Gary E. Bradfield

Recreating a Functioning Forest Soil in Reclaimed Oil Sands in Northern Alberta: An Approach for Measuring Success in Ecological Restoration

During oil-sands mining all vegetation, soil, overburden, and oil sand is removed, leaving pits several kilometers wide and up to 100 m deep. These pits are reclaimed through a variety of treatments using subsoil or a mixed peat-mineral soil cap. Using nonmetric multidimensional scaling and cluster analysis of measurements of ecosystem function, reclamation treatments of several age classes were compared with a range of natural forest ecotypes to discover which treatments had created ecosystems similar to natural forest ecotypes and at what age this occurred. Ecosystem function was estimated from bioavailable nutrients, plant community composition, litter decomposition rate, and development of a surface organic layer. On the reclamation treatments, availability of nitrate, calcium, magnesium, and sulfur were generally higher than in the natural forest ecotypes, while ammonium, P, K, and Mn were generally lower. Reclamation treatments tended to have more bare ground, grasses, and forbs but less moss, lichen, shrubs, trees, or woody debris than natural forests. Rates of litter decomposition were lower on all reclamation treatments. Development of an organic layer appeared to be facilitated by the presence of shrubs. With repeated applications of fertilizers, measured variables for the peat-mineral amendments fell within the range of natural variability at about 20 yr. An intermediate subsoil layer reduced the need for fertilizer and conditions resembling natural forests were reached about 15 yr after a single fertilizer application. Treatments over tailings sand receiving only one application of fertilizer appeared to be on a different trajectory to a novel ecosystem.

Adaptive Differentiation in Response to Water Stress by Edaphic Races of Lasthenia californica (Asteraceae)

Two edaphic races of Lasthenia californica sensu Ornduff (races A and C) grow in parapatry on a serpentine outcrop at Jasper Ridge Biological Preserve, California. The races occupy distinct edaphic habitats that have different water‐holding capacities. We predict that the two races will show differentiation in reproductive strategies related to their response to water stress. In order to test this hypothesis, we performed a greenhouse experiment to characterize the reaction norms of the two races exposed to a gradient in water availability. We measured the response of five variables to the watering treatments: early survivorship, days to flowering, root/shoot dry mass ratio, total dry mass, and a measure of reproductive fitness, number of flower heads. We found that the races differ in their allocation patterns to roots compared with shoots and in days to flowering, indicating genetic differentiation for these traits. Race A consistently allocates relatively more biomass to roots while race C flowers earlier. However, the reaction norms of the two races for all nonreproductive traits are parallel, indicating that races do not differ in their plastic response to drought stress. The number of flower heads, our measure of reproductive fitness, did, however, exhibit differential response to water availability between the two races. Under low watering treatment, race C plants are able to maintain flower head production, while race A plants show a monotonic decrease in head production as water stress increases. Results indicate that race C plants are better adapted to drought; they are able to maintain a high reproductive output under low water availability. However, as the phenotype of race A is affected by drought, reproductive output decreases, as we would predict for plants that rarely experience drought in their natural environment.

Epiphytic vegetation on Acer macrophyllum: a multivariate study of species-habitat relationships

Multivariate methods were used to examine epiphytic species composition on the lower trunk of Acer macrophyllum at five sites in south-coastal British Columbia, Canada. Differences in species composition and abundance between sites were attributed mainly to variation in relative humidity and light conditions. Bark chemistry differences accounted for only a small portion of the observed variation in epiphytic composition between sites. Within sites, compositional variation was examined over 0.5–5 m from ground level on the upper, vertical, and lower trunk surfaces of leaning trees. Compositional variation of the epiphytic vegetation with height and inclination tended to be more strongly developed at drier sites. Furthermore, at all sites compositional variation tended to be greater on upper (wetter) than on lower (drier) surfaces. Particular epiphytic species tended to occur in similar locations on the trunk surface at different sites, suggesting that some microhabitat specialization has occurred. Observed distributional shifts of epiphytic species appeared to be greatest among sites differing widely in prevailing microenvironmental conditions.

Succession in sub-boreal forests of West-Central British Columbia

Abstract Structural and compositional changes were analysed over the course of 400+ yr of post-fire succession in the sub-boreal forests of west-central British Columbia. Using a chronosequence of 57 stands ranging from 11 to 438 yr in age, we examined changes in forest structure and composition with complementary PCA and DCA ordination techniques. To determine stand ages and timing of tree recruitment, approximately 1800 trees were aged. Most early successional forests were dominated by Pinus contorta, which established rapidly following fire. Abies lasiocarpa and Picea glauca ×engelmannii were also able to establish quickly, but continued to establish throughout the sere. Few Pinus contorta survived beyond 200 yr, resulting in major changes in forest structure. In some stands P. contorta never established, which led to considerable variation among stands less than 200 yr old. The oldest forests converged on dominance by Abies lasiocarpa. Vascular plant diversity decreased during succession whereas canopy structure became more complex as gap dynamics developed. Although these sub-boreal forests contain few tree species, successional changes were pronounced, with structure changing more than composition across the chronosequence. Abbreviations: CWD = Coarse Woody Debris; DCA = Detrended Correspondence Analysis; DBH = Diameter at Breast Height; PCA = Principal Component Analysis. Nomenclature: Douglas et al. (1989–1994).

Correlations among vegetation strata and environmental variables in subalpine spruce-fir forests, southeastern British Columbia

A set of forest vegetation-environment data consisting of 110 plots from subalpine spruce-fir forests in southeastern British Columbia was analyzed with multivariate methods. The aims were to describe and compare relationships among plots using species composition data from four strata of the forest (trees, shrubs, herbs, bryophytes), and to compare patterns in the separate strata with patterns in the environmental data. Weak but statistically significant correlations were detected among PCA axes from all four strata, with a tendency for correlations to be stronger between axes of adjacent strata. Relationships between stratal patterns and environmental variation were examined by correlating PCA axes with environmental variables separately, and jointly with canonical correlation analysis. Linear composites of the environmental data identified by the first canonical axis were similar for shrub, herb, and bryophyte strata implying similar responses to environmental variation in understorey strata; however, < 16% of the total variance was explained. No clear relationships emerged between tree stratum and environmental variation. Probable determinants of pattern in the tree stratum include historical events such as fire and winter snowpack, as well as possible interactions between species. Collectively, these events bear little resemblance to existing environmental conditions in the forest.

Ordination of epiphytic bryophyte communities in a wet-temperate coniferous forest, South-Coastal British Columbia

Three coniferous tree species (Pseudotsuga menziesii, Tsuga heterophylla, and Thuja plicata) at Capilano Canyon, British Columbia, were studied for their epiphytic communities. Quantitative data were obtained for fourteen bryophyte species by sampling at heights of 0.5 m, 1 m and 2 m above ground level. Scapania bolanderi is an abundant and widely distributed species; Dicranum fuscescens, Bazzania denudata, Lepidozia reptans and Hypnum circinale are also common. An environmentally uniform study area was chosen to minimize the effects of factors other than bark and elevation on the distribution of epiphytes. In general, tree species are similar in terms of their epiphytic assemblages, but ordination methods using quantitative data exposed compositional variation that may be explained by differences in microclimate and bark-type. In this respect, the results point the way to further studies to examine epiphyte associations in closer detail, and to relate these associations to specific factors in the microenvironment.

An initial comparison of growth rates in the rare grass Achnatherum hendersonii and its common associate Poa secunda

The rare grass, Achnatherum hendersonii (Vasey) Barkworth, and the more widely distributed Poa secunda J. S. Presl grow together on shallow soils derived from basaltic rock that are subject to cryogenic disturbance. It has been proposed that the solifluction allows A. hendersonii to persist by inhibiting the competitive ability of P. secunda. A correlate of this proposal is that P. secunda will have a superior growth rate in undisturbed soils. This idea was tested by growing both species in potting soil, both singly and in combination. Under these conditions, P. secunda grew faster and attained a larger above-ground size than A. hendersonii. Thus, one factor allowing the survival of the rare A. hendersonii seems to be its occurrence on sites where the competitive ability of a wide-ranging species is restricted. The survival of A. hendersonii on disturbed sites may also be partly explained by its roots that are apparently adapted to growing where solifluction occurs.

Long-term grazing effects on rough fescue grassland soils in southern British Columbia

Krzic, M., Lamagna, S. F., Newman, R. F., Bradfield, G. and Wallace, B. M. 2014. Long-term grazing effects on rough fescue grassland soils in southern British Columbia. Can. J. Soil Sci. 94: 337-345. Rough fescue (Festuca campestris Rydb.) is a highly palatable forage species with little resistance to continuous grazing. The objective of this study was to evaluate the effects of long-term cattle grazing on soil properties, above-ground biomass, and canopy cover of key grass species on rough fescue grasslands in the southern interior British Columbia. Soil and vegetation properties were determined on a total of six open grassland sites located at the Lac du Bois and Hamilton Mountain. At all sites, grazing use has decreased over time, with the heaviest grazing occurring prior to 1960. The long-term (25-75 yr) elimination of grazing on these semi-arid grasslands has led to greater above-ground biomass and canopy cover of rough fescue, as well as increased soil polysaccharides; however, no differences in total soil C, N, and aggregate stability were found between pastures with and without grazing. Both soil bulk density and mechanical resistance were greater on grazed plots compared with those without grazing, with differences being more pronounced at the Hamilton Mountain location. The current grazing regime has not allowed for the elimination of negative effects of overgrazing on soil compaction on these rough fescue grasslands, especially at the location that continued to be grazed more heavily (i.e., Hamilton Mountain). Our findings suggest that soils in these grazing-sensitive grasslands need more than 75 yr to fully recover from the impacts of overgrazing.

Transient assemblage dynamics of terrestrial bryophytes in a subalpine forest

Abstract The concept of transient assemblage dynamics (TAD) is introduced relating to the fine-scale temporal and spatial variability in substrate locations that result in greater unpredictability in bryophyte-microhabitat relationships within certain sites. An analytical test for the occurrence of TAD in a subalpine forest floor bryophyte community is outlined based on a multivariate comparison of within-plot (400m2) heterogeneity in bryophyte species assemblages and concomitant habitat conditions in sites of differing ground level stability. Plots with a higher potential for ground level turbulence showed a weaker relationship between bryophyte and habitat heterogeneity (i.e., greater degree of TAD), whereas this relationship was stronger in plots with greater ground level stability. We conclude that TAD may result in a substantial decoupling of fine-scale species-habitat linkages and recommend use of a multi-scale sampling and analytical approach for ecological studies of bryophyte communities where explanatory relationships may change at different scales.

Pupal sampling of the western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst) (Lep., Geometridae) using burlap traps

Abstract: Three types of burlap traps were designed and tested for the western hemlock looper, Lambdina fiscellaria lugubrosa, in the interior of British Columbia from 1993 to 1994. While the first two trap types provided the means for examining the responses of pupating larvae to various layers of burlap band and pocket structure, the third trap type, which had the desirable burlap layers and structure, was used as a sampling tool for the insect. The effects of tree diameter, crown ratio, crown class, defoliation class and basal areas on trap capture appeared to vary with locations. However, a high correlation between trap capture and actual population density was consistently present. Therefore, trap capture can be used as an estimator of actual population density.