Differentiation of diploxylon and haploxylon pines in spatial distribution, and adaptational traits

It is established that pines persisted despite the Cretaceous rise of angiosperms by differentiating into two groups: Diploxylon pines (subgenus Pinus), adapted to various fire regimes, and Haploxylon pines (subgenus Strobus), adapted to abtiotic stress. However, the distribution and attributes of the pines have not been assessed at the group levels either globally or for regional entity like Himalaya. Here, we have addressed this knowledge gap by investigating Himalayan pines. While Diploxylon pines (e.g. Pinus roxburghii) occur in a relatively productive outer ranges, largely below 2000 m, the Haploxylon pines (e.g., P. wallichiana) occur in abiotically stressful environments of high ranges (between 2000 and 3800 m). Adapted to small, frequent, man-made surface fires, the Diploxylon pines have characters, such as thick bark, and self-pruning branches. The capacity of Diploxylon pines to take advantage of disturbance resulting from fire and biomass extraction has also contributed to their range expansion. The stress-tolerant, Haploxylon pines in Himalayas have shorter needle length (14.17 +/- 3.5 cm), longer needle longevity (3 +/- 0.5 years), and greater seed mass (146.1 +/- 101.7 mg/seed), as compared to Diploxylon pines (20.7 +/- 2.6 cm, 1.92 +/- 0.1 years, and 41 +/- 20.1 mg/seed, respectively). The Diploxylon and Haploxylon pines were neatly separated, both spatially and in adaptational traits.