Agroforest O' Systems 13: 203-224, 1991. ~C~1991 Kluwer Academw Pubhshers. Printed in the Netherlands. Design and development of agroforestry systems for Illinois, USA: silvicultural and economic considerations G.E. CAMPBELL, G.J. LOTTES and J.O. DAWSON Department of Foresto', 110 MumJbrd Hall. Umversitv of Illinois at Urbana-Champaign, 1301 W. Gregory Drive, Urbana, IL 61801, USA Key words: Multicropping, joint production, marginal land, timber and agriculture, net present value, income taxation Abstract. Recommended managerial inputs and associated outputs expected from practicing agroforestry on marginal farm lands in the central USA are discussed. Modeled management combinations are based on five timber species, three s~teindices, three timber growth rates, five agricultural crops, all common crop rotations, and three tillage systems. Black walnut (Juglans nigra L.), combined with row crop production, is used to illustrate a specific multicropping alternative. Based on net present value, modeled agroforestry systems incorporating black walnut performed better on the better sites and at the medium to high timber growth rates whereas management systems using red oak (Quercus rubra L.) with row crops performed better on the poorer sites and at the lower growth rates. For agroforestry to be competitive with traditional agriculture, medium to high timber growth rates were necessary. Also, lower interest rates and the existing U.S. income tax structure favored agroforestry versus traditional agriculture. Substantial increases in net income may be possible through incorporating other income producing activities such as nut production within the agroforestry system. Introduction Agroforestry in the central United States usually means multicropping (i.e., alternating rows of trees with strips of field crops). Benefits from a multicropping system may include land conservation, improved overall economic returns [16], and the opportunity to increase timber supply. Costs of plantation establishment can usually be offset by the early financial returns from the agricultural crop. Agricultural tillage, fertilizer, and weed- ing also benefit the tree crop [16], in return, the young trees in a multicrop system often serve as windbreaks or shield agricultural crops that benefit from partial shade [17]. Additional agroforestry benefits include easier stand access, reduced fire risk, and the potential of producing timber closer to processing facilities and markets [16]. The silvicultural and economic relationships of integrated forestry-farm- ing with black walnut in Missouri have been reported by Kincaid [18] and Thurman [28]. The general conclusions from these studies were that black