>>Also, it is worth mentioning that the U.S. Pacific Northwest has been all >>"abuzz" for a few years now about such an effect in Douglas-fir spacing >>trials, only it shows up in both diameter and height (greater in closer >>spacings) and appears well any self-sheltering could occur. Something more >>"mysterious" is going on there. Folks with Weyerhaeuser put in initial spacing trials about a decade ago. These covered a broad range of densities from 1200 trees per acre down to about 75. After several years the height effect was visible from casual observation. Subsequent measurement confirmed the occular estimates -- higher densities produced taller trees with greater diameter. In the early years I believe that the diameter effect is not suprising -- the chief correlate with diameter is time to breast height. Therefore, a tree that grows in height faster will for a time have greater diameter. The Stand Management Coop has since put in a number of initial spacing installations across Oregon, Washington and B.C. Early results from these tell a mixed story. Yet on some sites (anecdotally high site quality sites) the effect is there. Weyerhaeuser is reporting looking at several factors suspected in the response. They have trenched between trees to break up root grafts, compared intensive veg management treatments and measured microclimatic variables. They have not shared their results yet. Greg Johnson Veneta, Oregon 73062.146@compuserve.com
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