Kirigala forest fragments and the identity as a dipterocarp plantation or Hora Kele of Ingiriya

Iadn Dilrukshi,Smw Ranwala

doi:10.4038/jnsfsr.v44i3.8012

Abstract

Fragmentation has exposed the Kirigala forest to the influence of various neighbourhood land-use practices. The present study investigated the floristic, soil and micro-climatic conditions of the forest and demonstrated its degradation due to influences by human induced disturbances. Ten 50 m × 5 m gradsects each accommodating 3 pairs of 10 m × 5 m plots, a total of 60 soil samples and 20 seed traps provided floristic details, seedling emergence from seed bank and annual seed rain of the forest, respectively. Diversity of the edge and the forest interior were compared for the different neighbourhood land use types using the Shannon and Weiner (H) and Simpsons reciprocal (D) indices. Change in the forest structure was illustrated using profile diagrams. Differences in soil pH, soil moisture, nitrogen, available phosphorous and potassium, organic matter content, air temperature, humidity and light intensity between the forest edge and the interior were determined. Soil, microclimate and species richness were combined for clustering of similar areas. The site reported the presence of 55 tree, 12 shrub, 15 herb, 07 climber and 02 vine species including a total of 23 endemic species and 06 invasive species. A higher diversity was observed at the edge, and the highest was observed beside roads as indicated by both diversity indices H and D. Soil and microclimate of the forest varied significantly between the edge and the interior and reflected anthropogenic influences and neighbourhood land use practices. Dominance hierarchy of the trees was Dipterocarpus zeylanicus > Gaertnera vaginans > Aporusa lanceolata , while that for undergrowth/shrubs herbaceous species was Ochlandra stridula > Dracaena thwaitesii > Piper sylvestre . Annual seed rain contained propagules of 23 plant species, while invasive Alstonia macrophylla provided the highest density of seeds. Establishment of foot paths, selective removal of juveniles by root-balling technique and encroachment for crop cultivation have also facilitated the degradation process. It is vital to pay attention on maintaining the ecological stability of this forest before it loses its identity as the Hora Kele of Ingiriya.

Highlights

Forest fragmentation is considered as a major threat that challenges the conservation of biodiversity (Collinge, 1996; Echeverria et al, 2006; Dixo et al, 2009; Tawatao et al, 2011)
Important value and rank abundance curves were developed for trees, through which the dominance hierarchy of climax and colonising rainforest species DQGWKHLUIDPLOLHVZHUHLGHQWL¿HG,PSRUWDQWYDOXHLQGH[ (IVI) was calculated using IVI = RF + RD + RC where, relative frequency (RF) = frequency of one species / total frequency of each species × 100, relative density (RD) = density of one species / total density of all species × 100 and relative basal cover (RC) = basal cover for one species / total basal cover of all the species × 100 (Krebs, 2005)
Age structure analysis of the three most important woody species were constructed, while analysis of variance (ANOVA) was carried out using Minitab YHUVLRQWRLGHQWLI\WKHVLJQL¿FDQWYDULDWLRQDPRQJ the abundance of seedlings, juveniles and adult trees in WKH HGJH í P DZD\ IURP ERXQGDU\ DQG LQWHULRU íPDZD\IURPERXQGDU\RIWKHIRUHVW,QRUGHU to calculate the IVI for herbaceous species, density was considered as the sum of the Braun Blanquet scores / total number of quadrats, while frequency was calculated as the percentage occurrence of species

Summary

Introduction

Forest fragmentation is considered as a major threat that challenges the conservation of biodiversity (Collinge, 1996; Echeverria et al, 2006; Dixo et al, 2009; Tawatao et al, 2011). It creates an abrupt transition between ecosystems and exposes closed forest habitats to neighbourhood land uses directly affecting forest resources and its services (Murcia, 1995; Broadbent et al, 2008; Pokhriyal et al, 2010; Porensky & Young, 2013).

Methods

Results

Discussion

Conclusion