4. What is the biological diversity of the world’s forests?
- 4.1 How much primary forest is left on the planet?
- 4.2 How much of the forest are has been set aside for conservation?
- 4.3 What is the distribution of tree species in forests?
- 4.4 How many tree species are threatened?
The concept of biological diversity, or biodiversity, encompasses the variety of existing life forms, the ecological roles they perform, and the genetic diversity they contain. In forests, this diversity allows species to adapt continuously to changing environmental conditions and to contribute to the functioning of the ecosystem. From a human perspective, forest biodiversity also maintains the potential for tree breeding and improvement, in view of meeting human needs for goods and services.
While timber production often dominated the way in which forests were managed during the past century, new pressures have now given rise to a more balanced approach of sustainable forest management. This approach involves the conservation of biodiversity in view of obtaining multiple goods and services.
Though monitoring biodiversity and the way it is affected by forestry practices is important, there is no single measure that reflects all aspects of biodiversity.
For policy purposes, various ecological indicators can be used to monitor a few relevant aspects of biodiversity over time, though so far this has mainly been done at a local level. More...
4.1 How much primary forest is left on the planet?
Primary forests are forests where native tree species grow, where ecological processes are not significantly disturbed, and where there are no clearly visible indications of human activities. The size of primary forest is an important indicator for assessing the state of forest ecosystems even though primary forest in temperate and boreal zones may have fewer plant and animal species than some modified forests.
An estimated 13 million km2 of forest, a little more than a third of the world’s forest area, are considered primary forest. Nearly half of all primary forest is found in South America, a quarter in North and Central America, and nearly a fifth in the Russian Federation alone.
A number of countries reported that they have no primary forests left. These were mostly countries in Europe and in the arid zones of Africa and Western Asia.
Though primary forests still represent a little more than a third of the world’s forest area (36.4%), in absolute terms, the area of primary forest has been shrinking by about 60 000 km2 per year over the last 15 years. While the loss has been slowing down in some regions, it has been increasing in South America and some other regions. Brazil and Indonesia alone accounted for a loss of 49 000 km2 per year during the period 2000–2005.
Several western European countries as well as Japan noted an increase in the area of primary forests, mostly because they have been setting aside natural forest areas in which no intervention takes place; such areas eventually evolve into forests which meet the definition of primary forests. More...
4.2 How much of the forest are has been set aside for conservation?
Setting aside land as protected areas and managing it accordingly is a key part of ongoing global efforts to conserve biological diversity. The amount of land designated for the conservation of biodiversity is thus an important indicator of progress. This land can be located within a protected area, but may also be found outside such legally designated areas.
More than 4 million km2 of forest which represents more then a tenth of total forest area (11.2%) are designated as having conservation of biodiversity as their primary function [Table 3.3].
In absolute terms, the biggest forest area designated for conservation of biodiversity is found in South America, followed by North America.
In relative terms, the regions with the largest percentage of forests designated primarily for conservation are Central America as well as Western and Central Africa. Europe and Western and Central Asia have the lowest percentage of forests designated primarily for conservation.
Between 1990 and 2000, the area of forest devoted to biodiversity conservation has increased by at least 960 000 km2 or 32%. This increase has taken place across the world except in Northern, Eastern and Southern Africa. More...
4.3 What is the distribution of tree species in forests?
Monitoring the growing stock in forests and other wooded lands provides information on of the total standing volume of wood. However, focusing on the growing stock of the three or ten forest tree species, which are most common in that area, provides an indication of changes in forest tree composition.
In natural and semi-natural forests, generally, the larger the share of growing stock made up by the three most common forest tree species, the smaller the overall number of tree species in that area.
Quantitative information on the ten most common species has been gathered for 60% of the world’s total forest area located in 82 countries.
This information revealed a great variation in terms of species diversity. The ten most common tree species represent less than 30% of total growing stock in Congo, Viet Nam, Myanmar, Panama, Ghana, Madagascar, Indonesia and India. This small proportion of the total species represented by the most common species which indicates high species diversity. The lowest species diversity tends to be found in boreal forests of the Northern Hemisphere. Unfortunately, information is missing from areas of known high species diversity such as many countries in South America and the Congo Basin.
Five species groups – pines, oaks, spruces, firs, and beeches – make up almost a third of the most common species reported.
Between 1990 and 2000, the relative ranking of the top 10 tree species in the eighty-two reporting countries has remained the same. Moreover, no significant change in the share of growing stock occupied by the three main species was observed in the countries and areas that had provided complete data series (56 out of the 229 reporting countries).
The absence of an authoritative world list of trees and shrubs is a serious impediment to assessing and monitoring one of the most basic components of forest biodiversity – tree species richness at the national level.
A first global attempt was made to systematically record the number of native forest tree species by country and area, including species such as bamboo, palm and other woody species. The number of native tree species in individual countries ranged from a minimum of three to a maximum of 7 880 as illustrated in Figure 3.11
South America has the highest average number of native forest tree species per country. Brazil reports the largest number of native tree species and high species diversity in the Amazon basin and in the Atlantic coastal forest. High species richness is also reported by countries in Central Africa, Central America, East Asia, Madagascar as well as South and Southeast Asia. The lowest average number of trees per country is found in Europe (Iceland, for example has only three native tree species). Species diversity in boreal forests is usually relatively low, and vast expanses of such forests are dominated by a small number of tree species. More...
4.4 How many tree species are threatened?
Rare tree species and those highly valued for wood or non-wood forest products are often in danger of becoming extinct within parts of their range. On average, 5% of the tree species native to a country are threatened.
Countries across the world reported information on the number of forest tree species considered threatened. Threatened species were classified in accordance with the IUCN red list ranking system as either ‘vulnerable’, ‘endangered’ or ‘critically endangered’.
Most countries and areas reported that one or more tree species are threatened in their jurisdiction. The highest number of threatened tree species is found in South America as well as in South and Southeast Asia.
No simple relationship was found between loss of forest and number of threatened tree species. In some countries, though relatively high proportions of natural forests and protected areas remain, many individual tree species are at risk. More...