INTRODUCTION Chapter 1

Transcription

1 INTRODUCTION Chapter 1 Forests are the essential part of environment and they always maintain the physical features of an area providing protection to the environment. The forest cover with its floristic diversity is described in many forest types found throughout the globe. Among the different forest types, tropical forests, a store house of biodiversity, accounts for 52% of the total forest area of the world, of which 42% is dry.forest, 33% is moist forest, and 25% is wet and rainforest (Khurana and Singh, 2001). With a decrease in rainfall the wet evergreen rainforest changes into moist deciduous, which with further decrease in rainfall gives way to dry deciduous forest (Khurana and Singh, 2001). Dry forest is next to rainforest in ecological complexity which arises mainly due to strong seasonal and inter-annual variability in rainfall permitting the occurence of equally variable species. The cyclic change in climatic conditions in the tropical dry forest allows seasonal germination and establishment of the species with different consequences in size-age population distribution (Rincon and Huante, 1993). Native species of the forests are able to sense several environmental conditions and restrict their germination and emergence to particular periods of the year and habitat locations for successful establishment and survival (Bell et al., 1999). Knowledge on germination and seedling establishment is of pivotal importance for understanding such community processes as plant recruitment and succession and becomes a boon in the management of plant populations. 1.0 Depletion of forest resources and its biodiversity Ironically at global level forests are being destroyed at a very fast rate through currently in tropics, tropical forests are being lost at an estimated rate of 4-9% annually (Houghton, 1994). India is endowed with large tracts of tropical forest in its typical form in the Eastern Ghats (Ray and Behera, 2002). Now much of the tropical forests are either degraded or have been altered so mush due to human activities. Now we are left with 19.4% of total land area under the forest Cover (State forest report, 1999; Forest Research Institute, Dehradun) as against a mandatory of 33% in plain area. The alarming pace of destruction of the plant habitat resulted in the fragmentation of their population Seedling Growth, Regeneration and Age Structure of Two Dominant Tree Species vis-a-vis Conservation Perspectives of Chandaka Sanctuary 1

2 Introduction Chapter i and genetic flow. Thereby leading to the loss of viability and diversity. The depletion of one species in such ecosystem has led to the loss or migration of several dependent species of flora and fauna. The rapid shrinkage of vegetation wealth is considerably bringing many species to the verge of extinction. Myers et al. (2000) observed that at least one species is lost everyday in tropical forest alone and the situation may worsen to an extent when one species may disappear every hour. The rate of tropical forest loss is so rapid and concentration of world species in these ecosystems so great (Wolfe, 1979) that a significant proportion of all species of plants and animals are likely to become extinct in the next few decades (Myers et al. 2000). Apart from such activities in recent years, tropical forests have been modified into more open secondary forest or Savanna, or have been completely destroyed through different activities like agriculture, mining, various projects etc. The extensive deforestation and habitat conversion is recognized as the biggest factor in the present day biological diversity crisis (May et al., 1995). Recurring disturbances on forest covers through various anthropogenic activities proceed towards the formation of micro-habitats and also promote charges in species composition (Goldsmith et al. 2006; Dense low, 1998), 1.1 Eastern Ghat and the forest covers of Orissa The Eastern Ghat comprises of a chain of mountains in the east coast of India; Geologically it consists of 3 discreted sections i.e., the northern (Nilgiri Orissa), the central (Nalaimalai to near China) and the southern section that runs in a west south west direction meeting the Western Ghats in the Nilgiri, Orissa (Legris and Meher Homji, 1984). The state of Orissa constitutes the northern end of the Eastern Ghat range of India having a diversified topography and includes the districts of Ganjam, Gajapati, Kandhamala (Phulbani), Rayagada, Koraput, Malkanagiri, Nowarangpur, Kalahandi and Khurda. Out of these districts Ganjam, Gajapati, Kandhamala, Rayagada, Koraput, Malkangiri and Kalahandi are covered with thick forest vegetation while the vegetation of Khurda is sparse. Seedling Growth, Regeneration and Age Structure of Two Dominant Tree Species vis-a-vis Conservation Perspectives of Chandaka Sanctuary 2

3 Introduction ' ;, Chapter u As per the classification made by Champion and Seth (1968) a major part of the forest falling within Orissa corresponds to northern tropical dry deciduous type, whereas Chandaka wildlife sanctuary of the state representing a great aesthetic treasure is of the dry deciduous type (Champion and Seth, 1968). The chief feature of this sanctuary is a leafless period in the dry season (March to May). An appreciable number of deciduous trees, however, come into new flush and often flower before the onset of monsoon, when one would expect them to experience water stress. The floor in most places is covered by grasses and annual fire is a common phenomenon resulting in the spread of grass, which becomes heavy and continuous especially where the canopy is open presenting an appearance of tree Savanna. Besides the above characteristic feature, the sanctuary attains a considerable ecological interest due to interspersion of floral and faunal communities. This area is also well known for its fertile soil, moderate climate and a multitude of forest types. Extensive cultivation, lopping and fuel wood collection by local'as well as migratory pasturalists have led to degradation of forest and wildlife habitats. With the advent of India s new national forest policy (1988) the objectives of the forest management have shifted from timber production to biodiversity conservation. To meet this objective it is necessary to collect quantitative information on the vegetation to trace out age structure, regeneration status, survival and relative growth rate of woody perennials in terms of height. Informations obtained from the study of such parameters are helpful towards planning conservation strategies for the future sustainability of the protected areas. 1.2 Age Structure and Regeneration The fragmented and reduced populations of woody perennials in tropical forests that results from human disturbance are issues of growing importance in evolutionary and conservation biology (Sork et al, 2002). So indepth study of demographic stability of tree species in these forests are essential (Sagar and Singh, 2004). If the ratio of various age groups in a population is known, demography can be used to elucidate the current reproductive status and indicate future possible trends of that population (Odum, 1983; Barbour et al, Seedling Growth, Regeneration and Age Structure of Two Dominant Tree Species vis-a-vis Conservation Perspectives of Chandaka Sanctuary 3

4 Introduction Chapter LI 1987; Smith, 1996). A large population of young individuals indicates a rapidly expanding population, a more even distribution of old individuals a declining population (Sagar and Singh, 2004). In trees, circumference at breast height (cbh) is frequently used as a surrogate index forage. Thus cbh is used for demographic analysis or age structure analysis of woody perennials to identify the declining species. In addition to this age structure of woody perennials also depicts about the regeneration behaviour of tree species. Presence of sufficient number of seedlings, saplings and young trees in forest covers signifies about satisfactory regeneration while inadequate number of seedlings and saplings of tree species in a forest indicates poor regeneration (Saxena and Singh, 1984). The successful regeneration of tree species depends on its ability to produce large number of seedlings and the ability of seedlings and saplings to survive and grow (Good and Good, 1972). However the presence of sufficient number of seedlings, saplings and young trees is greatly influenced by interaction of biotic and abiotic factors of the environment (Aksamit et al., 1984). Moreover, the intensity, magnitude and frequency of disturbance also determine the structure and function of plant communities in the forest ecosystem (Armesto, 1985, Khan et al., 1987). Umashankar (2001), Rakthi Duchoke et al. (2005), Singh et al. (1986), Pandey and Shukla (2001) and Ganesan and Setty (2004) have stated that disturbances have a negative impact, disrupting the climax making it unstable. Along with these constraints germination must occur in a limited period of time so that seedlings have fovourable light, nutrients and water conditions to settle. Regeneration is a key process for the existence of species in the community. It is also a critical proof of forest management, because regeneration maintains desired species composition and stocking after biotic and abiotic disturbances (Khumbongmanyum et al., 2006). Various studies on regeneration of threatened and medicinal plants have been carried out in informally managed sacred grooves (Boraiah et al., 2003). The process of seedling development and growth of forest trees largely depend on gaps and canopy openings in the forest created due to natural disturbance. These influencing the regeneration and species composition by tree or limb falls in tropical forests cause a great degree of spatial heterogeneity (Brokow, 1985)). Seedling Growth, Regeneration and Age Structure of Two Dominant Tree Species vis-a-vis Conservation Perspectives of Chandaka Sanctuary 4

5 Introduction Chapter 1.3 Growth and survival of tree seedlings Spatial heterogeneity in environmental conditions affect the growth and survival of tree seedlings, which may act as filters that differentially affect tree species (Harper 1997). Environments favouring seedlings of particular species might function as regeneration niches that promote species coexistence (Grubb, 1977; Pacala and Roughgarden, 1982; Huston 1994; Pacala and Tilman, 1994; George and Bazzaz, 1999a. b).however, the potential for spatial heterogeneity in microenvironments to maintain forest diversity depends on interactions of different sources of heterogeneity across spatial scales. Fine-scale variability (less than one square meter) in environmental conditions in the forest understory is superimposed on coursescale (greater than one square meter) Variability represented by decrease in canopy cover or other large disturbances. Reduction in canopy cover, resulting from the death of overstory trees either due to natural way or due to anthropogenic activities can increase the levels of light in the forest understory (Pearcy, 1983; Canham, 1988, Denslow etal., 1990, Pacala etal.,.1994), all of which may limit seedling growth and survival. However, the forest understory further modifies resource heterogeneity at the seedling scale (Korstian and Coile 1938, Harmon and Franklin, 1989; Veblen, 1989; Facelli, 1994; Lorimeretal., 1994; Berkowitz et ah, 1995; George and Bazzaz, 1999a. Interactions between heterogeneity in the forest overstory and understory microenvironments may affect seedling performance, subsequent community composition, and the potential for species coexistence (Beckage and Clark, 2003; Beckage et al., 2000, Heinemann et al., 2000). The presence of canopy openers understory interactions could influence both the seedling competitive environment and the nature of the resource limitation on seedling growth and survival. For example, understory herbs, ferns, and shrubs may increase in response to high light availability in canopy gaps and may compete with tree seedlings. Conversely, microenvironments characterized by high mineral nutrients or soil moisture may have disproportionate effects on seedling performance in high light environments, e.g., canopy gaps, and little effect in light-limited environments, e.g., closed canopy, (Denslow et al., 1998, Fahey Seedling Growth, Regeneration and Age Structure of Two Dominant tree Species vis-a-vis Conservation Perspectives olchandaka Sanctuary 5

6 Introduction Chapter 8 et al., 1998, Coomes and Grubb, 2000). Tolerance of low light levels may be enhanced by environmental conditions such as increased moisture (Coomes and Grubb 2000). Performance of seedlings also depends on resource availability and their physiological ability to efficiently use the higher level of resources present in open Canopy areas than the close canopy areas (Brokaw, 1985). The recruitment, survival and growth pattern of tree seedlings both in open and close canopy of tropical forests have been studied in different parts of the world (Denslow, 1980). Recruitment and survival of naturally emerging seedlings of some woody species of tropical forests both in the open and close canopy areas have also been studied by several workers in India (Rao et al, 1997; Khumbongmayum et al, 2005; Ganesan and Setty, 2004). But very limited information is available on such type of studies in eastern ghat regions of Orissa, Moreover no such studies have been reported so far from the Chandaka Wildlife Sanctuary. Taking various ecological aspects of Chandaka Wildlife Sanctuary into account the present investigation has been made to study the phytosociology, regeneration status, age structure, growth and survival of two important tree species of the Sanctuary. 1.4 Aim and Objectives of the Study In order to carry out a thorough study on regeneration, seedling growth and age structure of two dominant tree species in Chandaka Wild life Sanctuary in relation to long term conservation strategy the following objectives have been set. 1. To measure the degree of disturbance and selection of dominant tree species of Chandaka sanctuary. 2. To study the spatio-temporal changes in forest cover and its density in side the sanctuary using Remote Sensing (RS) and Geographical Information System (GIS). Seedling Growth, Regeneration and Age Structure ol Two Dominant Tree Species vis-a-vis Conservation Perspectives of Chandaka Sanctuary 6

7 Introduction ; _ " Chapter i 3. To examine the regeneration potential of some woody tree species under controlled and natural condition to develop relationship with species distribution pattern. 4. To see the rate of transfer of seedling of dominant tree species to next stage at the disturbed and undisturbed sites of the sanctuary. 5. To study the physicochemical parameters of the sanctuary. 6. To study tree, shrub, and herb diversity of the sanctuary. 7. To see the effect of anthropogenic activity on physical and chemical characteristic of soils both in regenerating and natural forest stands of the sanctuary. 8. To explore the anthropogenic factors responsible for their changes & their degree of impact. 9. To verify the survival percentage and growth rate of two dominant trees. Seedling Growth, Regeneration and Age Structure of Two Dominant Tree Species vis-a-vis Conservation Perspectives ofchandaka Sanctuary 7