Introduction

Sacred groves are segments of the landscape, containing trees and other forms of life and geographical features, that are delimited and protected by human societies because it is believed that retaining them in a relatively undisturbed state is an expression of an important relationship with the divine or with nature (Hughes and Chandran 1998). The role of these natural sacred sites is attracting increasing interest in international organizations such as UNESCO and the World Wide Fund for Nature. International Union for Conservation of Nature and Natural Resources (IUCN) treats sacred groves under sacred natural sites (SNS) which can be clarified as “natural areas of special spiritual significance to peoples and communities. They include natural areas recognized as sacred by indigenous and traditional peoples as well as natural areas recognized by institutionalized religions or faiths as places for worship and remembrance” (Oviedo et al. 2005).

Sacred groves per se, as protected patches of natural vegetation, assumed increasing importance with the arrival of agriculture. Rapid spread of agriculture and pastoralism necessitated clearance of vast stretches of primeval forests. The fear of offending the gods of nature and the adverse consequences of forest clearance in the form of soil erosion, drying of watersheds, impoverishment of biodiversity, changes in microclimatic conditions and pest pressures propelled the emergence of sacred grove-centered worship. Groves existed in the past or continue to exist today in many parts of the world, among people with many religions and forms of social and economic organization. Groves were preserved in the name of gods in ancient Asia, Africa, Europe, America and Austro-pacific region (Hughes and Chandran 1998).

Throughout history, many people customarily respected sacred groves. These were sections of forest where spiritual beings were believed to reside, and where ordinary activities such as tree felling, gathering of wood, plants and leaves, hunting fishing, grazing of domestic animals, lowing or harvesting of crops, and building ordinary dwellings were prohibited (Hughes and Swan 1986).

Sacred grove culture in India has pre-Vedic roots. The Vedic people personified elemental forces of nature as divinities but had no association with sacred grove culture of non-Vedic inhabitants (Chandran 2005). The pan-Indian distribution of groves is a subject of great interest to biologists, social scientists, anthropologists and policy makers because groves represent a variety of ecosystems, social and ethnic identities, management regimes, legal tenures, and cultural traditions. Groves in Indian states/regions number in the hundreds or thousands (Malhotra et al. 2001).

The scientific community today recognizes this tradition as one of the tenets of sustainable use of natural resources. The spiritual ties that humans established from ancient times with prime patches of forests ensured not only the long-term subsistence interest of local people but also protected the dynamics of local ecosystems.

The term “biodiversity” is defined as “the variability among living organisms from all sources, including terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.” (Anonymous 2001). Biodiversity study can be of many types, including inventory and documentation, diversity assessment, population status and ecology, management and threat. Biodiversity can also be linked with ecosystem dynamics, social-cultural-religious practices and ethnic identity. Our focus is on biodiversity studies from the biologist’s perspective.

Biological studies of the sacred groves of India got a fillip with the pioneering work of Gadgil and Vartak (1975, 1976, 1980). For the first time the groves were studied in a holistic way encompassing biological, ecological and socio-cultural perspectives.  In subsequent years, a huge volume of literature was produced on sacred groves and natural sacred sites encompassing various facets. However, literature on biodiversity is to some extent limited because the regional or local characteristics of groves are often of interest to limited audiences.  Moreover, check lists of flora and fauna that are available for many groves list species inventories but provide little detailed understanding of biodiversity. Therefore, for comprehensive review one must depend on publications that are widely circulated through public/scientific communication systems and that follow scientific and logical criteria.

There are some interesting reviews on sacred groves of India, emphasizing biodiversity conservation (especially on floral aspects), natural resource management, cultural and conservation values but details of biodiversity and ecology are not yet covered (Chandrashekhara et al. 2011; Khan 2008; Kushalappa et al. 2005; Ormsby and Bhagwat 2010). In this review, we compiled all major publications on biodiversity assessment of sacred groves in India. We focused on the roles of groves in rare and/or endemic species conservation, economic potential and ecological processes. Our review is based on Indian groves but discussion of the biological and ecological importance of these relic forest fragments is pertinent for any region of the world. Along with well designed scientific studies, general observations have also been recorded especially on ecological issues. This review will hopefully prompt researchers to explore new areas in sacred grove studies and attempt to describe functional aspects and ecosystem services, using well-designed, locality-specific methods.