Competitive effects of a dominant palm on sapling performance in a Neotropical rainforest

Eradication of herbivores, due to human disturbances, produces a demographic outburst of highly competitive prey species, which in turn reduces plant species diversity. This happens at Los Tuxtlas tropical rainforest, Mexico, where a population outburst of the understory palm Astrocaryum mexicanum is ostensibly excluding tree species, but how this is occurring is still unknown. We used a neighborhood approach to explore the effects of palm shading and palm crowding on the survival and growth (RGR) of saplings of six common tree species. Sixteen to 32 saplings (1.5-2.5 m height) per species were used as focal individuals of circular neighborhoods (4 m radius), which included palms >= 1cm stem length potentially competing for light or soil resources. Shading was estimated using hemispherical photographs. Overall, survivorship was high combining all species (93.8%/yr). In most species, shading produced a displacement of the crown, which increased with specific leaf area of species. In three species, shading had a negative effect on RGR without any effect of crowding, the contrary occurred in two species, and in one species no effects were found. No effects due to trees (DBH >= 1cm) crowding were detected. The shading effect increased with species leaf dry matter content (LDMC), while the effect of crowding declined with LDMC and increased with sapling total leaf area. We argue that the species-dependent palm shading/crowding effects were related to the shade tolerance of sapling species. In the long-term, such species-specific responses could have consequences for forest structure and composition, as saplings develop to mature stages. Abstract in Spanish is available with online material.

Automated summary

Eradication of herbivores by human disturbances results in a demographic outburst of highly competitive prey species, leading to reduced plant species diversity. In the Los Tuxtlas tropical rainforest of Mexico, an understory palm species is reportedly excluding other tree species, potentially impacting forest structure and composition in the long term.