Temperate Agroforestry Systems

By Andrew M Gordon, Naresh V. Thevathasan, Shibu Jose and 9 more

Agroforestry is a land use system that allows for the concurrent production of trees and agricultural crops and/or animals from the same piece of land. It has a rich history of development and has been practised in some parts of the world for more than 6,000 years. In 1997, CABI published the seminal book on this subject, Temperate Agroforestry Systems, which was a break from the norm as almost all agroforestry texts up to that date were only relevant to tropical areas. The book explored the development of temperate agroforestry and agroforestry systems, concentrating on those areas within temperate zones where the greatest advances, adoptions and modifications had taken place up to that time: North and South America, China, Australia, New Zealand and Europe.

This second fully-updated and expanded edition includes additional chapters on India and Chile and, as a result of ongoing advances in the field, separate chapters on the US, Canada, the UK and continental Europe. Today's challenges of climate change, population growth and food security, in concert with the ongoing global requirement for the energy and water needed for a resilient agricultural paradigm, can be met through the wide-scale adoption of agroforestry practices, in both tropical regions and temperate zones. The 2nd edition ofTemperate Agroforestry Systems brings together many examples of temperate agroforestry and will make valuable reading for all those working in this area as researchers, practitioners and policy makers. The book is also of importance to students and teachers of agriculture, ecology, environmental studies and forestry in temperate regions.

• Language: English
• Publisher: CAB International
• Release date: Mar 7, 2018
• ISBN: 9781786393883

Book preview

Preface to the Second Edition

The first edition of Temperate Agroforestry Systems was published in 1997, the same year that the Kyoto Protocol was adopted in Kyoto, Japan. At that time, there were very few books that dealt with agroforestry practices and systems in temperate regions, and of those, most were very local and regional in nature (e.g. Reid, R. and Wilson, G. (1985) Agroforestry in Australia and New Zealand, Goddard and Dobson, Victoria, Australia, 255pp.); much of the attention and focus of those researching and practising agroforestry was in tropical and subtropical areas. The book had a unique focus in that, in addition to describing regional agroforestry systems utilized in their respective countries, chapter authors were asked to explore current and historical avenues of research that had brought about, or were interfacing with, current agroforestry systems. The emphasis was on a systems-level approach as compared to one that might be more commodity-driven.

In the original book, a brief overview of temperate agroforestry systems was followed by individual chapters on North America, New Zealand, Australia, China, Europe and Argentina. A synthesis chapter provided concluding remarks. Enough copies were purchased over almost two decades that the publisher deemed the book successful, leading to a call for a second edition. Our goal in pursuing this second edition was twofold: (1) to update existing chapters with the tremendous advances in temperate agroforestry knowledge that have come to light in the last 20 years, and (2) if possible, to add new global regional examples of temperate agroforestry. For both, we feel that we have been successful.

Following on the heels of the original Rio Summit, held in Brazil in 1992, and the 1997 Kyoto Protocol, which became operational in 2005, world leaders embraced (albeit, in very differing forms) the principles behind mechanisms to combat climate change and its physically and socially destabilizing components. The Copenhagen Accord (2009) and the most recently signed global agreement – the Paris Agreement of 2016 – are necessary steps that will hopefully unite the world in defeating climate change over the next century. Agroforestry, in all of its formats, is an important tool that can be utilized by government agencies and NGOs to combat climate change, alleviate poverty and improve regional environmental conditions. Agroforestry is no longer a poorly understood buzzword, but rather a key pillar to important programmes of many global agencies including the CGIAR and the FAO. In this second edition, the reader will find numerous references to carbon sequestration and the ability of temperate agroforestry systems to mitigate climate change explored around the world.

Several changes have been made to the second edition. North America has been split into separate American (US) and Canadian chapters as the discipline has advanced greatly in both countries in the time that has passed since the publication of the first edition. Similarly, the UK has been separated from Europe, and both are now presented as separate chapters. Chapters on New Zealand, Australia, China and Argentina have been retained as almost entirely new chapters and additional chapters have been added for temperate India and Chile, bringing the total number of regional temperate agroforestry endeavours to ten. We hope the reader can appreciate the tremendous strides that have occurred in research and development activities in temperate agroforestry around the world in the last 25 years – more importantly, we hope that they will see and embrace the important role that agroforestry systems in temperate regions can play with respect to mitigating the ecological footprint of modern farming systems.

Andrew M. Gordon

University of Guelph

Guelph, Ontario, Canada

Steven M. Newman

Biodiversity International Ltd

Faversham, Kent, United Kingdom

Brent R.W. Coleman

University of Guelph

Guelph, Ontario, Canada

April 2017

1 Temperate Agroforestry: An Overview

¹

A.M. G

ORDON,

²* S.M. N

EWMAN

,³ B.R.W. C

OLEMAN

²

AND

N.V. T

HEVATHASAN

²

²School of Environmental Sciences, University of Guelph, Canada; ³Biodiversity International Ltd, Faversham, Kent, UK

*Corresponding author: [e-mail]

¹ Peter A. Williams, Williams and Associates, Rockwood, Ontario Canada N0B 2K0 was an author on this chapter in the 1st Edition of this book. His contributions to this ensuing chapter are acknowledged.

Introduction

Agroforestry is an approach to land use that incorporates trees into farming systems and allows for the production of trees and crops and/or livestock from the same piece of land; it has a rich history of development and has been practised in some parts of the world for more than 6000 years. Many traditional farming systems around the world have evolved to include components of agroforestry, yet ironically the farmers that utilize these practices often never refer to them as agroforestry. A classic example can be found in the production of maple syrup from sugar maple (Acer saccharum) trees in small hardwood woodlots maintained within the farming landscape of southern Ontario, Quebec and the northeastern United States. This would certainly be considered an agroforestry activity but would rarely be referred to as such by practitioners, who are, in this case, ‘maple syrup’ farmers!

Indeed, the defining of agroforestry has been problematic down through the years, largely as a result of the broad global geographic range of regions within which agroforestry can be practised. As an example, the ‘original’ definition of agroforestry from the World Agroforestry Centre (WAC) in Nairobi, Kenya, is:

a collective name for land use systems and technologies where woody perennials (trees, shrubs, palms, bamboos, etc.) are deliberately used on the same land management unit as agricultural crops and/or animals, either in some form of spatial arrangement or temporal sequence. In agroforestry systems, there are both ecological and economic interactions between the different components.

Remove the words ‘palms’ and ‘bamboos’ (throwbacks to the tropical systems that the WAC deals with) and a definition of agroforestry in temperate regions begins to emerge. As our tropical colleagues did in the 1950s and 1960s, those of us in temperate regions who investigated, designed, developed and implemented agroforestry systems in the temperate zone in the 1980s and 1990s, also struggled to define agroforestry and the reader is referred to an excellent treatise on this subject by Gold and Garrett (2009). These authors additionally indicated that agroforestry in the temperate regions of the United States and Canada is defined as:

Intensive land-use management that optimizes the benefits (physical, biological, economic, social) from biophysical interactions created when trees and/or shrubs are deliberately combined with crops and/or livestock.

This is also the definition embraced by the Association for Temperate Agroforestry, based at the University of Missouri, Columbia, Missouri. At the University of Guelph, in southern Ontario, Canada, the definition of agroforestry took about a decade to emerge and went through many iterations as researchers and practitioners worked with different farming systems containing trees:

Agroforestry is a planned and systematic integration of trees (either spatially or temporally) into farming systems in order to derive multiple benefits that include: environmental, ecological, economic and social benefits from a unit land area in a sustainable fashion. These benefits are derived as a result of a series of biophysical interactions that occur at the tree-crop (or tree-animal) interface.

Condense it all down, and we might conclude that the aforementioned definition cited by Gold and Garrett (2009) might reasonably define agroforestry activities in the global temperate zone. However, over the years we have been impressed with the farming community’s ability to cut to the chase on many agroforestry-related matters, no matter how ecologically or economically complex the agroforestry activity might be. And so today we are happy to embrace shorter and perhaps more relevant definitions of temperate agroforestry: ‘the incorporation of trees into farming systems’ or even better, ‘farming with trees’ as indicated in Fig. 1.1.

Fig. 1.1. Farming ‘with’ trees in the temperate zone. One may farm ‘with’ trees where the crop of interest is either the tree itself, or something that the tree produces like a syrup, nut or pharmaceutical (Fig. 1.1A shows Scots pine (Pinus sylvestris) Christmas trees, southern Ontario, Canada). One may also farm ‘with’ trees, where trees are part of the farm landscape, as in a windbreak, or where products are derived from a farm woodlot (Fig. 1.1B shows a southern Ontario farm landscape).

Historical Perspective

In the two decades that have passed since the publication of the first edition of Temperate Agroforestry Systems, monumental strides have been made with respect to the development, implementation and understanding of temperate agroforestry systems, from both a biophysical (ecological) and socioeconomic standpoint. In 1997, however, the world was a simpler place and the role that agroforestry could play in the development of sustainable farming systems – from both a temperate and tropical perspective – was decidedly different than the role that it can play today. Today, agroforestry is synonymous with proposed solutions to climate change at large scales and for the maintenance of soil health at much smaller scales. It is often acknowledged as a system-level science that can embrace the conservation of genetic diversity in trees, the enhanced value of multiple-product value chains and the provision of a large number of ecologically valuable and economically important environmental goods and services (Nair and Garritty, 2012; Buttoud, 2013; Centre for International Forestry Research, 2015).

The agroforestry concept was developed in tropical regions, within the context of developing nations, where initially land shortages, brought about by the rapid population growth of indigenous peoples, demanded that efficient production systems be developed for both food and wood resources. As agroforestry systems were developed and refined, it also became obvious that the discipline had an important role to play in the maintenance of sustainability through its inherent resource, land and soil conservation properties. Indeed, in the tropics, because of the importance of organic matter in the maintenance of soil productivity (e.g. Ohu et al., 1994), research efforts continue to compare agroforestry systems with traditional cropping technologies in an attempt to understand their ameliorative properties, system by system. Like Grewal et al. (1994), many researchers have concluded that agroforestry systems are ‘more conservation effective than traditional crops on eroded marginal soil’ and hence are ‘suggested for inclusion in the basket of conservation technologies’.

Historically, early agroforestry textbooks explored these concepts, but usually from a tropical or developing countries perspective (e.g. Huxley, 1983; Gholz, 1987; Steppler and Nair, 1987; Young, 1989; MacDicken and Vergara, 1990; Kidd and Pimentel, 1992), although occasionally, a discipline-related (e.g. Prinsley, 1990) or regional approach has been taken (e.g. Reid and Wilson, 1985; Rocheleau et al., 1988).

During the formative years of the discipline, many agroforestry researchers, perhaps in an attempt to justify new-found non-traditional research interests, tended to belittle traditional agricultural practices as environmental failures, advocating that many problems (including those economic in nature) associated with these types of systems could be solved by the broad-scale adoption of agroforestry. However, some remarkable failures in agroforestry (Young and others, personal communication) have reinforced what many in the field have advocated for some time: an understanding of the biological, physical and chemical interactions present in operable agroforestry systems, to the level that has been achieved in other food-production systems (e.g. Stelly, 1983; Vandermeer, 1989) is required before the refined application of agroforestry to problem situations can occur with impunity. This understanding is well advanced for tropical systems (e.g. Tian, 1992; Ong and Huxley, 1996), and now references exist that clearly define the ecological basis of agroforestry in many temperate systems (see specific chapters in Batish et al., 2008; Jose and Gordon, 2008).

Since the publication of the first edition of this book in 1997, three World Agroforestry Congresses have taken place. The first was held in Orlando, Florida, USA in 2004, the second was held in Nairobi, Kenya in 2009, and the third was held in Delhi, India in 2014. At all of these events, specific temperate agroforestry systems were showcased. In association with the first Congress, Nair et al. (2004) initiated the Advances in Agroforestry series, which now comprises 11 published volumes between 2004 and 2016, many of which reference the successful implementation of temperate agroforestry systems (e.g. Thevathasan and Gordon, 2004). Region by region, country by country, temperate agroforestry is becoming organized, developed, refined and adopted. Many regional societies exist, many of which run their own temperate agroforestry conference series (e.g. the Association for Temperate Agroforestry (AFTA), which operates in North America, and the European Agroforestry Federation (EURAF) which operates in Europe). In the case of AFTA, the conference series on North American Agroforestry was initiated in Guelph, Canada, in 1989 (Williams, 1991), and since then, 15 well attended biannual conferences specific to temperate agroforestry have been successfully held. Links to the proceedings of these conferences can be found on the AFTA website.

Many temperate agroforestry systems are common-sense adaptations of historical knowledge that exists on the benefits of incorporating trees into farming systems (see Smith, 1929), but many are new applications of systems that have been successful in other situations (e.g. Gold and Hanover, 1987; Bandolin and Fisher, 1991). Up until 1997 most textbooks on agroforestry confined discussion of temperate systems to individual chapters (e.g. Byington, 1990), although both research and descriptive information on temperate agroforestry was available for localized regions such as New Zealand and Australia (Reid and Wilson, 1985) and China (Zhu et al., 1991). Nowadays, there is an increasing prevalence of reference to temperate agroforestry systems in both collected volumes (e.g. Nair et al., 2004) and in stand-alone texts. For example, two editions of a book describing temperate agroforestry in North America have been published since the first edition of Temperate Agroforestry Systems appeared (Garrett et al., 2000; Garrett, 2009).

There is also an increasing appreciation for the fact that the application of agroforestry technologies to temperate agricultural systems will help, when used appropriately, to sustain existing food production systems (cf. the historical work of Carruthers, 1990; Rietvelt, 1995). In addition, temperate agroforestry favours an integrated approach that can enhance many of the biophysical cornerstones of ecologically sound agricultural production (enhanced water quality, soil and crop productivity, reduced chemical inputs, enhanced biodiversity, lowered soil erosion, etc.) as well as embracing people and their social and economic fabric, production inefficiencies and surpluses, the uncertainty of future wood supply and demand and recreational opportunities. The key, of course, is to use agroforestry systems appropriately in order that not only its usefulness as a land-use system is realized, but that its potential to assess the value and benefits of farming in a particular manner is brought to bear upon the landscape.

The multidisciplinary nature of agroforestry accentuates the difficulty of incorporating its principles into commodity-based or reductionist approaches to agriculture, forestry or other types of land use. While agroforestry systems and practices are integrated approaches to production, there is a tremendous grey area that emerges when trying to distinguish between agricultural, agroforestry, forest and environmental practices. This fosters confusion and at times arguments about what agroforestry is and what it is not. Technically, an agroforestry system incorporates woody perennials and crops or livestock. However, woodlot management, biomass plantations, forest gathering, farmstead shelterbelts and forest range management are all practices that are considered the sole domain of either forestry or agriculture. For example, when medicinal plants or mushrooms are collected from a forest, we tend not to refer to this operation as agroforestry, but on the other hand, if the woodlot is managed to encourage the production of mushrooms or plants of this type, then it is referred to as an agroforestry practice. Similarly, poplar (Populus spp.) grown on short rotations for pulp and paper is not agroforestry, but if the trees are grown on a farm and grazed or fertilized with livestock manure, then it is.

The semantic discussion about what is and what is not (temperate) agroforestry is unproductive and unnecessary, and not really the issue. First, agroforestry is multidisciplinary and multi-objective in nature. That does not mean that the science of forest range management should be philosophically ‘disengaged’ from other aspects of range management, to be conducted by agroforesters, but that forest range management could benefit from an agroforestry perspective that incorporates the experiences of forestry crop science and ecology. The second reason can be found within disciplines such as farming systems and ecology that advocate a systems approach to understanding and garnering knowledge: for example, a vision of the whole farm as a system, that is greater than the sum of its fields, animals and barns.

Woodlots are essential components or farms and farming communities, providing many types of revenue and products that help make farmers, farms and rural communities viable. But when is woodlot management agroforestry and when is it forestry? There is no difference in strategy, practice or effect, and the implementation has little to do with an ‘agroforestry system’. From a research and development point of view, it may be possible to separate agroforestry systems and practices from farm forestry, but it is not possible or even advisable to make the distinction from an extension or policy perspective. When a farmer is seeking advice, the agroforestry extension agent must be able to provide advice on a wide range of tree and farm issues that farmers deal with on a daily basis. That is why the broader, operational definition of ‘agroforestry’ employed by some extensionists (‘any way that trees are used on farms’) includes some things that do not fit the definition of an agroforestry system or practice.

Key Systems and Species

The key systems utilized in temperate agroforestry follow a similar classification to those used in tropical agroforestry. Silvoarable systems consist primarily of timber trees intercropped with arable crops, silvopastoral systems involve the use of timber or fodder trees with pasture and/or range, and environmental systems consist of strips or belts of trees at stream or field edges for microclimate modification and/or soil protection or improvement. Orchard intercropping is a form of alley-cropping involving a horticultural component in either the understorey or overstorey, and forest grazing describes grazing in a forest or a plantation. Home gardens, a tropical agroforestry type used to describe the diverse array of plants and trees found adjacent to dwellings, is generally not considered an important form of temperate agroforestry, although small-scale forest farming is considered a system unto itself in some regions (e.g. North America). New to this edition is additional reference to bioenergy systems where fast-growing species like poplar and willow (Salix) are grown on short three-year rotations and the biomass utilized (sometimes as pellets) for heat and/or electrical generation. (See https://www.youtube.com/watch?v=k5oxiSTcycE for a short video on bioenergy systems in Canada.)

Given the breadth of the geographical, biophysical, socioeconomic and political environments throughout the temperate zone (see ‘Book Structure’ below), it would be impossible to provide a common categorical framework for all temperate agroforestry systems, and indeed this is not necessary. There are unique agroforestry systems to be found in every region and we have attempted to summarize these in the synthesis tables found in Chapter 12.

In some literature, the term ‘agroforestry species’ is often encountered. In our view this is a misconception in that many, if not all, species have an important and potential role to play in agroforestry. What is more relevant are ‘key agroforestry ideotype combinations’ where functional attributes of the components are described in detail (i.e. mixtures of deep- and shallow-rooted tree species, legumes and non-legumes, etc.).

Book Structure

Officially, the global North and South temperate zones extend from the Tropics of Cancer and Capricorn (23.5o N and S latitude respectively) to the Arctic and Antarctic circles (66.5o N and S latitude respectively). However, the true temperate zones in which temperate agroforestry can be realistically practised would lie between approximately 37o N and S latitude and the respective polar circles. This global band encompasses large swathes of almost all of the countries and regions addressed in this book. The exception of course is India: temperate agroforestry is practised in the Indian Himalayan Region in the north of the country, where elevations between 1000 and 4500 m foster temperate-like conditions, despite the more tropical latitude.

One can imagine the great variation that must exist in regional climates and local microclimates, photoperiods, soils and site conditions in the many varied regions found in the temperate zone, the combination of which fosters unique and varied agroforestry opportunities and pitfalls. Given this, and as we found in the First Edition, it did not seem to make much sense to force chapter authors to adhere to a strict protocol for reporting agroforestry activities. We instead asked authors to report on historical, common and emerging agroforestry practices that had some following in their respective regions, and to enhance this, where applicable, with interesting ongoing or historical research on these systems. The reader will therefore find different stories and approaches in each chapter – some will be commodity-based while others will be described from a systems perspective. The latter is certainly a useful framework to describe many agroforestry systems, given the interdisciplinary nature of agroforestry, but not necessarily appropriate all of the time. In many instances, for example, implementation of large-scale agroforestry endeavours – at least from a policy perspective – may initially require a commodity-based approach.

We believe that the reader will find this approach useful, as we explore, in order, agroforestry systems and potentials in Canada, the USA, the United Kingdom, Europe, India, China, Australia, New Zealand, Chile and Argentina. Some chapters explore the technical details of particular systems, while others take a more holistic perspective. We think that this has helped avoid redundancy and makes each chapter distinct and unique.

Many studies of agroforestry have been of a descriptive or agro-ecological nature, with an emphasis on tree–crop interactions. Little attention has been paid to developing or applying quantitative measures of effectiveness, which means that system optimization is impossible. Authors were encouraged to discuss this along with potential limitations to the adoption of agroforestry practices and systems, and the reader will find reference to these throughout the text. Some general synthesizing comments on measures of effectiveness and limits to adoption are found in Chapter 12.

Finally, this book describes some practices and applications that technically may not be a part of an ‘agroforestry system’, or even a system unto itself, but that are definitely agroforestry-related. They serve to show what agroforestry using a systems approach can offer to agriculture and the rest of society.

References

Bandolin, T.H. and Fisher, R.F. (1991) Agroforestry systems in North America. Agroforestry Systems 16, 95–118.

Batish, D.R., Kohli, R.K., Jose, S. and Singh, H.P. (eds) (2008) Ecological Basis of Agro-Forestry. CRC Press, Baton Rouge, Louisiana.

Buttoud, G. (2013) Advancing Agroforestry on the Policy Agenda - A Guide for Decision-Makers. Agroforestry Working Paper No. 1. Food and Agriculture Organization of the United Nations, Rome.

Byington, E.K. (1990) Agroforestry in the temperate zone. In: MacDicken, K.G. and Vergara, N.T. (eds) Agroforestry Classification and Management. John Wiley, New York.

Carruthers, P. (1990) The prospects for agroforestry: an EC perspective. Outlook on Agriculture 19, 147–153.

Center for International Forestry Research (2015) CGIAR (Consultative Group for International Agricultural Research) Research Program on Forests, Trees and Agroforestry: Livelihoods, Landscapes and Governance. Center for International Forestry Research, Bogor, Indonesia.

Garrett, H.E. (ed.) (2009) North American Agroforestry: An Integrated Science and Practice. American Society of Agronomy, Madison, Wisconsin.

Garrett, H.E., Rietveld, W.J. and Fisher, R.F. (eds) (2000) North American Agroforestry: An Integrated Science and Practice. American Society of Agronomy, Madison, Wisconsin.

Gholz, H.L. (ed.) (1987) Agroforestry: Realities, Possibilities and Potentials. Martinus Nijhoff, Dordrecht, Netherlands.

Gold, M.A. and Garrett, H.E. (2009) Agroforestry nomenclature, concepts and practices. In: Garrett, H.E. (ed.) North American Agroforestry: An Integrated Science and Practice. American Society of Agronomy, Madison, Wisconsin, pp. 45–55.

Gold, M.A. and Hanover, J. (1987) Agroforestry for the temperate zone. Agroforestry Systems 5, 109–121.

Grewal, S.S., Jtineja, M.L., Singh, K. and Singh, S. (1994) A comparison of two agroforestry systems for soil, water and nutrient conservation on degraded land. Soil Technology 7, 145–153.

Huxley, P.A. (ed.) (1983) Plant Research and Agroforestry. International Council for Research in Agroforestry, Nairobi.

Jose, S. and Gordon, A.M. (eds) (2008) Toward Agroforestry Design: An Ecological Approach. (Advances in Agroforestry. Vol. 4). Springer Science and Business Media, New York.

Kidd, C.V. and Pimentel, D. (eds) (1992) Integrated Resource Management Agroforestry for Development. Academic Press, San Diego, California.

MacDicken, K.G. and Vergara, N.T. (eds) (1990) Agroforestry Classification and Management. John Wiley, New York.

Nair, P.K. and Garritty, D. (eds) (2012) Agroforestry – The Future of Global Land Use. (Advances in Agroforestry. Vol. 9). Springer Science and Business Media, New York.

Nair, P.K.R., Rao, M.R. and Buck, L.E. (eds) (2004) New Vistas in Agroforestry – A Compendium for the 1st World Congress of Agroforestry , June, 2004. (Advances in Agroforestry Vol. 1). Kluwer Academic, Dordrecht, Netherlands.

Ohu, J.O., Ekwue, E.I. and Folorunso, O.A. (1994) The effect of addition of organic matter on the compaction of a vertisol from northern Nigeria. Soil Technology 7, 155–162.

Ong, C.K. and Huxley, P. (eds) (1996) Tree–Crop Interactions: A Physiological Approach. CAB International, Wallingford, UK and the International Centre for Research in Agroforestry, Nairobi.

Prinsley, R.T. (1990) Agroforestry for Sustainable Production: Economic Implications. Commonwealth Science Council, London.

Reid, R. and Wilson, G. (1985) Agroforestry in Australia and New Zealand – The Growing of Productive Trees on Farms. Capitol Press, Victoria, Australia.

Rietveld, B. (1995) Agroforestry in the United States. Agroforestry Notes, USDA Rocky Mountain Forest and Range Experiment Station, Fort Collins, Colorado.

Rocheleau, D., Weber, F. and Field-Juma, A. (1988) Agroforestry in Dryland Africa. International Council for Research in Agroforestry, Nairobi.

Smith, J.R. (1929) Tree Crops - A Permanent Agriculture. Island Press, Washington, DC.

Stelly, M. (1983) Multiple Cropping. American Society of Agronomy, Madison, Wisconsin.

Steppler, H.A. and Nair, P.K.R. (eds) (1987) Agroforestry: A Decade of Development. International Centre for Research in Agroforestry, Nairobi.

Thevathasan, N.V. and Gordon, A.M. (2004) Ecology of tree intercropping systems in the North temperate region: experiences from southern Ontario, Canada. Agroforestry Systems 61, 257–268.

Tian, G. (1992) Biological effects of plant residues with contrasting chemical compositions on plant and soil under humid tropical conditions. PhD thesis, Wageningen Agricultural University, Wageningen, Netherlands.

Vandermeer, J. (1989) The Ecology of Intercropping. Cambridge University Press, Cambridge, UK.

Williams, P.A. (ed.) (1991) Agroforestry in North America. Proceedings of the First Conference on Agroforestry in North America, University of Guelph, Guelph, Ontario, Canada.

Young, A. (1989) Agroforestry for Soil Conservation. CAB International, Wallingford, UK.

Zhu, Z., Mantang, C., Shiji, W. and Youxu, J. (1991) Agroforestry Systems in China. Chinese Academy of Forestry, Beijing and International Development Research Centre, Ottawa.

2 Agroforestry in Canada and its Role in Farming Systems¹

N.V. T

HEVATHASAN

,

²

* B. C

OLEMAN

,² L. Z

ABEK

,³ T. W

ARD

⁴

AND

A.M. G

ORDON

²

²School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada; ³Ministry of Agriculture, Kamloops, British Columbia, Canada; ⁴Agriculture and Agri-Food Canada, Indian Head, Saskatchewan, Canada

* Corresponding author: [e-mail]

¹Peter A. Williams, Williams and Associates, Rockwood, Ontario Canada N0B 2K0 was an author on this chapter in the 1st Edition of this book. His contributions to this ensuing chapter are acknowledged.

Introduction

History and background

With an area of more than nine million square kilometres, Canada stretches west to east from the Pacific to the Atlantic Ocean, and is bordered to the south by the USA and north by the Arctic Ocean. Although substantial agricultural production and tree growth occur in all regions south of Canada’s northern territories, a large proportion of Canada’s southern land area is home to temperate climates and fertile soils, which contributes to significantly higher rates of plant productivity. Following European settlement in the late 1700s, large tracts of native forest were removed to make way for intensive agricultural production, which continues to dominate a large portion of southern Canada to this day.

Prior to European settlement, First Nations communities across Canada employed a diverse assortment of agroforestry systems, integrating trees and food crops into a multitude of production systems as described by Williams et al. (1997). Swidden systems (rotational or slash and burn) were common, and fire was used extensively to increase wildlife foraging through enhancing edible vegetation, encourage berry-producing shrubs and medicinal plants and to clear underbrush to make it easier to hunt, travel and defend against enemies (Anderson, 1993; Boettler-Bye, personal communication, 1995). In the south-west, areas were burned to improve hunting, facilitate harvesting and produce needed woody materials (e.g. willow (Salix spp.) shoots of varying dimensions for different products). Burning was conducted in either the spring and/or fall or on varying yearly schedules of 5, 10 or 20 years. First Nations communities did not have livestock until European settlement, but they were known to herd elk (Cerrus canadensis) or caribou (Rangifer tarandus) (Child and Pearson, 1995). Although First Nations peoples would not have practised silvopasture in the strict sense of the word, they did utilize many of the same practices associated with silvopastoral systems including the aforementioned forage production and woody vegetation control.

First Nations peoples were applied ecologists who, in addition to being skilled in the use of fire, selected and planted seeds for annual and perennial crops including tree crops, and commonly transplanted trees and shrubs. In many areas, First Nations communities relied heavily on crops from trees for much of their sustenance, including the sugar from various maples (Acer spp.) and fruits from chestnuts (Castanea spp.), oaks (Quercus spp.), and pines (Pinus spp.) (Wolf, 1945; Farris, 1982; Bainbridge, 1986a, b; Bainbridge et al., 1990). Lands considered wild by European settlers and their descendants were often highly manipulated ecosystems, developed from the selection, transportation, planting and management of plant materials gathered by First Nations peoples from extensive areas. These land management practices enhanced intraspecific diversity (Nabhan et al., 1982) and shaped the distribution of many of the plants and animals seen today. The transportation and cultivation of trees by First Nations peoples had considerable influence on present-day distributions of these trees, and helps explain, for example, the presence of pawpaw (Asimina triloba) in southern Ontario.

In addition to bringing livestock, a variety of agricultural technologies were imported to Canada following European settlement in the late 1700s. Agroforestry practices were among the introduced technologies already employed across Europe, including tree-based intercropping systems integrating fruit trees and various annual crops, a variety of silvopastoral systems in both natural forests and orchards, and home gardens. European settlers also experimented with developing new agroforestry-related practices or adapting existing technologies to take advantage of their new environments. For example, utilizing the sap from sugar maples (Acer saccharum) to boil down to maple syrup was a practice learned from First Nations peoples and used to reduce the need for imported cane sugar. Other agroforestry-related practices probably used by European settlers include homestead plantings, windbreaks, range and farm woodlot management, and the use of fertile soils from beneath tree canopies, though little documentation is available about such practices.

When agroforestry was first described in the late 1970s, certain practices common in Canadian agriculture were quickly identified as agroforestry or as agroforestry-related practices: forest range and farm woodlot management, maple syrup production, plantations on marginal or degraded land (e.g. forest or Christmas tree plantations; riparian forest plantings), and windbreaks. Gold and Hanover (1987) identified several more contemporary combinations of trees and agriculture as agroforestry practices, which were touted as having great potential in the temperate zone. New developments or modern applications of traditional agroforestry practices include the intercropping of black walnut (Juglans nigra) with cash crops (Garrett and Kurtz, 1983), and the use of livestock to control weed competition in conifer plantations in British Columbia (Ellen, 1991).

Canadian farms and their forests or woodlots are closely integrated, both economically and ecologically, and form the basis through which many professionals and agencies are introduced to agroforestry. Woodlot management, plantation establishment, windbreaks and forest range management have been traditional areas where forestry agencies have been involved with agriculture and conversely where agriculturists have ventured into forestry. However, other traditional agroforestry practices such as using fruit or nut trees in intercropping would have developed with little input from foresters since the system components are horticultural in nature.

Farms, forests, woodlots and land-use changes

Forests and woodlots have always been an essential component of farming in Canada. Historically, farm woodlots and nearby woodlands have provided a variety of products to farmers, including wood (for fuel, building materials, and fencing), sugar, nuts (e.g. American chestnut (Castanea dentata)) and berries for food and supplementary income, wildlife for sustenance, and potash fertilizer from wood ash for use or sale. The term ‘woodlot’ generally refers to a small (1 to 40 ha) privately owned forested tract that is part of a larger property that may be farmed. Where large landholdings predominate, such as the eastern slopes of the Rocky Mountains and in other parts of the western continent, farmers or ranchers may own substantial timberlands that are an integral and important part of their farm operation.

Farm woodlots are often used as cash reserves (Nelson, 1991) and can generate regular income from the sale of wood or other products such as maple syrup, ginseng (Panax quinquefolius), mushrooms or herbs, or through the leasing of acreage for hunting or recreational purposes. Farmers may also benefit from nearby forestlands that can provide supplementary employment, wood products, seasonal pasturelands, hunting and recreational opportunities and a source of clean and constant water. However, since 1950, despite their many contributions to the farm economy across Canada, many woodlots (and other natural areas) have been cleared for cropland or pasture, subdivided and sold for rural homes, developed for intensive urban uses or targeted as routes for transportation corridors.

With the development of less expensive and easily obtainable fuel sources, such as oil, natural gas, and electricity, the importance of woodlands on farms has lessened. However, forests maintain a crucial role in many farm operations and are able to provide comparable or superior net annual returns on an area basis compared with adjacent conventional croplands. Additionally, forests or individual trees in general have the ability to drastically increase property values well in excess of the present or projected monetary value of the trees and/or their products. Further, while intrinsic and environmental values of trees are an important consideration for landowners, the bulk of tree planting and retention decisions come down to the cash value of trees versus their cost of ownership.

In Canada, the extensive conversion of woodlands and other natural areas to agriculture from the 1960s through the mid-1980s has been facilitated by high levels of farm subsidies. Many agricultural programmes support farmers based on the number of hectares cultivated, resulting in the development and cultivation of marginal farmland or land that could not be farmed profitably without subsidies. Conversion of farm woodlots to other land uses such as urban residential, urban industrial or rural residential has come about due to increasing real estate values in urban areas, reduced viability of many farming operations, and the development of improved transportation and communication networks that facilitate urban-based professionals living in rural areas.

Between 1951 and 1986 the farm population declined from 20% to 3% of the total Canadian population, but the corresponding decline in the rural population as a whole only decreased from 38% to 23%. ‘Farmers’ constituted about 53% of the rural population in 1951, but only 15% by the early 1980s (Statistics Canada, 1983). By 2006 the farm population as a percentage of the total Canadian population had declined further to 2.2% (Statistics Canada, 2006). The rural population as a whole had decreased to 19.7%, with ‘farmers’ now constituting a mere 10.3% of the rural population (Statistics Canada, 2006).

Historically, although farmers have constituted the bulk of landowners in Canada, a growing proportion of land classified as farmland is now owned by non-farmers. However, it is not reasonable to assume that these people are not land users simply because they are not farmers. If the concern in the agroforestry community is with land use in general, and if fewer rural residents and landowners conform to the typical ‘farmer’ stereotype, it is important to consider what these officially designated ‘non-farmers’ (including part-time farmers) are doing with their land (Raintree, 1991). An encouraging Ontario study found that landowners in a peri-urban area were familiar and experienced with agroforestry in the traditional farm-forestry sense but not with ‘agroforestry systems’ that would be suitable for use in that area (Matthews et al., 1993).

Buck and Matthews (1994) studied the range of livelihood strategies of self-identified agroforestry practitioners in southern Ontario. Former urbanites, having recently immigrated to rural areas, look to make positive impacts on the environment while partially or even completely replacing their income through agroforestry land-use systems. Canadian ‘agroforesters’ are often motivated to address environmental issues in an attempt to reduce ‘eco-guilt’, making reparations for their own negative impacts on the environment. This group, which also includes past and present dairy farmers, in addition to long-standing forest owners, is typically focused on novel land-use systems and enhancing the role of trees with respect to both their land-use strategies, as well as their own livelihood.

While conventional agriculture has become economically marginal for an increasing number of households and communities throughout Canada (Raphael, 1986), the land area devoted to agriculture has also been reduced through incentive programmes. The associated commodity price stabilization objectives of these programmes take advantage of land conservation provisions to reduce surplus production. Both provincial and federal programmes have encouraged the use of conservation practices and the retirement of fragile and marginal lands. The Ontario Ministry of Agriculture, Food, and Rural Affairs, for example, promotes the Conservation of Easements for Agricultural Land Use programme to allow land owners to partition portions of their land for conservation (OMAFRA, 2011).

Ironically, in many cases the most influential factors in the development of programmes that encouraged soil conservation and low-input sustainable agriculture (LISA) came not from the agricultural sector, but from assessments that pointed to agriculture as a major polluter of waterways. For example, the PLUARG (Pollution from Land Use Activities Reference Groups) report determined that non-source pollution from agriculture was a major source of excess nitrogen and phosphorus in the Great Lakes (Spires and Miller, 1978). This resulted in a number of international, federal and state/provincial programmes to assess and reduce pollutants from these sources.

The federal-funded Agricultural Greenhouse Gases Program (AGGP), which began in 2010, is one such programme aimed at enhancing the mitigation of greenhouse gas (GHG) emissions in Canada. Further details on this programme are provided under the subheading ‘Agricultural Greenhouse Gases Program’ later in this chapter.

Driving forces in agroforestry

Since the concept of agroforestry was identified, many traditional practices have been relabelled as agroforestry practices, and the development of new practices has occurred rapidly. Significant increases in agroforestry awareness and adoption have followed among academics, professionals and landowners. The main factors driving agroforestry adoption are often convergent and include environmental concerns, changes in demography, and shifts in land use and rural economies. Recent moves to make greater use of agroforestry practices in temperate agriculture have been driven by the real or perceived ability of agroforestry to help satisfy many different needs, including: (i) economic and agricultural diversification; (ii) environmental impact mitigation; (iii) land and water rehabilitation and restoration; (iv) increased or decreased food production; (v) sustainable use or retirement of marginal or fragile land; (vi) natural habitat enhancement; and (vii) profitability.

Agroforestry technology can be used to accomplish two primary goals: (i) improve economic gain; and (ii) improve resource conservation. The design and management of agroforestry systems significantly influences the aforementioned goals of economic gains and resource conservation (Williams, 1993). For example, Ontario peach producers employing vegetable intercropping practices among their peach trees during the first few years of orchard establishment have realized greater economic gains (Williams and Gordon, 1992). The aforementioned tree-based intercropping practices yield earlier returns from prime lands, in addition to providing a more diverse income for growers, enhanced labour and equipment utilization, and may even result in the peach trees (Prunus persica) bearing fruit earlier and reducing crop pest populations. Weed competition may also be reduced through the practice of intercropping income-generating agricultural crops when native hardwood plantations are being established on abandoned or marginal lands. It is therefore possible for intercropping to be cheaper than more traditional forms of mechanical and/or chemical weed control practices, while also contributing to furthering conservation goals. This is especially true if the plantation is being created to re-establish native forest or to retire marginal farmland.

With respect to the second goal of improving resource conservation, intensive agricultural production in Canada over the last century and a half has resulted in a host of environmental impacts including increased soil erosion and subsequent deposition, reductions in crop productivity on marginal lands, habitat losses for both native plants and animals, and water quality degradation as a result of excess nutrient and agrochemical leaching. All of these effects are, at least in part, due to the removal of trees from the landscape in the form of woodlands, wetlands, windbreaks, hedgerows and similar buffering features. Increasing cultivated acreages and bigger farm equipment, mostly resulting from industrial agricultural policies and advanced agricultural technologies and mechanization, is one of the main drivers contributing to fewer and fewer trees on agricultural landscapes. The re-introduction of these woodland features and their management for marketable products using agroforestry principles will help restore natural systems and enhance productivity, while mitigating some of the negative effects of production agriculture.

Agroforestry practices can also be used to protect the quality of the environment by reducing on-site degradation processes and by buffering adjacent areas from the negative impacts of activities in those areas (Williams, 1993). For example, forest plantations can be used to rehabilitate degraded fields by reducing soil erosion, and improving soil organic matter, nutrient status and soil structure. When planted as a buffer or contour strip, trees can trap sediment (Williams, 1993), reduce runoff and nutrients in groundwater (Correll, 1983; Daniels and Gilliam, 1996), and shade waterways (Gordon and Kaushik, 1987). Through the selection of the proper species and the application of good management strategies, increased financial gain can also be realized.

Agroforestry, wildlife and biodiversity

Intensive use of the landscape results in reduced or extirpated populations of many wildlife species through direct competition, predation by humans or habitat modification. In crop production, ecosystems are simplified by human manipulation to favour the production of a single crop species. The subsequent effects on wildlife populations are often obvious. For example, broad-scale habitat changes as a result of agricultural development have resulted in the displacement of the red-shouldered hawk (Buteo lineatus, a specialist species that favours woodlands, woodland edges and floodplains) by the red-tailed hawk (Buteo jamaicensis, a generalist species favouring open lands). However, the day-to-day interactions between agriculture and wildlife are less obvious and, in general, poorly understood.

Current issues surrounding agriculture–wildlife interactions include the preservation of both local and regional biodiversity, the retirement of marginal and fragile lands, the effect of agriculture on natural resources depended upon by wildlife (e.g. surface and ground water) and ecological and economic sustainability. Agroforestry is rooted in the concepts of sustainability and permaculture (Raintree, 1991) and, by definition, incorporates multiple species into production systems, adding diversity at a field, farm and landscape level. Agroforestry systems, through enhanced species and structural diversity, add complexity to agroecosystems, and in turn provide new opportunities for wildlife that do not exist in monocultural systems.

Natural fence lines and planted windbreaks interrupt the monotony of and add diversity to agricultural landscapes. They act as important refugia and corridors for wildlife, connecting areas of disparate natural habitat often separated by developed agricultural land. Best et al. (1990) found that bird numbers increased by a factor of five in wooded edges when compared with numbers in herbaceous edges, bird species using wooded and herbaceous edges differed, and more species used field perimeters than field interiors (30 as compared with 18 species).

The effects of windbreaks on wildlife and insect habitat can often be magnified in intercropping systems. A windbreak is a linear planting of trees between fields, whereas an intercropped field has rows of trees uniformly spread throughout and may include an array of other plants depending upon the management regime (e.g. weed-control practices). Williams et al. (1995) compared an intercropped field (primarily deciduous broadleaves and three crops) with an adjacent monocropped field (maize (Zea mays)) and found that the diversity and size of breeding and foraging bird populations were greatly increased in the intercropped plantation (seven compared with one (breeding species) and 16 compared with two (foraging species)). None of the species fed on the crop and many fed primarily on insects. Additional species in the intercropped field utilized shrubs and conifers planted within the tree rows as food sources or as perches. A similar study by Gibbs et al. (2015) in the same fields as the study by Williams et al. (1995) found that bird diversity continues to increase over time in maturing tree-based intercropping systems.

Not all species react positively to the presence of agroforestry systems and ‘ecological traps’ can be created that negatively affect wildlife populations. An ecological trap occurs when species are attracted by apparently favourable habitat to a location where they may be easily predated or otherwise harmed (Best, 1990). An example of this can occur when a narrow corridor (e.g. a single-row windbreak or grassed waterway) attracts a ground nesting bird, making it easy for a predator (also using the corridor) to locate and destroy the nest. Another example can be found in the spring of the year, when killdeer (Charadrius vociferus) are attracted to cornfields to build nests, only to have them destroyed when the field is tilled. Some of these conditions are unavoidable, but many can be minimized or even eliminated with subtle changes in tillage and agrosilvicultural practices.

Interactions between wildlife and farming systems can be positive, negative or neutral. The activities of wildlife can cause or worsen a pest problem, help prevent or reduce pest problems, or have little or no effect on agriculture and associated pests. Where pest problems occur, steps should be taken to reduce the damage to tolerable levels. Management practices can include setting ecological traps for pests by manipulating the habitat to discourage them or make them more susceptible to predation.

However, the beneficial impacts of wildlife are often overlooked; even apparently benign species like spiders (Araneae) provide a more balanced community structure and, in addition to their intrinsic value, may provide previously unidentified benefits to production. It is commonly accepted that windbreaks provide refuge for both pest and beneficial organisms, and recent studies have suggested that significant benefits may be provided by biocontrol agents of insect pests in or near wooded field margins or corridors. Birds associated with field edges, for example, undoubtedly help to reduce insect pest problems. It has been observed in many areas that downy woodpeckers (Picoides pubescens) are significant predators of overwintering maize rootworm (Diabrotica barberi) larvae. It is also likely that field windbreaks and intercropped trees facilitate the movement of tree-associated birds such as woodpeckers into croplands, helping to reduce pest problems.

Research from other temperate regions reinforces the importance of windbreaks as habitat for insect communities. Windbreaks and hedgerows often contain woody species that break bud before adjacent field crops emerge (e.g. winter wheat (Triticum aestivum) or are even sown. In addition, many windbreaks contain a mix of supplementary species that provide a source of pollen and nectar throughout the year. The result is a rich fauna of herbivorous insects that are non-ranging and host-specific to the windbreak species and very different from insect pests on the crops. Along with the increase in these hedgerow-dwelling insects is an ancillary population of parasites, many of which are generalist in nature. In Bavaria, for example, Schulze and Gerstberger (1994) indicate that the presence of these parasites controls the development of aphid (Aphididae) pests on adjacent cereal crops throughout the year, with the interesting result that Bavaria is one of the few regions in Germany where spraying for aphids on wheat is not required. Although more research along these lines is required in Canadian situations, it is likely that the scenario is similar in many places across the country.

To summarize, agroforestry systems, in addition to providing crop and income diversification strategies, are often utilized on degraded lands for their soil, water and nutrient conservation properties (Young, 1989). This is especially true in the tropics (e.g. Grewal et al., 1994). In contrast, in Canada agroforestry systems have been developed largely as a result of financial considerations, most likely because the adoption of agroforestry by the farming community is economically driven. For example, Ball (1991), working in southern Ontario, advocated the adoption of nut production and hardwood intercropping as a potential diversification strategy for tobacco (Nicotiana spp.) farmers faced with dwindling incomes from that crop.

None the less, there are many ‘conservation’ and environmental benefits (e.g. maintenance or enhancement of biological diversity) associated with the development and adoption of agroforestry systems in Canada, and recently, some of these benefits have been evaluated in tandem with economic returns (e.g. Simpson et al., 1994). All of the agroforestry systems mentioned in the following sections can be utilized in a ‘conservation technology’ mode to bring environmental benefits to the farmscape. However, the impacts can vary greatly in scale and quality. For example, intercropping systems can be used to promote terracing and organic matter build up in soils on sloping lands, windbreaks can provide transportation corridors between disparate woodlots for wildlife, and silvopastoral systems can provide relief to the animal component from the throes of extreme weather. In contrast to economic returns, which will likely be greatest on the best agricultural land, the greatest environmental returns from agroforestry practices will most often be associated with degraded, or marginal agricultural land. This is obviously scale-dependent, and will depend to a great extent on the nature of the surrounding landscape and its agricultural history.

Agroforestry Systems and Related Practices

In Canada, there are many farm practices that clearly fall within the realm of agroforestry, and in fact are agroforestry ‘systems’, when all of the components are intensively and integratively managed over time. Other agroforestry-related ‘practices’ might include technologies with the same elements but used in isolation. Most agroforestry practices can be grouped into one of the following: (i) windbreak systems (shelterbelts); (ii) silvopastoral systems (tree–animal systems); (iii) intercropping/alley cropping systems (tree–crop systems); (iv) integrated riparian management systems (riparian forest systems); and (v) forest farming (natural forest or specialty crop) systems. This section will describe the general background and concept of these systems, give examples of applications and, in some cases, provide suggestions for recommended cultural practices. Some plantation and biomass production systems are briefly described as they may be related to agroforestry.

Windbreak systems

Windbreaks or shelterbelts are defined as linear plantings of trees or shrubs established for environmental purposes (Loeffler et al., 1992); they have been a key agroforestry practice in North America since European settlement. As homesteaders moved west in Canada leaving the deciduous forests and moving into open prairies, they were forced to adjust to these new surroundings and soon realized the value of shelter from the harsh weather for their homes and livestock. Many settled in the shelter of existing trees along streams and rivers; others were forced to create shelter by planting trees.

Trees were often brought from the east and did not survive due to a lack of hardiness and for this reason nurseries were eventually established in the prairie region to grow reliable stock. The Canadian settlers of the prairies faced similar challenges and the Dominion Forest Nursery Station was established in 1902, and was in operation until 2013 at Indian Head, Saskatchewan.

In the early years, most plantings were for farmstead protection. The first strong encouragement to plant windbreaks for other purposes, such as soil and crop protection, came during the ‘Dust Bowl’ of the 1930s. In 1935 the Canadian Government passed the Prairie Farm Rehabilitation Act, which was set to combat the drought and soil erosion experienced in the preceding years. In the Canadian prairies alone, about 2300 km were planted during the following decade (Schroeder, 1990). Since 1937, over 43,000 km of field shelterbelts protecting approximately 700,000 ha have been planted in the Canadian prairies. In central Canada, windbreaks continue to dominate as the most popular and widespread agroforestry system to this day.

No matter where these agroforestry systems are located, well designed and maintained windbreaks provide economic returns and benefits to landowners and make living with the wind much more tolerable. This is accomplished by reducing wind speed in the protected zone, an area directly proportional to the height of a windbreak. Wind speed reductions occur on the leeward side of the windbreak to a distance of 30 times the height of the windbreak (30H) with the largest reductions occurring between 2H and 15H. Wind speed reductions also occur on the windward side for a distance of 2H to 5H (Heisler and DeWalle, 1988; McNaughton, 1988).

The magnitude of the wind speed reduction in the sheltered zone is highly dependent on windbreak structure. The key factor in structure is density and more specifically the amount and arrangement of the solid portions of the windbreak. For farmsteads, feedlots, and residences, a moderately dense to dense windbreak (60–80% density) is generally recommended. For most field windbreaks a summer density of 40–60% will provide the greatest wind speed reduction over the largest area. In northern areas, where uniform snow distribution across a field is an objective, field windbreaks should have a winter density of no more than 40% (Brandle and Finch, 1988). However, the overall effectiveness of a windbreak is determined not only by the height and density but also by the length, orientation, number of rows and spacing within the rows. Together, these factors can be manipulated to accomplish a range of objectives.

Density can also be expressed as porosity, the percentage of airspace, visual or otherwise, in a windbreak (i.e. where windbreak density is 60%, porosity is 40%). As foliage, branches and trees change shape at varying wind speeds, ‘optical’ porosity and shelter characteristics will also vary at different wind speeds. A number of studies in Ontario have found that optical porosity varies with species composition and windbreak width, and that narrow windbreaks with low porosity actually behave like impenetrable physical barriers (Kenney, 1985, 1987; Loeffler et al., 1992) (Fig. 2.1).

Fig. 2.1. High contrast black and white silhouette photograph of a Norway spruce (Picea abies) windbreak in southern Ontario, illustrating ‘optical’ porosity (from Loeffler et al., 1992) (photo, Anne Loeffler).

For maximum benefit, windbreaks should be located perpendicular to the prevailing or most troublesome winds. Farmstead and livestock windbreaks tend to have from three to six rows (more in northern areas), at least two rows of conifers, and are generally located on two sides of the area to be protected. For best wind protection, the tallest row is often placed a distance of 2–5H from the area needing protection. For wind and snow protection, the most windward row of the windbreak should be 30–60 m (varying with the geographic region) from the areas needing protection (Wight, 1988). If