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FORSEE : Indicateur évalué

Indicator 5.3.2 : Nutritive status
Forest area covered (1995): 4956,1 ha

Percentage of the total forest area in Sousa Valley: 14,3 %

Number of plots: 35

Cost

TOTAL COST: 1300,75 €

Costs/plot: 37,1 €

The total cost includes:

1-Data collection

462,5 €

2-Data analysis

838,25 €

Results

Chemical characteristics of soils in the FORSEE forests plots

table1

Source: UTAD laboratorial analysis

Pb- Pure stands of Pinus pinaster; Ec- Pure stands of Eucalyptus globulus; PbEc- Mixed stands of Pinus pinaster and Eucalyptus globulus; EcPb- Mixed stands of Eucalyptus globulus and Pinus pinaster.

Classes of soil fertility in the soils of Eucalyptus stands in Portugal

table2

Source: Fabres et al. (2005). Indicadores de fertilidade do solo e do estado nutricional da planta para o cultivo de Eucalyptus globulus. RAIZ – Instituto de Investigação da Floresta e do Papel.

Classes of acidity for forest soils

table3

Source: Fabres et al. (2005). Indicadores de fertilidade do solo e do estado nutricional da planta para o cultivo de Eucalyptus globulus. RAIZ – Instituto de Investigação da Floresta e do Papel.

Classes of acidity in Maritime pine stands

table4

Source: Gandullo, JM.; S. Gonzalez Alonso y O. Sanchez Palomares (1994). Estaciones Ecológicas de los pinares españoles. ICONA Madrid. 188p.

Remarks (1)

Fabres et al. (2005) parameters

Fabres et al. (2005) have developed applied research in the field of the forest soils and nutrition with the aim of establishing reference values to parameters of soil analysis and foliar concentration of nutrients that allow to a good interpretation of Eucalyptus’ cultivation. These authors suggest classes of soil fertility and classes of foliar concentration of nutrients to the evaluation of the fertility of the soil and its nutritional state. It was defined 5 classes corresponding to different levels of soil nutrients: Very low, Low, Mean, High and Very High. The classes Very Low and Low are considerate to have a level of nutrients that restrict the growing of eucalyptus, the classes Mean and High are considerate to have an adequate level of nutrients for the eucalyptus growing and the class Very High is considered to have an excessive level of nutrients for the eucalyptus growing.

The assumptions to the interpretation of the RAIZ table are:

1)The soil deepness referred by the levels is 40 cm, except for thin soils;

2)The average stony of soils considered was 15%;

3)The classes were established in order to include most of the forest productivities found in Portugal (between 10 m3 /o.b./ha/year and 40 m3 /o.b./ha/year;

4)The classification of the nutrients of the soils is only valid to the methods of analysis used by RAIZ (method of extraction of nutrients of Egner-Riehm - P and K in mg/kg - and acetate of ammonium - K, Ca and Mg in cmol/kg).

Gandullo et al. (1994) parameters

Gandullo et al. (1994) present reference values for Maritime pine, but the parameters available are only for pH in water. They define 4 classes of acidity: Very low, Low, High and Very high.

EUCALYPTUS GLOBULUS

The reference values were given by Fabres et al.(2005), RAIZ.

1) pH (in water): The results of soil analysis show that for a soil deepness between 30-60 cm the pH (H2O) is 4,6 in pure stands and is 4,7 in mixed stands where Eucalyptus is dominant. According to the reference values given by RAIZ the pH of forest soils in Eucalyptus stands in the pilot zone is Acid;

2) P2O5: The results of soil analysis show that for a soil deepness between 30-60 cm, the content of P2O5 is 3,9 in pure stands and 5 in mixed stands where Eucalyptus is dominant. According to the reference values given by RAIZ the content of P2O5 of forest soils in Eucalyptus stands in the pilot zone is Very Low to Low.

Remarks (2)

3) K2O: The results of soil analysis show that for a soil deepness between 30-60 cm, the content of K2O is 43 in pure stands and 49 in mixed stands where Eucalyptus is dominant. According to the reference values given by RAIZ the content of K2O of forest soils in Eucalyptus stands in the pilot zone is Mean (in the average).

4) Ca: The results of soil analysis show that for a soil deepness between 30-60 cm, the content of Ca is 0,3 in pure stands and 0,2 in mixed stands where Eucalyptus is dominant. According to the reference values given by RAIZ the content of Ca of forest soils in Eucalyptus stands in the pilot zone is Low.

5)Mg: The results of soil analysis show that for a soil deepness between 30-60 cm, the content of Mg is 0,1 in pure stands and 0,1 in mixed stands where eucalyptus is dominant. According to the reference values given by RAIZ the content of Mg of forest soils in Eucalyptus stands in the pilot zone is Mean (in the average).

MARITIME PINE

The only references one has are the values for pH in water given by Gandullo et al. (1994).

Then:

1) pH (in water): The results of soil analysis show that for a soil deepness between 30-60 cm the pH (H2O) is 4,7 in pure stands and is 4,4 in mixed stands where Maritime pine is dominant. According to the reference values given by Gandullo et al. (1994) the pH of forest soils in Pine stands in the pilot zone is Low.

Problématique et améliorations

The expert group for criterion 5 couldn’t provide reference values for the forest species of the Atlantic arc. The reference values for Portuguese forest soils presented in this report were given by RAIZ a private non-profit research institute committed to support the competitiveness of the Portuguese Pulp and Paper Industry. The link with future research related to FORSEE project and RAIZ should be kept given the knowledge and expertise accumulated through the years by this research institution in what is concerning to the cultivation of Eucalyptus.

Data provided by this institute was very convenient since the pilot zone is almost covered by Eucalyptus however for Maritime pine it was not founf references about their nutritive requirements or reference values for the soils where this specie is dominant.

The comparison between the reference values and the soil analysis in the pilot zone can give a general idea about soils nutrition and contents of O.M. but is it is hard to state if the sustainability of forests is being accomplished or not since there is a high number of variable interfering on that.

There was also a change in the methodology of soils collection that can be affecting the results. If FORSEE field guide was requiring 10 samples per plot, collected in a systematic way (see FORSEE field guide), the FORSEE field team decided to collect only 3 samples per plot in aleatory way.

This happened because:

a) Logistic reasons that impeded to transport in the car 10 soil samples per plot;

b) Financial reasons, given the high costs of the laboratorial analysis.

Other shortcoming is that the soil samples were only collected in the South part of the municipality of Paredes and not in all Sousa Valley.

Commentaires et conclusion

This indicator is feasible but costly given the human resources needed to collect the soil samples, the human strength that is needed to collect the samples and the laboratorial analysis per se.

However it seems important to assess the nutrient characteristics of the forests soils in determined intervals that can be more or less spaced in time according to soil researchers.

The main species in Continental Portugal are Maritime pine and Eucalyptus. For Maritime pine it was difficult to find reference values but for Eucalyptus the RAIZ institute could provide some reference values.

Since RAIZ can provide data on this indicator (for Eucalyptus globulus), the link and the contacts with this institute should be kept.

Information about other forest species would be also important since it could be used as a reference tool by forest managers (ex. foresters working at the local FOA) with the objective of helping them choosing the correct forest species for the new forest areas.

Indicator not considered by Criterion 5 of the Portuguese Norm 4406 2003.

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