Forest Biomass Generation in Degraded, Steep, Outcropped Ecosystems

A company in Uruguay is successfully using specially adapted bulldozers and the application of hydrated polymers to protect tree seedlings and develop plantations on marginal lands.
By Pablo Reali
In Uruguay, about half of the land is considered priority soils (those allowed by the state to be forested), this means about 1.5 million hectares (3.7 million acres) are hilly areas with shallow soils, frequent outcropping and steep fields. Most of these soils were degraded by sheep overgrazing for more than a century. Many of these areas remain unplanted because of traditional plantation technology, which is based on rubber-tired tractors that cannot be used in such crude conditions.

Most of these types of soils are in the Eastern and Northeastern regions of the country. The price of forestlands there is the most suitable for forest investments, taking into account that it takes a long time for investments to pay off in the saw timber industry. Using the technology described in this article, more than 2,500 hectares were successfully planted in northeast Uruguay (Treinta y Tres and Cerro Largo Departments) in the worst topographic conditions in the country.

This technology is based on the use of bulldozers for ripping and plantation bed preparation, and also utilizing specially adapted bulldozers to apply hydrated polymers at planting time. These polymers protect the seedlings from a lack of water and at the same time provide nitrogen, potassium and a root promotion hormone.

Servicios Forestales Integrales is a well-known Uruguayan company with broad experience in forest ripping and planting, having been involved in the forest generation of more than 50,000 hectares in the past 10 years. In 2007, through a joint venture with Tubron SA, a major chemical company in Argentina, SFI produced a new plantation system mixing bulldozer forest ripping and applying a super-absorbent acrylic polymer in the hole where the trees are planted. The polymer has chemical activity providing for the controlled release of nitrogen, phosphorus and potassium fertilizers and a rooting hormone, which gave the trees a good start, even in the worst drought conditions.

After a successful set of trials, SFI planted about 2,500 hectares of Eucalyptus grandis, E. saligna and E. dunnii in the hilly regions of Northeast Uruguay.

Although these plantations were developed for saw timber production (long rotations of 20 years), based on initial growth and national forest inventory data (conservative, as we expect from 20 to 30 solid cubic meters per hectare per year), SFI concluded that this new plantation technology could be valid for dendroenergetic forest crops in these degraded and marginal soils.

This type of project contributes greatly to local and national forest development because it increases the production of degraded soils, helps soils recover and creates jobs in one of the less developed zones of Uruguay (1 inhabitant per 15 square kilometers or 6 square miles).

Silviculture Development Summary

Silviculture development is basically an adaptation of the hydrated polymer and ripping shallow soil in hilly areas. Starting with conventional weed control, a bulldozer deep ripping using Caterpillar D6 and D8 machines, depending on how rough the conditions are, is applied with opposite discs that allow for plantation bed preparation. If field conditions permit it, the rubber wheels transit would be advisable for common bed preparation.

The greatest benefit of this adaptation is the use of the polymer hydrated mix, with or without the chemical action (nitrogen, phosphorus and potassium fertilizers and rooting hormone). This balance will depend on the soil's texture, water-holding capacity and its chemical fertility.

It's worth noting, that these hydrated polymer mixes function as effective starter fertilizers and aren't dependent on rainfall like common granulated fertilizers for soil dilution, where it can be taken up by the eucalyptus roots. The nitrogen, phosphorus and potassium, and rooting hormone with the electronic matrix of the polymer is control released into the water supply from the beginning when the root system is planted within the gel. In addition, the polymer works as a control-released fertilizer, which means that no fertilizer is wasted and it can be applied at the rate of 2 to 3 grams per seeding, instead of the conventional 80 to 150 grams of mineral granulated fertilizer. This saves the renewable resources of potassium and phosphorus and avoids groundwater pollution of the nitrogen.

Bioenergy Possibilities

Power consumption in Uruguay has been increasing annually at a rate of 50 megawatts per year (Dirección National de Energía y Tecnología Nuclear, MIE, 2007). As hydro sources are still in the development stage and nuclear is prohibited by law, this increase in consumption is being fulfilled by neighboring countries. Both options are costly and not environmentally friendly. So, the Uruguayan state is promoting energy generation using renewable sources, mainly wind and biomass, supporting that with long-term fixed-price contracts and priority in the grid dispatch.

Energy generation by dendroenergy plantations within many areas of Uruguay has the following advantages:

Middle- and high-voltage lines near the forest soils

Land permit prices conducive to forest investments

Presence of permanent and abundant water resources

Good forest sites

Ample wood production using fast-growing species

SFI estimated that 2,000 acres of Eucalyptus grandis, E. dunnii or E. maidennii planted in a 10-year rotation could fully supply a 10-megawatt power plant.

Although pellet production in Uruguay is almost nonexistent, several feasibility studies demonstrate its potential profitability and contribution to the sustainable development of the country. For instance, feasibility studies conducted by the engineering faculty at State University show that a 10,000 ton per month pellet mill would have an installation cost of about $13 million. Estimating the cost, insurance and freight via the Rotterdam pellet price of about 120 Euros ($169), the calculated internal rate of return was 37 percent, with a repayment investment of three to four years (Borsellino, Carrau and Maisonnave, 2007).

The new development described earlier, promotes better use of forest land with severe outcropping and slopes. With conventional planting techniques (based on rubber-tired tractors) these areas could not be planted and would be only suitable for grazing cattle and sheep. There are hundreds of thousands of hectares of this land in Lavalleja, Treinta y Tres, Cerro Largo Rocha and Maldonado departments.

Planting costs, using the proposed technology, don't differ much from the conventional method. The increase in the cost of the polymer and the bulldozer application are compensated by savings in the disking and manual fertilizer application. More importantly, the forest company using this technology could plant in hilly areas with no significant economical or ecological value.

The use of mixing polymers protects the seedlings against drought for about 20 to 30 days, and if conditions don't improve a single watering with about 2 to 3 liters (0.5 to 0.8 gallons) per seeding could assure full polymer recharging. The same recharging would also occur with about 10 millimeters (0.4 inches) of rain.

This will permit the use of marginal and degraded soils for different forest uses, including dendroenergy and other biomass applications, which depending on the situation could offer high profitability for the investor and a source of sustainable development for Uruguay.

The use of the hydrated polymer and the addition of fertilizers and root hormones in its composition, allows for a fast start even in dry conditions. Furthermore, there is field evidence that this treatment permits the seedlings to recover better from frost damage in the winter. BIO

Pablo Reali is a forest, bioenergy and carbon adviser for Servicios Forestales Integrales. Reach him at