The growth response of secondary vegetation to silvicultural treatments, soil and site conditions in the Carnation Creek Watershed, Vancouver Island
Date
1988
Authors
Hays, W. J.
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
A regenerating coastal watershed in the Pacific Northwest is examined to determine silvicultural treatment effects on t he revegetation of nine sites characterized by combinations of burning, scarification and herbicide application. Biophysical site differences are summarized using site factors (including aspect , slope, elevation and moisture regime) and floristic diversity. Differences in site fertility are investigated using essential nutrients in soil and foliage; and vegetative cover of five competing species (Alnus rubra Bong . , Rubus spectabilis Pursh, Gaultheria shallon Pursh, Vaccinium parvifolium Smith and Tsuga heterophylla (Raf . ) Sarg . ) . Principal component analysis (PCA) and analysis of variance (ANOVA) are the principal methods of analysis.
Differences in sites and in floristic diversity are distinguished primarily with respect to elevation, slope and moisture. Scarified soils are associated more with mineral (clay) colloids and often have lower nutrient availability than unscarified soils. Unscarified soils are associated more wit h organic (humic) colloids, often have better horizonation , higher CEC ' s and generally contain more organic matter and total elements N, K, ca, Mg and Na.
Differences in huckleberry cover are not explained by treatment . Although greater huckleberry cover occurs on mesic, south- facing slopes, it is <25% and probably not considered a threat to crop trees . Huckleberry cover is limited by low availability of rooting and canopy space (eg. interspecific competition with salmonberry, alder) .
Salal and Salmonberry cover is greater where available Kand Ca are not limited by alder (eg . in scarified sites) and where high silt and clay contents do not reduce nutrient availability in general. A reduction in available P and Mn that is not induced by alder (eg. in unscarified sites treated with glyphosate) may also limit salmonberry growth. Salal growth is limited by low light intensity (eg . in level or north-facing sites). Greater salal cover occurs in previously burned, south- , southwest- or west-facing sites with implicitly higher diurnal temperatures and minimal interspecific competition .
Greater alder cover is attributed to scarification (eg. production of a mineral seed bed), to the dispersal of clay colloids by high soil Na contents resulting in improved nutrient uptake, and to its inherent ability to fix N in nutrient deficient soils . Alder cover is limited by low availability of Kand Cain clay soils.
Low N availability does not limit hemlock growth but moisture and organic rooting media are fundamentally important. Hemlock is more abundant in hygric, moisture-receiving, low elevation sites treated with glyphosate where salmonberry cover is consequently less abundant . Drier , west-facing, slash-covered sites previously broadcast burned and presently dominated by salal are the poorest growing sites for hemlock.