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Old Fields
Dynamics and Restoration of Abandoned Farmland
By Viki A. Cramer, Richard J. Hobbs ISLAND PRESS
Copyright © 2007 Island Press
All rights reserved.
ISBN: 978-1-59726-075-6
CHAPTER 1
Why Old Fields? Socioeconomic and Ecological Causes and Consequences of Land Abandonment
RICHARD J. HOBBS AND VIKI A. CRAMER
Land abandonment is a type of land use change that is increasing as human influence on the globe increases and ecological, social, and economic factors conspire to force the cessation of agriculture and other forms of land management. The "old fields" resulting from abandonment display a variety of dynamics and have been the subject of much study and consideration, particularly in ecology where they have played a pivotal role in the development of ideas and concepts of ecological succession (see chapter 2). Surprisingly, however, there have been no previous attempts to synthesize what is known about the dynamics of abandoned farmland in different parts of the world. Does abandonment result in the same set of general dynamics everywhere, regardless of the type of system or its location? Alternatively, are the postabandonment dynamics inherently idiosyncratic and dependent on local context? What ecological theory do we have that can account for the observed dynamics of old fields? And what do old fields have to tell us that is of value to the growing field of restoration ecology? It is the purpose of this book to examine these questions and provide at least some answers.
Past and Current Trends in Land Abandonment
Land use change is a complex phenomenon, and various types of change can be identified, which can have markedly different outcomes, depending on the magnitude and abruptness of the change (Hobbs 2000). Houghton (1991) recognized seven broad types of land use change:
1. Conversion of natural ecosystems for permanent croplands
2. Conversion of natural ecosystems for shifting cultivation
3. Conversion of natural ecosystems to pasture
4. Abandonment of croplands
5. Abandonment of pastures
6. Harvest of timber
7. Establishment of tree plantations
Houghton discussed these in the context of impacts on carbon stocks and hence on atmospheric carbon dioxide, but they also provide a useful set of categories in a broader context. In addition to these categories, we can include urbanization as a factor that is growing in importance and likely to lead to the conversion of both natural and agricultural systems. In addition, restoration should be included as a factor that, although still relatively small scale compared to other types of conversion listed above, is growing in significance (e.g., Hobbs and Harris 2001; Cunningham 2002). In this book we cover primarily the changes encompassed by Houghton's (1991) categories 4 and 5.
Land abandonment has been a feature of humanity's relationship with the world's ecosystems for as long as history has been recorded. We know that past civilizations have developed agricultural systems that were subsequently abandoned for one reason or another (e.g., Lentz 2000; Diamond 2005). The abandonment of agriculture often coincided with the collapse of the civilization, and we are still today piecing together the evidence for the chain of events leading to both. Generally, the ancient civilizations had agricultural systems that were relatively localized and did not cover large areas of land. Here, we concentrate on more recent times, when humans have increasingly come to dominate the planet and its ecosystems (Turner et al. 1991; Vitousek et al. 1997). While the prevailing view of trends in land cover and land use over the last few decades is one of continuing deforestation and transformation of the earth's ecosystems, there is also a growing trend of abandonment of systems that were previously managed intensively.
It has proved very difficult to derive overview statistics on the rates and extent of land abandonment, either in particular parts of the world or globally, since relatively few attempts have been made to quantify these. Figure 1.1 presents data from Ramankutty and Foley (1999), which is the only published material we have found that includes a global analysis of abandonment of croplands. The key message from these data is the dramatic and ongoing increase in the amount of abandoned land worldwide over the twentieth century.
When considered on a regional basis (figure 1.1b), it can be seen that the first region to experience significant abandonment of cropland (in the timeframe over which these data were collected) was eastern North America, with farmland being abandoned from 1870 onward and abandonment continuing at significant rates to the present time. Abandonment started later in all other regions, with the western United States, Canada, the former Soviet Union, and southern Asia showing initial abandonment during the late 1800s and early 1900s. Land abandonment has been a relatively recent feature in regions such as Europe, South America, and China, although rates of abandonment have increased significantly in these areas since the 1960s.
In eastern North America, land abandonment commenced in the 1870s in the northeastern part of the country as a result of improved transportation and the availability of agricultural goods from the more fertile Midwest and Great Plains (figure 1.2; Waisanen and Bliss 2002). The area of agricultural land declined in this area from a peak of 187,900 km2 in 1880 to 48,800 km2 in 1997, with individual states within the region showing dramatic reductions in area of agricultural land (figure 1.2b). The other regions showed smaller declines from peaks in 1940.
Considerable emphasis in the popular press and conservation literature is placed on recent levels of deforestation and conversion of tropical forest ecosystems (e.g., Laurance 1999; Oldfield 1989; Skole and Tucker 1993; Whitmore and Sayer 1992). However, it is also important to recognize that the agricultural system that replaces the natural ecosystem is often fairly short lived and is abandoned after only a few years, in some cases leading to the rapid development of secondary forest (Uhl et al. 1988; Nepstad et al. 1991; Houghton et al. 2000). Data from the Brazilian Amazon also suggest large differences in deforestation rates from year to year, as well as the presence of large areas of abandonment each year (Skole et al. 1994; Alves and Skole 1996). Recent estimates suggest that about 30% of the deforested area in the Amazon is now secondary forest resulting from land abandonment (Houghton et al. 2000). Limited temporal data indicate that the abandonment rate can be as high as 82% of the deforestation rate (1991–92, in Alves and Skole 1996).
It should also be noted that large areas of Southeast Asia have been subject to shifting cultivation over many years. Although not particularly evident in figure 1.1b, this process has contributed to vast areas of grassland across the region. One estimate suggests there are 9.7 million ha of grassland or shrubland in Vietnam alone (Gilmour et al. 2000), while Mittleman (1991) suggests that 100 million ha of forest have been significantly altered or removed (and then abandoned?) in the lower Mekong subregion over the last few decades.
In Europe, land abandonment has undoubtedly been occurring for many centuries, either locally and sporadically or possibly more generally such as in times of the great plague that swept many parts of the continent. In modern times, extensive land abandonment is a relatively recent phenomenon, but there is considerable regional variation similar to that illustrated for eastern North America. For instance, Bunce (1991) indicated that relatively little abandonment occurred in the United Kingdom. On the other hand, recent estimates suggest that 10%–20% of agricultural land in central and eastern European countries is now abandoned (Van Dijk et al. 2005) (table 1.1). Of particular interest in these countries is the abandonment of previously managed seminatural grasslands, with up to 60% of these grasslands now being abandoned in some countries (table 1.1). While statistics specifically relating to land abandonment are not available for Mediterranean countries, figure 1.3 presents data on reforestation, afforestation, and deforestation that show significant amounts of reforestation and afforestation in most countries. Most of this activity is associated with lands previously used for agriculture or grazing and gives an indication of the extent of abandonment in these areas.
There is a problem with interpretation of the different types of data available, and estimates based on indirect measures may or may not reflect a true rate of abandonment. For instance, figures on the cessation of one type of agricultural enterprise may not take into account some of the land being transferred to another type of production rather than simply abandoned. There may also be definitional differences among regions. However, even given these caveats, the overall picture that emerges from both the global data and the regional analyses that are available is one of increasing levels of abandonment in most parts of the world.
Proximate and Ultimate Causes of Land Abandonment
What causes the abandonment of land previously under agricultural management of some kind? Causal factors are likely to vary regionally and are often a complex mix of social, economic, and ecological factors. Indeed, increasing recognition that agricultural systems can be viewed as complex social-ecological systems suggests that simple cause and effect relationships are unlikely to be apparent (Berkes and Folke 1998; Berkes et al. 2003; Allison and Hobbs 2006).
Ecological Factors
Ecological factors leading to the abandonment of land will often include declining soil fertility and productive capacity due to land degradation. Such degradation may result from the previous mismanagement of the land through overgrazing or inappropriate cultivation practices, fertilizer regimes, or fire treatments. It may also result from less proximate modifications resulting, for instance, from regional pollution problems, altered surface or groundwater hydrology regimes, or changing regional climatic conditions. Such factors are particularly important in areas where the agricultural enterprise was marginal in the first place.
Land abandonment may also occur, not because of ecosystem degradation, but rather because of ecosystem change, where changes in the management regime or biophysical settings result, for instance, in the loss of key pasture species or the invasion of aggressive weed species. Such processes are often set in motion by cessation of traditional management practices, such as mowing for hay in European meadows. This, in turn, is often the result of changed socioeconomic settings.
Changing Local and Global Economics
Current trends of globalization of markets and increased production capacity through technological advancements are leading to a loss of relevance and declining economic viability for traditionally produced local agricultural outputs, particularly on marginal agricultural lands. Declining terms of trade are likely to be a major driver of local enterprises going out of business and agriculture becoming locally nonviable. An opposing trend in some areas is one of increased land prices for nonagricultural purposes, such as development, hobby farms, or hunting, leading to small farms going out of production.
Changing Social and Political Settings
Depopulation of rural areas is an ongoing trend worldwide as the world's population becomes increasingly urbanized (United Nations Centre for Human Settlements 1996; McKinney 2002; Miller and Hobbs 2002). This results in the loss of infrastructure (schools, shops, banks, processing facilities, etc.), which in turn further accelerates the loss of people from rural areas. A flow-on effect of rural depopulation is the loss of traditional farming knowledge, making it more difficult for those wishing to return to rural areas, or those wanting to begin a career in farming. Additional underlying causes that can lead to forest loss and subsequent abandonment include rural poverty, a shortage of arable land, lack of land tenure, and limited or inappropriate institutional capacity.
In addition to the socioeconomic issues facing rural populations, national and supranational policies on farming and natural resource management can have large impacts on local and regional landscape management. In heavily regulated situations, such as the European Union, agricultural policies frequently dictate the course of land use change and to some extent determine the rate and extent of land abandonment or change from agriculture to other types of land use. In some cases, policies can lead to perverse incentives that result in poor environmental outcomes, and policy responses to environmental issues are often piecemeal and "Band-Aid" (Allison and Hobbs 2004; Allison and Hobbs 2006). There is increasing recognition of policy failure in dealing with such issues.
On top of the policies directed at agriculture at a national or supranational level, trade policies can have huge impacts on local economies. The current push for free trade and the removal of trade barriers has important implications for agriculture everywhere and will undoubtedly lead to the marginalization of agriculture in certain regions and, hence, increased land abandonment.
What Happens When Land Is Abandoned?
There are two predominant ways of viewing land abandonment. The first views abandonment as an opportunity for the redevelopment of an ecosystem similar to what was there prior to agricultural development, or at least as an opportunity for restoration activity of some description. The second views abandonment as more of a threat, resulting in the loss of specific ecosystem types that depended on ongoing agricultural management. Examples of the former include abandoned pastures in the tropics and old fields in eastern North America, while examples of the latter include hay meadows, semi-natural grasslands, and dehasas in various parts of Europe. Each of these instances is explored in detail in later chapters.
The difference in perspective relates to the history and duration of agriculture in the region and the presence or absence of systems that are dependent on human management for their persistence. Over much of Europe, there are many systems that have developed almost entirely in the presence of human influence, and traditional management of these systems has shaped the European landscape for centuries. Economic, political, and social change is resulting in the intensification of agriculture in some areas and extensification or abandonment in others. The resultant removal of traditional management practices almost inevitably leads to ecosystem change, which in turn potentially leads to the loss of important biological or cultural values (see van Andel and Aronson 2006 for examples). Thus, for instance, ecosystems such as managed grasslands or hay meadows are often very rich in species, but these species depend on continued management to persist. Once management is removed, other species are able to become dominant, and the ecosystem may lose species or be transformed into another ecosystem type, particularly if woody species are able to establish. In this case, therefore, ecosystem development after abandonment is viewed as degradation because the system is developing away from something that is valued and becoming something less valued.
In New World ecosystems, on the other hand, agriculture has not necessarily been such a dominant force on the landscape for such lengthy periods. Abandonment in such situations may result in the rapid return of a native ecosystem, if conditions are suitable. Alternatively, the abandoned land may change more slowly back to some preexisting ecosystem or change toward a completely different system. Depending on the management objective, these alternatives may be appropriate and provide something of greater value than the previous agricultural system. Another possibility is that the abandoned system remains "stuck" in a similar state to when it was abandoned. This may lead to further degradation or may be viewed as an opportunity for restoration, depending on the context.
Both perspectives on land abandonment result from the fact that abandonment invariably leads to change of some description. In some cases the change is welcomed, and in others it is considered a threat. The systems that arise from the abandonment may resemble the systems present prior to agricultural development or they may represent entirely new systems that arise because of changed environmental conditions and the presence of species not previously present in the area. These novel or "emerging" ecosystems are likely to have novel and unpredictable dynamics that may profoundly impact ecosystem structure and function, and the ecosystem services they provide (Milton 2003; Aronson and van Andel 2006; Hobbs et al. 2006).
(Continues...)
Excerpted from Old Fields by Viki A. Cramer, Richard J. Hobbs. Copyright © 2007 Island Press. Excerpted by permission of ISLAND PRESS.
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