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Amid concerns of the looming scarcity of agricultural land and rapidly growing global demand for food and biofuel, cropland abandonment is occurring in many parts of the globe, affecting millions of hectares of cultivated land. Although cropland abandonment trends have been widely reported and studied in European landscapes and other Western countries, this land use change phenomenon is relatively new in developing countries, including Nepal, and knowledge about the drivers and impacts of cropland abandonment is lacking. There is a need for a deeper understanding of why Nepalese farmers are abandoning farming, what are the impacts of cropland abandonment on rural households, and how abandoned croplands can be reutilised for the benefit of the rural community and the environment.

Drawing lessons from global evidence, this PhD work aimed to understand the underlying drivers and implications of agricultural land abandonment, and to explore potential reutilisation pathways to improve the rural economy, food security and sustainable land use in Nepal. To achieve this goal, four research objectives were formulated and investigated using a systematic literature review and quantitative and qualitative data collection from three districts of the hill agroecological region of Nepal, using a mixed methods research approach. Three districts – Kavre, Lamjung and Kaski – were selected considering the diversity of demographic and socioeconomic status of farmers, land use and farming practices, economic opportunities and livelihood systems, and land abandonment trend and prospect for reutilisation. Quantitative data was collected through a household survey and qualitative data were collected through focus group discussions and key informant interviews. In total 374 household surveys, 6 focus group discussions, and 15 key informant interviews were conducted.

The first objective of this study was to conduct a systematic review to understand the drivers and consequences of agricultural land abandonment and pathways for the reutilisation of abandoned agricultural lands reported across the globe (Chapter 2). For the review, 124 relevant articles were retrieved from a systematic search of CAB Abstracts, Scopus and Web of Science, applying exclusion and inclusion criteria in line with standard protocols. The spatial and temporal diversity of the reviewed articles showed that most of the research on the topic of land abandonment is concentrated in European (64 articles) and Asian Countries (44 articles). Although this land use change has received research attention from the early 1990s, about 95% of the articles were published only in the last 15 years. In the case of Asian countries, almost all of the studies took place after 2014.

The review identified seven categories of drivers responsible for cropland abandonment: demographic, household characteristics, farm characteristics, biophysical, economic, regulatory and socio-political. Cropland abandonment had mixed impacts on several abiotic and biotic components of the landscape, with contrasting views about the social and environmental implications. However, negative consequences were most frequently reported compared to positive consequences, particularly in the agricultural landscape, farmland and farm structures, food security, socio-cultural aspects and economic aspects. Positive impacts were observed on carbon sequestration, habitat availability and microbial abundance. Although previous studies often considered land abandonment as a global concern in land use assessment and management, few studies discussed the possible reutilisation pathways of abandoned croplands. Alternative land uses included various farm-forest and afforestation systems, highvalue crop farming and a range of communal land management approaches. Finally, this review chapter provided valuable insights for future research and knowledge about the trade-offs and opportunities associated with land abandonment.

The second objective of the study was to examine the extent, drivers and impacts of cropland abandonment in the hill agroecological region of Nepal (Chapter 3). The study revealed that, depending on the location, between 31% and 48% of croplands were abandoned in the region, with 60% of farming households having abandoned at least one parcel of cropland. Biophysical drivers (distance from homestead to parcel, the slope of the parcel, land fragmentation, land quality and irrigation availability) and socio-demographic drivers (family size, higher education of the household members and out-migration) were commonly responsible for agricultural land abandonment. Negative impacts of land abandonment were reported for rural landscapes, human-made farm structures, socio-economic systems, local food production and food security. In line with global studies, this research suggested that marginal land quality, demographic changes (particularly migration) and rising alternative economic opportunities elsewhere contributed to cropland abandonment.

The third objective of this study was to investigate the dynamics and potential pathways for reutilising abandoned cropland. To address this objective, Chapter 4 examined the potential reutilisation options, farmer preferences, and conditions that create an enabling environment for productive reutilisation of abandoned croplands. Regardless of their abandoned cropland holdings, the majority of the Nepalese hill farmers considered that abandoned croplands should be reutilised. The farmers identified seven options for reutilising abandoned croplands: Cash cropping, Fruit crop farming, Spice and medicinal crop farming, Fodder tree plantation, Cereal cropping, Woodlot plantation and Mixed subsistence farming. Despite the dominance of traditional mixed subsistence farming in the area, the majority of farmers did not consider this system as a viable option for reutilisation. Farmers preferred high value and cash-generating options for reutilisation. This implied that the use of relatively productive croplands for marketoriented farming could help to minimise abandonment and revitalise the Nepalese agricultural sector. The study showed that farmers' preferences and adoption of reutilisation options are influenced by their socio-economic attributes, household needs and availability of resources.

Chapter 4 also showed that the most important conditions that motivate farmers, apart from labour availability, were structural and institutional conditions that require state or commercial intervention to address. However, many aspects of these latter factors are beyond the control of farming households in the region. This highlighted the need for an in-depth understanding of how policies regulate structural, commercial and institutional settings, thereby shaping the reutilisation decisions of farmers at the local level. Chapter 5 addressed this need by analysing the policy constraints for reutilisation of abandoned farmlands and identifying possible policy solutions for the management of abandoned farmlands for productive use.

Chapter 5 found that policy provisions related to land rights, labour, incentives and governance play important roles in shaping decisions on reutilisation of abandoned cropland. Land-related issues rooted in ownership, tenancy rights, access, inheritance law and rising trends of land conversation to non-farm use, have played important roles in shaping the abandonment and reutilisation process. Migration-promoting policies, and agricultural policies that fail to support farming systems innovation or agricultural market development have further limited reutilisation. Similarly, the lack of effective implementation of programs to manage croplands sustainably, weak coordination within and between institutions, and conventional land governance systems are other constraints for reutilisation.

Based on these findings, five potential policy solutions to address these problems have been recommended: (a) provision of land use rights transfer to improve access to land, (b) promoting the consolidation of fragmented land parcels to help ensure economies of scale, (c) improved farm labour management and promotion of farm mechanisation to address labour shortage issues (d) commercially oriented policy priorities to reutilise relatively productive abandoned croplands for high-value, comparative advantage and export potential commodities, and (e) improved administrative and governance capacity of local governments to monitor and manage unauthorised land conversion, fragmentation and abandonment.

From a global policy perspective, abandoned croplands are often viewed as unproductive land, occupying marginal lands. But there is evidence that a significant portion of globally abandoned croplands is still economically viable for recultivation, a view reinforced in this study. Thus, development activities and policies should consider options for reutilising abandoned croplands sustainably to address the growing global socio-economic and environmental challenges associated with land abandonment. Against this backdrop, it is anticipated that the findings of this study will contribute to ongoing national and international discussions about practices, policies and trade-offs of cropland abandonment and its reutilisation pathways.

The challenge of the early 20th century was to remove the forests and woodlands to make room for agriculture; the challenge for the future is understanding the interactions between forests and farming and designing new agricultural landscapes that integrate them for conservation and profit. Agroforestry, a marriage of forest and agricultural science, is a pivotal discipline in the practical implementation of this change. This chapter lays the foundation for appreciating the urgency and nature of this change. We begin with a robust and pragmatic definition of agroforestry. Then follows an explanation of how agroforestry emerged in the efforts to secure sustainable agriculture and forestry in Australia. We mount our argument for agroforestry as a key strategy for on-ground action that integrates many natural resource management issues. Moving from theory to practice, we describe the design and planning processes by which farmers integrate their individual vision and resources with real and meaningful changes on the ground. We then introduce the rest of this book by summarising and linking each of its chapters.

'It's a great time to be involved in the management of agricultural lands and forests in Australia.' If we wrote that sentence 100 years ago, we would have probably substituted the word 'management' with 'opening up' and 'exploitation'. We might have added that this was essential to secure Australia's place as one of the leading economies and nations of the modern world. While the focus of the task is very different, the scale and urgency of the many issues facing land management in Australia today has not diminished. As we continue to develop the economic productivity of our land we are confronted with the question of how to sustain this development. Agriculture and forestry both impact, and are impacted upon by, soil and water resources, native and feral plants and animals, and by atmosphere and climate. The people who manage the land are responsive to community perceptions of appropriate land management, either by legislative coercion or by gradual changes in their own environmental awareness. The agriculture and forestry sectors share much in their response to the future, and for those involved there is a great opportunity to contribute to the development of truly sustainable and economically viable rural landscapes that are uniquely Australian.

Cyanogenic glycosides are anti-nutritional components capable of liberating hydrogen cyanide, a respiratory poison that has been reported to be responsible for the death of livestock that browse some Acacia species containing these compounds. The objective of the study was to improve the nutritive value of the pods of 'Acacia sieberiana' by reducing their contents of cyanogenic glycosides through ensiling, and to examine the influence of various levels of added molasses and urea on the aerobic stability of the silage. In experiment 1, laboratory silages, prepared by mixing ground pods with water in two ratios (60:40 and 40:60 w/w pod material:water), were put into 250 ml polythene bottles, ensiled for 4, 7, 14, 21, 28 or 35 days and analyzed for cyanide. In experiment 2, silages prepared as described above but using only one of the ratios (40:60), and with the addition of molasses (0, 30 or 60 g kg⁻¹) and urea (0, 2.5 or 50 g kg⁻¹) were included in a 3 x 3 factorial design, to study the effects of these additives on the stability of the silage. The period of ensilage was 14 days. In experiment 3, the concentrations of molasses and urea were modified to 0, 45 or 90 g kg⁻¹ and 0, 7.5 or 15 g kg⁻¹, respectively, and the period of ensilage was extended to 45 days. The parent material contained 130.6 mg CN kg⁻¹ DM and ensiling the material for 35 days reduced the concentration to 18.1 mg CN kg⁻¹ DM. Moisture content at ensiling significantly (P < 0.001) affected the concentration of cyanide in the stored silages. Silages opened after 14 days were unstable irrespective of the use of additives. However those with combined urea and molasses exhibited a slow rate of deterioration and low fungal counts. Extending the period of ensiling to 45 days improved the aerobic stability of all the silages. The addition of urea significantly (P < 0.001) increased the pH, crude protein content, gross energy and fermentation acids while molasses treatment increased (P < 0.001) the lactic acid and ash content of the silages. Ensiling ground pods for 45 days was enough to reduce the cyanide content to non-toxic levels and produced a silage which was aerobically stable, while the inclusion of additives further improved the quality of the silages.

There are many reasons for planting trees and managing them for wood and non-wood products. Large-scale commercial forestry enterprises focus on financial returns. Publicly owned companies are bound to inform investors of their strategies and financial positions. However, in agroforestry situations, the financial return may be an important but not a primary driver for a farmer to invest in tree planting or the management of native forests. With the changing expectations of society and the development of non-wood markets, there are new incentives for increasing the area and management of trees on farms. Changing societal expectations and their implications for forestry management involve the need to better understand and manage our natural resources. Despite the willingness of many land managers to adjust their practices to improve natural resource outcomes, there are few markets that allow for the trading of these services, to give a monetary return to the manager. There is, however, a role for planted or existing forests to deliver not only wood products, but also non-wood products such as improved agricultural production from stock shelter and environmental services including improved biodiversity, better water quality and carbon sequestration. There is a relatively clear understanding of the value of wood products via markets but there is still much work to be done in quantifying the full range of benefits, and in some cases the costs, of establishing forestry enterprises on farms and in determining a monetary value which allows economic and financial comparisons with alternative land uses.

The mating system, patterns of pollen mediated gene flow and levels of genetic contamination were investigated in a planted stand of 'Acacia saligna' subsp. 'saligna' via paternity analysis using microsatellite markers. High levels of outcrossing were detected within the stand (tm=0.98), and the average pollen dispersal distance was 37 m with the majority of progeny sired by paternal trees within a 50-m neighbourhood of the maternal tree. Genetic contamination from the natural background population of A. 'saligna' subsp. 'lindleyi' was detected in 14% of the progeny of A. 'saligna' subsp. 'saligna' and varied among maternal trees. Long distance inter-subspecific pollen dispersal was detected for distances of over 1,500 m. The results provide information for use in the breeding and domestication programme aimed at developing A. 'saligna' as an agroforestry crop for the low rainfall areas of southern Australia.

Agroforests are often recommended as alternatives to the shifting-cultivation and continuous-cropping systems that are blamed for much of the land degradation in Southeast Asia (Roshetko et al., 2007; Makundi and Sathaye, 2004). But, landholders may not consider tree-based systems as viable alternatives to crops because of high establishment costs, delayed revenues and lack of secure property rights. Recognizing the environmental and social services provided by trees, such as mitigating climate change by sequestering carbon, may assist in overcoming these obstacles.

Subspecific taxa of species complexes can display cryptic morphological variation, and individuals and populations can often be difficult to identify with certainty. However, accurate population identification is required for comprehensive conservation and breeding strategies and for studies of invasiveness and gene flow. Using five informative microsatellite markers and a Bayesian statistical approach, we developed an efficient polymerase chain reaction-based diagnostic tool for the rapid identification of individuals and populations of the 'Acacia saligna' species complex of Western Australia. We genotyped 189 individuals from 14 reference populations previously characterised based on morphology and used these data to investigate population structure in the species complex. High total genetic diversity (Ht=0.729) and high population differentiation (θ=0.355) indicated strong intra-specific structuring. With the provision of prior population information, the reference data set was optimally resolved into four clusters, each corresponding to one of the four main proposed subspecies, with very high membership values (Q>97%). The reference data set was then used to assign individuals and test populations to one of the four subspecies. Assignment was unequivocal for all test individuals from two populations of subsp. 'lindleyi' and for all but one individual of subsp. 'stolonifera'. Individuals from populations of subsp. 'saligna' and subsp. 'pruinescens' showed a degree of genetic affinity for the two subspecies in their assignments, although the majority of individuals were correctly assigned to subspecies. The diagnostic tool will assist in characterising populations of 'A. saligna', especially naturalised and invasive populations of unknown origin.