The
Loess Plateau
The
spatial of the ecosystem
Located
in the upper and middle reaches of China’s Yellow River, the Loess Plateau
covers a total area of 630,000 km2
[1]. Including almost three
provinces(Gansu, Shanxi, and Shaanxi), and parts of four other areas including
the western Taihang Mountain, the eastern Riyue-Helan Mountain, the northern
Qinling Mountain ridge, and the southern Yinshan, the Loess Plateau now is
sustaining the life of more than 100 million people.
Archaeological
evidence indicates that the Loess Plateau has been an inhabitant for human
beings for over 8000 year. Ancient Chinese civilizations established their
realms on this earth. Consequently, the Yellow River is also called the “Mother
River of China”, and the Loess Plateau is lauded as “the Cradle of Chinese
Civilization”.
Centuries
ago, the Loess Plateau was highly fertile and suitable for farming. However,
deforestation and over-gazing exacerbated the ecosystem years by years, and
with the increase of population, the ecosystem now is totally different from
what it was more than two thousand years ago. Soil erosion caused by
deforestation, reduction in the acres of farmlands caused by desertification,
and air pollution caused by the overexploit of underground coals all lead to the
degenerating environment and the underdeveloped local economy.
J.X.
Xu, Historical bank-breachings of the
lower Yellow River as influenced by drainage basin factors, Catena, 45 (2001), pp. 1–17
Excerpted
from Xu Jiongxin
The
Historical Overview of the Loess Plateau
There
is a debate about what was actually like in the Loess Plateau area. The common
idea about the landscape is that grasslands and forests covered the Loess
Plateau centuries ago. The natural forest coverage was “more than 50%”, and the
local climate of the studied archaeological sites was favoring forest cover.
(Li, Wang)
Other
researche suggest that the Loess Plateau could be divided into five parts: a
temperate forest zone, which contained a lot of broadleaved deciduous oaks, a
warm-temperate forest-steppe zone, a warm temperate steppe zone, a
warm-temperate desert-steppe zone, and a warm-temperate steppe-desert zone.
(Sun, P27) In the end, based on the pollen accumulated through years, the
researches concludes that the southern Loess Pleateau was dominated by “warm-temperate
broadleaved deciduous forest”, and the northern part was mainly “forest-steppe”
whose boundary is still debatable. (Sun, P35)
Li,
Wang, Historical Changes in the
Environment of the Chinese Loess Plateau, Environmental Science & Policy
Vol.9, Issues 7-8, November – December 2006, pages 675-684
Sun,
Xiangjun, Vegetation History of the Loess
Plateau of China During the Last 100,000 Years Based on Pollen Data, Institute
of Botany, Chinese Academy of Science, Beijing 100093, China, Quaternary
International, Vol. 37, pp 25-36
3.
How have people impacted the ecosystem?
1.
The Population Increase
Wang J.G., Lu J.F.
Studies on ecological limits to agriculture
development on Loess Plateau: from the change of population capacity (1996), Ecological Economy, 4, pp. 44-47.
As we can see from the chart above, the population of
China fluctuated in different periods, influenced mainly by natural disasters
and wars. As Xi points out, “an increase in population means the increase of
the area of cultivated land, especially of the area of cultivated slope land”.
On the other hand, the sharp decrease in population indicates the fact that
large areas of farmlands might be discarded and turned into wasteland instead.
The natural vegetation could only restore in a slow pace. (Xi)
According to Li, at the time by the Sui Dynasty
(606A.D.), “there were 2.81 ha of cultivated land per person and 14.6 ha per
family,” which was enough to subsist the population at that time. However, as
population increased after war periods, the area of cultivated land became
“1.80 ha per person” by the middle of the Tang. (~755 A.D.) To the Ming Dynasty
(1579 A.D.), there was only “0.77 ha per person.” The population had put an immeasurable
pressure on the environment and the demand for cultivable lands. Therefore,
large areas of grasslands and forests were removed.
2.
Deforestation
Forests are important
resources for ancient civilizations. In order to get more acres of farmable
lands, trees were massively cut off and used for construction. Also, in the
chilly and dry northwest area, woods were crucial as fuels in winter. In the highlands, deforestation often led to
serious erosion, which might expose sterile subsoil or bare rock, and prevent
further agricultural use of the degraded land, or even reestablishment of
native vegetation
Osborne,
Anne, The Local Politics of Land Reclamation in the Lower Yangzi Highlands,
Late Imperial China, Volume 15, Number 1, June 1994, pp. 1-46 (Article), published
by The Johns Hopkins University Press
Excerpted
from
Li,
Wang, Historical Changes in the
Environment of the Chinese Loess Plateau, Environmental Science & Policy, Vol.9, Issues 7-8, November – December 2006,
pages 675-684
The
chart above demonstrates the changes in the forest coverage of the Loess
Plateau overtime. For hundreds of thousands of years, the area decreased
steeply. The forest coverage in the year of 1990 was less than 19% of what it
was 3,000 years ago. Many factors have contributed to the disappearance of the
forest, both human and environmental.
For
instance, in the Qin Dynasty, the captial was Xianyang, now a city in Shaanxi
Province. From the map below it is obvious the city was in the center of the
Loess Plateau. (on the left hand of 西安)
In
history, the first emperor of Qin, Qin Shi Huang, ordered a large scale of
construction all over the country. In the mainland of the dynasty, “…massive
construction work began on palaces, gardens, and the imperial ancestral temples
on the south bank of the Wei River…”(Frances, P28) In addition, the emperor
created an integrated and convenient transportation network within the realm
which resulted in the massive disappearance of the forests.
It is
acknowledged that forests are indispensible for keeping water and soil. As a
result, deforestation deteriorated the ecosystem.
3. The Outbreak of Wars
Wars not only had a great impact on population, but also
the environment. According to Xi, the agriculture-animal husbandry boundaries
were usually affected by wars. When the nomadic nationalities invaded the south
from the steppe, the husbandry shifted southwards, and with the expansion of
the southern agricultural nationalities like the Han Dynasty, the line shifted
to north.
Several examples of the impact of the wars are given
below.
1.
The Qin Dynasty
In the Qin Dynasty, the authority conflicted with the
northern nomads called “Xiongnu”. In 215 BC, he “ordered General Meng north
with 300,000 men…”(Frances, P33) to begin the construction of the Great Wall,
which was designed as a defending system against the nomads in the north.
To
further stabilize the defense formed by the Great Wall, Qin Shi Hunag moved a
population of 500,000 in to the area of Ling Nan, and set up 44 different
settlements in He Tao area to reclaim the farmlands. (Baidupedia) Both the
migration and establishment of settlement played an important role in holding
the area behind the Great Wall and supplied food for the large number of troops
near the border against nomads.
http://baike.baidu.com/link?url=i_I_ioSElFOxz93l1XK4XiPfjOBYEUwEO7AaUACzgf2GUUQpnahKCqs9aDnpYq-K0JPG4Yqszd7zwFap12dIs_
Frances Wood, China’s First Emperor and His Terracotta Warriors, Google Scholar
2.
Han Dynasty
Han
Dynasty had a long history in battling against the nomads in the northwest
region. Those nomads, named as “Xiongnu” in Chinese, did not farm for food and
mostly rely on the livestock. However, nomadic groups needed all products like
garment, porcelain, spice, and perfume although they were not able to produce
any of those for daily life. The only solution to them was plundering those
people in south who lived on peasantry.
In
119 BC, the emperor of the Han Dynasty ordered a one-time migration of 700,000
people to the north. These people, especially men, were trained when the dynasty
assembled army. At the rest of the time, they played the role of peasants and
exploited the territory as farmlands for food. As a result, forests and
grasslands were destroyed in large scales and camps and farms were built
instead. The migration not only solved the food supply issue for the army, but
also provided a stable source of men for battle. However, the environmental
cost to sustain this huge group of population is enormous.
http://baike.baidu.com/view/1673346.htm
3. Song
Dynasty
Song
Dynasty struggled from the beginning of its ruling against the invasion of the
Liao Dynasty and the Jin Dynasty, and the later intrusion of the Mongolian
Empire. Due to its military composition, the Song’s army, which consisted of
footman and archers, was not able to fight against the horsemen of the nomads.
The government officials therefore created a series of military strategies to
minimize the disadvantages, but left a bad consequence on the environment.
First
of all, targeting at the nomadic troop’s reliance on the grasslands for food
supply, the Song officials burned the grasslands regularly in the Northwest to
cut off the food supply and decrease the mobility of nomadic horsemen. The
burning, as recorded by Jin, usually “extended to hundred of miles.”(P4)
Secondly,
the Northwest Plateau was cold and chilly for most times. Therefore timber and
woods were burned for warmth for the entire army. In a battle between 100,000
thousand men, the number of wood required for burning was tremendous. Moreover,
woods were also used for cooking. Both the military had a huge consumption of
timber.
Third,
woods were also crucial as weapons. For the Song’s military which depended
severely on archers, woods were the major component of arrows and crossbows.
With forest being cut in a large scale, the Song’s military acquired a hundred
thousand of arrows and few thousands of crossbows to counterbalance its
disadvantage in mobility.
Fourth,
settlements and camps required a lot of woods. “ In the war that lasted 140
years between Song and Jin, more than 500 cities, settlements, camps, and
fortress.”(P5) For shelter, the pillar of normal camps was wood. For larger
fortresses and settlements, wood was arranged as fences and protected the army
within it. Moreover, sharpened woods could be used as impediments to the
movement of horses, which was significant in battling against the nomads.
Jin,
Yongqiang, The Impact of the Battle
between Song and Jin Dynasty on the Plants of the Loess Pleateau, Journals
of Ningxia Teachers University (social science), vol.30, No4, August, 2009 (In
Chinese)
金勇强，《宋夏战争对黄土高原区植被的影响》， 宁夏师范学院学报（社会科学），第30卷第四期，2009年8月
4.
The
Qing Dynasty
At
the beginning of Qing Dynasty, the “foreign” nationality of Manchus attempted
to integrate the country and stabilize the royal ruling. The emperors put a
great emphasis on the burgeoning of population and land reclamation in order to
eliminate the hollowness created by war. The population in the Loess Plateau,
as a result, increased “even more quickly due to tax policies of the
government.”(Li, Wang)
Moreover,
as Guo mentioned in his research, the Qing authority had set up multiple
departments in remote areas of Shaanxi Province (central area of the Loess
Plateau) to oversee and assist the land reclamation. The local government
distributed lands according to the number of people per family, provided crop
seeds according the acres of farms, and offered cattle to each family.
“陕西的边邑之地，康熙末，官府多设“招徕馆”以鼓励垦荒，“民之来也，必计口授田，计田给种，朋户给牛”，使农民比较方便的得到小块土地。”
“ 清朝统治者出于稳定封建秩序，加强地主阶级专政的政治经济需要，对招徕垦荒给予很大的重视，先后颁布了一系列政策、法令。”
Guo,
Songyi, An Analysis of Early Qing
Dynasty’s Land Reclamation Policies, China Economic History Discussion
Forum, accessed on Nov. 24th, 2013 (In Chinese)
郭松义， 清初垦荒政策分析——《民命所系：清代的农业和农民》
Environmental
Factors
1.
Precipitation
The
precipitation of the Loess Plateau is concentrated in months of July, August,
and September, with an annual average between 200 to 600 mm. The rainfall in
these three months occupy 60-70% of the year total, usually in the form of high
intensity storms. These storms are capable of rooting up plants whose roots are
shallow, exacerbating soil erosion. Sediments transported by the Yellow River
and delta areas increase enormously in these three months.
Li, Wang
2.
Dust Storms
Dust storm is a new
factor of the environmental degradation for the region, which was not present
in the past, but common in the modern history of China. As the chart above
indicates, the frequency of sand storms increased in a rapid speed in recent
years. One explanation about the formation of the dust storms is that these
sands and silts are brought by strong winds from the Mongolian steppe to the
inner China, and even to South Korea and Japan. Due to deforestation, there are
no trees protecting the inner China as shields, nor grasses and plants serving
as water and soil keepers under the ground.
Beijing: Tiananmen Square is seen amid the sandstorm that has plagued
northwest China for the past few weeks
Photograph: Grace
Liang/Reuters, the Guradian
3. Soil Erosion
The Yellow river has
the largest sediment concentration of all rivers, 16.4 billion tons per year
(Sediment Specility Committee of Chinese Water Resources Association, 1989). A
large section of the yellow river flows through the loess plateau carrying all
the sediments along with it, causing the river bed to rise 8 to 10 cm every
year. This rise in the riverbed poses great risk of overflowing.
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yellow river delta
in 2009 source: http://earthobservatory.nasa.gov/Features/WorldOfChange/yellow_river.php
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 |
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highly eroded
landscape source: http://www.clw.csiro.au/ReVegIH/Photos.htm
|
The unique physical
and anthropogenic factors and their interactions in the loess plateau in China
make the place especially prone to soil erosion. First of all the soil in loess
plateau, sandy and mainly consists of loess, is highly erosive. Also the area
is very tectonically active, which forms gullies and causes large areas of land
slide. The valleys concentrates water and adds to its energy to take away soil.
Land without vegetation can be a thousand times more erodible than that with a
vegetation overage. Unfortunately, due to decades of deforestation, the forest
coverage on the loess plateau in China averages only 6.5% and in some areas it
can drop to 3%; the grass cover is only 25-65%. So the most part is just bare
soil, ready to be away by the heavy and concentrated summer rain, form July to
September, brought by the monsoon. All these elements explains why the loess
plateau in China is barren full of deep gullies and steep slopes, just like the
surface of a walnut. (Yangling 13)
Human activity is
the major factor that accelerates the soil erosion in the loess plateau. From
historical records, the loess plateau used to be contiguous with the Mongolian
steppe, vast and flat and nurturing grassland and forest with few gullies.But now
it is the most eroded place on earth; the population increase and irrational
use of land has destroyed the previous ecosystem. The increasing loss of soil
and water in the loess plateau can be seen from the flood record of the yellow
river. Before sui dynasty (A.D. 581 to 618) the Yellow River flood 1.1 times
per century on average, but the rate has increased to 155 times per century in
the Ming dynasty (A.D.1368 to 1644). The cultivation of slope lands contributes
the most to soil erosion. More than 50% of the total arable land in loess plate
is on slopes. But the growth of population has forced the cultivation of slopes
that are greater than 25 degrees where the risk of erosion is very high. Recent
developments in mining and oil and gas industries on the Loess Plateau, which
destroy vegetation and geological structure, can even double the amount of
erosion if left unchecked. (Yangling 15)
Yangling. “Soil and
Water Loss form the Loess Plateau in China.” Journal of Arid Environments
(2000) 45: 9–20. Print.
[1] J.X.
Xu, Historical bank-breachings of the
lower Yellow River as influenced by drainage basin factors, Catena, 45 (2001), pp. 1–17
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