Himalayan broadleaf forests
Himalayan broadleaf forests are a unique and diverse biome located in the lower elevations of the Himalayan mountain range, which spans eight countries in Asia, including India, Nepal, and Bhutan. These forests are primarily characterized by species such as Shorea robusta, known as sal, and various oak species, including Quercus leucotrichophora, which thrive at different altitudes. The region's climate is heavily influenced by the summer monsoon, with annual rainfall ranging from 59 to 98 inches, which supports rich biodiversity.
These forests are home to a variety of wildlife, including significant populations of mammals like tigers, Asian elephants, and the Himalayan langur, as well as over 300 species of birds. However, they face considerable threats from human activities, such as deforestation for timber and agricultural expansion, leading to habitat fragmentation and loss of biodiversity. The presence of invasive species like chir pine, which can outcompete native oaks, further complicates conservation efforts.
The ecological balance of the Himalayan broadleaf forests is critical, as they play a vital role in carbon sequestration and climate regulation. Yet, climate change poses additional risks, with altered precipitation patterns and rising temperatures potentially impacting forest structure and wildlife adaptation. As such, intensive conservation strategies are essential to protect and preserve this remarkable ecosystem for future generations.
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Himalayan broadleaf forests
- Category: Forest Biomes.
- Geographic Location: Asia.
- Summary: This is a highly exploited forest biome, dominated by Shorea robusta and Quercus leucotrichophora forest occurring in the lower mountain slope areas.
The Himalayan Mountains extend into eight different countries in Asia: Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal, and Pakistan. From the eastern border of western Pakistan to the frontiers of Myanmar, the Himalayas run a distance of 1,491 miles (2,400 kilometers) in the shape of an arc. The region is divided into three major subregions: the Sub-Himalayas, with an average altitude of 2,952 to 3,937 feet (900 to 1,200 meters); Lower Himalayas, with an average altitude of 12,139 feet (3,700 meters); and Greater Himalayas, with a single range rising above 19,685 feet (6,000 meters) and nine of the 14 highest peaks in the world, including Mount Everest.
The Tibetan Himalayas and the Tibet Plateau achieves the highest altitudes of 13,123 to 19,357 feet (4,000 to 5,900 meters). The annual rainfall across the ranges varies from 59 to 98 inches (1,500 to 2,500 millimeters). Rainfall patterns in the Himalayas are heavily influenced by the summer monsoon season; most rain here falls from mid-June through September.
Forest Vegetation
Broadleaf forests extend along the east-west arc of the region. The forest vegetation varies considerably, depending upon the elevation. At elevations lower than 3,280 feet (1,000 meters), where temperatures are tropical to subtropical, the forests are dominated by sal trees (Shorea robusta). Sal forests penetrate through mid-mountain ranges into the far north along river slopes and valleys, and extend across Nepal, Bangladesh, and India. While some researchers consider sal deciduous, others consider it evergreen or a borderline between deciduous and evergreen tree. In contrast to most of the deciduous tree species that are generally summer-flushing, sal is a spring-flushing species; vegetative budding breaks around the spring equinox in the region.
Oaks constitute the second-most dominant broadleaf forests in the region. Banj oak or Himalayan white oak (Quercus leucotrichophora) and other Fagaceae dominate at approximately 1,640 feet (2,000 meters). Tilonj oak or green oak (Quercus floribunda) and Rianj oak or wooly-leaved oak (Quercus lanata) are common at 6,230 to 7,870 feet (1,900 to 2,400 meters) in the Himalayas. Karshu oak (Quercus semecarpifolia) dominates at 7,870 to 9,840 feet (2,400 to 3,000 meters) in subalpine conditions. Both the Shorea and Quercus reach a height of about 82 to 130 feet (25 to 40 meters).
As elevation increases, sal is replaced by chir pine (Pinus roxburghii), which colonizes bare sites with a wide range of nutrient availability. Among deciduous trees, the subalpine Betula utilis dominates extensive areas. Other temperate trees occur in small patches through the forest, including maple, ash, walnut, horse chestnut, and dogwood. Oak trees are generally associated with shrubs of Rhododendron arboretum and Lyonia ovalifolia. Other major shrubs in these oak-dominated forests include Arundinaria falcate, Myrsine spp., Berberis asiatica, Randia tetrasperma, etc.
In the Nepal Himalayas, the subtropical broadleaf forests are dominated by deciduous species of Terminalia; the subtropical semi-evergreen species of the Schima-Castanopsis community; mixed Alnus-Dalgergia-Acacia forest stands; and mixed Shorea-Terminalia-Anogeissus-Lagerstroemia.
Fauna
The subtropical broadleaf environment forms an important habitat for mammals such as the Himalayan langur (Presbytis entellus), tiger (Panthera tigris), Asian elephant (Elephas maximus), gaur (Bos gaurus), and sloth bear (Melursus ursinus). Rich avian biodiversity has also been reported in the Himalayan subtropical forest biome. In the oak forests of Kumaun Himalaya, more than 300 species of birds have been recorded. These include the golden eagle (Aquila chrysaetos), collared falconet (Microhierax caerulescens), velvet-fronted nuthatch (Sitta frontalis), long-billed vulture (Gyps indicus), grey-headed woodpecker (Picus canus), four leaf warbler (Phylloscopus spp.), giant hornbill (Buceros bicornis), oriental pied hornbill, (Anthracoceros albirostris), Indian grey hornbill (Ocyceros birostris), pea-fowl (Pavo cristatus), hill myna (Gracula religiosa), Asia paradise flycatcher (Terpsiphone paradisi), and many others. In addition to resident birds, winter and summer migrant birds are also common. Summer migrants prefer the subtropical broadleaf environment, as compared to winter migrant birds, which show preference for aquatic and scrub habitat in the region.
Biome Threats
To a marked degree, these forests are over-exploited by humans, with mounting evidence of habitat fragmentation. With respect to its economic importance, sal forests yield valuable timber. Sal meets the subsistence needs of the local people, including fuelwood, leaves for plates, seed for oil, litter for animal bedding and composting, feed for cattle, resin or latex from heartwood, tannin and gum from bark. Oak is mostly used as firewood, as it burns hot and the coals last long. Locally, oak is also used to make charcoal. Its leaves and wood are known to burn even when green. The leaves and tender branches of oak serve as cattle fodder. Timber is also used for making agricultural implements. The seeds of banj oak are used for treating scabies and urinary disorders; roasted banj oak seed is also used as a coffee substitute.
Himalayan biodiversity is severely threatened due to natural and anthropogenic disturbances. With forest stands fragmented, some wildlife is disappearing. In particular, the subtropical forests that dominate in low elevation areas tend to be more highly populated. Large-scale felling of trees for timber and other industrial raw materials since the colonial period and forest conversion to agricultural lands are the major causes of deforestation. This deforestation has also impacted the region's ability to sequester atmospheric carbon, or to maintain its carbon pool, which is a vital element in biodiversity, climate regulation and adaptation, and ecosystem maintenance. Taller trees naturally store more carbon, so as they are removed, the carbon stocks decrease.
Oak forests here generally are moist, fire-free and close-canopied. The oak-dominated soils have higher water-holding capacity than the chir pine forests that have been overtaking them in many localities as an immediate-successor colonizing species. Chir pine is both fire-resistant and unpalatable to animals. Chir pine forests in the region are known as xerophytic edaphic climax forests, in other words, ideally adapted for moisture-lacking, nutrition-depleted soils. Replacement of oak by pine is a major concern and is not preferred by villagers, as once pine is established, it is highly susceptible to fire—also representing increased habitat-destruction risk to animals here. Low regeneration of oak in the region is attributed to excessive browsing and pruning, reduced seed production, and increased seed predation.
Much of the broadleaf forest in the Himalayans has in recent times been converting to scrub vegetation, which dramatically impacts habitat structure. Sensitive ungulates, such as Himalayan musk deer, are under severe pressure, for example, as their food sources and shelter choices here are disrupted. Other factors contributing to the poor wildlife outlook in this region are poaching and trade of animal parts and faulty land-use practices. In addition, recurrent fire is a major disturbance factor impacting the forest structure and function. Intensive conservation efforts are needed to save the remaining forests and wildlife of this biome.
Climate change is projected to impact snow and ice patterns here, with higher average springtime temperatures resulting in faster snowmelt and more water eroding mountainous slopes. Climate change may also affect the rainfall patterns in the Himalayas, causing changes in the duration or quantity of moisture released during the monsoon season. Such alterations to precipitation, humidity, and storm cycles will impose significant consequences on forest make-up and on the capacity of its inhabitants to keep up the pace of adaptation or migration.
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