The Impact of Forest Conversion to the Avifaunal Diversity in Northern Flank of Knuckles Mountain Forest Range

Abstract

Most of the natural forests throughout the world have been converted to human land-uses inrecent decades. Such conversions have affected the forest biodiversity at different levels.Knuckles mountain forest range (KMFR) in Sri Lanka that has been designated as a worldheritage site for its high level of biodiversity is heavily disturbed and fragmented due tovarious human activities mainly tea and cardamom plantation. In the present study the birdspecies richness, abundance and similarity of bird species composition were investigated inthree prominent agricultural land-uses i.e. Pinus, cardamom and abandoned tea plantations,and in an undisturbed sub-montane forest in Northern Flank of KMFR. Also vegetationstructure of each land-use type was studied to assess the significance of vegetation structuralcomponents (tree density, tree height, canopy cover, vertical stratification, herbaceous cover)to the avifaunal diversity.

Bird sampling was carried out between March and September, 2012 using the fixed radiuspoint count method. Each land-use type had 28 point count stations that were sampled bymeans of 10 minutes recording session. Point counts were taken between 6.00 to 9.30 am and3.30 to 5.00 pm. A total of 1,023 individuals belonging to 51 bird species were observedduring the study. The Pinus and abandoned tea plantations supported a fewer number of birdspecies than undisturbed forest (One-way ANOVA; p<0.05), but the cardamom plantationwith diverse, native shade trees, had a bird species richness comparable to undisturbed forest(One-way ANOVA; p>0.05). Relative abundance of birds in undisturbed forest wassignificantly higher than in abandoned tea plantation, but was significantly lower than incardamom plantation (One-way ANOVA; p<0.05). Jaccard index (Cj) has shown thatavifaunal species composition had higher similarity between undisturbed site and cardamomplantation site (Cj=0.56), compared to abandoned tea plantation (Cj=0.28) and Pinusplantation (Cj=0.19).

Of the vegetation variables considered, canopy cover and the vertical stratification has astrong positive linear effect on the bird species richness (canopy cover; r = 0.738, verticalstratification; r = 0.813). It can be concluded that although the conversion of forests couldsignificantly affect the avifaunal diversity and its composition, cardamom plantations couldplay an important role in the conservation of bird species. However, further studies areneeded to understand its long-term potential to sustain similar bird composition and richness.