Christian Laurent is forest engineer in the Forest Resources Service, Ministry of the Walloon Region, Directorate-General for Natural Resources and Environment, Nature and Forest Division, Belgium.
Management measures promoted by the government of Wallonia are intended to help increase the resilience of forests to environmental changes, while boosting the contribution of forests to climate change mitigation.
In Belgium, forestry policy and administrative functions are mostly decentralized, and forest management authority rests with the governments of the country's three regions, Flanders, Wallonia and Brussels. Wallonia, in the southern part of the country, is a small, densely populated region, and forest accounts for about one-third of its 16 844 km2 area. Measures developed in Wallonia to achieve a multifunctional forest management approach suited to a densely populated region encompass measures for adapting to future climate change. These measures follow two complementary thrusts.
The first is the maintenance, or preferably the improvement, of the capacity of forest ecosystems to adapt to environmental change through:
• development of broader biological diversity within stands, based on diversification of primary and companion species, but also on genetic diversification (through the use of more different provenances and seed stands) and appropriate silvicultural techniques;
• use of tree species and provenances best adapted to current site conditions so that they can tolerate both abiotic and biotic changes in the environment.
The second is the use of appropriate silvicultural techniques to anticipate the particular risks to forests from climate change, especially the expected increased frequency of storms, increased prevalence of pests, stress from extreme climatic episodes with alternating periods of drought and excessive rainfall and the predicted global rise in temperatures. Soil and water conservation measures improve the way forest ecosystems regulate hydrological cycles. Lower stand densities, earlier thinnings and multistorey forest systems enhance the ecosystem's resistance to climate stress and pests.The choice of well adapted species and provenances also contributes to carbon storage by increasing biomass increments in the forests and by favouring timber products suitable for longer-term use.
This article describes such measures for increasing the ability of forests to adapt to climate change and shows how they converge with the ecological, economic and social objectives of multifunctional forest management.
Multistorey stands enhance the ecosystem’s resistance to
climate stress, and in Belgium they are encouraged whenever possible
(Photo: O. HUART)
The population density in Wallonia is 199 persons per square kilometre, with 544 800 ha or 0.16 ha of forest land per person (Lecomte et al., 2003). Given the general context of intense pressure on land, multifunctional management is possible only through a system of multifunctional forest zones, in which each unit has a primary objective but is managed in such a way as best to guarantee the productive, ecological and social functions of the forest.
In the case of the 48 percent of forests that are publicly owned, their primary functions are defined in their management plans. Even when soil, water or biodiversity conservation is identified as the primary objective of management, the economic and social functions of the forest are also covered, although they are accompanied by restrictions to guarantee the fulfilment of the primary objectives. Similarly, general measures are adopted in production zones with a view to ensuring that the ecological functions of the forest are maintained. Production is focused on quality products that are suitable for high added value and not on mass production.
In the case of privately owned forests, incentives and sensitization measures are applied, with a view to ensuring a balance among the various functions of the forests.
Improvement in the adaptive capacities of forest ecosystems
Two routes are essential for improving the adaptive capacity of forest ecosystems: diversification and the adaptation of species to local conditions.
Diversification. Diversification means ensuring a wide diversity in the forests at all levels. In terms of genetics, diversity is sought through the use of a mosaic of productive and well-adapted provenances, whether these be of indigenous species or introduced ones such as Douglas fir (Pseudotsuga menziesii) or larches (Larix spp.). Monoclonal or oligoclonal plantations (i.e. plantations with less than 20 to 30 clones) are proscribed. In terms of species, mixtures of the dominating tree species are favoured, and understorey species are to be maintained or even introduced in plantations or natural regeneration. Ecosystem diversity is ensured by protecting natural ecosystems or those only slightly modified by humans, as well as secondary forests with high biological diversity.
In Wallonia, implementation of diversification measures is supported particularly by the efforts of two institutions:
• the Centre de recherche sur la nature, la forêt et le bois, a research centre that develops ecosystem conservation methods for field implementation and identifies provenances and seed stands of a broader range of species for use in both tree improvement programmes and conservation;
• the Comptoir des matériels forestiers de reproduction, a forest tree seed centre which manages seed stands and the harvesting, processing and distribution of reproductive materials to the public and private sectors.
Diversification is encouraged through subsidies for regeneration in which tree species mixtures are used. Finally, the inclusion of 150 000 ha of forest within the network Natura 2000 (a European network for the conservation of natural habitats and wild fauna and flora) will provide a major boost to diversification efforts.
Apart from its effects on biodiversity and on adaptation of forests to climate change, diversification of species may also have positive economic effects, potentially offering a greater capacity to cope with market fluctuations and opening access to specialized niches for quality wood and non-wood products. It also enhances the landscape and tourism roles of forests.
Diversification of species is a means of improving the adaptive
capacity of forest ecosystems; mixtures
of the dominating tree species are favoured, and understorey species are maintained
(Photo: SOCIÉTÉ ROYALE FORESTIÈRE DE BELGIQUE)
Use of species adapted to the site. It is recommended to regenerate or introduce those species and provenances that are best adapted to the current conditions of the site and climate, as these have a greater tolerance to both abiotic and biotic fluctuations in their environment. Certain tree species and species mixtures are also favoured for their rooting characteristics to address the specific problems of windthrow and drought.
The use of well-adapted species is also encouraged through information and incentives.
• Guidelines drawn up for the Walloon Region by an inter-university team (Weissen et al., 1991; Weissen, Bronchart and Piret, 1994) provide clear descriptions of the ecological requirements of the 14 conifer species and 30 deciduous species most widely used, including companion species, together with keys for choosing species according to the water and nutrient levels of sites in the region's 27 ecological sectors.
• Subsidies for regeneration are conditional on the use of species adapted to the site conditions as determined by the above guidelines.
The optimal choice of species helps meet production objectives by ensuring maximal sustainable production and a better quality of product. It also prevents adverse effects of species on the environment, an essential consideration for soil and water conservation.
An example of “dynamic silviculture”: Douglas fir with wide
spacing and early first thinning and pruning
(Photo: C. LAURENT)
A variety of silvicultural techniques widely promoted by the Walloon Region will reduce the dangers to forests from future climate change.
"Dynamic silviculture". The treatment termed "dynamic silviculture" in Belgium (André et al., 1994) involves the maintenance of relatively low densities (number of stems and basal area per hectare) through the establishment of wider spacing between stems or through rigorous early thinning of regenerated patches. The objectives with regard to climate change are:
• reduced risk of windthrow because of better-rooted trees;
• improved water balance through reduced interception and evapotranspiration, which will increase the drought resistance of the trees as a result of increased water reserves in soils;
• improved biodiversity and soil conservation as a result of more abundant understorey vegetation;
• more regular and gradual recycling of mineral elements, improving ecosystem functioning and preventing the leaching of nutrients during harvesting.
The use of "dynamic silviculture" to maintain an open-stand structure is encouraged through subsidies for regeneration which impose a certain planting density range, subsidies for early thinning and extension resources such as guides to good practices. For public forests, circulars are disseminated addressing silvicultural standards.
In terms of social and economic benefits, this type of silviculture, augmented by pruning (which is also encouraged by subsidies), increases the profitability of forest management by allowing a reduction in rotation times and faster production of timber of dimensions suitable for higher added-value processing. Maintaining fewer standing trees and less growing stock also reduces financial risks as less capital is exposed to potential biotic or abiotic disaster. An increase in forest cover and availability of forage will improve the balance between wildlife and trees and will thus also be favourable for hunting.
Water management. General water conservation measures include the use of certain tree species, reduced stand density and limitations on draining in certain situations, especially along watercourses and on hydromorphic (excessively moist) soils, even if this is to the detriment of the productive functions of the forest. Draining is not allowed on persistently waterlogged soils, and on peat soils silviculture is discouraged altogether (Ministry of the Walloon Region, 1997, 2002). These measures improve the water regulatory functions of the forest. The forest ecosystem will be more able to withstand periods of drought, while in periods of heavy rainfall it will steadily release excess water.
A circular dealing with soil and water conservation envisions these measures for public forests; zones assigned a water management function are to be identified and mapped in forest management plans. Conditions for regeneration subsidies include not only the use of certain species and species mixtures, but also a ban on draining.
In addition to the qualitative and quantitative benefits of water management, the moderation of peak flows helps prevent flooding and protect infrastructures.
Mixed multistorey forest system. Although not obligatory, a mixed multistorey forest system is recommended whenever the species in place and the site conditions allow. Advantages with regard to future climate change are more permanent forest cover, greater stability of stands in the face of storms and increased resistance of the forest ecosystem to climate stress and pests.
The circulars dealing with soil and water conservation and with forest management plans place great importance on the advantages of multistorey systems, whether within stands (stem-by-stem mixtures) or at the landscape level.
The conditions for allocation of regeneration subsidies for private forests containing conifers require the use of mixtures. In public forests, mixtures are required except in particular situations where site conditions do not permit them.
These measures, too, help meet the objectives of biodiversity conservation, while upholding the landscape and tourism roles of forests.
The contribution of forests to carbon storage is beyond the scope of this article and can only be touched on briefly here. Carbon storage in Wallonia's forests in 2003, estimated from data from the region's forest inventory, is about 52 million tonnes of carbon (solely in biomass), while the uptake of carbon by net photosynthesis is about 2.38 million tonnes or nearly 2.1 percent of the region's annual emissions (Laitat et al., 2003). The net annual increase in biomass after harvest is almost 500 000 tonnes. This figure is likely to decrease in the future because of the silvicultural methods recommended, which tend to reduce the timber capital per hectare. Given the significant pressure on land, the contribution of afforestation, reforestation and deforestation to Wallonia's carbon stocks may be deemed negligible.
The greatest contribution of forest management to the reduction of carbon dioxide emissions is likely to be indirect, through an increased share of products suitable for long-term use which might replace more energy-expensive materials (Roth, 2002).
Silvicultural choices being promoted in Wallonia which address the predicted effects of future climate change on forests also help meet the ecological, economic and social objectives of sustainable forest management. In addition, these measures could help boost the positive effect of the forest sector on climate change by improving carbon balance, both by preventing forest disasters and especially by favouring an increase in the proportion of wood products suitable for long-term use.
André, P., Buchet, V., Defays, E., Lhoir, P. & Reginster, P. 1994. Eclaircie en futaie résineuse. Fiche technique No. 3. Namur, Belgium, Ministry of the Walloon Region.
Laitat, E., Lebègue, V., Perrin, D., Pissart, G. & Sheridan, M. 2003. Séquestration du carbone par les forêts selon l'affectation des terres. Gembloux, Belgium, Gembloux Agricultural University.
Lecomte, H., Florkin, P., Morimont, J.P. & Thirion, M. 2003. La forêt wallonne, état de la ressource à la fin du 20ème siècle. Namur, Belgium, Ministry of the Walloon Region.
Ministry of the Walloon Region. 1997. La forêt et la protection de l'eau. Namur, Belgium.
Ministry of the Walloon Region. 2002. La forêt et la protection du sol. Fiche technique No. 14. Namur, Belgium.
Roth, B. 2002. La richesse écologique du bois. Silva Belgica, 109(6): 42-47.
Weissen, F., Baix P., Boseret, J.P., Bronchart, L., Lejeune, M., Maquet, P., Marchal, D., Marchal, J.L., Masson, J.L., Onclincx, F., Sandron, P. & Schmitz, L. 1991. Le fichier écologique des essences. Namur, Belgium, Ministry of the Walloon Region. 3 vols.
Weissen, F., Bronchart, L. & Piret, A. 1994. Guide de boisement des stations forestières de la Wallonie. Namur, Belgium, Ministry of the Walloon Region.