Print PageAdequate soil moisture availability is critical for determining the growth and productivity of trees and forests. At the Marcell Experimental Forest (MEF) in northern Minnesota, soil moisture has been monitored using a neutron probe technique at ten sites throughout the forest since 1961, giving unique insight into temporal and spatial soil moisture dynamics over the region for the past five decades. A pilot study was established to examine the relationship between forest productivity of three dominant upland cover types in Minnesota (aspen, red pine, and northern hardwoods) and soil moisture availability. Two 1/20th ha plots were established within each cover type and a total of 516 increment cores were collected for analysis. Increment cores were mounted, cross-dated, and measured according to standard dendrochronological procedures. Basal area increment (BAI) was used in place of common standardization techniques as a measure of annual tree growth and stand-level productivity. Growth-climate relationships were calculated using correlation analyses with seasonal soil moisture, mean monthly precipitation, and temperature measurements all collected at the MEF.
Results/Conclusions
Annual forest productivity varied between cover types and all cover types correlated significantly with soil moisture and climate variables (p < 0.05). As expected, red pine exhibited the higher annual growth rates than either aspen or northern hardwood stands. These preliminary results suggest that available soil moisture may be a limiting factor of forest growth in northern Minnesota. The information gleaned from this pilot study will be used to inform and design a larger experimental study comprised of a spatial soil moisture model, additional forest cover plots, and influences of topographic controls on the relationship between tree growth and available soil moisture.
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