Pollen-mediated gene flow in Himalayan long needle pine (Pinus roxburghii Sargent)

Pollen migration in Pinus roxburghii has been estimated under two different conditions, viz. isolated single trees and at the fringe of natural forest. Trapping of pollen grains was conducted at geometrically increasing distances, i.e., 0, 5, 10, 20, 40, 80, 160, 320, 640, 1280 and 2560 m from the source. The observations revealed that the scattering of pollen grains was not uniform in all directions and that they travelled up to 2.5 km towards the downhill direction, while in the uphill direction dispersion of pollen grains was restricted to 320 m from the source. Pollen frequency declined rapidly as the distance from the source increased, with the highest densities within 50–100 m.