|Title||Forest soil and site productivity considerations in intensive wood harvest systems in northern lower Michigan|
|Year of Publication||1980|
|Degree||Doctor of Philosophy|
|Number of Pages||199 pp.|
|University||University of Michigan|
|City||Ann Arbor, MI|
Regional and local trends and expectations in the demand and output of forest products indicate the continued or increased application of intensive wood harvest systems in northern lower Michigan. Pertinent soil and site considerations specific to the area were examined to help determine the likelihood of reduced productivity of succeeding forest stands under the use of these harvest systems. Biomass removals through intensive harvest were estimated for several major northern lower Michigan forest types over a range of stand conditions. These estimates were obtained by integrating available specific gravity and biomass distribution data with bole-wood volumes predicted from regression equations which relate these volumes to stand height and basal area. Nutrient removals associated with harvested biomass were approximated by applying published tissue nutrient concentrations to the biomass estimates. The biomass and nutrient estimates thus generated showed considerable variability attributable to such factors as forest type and site producitivity. Bulk precipitation collected for several months near Pellston, Michigan, was found quite variable among precipitation events, types and sampling periods, but was usually unnaturally acid (pH<5.6). Simulated natural and acid precipitation applied to local tree foliage samples and forest floor plots showed evidence of increased nutrient leaching from the foliage and surface soil due to precipitation acidity. Similar applications to laboratory soil columns showed no such effect, possibly due to the inclusion of subsoil in the columns. Laboratory soil leaching data were used to estimate annual areal leaching losses of nutrient cations from field sites. These estimates showed considerable differences between the soil types examined, and suggested that some of these soils may naturally exhibit relatively large cation leaching losses. Fine root (<5 mm) biomass and density of three contrasting bigtooth aspen sites were found greatest in the upper 30 cm of soil at each site. These and other observations supported the use of a 1 m depth to assess nutrient reserves in northern lower Michigan forest soil. Data compiled on such reserves showed considerable variation within and among different soil series in the area. Total cation and mineralogical analyses of selected soil samples revealed significant bound reserves of plant nutrients, but these reserves appeared to be in forms relatively resistant to release. Some short-term effects of forest harvest and burning on nutrients in the soil were evaluated for two northern lower Michigan sites harvested by contrasting methods. Abundant slash from clearcutting contributed to significant increases in soil element concentrations following fire, while minimal whole-tree harvest residues generally produced smaller nutrient increases. Cation leaching losses from both sites apparently increased somewhat after burning, and these losses seemed greatest from the clearcut site. Estimated or measured data on precipitation nutrients, leaching losses, nutrient reserves, mineral weathering, and stand nutrient content were compiled for four contrasting northern lower Michigan forest sites. Nutrient budget evaluations employing these data showed potential nutrient depletion on each of these sites under both whole-tree and stem-only clear-cut harvest systems. Alternatives to these harvest systems should receive serious consideration on similar sites in northern lower Michigan, since costly ameliorative techniques may otherwise be required to maintain site productivity.