Response of Understory Vegetation to Fertilization on Mature and Clear-cut Jack Pine Sites in Northern Lower Michigan

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Abstract
A study was established on jack pine sites in northern lower Michigan to investigate the effects of fertilization on the relative growth of understory vegetation on clear-cut and undisturbed sites. The primary objective was to discern if the dramatic increases in Carex pensylvanica following disturbance (e.g., fire and clear-cutting) were in part due to its ability to exploit newly available nutrient resources. Total live shoot biomass as well as live shoot biomass of Carex and blueberry were significantly increased on fertilized blocks in mature jack pine and on clear-cut sites. Fertilized-to-control biomass ratios showed that Carex consistently had an above-average response to fertilization in both mature jack pine and clear-cut sites compared to the community average. Biomass of Carex species from a recent prescribed burn site greatly exceeded that of any other species. During this experiment, neither C. pensylvanica nor any other species appeared to greatly suppress or exclude neighboring species. Although C. pensylvanica showed a preferential uptake of nutrient fertilizer, it is apparent that its expansion following clear-cutting and burning is in response to other factors such as increased space, light, soil temperatures and available moisture, as well as increased nutrient availability.