Establishment of Pinus wallichiana on a Himalayan glacier foreland: stochastic distribution or safe sites?
The establishment of tree seedlings in primary succession is thought to occur only after an adequate reserve of nutrients has accumulated in the soil. Individuals of Pinaceae are sometimes reported to grow on very recently deglaciated substrates. This study analysed the colonization of a glacier foreland by Pinus wallichiana. Physical, chemical, and biotic aspects of potential and observed seedling microsites were analysed with regression methods and tests for proportions. Microsites with intermediate to high moisture levels and alkaline nutrient-poor soils were found to be conducive to seedling establishment. The most recently deglaciated parts of the foreland have soils with little nutrients and high pH. There is a linear change in soil variables from low nutrient content and high pH at the most recently deglaciated parts to more nutrient-rich and neutral toward the pre-neoglacial moraines. Surrounding old-growth forests of Pinus wallichiana shed an abundance of seeds onto the foreland, are able to germinate and grow, and are predominant among the early pioneers, which makes this species an unusual pioneer of primary succession. Colonization by P. wallichiana is not restricted to particular safe sites. Even though individuals look chlorotic and stunted, they grow at near normal rates. Leaf discoloration of seedlings occurs in soils with high pH and low nitrogen content. P. wallichiana is also a canopy dominant on some of the oldest terrains and outside the foreland.