Effect of Low Vegetation on the Recruitment of Plants in Successional Habitat Types¹

Abstract

I assessed the role of low vegetation (plants ca 1 yr old and ≤50 cm tall) as a biotic facilitator or barrier in the recruitment of different growth forms and species in primary forests, secondary forests, and old‐fields (abandoned pastures) in southeastern Mexico. I removed by hand all plants (≤100 cm tall, including roots) and litter from 20, 0.25 m2 plots in each habitat. For 1 yr, I counted the number of plant species (5–50 cm tall) recruited, grouped them into different growth forms, and compared them to undisturbed control plots. Prior to manipulation, the standing density of trees and lianas was highest in primary and secondary forests. Shrubs were more abundant in secondary forests, whereas herbs, epiphytes, and hemi‐epiphytes were more abundant in old‐fields. Herbaceous plants appeared as important components of the community in all habitats. The removal of low vegetation increased total plant recruitment in all habitats. Considering each growth form, the absence of vegetation increased recruitment in primary forests for herbs, in secondary forests for epiphytes and hemi‐epiphytes, in old‐fields for trees, and for lianas in primary forests and old‐fields. In vegetation removal plots, recruitment of species was greater in pastures, lower in secondary forest, and similar in primary forest with respect to control plots. Depending on habitat type, species, and growth form, the presence of low vegetation may act as a recruitment barrier or facilitator for different species, affecting plant community structure, diversity, and composition in different habitats.

Ecological filtering by a dominant herb selects for shade tolerance in the tree seedling community of coastal dune forest

“…Although the tree overstorey may reduce the light levels reaching the forest Xoor, the most pervasive eVect on reduction of PAR levels is attributed to understorey vegetation (Montgomery and Chazdon 2001). The forest understorey plays a crucial role in determining tree recruitment and consequently forest structure and dynamics in both temperate and tropical forests (George and Bazzaz 1999;Wang and Augspurger 2004;Coomes et al 2005;LaFrankie and Saw 2005;Benítez-Malvido 2006). Diminished survivorship and growth of tree seedlings due to light attenuation by the understorey has been reported in many studies (George and Bazzaz 2003;Farris-Lopez et al 2004;Slocum et al 2004;GriYths et al 2007).…”

Seedling interactions in a tropical forest in Panama

“…As we purposefully planted experimental seedlings with their roots intermingled to maximize the possibility of detecting interactions, we conclude that interspeciWc interactions are relatively unimportant for seedling performance during the Wrst year of seedling life as well as during the subsequent establishment phase and clearly less important than intrinsic variability among species or variation in microsite conditions. The experimental removal of a large portion of all understory plants has twice had no detectable eVect and once had mixed eVects on those understory plants left in situ (Marquis et al 1986;Brown and Whitmore 1992;Benitez-Malvido 2006). Again, the evidence suggests that negative interactions among understory plants are relatively weak.…”

“…Twice the remaining understory plants failed to show competitive release (Marquis et al 1986;Brown and Whitmore 1992), in agreement with the hypothesis that competition is limited among understory plants. The third partial understory removal experiment had mixed results, with increased recruitment of lianas and herbs, but not of trees, shrubs, palms, or epiphytes in mature forest (Benitez-Malvido 2006). Here, we take a diVerent approach and test for competition between closely adjacent seedlings.…”

Lack of tree layer control on herb layer characteristics in a subtropical forest, China

“…An increasing top‐down control of the tree layer was also reflected in a decreasing bottom‐up control of the herb layer. As pointed out in the Introduction, woody saplings are supposed to be influenced by the herb layer, as an effect of competition and facilitation (George & Bazzaz 2003; Benitez‐Malvido 2006). Our fourth hypothesis suggested increased abundance of saplings with ongoing succession; instead, we found a strong decrease in sapling numbers.…”

“…Hence, not only the relationship of recruits to their congeneric neighbours (Janzen 1970) but also the interaction with herbaceous species might be crucial for specific tree species regeneration (George & Bazzaz 2003). This can be considered a ‘bottom‐up’ control (in a spatial rather than a trophic sense) of tree recruitment (Benitez‐Malvido 2006). In this sense, the herb layer can be expected to be a driver for tree layer diversity.…”