Trends in dynamics of global forest cover are defined by two groups of processes. A major driver of decreasing the world forest area is deforestation. Two definitions of deforestation are widely used in their respective international frameworks. By the definition accepted by the UN Framework Convention for Climate Change (UNFCCC)
this is an anthropogenic process: deforestation is defined as the direct human-induced conversion of forest to non-forest land. The FRA did not distinguish natural loss of forest from that caused by human impacts: deforestation was defined as the conversion of forest to another land-use or the long-term reduction of the tree canopy cover below the minimum 10% threshold. Both definitions refer to long-term or permanent change from forest to nonfor-est. Major alternative processes to deforestation are afforestation (establishment of forest on previously nonforest land), reforestation (natural or artificial development of forest on recently forest land), and natural expansion of forests into previously nonforest land. A superimposition of these four major processes results in net change of forest areas.
Here we apply the FAO definition which is used in most assessments and inventories: deforestation includes areas of forest converted to agriculture, natural nonforests such as shrubs and savannas due to anthropogenic impacts or natural disasters, nonvegetative land (e.g., water reservoirs and urban territories), etc. The term does not include areas where the trees have been removed as a result of forest management activities (e.g., logging) or due to natural disturbances (fire, insects), and where forest is expected to regenerate in a natural way or by silviculture activities. Deforestation also includes areas where some permanently impacted drivers (e.g., disturbance, overutilization, pollution, or other changing environmental conditions) do not allow for maintaining the tree cover above the 10% threshold during a long period of time.
Some other processes like degradation and fragmentation also contribute to the impoverishment of the world's forests and impact global biogeochemical cycling. Three mostly used definitions of degradation (of FRA, International Timber Trade Organization (ITTO), and UN Convention to Combat Desertification (UNCCD)) are comparable with respect to the main clusters. Forest degradation means a process leading to a temporary or permanent decline in the density or structure of forest cover or its species composition, and thus leading to a lower capacity of forest to supply products and/or services, and finally to reduction or loss of the biological productivity of the land. Many reasons can contribute to forest degradation, including diverse human-induced disturbances; unsustainable, excessive forest exploitation; insufficient logging; short rotation periods; etc. In many regions of the world, particularly where forest ecosystems are impacted by accelerated regimes of natural and human-induced disturbances, deforestation and degradation are usually closely interconnected. Fragmentation of forests often leads to decreasing vitality of remaining pieces of forest cover, acceleration of disturbance regimes, and, under the lack of integrated land management, can be a component of structural degradation of forest cover, impoverishment of ecosystem structure, and decline of productivity. Only 22% of the world's forests are classified now as 'intact' forests; 82 of 148 countries lying within the forest zone have lost all their intact forest landscapes.
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