Accepted Manuscript The impact of forest conversion on bird Communities in Northern Flank of Knuckles mountain forest range, Sri Lanka K. Subasinghe, A.P. Sumanapala, S.R. Weerawardhena PII:
S2287-884X(14)00045-4
DOI:
10.1016/j.japb.2014.07.004
Reference:
JAPB 29
To appear in:
Journal of Asia-Pacific Biodiversity
Received Date: 27 June 2014 Revised Date:
24 July 2014
Accepted Date: 24 July 2014
Please cite this article as: Subasinghe K, Sumanapala AP, Weerawardhena SR, The impact of forest conversion on bird Communities in Northern Flank of Knuckles mountain forest range, Sri Lanka, Journal of Asia-Pacific Biodiversity (2014), doi: 10.1016/j.japb.2014.07.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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The impact of Forest Conversion on Bird Communities in Northern Flank
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of Knuckles Mountain Forest Range, Sri Lanka
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K. Subasinghe*, A. P. Sumanapala , S.R. Weerawardhena,
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Department of Zoology, University of Kelaniya, Sri Lanka
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Manuscript type: Original Paper
Corresponding author: K. Subasinghe
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E-mail:
[email protected] Postal address: No. 258, Wedamulla lane, Kelaniya 11600, Sri Lanka. T.p: +94112910641/ +94779319100
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Abstract
The consequence of forest conversion into human land-use systems on tropical biodiversity is needed to be assessed in order to initiate proper conservation and management
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strategies. In this study the bird species diversity and composition were characterized along with the vegetation structural components in four land-use types in Northern Flank of Knuckles mountain fore range, which is a part of one of the world heritage site in Sri Lanka. This includes three human modified land-uses (cardamom, pinus and abandoned tea plantations), and an undisturbed forest. A total of 1,023 individuals belonging to 51 bird
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species were recorded using fixed radius point count method. The cardamom plantation with native shade trees, had a bird species richness and composition comparable to undisturbed
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forest (One-way ANOVA; p>0.05, Jaccard index Cj= 0.56). Overall species diversity in terms of Shannon Wiener index was highest in undisturbed forest. Pearson’s correlation coefficient suggested a strong positive linear relationship between bird species richness with canopy cover (r = 0.738) and vertical stratification (r = 0.813). This study reveals that the land-use systems formed with considerable alterations to vegetation structure significantly reduce the bird diversity and supports a bird community less comparable to undisturbed
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forest.
Key words: Bird species richness, Canopy cover, Cardamom, Point count method, Pinus,
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Vegetation structure.
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Introduction
Much of the natural forests throughout the world have been destroyed and converted to human land-uses in order to meet the ever growing demands for resources (FAO, 2012).
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Consequently, most of the remaining forest landscapes are with mosaic of human modified land-areas such as urban, agricultural and plantation lands. The conditions of these land areas are highly deviated from its previous undisturbed state.
Although the rate of loss of forest cover has slowed compared to the period of 1990–
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2000 (FAO, 2011), it is still occurs at an alarming rate (net annual loss of the world’s forests was 6.4 million ha between 2000 and 2010) which need a concerted effort to slow or reverse the trend. Most of the tropical forests that contain a large amount of world’s biological
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diversity are still being cleared for agricultural purposes and also for timber industry. Today forest plantations have established all around the world to compensate forest loss through agricultural and other anthropogenic disturbances which also have became a major contributor to local and global economies. However, most of these plantations that have established using tree species with fast growth rates greatly differ from the naturally
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regenerated forests in both composition and structure leading to different ecological processes and thereby different functional outcomes (Davis et al. 2012). It is clearly evident, that the conversion of natural forests into human land-uses
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negatively affects the rich biodiversity associate with forest ecosystems (Holloway, 1996; Houlahan and Findlay, 2011; Lupatini et al. 2012; Meijer et al. 2011; Pekin and Pijanowski, 2012; Pimm et al. 2006) and this trend is likely to continue with the rapid growth of
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population that results in increasing demands for forest resources. According to Birdlife International (2013), two-thirds of bird species are found in forests and much of them are restricted to forest ecosystems. Forest conversion has been identified as a factor that poses a major threat to the substantial number of bird species, as such it can destroy and degrade the habitats of species via reducing available food sources, roosting and nesting places and as well as restricting the movements. However, not all bird species are equally vulnerable to forest conversions (Sekercioglu et al. 2002; Sodhi et al. 2004). Rare and restricted range birds, rainforest habitat specialists and altitudinal migrants are more susceptible to habitat alterations than generalists (Raman, 2001). Several studies have shown that some of the human land-uses hold a considerable biological diversity. Agro-forestry systems such as 2
ACCEPTED MANUSCRIPT shade coffee (Coffea arabica) and cacao plantations (Theobroma cacao) shown to support greater number of forest birds species with higher diversity than open agricultural systems with few or no trees (Estrada et al. 1997; Greenberg et al. 1997; Petit et al. 1999). This has lead to a doubt how vital are to incorporate human land-uses in conservation planning. The Knuckles mountain forest range (KMFR) in Sri Lanka, which has been declared
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as a World heritage site for its rich biodiversity (UNESCO, 2012), was severely impacted by the economic trends over the past several decades. Some parts of the forest within the range had been cleared to cultivate coffee and subsequently to grow tea at the middle of last century (Gunawardane, 2003). Since the climatic condition in this forest range is favorable for
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cardamom plantation, several planters also engaged in under-planting of cardamom where they remove quarter of the over-story of the natural forest (Abeygunawardena and Vincent,
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1993). This under-planting had become a bigger threat to the forest range in 1960 when the government authorized individuals and groups to grow cardamom. With the initiation of new reforestation policies in 1960s a number of pinus plantations were established around the range (Medawatte et al. 2008). Several attempts have been made to analyze the differences in ecological functions and diversities in these human land-uses and undisturbed forest
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(Dharmaparakrama, 2006; Nizam, 2011; Weerakoon et al. 2010).
Present study reports on bird communities in four land-uses in Northern Flank of KMFR: 1. the undisturbed sub-montane forest (the type of forest formation common to the selected altitudinal range) 2. cardamom plantation 3. abandoned tea plantation 4. exotic pinus
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plantation. Thereby assess differences in bird community structure in terms of bird species richness, species diversity and species similarity. Also this study investigates the structural components of vegetation in all selected land-uses in order to examine the influence of each
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component to species richness of birds.
Materials and methods Study area This study was conducted in Northern region of KMFR. The study area was restricted to an elevation range of 600 to 1300 m asl which is the range specific to sub-montane forest vegetation (Bambaradeniya and Ekanayake, 2003). The study area consists of a continuous 3
ACCEPTED MANUSCRIPT and fragmented sub-montane forest, commercial plantations of pinus, cardamom, abandoned tea plantation and small patches of eucalyptus plantations. This study focused on the prominent human land-use types within the study area i.e. (1) cardamom plantations, (2) pinus plantations, (3) abandoned tea plantations and as well as the (4) sub-montane forest as unmodified land-use. The map of study location is given in Fig. 1.
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Figure 1: Map of the study area Bird sampling
Bird sampling was carried out during March 2012 to September 2012. A standard
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fixed radius point-count method (Ralph et al. 1995) with the radius set at 25 m was used to sample birds in all modified land-uses and undisturbed sub-montane forest. Sampling was
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carried out for three consecutive days in the months of March, April, June and September. In each visit a similar number of point count stations were sampled from each land-use type. A total of 28 point count stations were established within each of the four land-uses. All stations were established with a distance of 100 m from one another and 100 m from the edge of the each land-use. Sampling stations were visited between 0600 and 0930 in the morning and 1530 and 1700 in the evening. Each station was surveyed for 10 minutes period and all the
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birds detected visually were recorded to the species level using Harrison (1999) and Kotagama and Ratnavira (2010). The detected but doubtful, uncommon or rare bird species
were marked and identification was confirmed subsequently by the acoustical and visual
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recordings. Any flying birds that were not seen to take-off from the point count station were excluded from analysis. No surveys were made on rainy or windy days. Bird counting was
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not repeated on any of the point count station (Ralph et al. 1995). Vegetation sampling
To describe the vegetation structure of sub-montane forest and the human land-uses,
eight 10 × 10 m subplots were established in eight randomly selected point count station of each plantation type and forest. Vegetation variables were estimated in each subplot and then averaged for each land-use type. In each subplot, every tree with a diameter at breast height (dbh) greater than 10 cm was counted for tree density. Tree height was visually estimated within each subplot. A digital rangefinder was used to improve the estimates of tree height (Van Bael et al. 2007).
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ACCEPTED MANUSCRIPT Vertical stratification (distribution of foliage at different vertical levels) was assessed in 16 points by recording presence of foliage in height classes (in metres) of 0-1, 1-2, 2-4, 48, 8-16, 16-24, 24-32, and >32 in an imaginary vertical cylinder of 0.5 m radius around the observer (Sidhu et al. 2010). This was measured using two transects established along the center of the point count station with an interval of 5 m. Canopy cover was assessed using a
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sighting tube with a single central cross-wire (Ganey and Block, 1994; Goodenough and Goodenough, 2012). At each two meter point along the same transects, the observer looked directly overhead through the tube and recorded whether or not the crosshair intercepted overhead foliage (Ganey and Block, 1994). The result of each individual measurement is
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recorded as 1 if the crosshair intercepted and 0 otherwise. Canopy cover is then estimated as the percentage of points intercepted. Percentage of herbaceous cover (non-woody vegetation
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with height < 1 m) was measured using the point quadrat method (Sutherland, 2006). Data analysis
One-way ANOVA followed by the Tukey Test was used to compare species richness and relative abundance (number of individuals per point count station) among undisturbed forest and human modified land-uses after testing the normality of data sets using Anderson
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Darling test. Statistical analysis was conducted using MINITAB 14 statistical software. Shannon-Weiner diversity index (H´) was used to characterize bird species diversity in all land-uses. Jaccard coefficients (Cj) were used to study the similarities of bird species composition between human modified land-uses and the undisturbed sub-montane forest
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(Magurran, 2004).
The average number of strata with foliage across 16 points within each point count
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station was obtained to estimate the vertical stratification. Pearson correlation was performed in order to evaluate the relationship between bird species richness and each of the vegetation variable assessed. For that, only the bird community data obtained from the eight point count stations that have selected to determine vegetation structural attributes were considered.
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Results
Bird richness and diversity A total of 1,023 birds belonging to 51 species arrayed among 27 families were
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recorded on all point count stations during the study. From these, 11 species were endemic to Sri Lanka. Out of the 51 species recorded, 31 bird species were recorded from sub-montane forest whereas 33 bird species were recorded from the cardamom plantations. Only fewer number of bird species were recorded from abandoned tea plantations (13) and pinus plantations (20). The number of bird species recorded per point count station from the
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undisturbed forest was not significantly different from the number recorded from cardamom plantation (One way ANOVA; p>0.05), but was significantly higher than the pinus or
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abandoned tea plantations (One way ANOVA; p
