The Effect of Leaf Litter on Early Seedling Establishment in a Tropical Forest

Abstract

The presence of leaf litter of different depths within a tropical forest creates many different microsites for plant establishment. The amount and distribution of leaf litter within a forest can influence patterns of plant establishment. In this study, we determined the spatial variability in leaf litter in the forest understory, and investigated how different litter depths (bare, 1, 6, and 12 cm) affected the establishment of several tropical tree species in both growth house (sun and shade) and field (gap and understory) experiments in the semideciduous tropical forest of Barro Colorado Island, Panama. The tree species used in this study (Aspidospermum cruenta, Ceiba pentandra, Cordia alliodora, Gustavia Superba, Luehea semmannii, Ochroma pyrimidale) were chosen to represent a range of seed masses and a gradient in the light requirement for establishment of the species. The spatial distribution of leaf litter was not correlated between adjacent sampling points within the forest understory, suggesting that the establishment environment for seedlings, with respect to litter, is highly variable at scales of 1—20 m. The presence of litter affected five of the six species, but the nature and the magnitude of the effect were species specific. The smaller seeded shade—intolerant species had fewer seedlings establishing under leaf litter than on bare ground. The species ranged from strongly nagatively affected (Luehae) to moderately negatively affected (Cordia, Ochroma) to affected only by extreme amounts of litter (Ceiba). The presence of litter influenced Gustavia, one of the larger seeded shade—tolerant species, but did not affect Aspidospermum, the other large seeded species. The effect of litter on Gustavia depended on the light environment. Gustavia had more seedlings establishing under litter in the sun, but the presence of litter had no effect in the shade. Differences among the smaller seeded shade—intolerant species in the amount they were negatively influenced by litter were not correlated with seed mass. Data from our field study were consistent with our growth house results for the shade—intolerant species. Additional data from the field study indicated that these species with similar habitat requirements differed in the developmental stage at which they were affected by the presence of litter. Luehea had fewer seeds germinating under litter while the other two species, Ochroma and Cordia, were affected only after germination. Interspecific comparisons done for each light level and litter depth indicated that the presence of litter caused reversals in the relative ranking of species success. For example, Gustavia preferentially established under relatively deep litter depths in the sun where Luehea could not establish. In conclusion, the presence of litter can potentially increase seedling diversity within the forest by creating heterogeneity in the establishment environment and by causing reversals in species' rankings.

Forest spatial heterogeneity and palm richness, abundance and community composition in Terra Firme forest, Central Amazon

“…In tropical rain forest both leaf litter cover and leaf litter depth contribute to microenvironmental heterogeneity and are spatially unpredictable even at scales of few meters (Molovsky & Augspurger 1992, Cintra 1997a). In the Reserva Ducke, the microsite variation in leaf litter depth did not affect palm species richness, however it was inversely related to palm abundance, suggesting that palms are in higher numbers in areas of shallow leaf litter.…”

Forest Floor Decomposition Following Hurricane Litter Inputs in Several Puerto Rican Forests

“…The combination of relatively nutrient-rich disturbance-generated litter and fine-root and plant mortality (Parrotta and Lodge 1991;Silver and Vogt 1993) can affect rates of litter decomposition and mineralization, leading to temporary alterations in ecosystem-scale carbon (C) and nutrient cycling rates (Sanford and others 1991) and increasing nutrient export in stream water (Schaefer and others 2000). These modifications of the physical and chemical environment of the forest floor can also affect processes such as seed germination, seedling establishment, and the relative ranking of species, often in complex and speciesspecific ways (Facelli and Carson 1991;Guzmá nGrajales and Walker 1991;Molofsky and Augspurger 1992;Everham and others 1996;Harrington and others 1997). Although these observational, experimental, and modeling studies have demonstrated that hurricane litter can affect many ecosystem processes, the length of time that this hurricane-generated forest floor mass remains elevated above predisturbance levels, and thus has a direct physical and biogeochemical effect on ecosystem processes, is poorly documented.…”

Plant recruitment and range size: Transition probabilities from ovule to adult in two Ipomoea

“…This was another unexpected result since for these species the germination success of scarified seeds in germination chambers can be high (83% in I. rubriflora and 94% in I. purpurea; J. Astegiano, unpublished data). On the other hand, since species differ in seed mass and larger-seeded species may produce larger seedlings that may be able to emerge from deeper soil levels or more developed litter layers (Jurado and Westoby, 1992;Molofsky and Augspurger, 1992;Pearson et al, 2003), we expected higher probability of emergence in I. purpurea. We propose that the generally negative effect of litter on plant regeneration, by either preventing germination or suppressing seedling growth and which may be independent of seed size (Dalling and Hubbell, 2002;Fenner and Thompson, 2005), might explain the similar probability of emergence recorded for these two species of Ipomoea.…”