Armillaria species on small woody plants, small woody debris, and root fragments in red pine stands

The incidence of Armillaria on small woody plants, small woody debris, and root fragments was estimated in red pine (Pinus resinosa Ait.) stands in northeastern Minnesota. Soil core samples 10 cm in diameter, and extending to a depth of either 16 or 25 cm, were collected from 13 stands belonging to three age-classes. Half of the youngest stands had been treated using herbicide. Mycelial fans or rhizomorphs of Armillaria were observed on 13% of the small woody plants and isolated from 8% of them. Including small woody debris and root fragments, 38% of 0–16 cm deep samples had Armillaria. Armillaria was observed on 3% and isolated from 1% of individual substrate units from 0 to 25 cm deep samples. Within a single stand, 0%–67% of the samples and 0%–9% of the individual units had evidence of Armillaria. All but one isolate were Armillaria ostoyae (Romagn.) Herink. Herbicide-treated and untreated red pine stands had similar Armillaria incidence, and there was a trend of incidence inversely related to stand age-class. Large numbers of small woody plants, woody debris, and root fragments were found in red pine stands; varying percentages of these substrates were contributing to the survival of Armillaria and could also be serving as sources of root disease inoculum.

Long-term effects of resource limitation on stream invertebrate drift

We examined the effects of resource limitation on stream invertebrate drift by reducing inputs of terrestrial detritus to a headwater stream in western North Carolina. In the treatment stream, leaf-litter was excluded for 6 years (September 1993 – August 1999), small woody debris was removed for 2 years (September 1996 – August 1998), and large and small woody debris was removed for 1 year (September 1998 – August 1999). Invertebrate abundance in the drift was significantly lower in the treatment stream during the study, but total biomass of invertebrate drift was similar. Although drift densities were higher in the reference stream, a greater proportion of total benthic invertebrate abundance and biomass drifted out of the treatment stream. The proportion of shredder, gatherer, and predator benthic abundance in the drift was significantly greater in the treatment stream, but scraper proportions were higher in the reference stream and filterer proportions were similar for the two streams. Combined data from both streams indicated that the relationship between drift densities and benthic abundance was positive and significant. Our results demonstrate that bottom-up effects of resource reduction in a detrital-based stream influence invertebrate drift, increasing the proportion of the benthic community emigrating from the detritus-poor stream.