|
1. Definition
|
Name
|
FOREST
FRAGMENTATION
|
|
Brief
definition
|
The
process of transforming large, contiguous forest patches
into one or more non contiguous smaller patches, surrounded
by disturbed areas.
|
|
Unit
of measure
|
%
of territory involved
|
|
Spatial
scale
|
|
|
Temporal
scale
|
|
2.
Position within the logical framework DPSIR
|
Type
of Indicator
|
Driving
Force/State
|
3.
Target and political pertinence
|
Objective
|
This
indicator measures forest fragmentation. This refers
to a landscape-level process in which a specific habitat
is progressively sub-divided into smaller, geometrically
more complex, and more isolated fragments, as a result
of both natural and human activities.
|
|
Importance
with respect to desertification
|
The
primary cause of forest fragmentation is suburban
development, which causes many of the remaining large
parcels of forests to be converted for anthropogenic
uses, most notably as residential development.
The
fragmentation of forests by agricultural clearing
has been exacerbated by land taken for urban development
and infrastructures, as well as by large-scale and
repeated fires in Mediterranean regions. In addition,
human activity has utilized most of the remaining
forest. In the late 1990s this trend was partly reversed
by afforestation and spontaneous regrowth on former
agricultural land.
Increasingly,
previously extensive, continuous tracts of forest
are being reduced to widely dispersed patches of remnant
forest vegetation by logging and road-building, but
few measures of the effects of roads on forest fragmentation
are available. Fragmentation affects animal populations
in a variety of ways, including decreased species
diversity and lower densities of some animal species
in the resulting smaller patches.
Fragmentation
is also responsible for bringing about an alteration
in the microclimate within and surrounding remnant
patches of vegetation. This can result in altered
physical fluxes eg. radiation, wind and water.
An
important consequence of forest fragmentation is the
increase in forest edges, along which there are strong
microclimatic gradients, or edge effects. These include
variations in light, temperature, soil moisture content
and wind turbulence. It has been suggested that a
500-1,000 m (0.5 - 1.0 km) buffer zone is needed to
accommodate all edge effects. Edge effects increase
dramatically with fragmentation. Importantly, as fragmentation
and deforestation continues, the proportion of the
remaining total area of ancient forest affected by
fragmentation increases.
Habitat
fragmentation has become a problem of general concern.
The fragmentation concept encompasses three aspects:
(1) reduction of the total area,
(2) scattering of residual formations in a mosaic
in which the remaining individual elements are disjointed
and
(3) increasing of total edge, therefore enhanced exchanges
with the surrounding parts of territory.
The
latter is strongly related to fire because of a larger
and larger perimeter with increasing fragmentation,
therefore easier passage for running fires. In a very
fragmented forest scenario (Leone et al. 2001) it
has been observed that edge values of 83 m ha-1
are present.
Fragmentation
therefore involves changes in landscape composition,
structure and function at many scales, and occurs
on a backdrop of a natural patch mosaic, created by
changing landforms and natural disturbances.
Defined
in such a way, the fragmentation concept appears to
be scale-free: it addresses no particular scale because
the phenomena can occur at all scales. Also the definition
addresses no particular kind of habitat because the
fragmentation can occur in most types of habitat.
|
|
International
Conventions and agreements
|
The
UNCCD recognised the particular conditions of the
Mediterranean affecting desertification processes,
including the extensive forest coverage losses due
to different causes (deforestation, frequent wildfires,
intensive grazing etc) (Convention text as of September
1994 and as of September 2001)
|
|
Secondary
objectives of the indicator
|
This
indicator represents the impact due to reduction or
loss of forest surface. Information about forest fragmentation
can help in addressing political measures to recognize
the loss of cover vegetation in a specific area and
to organize efficient control and indirectly reduce
desertification.
|
4.
Methodological description and basic definitions
|
Definitions
and basic concepts
|
Fragmentation
describes vegetated land cover shrinkage, scattering
and disjointing. These conditions induce the transformation
of a continuous cover into a "porous" mosaic.
Fragmentation involves changes in landscape composition,
structure, and function at many scales and occurs
on a backdrop of a natural patch mosaic, created by
changing landforms and natural disturbances.
|
|
Benchmarks
Indication of the values/ranges of value
|
Pf<0.4
= low incidence
0.4 < Pf < =0.6 = moderate incidence
Pf>0.6 and Pf-Pff>0 = high incidence
Pf > 0.6 and Pf = Pff = very high incidence
|
|
Methods
of measurement
|
There
are numerous measures of forest fragmentation and
forest connectivity currently described in the literature.
These include average forest patch size, percent interior
forest, mean forest patch density, number of forest
patches, interpatch distance, forest patchiness, forest
contiguity, forest continuity, and proportion of forest
in the largest forest patch (Vogelmann, 1995; Trani
and Giles, 1999; Wickham et al. 1999). Several of
these measures were assessed in a study conducted
by Trani and Giles (1999) to determine how change
in forest loss influenced their results.
The
model of Riitters et al. (2000), developed to assess
forest fragmentation at the global level, generates
categories that describe the type of forest fragmentation
condition that exists for a given forest pixel. Two
values that characterize a forest pixel at the centre
of a moving window are necessary. The first is the
proportion of forest, or Pf. In a window where the
centre pixel is forest, Pf is the number of pixels
in the window that are forest divided by the number
of pixels in the window that are not forest.
pF
= (forest pixels in window)/(pixels in window that
are not forest)
The
second measure is the connectivity of the forest,
or Pff. Pff measures connectivity using pixel pairs.
It is the number of pixel pairs where both pixels
are forest divided by the number of pixel pairs with
at least one forest pixel.
Pff
= (pixel pairs that are both forest)/((pixel pairs
that are both forest)+(pixel pairs with one forest))
Pf
and Pff are used to distinguish between six types
of forest pixels:
Interior forest (Pf = 1) All of the pixels
surrounding the centre pixel are forest.
Patch forest (Pf<0.4) Pixel is part of a
forest patch on a non-forest background, such as a
small wooded lot within an urban region.
Transitional forest (0.4 < Pf < 0.6)
About half of the cells in the surrounding area are
forested and the centre forest pixel may appear to
be part of a patch, edge, or perforation depending
on the local forest pattern
Edge forest (Pf>0.6 and Pf-Pff<0) Most
of the pixels in the surrounding area are forested,
but the centre pixel appears to be part of the outside
edge of forest, such as would occur along the boundary
of a large urban area, or agricultural field.
Perforated forest (Pf>0.6 and Pf-Pff>0)
Most of the pixels in the surrounding area are forested,
but the centre pixel appears to be part of the inside
edge of a forest patch, such as would occur if a small
clearing was made within a patch of forest.
Undetermined forest (Pf > 0.6 and Pf = Pff)
Most of the pixels in the surrounding area are forested,
but this centre forest pixel could not be classified
as a type of fragmentation in the surrounding area.
|
|
Limits
of the indicator
|
One
limit of the indicator is the difficulty in evaluating
the protective cover effects of the mosaic.
|
|
Linkages with other
indicators
|
Deforested
area, Area of matorral,
Biodiversity
conservation, Forest
productivity, Forest
management quality
|
5.
Evaluation of data needs and availability
|
Data
required to calculate the indicator
|
E.O.
data, land-cover maps, forest maps.
|
|
Data
sources
|
Land
cover maps, forest maps, aerial photos, digital land
cover maps classified from remote-sensing data.
|
|
Availability
of data from national and international sources
|
Data
on forest surface can be provided by the Eurostat
and National Statistic Organizations. Satellite data
too can be used to measure current forest cover.
|
6.
Institutions that have participated in developing the indicator
|
Main
institutions responsible
|
University
of Basilicata, Italy
|
|
Other
contributing organizations
|
|
7.
Additional information
|
Bibliography
|
Forman, R.T.T. 1995. Land mosaics: the
ecology of landscape and regions. Cambridge University
Press, Cambridge.
Riitters, K., J. Wickham, R. O'Neill,
B. Jones, and E. Smith. 2000. Global-scale patterns
of forest fragmentation. Conservation Ecology 4(2):1-28.
URL: http://www.consecol.org/vol4/iss2/art3
Trani, M.K. and R.H. Giles, Jr. 1999.
An analysis of deforestation: metrics used to describe
pattern change. Forest Ecology and Management. 114:459-470.
Vogelmann, J.E. 1995. Assessment of forest
fragmentation in southern New England using remote
sensing and geographic information system technology.
Conservation Biology 9(2):439-449.
Wickham, J.D., K.B. Jones, K.H. Riitters,
T.G. Wade and R.V. O'Neill. 1999. Transitions in forest
fragmentation:implications for restoration opportunities
at regional scales. Landscape Ecology 14: 137-145.
Leone V., Lombardi V., Lovreglio R.,
Mininni M., Semerari P.,2002 Inventario dei boschi
dell'Alta Murgia. Primi risultati in "Studi per
il Piano d'area dell'Alta Murgia" a cura del
DAU, Dipartimento di Architettura e Urbanistica, Politecnico
di Bari
|
|
Other
references
|
|
|
Contacts
Name and address
|
Prof.
Agostino Ferrara
University of Basilicata
Via dell'Ateneo Lucano
85100 Potenza, Italy
e-mail: ferrara@unibas.it
|
|
|
