Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2003
Publication Date: N/A
Interpretive Summary: Small farms have been marginally profitable in recent years due to low prices at the farm gate for most agricultural commodities. Agroforestry, the schematic co-production of trees and crops, is one means that small farms can diversify the products they produce, thus providing avenues of alternative income. To increase the adoption of agroforestry in the United States, ARS in cooperation with NRCS and U.S. Forest Service has been developing the U.S. Agroforestry Estate Model (AEM) as a tool to educate natural resource professionals and landowners of the potential profitability of agroforestry practices. Although the software for the model has been developed, data to use the model is lacking. This publication represents the first gathering of tree growth data from which U.S. AEM can be used to predict the profitability of agroforestry practice with eastern black walnuts. This information is of interest to natural resource professionals working with landowners who are interested in initiating agroforestry practices on their farms.
Technical Abstract: Black walnut (Juglans nigra) is a prime tree species for agroforestry practices in the United States providing highly prized wood and nuts for human consumption and wildlife. In 54 black walnut stands in south central United States, the site index (i.e., mean dominant height [DH], at age 25 years) ranged between 5.2 and 21.4 m, and was independent of stand density. There were no differences in height and stem diameter (DBH) growth rates between stands with improved varieties and native stock. Most stands were in a "free growth" stage because of either early age or wide spacing. Mean annual increments in DBH and height were positively related both for improved varieties and native stock. Understory competition had a substantial detrimental effect on DBH. In a 26 year-old stand, trees growing within Kentucky blue grass (Poa pratensis) had a site index 5 m greater than trees growing within tall fescue (Festuca arundinacea). Predicted nut yields in 2002 varied between 0 and 1370 kg of hulled nuts per ha. Improved varieties had, in general, higher nut yields than predicted from a DBH-nut yield equation developed for individual trees. Nut yields were highly variable both within and among stands, and were related to DBH in native stock but not in improved varieties.