|
1. Definition
| Name |
VEGETATION
COVER |
| Brief
definition |
The percentage of soil
which is covered by green vegetation. Leaf area index (LAI)
is an alternative expression of the term vegetation cover
which gives the area of leaves in m² corresponding to an area
of one m² of ground.
 |
Hilly
area cultivated with olive groves in which vegetation
is partially covering and protecting the soil (photo by
C. Kosmas). |
|
| Unit
of measure |
% |
2. Position
within the logical framework DPSIR
3. Target and
political pertinence
| Objective |
Contribution
to the definition and mapping of ESAs and assessing the desertification
risk of an area. |
| Importance
with respect to desertification |
Vegetation
cover is key factor on land degradation. Reduction in the perennial
cover is regarded as an important indicator of the onset of
desertification. Vegetation cover plays very important role
on protecting the soil surface from raindrop splashing, increasing
soil organic matter, soil aggregate stability, water holding
capacity, hydraulic conductivity, retarding and reducing surface
water runoff, etc. Many authors demonstrated that in a wide
range of environments, both water run-off and soil sediment
loss decrease exponentially as the percentage of vegetation
cover increases. |
| International
Conventions and agreements |
The CCD emphasizes
that combating desertification must be tackled within the general
framework of actions to promote sustainable development.
|
| Secondary
objectives of the indicator |
Vegetation
cover is closely related to annual rainfall and soil depth.
As rainfall and soil depth decrease, vegetation cover decreases.
|
4. Methodological
description and basic definitions
| Definitions
and basic concepts |
Many authors have demonstrated
that in a wide range of environments, both run-off and sediment
loss decrease exponentially as the percentage of plant cover
increases. A value of 40% vegetative cover is considered the
critical threshold below which accelerated erosion dominates
in a sloping landscape. This threshold may be modified for
different types of vegetation, rain intensity and land attributes.
In the case of poor plant cover, the erosion processes may
be very active and the regeneration of natural vegetation
may be irreversible.
Soil erosion and degradation
begins only when a substantial portion of the land's surface
is denuded of vegetation, then it proceeds with an accelerated
mode, that cannot be arrested by lands resistance alone. Deep
soils on unconsolidated parent materials show slow rates of
degradation and loss of their biomass production potential.
In contrast, shallow soils with lithic contact on steep slopes
have low productivity, and low erosion tolerance if they are
not protected by adequate vegetation. Soil and vegetation
survey data from the island of Lesvos clearly indicated that
the percentage plant cover was greatly affected by the soil
depth in the various climatic zones. Vegetation cover increased
with increasing soil depth and decreasing longevity of drought.
In the soil depth class of 15-30 cm, the vegetation cover
class of 25-50% had the maximum frequency of appearance (93%)
in the semi-arid zone, whereas areas with soils having the
same soil depth class had a higher vegetation cover with a
64% maximum frequency of appearance of the cover class 75-90%
cover in the dry sub-humid zone. Soil erosion measurements
conducted in eastern Spain showed that soil erosion rates
for bare soils ranged from 0 to 3720 g m-2 h-1, while the
densely vegetated soils show negligible runoff and erosion.
|
| Benchmarks
Indication of the values/ranges of value |
|
| Methods of
measurement |
Vegetation
cover can be easily measured in the field by assessing the percentage
of the ground that it is covered by the existing vegetation.
Aerial photographs or satellite images can be use for measuring
vegetation cover of an extensive area. |
| Limits of the
indicator |
Vegetation
cover can be altered with time especially for perennial deciduous
plants or annual vegetation. Measurements for vegetation cover
is especially important during the wet period when soil erosion
occurs. |
| Linkages
with other indicators |
Soil
texture, Soil depth, Drainage,
Aridity index (1), Rainfall,
Slope aspect, Land
use type. |
5. Evaluation
of data needs and availability
| Data required
to calculate the indicator |
Percentage
vegetation cover per soil mapping unit for the crucial period.
|
| Data sources |
Necessary data
are usually available and accessible and the cost/benefit ratio
is reasonable. |
| Availability
of data from national and international sources |
Data
can be obtained from various regional, national or international
institutions involved in collecting and elaborating such data.
|
6. Institutions
that have participated in developing the indicator
| Main institutions
responsible |
Agricultural
University of Athens
|
| Other contributing
organizations |
Universities
of Lisbon, Murcia, Basilicata, Amsterdam, Leeds
|
7. Additional
information
| Bibliography
|
Kosmas, C.,
Kirkby, M. and Geeson, N. 1999. Manual on: Key indicators of
desertification and mapping environmentally sensitive areas
to desertification. European Commission, Energy, Environment
and Sustainable Development, EUR 18882, 87 p. |
| Other
references |
Cerda, A., 1999. Parent
material and vegetation affect soil erosion in Eastern Spain.
Soil Sci. Soc. of America, 63: 362 - 368.
Francis C. F. and Thornes,
J. B., 1990. Runoff hydrographs from three Mediterranean vegetation
cover types. In : J.B. Thornes (ed.), Vegetation and Erosion,
Processes and Environments. Wiley, Chichester, pp. 363-384.
Kosmas, C., Gerontidis,
St., and Marathainou, M. 1999. The effect of land use change
on soil and vegetation over various lithological formations
on Lesvos (Greece). Catena, 40:51-68.
Kosmas, C., Danalatos,
N.G, and Gerontidis, St. 2000. The effect of land parameters
on vegetation performance and degree of erosion under Mediterranean
conditions. Catena, 40:3-17
Thornes, J., 1996. Desertification
in the Mediterranean. In: J. Brandt and J. Thornes (eds.),
Mediterranean Desertification and Land Use. J. Wiley &
Sons, Chichester, England, p. 1-12.
|
| Contacts
Name and address |
Agricultural University
of Athens, Laboratory of Soils and Agricultural Chemistry,
Iera Odos 75, Athens 11855, Greece
Dr Constantinos Kosmas
email: lsos2kok@aua.gr
|
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