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Pine Invasion into Oak Forest
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Pine Invasion into Oak Forest

The oak forests have an intimate social and ecological relevance by providing the area with large array of ecosystem services

Post by on Monday, December 20, 2021

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The Himalayan state, Uttarakhand, is bestowed with rich biodiversity. The forests are distributed along the different attitudinal gradients ranging from broad leaved deciduous, evergreen oak, mixed oak, pine to coniferous and alpine meadows. There are five species of oak namely Quercus glauca,Q. leucotrichophora,Q. floribunda,Q. lanata and Q.semecarpifolia found growing naturally at various altitudes. Among these Quercus leucotrichophora or banj oak forms extensive forests. Infact, Banj oak and Chir pine (Pinus roxburgii) are the two predominant forest tree species in the Himalayan state occurring between the altitudes of 1200-2200m. 
The oak forests of Uttarakhand are mostly evergreen and maintain a dense canopy. They represent climax vegetation and play a vital role by providing various natural ecosystem services like conservation of soil from erosion and landslides, regulation of water flow in watersheds and maintenance of water quality. It is reported that an undisturbed oak forest sequesters carbon at in huge amount. Further, they also serve as a major component of the natural habitat and as a key food resource for the inhabiting wildlife in the region. The tree has been widely exploited by local inhabitants for litter and domestic collection. The ability of leaf litter to decompose quickly makes it a promising compost fertilizer. It is collected by locals and used for agricultural terraces. Further, the high calorific value of oak makes it an excellent fuel, and its leaves being nutrient rich and palatable are used as cattle fodder in the scarcity of fodder or in pinch period i.e., winter and dry seasons.
Chir pine has numerous advantages over other species like fast growth and wide climatic adaptation and naturally occurs on the driest and rockiest slopes. In the past decades, it has spread greatly under the influence of cutting and burning, replacing oak forest in vast and disturbed areas. Moreover, pine is a light-demanding, fire-adapted but fire-promoting species being taped regularly by the local for the resin collection, the Oak though itself being non-inflammable, have suffered a lot from fire spreading from the nearby pine forests. Sporadic forest fire, heavily lopping for fodder collection and site disturbances due to anthropogenic activity have led failure of oak to regenerate and subsequent encroachment of chir pine in many areas.
The invasion of oak forest with chir pine is quiet unnatural. The successional sequence in natural succession begins with warm temperate grasslands followed by early successional pine forests, mid-successional mix pine-oak forest and culminating in late successional oak forests. The oak is associated with nutrient rich sites, contrarily chir pine have an ability to survive well in nutritionally poor and less fertile soil. Excessive lopping of oak branches by locals has led to a sparse canopy and low litter fall; this has in turn led to a short residence time of litter on the ground impairing the return of nutrients on the site for oak regeneration. 
Additionally, litter removal has disturbed the habitat of other flora and fauna which would have otherwise helped breakdown of litter and moisture conservation that aids decomposition of leaf litter at faster rate. The oak tree requires nitrogen rich soil for the development and proper growth meanwhile frequent fires in pine forests have made soil nitrogen deficient and made soil unsuitable for oak regeneration. Thus, the greater capacity of pine to conserve nutrient and create nitrogen shortage have made it tough for oak to reinvade pine occupied areas while pine can easily invade oak forests under these soil and environmental conditions.
Further, the pruning of oak trees greatly opens the forest canopy, the seeds of oak known as “acorns” being highly sensitive to direct sunlight, on exposure lose their viability within a week or days. Moreover, they tend to germinate in soils with proper moisture content but due to diversions of river water for human consumption, there is scarcity of soil moisture to regenerate naturally. This has lead reduced oak germination while pine seeds, which having an ability to thrive on bare mineral soil with low soil moisture show increased germination rates. Also, indiscriminate litter removal by locals usually sweeps away viable acorns fallen on the forest floor. 
The problems of Himalayan forests are complex and entwined between socioeconomic and ecological concerns. The oak forests have an intimate social and ecological relevance by providing the area with large array of ecosystem services. It is quite evident that anthropogenic activities as well as climatic conditions have led to restrict the growth and germination of oak forests and favour the growth as well as regeneration of pine forests. Providing an alternative to fuel wood and fodder for the local people may tend reduce pressure on oak forests and reverse forest degradation, which can help them to flourish again. And oak forest may be occupying their natural habitat in the natural environment again without interference of biotic or abiotic pressure.
(The Author is a Research Scholar at Forest Research Institute, Dehradun. Email: sakinagul7@gmail.com)


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