Tải bản đầy đủ - 0 (trang)
1 Introduction: The Importance of Forests

1 Introduction: The Importance of Forests

Tải bản đầy đủ - 0trang


Z. Karancsi

reduce the rate of surface runoff, and in the meantime increase infiltration. (Leaflitter covering the surface has a high water-retaining capacity. The infiltration of

water into forest soils is 7–8 times higher, surface runoff 2–3 times higher in forested

surfaces compared to areas not covered by forests.) The age of forests can also

impact water budget in various ways. The older the forest stand is, the more surface

runoff it is capable to retain (Illés and Konecsny 2000). In addition, forests are

habitats of a number of plant and animal species, thus unreasonable deforestation

is most dangerous to the biosphere. Apart from their genetic values, forested areas

are also valuable from the point of view of the adequate functioning of the Earth’s

system. Forest stands have an important role in the exchange of CO2 and O2 gases.

Trees incorporate a significant amount of CO2 into their bodies. (Each square metre

of the tropical rain forests absorbs about 1 kg coal from the atmosphere, i.e. 10

t/ha (Kerényi 2003).) With forests cleared, atmospheric CO2 content increases and

the greenhouse effect intensifies. Forests are also capable of binding high amounts

of dust (30–70 t/ha), thus contributing to cleaning the air from pollutants (Kerényi


Wood is one of the civilisation’s most important raw materials and energy

sources. Finally, forests play an important role in recreation as well. Their

favourable climatic impacts advance the regeneration of the human body as well

as satisfy the soul.

About 2,000–3,000 years ago, along with the development of transportation

(shipbuilding, the appearance of wheeled carts), the destruction of temperate forests

started to take place in the Mediterranean. (Many researchers associate the intensive

transgression of almost all river deltas into the Mediterranean Sea and the silting of

a number of antique harbours (Ephesos, Miletos, Ravenna, etc.) with the increased

amount of debris resulting from deforestation.) Widespread grazing also impeded

the regeneration of forests. Roughly 200 years ago, the majority of the forests in

most of Europe and in Southeast Asia underwent the same process, partly due to the

population growth and the demands by the developing industry. The natural forest

cover fell victim to European settlers gaining ground in North America ca. 100 years

ago (Plate 8.1). By the 20th century, deforestation became focused on the tropics.

Today the destruction of the tropical rain forests takes place at an intensity never

witnessed before, for which the primary explanation is given by the economic and

social backwardness and the financial exposedness of the tropical countries.

Ten thousand years ago, an area of approximately 62.2 million square kilometres was covered by natural forests. (According to the definition by FAO, forests

are areas at least 0.5 ha in size and in which at least 10% of the area is covered by

foliage.) The area of natural forests, which represented nearly 42% of the land surface, dropped to 38.7 million square kilometres (26%) (Rakonczai 2003; Fig. 8.1).

Each year, ca. 3 billion tonnes of wood is used. More wood is used in Europe for furniture, construction material, firewood and paper than metals for any other purposes.

The rate of deforestation at the beginning of the 21st century is estimated to be

16 million hectares per year. Of this, about 14 million hectares are cleared in the

tropics. As a result of afforestation, the net loss of forested areas is ‘only’ ca. 10

million hectares.


Agriculture: Deforestation


Plate 8.1 A typical deforested landscape in the Midlands of England (Karancsi 1998)

The uppermost map in Fig. 8.1 indicates former natural forested areas, the middle one the total area of present-day natural and planted forests whereas the lower

one indicates the extension of natural forests now. Monoculture, i.e. when only a

single tree species is planted over large areas, is a feature of artificially planted ‘cultivated forests’. With the trees of such forests becoming exploitable at the same time,

clear-cutting, entailing intensified erosion processes (Plate 8.2) and land degradation

(Plate 8.3) seem to be nearly unavoidable. In times of forest renewals, for economic

reasons, alien species are often planted replacing indigenous ones with mostly negative impacts on the whole ecosystem (soil acidification, severe species degradation,


Hereafter, an overview will be provided on the relevance of tropical rainforests

and on the consequences of clear-cutting on their environment (Fig. 8.2).

These forests with complicated vertical structures are extremely abundant in

species. In certain regions of Amazonia, a single hectare contains as many plant

and animal species as the total of European forests. (Here, as many as 2,000 tree

species can be present on 1 ha in contrast to the forests of the moderate climate

where only a maximum of 20 tree species can be found.) This is the richest ecosystem of our planet. At its greatest extension, it is found in the Amazon and Congo

basins and also in Southeast Asia and Central America.

Tropical rainforests are also cleared to provide area for crop cultivation and

animal husbandry as well as for the trading of tropical wood.

During forest clearance, first the multi-storied abundant foliage, responsible for

the transpiration of large amounts of water, is removed. As the transpiration surface is reduced, the moisture content of the air drops and this results in lesser and

more sporadic rainfall. The existence of a tropical forest is based on rainfall. With

decreasing amounts of rainfall, the vegetation also begins to grow less dense and


Z. Karancsi

Fig. 8.1 Forested areas in the past and at present (Bryant et al.1997)

degraded. With a sparse foliage, irradiation increases and, due to the more intensive

vertical turbulent air movement, violent hailstorms become common.

The water-retaining capacity of the vegetation cover reduced by the clearance of

rainforests will have serious consequences. The foliage, coats of moss and lichen as

well as epiphyte plants of the rainforests intercept rainwater conveying it towards

the soil slowly (by drops). On the contrary, rainwater in deforested areas reaches

the ground surface unhindered, washing away soil particles (erosion). The otherwise thin soil of the rainforests is gullied by erosion into badlands. In deforested

areas, the increasingly scarce vegetation will be composed of less demanding plant

species. Violent hails, after a while, can entirely wash away the laterite soils from

the bedrock and make revegetation impossible.


Agriculture: Deforestation


Plate 8.2 Gully development after clear-cutting at the western rim of the Medves Plateau

(Karancsi 2003)

Plate 8.3 Typical ‘badland’ formation after deforestation at Kazár, North-Hungary (Karancsi


Intense rainfall will raise the water-level of rivers causing floods, which destroy

agricultural lands and settlements along the river banks. Fluvial sediments will fill

up lakes furthering large-scale eutrophication.

Tropical rainforests evenly use solar energy and reflect only 8–14%. The albedo

of the bushland formed after forest clearance is 15–20%, whereas that of an eroded

surface can exceed 30%. Intensive inward and outward radiation also mean a great


Z. Karancsi

Fig. 8.2 The impact of

tropical forest clearance on

the environment (Balázs


fluctuation of temperature that is not tolerated by plants accustomed to evenly warm

and humid climate. Further species will be extinct.

The clearance of tropical rainforests also has an influence over further regions,

where the amount of precipitation is also reduced and seasonal droughts become

more frequent there. Thus former deciduous closed forests are replaced by savannas

with groves, wooded savannas become treeless grasslands, whereas in former grasslands, grass becomes sparse and desertification begins to take place. This process

has a disastrous impact on farming. Farmers are forced to move closer to areas under

equatorial climate and with a higher amount of precipitation, where, on the contrary,

endowments for production (shallow soils poor in nutrients) are less favourable and

new agricultural areas are gained by forest clearance. Stock keepers are also forced

to leave their pastures abandoned under desertification and have to form new grazing

lands for either farmers or forested areas.

Tropical rainforest clearance is also associated with the destruction of local

peoples’ lifestyles.


Agriculture: Deforestation


8.2 History of Woodlands in the Carpathian Basin

The Holocene was the period when the Carpathian Basin became forested and the

stock-breeders and farmers appeared. This is, therefore, also the advent of deforestation. The parallel processes of the natural expansion of forests and anthropogenic

impacts influenced the history of Hungary’s forests in the past ca. 8,000 years.

(Traces of the first settlements of farmers in Hungary are from the 6th millennium

BC. The age of the earliest Neolithic site (Szeged-Gyálarét) is dated by the radiocarbon method at 7090 ± 100 BP (Bácskai 1982)). It is estimated that without human

influence on the environment, the natural vegetation of Hungary at present would

be forest steppe and more than 60% forested (Medzihradszky 1996).

Forested areas reached their greatest extension during the Paleolithic and the Iron

Age, as climate provided the most favourable conditions to the expansion of woods

while nature transformation by humankind were only of a minor scale at that time.

During the Neolithic Period with more arid climate, there was a decrease in wooded

areas, while grasslands expanded. Prior to the beginning of human landscape transformation, approximately 60% of Hungary was covered by forests. By the time of

the Magyar Conquest, forest clearance reduced the cover to 43%. The country witnessed the lowest rate of forested areas (11.8%) in 1913 (the data is for the area of

present-day Hungary). Today, forests cover more than 20% of the area; however,

only one-third of this resembles former (potentially) natural forests whereas the rest

is plantation or intensively transformed forests (Németh 1998). [Here, the notion

of (potential) natural forest refers to the presence of zonal associations (Turkey

oak-sessile oak, hornbeam-oak on higher terrains, and beech on cooler slopes with

northern exposure) less disturbed by humans.]

According to the results of pollen analyses, the Hungarian low mountains could

have been mostly covered by beech woods in the Subboreal (2,500–5,000 years

ago) (Pócs 1981). In the Subatlantic, lasting to the present, such beech woods

retreated to higher regions. Human appearance in the Carpathian Basin is estimated

at about 6000 BC. Anthropogenic impacts were, in the Neolithic, restricted to rather

small patches, landscape transformation only accelerated later. Farming and animal

husbandry have been gaining ground at the expense of forests along the lowland

margins from the Copper Age. Forest clearance involved accelerated soil erosion

and renewed movements of wind-blown sand.

8.3 Case Study: Geomorphological Impacts of Deforestation

Through the Example of the Medves Region

The research area of 32 km2 , henceforth called the Medves Region, is part of one

of the micro-region of the North Hungarian Mountains, called the Medves Plateau,

Central Europe’s largest basalt plateau (with an area of 13 km2 , of which an 8 km2

section falls within the territory of Hungary) and the adjacent regions with a more

varied morphology and basalt peaks of higher elevations (e.g. Salgó – 625 m,


Z. Karancsi

Fig. 8.3 The Medves Region with the study area (Karancsi 2005)

Szilvásk˝o – 628 m) (Horváth et al. 1997; Karancsi 1998a,b). This area with diversified morphology neighbouring Slovakia has been part of the Karancs–Medves

Landscape Protection area since 1989 (Fig. 8.3).

8.3.1 A Historical Review of Agricultural Landscape Alterations

To understand anthropogenic impacts, the temporal and spatial variations and

human activities in the region have to be studied. In lack of a comprehensive

archaeological survey, general data as well as written and mapped sources found

in archives provide information on the area (Erd˝osi 1978; Gazdag 1964).

The majority of the research area has been used by agriculture and forestry

for a long time (Dornyay 1928). In the Copper Age, beginning here around 2500

BC, an ethnic group similar to the Badenian Culture populated the area. Unlike

Stone Age people, they were primarily stock keepers, thus were often forced to

change their locations. During herding, new pastures were created by, in addition

to migration, forest clearance, i.e. the appearance of anthropogenic impacts can be

estimated by and large to this period in the region. Migratory herding caused trampling; deforestation accelerated erosion, in other words, gradual land degradation

and dissection.

The Bronze Age (1800–750 BC) witnessed population growth. Among the

people of the Iron Age starting around 750 BC, Scythians involved in animal husbandry (mainly of horses dominated the area for nearly 300 years).

Tài liệu bạn tìm kiếm đã sẵn sàng tải về

1 Introduction: The Importance of Forests

Tải bản đầy đủ ngay(0 tr)