Читать книгу North American Agroforestry - Группа авторов - Страница 31

Because domestic agroforestry has evolved within a modern society primarily located in a temperate region of the world, it has faced inherent constraints not found in most developing countries. First, the climate in much of North America is not conducive to fast plant growth, especially by long‐lived woody perennials. In addition, some of our indigenous tree species are naturally slow growing and yield only one primary product—usually timber. As a consequence, the use of trees for timber in many types of agroforestry practices do not directly yield useful or marketable products for many years—often after the life of the persons who planted them! Knowing this, domestic agroforestry has instead focused on overstory nut‐ and fruit‐bearing trees and shrubs that come into economic production in 3‐15 yr (e.g., elderberry [Sambucus nigra L. ssp. canadensis (L.) R. Bolli], aronia [Aronia sp.], eastern black walnut [Juglans nigra L.], pecan [Carya illinoinensis (Wangenh.) K. Koch], Chinese chestnut [Castanea mollissima Blume]). Furthermore, fast‐growing species of the genus Populus (hybrid poplar, cottonwood, etc.) and Salix (clonal willow) (Robertson et al., 2017; Volk et al., 2006) are being used for biomass (MacPherson, 1995) and as woody florals (Gold, Godsey, & Josiah, 2004) and are integrated into riparian forest and upland buffer production systems to provide multiple products and environmental services. Finally, native perennial grasses (e.g., switchgrass [Panicum virgatum L.]) are also being used for biomass and other ecosystem services within a variety of agroforestry practices (Gamble, Johnson, Current, Wyse, & Sheaffer, 2016; Schulte et al., 2017)

The United States is a modern, industrialized nation with an increasingly large educated, urban population. Therefore, agroforestry practices are being developed to simultaneously address the market opportunities in urban areas while also meeting specific interests, needs, and problems of rural landowners. Currently, obstacles to agroforestry adoption exist but are in the process of being overcome (de Jalon et al., 2018; Wilson & Lovell, 2016). Barriers include the expense of establishment, landowners’ lack of experience with trees (Faulkner et al., 2014), the time and knowledge required for management and marketing (Valdivia, Barbieri, & Gold, 2012), and a lack of understanding by extension and state and federal agency professionals.

Agroforestry practices also have to compete with commodity crops, which have well‐developed government support systems providing insurance and price guarantees that significantly reduce landowner risk. Agroforestry practices do not, at present, have the same level of support, requiring that the landowner take on significant risk in adopting agroforestry practices. That said, the support structure and knowledge network for agroforestry is growing rapidly, addressing many of the issues constraining agroforestry adoption (Schoeneberger et al., 2017).