The impact of lianas on tree regeneration in tropical forest canopy gaps: evidence for an alternative pathway of gap‐phase regeneration

Abstract

Summary1 Regeneration in forest canopy gaps is thought to lead invariably to the rapid recruitment and growth of trees and the redevelopment of the canopy. Our observations, however, suggest that an alternate successional pathway is also likely, whereby gap-phase regeneration is dominated by lianas and stalled in a low-canopy state for many years. We investigated gap-phase regeneration in an old-growth tropical forest on Barro Colorado Island (BCI) in Panama to test the following two hypotheses: (i) many gaps follow a pathway in which they remain at a low canopy height and are dominated by lianas and (ii) the paucity of trees in this pathway is a function of liana density. 2 We surveyed a total of 428 gaps of varying ages (c. 5, c. 10, and 13 years old) and identi®ed those which followed the conventional pathway of regeneration and others that remained stalled in a low-canopy state for many years and were dominated by either lianas or palms. Each of these pathways will likely have dierent successional trajectories that will favour the growth of a distinct suite of mature species and ultimately result in contrasting species composition. 3 The successional pathway of liana-dominated, stalled gaps is common throughout the forest. We estimate conservatively that 7.5% of the gaps that form each year will follow this pathway, probably due to the suppression of tree regeneration by lianas, and that many of these stalled gaps will persist for much longer than 13 years. Consequently, a high proportion of gaps in the forest at any given time will be stalled. Furthermore, liana tangles, which persist in the tropical forest understorey for extended periods of time, almost certainly originate in these gaps. 4 Liana abundance was positively correlated with pioneer tree abundance and diversity while negatively correlated with non-pioneer tree abundance and diversity. Thus, lianas appear to inhibit non-pioneer tree survival while indirectly enhancing that of pioneer trees. 5 Lianas are abundant in many types of tropical and temperate forests and a successional pathway involving liana-dominated, stalled gaps may therefore be frequent and widespread.

Forest understory soil temperatures and heat flux calculated using a Fourier model and scaled using a digital camera

“…The spatial variability of leaf area index makes even evapotranspiration impractical to model over heterogeneous lands (Suleiman and Crago, 2004). This limitation is important to consider in both studies of forest soil CO 2 efflux, with the greatest temporal variations of temperature occurring near the soil surface, as well as those of plant distribution, where forest gaps and their associated microclimates are thought to play a major role in the regeneration of many plant species in both tropical and temperate areas (Balisky and Burton, 1995;Schnitzer et al, 2000).…”

Detecting and projecting changes in forest biomass from plot data

“…Thus, for example, all areas of low biomass have the same transition probabilities to various higher (and lower) biomass states. In reality, some areas of low biomass may represent arrested gap succession owing to liana tangles (Schnitzer, Dalling & Carson 2000), or may be likely to stay in low biomass because of habitat effects such as location in a swampy area (Chave et al 2003). Second, projections are made under the assumption that future transition probabilities are distributed in the same way as previously observed probabilities, in our case choosing randomly among the observed census intervals.…”

Nursery growth and rhizobia symbiosis of scandent Leguminosae species native to the Amazon region

“…There is positive correlation between abundance and diversity of pioneer trees and scandent legumes (Schnitzer et al 2000), which may facilitate the process of ecological succession, and speed recovery from disturbances that occur within a forest. However, studies on the characteristics of legumes growth under controlled conditions are practically non-existent, as well as studies on nodulation capacity, and phenotypic and genetic characterization of rhizobia strains symbiotic with these legumes (Moreira et al 1993;1998).…”