Effects of seedling size, El Niño drought, seedling density, and distance to nearest conspecific adult on 6-year survival of Ocotea whitei seedlings in Panamá

Abstract

We present an analysis of the long-term survival of two cohorts of seedlings of the tropical canopy tree Ocotea whitei (Lauraceae) on a 1-ha plot of mature, lowland moist forest on Barro Colorado Island, Panamá. In 1980, we counted an even-aged cohort of seedlings that germinated in 1979, then measured and tagged survivors in 1981. We also measured and tagged a second, smaller cohort of seedlings that germinated in 1981. We followed the subsequent survival of all seedlings through 1985. Seedling mortality was phenotypically, temporally, and spatially non-random. Important correlates of non-random mortality included: (1) seedling size and age, (2) an El Niño drought, and (3) biotic neighborhood. Larger and older seedlings survived better than smaller and younger seedlings, respectively, and the El Niño-related drought of 1982-1983 was associated with elevated mortality rates. Seedling density, which was strongly correlated with the proximity to the nearest conspecific adult, increased mortality. The observed mortality patterns suggest that processes consistent with the Janzen-Connell hypothesis operate during the recruitment phase of O. whitei population dynamics. However, the processes causing the observed density- and distance-dependent mortality may vary with factors such as total seed number, seedling size, and climatic variation, making it difficult to determine whether time-integrated seedling-to-adult spacing mechanisms other than self-thinning operate on a given plant population. After 6 years in the hectare studied, survivors remained densest and most numerous underneath the adult trees. We conclude that only long-term demographic data, collected at a variety of scales on a variety of species, will ultimately answer the question: do Janzen-Connell effects contribute substantially to structuring tropical forests?

Local neighborhood and species' shade tolerance influence survival in a diverse seedling bank

“…Both pathogens and insects have been shown to cause densitydependent mortality in established seedlings and saplings (Wong et al 1990, Gilbert et al 2001. Negative effects of conspecific neighbors may also result from intense competition between conspecifics.…”

Relaxation of species‐specific neighborhood effects in Bornean rain forest under climatic perturbation

“…In a wider analysis of 60 species using the same size class and a nearest neighborhood modeling approach, Uriarte et al (2004b) found only weak evidence of conspecific effects for six species: they suggested that once a tree at BCI moved from seedling to sapling or pole sizes, NDD was lost (Uriarte et al 2005). Gilbert et al (2001) showed a pathogen-specific small-tree effect for one particular species at BCI. Interestingly, we are not aware of any literature reporting main tests of NDD on growth of trees !4 cm dbh at BCI.…”

CARACTERIZACIÓN DE MICROSITIOS PARA EL ESTABLECIMIENTO DE PLÁNTULAS DE Espeletia uribei (Asteraceae)

“…La heterogeneidad en la estructura de tamaño en las plántulas de E. uribei es una situación común dentro de las poblaciones vegetales y se asocia a diferencias en el acervo genético de los individuos, el tiempo de germinación, las tasas de crecimiento, interacciones de competencia, de facilitación (Hutchings, 1997;Silvertown y Charlesworth, 2001;Lopera, 2010), efectos denso-dependientes, depredación por herbívoros, el ataque de patógenos, la caída de ramas o la falta de recursos suficientes para el crecimiento (Gilbert et al, 2001).…”