Effects of Mohe-Daqing oil pipeline project construction on typical forest ecosystems in Daxing'an Mountains.

Mohe-Daqing section of the China-Russia oil pipeline project runs through Daxing’an Mountains and the Songnen Plain. Project construction would disturb vegetation and soil of the forests. In this study, we measured soil properties, plant biomass and species biodiversity in the operational region of the oil pipeline and the non-operational region in theRhododendron dauricum--Betula platyphylla forest, Vaccinum vitis-idaea--Larix gmelini forest and Lespedeza bicolor--Pinus sylvestris var. mongolica forest. The results showed that: 1) Pipeline construction had no effects on soil pH; however, total P concentration decreased significantly (P＜0.05). Total N concentration decreased significantly (P＜0.05) in the soil layer of 0--10 cm; however, it increased in the soil layers of 10--20 cm and 20--30 cm in all of the three forests. Total K concentration decreased significantly (P＜0.05) in the soil layers of 0--10 cm and 10--20 cm in R. dauricum--B. platyphylla forest; however, there was no change in the total K concentration (P0.05) after pipeline construction in V. vitis-idaea--L. gmelini forest and L. bicolor--P. sylvestris var. mongolica forest. 2) Tree biomass decreased significantly (P＜0.05) in R. dauricum--B. platyphylla forest. However, shrub and herb biomass did not change significantly (P0.05) in this forest. Tree and shrub biomass decreased significantly (P＜0.05) in V. vitis-idaea--L. gmelini forest and L. bicolor--P. sylvestris var. mongolica forest. In contrast, herb biomass increased significantly (P0.05) in these two forests. 3) Oil pipeline project construction had more effects on tree and shrub species diversity than on the herb species diversity. Tree and shrub species biodiversity decreased at all sites after construction except for shrub species biodiversity in the V. vitis-idaea--L. gmelini forest. Herb species biodiversity increased in L. bicolor--P. sylvestris var. mongolica forest; however, it decreased in R. dauricum--B. platyphylla forest and V. vitis-idaea--L. gmelini forest. Our results indicated that restoration of the vegetation was difficult after oil pipeline project construction due to the damage to both vegetation and soil. More artificial measures are necessary to restore the vegetation. Otherwise, the degraded ecosystem would be harmful to the pipeline at sites with poor soil textures.