Topic 11.4: Environmental and Economic Concerns about Plantation Forestry

Providing a brief introduction to the ecology of plantation forestry is difficult because there are so many different types of plantations that are managed for so many different purposes by an equally diverse variety of people.  It is hard to compare, for example, a 5 ha mixed species coppiced fuelwood plantation run by a rural community with a 50,000 ha monospecific pulpwood plantation managed by clearcutting on short rotations by a multi-national corporation.  Furthermore, once an area has been converted, plantations can be run in an environmentally sound manner (e.g., with buffer zones along water courses and erosion-control measures on slopes) or can represent environmental disasters of global concern.

Plantations typically differ from natural forests as much as maize or wheat fields differ from natural savannas or grasslands. But like other cropping systems, well run plantation forests can be extremely productive. Achieving this high productivity requires substantial inputs, makes great demands on the site, and generally involves short rotations and thus frequent disturbances.  Short rotations, in turn, provide frequent opportunities from genetic improvement of the growing stock.  Here we will focus on some of the ecological constraints on plantation forests, most of which are similar to those discussed in relation to natural forest management.

Products for which plantations are managed include wood chips and pulp for paper and various types of composite sheathing (e.g., oriented strand board or chipboard), fuelwood and charcoal, building poles, saw timber, and veneer.  In terms of land area under plantations, short-rotation crops such as pulpwood are much more extensive than long-rotation timber stands.

There are many socio-economic and ecological settings in which plantation forestry may be the most appropriate land use. For example, where natural secondary succession is slow or arrested due to lack of nearby seed sources, competition with grasses and other non-arboreal vegetation, frequent fires, soil degradation, and other stresses, plantations can be used to promote ecosystem recuperation.  Large pastures, particularly if they were plowed during grass establishment operations,and then overgrazed for several years, often recover their forest cover only very slowly after abandonment. Although the resulting secondary forest may be rich in fast-growing trees of commercial species, more intensive land uses than managed fallows such as plantation forestry might be preferred by landowners and other stakeholders.  Restoration of mine spoils can also be enhanced by plantation establishment.  The labor requirements of plantations are considerable, especially during the establishment process, so there are employment opportunities that might benefit local people.

Many economic and ecological mistakes can be made during site selection for plantation establishment.  First of all, it is important to differentiate between “reforestation”, which is the replacement of forests in recently deforested areas, from “afforestation”, which is the establishment of forests in areas that were not previously forested.  From an environmental perspective, reforestation is more often desirable than afforestation because of the substantial biodiversity losses associated with conversion of natural grasslands and other non-forest ecosystems to plantations.  From a financial perspective, plantations dedicated to production of large volumes of low value materials, such as pulpwood, need to be located close to mills or ports to avoid high transportation costs. Another concern is the local availability of a sufficiently large labor force to run the plantation. And when the local population density is high, concerns about potential land-use conflicts become heightened.  Too many large industrial plantations in the tropics have been established on land that might have appeared abandoned but was in fact being used by local people. The results of these conflicts have included burned plantations, dispossessed people, and a range of other less-than-satisfactory outcomes.

The sites available for plantation forestry are typically un-suited or barely suited for agricultural use due to poor soil, susceptibility to drought, or poor access. The productivity and profitablity of short rotation plantation forests are accordingly limited by low soil nutrient reserves, poor nutrient retention capacity, moisture deficits, and high transportation costs.  Past land uses may have resulted in substantial soil loss due to erosion, soil compaction, and other site-degrading processes.  Sustaining high yields on such sites requires soil protection and amelioration measures that are discussed below.

Prior to planting, most plantation crops require substantial site preparation.  For direct seeding, mineral soil often needs to be exposed.  Where seedlings are planted, competition generally needs to be controlled by herbicide application or mechanical treatments (e.g., plowing or slashing) with or without burning.  During site preparation, natural regeneration of species of commercial or other value can be retained, but more often are not (at least in industrial plantations).  Where plantations are established by shifting agriculturalists during the final period of their cropping cycle (e.g., the “taungnya” system developed in Myanmar or the “tumpangsari” method used in Indonesia), site preparation treatments are integral components of their agriculture.

Plantation size and the inclusion of protected patches of natural forest are issues of concern to environmentalists. If properly located and sufficient n size, set-asides within plantations can contribute a great deal towards regional biodiversity maintenane. For the purposes of maximizing profits from industrial plantations, economies of scale argue for large and uninterrupted stands.  On the other hand, plantation managers who retain natural forest around wetlands and along water courses generally report that the costs of these set-asides are minimal for various reasons including the increased operating costs on wet soils and steep slopes.  In some cases the natural forest remnants serve as refuges for insectivorous birds that prey on plantation pests whereas in others, the same areas might provide refuge for the plantation pests themselves.  The beneficial or detrimental roles of remnants of natural vegetation for controlling pests and pathogens in plantations therefore needs to be assessed on a case-by-case basis.

As affluence and societal concern about environmental degradation increase, and people become more interested in forests for recreation and other low-impact uses, plantation managers often feel pressure to modify their silvicultural methods. One result of this heightened interest in natural forests is the popular desire to manage plantations so as to more closely resemble old-growth stands.  Creating mixed-age stands through group selection cuts rather than large clearcuts often helps in this reformation, as does allowing natural regeneration of native species to develop within the planted stands.  Given that as every year passes people have fewer and fewer opportunities to become familiar with natural forest and particularly with old-growth stands, it will become easier to satisfy much of society with few modifications of now standard plantation management techniques.  In a few noteworthy cases (e.g., mushroom harvesting in Pinus plantations in Korea), the intended uses of planted trees for their wood have become outweighed by the amenity and other values of the managed stands.  Surprisingly enough, public affection for planted stands of exotic tree species can become a factor to consider in our silvicultural decisions.

Plantation forestry has high associated costs but also has some high potential benefits.  On the cost side, plantations are more intensively managed than natural forests and consequently the operational costs per unit area are likewise higher.  Depending on whether plantations are established on extremely degraded sites (e.g., mine spoils or anthropogenic grasslands), or in place of semi-natural forest (e.g., secondary forest or forests degraded by uncontrolled logging), the costs in terms of biodiversity loss can be either minimal or substantial.  If local people were actually making use of the degraded and seemingly abandoned areas converted into plantations and these uses are precluded by the existence of the plantation, the social costs can also be great (and are often manifest in the unwillingness of local people to help protect plantations from wildfires). If plantation establishment involves severe site preparation treatments (e.g., broadcast herbiciding or plowing), soil erosion and associated hydrological costs can be considerable.  Although natural forest-like hydrological functions are often restored when the crowns of the planted trees close over the ground and their root systems close the gaps below-ground, but the disruption is suffered between every rotation (which may be at <10 year intervals).  Conversion of secondary and degraded forest into plantations also results in large losses in sequestered carbon that may never be recovered by the planted stand. Finally, for a variety of reasons that may include lack of genetic variability amongst the planted trees, plantations are more susceptible than natural forests to cataclysmic disturbances such as stand-destroying fires and pathogen outbreaks; higher risk has its own associated (but harder to calculate) costs.

Wood yields from well-managed monospecific plantations of genetically improved trees on productive sites in the lowland tropics can be as much as 10 times higher than commercial timber yields from managed natural forests.  This great potential difference in yields is the result of higher per-tree growth rates and much higher stocking of commercial trees in plantations. Also in plantations, few of the resources needed for high stand productivity are utilized by vines, shrubs, and other growth forms of little value to plantation forest industries.  Although the per-unit volume values of the most common plantation woods are lower than for timber from natural forest trees, some plantation forestry operations can be quite profitable.

Evaluating the profitability of plantation forestry operations is often particularly difficult due to a multitude of direct and indirect subsidies (e.g., low interest loans and under-priced land).  When non-market values such as biodiversity losses due to plantation establishment are considered, economic comparisons of plantation forestry and natural forest management become extremely complicated and controversial. The extent to which production from plantations serves to reduce harvesting pressure on natural forests is likewise controversial, but has been shown to be of some importance in New Zealand and several other wealthy nations.