Trends and dynamics

Photo 15. Policy of maintaining rows of trees along rural roads attractive to tourists, in the Allier region of France. (© Bellefontaine/Cirad).

The important uses and services of Trees outside forests are known and valued but the global facts and figures on tree cover, wood production and wood products for this resource still need to be quantified and and assessed in economic terms. What indications we do have come from local or national assessments. In Sri Lanka, for example, 73 percent of the wood and 80 percent of the fuelwood is derived from home gardens and trees growing on farmland (Gunasena 1997, cited in Simons et al., 2000). In China, 1.8 billion eucalypts have been planted on farmland, but under one billion (0.95) on industrial plantations. In Viet Nam and Thailand, 15 times as many trees grow in fields as in plantations (Harwood 1997, cited in Simons et al., 2000). It is accordingly not a simple task to tease out the dynamics of Trees outside forests. Combining data on forest dynamics with the dynamics of trees growing on agricultural and urban land should give new insight into world trends for wood resources, confirming locally observed trends for shrinking or expanding tree cover.

State of forest resources

The 1980 and 1990 world Forest Resources Assessments inventoried areas under forest and forest plantations, drawing on statistics supplied by the relevant national institutions. In 1996, the objectives of this world forest inventory were reviewed in the course of an expert consultation held in Kotka, Finland (Nyyssön and Ahti, 1996). Following this meeting, Forest Resources Assessment 2000 was divided into three major fields of activities: assessment based on existing data (especially at the country level), remote sensing surveys and special studies. Special studies stressed issues mostly theretofore unaddressed, including Trees outside forests.

The data from the Forest Resource Assessment Programme for the year 2000 (See Box 18) reveal particularly heavy deforestation in the tropics. While we do know that forest clearing is often followed by the establishment of production systems incorporating trees, the fate of formerly forested land is not known. Nor do we know much about the dynamics of tree cover on farmland, including whether trees are still present. Further avenues needing exploration are the various types of tree formation, their spatial distribution, the extent to which such resources might offset forest decline, and how much wood and other products they might provide.

The dynamics of Trees outside forests

Forest tree dynamics and those of Trees outside forests are often interlinked, though the link may be tenuous or indirect. Forest decline was observed in several countries to have prompted farmers to plant trees in their own fields to ensure the supply of forest products (Arnold and Dewees, 1995). Often enough, Trees outside forests progress from forested to non-forested areas. The introduction of trees onto farmland is now perceived as a way of meeting the demands of rural and urban communities for both wood and non-wood forest products.

Trees outside forests are of particular concern to the developing countries. They are one way of meeting the needs of a growing population on the move which is pushing back the agricultural frontier and encroaching upon the forest in order to feed both rural and urban dwellers, and not leaving land fallow long enough to re-establish the fertility of the soil. The gathering of wild products, such a fundamental and varied part of everyday rural life, can, where repetitive and excessive, lead to plant resource degradation in semi-arid and peri-urban zones and around sources of fodder and browse. At the same time, certain farm practices involving trees, such as parklands and woodlots, multi-story farming and grazing on treed pastures, are still in good use. A whole series of ancient or modern agroforestry practices such as corridor cropping, hedgerows along contour bunds, and planted fallow also come into play.

While in the developing countries the dynamics of trees outside forests are driven by the logic of production, the rising trend in the industrialized countries is instead pro-environment. Market-oriented agriculture leaves little room for trees, but urban and peri-urban trees, green belts, noise-abatement `green walls', riparian trees and line-plantings are increasingly prominent features. As urban forests gain ground, Trees outside forests are less apt to be alternatives to forest resources than in the developing countries.

Tree cover expansion and decline trends alike have been observed on farmland, grassland, and where trees border the forest. What is important to know is that situations vary, and that the dynamics of Trees outside forests are neither uniform at the scale of the region nor similar for the same system at different locations. Shrinking tree cover can exist side by side with the reverse trend. The agroforestry parklands of West Africa offer an example. Many authors agree that less area is now covered by these parklands, that the trees are less dense, and that there is less old growth. And yet, Faidherbia albida parklands in Mali are expanding. In Hyphaene thebaica parklands, the density of young trees exceeds that of mature trees, although Sylla (1998) did observe a great many sick, dead, topped or mutilated trees (70 percent), which limits the prospects for regeneration. In heavily populated areas of Nigeria, per hectare tree density in parklands increased by a factor of three between the 1970s and 1980s (Boffa, 2000b).

Remote sensing now makes it possible to monitor these trends, though both the techniques and procedures leave room for improvement and fine-tuning. Properly adapted, these advances could be beneficial in assessing Trees outside forests. On the other hand, some off-forest tree systems are so dispersed that aerial photography is a more appropriate option. What we still need to understand, then, are the underlying dynamics of tree cover expansion, and how to support the trend where observed and encourage similar processes in other areas, while keeping one eye on the future.

Shrinking tree cover

In the developing countries, the following factors have considerably thinned tree cover in the tropics since the dawn of the twentieth century: drought, clearing for agriculture, overgrazing and forest fires. Much logged-over forest was developed as farmland or tree plantations. This happened in Côte d'Ivoire, where a great many cocoa, coffee and fruit plantations were established on cleared forest land. Deforestation also accompanied the implantation of irrigation schemes and the introduction of farm mechanization in the 1970s and 1980s, as in Senegal along the river. Deforestation was also favoured by "village development" schemes, most of which failed to include trees in their development plans. Tanzania is a striking example. At the same time, in much of the world the mounting demand for fuelwood has ringed towns and villages with deforested areas. All of these logged-over or transformed forests have, at best, given way to impoverished forest, and, in the worst-case scenarios, to scattered, orphan trees. Some tree formations look at first like degraded forest, which is mostly not the case, as witness many of the `tiger bush' formations in Niger (d'Herbès et al., 1997; Ichaou, 2000).

Photo 16: Agricultural fronts, deforestation and "orphan" trees (Rwegura, Burundi) - © R. Bellefontaine

Agricultural development in the industrialized countries, which has gone through the various stages of mechanization, drainage, irrigation, land consolidation, and ever larger plots and farms, has been responsible for the gradual but steady eviction of most of the trees that used to be found in rural landscapes. In France over the last thirty years 100 million single or line-planted trees have disappeared (Pointereau and Bazile, 1995). This destruction has been paralleled by a drop of 4.5 million ha of non-forest wooded areas in the 1900s to 1.6 million ha in 1990, whereas forested areas grew steadily over the course of the twentieth century. In England and Scotland, there was a 25 percent drop in the linear coverage of hedgerows from 1950 to 1970. Fruit-tree meadows have become a rarity everywhere, and non-forest trees are an aging resource (ibid). Braudal (1986) pointed out the link between the frequency of Trees outside forests and the type of crop rotation practiced a clear proof of the interrelatedness of tree presence and farm practices in rural areas.

Expanding tree cover

Paralleling the conversion of forest into farmland is the reverse trend: rural landscapes where tree cover is expanding through natural regeneration or tree-planting on cleared land (Bellefontaine and Ichaou, 1999).

Photo 17. Degraded forest in the mid-altitude range in the Himalayas in Pakistan. (© Hofer/FAO)

In developing countries, population growth is frequently cited as a cause of deforestation. But in the humid zones, above a specific threshold of deforestation, tree cover tends to be restored by the people who live there. A study in Rwanda showed that farmers planted more trees where the pressure on the land was heaviest, and where cash crops predominated (Messerschmidt et al., 1993). The overpopulated but heavily treed island of Java is an edifying case in point, despite the island's omnipresent rice paddies. A time-study of aerial photos of the Mahaweli watershed in north-western Sri Lanka covering the period 1956 to 1991 showed a spectacular 60 percent gain in tree cover, due in part to the rise in home gardens and plantations at the expense of tea or rubberwood, and in part to forest expansion (White et al., 1995). Despite Kenya's annual population growth rate of 3.7 percent, the actual per hectare density of trees in the Madhakos district has increased (Banana et al, 1999). In other cases, as in Nepal, economic changes have prompted farmers to replant trees in accordance with their needs (Box 19), giving the lie to the dire predictions of the 1970s concerning mountainside deforestation in Nepal (Gilmour and Nurse, 1991).

Photo 18. Dynamism of natural plant propagation by root cuttings and layering (Combretum micranthum) in Niger under 400 mm/yr. (© Ichaou)

Farmers have frequently promoted the maintenance, improvement and even planting of trees on farmland. This is why the ratio of tree cover to population expansion is not always negative. In the Comoros, for example, tree stands are quantitatively greater today than they were thirty years ago. The so-called natural forest has shrunk, but a treed landscape has sprung up in farmers' fields (Karsenty and Sibelet, 1999). In Ethiopia, the more people there are, the more trees they grow, according to Mesfin Wolde (1991). The changing pattern of tree cover is often more telling than the always problematic and rarely exhaustive quantification of forest formations.

In the industrialized countries, the steady expansion of temperate, boreal forest owes more to simple natural regeneration in connection with the en masse flight of people from the countryside than to any other factor. In Europe, Trees outside forests are springing up in great numbers as seedlings colonize fields left untilled under the agricultural set-aside provisions of the European Union. This raises a number of questions concerning the issue of local development and the future of these trees, which may well develop into mature forests... but after how many years of brush or forest fires, people ask. One thought is that such plots should be managed under a landscape policy scenario where local communities and farmers contract to maintain them as scenic landscapes or perhaps a new kind of officially (i.e., taxes) sanctioned cohabitation should be envisioned, with trees and crops sharing the same land.

Since the 1980s, bocage landscapes, hedgerows, rural and urban line-plantings, and riparian woods have been officially promoted in Europe (Switzerland, Denmark, the United Kingdom, the Netherlands, and some of the German länder). The development of local markets for sawnwood (mainly from trees in hedgerows), aid to the development of small-scale units, the study or promotion of wood-based power plants in collective heating facilities have all opened new outlets for non-forest tree products.

Photo 19. Pinus merkusii invades a clearing in Cambodia (© Aubreville)

Looking to the future

The social and ecological dynamics of Trees outside forests are intimately linked (Alexandre et al., 1999), especially in built-up areas. The population of the world is increasingly urban-dwelling: the projections see 60 percent living in cities by the year 2025 -- the percentage of urban dwellers is already much higher today in the industrialized countries (World Bank, 1995). Urbanization will thus exert a growing influence on the dynamics of Trees outside forests.

In some of the developing world's big cities - Mexico City, for instance - tree-planting is managed by the municipality, and is ecologically oriented. In the poorest cities, trees are often planted by homeowners in and around their properties for social, cultural and economic reasons having little to do with scenic or environmental considerations. Cities are, in fact, becoming more rural, mainly in an attempt to cope with the everyday problems caused by widespread and growing impoverishment. Urban growth and the proximity of large-scale irrigation schemes are creating strong pressure on tree resources. Small animal-rearing and tree-growing within the nooks and crannies of built-up areas are an increasingly familiar component of the urban landscape (Moustier et al., 1999), in a cycle of mutual influence that blurs the distinction between urban and rural. A popular form of urban forestry is taking root in which people and their needs have priority. Founded on an unplanned approach to land management, this groundswell is making a positive contribution to the physiological and economic welfare of urban society (El Lakany et al., 2001). And these individual approaches, driven by the need to feed the family, are increasingly backed in the developing countries by community undertakings, as well as municipal initiatives addressing the urban environmental need for greater comfort, pollution control and waste-water management.

Trees have also become an increasingly visible feature of city landscapes in the mainly urbanized industrialized countries in the last thirty years or so. The proliferation of landscape planning studies of per urban areas, highway rest stops, and roadsides have shown how trees beautify the landscape and break the monotony of highway travel (Bourgery and Castaner, 1988). The perception of tree resources has evolved over time from an aesthetic approach to one of incorporating the ecological and socioeconomic benefits. Urbanization in the developed countries also entails environmental and social problems. Some, such as disease and poor hygiene and limited access to drinking water, food and fuel, have to do with urban poverty, while others, such as air and water pollution, urban congestion and the loss of biodiversity, are more the outcome of economic growth or prosperity (FAO, 2000a.).

There is a certain observable similitude, though not for the same reasons, between the problems of pollution, poverty and threats to the environment faced by the denizens of both northern and southern cities. In both situations, however, these problems can be partly addressed by the goods and services of trees, including air and noise pollution abatement, restoring climatic equilibrium, improving microclimates and maintaining natural resource quality in the urban environment. This includes water, which is becoming a scarce commodity in many towns¹⁰ .

It is absolutely essential for planners and policy-makers to reckon the benefits of urban and per urban tree resources into the equation of progressive-minded management to improve the quality of life in the urban context. The potential contribution of trees to the subsistence needs of the poorest members of society is equal to their ecological and aesthetic benefits. Based on the positive interaction of all actors, urban tree resources can be appropriated and managed as a dynamic ecosystem, dampening the harmful impact and multiplying the positive benefits.

¹⁰ International institute planners predict shortages of freshwater in arid zones. By the year 2050, over 2.5 billion people in 29 countries will lack water, mainly in North Africa, sub-Saharan Africa, and in the Middle East.