Allometric projections of time-related growth trajectories of two coexisting dipterocarp canopy species in India

Abstract

Background: The Western Ghats of India contain the westernmost dipterocarp forests of Asia. However, only a few dipterocarp tree species actually coexist in the forest canopy among which Vateria indica and Dipterocarpus indicus are the most common. The mechanisms contributing to the coexistence of these phylogenetically closely related species have not been identified.

Aims: We investigated the time-related growth trajectories in diameter, height and crown size of these two species in the Uppangala Permanent Sample Plot to determine if trade-offs in their three-dimensional developmental strategies could contribute to their long-term coexistence.

Methods: From annual diameter growth data of 692 trees >9.55 cm in diameter at breast height over a 21-year period, we developed time-related diameter growth models for the two species, accounting for local density-dependent competition effects and topography. Combining the diameter growth models with static stem and crown allometries, we projected time-related tree growth trajectories in height and crown size.

Results: While both species can reach similar dimensions, V. indica grows much faster, or at least as fast as D. indicus in diameter, height and crown size in all the observed situations. Both species respond similarly to topography, but V. indica appears to be more responsive to local density-dependent competition than D. indicus. Finally, V. indica shows higher mortality and recruitment rates and a greater basal area increase than D. indicus.

Conclusions: These results refute our hypothesis that D. indicus coexists with the outperformer V. indica by a growth strategy allowing selected individuals in favourable conditions to reach the canopy more quickly than their competitors. The current coexistence of the two dipterocarp species at Uppangala appears not to be at a static equilibrium; V. indica probably being in a phase of canopy stand colonisation.

Keywords:

• density-dependent competition
• Dipterocarpus indicus
• stem and crown dimensions
• terrain slope intensity
• terrain aspect
• Vateria indica

Acknowledgements

UPSP is a joint research station of the Karnataka Forest Department, Bangalore, and the French Institute of Pondicherry. We are very grateful to the many field workers, technicians, engineers and researchers who contributed to its long-term monitoring. We thank Francis Brearley and three anonymous reviewers for their thoughtful and constructive comments and Philippe Verley for assistance in realisation of Figure 5.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the French Academy of Agriculture through a Dufrenoy grant to CA; French Academy of Agriculture [Grant Dufrenoy 2007].

Notes on contributors

Cécile Antin

Cécile Antin is a researcher in forest and agroforest ecology. Her interests include forest dynamics and rules governing biomass allocation in trees in undisturbed forests as well as in agroforests.

Jimmy Le Bec

Jimmy Le Bec is a researcher in forest and agroforest ecology. His interests include forest and agroforest dynamics, tree demography and individual tree variability.

Narayanan Ayyappan

Narayanan Ayyappan is a researcher in tropical forest ecology in charge of the management of the Uppangala Permanent Sample Plot. His interests include plant systematics, diversity, structure and dynamics of disturbed and undisturbed forests.

Bramasamdura Rangana Ramesh

Bramasamdura Rangana Ramesh is a researcher in tropical forest ecology. His interests include phytogeography, tropical forest tree dynamics and forest landscape ecology.

Raphaël Pélissier

Raphaël Pélissier is a senior researcher in tropical forest ecology, with a special interest in the spatial organisation of tree species diversity, and in 3-D forest stand structure and dynamics.