1. Definition
Name |
FOREST
PRODUCTIVITY |
Brief definition |
The net primary
production (NPP) of a forest is a well suited indicator of forest
productivity. It consists of the accumulation of stem wood in
standing trees plus the growth of all the other tissues or components
including those that are short- lived and roots. |
Unit of measure |
Mg C * ha-¹
* yr-¹ ( g C * m-² * yr-¹ ) |
Spatial scale |
|
Temporal
scale |
|
2. Position
within the logical framework DPSIR
Type of Indicator |
Driving Force/State |
3. Target and
political pertinence
Objective |
The
indicator contributes to define the forest productivity which
represent a indirect indicators of degradation of forest for
this reason contributes to quantified the process of deforestation
in a definite area. |
Importance
with respect to desertification |
Land degradation means
the loss of biological and/or economic productivity and complexity
in croplands, pastures, forests and woodlands due to soil
use, to a process or a combination of several processes amongst
which: water and wind erosion, modification of the physical,
chemical and biological properties of soils; destruction or
modification of the vegetation cover. Amongst the causes of
degradation linked to human activities, the cultivation of
inappropriate areas, overgrazing, deforestation and inadequate
irrigation practices. The intensification of these activities
has resulted in the loss of resilience in arid land ecosystems.
Maintaining the health
and productivity of forest ecosystems is an important prerequisite
to sound stewardship and the sustainable development of forested
lands. Slow productivity of forests means reduced amount of
biomass, consequently the forest cover is less resistant and
more prone to irreversible transformations.
A piece of land is considered
desertified when the biomass productivity drops below a certain
threshold value. A value of 40% vegetative cover is considered
critical below which accelerated erosion dominates in a sloping
land (Thornes, 1988). This threshold may be modified for different
types of vegetation, rain intensity and land attributes.
|
International
Conventions and agreements |
UNCCD recognised
about the particular conditions of the Mediterranean causes
of desertification process 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 |
It represents
a fundamental indicator for regard the impact of degradation
of forest surface and to value the quality of forest management..Information's
about desertification can help in addressing political measures
to recognise the loss of cover vegetation an area and to organise
an efficient control activity of phenomena and indirectly the
reduction of desertification process of the territory. |
4. Methodological
description and basic definitions
Definitions
and basic concepts |
The net primary production
(NPP total=aboveground+beloveground) of a forest consists
of the accumulation of stem wood in standing trees plus the
growth of all the other tissues or components including those
that are short lived. The definition of NPP also includes
the accumulations of all other plant and animal life in the
forest. In more detail, forest productivity considers the
accumulation of photosynthetic by the tree canopy and its
allocation into tissue, losses due to respiration by the trees,
the photosynthesis and respiration by other plant life, and
the consumption and respiration by animals and microbes. Further,
material or residues that are not metabolised add to the organic
content of the forest floor and soil. We measure this productivity
through annual observations of the biomass of various tissues
comprising the forest.
The balance between carbon
fixation in photosynthesis and carbon loss in plant respiration
is the Net Primary Productivity (NPP).
NPP has been defined by
Odum as "the rate of storage of organic matter in plant
tissues in excess of respiratory utilization by plants".
Leaf area index (LAI)
is an important structural characteristic of forest ecosystems
which has been shown to be strongly related to forest mass
and energy cycles and forest productivity. LAI is more easily
measured than forest productivity, and so a strong relationship
between LAI and productivity would be a valuable tool in forest
management.
|
Benchmarks
Indication of the values/ranges of value |
|
low |
medium
|
high |
Temperate
forest |
376 |
883 |
1015 |
Boreal
conifers |
201 |
283 |
365 |
Boreal
forest |
162 |
365 |
568 |
Mixed
forest |
320 |
505 |
720 |
Subtropic
forest |
358 |
741 |
1124 |
Tropical
forest |
500 |
891 |
1500 |
Woodland
and wooded grassland |
20 |
238 |
562 |
Open
shrubland |
4 |
192 |
380 |
Grassland |
37 |
295 |
554 |
Crop |
274 |
493 |
712 |
Bare
ground |
3 |
28 |
52 |
Values in: g C * m-² * yr-¹ ; from Zheng, D. L., et
al. 2003 |
Methods of
measurement |
In studies of forest productivity
and "health", high resolution spectral data have
the potential to become powerful tools for scaling of physiological
activity from the canopy to the landscape level. If well corrected,
they can also become flexible & accurate tools for long-term
monitoring of changes in vegetation structure (LAI) and function
(photosynthesis), in response to long- and short-term stresses.
The theory and rationale
of the use of remote sensing in estimating photosynthesis
activities and NPP are described in Sellers (1987) and Ruimy
et al. (1994).
The methods proposed are
often descended from the original formulation of Monteith
(1972) and Kumar and Monteith (1981), and take the form of:
NPP(t) = e (t) APAR (t)
where,
- NPP is the net primary
productivity at time (t);
- e is the conversion
efficiency at time (t) [g/MJ];
- APAR is the fraction
of intercepted photosynthetically active radiation at time
(t)
APAR quantifies implicitly
the amount of leaf area that the vegetation is displaying
to absorb radiation, that is the leaf area index (LAI).
The conversion efficiency
e, translates the APAR in energy units to final tissue growth
(NPP, biomass). Early efforts assumed a constant value of
e (1.5 g/MJ); more recent efforts have either specified "e"
as function of biome type (Ruimy, et al., 1994); these authors
gave biome-mean values of "e" ranging from 0.37
(dry tropical and subtropical forests) to 2.07 (in croplands).
Many projects demonstrated
to obtain an accurate and repeatable measure of the Net Primary
Productivity (NPP) of terrestrial vegetation, using SPOT4
- VEGETATION data (Sabbe H., Veroustrate F.,)
The estimation of NPP
is based on C-Fix model.
|
Limits of the
indicator |
Each model
can provide different results on the basis of the complexity
of the considered factors. Models providing better results require
input data that is not easy to find. |
Linkages
with other indicators |
Forest
fragmentation, Deforested
area, Biodiversity
conservation, Area of matorral,
Forest management quality |
5. Evaluation
of data needs and availability
Data
required to calculate the indicator |
Remote sensing images,
registered by optical sensors with high temporal frequency,
such as NOAA-AVHRR or SPOT4-VEGETATION, MODIS
The meteorological inputs
(daily incoming solar radiation and mean air temperature T,
etc.) obtained from weather stations.
|
Data sources |
E.O. data,
meteorological data, soil data. |
Availability
of data from national and international sources |
Satellite
data can be used to measure the Net Primary Productivity (NPP) |
6. Institutions
that have participated in developing the indicator
Main institutions
responsible |
University
of Basilicata |
Other contributing
organizations |
|
7. Additional
information
Bibliography
|
Odum, E., 1971. Fundamental
of Ecology. Philadelphia: Saunders
Thornes, J. B. (1988).
Erosional equilibria under grazing. In J. Bintliff, D. Davidson
and E. Grant (eds.) Conceptual Issues in Environmental Archaeology,
Edinburgh University Press, pp. 193-210.
Monteith, J.L, 1972. Solar
radiation and productivity in tropical ecosystems. J. Appl.
Ecol. 9, 747-766.
Ruimy, A. and Saugier,
B., 1994. Methodology for the estimation of terrestrial net
primary production from remotely sensed data. Journal of Geophysical
Research, 99: 5263-5283.
Sabbe H., Veroustrate
F., Project: Demonstration of a standard net primary productivity
product for the SPOT 4-VEGETATION instrument. http://www.geosuccess.net/Geosuccess/Documents/main.htm.
Seller P.J. 1987, Canopy
reflectance, photosynthesis and transpiration. The role of
biophisics in the linearity of their interdependence. Remote
Sensing of Environment, Issue 21, 143-183.
Zheng, D. L., S. D. Prince,
and R. Wright. 2003. NPP Multi-Biome: Gridded Estimates for
Selected Regions Worldwide, 1989-2001i, R1. Data set. Available
on-line: http://www.daac.ornl.gov/ from the Oak Ridge National
Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee,
U.S.A
|
Other references |
|
Contacts
Name and address |
Prof.
Agostino Ferrara
University of Basilicata
Via dell'Ateneo Lucano
85100 Potenza, Italy
e-mail: ferrara@unibas.it |
|