The Restoration of Forests in the
Temperate Zone of China
CHEN Lingzhi
(Institute of Botany,
Chinese Academy of Sciences)
Introduction
Most parts of the northeast and northern regions in China belong to the temperate zone. The temperate zone is divided into cold, middle and warm temperate zones. The forests of the northern region in the warm temperate zone have been removed unsustainably since 1,127, while the forests of northeast region in the mid-temperate zone were first disturbed in the late 19th century. The primeval forests in the warm temperate zone have almost disappeared; only a small area of fragmented forest has survived[7]. However, the northeast forest region is one of the largest bases for timber production in China. The restoration of forests in the northeast and northern China, including the loess plateau, is of benefit to biodiversity conservation and the improvement of the natural environment.
1. The status of forests in temperate zone
1.1 The status of forests in the northeastern region of cold and middle temperate zones
The northeastern region includes the provinces of Heilongjiang, Jilin, Liaoning
and parts of Inner Mongolia. They include the major distribution regions of the cold-temperate coniferous forest, mid-temperate mixed coniferous, and deciduous broad-leaved forests. The largest forest area is located in Heilongjiang Province, with a forest area of 155,710km2 and a forest coverage of 34.7% according to data from the forest survey of 1982-1986. The area and stock volume of these forests occupied 13% and 17%, respectively, of the total amount in China.
The largest forest area of Daxinganling
in Inner Mongolia is named Yakeshi. The forest coverage was about 64%. It occupied 10% of the total forest area in China. The forest coverage in Jilin Province was 32.2%. Most of the forests there are natural. The forest coverage in Liaoning Province was 23.5%. These forests were mainly distributed in the eastern mountains of the province. As mentioned above, the northeastern forest region is the primary forestry base in China, with an average forest coverage of about 28%.
1.2 The status of forest in north region of warm temperate zone[1, 2]
Northern China in this paper only refers to the provinces of Hebei,
Shanxi, Henan, Shandong, Beijing and Tianjin. Here, the primary forests have almost disappeared; only small patches of fragmented natural forests occur in the mid-mountains. The forest coverage was about 8.3%, and the forest area was 59,730km2[12]. Most of these forests were plantations and restored stands. Northern China contains one of the most important regions for agriculture. The population in this region occupies 1/4 of the total population of China. In the region human activity exerts a strong influence on the natural forests, as local people need firewood, timber, fruit, and meat, etc. Local people cut down the forests to develop a diversified economy in the mountain area.
The major mountains in this region are Yanshan
and Taihang Mt., and forest coverage was 12% in the warm temperate zone. The forest area was very limited. For example, the total area of the eastern slope of Taihang Mt. was 30,958km2, but the forested area only occupied 660km2. Most of this forested area consisted of young and sparse stands.
2. The problems
Currently, the forest area is decreasing, and the wood quality is becoming worse. Cutting is proceeding at a much faster pace than reforestation. People often do not pay enough attention to timber processing. The risk of wood shortage appears to be obvious in the important timber base of northeastern China.
2.1 Neglect of proper reforestation after logging
From 1976-1981, 352,000km
2 of natural forest was cut in Heilongjiang Province. More than 50% of the land that had been clear-cut was neglected and not properly reforested, leaving such large areas of clear-cut land so as to make natural regeneration difficult.
2.2 Irregular thinning of stands
The overall quality of forest stands is a very important measure of potential growth of the trees. During thinning of young and mid-aged stands, people have intensively harvested the good quality pole size trees and left standing the poorly formed trees. Over time the young and mid-aged stands became sparse woods. However, if people were to remove poorly formed or diseased trees, wood quality of the remaining trees would improve and the forests could be used sustainably.
2.3 Repeated fires
2.4 Illegal logging
2.5 Deforestation for agriculture and other economic activities
From 1976 to 1981, the loss of forest area in Heilongjiang
Province was 7,950km2. It has been estimated that 61% of the total forest area lost was unreasonably destroyed. Forest cutting due to reasons other than silviculture accounted for 32% of the cut area. The cutting area of forests was 1,970km2 from 1981-1986[9]. The situation of deforestation in other provinces of northeastern China is similar to that in Heilongjiang Province.
3. The strategy of forest restoration
3.1 Conservation of primary and secondary forests within and outside protected areas
The scientific management and public awareness of protected areas should be strengthened. Intensive exploitation of forests surrounding protected areas must be prohibited, otherwise, protected areas will form isolated islands among the degraded ecosystems.
There are small areas of preclimax forest that are still suffering from human disturbances in the warm temperate forest zone. The secondary forests (those containing birch, poplar, and even restored oak) often have been converted to pure coniferous plantations, an action that has resulted in decreased biodiversity and loss of wildlife habitats. Most of the secondary forests were located in the river source of the mid-mountains. These forests are very significant for water and soil conservation. The area of natural forests is already very limited, so these preclimax and, secondary forests, and various successional stages of forest, should be protected. This action will enhance the restoration of forest. The establishment of protected areas has been relatively ignored in the warm temperate zone, primarily because of the lack of primary forests.
3.2 Sustainable management of forest [3][5]
The sustainable management of forest is a key measure to restore and sustainably use the forest resources. The volume of tree harvest has been unsustainable because of intensive exploitation. Thus, the scale of forest cutting must be controlled. Seedlings, saplings and mother trees should be protected before logging. The thinning of young and mid-aged stands must be carried out over time. Properly thinned forest stands yield higher sustainable yields.
3.3 Closing the mountain to facilitate afforestation
Closing the mountains to accelerate the natural regeneration of sparse woodlands is an effective and economic method for the restoration of forests. Larch stands coming from the seeds of remaining mother trees have regenerated naturally in Daxinganling
after fires[8].Large areas of shrub lands occupy the hills and mountains in the warm temperate zone. There are many dwarf coppices of oaks and other trees growing in the shrubs. To close the mountain and stop human disturbance will result in replacement of the shrub lands by forests. The biomass and species diversity of shrubs are quite different between closed mountains and unclosed mountains. But if people fail to tend to the shrub lands, the competition between trees and shrubs will become severe during the period when the mountain is closed. Thus, the treatment of cutting the shrubs surrounding young trees, and keeping 1-2 strong tree trunks to mature, will helpful to restore the forest. According to data from Shanxi
Province, the forest area expanded to 3,340km2 in 1975, and has increased to about 200km2/year since 1957[1]. The forest area in Hebei Province was 24,670km2, about 34% if the current forest area was naturally restored through closing mountains[10]. Using this approach, the area of natural forests increased 388,200km2 all over the country, doubling the total artificially forested area[12].
3.4 Afforestation
Cultivation of native trees in clear-cut lands is another approach for restoring forests. Usually, people prefer pure coniferous plantations. The larch is a suitable tree species for the first stage of afforestation in open land in cold temperate and mid-temperate zones. Pinus koraiensis
is a high-quality wood, it often grows in open landscapes. Afforestation is usually unsuccessful. Now some scientists have suggested that broadleaved trees about 2-3 m wide could be harvested selectively within the deciduous broadleaved forest. Then the pine saplings would be planted in the resulting open space where they would grow well in the forest environment. Through this process, the mixed pine and deciduous broadleaved forest would be restored gradually in the mid-temperate zone.
Afforestation in the grasslands and shrub lands is an important approach in warm temperate zone. The slopes of hills and mountains are steep, and the soil layer is thin and relatively dry. Air seeding is not a successful method for this type of site, since the seeds have difficulty reaching soil surfaces that are covered by grasses and shrubs. Even seeds that reach the soil face difficulty in growing making it necessary to tend to these seedlings. Air seeding needs more funding to be successful. The percent of success of Air seeding was 30%, according to data from Hebei
Province[10]. The area of afforestation all over the country from 1949-1981 was 1,126,700km2, but only 278,100km2 of forest plantations were alive. The area of man-made forests occupies 11.3% of the total area of afforestation throughout China[12]
Selection of tree species is a key problem for successful afforestation. The different species of Quercus, Acer,
Tilia, Ulmus, Fraxinus, Juglans, Ailanthus, Robinia, Larix, Pinus, Platycladus, etc. are suitable trees that have been cultivated at various elevations of the mountains. It is necessary to close the mountains and treat the young stands actively to ensure their propagation. Grazing, fuel, grass and litter collections have to be forbidden, otherwise, human activity will influence negatively the growth of young stands.
3.5 The restoration of vegetation in the loess plateau
Ecological engineering is a way for restoration of vegetation in the severely eroded region. The loess plateau is located in the warm and middle temperate semi-moist, semi-arid and arid regions. The forest, steppe desert, bush and meadow occur in different regions.
Afforestation in loess plateau and planting shrubs and grasses can be carried on in the semi-moist region. Bushes and grasses are adaptable plants in semi-arid regions for restoration of vegetation. Bushes and semi-bushes may only grow in the desert area of the arid region.
Terraced fields have been built for agricultural development on the slopes below 15o
in the forest region of the loess plateau. The horizontal terraces or pits, which look like fish scales on the steeper slopes, were established for planting trees and shrubs[11]. The natural vegetation between terraces or pits must be protected to play an important role in soil conservation.
The cultivation of trees, shrubs and grasses in the loess plateau, northeastern, and northern China is part of the shelter forest engineering of three north (northeast, north, and northwest parts) of China.
3.6 Establishment of forest shelter belts and green belts
Agriculture is the key economy in the plains of the temperate zone. Combining green belts along the road and forest shelter belts around the farmland, networks of sheltered forests should be developed. It will improve the microclimate of farmland and provide fuels and timbers for local people. The man-made forests and large shrubs can also be cultivated along the river banks and river alluvial lands. Hedges consisting of native trees are suggested for cities. All these forest and shrub belts will become corridors for migration of wildlife.
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