Abstract
Our understanding of nutrient limitations to jack pine (Pinus banksiana Lamb.) growth is lacking across the Lake States of the USA (Michigan, Wisconsin and Minnesota), where this species makes up an important forest cover type on nutrient poor sands. Currently this cover type is managed using whole-tree harvesting (WTH) across large areas of state and federal forestland, which raises concerns for long-term declines in soil fertility and future productivity. In this study, I carried out a factorial fertilization experiment to better understand potential nutrient limitations to jack pine growth on excessively drained sandy soils in northern Lower Michigan. Treatments were nitrogen (N), phosphorus (P) and base cations applied singly and in all factorial combinations. In addition, I constructed input-output nutrient budgets for jack pine management in northern Lower Michigan using existing data on atmospheric deposition, weathering and harvest nutrient removals. In no case did I observe an increase in tree growth rate to fertilization, instead I observed an overall decline in growth rates, and an increase in mortality rates, in trees fertilized with N. Nitrogen-induced imbalances of foliar N: potassium (K) were strongly correlated with decreased growth in N amended plots. Together with nutrient budget analysis, which indicated that harvest removals of K greatly exceed inputs over the planned rotation, this suggests that WTH may not be sustainable over multiple rotations. Furthermore, the impacts of WTH on ecosystem K status are likely to be exacerbated over time by anthropogenic N deposition.
Highlights
The degree and nature of nutrient limitations to forest productivity have important implications for designing silvicultural systems that will sustain long-term soil productivity, as well as for understanding the impacts of anthropogenic nitrogen (N) deposition on forest productivity
I investigated the nature of nutrient limitations to tree growth in young jack pine (Pinus banksiana Lamb.) plantations in Michigan, USA, in order to better understand the sustainability of current silvicultural practices, and to assess the likely response of this system to anthropogenic N deposition
Both plantations were established by the Michigan Department of Natural Resources (MDNR) to provide breeding habitat for the endangered Kirtland’s warbler (KW; Setophaga kirtlandii) following whole-tree harvesting of a preceding stand of mature jack pine
Summary
The degree and nature of nutrient limitations to forest productivity have important implications for designing silvicultural systems that will sustain long-term soil productivity, as well as for understanding the impacts of anthropogenic nitrogen (N) deposition on forest productivity. A global review of the literature on potassium (K) biogeochemistry has argued that K availability may be as limiting as either N or P for terrestrial productivity [5]. I investigated the nature of nutrient limitations to tree growth in young jack pine (Pinus banksiana Lamb.) plantations in Michigan, USA, in order to better understand the sustainability of current silvicultural practices, and to assess the likely response of this system to anthropogenic N deposition.
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