In February 1938 a severe caterpillar outbreak stripped 800 ha of natural forest on Mt Lawu, East Java.[1] In 1990 a conifer aphid had infested over 80% of Kenya's forests—just three months after it was first discovered.[2] In Ghana, the yield loss of cocoa attributable to insect infestation is estimated at 25-30% per annum, and may be as high as 75% in farms attacked by pests and left unattended for over three years.[3] Meanwhile, in Europe and North America Dutch elm disease has been spreading since 1910: by 1990 very few mature elms were left in Britain or much of continental Europe.[4]
Insects and diseases are integral components of forest dynamics, in which they fulfil important roles. Occasionally, however, they grow to damaging proportions with catastrophic impacts, including complete destruction of large tracts of natural and/or planted forests. In some countries, severe outbreaks may compromise national economies, threatening economic stability and food security.[5]
The impact of forest diseases and pests has been profound over the centuries. Researchers have worked tirelessly to identify causal agents, feeding ecology, host range, geographical range and efficient means of control. However, the lack of effective quarantine measures coupled with increases in international trade of agricultural and forest products, exchange of plant materials and long-range air travel has resulted in the introduction of pathogens and insects into new environments. Not only will researchers have to study the impacts of these new insect pests and diseases alongside increased disturbances from native pests, but they will now have to do so under various climate change scenarios. A further twist is that in several parts of the world forests are in transition, being converted from natural forest to plantations at a faster rate than ever before.
In plantations the emphasis is on fast growing species suitable for pulpwood. Risk of pest and disease damage should be an important criterion for species selection in large-scale planting, but research takes time and the plantation industry cannot always wait for scientists to guide its choices.[6] Inevitably, the wrong choices are made.
What happens if we continue to make choices without taking the threat of pests and diseases into consideration? What happens if we do not arrest the spread of these harmful pathogens? Leaving aside the devastating ecological damage, let’s look at some past economic impacts. In east and southern Africa it is estimated that the cypress aphid Cinara cupressivora has killed trees to an estimated value of US$ 41 million and caused a loss in annual growth increment of a further US$ 14 million per year. The two pine aphids, Pineus boerneri and Eulachnus rileyi caused a further loss of US$ 2.25 million per year in the region.[7] In the United States, insects cause a total loss of more than $100,000,000 annually to forest products. Brazil once lost 300,000 ha of pine, equal to a loss of US$ 7 million/year.[8]
A lot is at stake and forest health research must provide answers to a set of ever-evolving questions. Research capacity is inadequate in many African countries, but still remarkable strides are being made on the continent. At the New Frontiers in Forest Health session of the IUFRO/FORNESSA Regional Congress held 25–29 June 2012 at the World Agroforestry Centre (ICRAF) in Nairobi, scientists from various parts of Africa presented interesting new findings.
Jolanda Roux works for the Forestry and Agricultural Biotechnology Institute (FABI)—a globally recognised centre of excellence for research and training in tree health—at the University of Pretoria, South Africa. According Roux, there are now lots more pests and pathogens on exotics in Africa than there were before. Studies show that old and well-known pathogens are now attacking non-native hosts, for example a native fungi Chrysoporthe cubensia is now causing canker on eucalyptus—a non-native host—in South Africa, Kenya, Malawi and other African countries. Scientists have also discovered a number of completely new pathogens and several new fungal species; invasive insect species have also been recorded and, disturbingly, some species that have been controlled in the past are re-emerging. In some cases, new diseases, never seen before in Africa and some not even anywhere in the world have been recorded.
Bernard Slippers, also from the same institution, discussed the potential of genomics for tree health research, remarking that the reduction in the cost of DNA sequencing and the revolution in marker development have allowed a number of species to be separated that were previously thought to be homogenous. “Genomics lets you pull into separate species, what was considered phenotypically similar,” he stated, adding that the sequencing of bacterial pathogens has increased the understanding of toxic genes, their location in the genome and infection mechanisms. Genomics completely transforms the type of research questions that can be asked related to pests, pathogens, symbionts and biological control organisms—radically transform our understanding of organisms that affect tree health.
Since 1988, the FAO has provided technical assistance for forest health related issues to 20 countries through Technical Cooperation Programmes (TCP). Over the past 14 years, a growing number of requests from member countries—for technical assistance related to forest health problems—indicates an increasing threat to forests from biotic agents.[9]To tackle this threat effectively countries must develop clear tree health management structures and introduce policies to select only those investors with a long-term commitment to the environment.
Researchers need to address emerging challenges in forest health; secure funding for long-term research programmes that will provide essential support in the future; solicit financial support to set up adequate research facilities; and strengthen regional and international partnerships. They must disseminate their research findings to create awareness of the issues, and garner support with donors and the private sector. In South Africa researchers are drawing private companies into collaborative research programmes, and the rest of Africa will need to follow suit by engaging with the private sector in strategic collaborations. It also falls upon the research fraternity to educate investors about the long-term effects of their choices. Perhaps most importantly, as Roux emphasized, the forest health fraternity needs to keep the small farmer in mind—how can they be assisted and how can we ensure that they have access to new genetic material?
Successful pest management programmes require the clear and unified vision by all stakeholders—countries, investors, researchers and the donor community—that tree health is a key component in forestry enterprises. Only then can strategies for sustainable management of current and potential tree health problems be successfully implemented.
Author bio
Rebecca Selvarajah-Jaffery is a novelist and writer with over 13 years of experience in corporate, creative and science writing. Having worked as Copy Head, Information Officer and Science Writer at Wunderman Nairobi, ICRAF and Green Ink, respectively, Rebecca is now a freelance Writer and Publishing Consultant. Originally from Sri Lanka, but Kenyan at heart, Rebecca holds a BA honours in Psychology, with minors in Gender Studies and Sociology. She can be reached on r.selvarajah@cgiar.org
