To practice sustainable forest use and maximize timber yield it is essential to understand the processes affecting forest growth and how management practices affect these processes (Landsberg and Gower 1997). Recent research, partially funded by NCASI, has shown that aboveground net primary production (ANPP) of northern hardwood forests is correlated to nutrient availability, which can be directly or indirectly affected by forest management. ANPP was significantly greater for managed even-aged and uneven-aged stands than unmanaged old-growth stands (Gries and Gower 1997). These results are consistent with the observed age-related decline in ANPP for northern hardwood age sequence (Gries and Gower 1997). Gries and Gower (1996) reported a strong positive correlation between both exchangable calcium and potassium and ANPP for different-aged northern hardwood forests in the the Porcupine Mountains Wilderness State Park, Michigan. A similar age-related decline in tree growth and increase sequestration of base cations in woody biomass has been observed for a beech (Nothofagus) forest age sequence in New Zealand (R. Allen, personal communication). Furthermore, Fassnacht and Gower (1997) reported a significant positive relationship between available potassium and ANPP for the dominant upland forests in north central Wisconsin. Although these correlative relationships do not demonstrate cause and effect, they do suggest that soil productivity of northern hardwoods may be constrained by nutrient limitations. Nutrient deficiencies, especially nitrogen, limit timber yield by decreasing canopy photosynthesis and shifting biomass allocation from the stem to fine roots (Linder and Axelsson 1982, Gower et al. 1992, Gower et al. 1996). While it is often assumed that nitrogen is the nutrient that limits forest growth (Kimmins 1987, Vitousek and Howarth 1991), few empirical studies have systematically examined which nutrient(s) limit(s) the growth of northern hardwoods.

In 1997 we initiated a cooperative study (funded by NCASI) with Jim Ferris, Champion International, (Norway, MI) to examine the influence of nutrient amendments on the productivity of northern hardwoods growing on a moderate to fertile soil. This proposal requests funds to continue the ongoing research study to answer the following questions. Are northern hardwood forests nutrient limited? If so, which nutrients are limiting and what is the range of potential increased growth in response to nutrient additions? Lastly, can we use a combination of biosolids (mill sludge and wood ash) to improve the long-term soil productivity of a site and maximize the growth of northern hardwoods? We also propose an optional study to further broaden our understanding of nutrition limitation of growth of northern hardwoods on soils of lower fertility than the current study. The proposed suite of measurements that we will continue to make and initiate (funded by a McIntire-Stennis grant) will improve our understanding of the physiological processes controlling the productivity of northern hardwoods, providing the needed information to place information from this study into a larger context and determine which northern hardwood stands are likely to respond to nutrient amendments.

Publications
Fassnacht, K.S. and S.T. Gower. 1999. Comparison of the litterfall and forest floor organic matter and nitrogen dynamics of upland forest ecosystems in north central Wisconsin. Biogeochemistry 45:265-284

Campbell, J.L. and S.T. Gower. 1999. Detritus production and soil N transformations in old -growth eastern hemlock and sugar maple stands. Ecosystems 3:185-192.

Gower, S.T. and J.R. Gries. 1999. Disturbance effects on aboveground net primary production and the distribution of organic matter and nutrient distribution of northern hardwood forests. Ecosystems 3:185-192.