The importance of humus form or forest floor as a principal component of terrestrial forest ecosystems has led to the development of a taxonomic classification of humus forms for BC (first approximation: Klinka et al. 1981; second approximation: Green et al. 1993). This classification, as all others, is based on the field-observable (morphological) features because we expect that they reflect differences in the nature and development of humus forms. However, there is a continuing need to test (1) whether humus forms that appear different are in fact different in their physical, chemical, and biotic properties, and (2) the portability of the classification outside the area in which it was developed. As a result of recent studies of the biotic component of humus forms and recent testing of the classification outside British Columbia (Scandinavia, southeastern Russia, and northeastern China), we have recognized several new diagnostic horizons, and hence new taxa. In this pamphlet, we present synopsis of the third approximation of the classification for review and testing. For more detailed information on the background, methodology, and classification of humus forms, the readers should consult Green et al. (1993). Each humus form is represented by the sequence of organic and mineral horizons that constitute the humus form profile. Identification of a humus form, i.e., giving it a name, requires description of the humus form profile – the identification of master and subordinate horizons. For this reason we have included a description of the horizon designations as well as a synopsis of the classification and a key to the identification of humus forms.

In British Columbia, humus form identification is widely use to infer the level of plant-available soil nutrients. This identification is based on field-observable (morphological) features. We recognize three major humu forms: Mors, Moders, and Mulls - which are differentiated according to the type of F horizon, and the presence/absence of organic matter-enriched Ah horizons. Mors represent humus forms where decomposition is dominated by fungi, with slow decomposition rates and accumulations of organic matter on the soil surface. Mors are characterized by the presence of a Fm (m - mycogenous) horizon. In contrast, Mulls represent humus forms with high rates of decomposition and faunal activity resulting in organic matter being intimately incorporated into the upper mineral soil layer instead of accumulating on its surface. Intermediate on the humus form gradient from Mors to Mull are the Moders. Moders are similar to Mors in that they have accumulations of organic matter on the surface of the mineral soil but decomposition is not fungus dominated, so they lack the diagnostic Fm horizon. The central concept of the Moder is represented by the Leptomoder, which is characterized by a Fz (z - zoogenous) horizon with an active population of soil meso- and microfauna, fungal mycelia are not present or present in small amounts. When both fungal mycelia and faunal droppings can be found, but neither clearly predominate over the other, an Fa (a - amphimorphic) horizon results. Fa horizons are characteristic of Mormoders, an integrade between Mors and Moders. Considering the prevalence of Mormoders and Leptomoders in B.C. and the difficulties in identifying Fa horizons, the aim of this study was to determine whether the morphological features used to differentiate these two Moder humus forms reflects differences in their physical, chemical and biotic properties.

The influence of salal on tree growth has attained considerable attention in coastal British Columbia. Field observations, surveys, and studies in the CWH zone have indicated poor growth performance of crop tree species in salal-dominated plantations and natural immature and old-growth stands. Where sites have been burned and planted, tree growth has improved; similar effects have been observed for naturally regenerated stands. Immature stands that developed after wind disturbance or harvesting feature rapid growth and nearly complete absence of salal. As studies have shown that ericaceous plants negatively impact tree growth, the salal on potential harvest sites has been considered undesirable. This study examined (1) the possible influence of salal on the stand, soil nutrient status and site index, and (2) the relations between site index, salal, plant communities, and site in disturbed, immature, coastal Douglas-fir ecosystems. We compared vegetation and environmental characteristics of 101 ecosystems, and examined differences in foliar and soil nutrient characteristics and site index between stands with high and low salal cover through analysis of variance (ANOVA) and regression analysis.

Changes in forest ecosystem vegetation also bring about changes to the associated soil. In order to maintain forest productivity, it is important to know the effects of tree species upon the soil, especially the influence of deciduous versus coniferous tree species. Many deciduous species increase pH, nitrogen, base saturation and/or accumulation of organic matter in the forest floor. The chemical properties of the forest floor may, in turn, influence the chemical properties of the underlying mineral soil. If a tree species significantly alters the soil, then silviculturists may consider crop rotation between deciduous and coniferous trees or growing mixed-species stands to maintain greater nutrient availability and maintain site productivity. Trembling aspen (Populus tremuloides) and black spruce (Picea mariana) may occupy similar sites in the North American boreal forest. Shade-intolerant aspen is generally a seral species while shade-tolerant black spruce can be a seral species but also forms a major component in late successional stages. This study investigated differences in nitrogen-related soil properties between trembling aspen and black spruce stands on upland sites in the BWBS zone of northeastern BC. We asked two questions: (1) are the differences in soil nutrient properties manifested in both forest floor and mineral soil? (2) To what extent are these differences reflected in the floristic composition of understory vegetation?

Forest managers concerned with maintaining soil productivity must consider the impacts of forestry practices upon the features of a site. One critical feature is the amount and type of organic matter on a site, which may affect soil development. This study addresses the question of whether CWD accumulations increase the intensity of podzolization, thus reducing the long-term productivity of a site.

The boreal forest is confined to the Northern Hemisphere and is the most continuous and extensive forest in the world. In North America boreal forest extends from the Pacific to Atlantic coast spanning over 10° latitude. White spruce (Picea glauca (Moench) Voss), black spruce (P. mariana (Mill.) B.S.P.), and trembling aspen (Populus tremuloides Michx.) are among the dominant tree species. Black spruce and trembling aspen may form pure stands and occupy similar sites as their edaphic amplitudes overlap; however, spruce is rare on water-deficient sites and aspen does not tolerate excess water. Despite many studies conducted in the North American boreal forest, little is known about relationships between the boreal understory vegetation and softwood or hardwood canopy species in different climate regions. Furthermore, the variation in species diversity and succession between the stands dominated by coniferous trees and those dominated by broadleaved trees within the same region is unknown. The objectives of this study are to determine (1) the difference in the species diversity and floristic composition of understory vegetation between black spruce and trembling aspen stands within the same climatic region, and (2) how the species diversity and floristic composition of understory vegetation in each stand type vary with climate, and soil moisture and soil nutrient conditions.

About 100 years ago, groups of European beech were reintroduced into Norway spruce stands in some parts of Germany as a restoration approach. The aim of this approach was to maintain or rehabilitate the ecological function of soil fertility and the regeneration option of beech for the next generation. The effect of beech groups on surrounding spruce stands was studied in the Ore Mountains by recording natural regeneration of beech and humus layer thickness and form. Point pattern statistics were used to analyse the spread of beech regeneration and to determine factors influencing its establishment. It was found that the density of regeneration decreases with increasing distance from the beech group. However, beech regeneration was found up to distances of 69 m. Furthermore, it becomes evident that PAR radiation (maximum regeneration densities at PAR values of 35 W/m²) and fencing (3.41 times higher regeneration density compared to unfenced areas) against deer have a positive influence on beech regeneration density. Ordered categorical models were used to model humus form and non-linear models were used to model humus layer thickness. It could be proven that the most bioactive humus forms and lowest humus layer thicknesses were found within the beech group. With increasing distance to the beech group, the total humus layer thickness and the proportion of mormoder in the spruce stand increased. The positive influence of the beech group on the humus composition extends to about 40 m from the centre of the beech group. Due to the former arrangement of the beech groups in the terrain, the effects can also extend to the spruce stands in between. The hypotheses on the restoration approach of reintroducing groups of beech into spruce stands formulated by foresters 100 years ago can thus be confirmed. For future restoration approaches of spruce stands, groupwise mixtures of beech should be established with a distance of 40–50 m.

The influence of tree species on forest soils has been the subject of study for at least a century. Of particular interest have been western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata Donn ex D. Don) – two of the most common tree species in coastal and southern British Columbia, but each with a different nutrient amplitude. It has generally been found that acid, mycogeneous Mor humus forms develop in hemlock stands, while less acid and more zoogenous Mormoder, Moder, or even Mull humus forms develop in redcedar stands. The objective of this study was to determine the influence of hemlock and redcedar, growing separately and together, on forest floor nutrient properties. The questions addressed were: (1) does each stand type have unique forest floor nutrient properties? and (2) can any forest floor nutrient property discriminate between stand types?