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Chapter
Species richness, diversity and phytosociology along the elevation gradient Chapter 5
SPECIES RICHNESS, DIVERSITY AND PHYTOSOCIOLOGY ALONG THE ELEVATION GRADIENT
Objectives 1. To analyse the species richness and diversity of riparian forests of Pamba river basin, Kerala based on quadrat method along the elevation gradient. 2. To analyse the phytosociology of riparian forests of Pamba river basin, Kerala based on Braun-Blanquet method along the elevation gradient. 3. To analyse the phenology regeneration status of major riparian trees in the Pamba river basin, Kerala based on vegetation survey and quadrat methods.
5.1 Introduction Riparian plant communities along the rivers are dynamic, species rich (Salo et al., 1986; Kalliola & Phuhakka, 1988; Nilsson, 1991) and sensitive to anthropogenic interference (Malanson, 1993) resulting disturbance adapted communities. Plant communities in these systems are likely to be affected by both longitudinal [i.e. upstream-downstream (Vannotte et al., 1980; Noss, 1983)] and transversal [i.e. stream-floodplain or floodplain-basin (Newbold et al., 198l)] linkages for species recruitment and diversity. The spatial heterogeneity resulting from geomorphological processes is viewed as one of the major causes of high species richness (Hupp, 1988; Gould & Walker, 1997; Ferreira & Stohlgren, 1999). As a consequence of the shifting mosaic of landforms and communities resulting from natural disturbance (Whittaker, 1977), high levels of species richness are usually found along rivers. Studies on species richness patterns in river corridors indicated that total species richness in a river is maximum in the middle reaches (Vannotte et al., 1980). According to intermediate disturbance hypothesis (IDH), intermediate intensity and frequency of disturbance would create the highest diversity (Connell, 1978). IDH has been supported by Huston (1979), Sousa (1979), Pollock et al. (1998) Chapin et al. (2002) even though both negative (Englund, 1991; Wilson & Tilman, 1991) and positive (Tilman, 1983; Philips et al., 1994) linear relationships between diversity and disturbance existed. Nilsson et al. (1989) found such a pattern of species richness for riparian plants in northern Swedish rivers. Planty-Tabacchi et al. (1996) have subsequently described a similar pattern in French and North American rivers, suggesting similarities in underlying processes. Mechanisms proposed to explain this pattern include: (1) intermediate disturbance, or (2) maximum heterogeneity in the most species-rich, middle reaches, and (3) downstream TAXONOMY, DISTRIBUTION AND ECOLOGY OF THE RIPARIAN FLORA OF PAMBA RIVER, KERALA /Ph.D Thesis /Page 199
Chapter 5 Species richness, diversity and phytosociology along the elevation gradient
dispersal of plants (hydrochory) successively building up species richness downstream to the middle reaches, where after riparian substrates become too homogeneous and erosive to allow realization of the potential species richness (Nilsson & Jansson, 1995). In addition, the invasibility of the river corridor has been suggested as a potential pattern-forming mechanism (Renofalt et al., 2005b). Species richness patterns in the riparian corridor change in response to the dynamics of flood disturbance (Renofalt et al., 2005a) but regular moderate flooding is required to sustain high levels of diversity in riparian ecosystems (Naiman & Decamps, 1997). The local species richness has been considered a product of competition, disturbance and niche diversification (Pianka, 1966) which are greatly manifested in the tropics due to high humidity and temperature (Ojo & Ola-Adams, 1996). The relationship between local and regional richness has been analyzed by Caley & Schluter (1997), Cornell & Karlson, (1997) and Karlson et al. (2004). The understanding of internal (river-related) and external control in riparian communities provide the basis for efficient management strategies for biodiversity conservation (Naiman et al., 1993) at the local scale (riparian reaches) or at the regional scale (catchment area and hydrological network). Human activities have been drastically transformed the major rivers of Asia such as Indus, Ganges and Yangtze (Dudgeon, 2000) and are now categorized as threatened ecosystems (Dudgeon, 1992; Johnsingh & Joshua, 1989) due to the loss of species richness. In India, the phytodiversity riparian forests are under threat due to anthropogenic disturbances such as deforestation, overgrazing and land reclamation (Gopal, 1988). The Ganga river has lost 80% of its original forest cover in its basin (Smakhtin et al., 2007). Riparian forests adjoining stream and river banks have been almost entirely eliminated outside the protected areas (Gadgil, 2004). Moreover, there has been no quantitative estimation of riparian diversity in Indian rivers. In Peninsular India, although a few quantitative plant biodiversity inventories are available from the forests of the Western Ghats (Sukumar et al., 1992; Ganesh et al., 1996; Pascal & Pelissier, 1996; Ayyappan & Parthasarathy, 1999; Parthasarathy, 1999, 2001; Muthuramkumar et al., 2006; Davidar et al., 2007) but none of them were in riparian forests except Chalakkudy river (Bachan, 2003), Valapattanam river (Sreedharan, 2005) of Kerala and Cauvery river of Tamil Nadu (Sunil et al., 2010). 200 Page /Ph.D Thesis /TAXONOMY, DISTRIBUTION AND ECOLOGY OF THE RIPARIAN FLORA OF PAMBA RIVER, KERALA
Species richness, diversity and phytosociology along the elevation gradient Chapter 5
The Southern Western Ghats (SWG) region is an important centre for plant diversity and endemism (Ramesh et al., 1997) where the Pamba river basin located. Even though Pamba River has been undergone great materialistic and cultural changes, so far there is no riparian vegetation assessment. The present chapter aims: (1) to analyze the species diversity along the general elevation gradient in the tropical riparian forest of Pamba river basin, Southern Western Ghats, India, (2) to analysis the density, distribution and abundance of riparian trees along the elevation gradient of Pamba river, (3) to determine community structure, stand type, dispersion pattern of riparian trees in the river basin along the elevation gradient and (4) to study the regeneration status of major riparian trees in the Pamba river basin.
5.2 Review of Literature Species richness, diversity and phytosociology of riparian vegetation have been studied in many rivers of America, Europe, Africa and Australia. Significant research on riparian diversity has been conducted by Thompson (1961) in Sacramento River, Tabacchi et al. (1990) in Adour River, Roberts & Ludwig (1991) in Murray River, Baker (1990) and Tiegs et al. (2005) in Colorado River, Nilssion et al. (1994) in Vindel River, Metzger et al. (1997) in Jacare-Pepira river, Salinas et al. (2000) in Andarax River, Rosales et al. (2001) in Caura River, Boutin et al. (2002) in Boyer river, Wassen et al. (2002) in Biebrza River, Johnson (2002) in Missouri River, Heartsill-Scalley & Aide (2003) in La Plata River, Fierke & Kauffman (2005) in Willamette River, Balian & Naiman (2005) in Queets River, Urban et al. (2006) in Macal River, Wittmann et al. (2008) in Miranda River and Molder & Schneider (2011) in Danube River. In Asian rivers, limited riparian diversity studies have been conducted. Sugimoto et al. (1997) studied riparian vegetation of Toikanbetsu River and Nakamura et al. (1997) studied riparian vegetation of Tokachi River. In Indian scenario, riparian vegetation diversity research has been conducted in Tambiraparani River (Johnsingh & Joshua, 1989), Chalakkudy river (Bachan, 2003), Valapattanam river (Sreedharan, 2005) of Kerala, Yamuna river (Chauhan & Gopal, 2005) of Delhi and Cauvery river (Sunil et al., 2010) of Tamil Nadu. None of them discussed the regeneration and phenology of riparian trees. TAXONOMY, DISTRIBUTION AND ECOLOGY OF THE RIPARIAN FLORA OF PAMBA RIVER, KERALA /Ph.D Thesis /Page 201
Chapter 5 Species richness, diversity and phytosociology along the elevation gradient
5.3 Materials and methods The study area and physiography of has discussed in Chapter 2; Section 2.3.1 (Page no.: 25) and Figs. 2.1 & 2.2. The study was conducted during 2007–2012. The voucher specimens of riparian species were collected and identified with standard floras (Hooker, 1872–1897; Gamble & Fischer, 1915–1936; Anilkumar & Sivadasan, 2005) and nomenclature validation with IPNI (2011) and The PlantList (2011). The herbarium specimens were deposited in the School of Environmental Sciences Herbarium, Mahatma Gandhi University, Kottayam, Kerala, India. 5.3.1 Field methods Variation of elevation in meters above sea level (m asl) was considered as an indicator of topographic species diversity and compared between the four stretches. The entire river stretch was divided in to four fragments such as Lowland (abbreviated as LL, 1–7m asl, 10km), Midland (abbreviated as ML, 8–70m asl, 90km), Highland (abbreviated as HL, 71–700m asl, 35km) and Highrange (abbreviated as HR, ≥701m asl, 41km) as equivalent to the general elevation ranges of the Kerala state. The elevation of each stretch and location of quadrat sites were obtained with GPS 72 (Table 5.1). The quantitative data were gathered by nested quadrat method along the elevation gradient, standardized to the length of stretch and natural vegetation in both banks of the river (54 quadrats) (Fig. 5.1). Quadrats of 10×10m for trees, 5×5m for shrubs, climbers and epiphytes and 1×1m for herbs were employed. The sizes of the quadrats for diversity and phytosociology were determined by species-area curve method (Braun-Blanquet, 1932). Species–area curve was plotted for all species, as the sequence of enumeration proceeded i.e., by sequential arrangement of fifty-four 1×1m, 5×5m and 10×10m quadrats. A total of 0.54ha was sampled from the study area. The girth at breast height (GBH) of all trees (≥15 cm) was measured with a measuring tape. The GBH classes of trees were analyzed for vegetation profile and community structure. The arrangement of quadrats for phytosociology has been modified (Fig. 5.3) due to specific topography, linear shape of the ecosystem and floodplain width (ranges from 10– 202 Page /Ph.D Thesis /TAXONOMY, DISTRIBUTION AND ECOLOGY OF THE RIPARIAN FLORA OF PAMBA RIVER, KERALA
Species richness, diversity and phytosociology along the elevation gradient Chapter 5
Fig. 5.1 Study area and quadrat locations of the riparian diversity and phytosociology analysis 30m) in the entire stretches of the river. Community or stand types were analyzed by the Braun-Blanquet table analysis approach (Braun-Blanquet, 1964). Relative frequency classes of trees were noted from the 54 releves (quadrats) in the entire study area along the elevation gradient and constancy table prepared. Total number of individuals, occurrence and relative frequency were considered for analyzing stand type. We excluded herbs, shrubs, climbers, epiphytes and parasites from the phytosociological analysis due to their low relative
Fig. 5.2 Nested quadrat used for the diversity and phytosociology analysis
density in the quadrats studied. Moreover the frequent flood disturbance modifies herbaceous vegetation and woody tree species were persisted to form the dominant component in community. The Braun-Blanquet table analysis approach was also validated with TWINSPAN (Hill, 1979). Regeneration status was analyzed for saplings from the 5×5m quadrats of 54 releves. Tree species with a diameter of
