Spatiotemporal Dynamics of Seed Rain and Seedling in a Montane Cloud Forest, Taiwan

• Main Authors: Chi-Yu Weng, 翁其羽
• Other Authors: Chih-hao Hsieh
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/7eaq9j

博士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 105 === Seed dispersal and seedling dynamics are crucial for tree species in their long-term regeneration processes by affecting community assembly of a forest. However, the discordance in seed-to-seedling transition, which is due to loss by predation and dispersal limitation, constitutes a great spatiotemporal variation in recruitment of tree species. Seeds are not guaranteed to be able to disperse to the microhabitats favorable to seedling establishment or survival; this results in weak association between seedling distributions and environmental factors. Moreover, the uncoupling between seedling and adult tree assemblages further obscures our understanding of the role of ecological niches specific to the seedling stage (regeneration niches) in forest community assembly. To address the discrepancies at the seedling stage, detecting local heterogeneity in microenvironments, to which seedling assemblages respond, is a prerequisite. I propose that understory plants, which may interact with microenvironments and seedlings at local scale, can be a better spatial descriptor for regeneration habitats. To test this, a demographic survey for tree seedlings and understory plant assemblages was conducted in 2009 in the Nanhsi forest dynamics plot (23° 27''40.7" N, 120° 54''22.2" E), a montane cloud forest of Taiwan. I find that the understory plant spatial structure contributes most in explaining spatial variations of the seedling assemblages and facilitates the identification of patches of different regeneration habitats. Among these regeneration patches, the neighboring effects from tall herbs play an important role in affecting seedling density, diversity, and its coupling with conspecific adult trees. A consecutive seedling dynamics survey for three years (2010–2013) provides further supporting evidences for the neighboring effects from tall herbs. The nurse-plant effect by tall herbs can co-operate with seedling species traits (shade-tolerance, and seedling initial height) against ungulate herbivory, resulting in uneven species-specific mortality at an early stage of seedling establishment. Ungulate herbivory greatly caused seedling mortality here; however, it was not really detrimental to seedling species coexistence. The uneven species-specific mortality by herbivory and density-dependent mortality after bursts of recruitments suppress the abundant seedling species. Furthermore, by dynamic modelling, I also find that fluctuating recruitment, which increases temporal heterogeneity in recruitment dynamics, may prevent rare species from apparent competition from the abundant species. The temporal heterogeneity in recruitment dynamics and the consequence of seed-to-seedling transition are studied using seed rains that had been collected in seed traps nearby the seedling sites for five years (2008–2009, 2010–2012). Most of the abundant tree species reproduced annually and periodically, correlating to the climatic seasonality. But the seed arrival uncoupled with recruitments in space, and in time, as well as in the level of species abundance. By analyzing the specific seed-to-seedling transition across years in each site associated with various biotic and abiotic factors, I find that the influential factors (such as the pre-dispersal loss of seeds, dispersal limitation, seed-bank buffering, etc.) had different impacts among tree species with different seed dispersers. My studies highlight the importance of bio-interactions with animals and neighboring plants that can interplay with the dynamic nature of seeds and seedlings from the dispersal, recruitment, to establishment stage, and thereby facilitate species coexistence in the forest community.