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2.1 The PWA project area

The study was conducted at Precious Woods Amazon (PWA), the Brazilian subsidiary of Precious Woods AG (Zurich, Switzerland). PWA is located about 230 km east of Manaus and 40 km west of Itacoatiara. The forest area of PWA expands between 2° 43' and 3° 04' south latitude and between 58° 31' and 58° 57' west longitude.

The Precious Woods Amazon project covers a total area of 80,571 ha. An area of 5,845 ha had been deforested prior to the purchase of the area by Precious Woods; 800 ha of the deforested portion are used for agricultural purpose by settlers living on the PWA area. In the northwestern part of the area lies a coherent preservation area of 5,164 ha which is maintained as a permanent genetic reserve, untouched by harvesting operations or any other use. Buffer zones totalling 7,844 ha adjacent to springs and rivers are excluded from treatment in accordance with Brazilian environmental law. About 10,800 ha of the remaining forest are excluded from harvesting operations due to low productivity or difficult access. The remaining area of 50,918 ha, or 63% of the total area, represents the “productive” forest area of the PWA project where active forest management is carried out.

Products from PWA's sawmill are transported by truck to harbours on the Amazon River at Itacoatiara and Manaus. Both cities are accessible from PWA by permanent, year-round roads.

2.2 Climatic conditions

The average annual rainfall in the vicinity of the PWA forest is 2200 mm, with three-quarters of this typically falling between December and May. The mean annual temperature is 26°C, the average relative humidity about 80%, and strong winds are rare.

2.3 Soil conditions

Following EMBRAPA (1981), the soils are classified as yellow latosols. Soil nutrients are extremely low, with an average basal saturation around 10% and pH (acidity) values ranging from 3.7 to 4.7. Organic substances in the soil are very scarce, and can only be found on the surface.

2.4 Forest composition

The forests on the two plots examined for this study are evergreen, with an average canopy height in both plots of 30–40 m and individuals that occasionally reach up to 50 m in height. The forests are dominated by species of the families Lauraceaea, Lecythidaceae, Leguminosae, and Sapotaceae. The most common commercial species are Abiurana vermelha (Pouteria spp.), Cupiuba (Goupia glabra), Acariquara (Minquartia guianensis), Louro gamela (Nectandra rubra), Castanharana (Lecythis prancei), Uchi torrado (Sacoglottis guianensis), Arura vermelho (Iryanthera grandis), and Massaranduba (Manilkara huberi).

Lianas (climbing vines) are common throughout the plots. Palms occur with moderate frequency but are mainly those without stems that occur in the undergrowth. Epiphytes are rare.

In 1993, a pre-operation general forest inventory was conducted as a sampling inventory comprising 160, 0.5-ha sample plots with a total area of 80 ha, representing about 0.11% of the total forest area. The results show an average density of commercial species with DBH ≥ 50 cm of 20 trees per hectare. The average wood volume of these harvestable trees is 83.7 m3/ha over the entire forest area. As the variability of commercial tree density over the whole forest area is very high, only a comprehensive forest inventory can provide the information needed for sustainable forest management. The wood volume to be harvested is 30–35 m3/ha of trees with DBH ≥ 50 cm and preferably over 60 cm. An exception is with the species Acaricuara (Minquartia guianensis), for which trees with DBH 20–40 cm may be harvested for use as masts and breakwaters.

Most important for future wood harvesting are the potential crop trees (PCT) that will form the basis of volumes to be harvested in the next harvesting cycle. PCTs are defined as trees of commercial species with DBH between 20 and 50 cm. According to the inventory, there are 47 PCTs per hectare on average, representing a current wood volume of 58.9 m3/ha. More detailed information for all diameter classes is shown in Tables 1 and 2.

Table 1. Number of trees per hectare by DBH class on the PWA production forest area.

ClassificationDiameter Class, cm
<2020–3031–4041–5051–6061–7071–80> 80Total
All species77995512814644981
Commercial species29345291810433404

Table 2. Wood volume in m3/ha by DBH class on the PWA production forest area.

ClassificationDiameter Class, cm
<2020–3031–4041–5051–6061–7071–80> 80Total
All species53.143.449.346.035.922.818.135.0303.6
Commercial species21.020.727.931.024.716.313.729.0184.3

The wood species harvested by PWA can be separated into three classes:

A large number of additional species have some potential for high-grade use but are not yet recognised in forest products markets and thus are not currently harvested.

In 1999, wood of the species shown in Table 3 was sold in substantial volumes by PWA. Apart from Amapá (Brosimum parinarioides) which is used for the production of plywood, all species shown in the table are converted into sawnwood and sold in national and international markets. In addition, Acaricuara (Minquartia guianensis, family OLACACEAE), is used locally for masts and pylons and is also exported to Europe, where diameters of 25–40 cm are used as breakwaters.

A comprehensive list of all softwood and hardwood tree species found in the area of the PWA project that have been identified as having a potential to be harvested and processed into commercial forest products can be found in Appendix 1 of Winkler (1997).

Table 3. Tree species commercialised by Precious Woods Amazon in 1999.

Common nameScientific nameFamilyDiameters utilised, cm
AmapáBrosimum parinarioidesMoraceae55–300
Angelim pedraHymenolobium heterocarpum
Hymenolobium nitidum;
Angelim vermelhoDinizia excelsaMimosaceae50–300
CumarúDipteryx odorataFabaceae50–300
GuariubaClarisia racemosaMoraceae50–300
JatobáHymenaea courbarilCaesalpiniaceae50–300
Louro gamelaNectandra (Ocotea) rubraLauraceae50–300
Louro itaúbaMezilaurus sinandra
Mezilaurus duckei
Louro pretoOcotea fragantissimaLauraceae60–300
MassarandubaManilkara huberiSapotaceae60–300
Sucupira pretaDiplotropis trilobaFabaceae50–300
Sucupira vermelhaAndira unifolialataFabaceae60–300
Uchi torradoSacoglottis guianensis
Vantanea parviflora

2.5 Description of the study plots

The study was conducted in Block 312/9668 of Compartment B of the PWA Project. Plots B/F09 (“conventional” logging) and B/G09 (“environmentally sound” logging) were harvested in 1996, when the two plots were the subject of an FAO Forest Harvesting Case-Study undertaken by Winkler (1997). Since then, no further treatments have been applied.

The study site lies at an altitude of 45 m above sea level and is generally flat except that a gentle slope of 4% inclination can be found along the eastern boundary of Plot B/G09. Each plot has an area of 10 ha, measuring 250 m × 400 m. Within each plot a 2.25 ha (150 m × 150 m) subplot was delineated by Winkler and is referred to later in this report as well. The layouts of the main plots and the two subplots are shown in Figure 4 in Winkler (1997). The two 10 ha plots lie on opposite sides of the forest road that provides access to Compartment B. Site conditions in the two plots can be considered identical, and neither plot has running water or any other condition that would require delineation of zones to be excluded from harvesting.

An unsealed public road passes Compartment B, from which a forest road with a total length of 20 km leads into the compartments. Plots B/F09 and B/G09 are both situated roughly 6 km from the public road.

According to a 1995 commercial inventory of the study plots, the stem density of commercial species with diameters above 50 cm was 21 trees per hectare in Plot B/G09, where 42 commercial species were found, and 23 trees per hectare in Plot B/F09 with 39 commercial species.

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