| This article takes 5 types of Larix gmelinii Forests, one of zonal forest vegetation, as research objects. These plants grow across from Mohe-Daqing Engineering Faculty of Petroleum Transmission Pipeline to the hilly area of Great Khingan. Based on those objects, we compare and analyze the variation of forest cover growing in the operational and non-operational areas, as well as the diversity of species, characteristic changes of nutrient and heavy metals in soil. The results indicate that:(1) Arbor species are single in non-operational areas where pipeline project passed through. There are only 3 families,4 genera and 4 species. The dominant species are Larix gmelinii, associated Betula platyphylla, Pinus sylvestris var. mongolica and Populus clavidiana; The shrub species have 4 families,8 genera and 14 species, and the dominant species are Vaccinium vitis-idaea, Rhododendron dauricum and Ledum palustre; The herb species are summed up to 44 species, respectively belonging to 20 families,32 genera. Relatively speaking, the composite family, grass family and lily family are in a dominant position. Due to the construction demands of crude oil pipeline, the entire arbor is chopped down in operational areas. Currently,5 forest types are updated the tree seedlings. However, the soil was suffered severe damage and just had short recovery phase, so that seedling renovation result is bad; Besides that, the trees are limited to grow up high in operational areas due to the safety requirements of pipeline operation. Considered that, after construction finished, the phytocoenosium are focused on the shrub and herbal there. The herbaceous plants growing in operational areas have not involved special edificator, total, having 47 species in all that belong to 23 families and 37 genera. Among them, the composite family and leguminosae are in dominant position relatively. By calculating the Jaccard index, the species co-possession in non-operational and operational areas is 35.48%.(2) The diversity index of 5 types of Larix gmelinii Forests in non-operational areas roughly are:herbaceous layer> shrub layer> arbor layer. The composition of sarbor species in this forest is single. Rhododendron dauricum, and shrub layer of arch forest in operational areas has highest diversity index, Simpson index and Shannon-Wiener index, and the evenness index ranks second. This kind of operational areas covered herbaceous layer of forest type all have highest diversity index. The content mentioned above explains the operational area with that forest type has higher diversity, and its community composition is more stable than other forest types.(3) The average coverage and biomass about the 5 types of shrub is decreasing after crude oil pipeline had been construction. The Vaccinium vitis-idaea-Larix gmelinii Forests and Betula platyphylla-Pinus sylvestris var. mongolica-Larix gmelinii Forests had been constructed, all the shrub layers had gone. The shrub coverage and bio mass are down to zero. Rhododendron dauricum-Larix gmelinii Forests is the only ones that the average shrub coverage is above 10%. The average coverage of this kind forest type is less than 1/5 of original data; The average biomass is also down to 1/20 of original data. This forest type’s shrub is affected greatly. The average coverage and biomass of 5 forest types increase after crude oil pipeline had been constructed. The average coverage of herbaceous layer belonging to Rhododendron dauricum and Larix gmelinii Forests is increasing, and higher than other plants. The average coverage of herbaceous layer in operational areas has increased from 9.2% before the construction to 42.8% after the construction, the latter data is 4.7-fold than before. The average biomass of herbaceous layer also increases from 19.1 gm-2 before the construction to 66.4 gm-2 after the construction, the latter data is 3.5-fold than before.(4) The pH value has increased universally after the laying of the oil pipeline, with Betula platyphylla-Larix gmelinii Forests affected the most, which saw an increase of 1.0. Concentration of soil organic matters have dropped significantly (p<0.01), with Betula platyphylla-pinus sylvestris var. mongolica-Larix gmelinii forests plummeting by 74.11%.(5) After the pipe laying, changes in concentration of soil nutrients in the 5 types of Larix gmelinii Forests have been found, with the cranberry-Larix gmelinii Forests affected the most, where concentration of total nitrogen and available nitrogen of the soil drops by 93.42% and 77.78% respectively, total phosphorus rises by 59.00%, total potassium rises by up to 3.63 times, and available potassium in the soil drops by 65.75%. Besides, concentrations of total nitrogen, available nitrogen and available potassium in soils of the 5 types of forests have seen significant drops (p<0.01).(6) Concentration of Cu in soils of the 5 types of Larix gmelinii Forests has seen a very limited rise in the pipe laying zone, as compared with that in the non-operation zone, which indicates that the concentration of Cu is less affected. In the meantime, concentrations of Mn, Zn, Pb have risen, with Betula platyphylla-Larix gmelinii Forests affected the most, where concentration of Mn increases by up to 1.77 times, while Zn and Pb rise by 1.35 times and 1.11 times respectively. Assessment by Nemerow index has indicated that soils of the 5 types of Larix gmelinii Forests have suffered from heavy metal contamination of different degrees, with Betula platyphylla-Larix gmelinii Forests more severely affected, hitting 2.95 in the index. |
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