LITTERFALL, NITROGEN AND PHOSPHORUS INPUTS AT VARIOUS LEVELS OF CANOPY REMOVAL IN OAK AND PINE STANDS IN NORTHERN LOWER MICHIGAN

Relatively little is known about the comparative effects of varying de grees of canopy cover in oak and pine stands on litterfall quantity an d quality, which in turn have a major influence on litter decompositio n rates and nutrient cycling processes. Thus, changes in litterfall an d nutrient (N and P) inputs were examined over the 1st 2 yr following various levels of canopy removal in northern red oak (Quercus rubra L. ) and red pine (Pinus resinosa Air.) stands in northern Lower Michigan . Selective canopy removal in experimental plots resulted in 25% (50% during the 1st yr) and 75% canopy cover. Comparisons were made with un cut references, which had an average canopy cover of 85%. As expected, the uncut stands had the highest litterfall during the 2-yr period (o ak, 393 g m(-2) yr(-1); pine, 430 g m(-2) yr(-1)), whereas the most he avily cut stands (25% canopy cover) had the lowest values (oak, 118 g m(-2) yr(-1); pine, 104 g m(-2) yr(-1)). A small amount of canopy remo val (75% canopy cover) in red oak stands led to significant reduction of litterfall and nutrient inputs, whereas the same treatment in red p ine stands had little effect. In contrast, litterfall following the 25 % canopy cover treatment decreased more in red pine stands than in red oak stands compared to the uncut stands. Annual total leaf litter N i nputs at the same canopy cover levels were higher in red oak stands th an in red pine stands. Lower N inputs in red pine stands were attribut ed to the low N concentrations in needle litter throughout the year, n ot to total leaf litter mass differences. These results indicate that the amount and quality of canopy removal were key factors in determini ng litterfall and nutrient inputs in these stands.