Widespread abandonment of agricultural land has occurred in northeastern North America over the past two centuries. Soil carbon often increases as sites naturally regenerate towards perennial grasslands or forests. Understanding the large-scale controls on the potential and rate of soil carbon sequestration is necessary in order to evaluate the significance of this sink to the global carbon cycle. Furthermore, we need to understand the key roles soil microorganisms play in regulating ecosystem processes through their control over soil carbon and nitrogen dynamics. Such studies are rare at the century long time scale of temperate forest succession. Additionally, research has taken place primarily on productive agricultural soils, while abandonment is more common on marginal agricultural soils. We characterized patterns of total and labile soil carbon and nitrogen and microbial dynamics in mature forest and adjacent agricultural field sites, and in replicated chronosequences of forest successional sites on marginal soils of southeastern Ontario, Canada. Total soil carbon was significantly depleted in the top 10 cm of current agricultural fields as compared to forest sites and increased at a rate of 10 g C m-2 yr-1 across our 100-year chronosequences. There was no difference in carbon loss or accumulation over time in three soil types differing in texture and parent material, suggesting that time since abandonment is more important than soil type in determining carbon accumulation within this climatic region. In contrast, free-light fraction carbon did not increase over time and thus most carbon accumulated in pools with slower turnover times. Soil microbial biomass carbon and nitrogen increased significantly following abandonment and our results strongly suggest that microbial growth during all phases of succession was limited by carbon supply. In contrast, net nitrogen mineralization and nitrification rates during mid-summer did not change consistently over the first 100 years following agricultural abandonment. Therefore, inorganic nitrogen supply rates into the plant available pool were similar across the entire successional sequence. Together, the results of these two studies demonstrate the potential for carbon sequestration in abandoned agricultural soils across this climatic region and highlight the importance of plant-soil interactions for understanding carbon cycling during ecosystem development. / Thesis (Master, Biology) -- Queen's University, 2007-12-14 10:04:57.395

This thesis investigates the impact of rural to urban migration on long-standing commons regimes in the Sierra Norte (northern highlands) of Oaxaca – the most biologically and culturally diverse state in Mexico. Since the second half of the twentieth century, local communities have been engaged with regional, national and international markets for wage labour, with many losing a significant percentage of their resident populations. The study shows how demographic and cultural change is impacting the two social institutions – cargos and tequios – that underpin the highly autonomous form of governance the region is famed for. The loss of able-bodied men and women has meant that these customary systems are struggling to remain operational. In response, a number of far-reaching changes have been introduced, including institutional adaptations and the forging of strong translocal ties that show potential for reducing the vulnerability of affected communities. However, while migration was temporary or circular for much of the 1970s, 1980s and 1990s, thus helping to maintain a balance between subsistence production and market engagement, a form of semi-permanent or permanent migration has come to dominate over the past decade and a half. This critical yet poorly recognised shift in migration dynamics has seen new and increased pressures emerge, and served to reduce the effectiveness of adaptive strategies at the community level. Within this context, the implications for commons theory are discussed, with two alternate frameworks (rational choice vs. moral economy) utilised to explain why institutions may persist, transform or fail in the face of change. In addition, a layer of complexity is added to the body of work examining the consequences of rural depopulation on Mexican forest landscapes and associated biological diversity. The study questions the assumption that rural to urban migration necessarily stimulates ecosystem recovery and enhances biodiversity conservation at a landscape scale. In fact, because of abandonment of a mosaic of use, the net effect may be an overall loss of biodiversity. From a policy perspective, the principal contributions of the study are especially pertinent at a time when funding agencies and government programs show belated interest in the consequences of out-migration for environmental management, resource use and rural livelihoods in tropical country settings.

This thesis investigates the impact of rural to urban migration on long-standing commons regimes in the Sierra Norte (northern highlands) of Oaxaca – the most biologically and culturally diverse state in Mexico. Since the second half of the twentieth century, local communities have been engaged with regional, national and international markets for wage labour, with many losing a significant percentage of their resident populations. The study shows how demographic and cultural change is impacting the two social institutions – cargos and tequios – that underpin the highly autonomous form of governance the region is famed for. The loss of able-bodied men and women has meant that these customary systems are struggling to remain operational. In response, a number of far-reaching changes have been introduced, including institutional adaptations and the forging of strong translocal ties that show potential for reducing the vulnerability of affected communities. However, while migration was temporary or circular for much of the 1970s, 1980s and 1990s, thus helping to maintain a balance between subsistence production and market engagement, a form of semi-permanent or permanent migration has come to dominate over the past decade and a half. This critical yet poorly recognised shift in migration dynamics has seen new and increased pressures emerge, and served to reduce the effectiveness of adaptive strategies at the community level. Within this context, the implications for commons theory are discussed, with two alternate frameworks (rational choice vs. moral economy) utilised to explain why institutions may persist, transform or fail in the face of change. In addition, a layer of complexity is added to the body of work examining the consequences of rural depopulation on Mexican forest landscapes and associated biological diversity. The study questions the assumption that rural to urban migration necessarily stimulates ecosystem recovery and enhances biodiversity conservation at a landscape scale. In fact, because of abandonment of a mosaic of use, the net effect may be an overall loss of biodiversity. From a policy perspective, the principal contributions of the study are especially pertinent at a time when funding agencies and government programs show belated interest in the consequences of out-migration for environmental management, resource use and rural livelihoods in tropical country settings.

Selon des thèses développées au cours des années 1990 et 2000, le développement économique constitue à la fois la source et la solution aux problèmes environnementaux. Au sujet des forêts, les transitions forestières (c’est-à-dire le passage de la déforestation à la reforestation) documentées dans certains pays développés seraient causées par des dynamiques universelles intrinsèques au développement et à la modernisation des sociétés. Nos travaux ont porté sur l’application de cette vision optimiste et controversée à l’évolution des superficies forestières en Thaïlande. S’appuyant sur une recension de la littérature, sur des données secondaires ainsi que nos travaux de terrain dans la région de Phetchabun, la thèse offre les apports suivants. Elle démontre que contrairement à l’idée répandue en Thaïlande, le ralentissement de la déforestation a été suivi par une expansion forestière substantielle entre environ 1995 et 2005. Ce regain forestier est lié à la disparition presque complète de l’expansion agricole, à l’établissement de plantations sylvicoles et, surtout, à l’abandon de terres agricoles. Cet abandon agricole découle d’abord et avant tout de la faible et incertaine rentabilité de l’agriculture dans certaines zones non irriguées. Ce phénomène s’explique, entre autres, par la dégradation des sols et par l’incapacité des agriculteurs à contrer l’impact des transformations économiques internes et externes à la Thaïlande. L’accroissement de la pression de conservation n’a pu contribuer à l’expansion forestière que dans certains contextes (projets de reforestation majeurs appuyés par l’armée, communautés divisées, terres déjà abandonnées). Sans en être une cause directe, l’intensification agricole et la croissance des secteurs non agricoles ont rendu moins pénibles la confiscation et l’abandon des terres et ont permis que de tels phénomènes surviennent sans entraîner d’importants troubles sociaux. Dans un contexte d’accroissement des prix agricoles, notamment celui du caoutchouc naturel, une partie du regain forestier aurait été perdu depuis 2005 en raison d’une ré-expansion des surfaces agricoles. Cela illustre le caractère non permanent de la transition forestière et la faiblesse des mesures de conservation lorsque les perspectives de profit sont grandes. La thèse montre que, pour être robuste, une théorie de la transition forestière doit être contingente et reconnaître que les variables macro-sociales fréquemment invoquées pour expliquer les transitions forestières (ex. : démocratisation, intensification agricole, croissance économique) peuvent aussi leur nuire. Une telle théorie doit également prendre en compte des éléments d’explication non strictement économiques et souvent négligés (menaces à la sécurité nationale, épuisement des terres perçues comme arables et libres, degré d’attachement aux terres et capacité d’adaptation et résilience des systèmes agricoles). Finalement, les écrits sur la transition forestière doivent reconnaître qu’elle a généralement impliqué des impacts sociaux et même environnementaux négatifs. Une lecture de la transition forestière plus nuancée et moins marquée par l’obsession de la seule reforestation est seule garante d’une saine gestion de l’environnement en respect avec les droits humains, la justice sociale et le développement durable. / Recent popular ideas and theories portray economic development as both a cause and a solution to environmental degradation. Concerning forest cover, many authors view forest transitions (the passage from deforestation to reforestation) as resulting from near-universal causal dynamics linked to economic development. The thesis evaluates the validity of these controversial ideas and their relevance to the Thai case. Based on an analysis of secondary literature and official data as well as extensive fieldwork in Phetchabun region, the thesis makes the following points. Contrary to the dominant view, forest cover did expand significantly between ~1995 and 2005. Forest regrowth is linked to the near-interruption of agricultural expansion, the establishment of forest plantations, and, most importantly, agricultural abandonment. The latter derives first and foremost from the declining and currently uncertain profitability of agriculture in non-irrigated zones. These agricultural problems are linked to declining soil fertility and the incapacity of some farmers to counter the impact of rapid economic changes occurring within and outside Thailand. Conservation efforts contributed to forest expansion only in some contexts (ex.: military-backed projects, divided communities, land already abandoned). Agricultural intensification and the growth of non-agricultural sectors made land confiscation and agricultural abandonment less distressing and allowed these land transformations to occur without leading to major social troubles. Since 2005, part of the forest regrowth has been lost to the rubber boom. This illustrates both the potentially non-permanent nature of the forest transition and the limited power of forest conservation in the face of major politico-economic interests. A robust forest transition theory must be contextually-bounded and recognize that forest transitions can be encouraged, blocked or countered by the same frequently invoked macro-social variables: economic growth, agricultural intensification, and democratisation. It must also take into account neglected causal factors, such as geopolitical threats, the resilience of agrarian systems, the perception of land scarcity and the degree of attachment to the land and an agrarian life. Typically, social distress, violence and, in some cases, negative environmental impacts have accompanied forest transitions. Human rights, social justice and sustainable development principles require that a more nuanced view of forest transitions be adopted.

Selon des thèses développées au cours des années 1990 et 2000, le développement économique constitue à la fois la source et la solution aux problèmes environnementaux. Au sujet des forêts, les transitions forestières (c’est-à-dire le passage de la déforestation à la reforestation) documentées dans certains pays développés seraient causées par des dynamiques universelles intrinsèques au développement et à la modernisation des sociétés. Nos travaux ont porté sur l’application de cette vision optimiste et controversée à l’évolution des superficies forestières en Thaïlande. S’appuyant sur une recension de la littérature, sur des données secondaires ainsi que nos travaux de terrain dans la région de Phetchabun, la thèse offre les apports suivants. Elle démontre que contrairement à l’idée répandue en Thaïlande, le ralentissement de la déforestation a été suivi par une expansion forestière substantielle entre environ 1995 et 2005. Ce regain forestier est lié à la disparition presque complète de l’expansion agricole, à l’établissement de plantations sylvicoles et, surtout, à l’abandon de terres agricoles. Cet abandon agricole découle d’abord et avant tout de la faible et incertaine rentabilité de l’agriculture dans certaines zones non irriguées. Ce phénomène s’explique, entre autres, par la dégradation des sols et par l’incapacité des agriculteurs à contrer l’impact des transformations économiques internes et externes à la Thaïlande. L’accroissement de la pression de conservation n’a pu contribuer à l’expansion forestière que dans certains contextes (projets de reforestation majeurs appuyés par l’armée, communautés divisées, terres déjà abandonnées). Sans en être une cause directe, l’intensification agricole et la croissance des secteurs non agricoles ont rendu moins pénibles la confiscation et l’abandon des terres et ont permis que de tels phénomènes surviennent sans entraîner d’importants troubles sociaux. Dans un contexte d’accroissement des prix agricoles, notamment celui du caoutchouc naturel, une partie du regain forestier aurait été perdu depuis 2005 en raison d’une ré-expansion des surfaces agricoles. Cela illustre le caractère non permanent de la transition forestière et la faiblesse des mesures de conservation lorsque les perspectives de profit sont grandes. La thèse montre que, pour être robuste, une théorie de la transition forestière doit être contingente et reconnaître que les variables macro-sociales fréquemment invoquées pour expliquer les transitions forestières (ex. : démocratisation, intensification agricole, croissance économique) peuvent aussi leur nuire. Une telle théorie doit également prendre en compte des éléments d’explication non strictement économiques et souvent négligés (menaces à la sécurité nationale, épuisement des terres perçues comme arables et libres, degré d’attachement aux terres et capacité d’adaptation et résilience des systèmes agricoles). Finalement, les écrits sur la transition forestière doivent reconnaître qu’elle a généralement impliqué des impacts sociaux et même environnementaux négatifs. Une lecture de la transition forestière plus nuancée et moins marquée par l’obsession de la seule reforestation est seule garante d’une saine gestion de l’environnement en respect avec les droits humains, la justice sociale et le développement durable. / Recent popular ideas and theories portray economic development as both a cause and a solution to environmental degradation. Concerning forest cover, many authors view forest transitions (the passage from deforestation to reforestation) as resulting from near-universal causal dynamics linked to economic development. The thesis evaluates the validity of these controversial ideas and their relevance to the Thai case. Based on an analysis of secondary literature and official data as well as extensive fieldwork in Phetchabun region, the thesis makes the following points. Contrary to the dominant view, forest cover did expand significantly between ~1995 and 2005. Forest regrowth is linked to the near-interruption of agricultural expansion, the establishment of forest plantations, and, most importantly, agricultural abandonment. The latter derives first and foremost from the declining and currently uncertain profitability of agriculture in non-irrigated zones. These agricultural problems are linked to declining soil fertility and the incapacity of some farmers to counter the impact of rapid economic changes occurring within and outside Thailand. Conservation efforts contributed to forest expansion only in some contexts (ex.: military-backed projects, divided communities, land already abandoned). Agricultural intensification and the growth of non-agricultural sectors made land confiscation and agricultural abandonment less distressing and allowed these land transformations to occur without leading to major social troubles. Since 2005, part of the forest regrowth has been lost to the rubber boom. This illustrates both the potentially non-permanent nature of the forest transition and the limited power of forest conservation in the face of major politico-economic interests. A robust forest transition theory must be contextually-bounded and recognize that forest transitions can be encouraged, blocked or countered by the same frequently invoked macro-social variables: economic growth, agricultural intensification, and democratisation. It must also take into account neglected causal factors, such as geopolitical threats, the resilience of agrarian systems, the perception of land scarcity and the degree of attachment to the land and an agrarian life. Typically, social distress, violence and, in some cases, negative environmental impacts have accompanied forest transitions. Human rights, social justice and sustainable development principles require that a more nuanced view of forest transitions be adopted.

Development for sustainable poverty alleviation requires engagement with the values and cultural frames that enable or constrain communities to steward ecosystems and maintain their capacity to support human well-being. Rooted in a social-ecological systems (SES) perspective, this thesis explores the concept of sense of place to understand how emotional and cultural connections to place mediate human responses to change and influence interventions for development. Sense of place is both the attachments to place, as well as the descriptive meanings to which one is attached. Paper I presents an approach and agenda for studying sense of place in SES that emphasizes place attachment and meaning underlying stewardship actions and responses to change. This is empirically explored through a case study on the Wild Coast, South Africa - an area with multiple contested meanings. In this former Bantustan (an area set aside for black South Africans), Apartheid created interdependence between small-holder agriculture and labour migration, where rural homesteads relied on remittances from migrant household members. Today, the contribution of agriculture to livelihoods has declined and many households rely on income from social grants. Interacting social and ecological factors in this region have resulted in social-ecological trap conditions and circular migration continues to be the pattern. Community conservation and ecotourism is one strategy for local socio-economic development. Papers II and III explore community tensions around a proposed nature reserve declaration. In Paper II, a focus on the meanings of locally-defined ecotopes (e.g. forest and abandoned fields) illuminates the interpretations of underlying social-ecological processes. Paper III examines the use of place meanings in narratives of change to show tensions in the discourse of win-win conservation. The stalling of this particular intervention indicates the importance of engaging with multiple meanings of place and the cultural importance of nature. Papers IV and V focus on declining agriculture and continued labour migration. From a theoretical model of people’s abilities, desires and opportunities, Paper IV develops a typology of responses that may contribute to maintaining or resolving social-ecological traps. For this case study, the model identifies the mismatch between i) cultural expectations that frame the desire to farm, and ii) the decline in opportunities for off-farm income to support agriculture. Paper V demonstrates that these expectations are expressed in the idea of emakhaya (the rural landscape of home) as well as reinforced through cultural rituals. The paper identifies a place-based social contract between the living and the ancestors that helps to maintain circular migration and agricultural practices. This suggests that sense of place contributes to system inertia but may also offer opportunities for stewardship. Sense of place is socially constructed as well as produced through experience in ecosystems, and thus constitutes an emergent property of SES. The thesis demonstrates the use of participatory methods to produce an inclusive understanding of place and SES dynamics. The application of place meanings through these methods facilitates critical engagement with imposed interventions. Finally, the thesis shows that sense of place and culture are key for understanding inertia in SES and the capacity for transformation towards stewardship. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Manuscript. Paper 3: Manuscript. Paper 5: Manuscript.</p>