Change in liana density over 30 years in a Bornean rain forest supports the escape hypothesis

D M Newbery,C Zahnd

doi:10.1002/ecs2.3537

Abstract

AbstractLiana dynamics may influence tree dynamics and vice versa. Only long‐term studies can perhaps disentangle them. In two permanent plots of lowland dipterocarp forest at Danum, a liana census in 1988 was repeated in 2018. The primary forest was still in a late stage of recovery from an inferred large and natural disturbance in the past. Mean number of lianas per tree decreased by 22% and 34% in plots 1 and 2, and in different ways. By 2018, there were relatively more trees with few lianas and relatively fewer trees with many lianas than in 1988. The redistribution was strongest for overstory trees of the Dipterocarpaceae (more with no lianas by 2018) and understory trees of the Euphorbiaceae (many losing high loads in especially plot 2). Proportion of trees with lianas increased overall by 3.5%. The number of lianas per tree showed a quadratic relationship with tree size: maximal for large trees, and fewer for smaller and very large trees. Tree survival and stem growth rate were significantly negatively related to the number of lianas after accounting for spatial autocorrelation. Monte Carlo random subsampling of trees in 1988 and 2018, to achieve statistical independence, established significance of change. Dipterocarps and euphorbs clearly differed in their liana dynamics between plots. Regression models had different forms for the two plots, which reflected a complicated structural–spatial variability in host–liana dynamics. Analysis of the abundant tree species individually highlighted a group of emergent dipterocarps with low liana counts decreasing with time. Building on an earlier hypothesis for this forest type and site, these very large trees appear to have been losing their lianas by branch shedding, as they moved into and out of the main canopy. They were evidently escaping from the parasite. The process may in part explain the characteristically very uneven forest canopy at Danum. Change in liana density was therefore contingent on both forest history and site succession, and plot‐level structure and tree dynamics. Liana promotion in the intermittent ENSO dry periods was seemingly being offset by closing of the forest and dominance by dipterocarps in late seral stages.

Highlights

Lianas, or woody vines, are a conspicuous component of most tropical forests (Richards 1996)
Background tree dynamics At census 1 (1986|1988), there were 1704 and 1659 trees of ≥30 cm gbh in MP1 and MP2, respectively, and by census 2 (2015|2018) correspondingly 1699 and 1832 (3531), discounting the few that died between matched tree and liana censuses
926 and 716 trees died in MP1 and MP2, and correspondingly 921 and 889 (1810) trees recruited into the size class

Summary

Introduction

Woody vines (climbers), are a conspicuous component of most tropical forests (Richards 1996) They are structural parasites: Climbing trees allows them to reach the forest canopy with minimal investment in mechanical support. Three studies in Africa all showed decreased liana infestation (Caballe and Martin 2001, Thomas et al 2015, Bongers et al 2020), as did the one only study in SE Asia (Wright et al 2015) These four paleotropical cases though, as with the ones from the neotropics, vary so widely in their site conditions, historically contingent factors, sampling approaches, and ways of recording lianas abundance, that drawing generalizations is at present unreliable. Experience one sharp or, more often, two moderate dry seasons per year, those in SE Asia have very slight or no seasonality (Walsh 1996a)

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Results

Conclusion