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Desertification Indicator System for Mediterranean Europe


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