbs and Lauraceae seedlings, indicating that tall herbs shape seedling assemblages and uncouple the association between seedling and adult stages. However, positive covariations between seedlings/tall herbs and between seedlings/adults were found for Fagaceae and Pentaphylacaceae in different regeneration patches, suggesting that positive, neighboring effects and dispersal limitation may cause the patchy distribution of seedling assemblages and affect their coupling with adults. Thus, the understory plant spatial structure shapes seedling assemblages and provides a better link to spatial associations with regeneration habitats.

Forest seedling community response to understorey filtering by tree ferns

“…Overstorey shading and litter size, quality and quantity are significant filters for vascular seedling establishment (Gillman & Ogden, 2001;Ibáñez, Clark, LaDeau, & Lambers, 2007;Valladares, Laanisto, Niinemets, & Zavala, 2016). These biotic drivers are commonly considered under the dominant influence of canopy species, but understorey vegetation can also contribute to the forest regeneration niche (Caccia, Chaneton, & Kitzberger, 2009;Farris-Lopez, Denslow, Moser, & Passmore, 2004;Takahashi, 1997;Weng, Yang, Hsieh, Hsieh, & Su, 2017). Demonstrating biotic influence on community assembly requires careful consideration of a suite of processes including dispersal limitations, environmental filters and within-site heterogeneity (Kraft et al, 2015).…”

Filling the gaps in ecological studies of socioecological systems

“…These theories are roughly categorized into deterministic and stochastic views. The deterministic view focuses on environments as direct determinants of community structure, because these can directly affect physiological processes of species or, indirectly, biological interactions such as competition and predation (e.g., Weng et al 2017). Some community ecology theories, e.g., ''Paradox of plankton'' (Hutchinson 1961), theories of keystone species (Paine 1969), and trophic cascade (Carpenter and Kitchell 1996), rely on such deterministic forces.…”

Establishment of an ecological research network involving Taiwan and Japan: developing a better understanding of ecological phenomena unique to East Asia

“…Laplace et al (2017) showed greater stand transpiration in Moso bamboo forests than that in a surrounding Japanese cedar plantation in both Taiwan and Japan, although their seasonality was very different across the two countries. Weng et al (2017) examined a weak association between seedling distribution and environmental factors in a montane cloud forest of Taiwan. They showed a stronger link to habitat association of seedling assemblages using the spatial structure of understory plants.…”