Silvicultural Techniques for Short Rotation Eucalyptus Plantations in Brazil

Ken McNabb, Auburn University, Auburn, Alabama

ABSTRACT

Brazil has established several millions of ha of Eucalyptus plantations primarily on abandoned agricultural lands. Intensive management of these sites has resulted in average annual growth rates of 20 to 30 m3/ha/yr. Genetics programs over the past 15 years have produced superior genotypes routinely used for plantation establishment. Selected and tested individuals are clonally propagated on a large scale in specially designed nursery facilities. Rooted clonal cuttings are hand planted to a site prepared using machinery or a chemical/machine combination. Nitrogen and phosphorus fertilizers are applied according to soil diagnostic recommendations at the time of planting or as top dressing during the first year. Herbaceous weeds are controlled during the first year after planting by a combination of a preemergent herbicide, manual weeding, and mechanical weeding. Weed control is not necessary after about 12 months due to crown closure. Although insect and disease problems have occurred, their influence on plantation productivity has been limited through a combination of clonal selection and silvicultural treatments. The most serious insect pest is the leaf cutting ant. The vast majority of Eucalyptus plantations are managed to maximize raw material production for fiber or energy industries and are therefore not thinned. Clearcut harvesting usually occurs at age 6 to 8 years.

INTRODUCTION

Brazil is a large country with abundant natural and human resources. Covering 48 percent of the total land mass of South America, Brazil is the 5th largest country in the world geographically. Ranging from about 330 South latitude to 50 North latitude, the climate varies from subtemperate grasslands in the south, semiarid scrub forests in the northeast, and the humid tropical rainforests of the Amazon Basin. Images of Brazil are frequently linked to the Amazon region with its exotic animal and plant life, indigenous populations, and problems associated with tropical deforestation. Most of the economic activity, however, is concentrated in the bottom third of the country and Brazil is highly industrialized in several sectors such as automobile manufacturing, iron production, and agriculture. A country of 150 million people, Brazil may be generally considered an intermediate income developing nation with the 9th largest economy in the world (Swann 1993).

Although deforestation may often be associated with Brazil, the country has been very active in establishing tree plantations. By some estimates, the country has at least 5 million ha of plantations (Mather 1990) which is approximately 65 percent of the plantation area in all of Latin America (Sedjo and Lyon 1990). Eucalyptus is a significant part of the Brazilian planting effort. For example, Eucalyptus accounts for 76 percent of the total .95 million ha reforested in the state of São Paulo (Florestar 1993).

Eucalyptus plantations contribute 25 percent of the total amount of wood consumed in Brazil (Sociedade Brasileira de Silvicultura 1990) where the primary uses are as an energy source and industrial roundwood for pulp and paper production. Energy production in the form of charcoal and firewood account for the majority of Brazil's total wood consumption, 26 percent and 53 percent, respectively (Lima 1993). The largest consumer of charcoal is the iron industry which used close to 80 percent of the total 1991 Brazilian charcoal production of (Magalhães 1993). The exact contribution of Eucalyptus plantations to the overall wood energy consumption in Brazil is difficult to ascertain, but there is little doubt that Eucalyptus because of its availability and excellent wood properties, is widely used as an energy source. Swann (1993) estimated that Eucalyptus covered .8 million ha of a total 1.4 million ha (57 percent) of the industrial plantations used for pulp and paper production in Brazil.

SPECIES AND PRODUCTIVITY

Eucalyptus plantations in Brazil are found mostly in the southern third of the country with concentrations in the states of São Paulo, Minas Gerais, and Espirito Santo. The region is humid subtropic with an evenly distributed annual rainfall varying from 1000 to 1500 mm (Golfari and Neto 1970). The more commonly planted Eucalyptus species for this region are grandis and urophylla. Other species commonly planted in the past include saligna, alba, tereticornis, and citriodora. Eucalyptus species easily hybridize and one of the more commonly utilized hybrids is grandis x urophylla (urograndis). Because a key component of maximizing plantation productivity is matching genotype to site characteristics, many of the industrial plantations in Brazil are currently using a mixture of species and hybrids.

Growth rates for Eucalyptus will range from 20 to 40 m3/ha/yr (based on site visits and interviews with company personnel) and phenomenal growth rates of up to 75 m3/ha/yr (Kageyama 1980) have been reported for specific sites. Rotation lengths for industrially grown Eucalyptus is normally from 6 to 8 years. Such high productivity is due to not only to the inherently aggressive growth characteristic of Eucalyptus, but also because Brazil has developed modern silvicultural systems that accelerate this growth. Eucalyptus plantations in Brazil are tree farms, where there is considerable investment made into intensive site preparation, genetic improvement, and weed control Table 1.

Table 1. A Typical sequence for Eucalyptus plantation establishment in Brazil

site preparation

intensive mechanical, or mechanical/herbicide combinations

leaf-cutting ant control

fertilization

hand plant container grown stock

water

pre-emergent herbicide

replant, if necessary

machete, rotary mower, and/or chemical weed control (1st year only)

NURSERY PRODUCTION AND GENETICS

Eucalyptus plantations are established with seedlings and rooted cuttings produced in container nurseries based on systems using small "bullet type" plastic containers placed in racks above the ground. These containers are normally round with 2 to 3 cm diameter and 18 to 22 cm in length and filled with a potting medium before receiving seed or a cutting. This filling process is usually mechanized and the soil medium a mixture of vermiculite and locally produced organic wastes such as burned rice hulls or composted bark. When growing seedlings, most growers sow directly into the container and cover the racks with shade cloth until germination is complete. Seedlings are fertilized and protected from pathogens until reaching 4 to 6 months in age and approximately 30 cm in height. Planting is usually seasonal, with the best results in the cooler part of the year (May through October), although some companies will plant throughout the year and therefore have continuous nursery production throughout the year.

One of the key factors in Brazilian Eucalyptus productivity is related to the clonal planting program pioneered in Brazil during the 1970's (Brandão 1984). Individual Eucalyptus trees are selected in the field based on growth, form, health, and wood characteristics. These individuals are felled and the coppice sprouts vegetatively propagated to be tested for both rootability in the nursery and field performance. Individual clones are tested to specific site (soil) conditions. If a clone is selected because of its superior performance, then it is placed into a "clone bank" near the nursery which is managed to produce cuttings used for propagation. Coppice shoots are cut into approximately 15 cm segments used for rooting into the "bullet" containers. The cuttings go through an initial 45 day rooting phase under mist in a shade house then are moved to the sun for an additional 45 days. Rooted cuttings are therefore ready for planting in 90 to 100 days.

Most Brazilian companies involved in clonal propagation also have tissue culture programs. Small amounts of stem tissue from an individual tree can be grown under highly controlled laboratory conditions to a propagule that can be transplanted to the nursery for growth to plantable size. Such techniques allow for an even more rapid expansion of a specific genotype. The process is very expensive and the economic justification for using tissue culture over the traditional stem propagation techniques has not been entirely established (Zobel 1993). Nevertheless, Brazilian companies are steadily accumulating valuable experience in the practical implementation of Eucalyptus plantation establishment based on tissue culture propagation. Whether future advances in genetic manipulation (an introduction of herbicide resistance, for example) can be integrated into a tissue culture program is only speculative at this point, but undoubtedly being considered.

The use of asexual propagation (cuttings) provides several important advantages over sexual propagation (seedlings). Clonal propagation allows for the genetic superiority of an individual to be amplified over large areas in a relatively short period of time. With a rotation length of 6 to 8 years, a genotype evaluated at 3 years of age is already halfway through the rotation. This is especially pertinent to selection for disease resistance. E. grandis, for example, was known to be susceptible to a stem canker. Through hybridization with E. urophylla and the selection of resistant clones, this problem has been mostly controlled. Asexual propagation also allows for the matching of individual genotypes to specific sites, which can maximize site productivity.

SITE PREPARATION PRIOR TO PLANTING

The sizable investment made in planting stock quality is supplemented by intensive planting site preparation. The Brazilian philosophy regarding preparation for planting has been influenced by an agronomic history. First, the vast majority of sites now used for tree plantations are abandoned agricultural lands. With the notable exception of the Jari Project in the Amazon (Mc Nabb and others 1994), Brazilian forest plantations are on lands previously used for crops such as coffee, sugar cane, and cattle. These sites therefore may be some of the better soils and topography for the region they are located in. Such sites are more amenable to intensive management as they can be worked well with machinery and respond to cultural inputs. Second, because the first foresters in Brazil were trained in agronomy, they tended to view cultivation, weed control and fertilization as an entirely normal part of any crop system, including forestry. This philosophy continues today, although many companies are now experimenting with "minimum cultivation" to reduce the amount of times machinery pass over any given site.

Most industrial operations will use dozer mounted root rakes to clear any stumps, branches, or other debris from the site. In the past it was common to grade the area prior to planting leaving the appearance of an agronomic site. The site may be ripped (subsoiled) depending upon soil conditions, usually at a spacing identical to the recommended between-row planting spacing. It is a common practice that fertilization be done simultaneous to ripping. Granular fertilizer is placed either in the slit or at the surface. It is more common for phosphorus fertilizers to be placed right below the depth of planting, while nitrogen fertilizers may be laid at the surface during ripping. Fertilizers are also manually placed at the surface beside each seedling within the first 3 to 6 months after planting. Fertilization recommendations are made after soil analysis with most forest plantation operations having their own soils analysis laboratory.

With the current emphasis on "minimum cultivation", herbicides are becoming more common in site preparation. Glyphosate is applied prior to planting to kill existing vegetation including stump sprouts from a previous Eucalyptus rotation. Branches or other woody material may be manually stacked in rows between planting lines before or after herbicide treatment. Some companies allow local people to enter recently harvested plantations to remove woody debris for their use in charcoal manufacturing. Fire as a site preparation tool is rarely used in Brazilian silviculture. Brazilian foresters generally regard fire as environmentally destructive, due to what they feel is excessive soil organic matter consumption, nutrient volatilization, and soil erosion.

An integral part of site preparation in Brazil is the ant patrol. Leaf cutting ants (Atta spp.) are the most serious insect pest throughout Brazilian agriculture and forestry is no exception. After site preparation and prior to planting, company crews will pass through an area scheduled for planting to locate and destroy leaf cutting ant nests. Fumigation with methyl bromide or placement of baits are used to control this pest. A single pass is usually not sufficient to find all the nests, however, and it is not uncommon for companies to search each site for ants three or four times during a six to eight year rotation. Obviously, ant control is more critical during the establishment phase when there is little forage for the ants and small recently planted trees are most susceptible to damage.

PLANTING

Eucalyptus container grown stock is planted by hand at a spacing of 3 by 3 m (1,111 stems/ha) or 3 by 2 m (1,667 stems/ha). Planting stock is forwarded from the nursery to the planting site in specially designed trucks where boxed seedlings can be carried on shelves. The most common planting tool is a small hoe 6 to 10 cm in width with a 40 to 60 cm handle. An appropriately sized hole is dug using this hoe then the seedling is removed from the "bullet" sleeve and planted. Workers carry seedlings with them in small trays, bags, or boxes. Because planting is so labor intensive, Brazilian foresters are trying to find ways to improve planting efficiency. Although machine planting has not yet proven satisfactory, Scandinavian style planting tubes are being tried by some companies. In this case, the worker does not have to bend over to plant the seedling. The planter has a cone at the bottom of a 1 m long tube. As the worker drops a seedling in the top of the tube, he then opens the cone at the bottom of the tube to deposit the seedling in the ground. The planter then closes the slit with his foot. Replanting is done on a few occasions. Survival rates of above 90 percent are routinely obtained, although weather, poor planting, and poor seedling handling can reduce this. Usually replanting is done only when a general area failure occurs.

An integral part of planting in many Brazilian Eucalyptus operations is the watering of planting stock immediately after planting. This operation is obviously weather dependent but forestry personnel do not hesitate to invest in a post planting watering operation when deemed necessary. For some parts of the year in some parts of the county, this means all planting stock is watered. The procedure usually calls for a tanker truck or tractor to pass through the recently planted area. Hoses feeding directly from the water tank are used to apply between 1 to 2 L of water to each plant. This is done only once as soon after planting as possible. This operation "seats" the seedling or cutting in the soil and reduces moisture stress related to the disturbance of planting.

POST PLANTING CARE

Eucalyptus is sensitive to weed competition and considerable efforts are made to ensure virtually total weed control. Not only do the plantations begin with a very clean site, but through a combination of chemical, mechanical, and manual means, the site is kept weed free until the point of crown closure which usually occurs at about 1 year. Although confronted with a broad spectrum of weeds, grasses tend to be the most numerous and troublesome. Weed control begins immediately after planting with an over-the-top application of oxyfluorfen preemergent and early postemergent herbicide. Eucalyptus shows considerable resistance to oxyfluorfen and rates of 1 to 3 L/ha are commonly used. Application technique varies between companies but most will apply to a band of about 1 m in width with a typical farm tractor mounted boom sprayer, while some companies apply broadcast with a tractor or from the air. Oxyfluorfen provides weed protection for approximately 6 to 12 weeks. At this point manual cleaning using machetes or hoes is used and rotary mowers cut weeds between the planting lines when possible. Eucalyptus is between 1 to 2 meters tall at an age of 6 to 8 months and a directed spray of glyphosate can be used alone or in conjunction with rotary mowing. Shading is sufficient to suppress herbaceous weed growth after crown closure. Some companies will make a directed spray of glyphosate to weeds during the last year of Eucalyptus rotation. This is not to help the current plantation growth but rather to get a head start on site preparation. Any weeds that can be taken out before harvest, improves the effectiveness of site preparation for the next rotation. Unfortunately, Brazil depends heavily on the continued availability of glyphosate and oxyfluorfen. The number of chemicals labeled for forestry use are very limited and at present virtually all companies engaged in Eucalyptus production uses these two chemistries.

PESTS

As a general rule, Eucalyptus plantations in Brazil have not had serious insect or disease pests, at least not to the extent to make plantations unfeasible. Stem canker has been a problem in the past but seems to under control now due to improved genetic selection and hybridization. Lepidoptera outbreaks routinely occur but to this point have been easily combated with aerial applications of Bacillus or insecticides. There have been reports of a "tip dieback" condition which appears to be a physiological problem and not a disease problem. Correct matching of genotype to site is expected to solve this.

SUMMARY

In the last twenty years, Brazil has developed a highly productive silvicultural system based on Eucalyptus. High levels of productivity are based on intensive management with considerable investment in site preparation, planting stock quality, genetic improvement, fertilization, and weed control. This investment appears to be cost effective. As evidence, Brazil has one of the lowest raw materials costs in the world for the manufacture of pulp and paper (Mather 1990). Moreover, there is every reason to believe that further improvements in Eucalyptus productivity will occur. Clonal testing and propagation is still gradually improving average company productivity. Not only is there opportunity for the selection of faster growing clones with optimum wood properties, there will be more precise matching of individual clones to fertilization regimes. Further refinements in the "minimum cultivation" should result in improved soil stability and long term sustainability and in all likelihood a reduction in plantation establishment costs.

LITERATURE CITED

1. Florestar 1994. Florestar Estatístico V2 No. 4. Fundação Florestar: Fundo Florestar. Governo do Estado de São Paulo, Secretaria do Meio Ambiente, SP. Brazil. 77 pp.
2. Golfari, L. and Neto, F.A.P. 1970. Escolha de espécies de eucalipto potencialmente aptas para diferentes regiões do Brasil. Brasil Florestal (1)3:17-38.
3. Kageyama, P.Y. 1980. Variação genética em progênies de uma população de Eucalyptus grandis Hill (Maiden). Tese de doutorado. Escola Superior de Agricultura Luiz de Quieroz. Universidade de São Paulo. Piracicaba, SP. Brazil. 113 pp.
4. Lima, W. de Paula. 1993. Impacto Ambiental do Eucalipto. Editora da Universidade de São Paulo. São Paulo. SP, Brazil.
5. Magalhães, J. L.de. 1993. Futuro do carvão vegetal no contexto nacional e no exterior. In Anais do I Simpósio Brasileiro de Pesquisa Florestal. Belo Horizonte, Minas Gerais, Brasil, 11 a 14 de maio de 1990. Coordenado por Carlos Cardoso Machado.
6. Mather, A.S. 1990. Global Forest Resources. Timber Press, Inc. Portland OR.
7. McNabb, K., J.Borges, and J. Welker. 1994. Jari at 25, an investment in the Amazon. J. of Forestry (92)2:21-26.
8. Sedjo, R.A., and K. S. Lyon. 1990. The long-term adequacy of world timber supply. Resources for the Future. Washington. D.C.
9. Sociedade Brasileira de Silvicultura. 1990. A Sociedade Brasileira e seu Patrimônio Florestal. 20 pp.
10. Swann, C.E. 1993. South America, the promise and the problems. International Papermaker. August pp. 23-31.
11. Zobel, B. 1993. Vegetative propagation in production forestry. J. of Forestry (91)4:29-33.

File posted on March 5, 1996; Date Modified: February 21, 1999