The Influence of Canopy Dominants on Understory .
Vegetation Patterns in an Old-growth Cedar-hemlock Forest.
In stands of western hemlock and western red cedar in Northern Idaho, soils of the two species are clearly dissimilar. Soil around Cedar has a higher pH, extractable calcium, base saturation and nitrification potential than hemlock soil. .
The hemlock and red cedar for this study are located 1km S. of the Roosevelt Grove of Ancient Cedars in N. Idaho and is situated on a glaciofluvial flat along the N. Fork of Granite Creek in the Panhandle National Forest. Annual precipitation on average is 115cm and the elevation is around 1050m. Trees over 1m dbh are frequent and the largest are estimated to be over 500 years old. Also there is no evidence of human disturbance.
In July of 1981, understory vegetation was originally sampled under 10 randomly chosen large hemlock and red cedar. Trees that did not have any large neighbors within a 5m radius of the bole and lacked branches below 3m were used. A transect of four 1-m plots were sampled on the N. and S. sides of each tree. Frequency and mean cover was calculated for each understory species and frequency values from hemlock were compared to the values under cedar using confidence intervals. .
Three years later the same study was surveyed along transects. Forty pairs of hemlock and cedar were selected, each pair consisted of on tree of each species with a dhb greater than 0.5m, trees were between 10 to 15 m apart, and had no low branches. A transect was used sample 18 20x50cm plots, six adjacent and six near the midpoint. Total cover was estimated and stem density of each was determined in each plot. When a species" frequency exceeded 25%, stem densities at all three locations were compared using the Kurskal -Wallis test. Plot locations were also compared using indirect polar ordination.
For both trees cover increased with distance from the bole, but at each of the six plot locations cover under cedars were greater.