- While reports by Forest Survey of India indicate a largely stable forest cover in the country, there are micro-scale changes in Indian forests, like tree species lacking in regeneration in large parts of their natural habitat, that are being overlooked.
- The causative factors for poor tree regeneration are a combination of human over-use, climate change and forest management itself, says the author in this commentary.
- It is becoming evident that regeneration of key tree species needs to be studied in more detail using surveys in different forest biomes of India.The first step to securing the future of forests is to record and understand such changes, and incorporate this knowledge into mapping, restoration and afforestation activities.
- This post is a commentary. The views expressed are those of the author, not necessarily Mongabay.
With the growing impacts of climate change, forest denotification and land use changes, one can ask the question: will our forests survive the next fifty years? But it is also pertinent to ask: what kind of forests will survive? With the growing debates on ‘greening’ and ‘re-greening’ of India, such questions have lately become very relevant.
While reports by Forest Survey of India indicate a largely stable forest cover in the country, there are micro-scale changes that are being overlooked in our debates. For instance, there is increasing evidence that several tree species are lacking in regeneration in large parts of their natural habitat – showing poor levels of seed germination and sapling survival. This is significant for a number of reasons. One, the forest tree assemblages of the future may be very different from those existing today, as many of these vulnerable species will not be adequately replaced. Second, several animal species, including endangered ones, are likely to be affected, as native trees provide critical resources for food and nesting.
Two ecological processes are at stake – the germination of seeds into seedlings and the subsequent growth of saplings into sub-adult stages (that are likely to become mature adults). Seeds of most tree species need a minimal level of soil nutrients, adequate soil moisture and tree shade to germinate. Additionally, many trees may require dispersers such as hornbills or civets who eat the seeds, which then germinate better due to breakdown of the seed-coats. It is important to note that large-seeded species are particularly vulnerable to germination failure under changed conditions, as they require more humidity than small seeded species, as well as animal dispersers.
For the tiny seedlings to then grow into robust saplings, they need sufficient soil moisture and require intermediate levels of sunlight in order to put out leaves. Seedlings also require protection from fire, extreme heat conditions, and anthropogenic disturbances (such as grazing or trampling) in the early stages. Thus, both climate change and human interference can result in regeneration failure.
While visiting the remaining tracts of natural forest in the Haryana Aravalli Hills, such regeneration failure immediately become visible. Sunil Harsana, an ecologist who is working on forest restoration in Mangar Bani, says that there has been a dramatic loss of a number of tree species during the last two or three decades, and the change has been rather sudden. This list includes palash (Butea monosperma), black siris (Albizzia lebbeck), marodphalli (Helicteres isora), drumstick tree (Moringa oleifera) and the khejdi (Prosopis cineraria), all of which are native to the dry deciduous forests of the Aravallis.
According to the village elders, too, all of these species were abundant earlier. Today, there are hardly any saplings or even adults to be seen of these species. In contrast, the invasive vilayati kikar (Prosopis juliflora), which was earlier planted by the government in degraded areas, spreads easily into native forests, taking up the gaps created by disturbances of various kinds.
About 50 km east, in the forests of Sariska Tiger Reserve, similar processes seem to be at work. These forests represent an eastern continuation of the tropical dry forest biome of Haryana. In 2004-2005, as part of research with Wildlife Conservation Society-India Programme and Wildlife Protection Society of India, we conducted vegetation sampling over two hectares of our sampling, in 90 separate plots that were located across the entire core zone of Sariska Tiger Reserve. We found only 274 tree saplings in the sampled area, as compared with 213 adult trees (>20 cm gbh). Further there were no saplings of wild ber (Zizyphus mauritiana) or of palash (Butea monosperma), both of which were well-represented as adults. Ronj (Acacia leucophloea) was another otherwise common tree species in this area, which showed poor regeneration – only 4 saplings for 24 adults. Thus, there is extreme lack of seed germination and sapling recruitment in historically worked forests such as Sariska, which have now been well-protected for over 50 years. Such forest conditions can result in low herbivore densities in future, particularly as many disturbed areas are now covered by vilayati kikar (Prosopis juliflora).
Based on field knowledge, I believe that the causative factors for poor tree regeneration are a combination of human over-use, climate change and forest management itself. The soil and the other vegetation factors may be aggravated by the changing rainfall patterns throughout India, particularly in the dry forest zone of the Aravallis. Due to repetitive human intervention, such as leaf extraction and livestock grazing, the soil tends to get compacted. Compacted soil is unable to absorb rainfall in the same way as in a forest with an organic leaf litter layer. Prolonged drought and heightened temperatures in recent times, further reduce soil moisture and ambient humidity. In areas subject to frequent fires, forest soils are subjected to drying over a short timespan, affecting seedlings and sapling growth. Even if germination takes place abundantly in the post-monsoon period, the survival of the tiny seedlings over the next one year is often compromised, as they are critically dependent on adequate soil moisture and appropriate canopy conditions. With rainfall getting concentrated over shorter periods, and temperatures increasing as a consequence of climate change, soil and ambient moisture are bound to be affected.
Effects of fire are considered to be the key to declining regeneration of banj oak trees in Himalayan foothills too (Shahabuddin and Thadani 2018). In places where animals are subject to hunting, the lack of suitable dispersers such as hornbills and pigeons were found to significantly affect seed germination of several tree species in rainforests of Arunachal (Sethi and Howe 2009). In Himalayan oak forests, there is now evidence of changing tree composition due to differential survival of tree species.
In the future, it is likely that only the resilient species will survive, leading to impoverished and altered tree assemblages. Further, invasive species creep into the gaps created by tree death which have additional long-term effects on both flora and fauna. In the sal forests (Shorea robusta) of the Shivaliks, this role is taken up by exotics such as Lantana camara which strangle any new native regeneration. In the Himalayas, disturbed forest gaps are quickly covered by ghoraghaas (Eupatorium odoratum), another invasive.
Such ongoing changes in tree assemblages also have significant effects on native fauna. A study by Sharma et al. (2013) in tropical dry forests of Panna Tiger Reserve, showed that the probability of occurrence of the endangered four-horned antelope was strongly related to local tree species diversity. As it subsists largely on fruits and flowers, this antelope requires a variety of tree species that can together provide resources throughout the year. In this context, it is important to note that herbivores such as wild boar are least affected by such forest degradation as they live on a range of food including roots, fruits, leaves and even carrion! Birds are also well-known to respond to forest tree assemblages (Mandal et al. 2015), particularly in harsh mountain environments.
It is becoming evident that regeneration of key tree species needs to be studied in more detail using surveys in different forest biomes of India. Further, FSI’s area estimation methods for their different categories of forest, such as dense, moderately dense and open, as well as compensatory afforestation projects, should take into account such adverse changes in Indian forests. The first step to securing the future of forests is to record and understand such changes, and incorporate this knowledge into mapping, restoration and afforestation activities.
Shahabuddin, G. & R. Thadani. 2018. ‘Biodiversity in Managed Landscapes: A View of Potential and Constraints in Van Panchayats of Kumaon Himalayas, India.’ Pp. 109-131 In Shonil Bhagwat (Ed.) Conservation and Development in India: Reimagining Wilderness. Taylor & Francis, London.
Sethi, P. and H. Howe (2009). Recruitment of hornbill-dispersed trees in hunted and logged forests of the Indian Eastern Himalaya. Conservation Biology 23: 710-718.
K. Sharma, R.S. Chundawat, J. Van Gruisen and A. Rahmani. 2013. Understanding the patchy distribution of four-horned antelope Tetracerus quadricornis in a tropical dry deciduous forest in Central India. Journal of Tropical Ecology Vol 30 (1): 45-54.
Mandal, J. and T.R.S. Shankar Raman. 2016. Shifting cultivation supports more tropical forest birds than oil palm or teak plantations in Mizoram, northeast India. Condor 118: 345-359.
Ghazala Shahabuddin is an ecologist working on forestry and biodiversity issues as well as the role of science in conservation. Her book ‘Conservation at the Crossroads’ (Permanent Black 2010) analyses paradigms of nature protection in India with respect to social, economic and historical factors.
Banner image: Adult date palms are seen standing inside Sariska Tiger Reserve showing poor regeneration in degraded forest habitat. Photo by Pratibha Pande.