Treeline Ecotonal Dynamics: A Case Study from Pinus wallichiana Forest in Ngawal, Manang, North-Central Nepal
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Department of Environmental Science
Abstract
Global warming is now a scientifically established fact and this is also known to
influence treeline structure. This study tried to have a glance and inkling through size,
age structure and regeneration of Himalayan Blue Pine (Pinus wallichiana) on the
treeline ecotone of Ngawal, Manang in south facing slope of the trans-Himalayan dry
valley. Three vertical transects (20 m width) were laid across the treeline ecotone
from forest line to treeline. Age of individual trees within the transects was
determined based on the number of annual rings counted from increment cores
whereas age of juveniles saplings and seedlings was estimated by counting branch
whorls and scars left on stem. Almost reverse J-shaped size and age structure showed
that the majority of the pine population was recruited from 1970s. The current
timberline position is ca. 3930 m a.s.l. whereas the treeline position in the area is ca.
4020 m a.s.l. that with age-height regression model is estimated to be attained by
early 1990s. Despite the absence of recent treeline advance, the progressive
densification in the treeline ecotone as well as seedlings and saplings establishment
above the treeline may indicate the future potential for the advance. Even under the
current warming scenario of Nepal Himalaya, the ecotonal responses could not be
predicted by climate warming alone but marked release in human pressure might
have synchronous effect and for the disentangling pursuit, future studies
incorporating both climate and anthropogenic aspects are proposed.