Regeneration of <i>Pinus wallichiana</i> AB Jackson in a trans-Himalayan dry valley of north-central Nepal

Abstract

We studied the elevational pattern of forest composition and regeneration of the subalpine conifer tree species Pinus wallichiana in Manang, a trans-Himalayan dry valley in north-central Nepal. Thirty-five quadrats (10 m × 10 m) were laid between 3300 and 4000 masl on both north-and south-facing slopes. We measured diameter at breast height (DBH) of each mature individual of all tree species (DBH ≥10 cm), and recorded the number of seedlings (DBH <10 cm, height <30 cm) and saplings (DBH <10 cm, height >30 cm). We also measured soil moisture and soil pH, estimated canopy cover, and recorded slope and altitude in each quadrat. For all species together and for several species individually, tree density, seedling density, sapling density and tree basal area were found to decrease with elevation on both north and south aspects. This trend is largely explained by the progressively harsher environment at higher elevations. The north-facing slopes in our study area have denser forests than the south-facing slopes, the density of all size classes (seedling, sapling and mature plants) and basal area being greater on the northern aspects. These aspect-wide differences are attributable to the stark difference in soil moisture between northern and southern aspects, which is in turn due to the difference in insolation. Irrespective of elevation and aspect, all the forests studied are regenerating, as indicated by inverse J-shaped density-diameter curves. The elevational pattern of seedling and sapling abundance is explained only by elevation. Whereas other variables (e.g., canopy) are considered to have an important influence on seed germination and seedling establishment, they turn out not to be significant predictors of density of seedlings and saplings. This failure to identify a relationship is probably due to our use of non-parametric test (tree regression analysis) that we used to establish the relationship between density and its potential explanatory variables or due to our selection of 1 standard error rule yielding sub-optimal models for regression trees.

Regeneration status of woody species in a protected area of Western Himalaya

“…Inverse J-shaped distribution is indicative of a forest in a state of regeneration [32]. A shift from inverse J-shaped to unimodal or multiple-peaked distribution is the result of substantial changes in the state and pattern of forest regeneration, suggesting that forest is in trouble [33]. Such a shift is generally caused by both anthropogenic and natural causes (climatic or biotic), as reported for Pinus roxburghii forest on dry valley slopes along the Punatsangchu river in west-central Bhutan [34].…”

Do Himalayan treelines respond to recent climate change? An evaluation of sensitivity indicators

“…Canopy cover (light) and soil moisture largely determined reproductive success. Seedlings of Abies spectabilis were abundant up to 3900 m but absent above 4000 m. Continuous regeneration as indicated by reverse J-shaped density-diameter curves and high densities of seedlings and saplings was also assessed in other studies in treeline forests in Manang, focusing on Abies spectabilis and Pinus wallichiana (Ghimire et al, 2010). Abies seedling abundance was positively correlated with soil moisture and nutrients (phosphorus), whereas altitude was the only significant predictor of Pinus seedling density.…”

Regeneration Pattern of Tree Species in Forested Landscapes of Himachal Pradesh, Western Himalayan Region, India

“…Thus there is possibility of conversion of Q. leucotrichophora LSE into R. arboreum LSE as there was inadequate regeneration of Q. leucotrichophora in this zone [40]. The regeneration potential of P. wallichiana in zone II was higher as compared to zone III and zone IV because its seedling and sapling density decreases with altitude, which is characterized by shorter growing season [41]. P. gerardiana had restricted distribution only in zone IV mostly in its pure patches with overall fair regeneration.…”