Ecology Environment And Resource Conservation Js Singh Pdf Download
The dry tropical forests are among the most vulnerable ecosystems of the world and, however, are relatively understudied. These forests provide various ecosystem services, and are progressively being converted into patches of dry scrubs, savanna and marginal cropland systems, due to various anthropogenic perturbations. Soils of these regions are relatively nutrient poor with a patchy nutrient and water distribution pattern. Therefore, the variability in these natural resources imposed by the present climate change scenario may affect the forest plant community of dry tropics via its impact on seedling growth and recruitment. Seedlings are considered as the most sensitive stage of plant lifecycle, and therefore, understanding of seedling regeneration may help in restoration of forest ecosystems. Seedling growth is majorly regulated by various naturally occurring resources (such as light, water, nutrient, etc.) and disturbances (such as defoliation, grass competition, fire, etc.). Therefore, efforts on the regeneration of these forest systems are highly necessitated. In the present study, we critically reviewed the studies on seedling survival and growth under different resource and disturbance regimes with a special focus to dry tropical environment. We found that water, light, nutrients, herbivory, and grass competition majorly regulates recruitments, growth, and establishment of the tree seedling in dry tropical environment. Most of the studies are limited to observe the effect of one or two factors over the seedling survival and growth. However, the resources and disturbances may have an interactive effect over seedling growth. Therefore, studies encompassing the interactions of various growth factors (resources and disturbances) under different climatic conditions are urgently needed for the successful regeneration of tree seedlings and for the restoration of plant community. Moreover, it will improve our ability to manage the tropical vegetation under changing climatic scenario.
ecology environment and resource conservation js singh pdf download
Dry tropical ecosystems experience a more arduous and less anticipated environment, thus resulting into its proneness to environmental stress during the successional process of plant community development (Murphy and Lugo 1986). In India, most of the dry tropical vegetation occur in nutrient poor soils (Singh et al. 1989), which may have a tendency to conserve the nutrients (via immobilization in microbial biomass) and act as potential C sinks (Srivastava et al. 2016). Forest composition in such soils consists of species varying in their life history traits, such as leaf types (i.e., broad-leaved species and fine-leaved species), successional statuses (i.e. pioneer and non-pioneer), N2 fixation ability, tree size, and habitat preference (Chaturvedi et al. 2011). These species, therefore, respond differently to the resource availability and disturbance gradients (Chapin et al. 2003). For example, pronounced spatio-temporal variability in resources, such as light, nutrient (Raghubanshi et al. 1990), and water (Kottek et al. 2006; Singh and Ranade 2010; Chaturvedi et al. 2011, 2013, 2014), as well as the disturbances, such as herbivory (Staver et al. 2009; Chaturvedi et al. 2012; Juan-Baeza et al. 2015) and fire (Russell-Smith et al. 2003; Otterstrom and Schwartz 2006), has been reported in dry tropical environment. Therefore, a better understanding of tree plants, especially seedling response under varying environmental conditions (i.e., resources and disturbances), may hold considerable importance in the restoration of these degrading forest ecosystems.
Several abiotic and biotic growth regulators are known to determine the vegetation structure and composition of dry tropical ecosystems, especially via its impact at the seedling stage of the plant (Fig. 2). These can be broadly classified as: (1) resources, such as water (Reich and Borchert 1984; Chaturvedi et al. 2013; Vadigi 2013; Barbosa et al. 2014), light (Ceccon et al. 2006; Tripathi and Raghubanshi 2014), and soil nutrients (Huante et al. 1995; Ceccon et al. 2006; Chaturvedi et al. 2012; Tripathi and Raghubanshi 2014) and (2) disturbances, such as fire (Khurana and Singh 2001; Otterstrom and Schwartz 2006, Pluchon et al. 2014), herbivory (Higgins et al. 2000; Chaturvedi et al. 2012; Norghauer and Newbery 2014; Juan-Baeza et al. 2015; Torres and Renison 2015), grass competition (Riginos 2009; Ortega-Pieck et al. 2011; Griscom et al. 2014), and atmospheric CO2 (Khurana and Singh 2002). A series of experiments have been conducted across the dry tropical environment, which suggest that tree-seedling survival and establishment are highly susceptible to water stress, nutrient shortage, shade, herbivory, and competition with grasses (Table 1). In the later section of this review, we have given a brief insight on the effect of various resources and disturbances individually as well as interactively on tree-seedling growth and establishment to understand the involved ecology for management perspective under dry tropical environment.
The nutrient poor soils of dry tropical environment generally show strong seasonal variability in nutrient release (Singh et al. 1989; Raghubanshi et al. 1990; Singh et al. 2009; Powers et al. 2015). These soils are characterized by the inherent patchy distribution of nutrient and water availability (Roy and Singh 1994; Chaturvedi et al. 2011). This distribution pattern is also governed by many external factors, such as fire, fertilizer addition, herbivore density, and forest degradation (Elmqvist et al. 2007; Balvanera et al. 2011). Water availability and soil nutrient availability are closely interrelated (Van der Waal et al. 2009; Sardans and Peñuelas 2013). In the presence of grasses, an increase in soil nutrient availability induces water stress, which further leads to a lower growth performance in the tree seedlings (Hu and Schmidhalter 2005, Akıncı and Lösel 2012). Interestingly, a more constrained seedling establishment is reported under higher soil fertility in dry tropical ecosystems. It is attributed to an increased competition of tree seedlings with grasses for t resources in the soil (Kraaij and Ward 2006; Griscom et al. 2005; Sankaran et al. 2008; Van der Wall et al. 2011; Mills et al. 2013). Therefore, it is imperative to consider the impact of soil nutrients under the combined effect of water and grass competitions on tree species recruitment for a holistic understanding of the drivers of tree-seedling growth.
In general, grasses pose severe competition to tree-seedling survival, growth, and establishment (Griscom et al. 2009), mainly by affecting their recruitment (Khurana and Singh 2001; Thaxton et al. 2012). Most of the studies have explained tree-seedling growth with grass in terms of competition for above- (e.g., light) and below-ground resources (e.g., water and nutrients) between them (Hardwick et al. 2000; Hoffmann and Franco 2003). Grasses suppress the seedling growth of tree species due to the depletion of resources (i.e., water or nutrient) under dry tropical environments (Sankaran et al. 2004; Kambatuku et al. 2011). In a study under dry ecosystems, Donzelli et al. (2013) found that grasses compete more for water, whereas trees are the better competitor for soil nutrients. However, studies highlighting the interactive effects of water, light, nutrients, and grass competition on the survival and growth of tree seedling are limited under dry tropical environment (Gerhardt 1996; Cabin et al. 2000; Tripathi and Raghubanshi 2014).
Several experiments on the tree-seedling growth under grass competition in dry tropics have led to two schools of thoughts, depending upon the level of competition. Some studies showed a positive (Duncan and Chapman 2003; Anthelme and Michalet 2009) or negligible effects of grass presence on tree-seedling growth (Scariot et al. 2008). However, other studies reported negative effects of grass presence on growth of tree seedling (Cramer et al. 2007; Hooper et al. 2005; Grellier et al. 2012). Therefore, a dilemma still prevails in the identification of optimal growth condition for various resources under which grass presence either suppresses or facilitates the tree-seedling growth. Tree seedling shows greater mortality during dry season as compared to wet season, which may be attributed to its competition with grasses for nutrient resources (Chirara et al. 1999). On the contrary, under limited or lower resource conditions, grass competition has been reported to have a less negative or even a positive role on the establishment of tree seedling during dry season (Vieira and Scariot 2006a, b; Cardoso et al. 2016). Therefore, field experiments are needed to elucidate these conflicting observations and to understand how grass competition determines the tree recruitment in dry tropical environment under the effect of other set of environmental drivers.
Interaction among the various resources and disturbances has been found to regulate the survival, growth, and establishment of the tree seedlings (Rincón and Huante 1993; Khurana and Singh 2001; Ceccon et al. 2006; Tripathi and Raghubanshi 2014). Therefore, a thorough understanding of this interrelationship would help in a better management of the forests in dry tropical ecosystem. A brief account of the interactive effects of major regulatory variables on the seedling growth has been discussed below with a particular emphasis on dry tropical environment.
As stated earlier, the survival and growth of the tree seedlings are intensely determined by light availability (Rincón and Huante 1993; Poorter 2001; Khurana and Singh 2006; Tripathi and Raghubanshi 2014), nutrient availability (Khurana and Singh 2004; Tripathi and Raghubanshi 2014), and grass competition (Ludwig et al. 2004; Grellier et al. 2012) in the dry tropical environments. The plant diversity and distribution are mainly governed by the interaction among these factors in dry tropical ecosystems (see Table 1). Therefore, studies focusing on this complex interaction would help us to understand how dry tropical tree species responds to variable nutrient availability and grass competition across the irradiance levels. In general, nutrient addition significantly affects plant growth in high light availability than the low light availability (Ingestad and McDonald 1989; Rincón and Huante 1993; Tripathi and Raghubanshi 2014). Above- and below-ground resource competition by grasses may suppress the tree-seedling growth under adequate light conditions (Kambatuku et al. 2011). Moreover, grasses have been reported to facilitate the tree-seedling growth via moderating the microclimatic conditions (Vieira and Scariot 2006a, b; Barbosa et al. 2014; Guarino and Scariot 2014). The interactive grass-seedling growth dilemma still prevails, which further gets impetus under the resource variability. Therefore, studies covering tree-seedling growth under grass competition in the effects of nutrients and light are urgently required under the dry tropical environments for a clear understanding and restoration of such vegetation. 350c69d7ab