Biosecurity is clearly an important issue in forestry, although specific aspects of the issue (and their importance) differ from other sectors. The dominant concern in forestry is the risk posed by invasive alien species, either to the forestry sector itself, or to other ecosystems. Since the problems caused by invasive species are often complex and frequently impinge on other sectors, the forestry industry should work in close collaboration with other sectors and stakeholders in order to reduce the risks associated with the movement of alien species. Apart from protecting their own forestry industries from invasive alien species, countries also need to be able to objectively and realistically assess the risks of introducing alien species to other countries via their trading activities. This is a large task, even within the forestry sector, and there is considerable scope for experience-sharing between countries and international support from organizations such as FAO.
The Convention on Biological Diversity and World Trade Organization's SPS agreement have placed countries under new obligations with regard to alien species and biodiversity. To address their obligations under the CBD, signatory countries have agreed to "prevent the introduction of, control or eradicate those alien species which threaten ecosystems, habitats or species". However, predicting which alien species are likely to cause serious damage if introduced is not easy. Many species are innocuous or minor pests in their area of origin, but can be devastating when introduced elsewhere. At present, the best guide to potential invasiveness and pest status seems to be a prior history of causing problems elsewhere, particularly in regions with similar habitats and climatic conditions to those of the country under consideration. Thus, access to reliable information is critically important for assessing the potential risk of invasiveness.
In many cases, developed countries have already established procedures to address some of the key risks associated with alien species, although developing countries have tended to lag behind. Historically, small island stateshave suffered some of the worst damage by invasive alien species, and small island developing states are now the most vulnerable. Such states often have only a very small public sector budget and hence may need considerable external assistance to develop appropriate biosecurity programmes.
Of the various threats posed by alien species, pests (in the broadest sense) are an important consideration in forestry. While indigenous pests may be chronic or occur in outbreaks, introduced pests usually occur in an initial outbreak followed by continuous chronic damage. Both can be extremely damaging, to the extent that some species of trees cannot be economically grown in some areas. However, the option of substituting tree crop species is an important difference between forestry and agriculture, and may offer a solution in some cases.
There is an urgent need for more research on tropical forestry pests, both to develop management methods and for developing pest risk assessments. Plantation forestry, particularly agroforestry, is relatively new to the tropics, but in recent years has grown rapidly (e.g. in terms of new trees, new technologies, etc.). However, knowledge of pests and pest management methods in such systems has not developed at the same rate. In this respect, it would be useful to compile information on the actual composition of forestry tree species in different areas, since pests are often specific to their hosts at the species level and such information would highlight species at risk. International cooperation and information exchange on pest distribution, impact, pathways, interceptions, etc. should therefore be encouraged, especially between neighbouring countries and trading partners.
Tropical and subtropical plantation forestry has typically focused on a small number of fast growing, colonizing species, normally planted as monocultures. However, it is generally accepted that monocultures, especially of genetically similar trees, increase the probability of pest outbreaks. Monoculture also tends to transform sporadic pests into more permanent problems. Mixed planting of native (and exotic) trees is therefore preferred as a strategy for avoiding pest problems.
There has been some debate over the relative risk of pest outbreaks on exotic versus indigenous trees, especially in plantation settings. There appear to be no firm conclusions, except that monoculture of either indigenous or exotic trees increases the chances of pest outbreaks. The pest risks associated with a particular tree/location combination should therefore be evaluated on a case-by-case basis and pilot plots established before widespread planting is undertaken.
Alien weeds can be particularly damaging during plantation establishment, but can also have important effects on biodiversity, particularly in the tropics. In contrast to most insect pests and plant pathogens, alien weeds tend to affect not just forestry but also various other sectors, and hence may need to be addressed with a multisectoral approach.
As far as addressing these various issues is concerned, the best approach is obviously prevention, but managing potential pathways for the introduction of alien species is often more efficient than trying to prevent the introduction of individual species. Most of our current knowledge on this issue comes from developed countries, and although much of it can be transferred to developing countries, there are likely to be large differences between the two situations - not just in the actual risks, but also in the perception of those risks and in the resources available to address them. Hence, further research is necessary on the possible introduction pathways for all types of pest in tropical/developing countries.
At present, the principal known pathways through which forestry can contribute to the introduction of alien species include the movement of germplasm, solid wood packaging materials, trade in unprocessed timber, aid programmes and contaminants of forest seeds and other products. Once identified, potential pathways must be prioritized according to each country's most serious and immediate invasion threats and managed accordingly. Pathways known to have led to introductions (e.g. timber and solid wood packaging materials) merit immediate attention. Imported material, such as germplasm, should be subject to assessment and quarantine procedures, reinforced where necessary with legal powers to treat, destroy or ban suspect material. Deliberate introductions of other species associated with forestry, including biological control organisms, pollinators, mycorrhizae, etc., constitute an additional risk and should be considered with caution and on a case-by-case basis.
However, despite various approaches to managing these risks and preventing accidental introductions, the increase in world trade and the difficulties involved in providing adequate inspection and quarantine services make it virtually inevitable that alien species will continue to be inadvertently introduced to suitable new habitats in different parts of the world. When preventative measures fail, an eradication programme is then generally the preferred method of action, provided that its feasibility has been adequately assessed by suitable cost-benefit analyses. The success of such an approach is critically dependent on early detection, surveys for which should be carefully designed to provide maximum information at minimum cost.
If establishment occurs and eradication is no longer an option, containment and control is necessary. Various options are available for the control of alien species, amongst the most useful of which is biological control by the introduction of exotic natural enemies from the pest's area of origin. Again, however, such an approach should only be adopted after appropriate risk assessment.
Further research is needed on the best ways of managing forestry plantations so as to minimize the impact of indigenous (or alien) pests. In particular, tactics such as multispecies planting need further evaluation in developing countries. In some cases (notably for rubber), the development of pest or disease-resistant clones may be the only effective solution, although this is obviously a long-term and expensive approach. Other options for containment (e.g. buffer zones) should be evaluated further and examples of good practice made more widely available.
Many species of tree used in forestry and agroforestry have the potential to become invasive when grown as exotics, particularly in the tropics. Further work is needed to identify the biological characteristics that make a species invasive, and those that tend to make tropical trees more invasive than temperate species; for example, many trees used in tropical agroforestry produce seeds after only two to three years growth, which radically changes the population dynamics of the plant and may well contribute to invasive tendencies. Protocols need to be developed and validated to assess these risks. Pilot schemes should include monitoring for any indications of invasiveness, and safer options for introductions (e.g. sterile trees) should be identified and evaluated.
The advent of GM technology poses new challenges to the forestry industry, since assessing risks in long-term crops such as forestry trees is particularly difficult. As yet, there are no generally accepted protocols for these types of assessment, and priority should be given to their development and testing. The large-scale uptake of this technology is likely to be slow until such protocols are available.
Finally, in establishing the objectives of a biosecurity activity, it is critically important to consider the full range of stakeholders, as well as their various interests and mandates, in order to identify areas where cooperation is necessary and where synergies and efficiencies can be achieved. In formulating and developing an appropriate approach to biosecurity, the whole regulatory cycle and the views of all interested parties must be considered.
