North American Agroforestry. Группа авторов

2014; Russell, 1982). The widespread use of these strategies, however, largely disappeared during the last century with the concurrent development of separate agricultural and forestry research and management infrastructures. Today, an integrated, subsistence lifestyle is the chosen standard of living for a few independent, free‐spirited individuals and an unfortunately necessary one for the economically marginalized rural poor. A few agroforestry practices survived into the mid‐20th century associated with long‐established organizations (e.g., the Northern Nut Growers Association) or as culturally acceptable complements to traditional farming enterprises (e.g., maple syrup production).

Periodic agricultural disasters have stimulated unique forestry activities that can also be considered agroforestry practices. In the 1930s, the Great Depression combined with the drought‐induced Dust Bowl in the Great Plains caused severe economic and environmental perturbations throughout the agricultural community and the nation. The formation of the Civilian Conservation Corps promoted many conservation activities including the planting of millions of trees as windbreaks and plantations to help protect eroding farmlands (Hudson, 1981). Such ecological problems also stimulated interest in the use and genetic improvement of nut trees to reclaim and promote production from lands marginal for conventional farming practices (Smith, 1950). The farm crisis of the 1980s was less dramatic on a large scale, but it had devastating economic and social impacts on many rural communities (Fitchen, 1991). In response, congressional actions established alternative agricultural programs such as the Conservation Reserve Program, Low Input Sustainable Agriculture (renamed the Sustainable Agriculture Program), and the Integrated Pest Management Program.

      In the first decade of the 21st century, there was an increased interest in the production of biofuels and a concerted government effort to develop the technologies to make biofuels a reality. One unintended impact of the interest and support for biofuels, and particularly corn‐based ethanol, has been periodic increases in corn prices in the United States and around the world, igniting a “food versus fuel” debate. High commodity prices linked to the demand for biomass feedstocks for biofuels coupled with huge demand from China also resulted in farmers opting out of conservation programs and replacing conservation acres with commodity crops, with environmental consequences including increasing sediments and chemicals entering surface and ground waters (Jordan et al., 2007).

      Simultaneously, spurts of environmental consciousness by the American public have promoted alternate land use practices, often involving unique mixes of trees, food crops, and livestock by non‐traditional rural landowners. For example, the 1960s spawned a group of “back‐to‐the‐land” environmentalists desiring low‐impact communal lifestyles. Although most of these groups eventually disappeared, individuals committed to integrated land use practices remained to practice their more ecosystem‐friendly forms of agriculture and to develop such organizations as the Land Institute, Rodale Research Center, and Wallace Center. The fact that the Northern Nut Growers Association was founded in 1910 is a testimony to the existence of such individuals for many years.

      The past 40 yr have witnessed a growing understanding of the potential usefulness of agroforestry practices in addressing today’s concerns over the economic and environmental sustainability of forest and farm lands. Gold and Hanover (1987) discussed two such practices: managing conifer sawlog with cattle grazing practices (silvopasture) and multi‐cropping valuable hardwoods with agricultural crops (alley cropping). There are five widely recognized agroforestry practices in the United States today: (a) alley cropping, (b) riparian and upland buffers, (c) windbreaks, (d) silvopasture, and (e) forest farming. In addition to the five recognized practices, there is an emerging agroforestry practice called urban food forests that has gained considerable attention in the past decade (Bukowski & Munsell, 2018). The specifics concerning these six practices are examined later in this volume. In addition, with the growing interest in terrestrial carbon sequestration and alternative fuels provided by woody and herbaceous growth, there has been increasing interest in the role of agroforestry practices to sequester and store carbon as well as systems that produce biofuels. The National Agroforestry Center has continued to add support to those practices, providing publications and guidance to landowners and practitioners (Schoeneberger, 2005; USDA, 2015, 2019). Much progress has been attained toward the building of research, education, and application for domestic agroforestry that will foster the development of these practices (Gold, 2007; Gold, Hemmelgarn, & Mendelson, 2019; Gold & Jose, 2012). However, before discussing these concepts relative to the challenges still facing the development of agroforestry in the United States, we must first provide an appropriate context by considering opportunities for its development.

Opportunities for Agroforestry

      There is a range of opportunities for the development of agroforestry in the United States, a topic first addressed relative to nut‐tree crops in 1989 (Lassoie et al., 1991) and then more comprehensively by Lassoie and Buck (1991) and more recently by Jose et al. (2018). What follows is a consideration of the importance of agroforestry to the development of newly emerging (a) land use systems, (b) institutional arrangements, (c) scientific opportunities, and (d) knowledge systems. It is important to note that many of the following statements are in the process of ongoing validation and are areas under active evaluation by agroforestry professionals.

      Opportunities for Practical Application

The possibilities for developing agroforestry for use in rural and urban areas of the United States is encouraging. It did function extensively at one time throughout North America (Carroll, 1973; Cronon, 1983; Russell, 1982), and refugia of such practices still exist today (e.g., see Campbell et al., 1991; Gold & Hanover, 1987; Schultz et al., 1995). Agroforestry is currently working effectively in many other developed (Burgess & Rosati, 2018; Gordon, Newman, & Coleman, 2018; Mead, 1995; Von Maydell, 1995) as well as developing (Hillbrand, Borelli, Conigliaro, & Olivier, 2017; Nair, 1989, 1993) countries. The political and social climate in the United States is rapidly changing, which is likely to allow the development of the new land use strategies that include agroforestry (Jose et al., 2018; Lovell et al., 2018; National Research Council, 1996; USDA, 2019). Opportunities for the development and application of domestic agroforestry practices can be separated into ecological, economic, and social components for discussion purposes; however, one needs to keep in mind that these components are interrelated, interlinked, and interactive.

      Ecological

      One of the primary advantages of agroforestry in the United States probably rests in its ecological benefits and resultant environmental protection characteristics (Garrett et al., 1994; Jose, 2009; Jose & Gordon, 2008; Jose, Walter, & Kumar, 2019; Kremen & Merenlender, 2018; Udawatta & Jose, 2012). As an ecologically based land management strategy, agroforestry practices help maintain ecosystem diversity and processes that are important to the long‐term sustainability of any extractive land use practice such as agriculture and forestry. This approach offers the opportunity to maintain and possibly improve the quality of the soil resource by reducing erosion, enhancing nutrient capital, and improving water infiltration and retention rates (Dollinger & Jose, 2018; Udawatta, Gantzer, & Jose, 2017). Trees also moderate microclimatic extremes, assuring cooler summers and warmer winters. Such conditions are beneficial to the production of certain food crops and livestock under severe environmental conditions as well as to human comfort. Agroforestry practices can also result in decreases in chemical (e.g., fertilizers and pesticides) and energy inputs of farming systems, all important to an environmentally sensitive society (Jose, 2019; Lerch, Lin, Goyne, Kremer, & Anderson, 2017). There is a growing movement to value some of the environmental services provided by agroforestry practices, allowing their benefits to be translated into economic incentives for landowners.

      Economic

      Agroforestry offers financial opportunities associated with enhancing the profitability of traditional farming systems (Alavalapati & Mercer, 2004; Campbell et al., 1991; Nair, 1993; Van Vooren et al., 2016). One option is to reduce production costs by decreasing the need for external chemical, water, energy, and/or labor inputs. Another is that agroforestry might increase the net value of production