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Land change science has emerged as a fundamental component of global environmental change and sustainability research. This interdisciplinary field seeks to understand the dynamics of land cover and land use as a coupled human-environment system to address theory, concepts, models, and applications relevant to environmental and societal problems, including the intersection of the two. The major components and advances in land change are addressed: observation and monitoring; understanding the coupled system-causes, impacts, and consequences; modeling; and synthesis issues. The six articles of the special feature are introduced and situated within these components of study.

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The emergence of land change science for global environmental change and sustainability

The future of tropical forest biodiversity depends more than ever on the effective management of human-modified landscapes, presenting a daunting challenge to conservation practitioners and land use managers. We provide a critical synthesis of the scientific insights that guide our understanding of patterns and processes underpinning forest biodiversity in the human-modified tropics, and present a conceptual framework that integrates a broad range of social and ecological factors that define and contextualize the possible future of tropical forest species. A growing body of research demonstrates that spatial and temporal patterns of biodiversity are the dynamic product of interacting historical and contemporary human and ecological processes. These processes vary radically in their relative importance within and among regions, and have effects that may take years to become fully manifest. Interpreting biodiversity research findings is frequently made difficult by constrained study designs, low congruence in species responses to disturbance, shifting baselines and an over-dependence on comparative inferences from a small number of well studied localities. Spatial and temporal heterogeneity in the potential prospects for biodiversity conservation can be explained by regional differences in biotic vulnerability and anthropogenic legacies, an ever-tighter coupling of human-ecological systems and the influence of global environmental change. These differences provide both challenges and opportunities for biodiversity conservation. Building upon our synthesis we outline a simple adaptive-landscape planning framework that can help guide a new research agenda to enhance biodiversity conservation prospects in the human-modified tropics.

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Prospects for tropical forest biodiversity in a human-modified world.

Ecological systems are vulnerable to irreversible change when key system properties are pushed over thresholds, resulting in the loss of resilience and the precipitation of a regime shift. Perhaps the most important of such properties in human-modified landscapes is the total amount of remnant native vegetation. In a seminal study Andren proposed the existence of a fragmentation threshold in the total amount of remnant vegetation, below which landscape-scale connectivity is eroded and local species richness and abundance become dependent on patch size. Despite the fact that species patch-area effects have been a mainstay of conservation science there has yet to be a robust empirical evaluation of this hypothesis. Here we present and test a new conceptual model describing the mechanisms and consequences of biodiversity change in fragmented landscapes, identifying the fragmentation threshold as a first step in a positive feedback mechanism that has the capacity to impair ecological resilience, and drive a regime shift in biodiversity. The model considers that local extinction risk is defined by patch size, and immigration rates by landscape vegetation cover, and that the recovery from local species losses depends upon the landscape species pool. Using a unique dataset on the distribution of non-volant small mammals across replicate landscapes in the Atlantic forest of Brazil, we found strong evidence for our model predictions - that patch-area effects are evident only at intermediate levels of total forest cover, where landscape diversity is still high and opportunities for enhancing biodiversity through local management are greatest. Furthermore, high levels of forest loss can push native biota through an extinction filter, and result in the abrupt, landscape-wide loss of forest-specialist taxa, ecological resilience and management effectiveness. The proposed model links hitherto distinct theoretical approaches within a single framework, providing a powerful tool for analysing the potential effectiveness of management interventions.

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Beyond the fragmentation threshold hypothesis: regime shifts in biodiversity across fragmented landscapes.

This paper reviews recent achievements in sustainability science and discusses the research core and framework of sustainability science. We analyze and organize papers published in three selected core journals of sustainability science: Sustainability Science, Proceedings of the National Academy of Sciences of the United States of America, and Sustainability: Science, Practice, & Policy. Papers are organized into three categories: sustainability and its definition, domain-oriented research, and a research framework for sustainability science. First, we provide a short history and define the basic characteristics of sustainability; then we review current efforts in the following research domains: climate, biodiversity, agriculture, fishery, forestry, energy and resources, water, economic development, health, and lifestyle. Finally, we propose a research framework for sustainability science that includes the following components: goal setting, indicator setting, indicator measurement, causal chain analysis, forecasting, backcasting, and problem–solution chain analysis. We emphasize the importance of this last component for improving situations and attaining goals.

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Research core and framework of sustainability science

The long-term ecological response to recurrent deforestation associated with shifting cultivation remains poorly investigated, especially in the dry tropics. We present a study of phosphorus (P) dynamics in the southern Yucatan, highlighting the possibility of abrupt shifts in biogeochemical cycling resulting from positive feedbacks between vegetation and its limiting resources. After three cultivation-fallow cycles, available soil P declines by 44%, and one-time P inputs from biomass burning decline by 76% from mature forest levels. Interception of dust-borne P ("canopy trapping") declines with lower plant biomass and leaf area, limiting deposition in secondary forest. Potential leaching losses are greater in secondary than in mature forest, but the difference is very small compared with the difference in P inputs. The decline in new P from atmospheric deposition creates a long-term negative ecosystem balance for phosphorus. The reduction in soil P availability will feed back to further limit biomass recovery and may induce a shift to sparser vegetation. Degradation induced by hydrological and biogeochemical feedbacks on P cycling under shifting cultivation will affect farmers in the near future. Without financial support to encourage the use of fertilizer, farmers could increase the fallow period, clear new land, or abandon agriculture for off-farm employment. Their response will determine the regional balance between forest loss and forest regrowth, as well as the frequency of use and rate of recovery at a local scale, further feeding back on ecological processes at multiple scales.

https://www.pnas.org/content/pnas/104/52/20696.full.pdf

Ecological feedbacks following deforestation create the potential for a catastrophic ecosystem shift in tropical dry forest

As of 2013, 42 million American households were involved in growing their own food either at home or in a community garden plot. The purpose of this pilot study was to document the extent to which gardeners, particularly less affluent ones, increase their vegetable intake when eating from either home or community garden spaces. Eighty-five community gardeners and 50 home gardeners from San Jose, California, completed a survey providing information on demographic background, self-rated health, vegetable intake and the benefits of gardening. The gardeners surveyed were generally low income and came from a variety of ethnic and educational backgrounds. Participants in this study reported doubling their vegetable intake to a level that met the number of daily servings recommended by the U.S. Dietary Guidelines. Growing food in community and home gardens can contribute to food security by helping provide access to fresh vegetables and increasing consumption of vegetables by gardeners and their families.

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Community and home gardens increase vegetable intake and food security of residents in San Jose, California

https://doi.org/10.1016/j.ufug.2022.127483

Gardening can relieve human stress and boost nature connection during the COVID-19 pandemic

The role of secondary vegetation in restoring soil fertility during shifting cultivation in the tropics is well known. Yet the effect of secondary succession on the spatial patterns of soil properties has received little attention. To determine whether changes in the plant community as a result of shifting cultivation affect the scale of spatial dependence for biologically important soil nutrients, we sampled three dry tropical forest stands in Campeche, Mexico. These stands represented a gradient of cultivation history: one mature forest stand, a forest fallow that had undergone one cultivation-fallow cycle, and a forest fallow that had undergone two cultivation-fallow cycles. We used an analysis of semivariance to quantify the scale and magnitude of spatial dependence for organic matter content (OM), phosphorus (P), potassium (K), and aluminum (Al) in each stand. The scale of spatial dependence varied with cultivation history, but the degree of spatial dependence did not differ among stands. In the mature forest P and K were autocorrelated over distances >7.5 m. In the forest fallows 48–88% of the variation in soil P and K was autocorrelated over distances up to 1.1–5.1 m. In contrast, the range of autocorrelation for Al (∼2.5 m) did not differ among stands. We conclude that shifting cultivation changes the range of autocorrelation for biologically important soil nutrients at a scale that may influence plant growth. The finer scaled pattern of soil nutrients in forest fallows is likely to persist with continued shifting cultivation, since fallows are cleared every 3–15 years.

Changes in the spatial variation of soil properties following shifting cultivation in a Mexican tropical dry forest

Participation in home food gardening in the United States has been growing. From 2008 to 2013, the number of home gardens increased by 4 million, and the number of households with annual incomes of less than $35 000 that are food gardening rose by 38%. The purpose of this study was to measure crop output, cost savings, and nutritional value of low-income home gardeners in San Jose, California. This pilot study included administering a background survey to a convenience sample of low-income home gardeners with a subset of gardeners weighing vegetable output of plots during the 2104 spring–summer growing season. Participants included an ethnically diverse group of 50 low-income families who completed the survey and 8 gardeners who weighed vegetable output of their garden. The gardeners produced an average of 1.23 lb vegetables/ft2 and saved an average of $339 by growing their own vegetables. Cost savings were greatest when vertical high-value crops such as tomatoes and cucumbers were grown. All weig...

Lucy O. Diekmann

Papers

Ecological feedbacks following deforestation create the potential for a catastrophic ecosystem shift in tropical dry forest

Community and home gardens increase vegetable intake and food security of residents in San Jose, California

Gardening can relieve human stress and boost nature connection during the COVID-19 pandemic

Changes in the spatial variation of soil properties following shifting cultivation in a Mexican tropical dry forest

Vegetable Output, Cost Savings, and Nutritional Value of Low-Income Families’ Home Gardens in San Jose, CA