Effect of gliricidia sepium on establishment of native tree species at Knuckles Forest Reserve, Sri Lanka

Abstract

The steep slopes covered with lower montane forests of the Knuckles Forest Reserve (KFR), were exploited for plantation of coffee and tea during the colonial era. At present, the lower montane forest patches on the eastern slopes are highly fragmented. These isolated forest patches are frequently interspersed with grasslands with poor regeneration potential. Reforestation of these grasslands using native tree species is difficult mainly due to harsh microclimatic conditions prevailing in them. Studies have shown that amelioration of microclimatic conditions by nurse plants facilitate the growth of target plant species in degraded lands. Therefore, we hypothesize that the use of 𝘎𝘭𝘪𝘳𝘪𝘤𝘪𝘥𝘪𝘢 𝘴𝘦𝘱𝘪𝘶𝘮 ((Jacq.) Kunth ex Walp.) as a nurse plant would facilitate the initial growth and establishment of native tree species in degraded grasslands at KFR. A field study was conducted using three different island sizes (4, 16 and 64 m²). One set of islands were planted with 2 m long 𝘎. 𝘴𝘦𝘱𝘪𝘶𝘮 stakes at 2 m intervals in a grid format. The other set was planted without 𝘎. 𝘴𝘦𝘱𝘪𝘶𝘮 (control). In all treatment and control islands, seedlings of 𝘔𝘢𝘤𝘢𝘳𝘢𝘯𝘨𝘢 𝘪𝘯𝘥𝘪𝘤𝘢 Wight, 𝘉𝘩𝘦𝘴𝘢 𝘤𝘦𝘺𝘭𝘢𝘯𝘪𝘤𝘢 (Arn.) Ding Hou, 𝘚𝘺𝘮𝘱𝘭𝘰𝘤𝘰𝘴 𝘤𝘰𝘤𝘩𝘪𝘯𝘤𝘩𝘪𝘯𝘦𝘯𝘴𝘪𝘴 (Lour.) S. Moore and 𝘌𝘶𝘨𝘦𝘯𝘪𝘢 𝘣𝘳𝘢𝘤𝘵𝘦𝘢𝘵𝘢 ((Willd.) Roxb ex DC.) were planted randomly at 1 m intervals. Survival, height, number of leaves per seedling in transplants and the survival, height and number of sprouts in 𝘎. 𝘴𝘦𝘱𝘪𝘶𝘮 stakes were recorded.

After six months of establishment survival rates of 𝘚. 𝘤𝘰𝘤𝘩𝘪𝘯𝘤𝘩𝘪𝘯𝘦𝘯𝘴𝘪𝘴 (14.06 %, P = 0.012, F = 12.79), 𝘉. 𝘤𝘦𝘺𝘭𝘢𝘯𝘪𝘤𝘢 (15.62 %, P = 0.008, F = 15.00) and 𝘔. 𝘪𝘯𝘥𝘪𝘤𝘢 (12.62 %, P = 0.025, F = 8.76) were significantly different between the 8 m² islands with 𝘎. 𝘴𝘦𝘱𝘪𝘶𝘮 than without 𝘎. 𝘴𝘦𝘱𝘪𝘶𝘮. Relative growth rate in height (RGR) of the four tree species in treatment and control islands were not significant after six months of establishment. However, RGR of 𝘚. 𝘤𝘰𝘤𝘩𝘪𝘯𝘤𝘩𝘪𝘯𝘦𝘯𝘴𝘪𝘴, 𝘉. 𝘤𝘦𝘺𝘭𝘢𝘯𝘪𝘤𝘢 and 𝘌. 𝘣𝘳𝘢𝘤𝘵𝘦𝘢𝘵𝘢 were higher in 2 m² islands with 𝘎. 𝘴𝘦𝘱𝘪𝘶𝘮 than without 𝘎. 𝘴𝘦𝘱𝘪𝘶𝘮. The higher survival and growth rates of native tree species under 𝘎. 𝘴𝘦𝘱𝘪𝘶𝘮 at the initial stages of establishment is probably due to the amelioration effect of the microclimatic conditions by 𝘎. 𝘴𝘦𝘱𝘪𝘶𝘮 in the grasslands. Our research indicates the potential use of 𝘎. 𝘴𝘦𝘱𝘪𝘶𝘮 as an effective nurse plant in initial stages of reforestation efforts on highly degraded grasslands.