Global deforestation has become a major concern of human society. Belonging to the last untouched and pristine terrestrial ecosystems on earth, tropical forests in particular are a central issue of many conservation movements. Safeguarding global biological diversity has been widely approved as a political goal throughout the global community with forests playing a major role. Large and rare animals and pictures of burned forests have strengthened the belief in the moral and ethic injustice currently taking place in the tropics. Yet, we have to consider that this point of view originates in western society and mainly remains widely accepted in the developed world where for the most part no tropical forests exist. In contrast to the (partly) intact and less degraded forest ecosystems of the tropics, in the highly developed countries of the northern hemisphere large parts of temperate forest ecosystems have long vanished and been replaced by anthropogenic landscapes. This change in land use has resulted in the creation of severely transformed ecosystems fundamental for the economic and social development. These include, for instance, agricultural, pastoral, industrial and urban landscapes. The long time that has passed since their clearance often leaves temperate forests out of the current investigation on deforestation patterns. Rather, scientists concentrate on patterns of tropical deforestation, which is currently the most alarming regarding the net loss of forest cover.

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Generally, land degradation occurs to a great extent in forested areas since about 25% of total land degradation is associated with broad-leaved forests and 17% with boreal forests (UNEP 2007). With the severity of the consequences of global deforestation becoming evident, environmental and economic science is increasingly addressing the issue. Just recently, beginning in the late 1980s, environmental economists have been publishing new thoughts on valuing the environment and considering its ecological functions in economic decision-making (see de Groot 1987, 1992; Daily 1997; Costanza et al. 1997; among others). Nowadays, the interdependence and importance of forest ecosystem functions and services is widely accepted throughout scientific and economic literature. This development has raised the general awareness of the importance of well functioning and sustainably managed forests and has augmented the acceptance of forest conservation movements (at least in western societies). Supported by new technologies, such as satellite imagery and remote sensing methods, the study of deforestation processes and spatial patterns of deforestation has been facilitated at various levels and different scales at affordable costs. By using new technologies and approaches, many studies have been conducted in an attempt to estimate the extent of deforestation and to explain its causes. A great amount of studies focuses on the processes of tropical deforestation which is doubtlessly most alarming at the moment. However, other studies have approached deforestation from a global perspective and also for temperate forest ecosystems in particular.
In light of the ongoing debates on deforestation, this paper first defines forest degradation and deforestation and then explores potential misunderstandings of such definitions. This discussion is followed by an analysis of the causes of global deforestation process and concludes with some key findings for tropical as well as temperate deforestation patterns.
2 Defining forest degradation and deforestation
Drawing on the publication by the Food and Agriculture Organization (FAO) (2009), the following section will shortly present the debate on the definition of forest degradation and deforestation in a global context. As the number of studies and policy instruments concerning forest degradation and deforestation are numerous it is necessary to establish a common language in order to draw mutual conclusions and to find applicable solutions.
Being a serious environmental, social and economic problem, forest degradation and deforestation are issues of major concern discussed at various political levels as well as by the public. As consequences of deforestation become evident not only on the local but also on the global scale, finding consensus among different parties is of great importance for responding adequately to a daunting challenge. The definition of forest degradation and deforestation, however, is technically and scientifically difficult to define because it is viewed and perceived differently by various stakeholders who might have different objectives regarding forest use or conversion. Furthermore, discrepancies in the definition can have implications on forest related policy making processes as well as on the monitoring and enforcement of policies (FAO 2009). The FAO report argues that “forest-related definitions […] which are outcomes of international processes are policy tools and can have major economic, social and environmental implications” (FAO 2009, p. 8). Besides monitoring purposes, forest-related definitions also determine financial flows and the allocation of financial incentives for various purposes (e.g. restoration or improvement measures, projects under the Clean Development Mechanism (CDM) or the Reducing Emissions from Deforestation and Degradation (REDD) program) (FAO 2009).
2.1 Deforestation
Deforestation describes the process of land use change from “forest” to “non-forest” (FAO 2009). However, this quite simple definition based on certain thresholds of deforestation has the potential to cause conflicts when the individual factors are evaluated. Different nations, international organizations or ethnic groups might have differing perceptions and definitions of “forest” or “non-forest”. Drawing on the definition provided by the FAO, forests are defined as “land spanning more than 0.5 hectares with trees higher than five meters and a canopy cover of more than ten percent, or trees able to reach these thresholds in situ” (FAO 2005, p. 16). This definition does not include land that is predominately under agricultural or urban use (FAO 2004). Furthermore, deforestation can occur on different spatial and temporal scales which will be discussed later in the following section.
2.2 Forest degradation
While deforestation is relatively easy to define, much more effort is required to define forest degradation. In 2002, a symposium of international forestry-related organizations consisting of the FAO, the Intergovernmental Panel on Climate Change (IPCC), the Center for International Forestry Research (CIFOR), the International Union of Forest Research Organizations (IUFRO) and the United Nations Environment Program (UNEP) agreed on a common definition of forest degradation, defining it as “the reduction of the capacity of a forest to provide goods and services” (FAO 2009a, p. 9). This process occurs within the forest and negatively affects the characteristics of the forest, which can be of structural or functional nature and which determine the capacity to provide goods and services. Defining the latter two terms well is a challenging and demanding task. The definition can be comprehensible for one party but could be understood very differently or be misunderstood. For instance, with regard to the REDD mechanism, forest degradation considers particularly the reduction in carbon stocks within a forest (FAO 2009b). However, there is still a lack of practically applicable approaches to measure the extent of forest degradation because the existing definition is not an operational formulation due to different perceptions of what forest degradation furthermore entails (FAO 2009). Therefore, “the United Nations Forum on Forests (UNFF) has called for greater harmonization of internationally applicable definitions related to forests to facilitate monitoring and reporting on progress towards the achievement of the global objectives on forests and sustainable forest management […]”(FAO 2009, p. 8).
3 Processes of deforestation
As described above, deforestation is a process of change in land use. Although it is currently being addressed widely at different political levels as well as by the public, it is not a new phenomenon. Since humankind began to control fire and to domesticate animals, forests needed to be cleared for various purposes. However, among great parts of western society forests nowadays are being valued very differently than even a hundred years ago. Scientific progress, environmental awareness, technical innovations and deliberative policies have made clear that deforestation has become an important and global issue. The following section shortly depicts the process of deforestation after which the underlying causes for this development and typical observable spatial patterns of deforestation will be presented.
In general, it can be distinguished between natural and anthropogenic disturbance processes. Natural interferences occur naturally in the environment, in contrast to anthropogenic interferences which are human induced. While natural stresses occur rather on a small to medium scale and are of relatively short term, anthropogenic disturbances often occur on a medium to large scale and are long term processes. The former include forest clearances by natural wildfires, wind (storms), extreme weather events or changing climatic conditions (though being argued to be human induced). The latter includes timber extraction, pastoral uses, small shifting cultivation plots, induced forest fires and large scale forest conversion activities. Anthropogenic disturbances can either be intentional (direct), e.g. logging or land conversion, or unintentional (indirect), e.g. introduction of invasive species (FAO 2009). However, forest disturbance regimes become less predictable once natural and anthropogenic factors combine (FAO 2009). The two factors are often dependent on each other and combinations can be complex and take various forms. For instance, anthropogenic impacts on forest structure and dynamics in tropical mountain regions can have severe consequences for downstream areas during naturally occurring storm events in the form of floods and landslides. Further, human impacts influence the vulnerability of forests to degradation from natural causes, can negatively affect the successional regeneration process in naturally disturbed forests, and naturally occurring drought periods can be the cause for large scale forest fires ignited by escaped land clearing fires (Goldammer 1992). Moreover, global ecological feedback mechanisms can have far reaching impacts on anthropogenic forest interferences (Goldammer 1992); this will be addressed later in the paper.
Usually, forest degradation is associated with a reduction of the vegetative cover (Lund 2009 in FAO 2009). Considering forest degradation as a continuous internal process caused either by natural or human induced disturbances, various thresholds can be defined, for example, in terms of percentage of canopy cover. Thus, when passing a certain threshold, a forest can be classified into various levels of degradation and eventually, when reaching a high level of openness, the forest cannot longer be defined as a forest (i.e. 10% canopy cover), although administratively it still might be considered forest land (FAO 2009).
Deforestation can occur abruptly in a very short period of time by simply removing the land’s tree cover. Under those circumstances, the forest is usually cleared for the purpose of land conversion for other forms of land use or for the substitution by monoculture plantations of exotic tree species. This form of deforestation, if sufficiently large, is easily detectable by remote sensing (FAO 2009).
However, deforestation can also occur over a longer period of a subsequent forest degradation process caused by disturbances which vary in terms of severity, quality, origin, extent and frequency. The impacts occur on varying spatial and temporal scales and are dependent on the type and specific characteristics of the forest (FAO 2009). Its detection and measurement is relatively difficult “as it implies a long-term loss of biomass, productivity or species composition that is difficult to assess, especially the impacts on soils, water, nutrients, biodiversity and the landscape.” (FAO 2009, p. 13). Yet, forest degradation is not inevitably a prerequisite for deforestation. Forests can also exist as degraded forests for a long period of time without reaching the level of deforestation (Angelsen et al. 2008).
4 Causes for deforestation
Various direct and indirect causes for tropical deforestation exist (Geist and Lambin 2002). Drawing on an earlier publication by the two authors (2001), the results are based on the analysis and interpretation of 152 subnational case studies within the tropics.
Direct or “proximate causes are human activities or immediate actions at the local level […] that originate from intended land use and directly impact forest cover” (Geist and Lambin 2002, p. 143). Indirect causes or “underlying driving forces are fundamental social processes […] that underpin the proximate causes and either operate at the local level or have an indirect impact from the national or global level” (p. 143). In other words, direct causes for deforestation are the actual physical impacts on forest cover that degrade the forest or convert it to other forms of land use. Indirect causes, on the other side, are institutional arrangements or socio-demographic forces which facilitate the existence and emergence of the direct causes.
At the proximate level, the results clearly show that deforestation in the majority of cases is caused by multi-factorial terms, that is, a combination of direct causes rather than by a single variable. The four single causes are (decreasing in relevance): agricultural expansion, infrastructure extension, wood extraction and other factors (land characteristics, biophysical drivers and social trigger events). The most frequent combination of direct causes is the “agricultural – wood extraction – infrastructure expansion” combination that ultimately leads to deforestation (3-factor term of causation) (Geist and Lambin 2001). However, it is questionable to just project this result to the entire tropical forest biome. Each individual case of (small to large scale) deforestation can have a distinct history of the cause or need to change the land use form and might statistically not be represented in the current literature.
Likewise, at the underlying, institutional level tropical deforestation is associated with synergetic driver combinations rather than individually operating forces. The five single driving forces are (decreasing in relevance): Economic factors, policy and institutional factors, technological factors, cultural factors, demographic factors (Geist and Lambin 2001). Here, the indirect factors are in the majority operating at the 5-factor term of causation, that is, all underlying factors together are argued to be driving deforestation in more than a third of all cases.
In Lambin and Geist (2003), the two authors discuss regional differences in tropical deforestation in more detail. In fact, they argue that the processes of humid tropical deforestation in the three most important areas, namely Latin America, Southeast Asia and Africa, can vary to a great extent. Reasons for the regional differences are derived from three sets of factors: “the environmental and land-use history”, “the particular combination of causes triggering and driving land-use change”, and “the feedback structure, that is the social and ecological responses to land-cover changes” (p.24). Though, Rudel (2006) distinguishes more precisely the most important tropical forest areas (Central America & the Caribbean, South America, West Africa, Central Africa, East Africa, South Asia, and Southeast Asia) and depicts a detailed image of the relevant agents of deforestation (road builders, corporate loggers, forest managers, reserve advocates, urban enterprises and consumers). He argues that while the size of the forest area decreases, the agents of change adjust their behaviour and act differently in respect to the actual forest size. The author’s main conclusions can be shortly summarized as follows. As forests decline in size roads are ceased to be built, corporate enterprises stop exploiting the forests, community forest management becomes more effective, protected forest areas become less applicable for conservation measures, and degraded sites are reforested by urban consumers (Rudel 2006). Thus, the causes for deforestation and land use change are not static and since all factors are interdependent it is difficult to assess causes in a biome wide or global perspective.
However, the quite general conclusions that are drawn by Geist and Lambin for the three major tropical forest areas (Latin America, Southeast Asia, and Africa) must be viewed cautiously. For instance, an extensive and diverse area such as central and western Africa is reviewed by means of only 19 case studies from eight countries. The results then are treated non-exclusive, are thus assumed to be comparable (although being quantitative as well as qualitative) and are used for drawing representative conclusions on the entire tropical Africa (Geist and Lambin 2001). Furthermore, the definition of deforestation that is used by the authors must be viewed critically since they use a “broad and inclusive” (Geist and Lambin 2001, p.17) definition which considers “not only forest conversion (…) but also different types of [forest] degradation” (p.17). Nevertheless, Geist and Lambin (2001, 2002, 2003) provide a good overview of the existing causes for deforestation in the tropics and relate underlying and direct causes (as well as accompanying occurrences) before they conclude with a quantification of the causative linkages. Also, they discuss the strengths and weaknesses of their chosen methodology and address potential biases and ambiguities to the reader adequately (2001, p. 17 ff).
Also, it is important to stress the importance of roads or access in general to (remote) forest areas, which is a prerequisite for large scale anthropogenic interferences. This is true not only in the tropical forest biome but also in the temperate forest biome. In many logistic regression models for the assessment of deforestation patterns, the distance to roads is a major factor and closely related to deforestation processes (Mertens and Lambin 1997; Altamirano and Lara 2010; Echeverria et al. 2008; Wilson et al. 2005; among others).
Although agricultural expansion is mentioned to be the most significant cause for deforestation, it should be mentioned that the intensification of agricultural practices, however, can have a positive effect on remaining forests since productivity increases and the pressure of expansion thus is reduced (cf. Barbier 2001). As the global human population and the demand for food and agricultural products increase, the importance of agriculture must not be neglected and should be incorporated into policy responses.
In his book Logjam – Deforestation and the Crisis of Global Governance, David Humphreys (2006) shortly describes the European deforestation process from an institutional economics perspective. He argues that, in contrast to Garret Hardin’s theory of the tragedy of the commons, common property regimes are crucial for the conservation of forest public goods (such as watershed protection or climate regulation) as long as land tenure rights and legal ownership are secured. Likewise, Elinor Ostrom (2002) argues similarly in her essay “Reformulating the Commons” and identifies several requisite attributes for the resource system and the appropriators in order for efficient self-governing associations to form. The most important attributes mentioned are the spatial extent of the resource system, the salience or dependence of the appropriators on the resource for a major portion of their livelihood, trust and reciprocity and autonomy, among others (Ostrom 2002, p. 5). Common property regimes can be defined as “institutional arrangements for the cooperative (shared, joined, collective) use, management, and sometimes ownership of natural resources.” (McKean 2000 in Humphreys 2006, p. 4). Humphreys (2006) states that in Europe the common use of forests under public ownership was widely respected until the Middle ages “when the aristocracy and political elites organized the systematic and widespread displacement of commoners from common land, and the subsequent enclosure of this land by fencing” (p. 6), thus, changing the property regime from public to private. Then, with the rise of the centralized state during the 16th to 18th century, forests were further enclosed and exploited with timber as a steady revenue source. In central Europe soon only few species were considered economically profitable. “By conserving only economically valuable species, this instrumental, utilitarian and abstractionist logic eroded biodiversity in the forest and promoted the development of scientific forestry […]” (Humphreys 2006, p. 6). This socioeconomic development, an increasing demand for timber and fuel wood and a steadily growing population promoted the exploitation of temperate forests across Europe and lead to the degradation of the forest public goods which were considered unproductive in economic terms. The practices of enclosure and scientific forestry were later also brought to the European colonies in Africa, Asia, Australia and the Americas (Humphreys 2006) where currently remaining pristine tropical forests are experiencing a similar trend. To sum up this paragraph, again I use the words of David Humphreys since they convincingly make a point and cannot be formulated better. “Enclosure during the medieval and colonial eras degraded and destroyed forest commons across the world. Forest degradation in the 20th and 21st centuries has rarely been due to poorly functioning common property regimes. It is invariably the result of the enclosure of commons by state and private interests, who overexploit the forests for economic gain and who have a totally different relationship to the forest than the commoners whom they displaced.” (p. 7).
5 Spatial change patterns
Only as recent as the last 150 years have tropical forests experienced a drastic human induced change in terms of forest cover and species composition in contrast to many temperate forest ecosystems which have experienced severe and large scale changes for much longer. While vast areas of tropical forest were still without anthropogenic pressure, temperate forest landscapes (in Europe i.e.) were, in relation to available land area, highly populated and forest ecosystems largely impacted and altered (Potapov et al. 2009). Today, it is estimated that over one half of the temperate forest biome has been fragmented or removed by humans, in comparison to nearly one quarter of the tropical forest biome (Wade et al. 2008)
Tropical forests have recently experienced a constant loss of forest area. Achard et al. (2002) estimated a loss of tropical forest of 0.52 % for the period 1990-1997 and Hansen et al. (2008) estimated that 1.39 % of the total tropical forest area were lost between 2000 and 2005. Temperate forests, however, recently experience neither large net gains nor losses in forest area and some areas even show an increase in forest cover (FRA 2010).
For the tropics, six general spatial patterns of the forest/non-forest interface were developed by Husson et al. (1995) which were used for example in Mertens and Lambin (1997) or Geist and Lambin 2001. The six types of patterns are: geometric, corridor, fishbone, diffuse, patchy, and island. Geometric patterns are related to large-scale clearings for modern sector activities, corridor patterns to roadside colonization by spontaneous migrants, fishbone patterns to planned resettlement schemes (yet limited to the Brazilian Amazon), diffuse patterns to smallholder or traditional subsistence agriculture, patchy patterns to high population density areas with residual forest patches, and island patterns to (peripheral) urban areas (Geist and Lambin 2001, p.66). Such spatial patterns are easily detectable once the deforestation process occurs quickly and when the connectedness of the forest area was large hitherto. These characteristics are more likely to be found in the tropical moist broadleaved forest type (especially in South America and Africa (Wade et al. 2003)) and thus the spatial models depicted here are more adequate to be used in the tropical forest biome.
Source: Geist and Lambin (2001), p. 66
For the temperate forest biome (here: Europe) Estreguil and Mouton (2009, p. 6) present four different and typical patterns of forest loss. Drawing on publications by Forman (1995) and Bogaert et al. (2004) they characterize local spatial forest loss by a) attrition (the disappearance of patches), b) shrinkage (decrease of the size of remaining patches), c) perforation (cleared holes within forest patches), and d) fragmentation (braking up of forest areas).
Source: Estreguil and Mouton (2009), p. 7
6 Consequences of deforestation
The consequences of deforestation can cause local scale and far reaching ecological feedback mechanisms such as atmospheric, hydrological and climatic changes (Goldammer 1992) and can furthermore have implications on the socio-economic environment. This, in turn, affects the whole forest ecosystem at large scale and in the long run.
Regarding the current debate on a changing global climate, forests are of major concern since they serve as a great sink for atmospheric carbon. The wooden and photoactive biomass as well as forest soils sequester large amounts of atmospheric carbon. In comparison, forests store and sequester more carbon than any other terrestrial ecosystem (Gibbs et al 2007). A great amount of the total human induced global carbon emissions is argued to be released from forest degradation and deforestation; a great amount in tropical regions since here deforestation rates are currently most striking. Calculations that not even include tropical forest fires estimate the amount of carbon released at 10-25% of the total human induced carbon emissions (Santilli et al. 2005; Houghton 2003). The proportion of carbon released by forests fires and burning of biomass is still difficult to determine but is practically responsible for great amounts of carbon and other harmful substances released into the atmosphere (Goldammer 1992; Houghton 2003). While tropical deforestation processes are estimated to significantly add to global carbon emissions and act as a source, temperate forests of the northern hemisphere are considered a carbon sink (Heath et al. 1993 in Potapov 2009; Goodale et al. 2002 in Houghton 2003).
7 Forest rehabilitation
At any level of degradation, forest conditions can be improved and the process of degradation halted or even reversed. Essential for the rehabilitation of degraded forests are silvicultural or protection measures on degraded forest land or reforestation measures on non-forest land. These rehabilitation measures must be adapted to the specific ecological conditions of each individual area. If successful, those measures might eventually lead to a level of non-degraded forest (FAO 2009). In general, tropical forest rehabilitation is more complicated and requires more efforts than in temperate forests.
From an institutional perspective, the implementation of rehabilitation or conservation measures by corporate enterprises is seldom achieved on a voluntary basis because (tropical) forests are mostly characterized by open access conditions and forest ecosystem services are public goods. Only if secure property rights are allocated, monitored and enforced and incentives for action are being provided are such measures more likely to be realized. Moreover, forest degradation and deforestation can be argued to be negative externalities that are often neglected by forestry or agricultural enterprises or even small-scale users. David Humphreys (2006) puts it as follows: “While corporations are effective in supplying private goods, their efficacy in public good provision is highly questionable. Corporations have one overwhelming responsibility, namely to maximize shareholder value. This is a fiduciary responsibility in private law in most countries […] (and) rationalizes both the internalization of monetary benefits and the systematic externalization of social and environmental costs.” (p. 11). For those ecologically negative externalities to be considered during decision making processes adequate policies and governance structures are required. In our current capitalist system of neoliberal economic policies, an ecologically and socially sustainable economy will be very difficult to achieve, if not impossible.
8 Conclusion
The scientific progress towards an understanding of ecological forest processes and deforestation patterns has recently fueled the debate on the true value of intact forest ecosystems. With the recent tendency of accelerated anthropogenic forest conversion into other land uses, the impacts of considerable small-scale disturbances along with large-scale conversions accumulate to such an extent that they become measurable on a regional and even global level.
Although forest ecosystems are of central importance regarding the economic development especially in humid tropical countries, Hansen et al. (2008) argue that forest governance is still impaired by a lack of timely information on forest cover change. They conclude that a mixed strategy for monitoring should include data at “multiple temporal and spatial resolutions” (p. 9443) providing a feasible and cost-effective methodology to produce “timely, precise, and internally consistent estimates of biome-wide forest clearing” (p. 9443) (Hansen et al. 2008). However, global governance on forest ecosystems is currently not sufficiently developed. A biome-wide assessment of the forest development must therefore be viewed critically. Rather, a decentralized assessment of the causes and processes of deforestation should be aimed at to find appropriate political answers to halt deforestation and promote a socially and environmentally sustainable forest management.
Goldammer (1992) points out that a reliable assessment of tropical forest development requires detailed knowledge of interacting ecological processes, namely the consideration and connection of small-scale impacts with large-scale feedback mechanisms. Thus, not underestimating the social importance forests play, a comprehensive understanding of deforestation processes and patterns requires an interdisciplinary approach from an ecosystem perspective that considers ecological, economic and social sciences.
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