Demographic consequences of heterogeneity in conspecific density dependence among mast fruiting tropical trees



The role of conspecific density dependence (CDD) in the maintenance of species richness is a central focus of tropical forest ecology. However, tests of CDD often ignore the integrated effects of CDD over multiple life-stages and their long-term impacts on population demography. We combined a 10-year time series of seed production, seedling recruitment and sapling and tree demography of three dominant Southeast Asian tree species that adopt a mast fruiting phenology. We used these data to construct individual-based models that examine the effects of CDD on population growth rates (λ) across life-history stages. Recruitment was driven by positive CDD for all species, supporting the predator satiation hypothesis, while negative CDD affected seedling and sapling growth of two species, significantly reducing λ. This negative CDD on juvenile growth overshadowed the positive CDD of recruitment, suggesting the cumulative effects of CDD during seedling and sapling development has greater importance than the positive CDD during infrequent masting events. Overall, CDD varied between positive and negative across life-history stages for all species, suggesting that assessments of CDD on transitions between just two stages (e.g. seeds-seedlings or juveniles-mature trees) likely misrepresents the importance of CDD on population growth and stability.,We placed nine plots of 2 × 2 m around each mature tree, located along three transects radiating from the stem at 0°, 120° and 240° N to prevent directional biases in seed fall from factors such as wind and slope. Along each transect, plots were centred at 2 m (directly under the crown), 6 m (crown edge) and 18 m (outside the crown) from the stem. There was a total of 81 plots (3 species × 3 mature trees per species × 9 plots per tree = 81 plots). These plots allowed us to assess the role of conspecific density dependence on seed, seedling and sapling dynamics.In addition to the detailed seedling data, we used the two censuses from the Forest Global Earth Observatory plot (ForestGEO; 50-ha area of primary forest), located in the Danum Valley Conservation Area (approximately 20 km from the seedling census plots), to estimate growth and survival of trees. These data were collected following standard protocols, which includes mapping, identifying and measuring the diameter at breast height of all stems greater than 10 mm. The first census began in 2010 and finished in 2016, and the second census began in 2018 and finished in 2019.,Part of this data comes from the ForestGEO plot network and use of this data comes with restrictions. It should be accessed from the ForestGEO portal directly. The use of the seed and seedling should consider including Michael O'Brien on any publications as it represents over a decade of continuous data collection.,
Date made available1 Jan 2022

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