Spatial Distribution and Growth Characteristics of Gyrinops walla Gaertn. (Thymelaeaceae) in Sri Lanka

Abstract

Gyrinops walla Gaertn. (Family: Thymelaeaceae), an understory tree species, grows naturallyin moist forests of Sri Lanka, where it is vulnerable and in south-west of India, where it isvery rare. With indiscriminate felling in the wild, for its high-valued resin products, itscurrent threat status may be even higher. The objective of this study is to gain anunderstanding of the spatial distribution and some growth characteristics of Gyrinops wallaimportant for its conservation in the wild and for its domestication.

This study is based on (i) botanical surveys/inventories for information on geographicaldistribution, (ii) multiple plot-based research in nine wet lowland and four intermediate zoneforests to understand its population demography, and (iii) a 25 ha forest dynamics plot atSinharaja (Sin-FDP), where the local distribution of G. walla, its growth and survival ofindividuals >1cm dbh have been censused thrice over 10 years.

In Sri Lanka, G. walla grows in lowland and lower montane rain forests, and moist seasonalforests, distributed in at least 20 different agro-ecological zones, indicating potential areas forits restoration and domestication. In natural habitats, its populations show a typical reverse-Jpattern, with a higher abundance of juveniles, depicting a stable and self-thinning population.In the ridge-valley catenal landscape of the Sin-FDP, G. walla grows better on the higherwell-drained slopes (490-575 m), compared to the wetter lower slopes (424-490 m). In the25 ha of the Sin-FDP, there were only 338 individuals of G. walla, the largest <50 cm dbhand 67% of the population only between 1-4 cm dbh. The relative diameter growth rate ofindividuals measured in two censuses in the Sin-FDP showed a decreasing trend withincrease in the size of individuals.

These results suggest that extensive removal of large reproductively mature individuals mayadversely affect the future population demography of this threatened species. Investigatingits reproductive ecology and low-cost propagation methods are imperative prerequisites touse G. walla in restoration forestry programs and in domestication, thus reducing pressure onthis rapidly dwindling natural resource.