loading  Checking for direct PDF access through Ovid


Disturbed areas within the Grand Fir Mosaic (GFM) ecosystem of northern Idaho show little to no natural conifer regeneration. Clear-cut sites are invaded quickly by bracken fern successional communities and seem to be in an arrested state of secondary succession. This study compared the soil solution composition of Andisols supporting bracken fern successional communities with undisturbed forest to determine the effects of shifts in vegetation communities. Treatment areas included undisturbed forest, a 30-year-old bracken fern glade (clear-cut in 1965), and a natural bracken fern glade estimated to be centuries old. The natural bracken fern glade was divided into subplots, one of which has been weeded 2 to 3 times each growing season since 1988. Soil solution was collected in porous ceramic cup lysimeters at 12- and 25-cm depths. Samples were collected from May to July in 1994 and 1995. Solutions were analyzed for pH, Al, and dissolved organic carbon (DOC). The soil solution pH in the 30-year-old glade was consistently lower than in the other sites throughout the sampling period, and the 30-year-old glade was the only site to periodically register below pH 5. The natural bracken fern glade that had been weeded was more similar to the undisturbed forest, suggesting that bracken fern biomass does have an acidifying effect on soil solution. The highest Al concentration recorded was 1.6 mg/L in the 30-year-old glade, whereas in the undisturbed forest Al was often below the detection limit. Aluminum and DOC were found to be positively related, with r values of 0.533 and 0.824 for 1994 and 1995, respectively. These results indicate that bracken fern does have an acidifying effect on soil solution. Aluminum concentrations were lower than reported toxic levels for other conifer species and were correlated with DOC. These two findings suggest that Al toxicity may not be a major factor contributing to the lack of conifer regeneration within the GFM.

Related Topics

    loading  Loading Related Articles