Pine Is Ten Times As Sensitive As Maple
Coniferous trees are widespread in Russia, especially in Siberia, where taiga extends over tens of millions of hectares. Cedars and pines grow also in the environs of cities and in city parks and suffer from human-induced changes in environment.
Of course, coniferous trees can withstand a low-level pollution. Acid gases or soil pollutants that trees absorb are actively transported and deposited in those parts of wood, which do not perform important functions, and some elements are removed with needles and root exudates. Trees are armed with several biochemical reactions preventing harmful oxidation processes. According to the data obtained in the Main Botanical Garden in Moscow, the ability of pine species to withstand the human-induced pollution decreases in the following range. Common pine (Pinus silvestris) is most sustainable; mountain pine (Pinus montana) and North American species – Labrador pine (Pinus banksiana) and Weymouth pine (Pinus strobus) – are less sustainable; cembra pine (Pinus cembra), Siberian cedar (Pinus sibirica), dwarf pine (Pinus pumila), and Korean pine (Pinus koraiensis) are most vulnerable.
Conifers are ten times as sensitive to the air pollution as foliage trees. Because of such a susceptibility to ecological changes, conifers are good objects for the biological monitoring of the environment. This method allows one to assess a combined impact of all toxic substances on live organisms. This is very advantageous in urban conditions, since the heterogeneity of the city climate, soil cover, topography, and other factors make it difficult to determine the degree of pollution and the level of toxicity of various substances in certain points within the town area. Such an assessment could not be based, e.g., only on the chemical analysis of gaseous pollutants, because the latter cannot characterize the transformation and migration of gases in different layers of the atmosphere. In this situation, the observation on plants that suffer from these gases is a better way of ecological control.
Pines from 20 to 25 years old growing in town Tomsk, in areas polluted to different degrees, were observed by research assistants from the Tomsk State University. They discovered that urban conditions cause structural defects and changes in main physiological and growth processes in coniferous trees. The photosynthesis efficiency is decreased by 25-30%, observed trees grow slower than similar conifers in the suburbs and have a distorted (split) upper part of the crown and a low-quality wood.
On the basis of assessing the state of coniferous trees in the area of the Baikal Lake, Dr. Mikhailova, the research assistant from the Siberian Institute of Plant Physiology and Biochemistry of the Russian Academy of Sciences, classified the state of conifers depending on the environmental conditions, in particular, on the air pollution by industrial gases. The pollution-induced sickness of trees develops in several stages. First, a small, but visible metabolic disorder appears. At a medium-level pollution, the disorder grows into a persistent chronic disease, the adaptive mechanisms do not work properly, and the tree growth is retarded. As pressing becomes stronger, the tree enters the phase of an irreversible degradation. And at the last stage, the tree slowly dies.
Plants are very vulnerable to high concentrations of atmospheric ozone. The study of the ozone influence on trees is hardly possible in natural conditions because of a high reactivity and a wide spectrum of impacts of this agent. In laboratory, special equipment allows to monitor the ozone concentration during the experiment. Scientists from the Institute of Atmospheric Optics (Siberian Division, Russian Academy of Sciences), the Tomsk State University, and the Institute of Forestry (Siberian Division, Russian Academy of Sciences) found that six-hour-long exposure of four-year-old Siberian cedars to an atmosphere with an increased ozone concentration (8 mg/m3) results in the decomposition of photosynthetic pigments. This effect is better expressed in the needles of rapidly growing cedars. Needles of slowly growing plant individuals are less sensitive to the stress. However, a low rate of growth is disadvantageous from the viewpoint of park designers.
To sum up, we may say that urban conditions are too difficult for pines and cedars. Their right place is taiga with a clean air that is never present in a large city. That is why pines, which are planted now by many people on lawns in front of their houses, get sick and die when very young.
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