Use of Gliricidia sepium as a Nurse Plant to Reforest Man-made Grasslands in the Knuckles Forest Reserve, Sri Lanka

Abstract

Biodiversity richness and socially beneficial watershed services are high in the KnucklesForest Reserve. However, the lower montane forest patches on the eastern slopes of the KFRare highly fragmented mainly due to anthropogenic disturbances. If these forest fragments arenot connected in the near future, they will disappear from the landscape due to their lowregeneration rates. Native tree species when used for restoration of these lands faces manydifficulties due to various biotic and abiotic stresses including harsh microclimatic conditionsand infertile soils. Therefore, usage of a nurse plant will facilitate the growth of target speciesdue to creation of favourable microclimatic conditions. Gliricidia sepium has been used as ashade plant in Sri Lanka, since colonial times. More recently it has been used for indigenousfarming practices, soil stabilization, living fences and as fuel wood, animal forage, greenmanure. In our research we investigate the potential of G. sepium as a nurse plant to establishfour native tree species on man-made grasslands in central Sri Lanka. The study wasconducted on four blocks of grasslands. Four replicates of each of the three island sizes(small 4 m2, medium 16 m2, and large 64 m2) were created inside each block. One set ofislands in each block were planted with G. sepium stakes at 2 m intervals in a grid format.The other set of islands in each block was kept as a control without planting G. sepiumstakes. Seedlings of Macaranga indica, Bhesa ceylanica, Symplocos cochinchinensis andEugenia bracteata were planted randomly in islands with and without G. sepium stakes.

After three months of establishment, the survival rate of G. sepium in the four blocks wasmore than 80% and the survival rate of the G. sepium was 20% higher in the small andmedium islands than the large islands. The mean number of sprouts per stake was more thaneight in medium and large islands and less than six in small islands. The mean survival ratewas higher (5.8%) and the mean growth rates was lower (0.006%) for all the four nativespecies with G. sepium than without G. sepium after three months of planting. G. sepiumincreased the survival rates of native species after three months of establishment due tofavourable microclimatic conditions created by them. However, growth rate of the nativespecies which were planted with G. sepium was lower probably due to interspecificcompetition. Therefore, G. sepium can be used as an effective nurse plant in initial phases ofreforestation programmes to increase the survival rates of native tree species on degradedsubmontane sites in Sri Lanka.