From The News Room
Let's Not Wait for a Silent Spring in the Kumaon Himalayas
The Himalayas are no exception. During the last few decades, the rich forests of these great mountains have become degraded and fragmented due to similar pressures. Since 2013, our research team (including Rajkamal Goswami, Munish Gupta, Tarun Menon and Ritobroto Chanda) has been studying the birds of the oak hardwood forests in the mid-altitudes of the Himalayas (1,700 m to 2,400 m).
Oak forests form a fascinating ecosystem with many unique features, not the least of which is the high structural complexity and weather-modulating characteristics. Oak forests are known to be relicts from the Pleistocene epoch, when temperate oak forests covered the Himalayas due to the prevailing low temperatures. The glaciers’ retreat left temperate hardwood forests in their wake, the only ones in a largely tropical country.
These forests generally have few other tree species, with a single oak species dominating at a given altitudinal belt, mixed in with 10-12 other species. Yet the small-scale diversity in the herbaceous flora, shrub community, lianas and epiphytes is immense. In a protected oak forest, the canopy is dense, with some giant trees growing up to 30 m tall. Their complex branching pattern, high density of snags and cavities, presence of mosses, lichens and epiphytes, and a diverse understorey gives rise to abundant niches for fauna.
Forest soils are rich due to old, collected layers of decomposing leaf litter. The Banj oak (Quercus leucotrichophora) is known to be a hydraulic pumping machine, literally drawing water out of the atmosphere. This is responsible for the considerably lower temperatures and higher humidity inside an oak patch, as well as the presence of perennial streams.
Oak forests are no less important for supporting rural livelihoods as well. Local people use the nutrient-rich leaf litter as manure, cut oak foliage for feeding their livestock, and extract fuelwood and numerous food plants. They get their water from clear mountain streams sustained by dense oak cover.
These observations have, over the years, prompted a thought: if the Banj oak could be a keystone species in this system.
Chir pine forest coexists with banj oak at this altitude, but has a much more open canopy thanks to needle-like leaves, barely any shrubs and a drier microclimate. While both forest types are native to the study region, the chir pine is a pioneer species that gradually gives way to hardwoods, including oak, if there are no stressors. There is considerable evidence that chir pine forests have been historically extending their range at the cost of oak forests.
Pine is commercially important because it yields construction timber as well as pine resin. Pine is also more hardy and resilient to habitat degradation as its germination and growth can take place in drier soil and in higher light conditions. In pine forests, there are none of the mosses, epiphytes, lichens or leaf litter depth to complicate the vegetation structure. But in Kumaon, oak stands have been transforming to pine under anthropogenic stressors, a sort of backward succession process.
Structurally complex oak forests could very well be the key to survival of faunal diversity in the Himalayas, in the face of prevailing land use change. Since May, we have been undertaking systematic bird counts in about 200 sites located within the oak-pine forest belt, equally distributed among six different kinds of land use: protected forest, partially degraded forest, heavily lopped forest, cultivation, built-up tourist areas and pine forest.
Our surveys took place within a window of 20 km by 20 km located in Nainital and Almora districts (Uttarakhand) and limited to the pine-oak forest belt. Winter counts have also been undertaken to see if the patterns of species distribution changed considerably in that season. Given the harsh winters, with sub-zero temperatures, one would think that most bird species would need to migrate downhill to meet their energy requirements. If they do not migrate, then what are the plant and insect resources that allow them to cope?
While our data is still being collected, some interesting results have been unearthed, with some of my intuitions being borne out. We found the Banj oak to be a highly diverse forest ecosystem, with over 160 species recorded so far. Surprisingly, as many as two-thirds are breeding birds (either summer migrants or year-round residents). There are relatively few vagrants, passage migrants and winter migrants in this habitat.
The breeding activities of birds in the summer showed how important the mosses and lichens were for nest-building. Every little tit, flycatcher, nuthatch and dove was seen carrying these materials. A large number of shrub species bloomed and bore fruit in the spring and summer, providing abundant food for breeding birds. The oak forests rang with a medley of birdsong in this season. During this time, we also realised the significance of leaf-litter for bird survival in winter. In protected oak forests that retained a rich layer of decomposing leaf leaves, the white-throated laughingthrush and grey-winged blackbirds were able to continue foraging. Further, the complex vegetation structure supported insects
Our observations also show that there is a rich variety of plant resources that support breeding residents through winter. Oak acorns, veritable packets of nutrition that ripen during winter, seemed to be important food for some of the larger bird species, such as the Kalij pheasants, white-throated laughingthrushes and Eurasian jays. We also witnessed fruiting in tree and shrub species that provided much needed resources for birds in a sequential pattern as the winter progressed. Importantly, only protected oak forests retained the diversity of shrubs and trees that could support avian foraging to this extent.
The impact of land use shines through in our data. A preliminary analysis showed that species diversity of birds drops drastically along the use gradient, with protected oak forests estimated to harbour 70 species, and the built-up and pine sites being the least diverse, both at 49 species. The number of forest specialists drops drastically, too, from 32 in protected oak to six in built-up sites. (The latter group includes the white-throated laughingthrush, black-faced warbler, rufous sibia, chestnut-capped laughingthrush, rufous-bellied woodpecker, greater yellownape, scaly thrush, brown wood owl and the rufous-bellied niltava.)
However, there still are a number of adaptable forest species that appear to use human habitats when the opportunity arises, while nesting in protected forest habitat. While the latter category of avifauna is relatively adaptable, being able to use resources in forest edge habitat and cultivation, they still require high quality forest habitat to survive. (This group includes the whiskered yuhina, brown-fronted woodpecker, ultramarine flycatcher, grey-winged blackbird, streaked laughingthrush, great barbet, green-tailed sunbird and the red-billed blue magpie.)
Our findings also confirm the oft-repeated prediction that pine forests support less species diversity than oak, and do not harbour the stable bird communities. Community-managed forests also seemed to support biodiversity as much as protected forests do, as long as they had good forests nearby or were moderately used.
We categorised each bird species according to its breeding and migrant status, degree of forest specialisation and geographic endemism, in order to better understand vulnerability. According to our analysis, species that are breeding residents, forest-specialised and also endemic to Himalayas will be the most vulnerable to extinction in the event of hardwood forest loss. Among them is the rufous-bellied woodpecker, a species that partially feeds off tree-sap and hardly strays out of dense oak forest, and the common hill partridge that forages only in dense forest with deep litter layer. The less conspicuous Himalayan shrike-babbler and the striated laughingthrush are other identified vulnerable species.
There are huge implications of our findings for conservation planning. If the area of protected oak forest habitat declines further, we will likely lose the majority of our forest specialists. As the other land uses are considerably less diverse than protected oak, landscape-level diversity will go down as well. Further, the forest-specialised Himalayan endemics that are also resident in oak forest are likely to be the first to suffer, given their narrow altitudinal ranges and vulnerability to degradation.
Our analysis is still in very early stages, but it does appear that we have explored just the tip of the iceberg. The ultimate goal of our study is to understand how Himalayan birds survive and cope with the twin threats of land-use change and global warming. Studying this is all the more urgent as there will likely be synergistic effects between land-use change and climate change, with each amplifying the negative effects of the other. Such synergism shows up in the breeding populations of plains species such as jungle babblers, rock pigeons and red-vented bulbuls in cultivation and built-up tourist areas at altitudes beyond 2,000-2,200 m above sea level.
Could such land use be catalysing the upward movement of generalist bird species ranges in the middle Himalayas, as the climate gets more conducive to plains and foothills species? This remains a question for future research.
From our data, it is clear that intensive bird surveys across different landscapes are required within each altitudinal belt in the Himalayas if we wish to understand these phenomena even half-way. Further, the role of plant diversity in supporting high bird diversity should be explored because the diversity of plant species in hardwood forest enables bird survival throughout the year as well as long-distance migrations to continental Asia.
Birdwatchers and scientists need to join forces to explore these issues more systematically and widely. The expanding tribe of birdwatchers in India could be recruited to help with some of these projects. For instance, just a few days of systematic birdwatching, repeated every year in the same sites, can lead to useful insights the way the Breeding Bird Survey in the US has.
For now, our team is studying one vulnerable group in detail in these forests – the woodpeckers – to understand the habitat factors that underlie their occurrence and abundance at this altitude and the variation of these factors with season and human use. There ten species recorded in this forest association, and most appear to be breeding residents. Our team is also actively uploading birdlists onto the e-Birds portal to help expand our knowledge of rare-bird distribution and habitat in the middle Himalayas.
We cannot afford to wait for a silent spring before we begin our surveying. Armed with the right combination of natural history expertise and quantitative modelling, we may just be able to preempt local extinctions of largely under-studied bird species in the fragile Himalayan forests.