Bradley D. Pinno

Competition control in juvenile hybrid poplar plantations across a range of site productivities in central Saskatchewan, Canada.

The response of hybrid poplar plantations established on former agricultural land in Saskatchewan to competition from weeds on a range of site productivities was studied. The short-term impact of competition control on the growth of juvenile trees and how tree responses to competition control differed across the productivity gradient was of particular interest, as was the determination of which resource was most highly competed for and was most important in determining tree growth. Eight sets of paired plots in juvenile hybrid poplar plantations were established in central Saskatchewan across a range of site productivities. In each pair, one plot had complete weed control (weed-free) while in the other plot weeds were allowed to grow. The best soil predictor of tree growth was soil texture, represented by a combination of the percentage silt and clay, with finer textures showing better growth. Competition control significantly increased tree growth on all sites with the benefit being greatest on the higher productivity sites. Soil water appeared to be highly competed for between trees and weeds and was a dominant resource controlling growth. For soil nutrients, nitrogen and phosphorous were highly competed for between trees and weeds. However, leaf phosphorous concentration of the weed-free plots had a strong positive relation to tree growth while nitrogen did not, indicating that when trees are free of competition they can access sufficient nitrogen from these soils.

Fine root dynamics of trembling aspen in boreal forest and aspen parkland in central Canada

Abstract• Fine root responses to potential climate change are relatively unknown in spite of their central role in ecosystem functioning.• We quantified fine root length, production, and turnover in boreal forest and aspen parkland of central Canada because the future climate of the boreal site is expected to be similar to the current climate of the parkland site.• Root depth distribution and turnover were similar between sites. Fine root mass was 4× greater at the parkland site and root length was 10× greater. Accordingly, the ecosystem level fine root: leaf mass ratio was 1.6 in the boreal site compared to 4.3 in the parkland site. On a per tree basis, however, fine root biomass was similar between sites due to the higher stem density of the parkland site.• The parkland site had a greater proportion of very fine roots (62% of the fine roots were < 0.1 mm in diameter) compared with the boreal site (82% of the fine roots were between 0.1–0.5 mm in diameter).• These differences indicate a large-scale shift towards increased root allocation at the parkland site associated with decreasing water availability and earlier successional stage.

Early Successional Plant Community Dynamics on a Reclaimed Oil Sands Mine in Comparison with Natural Boreal Forest Communities

ABSTRACT Forming the majority of plant diversity in boreal forests, understory communities are important drivers of nutrient cycling and overstory succession. In western Canadian boreal forests, fire is the primary mechanism of natural disturbance, with oil sands mining a substantial anthropogenic disturbance in north-eastern Alberta. An operational reclamation trial, at an oil sands mine, was established the same year as a nearby forest fire, allowing for direct comparison of plant community development between reclaimed and naturally regenerated fire-origin and mature stands. This work reflects a case study with large, but unreplicated, areas of both fertilized and unfertilized reclamation treatments on forest floor-mineral mix (FFMM) and peat-mineral mix (PMM) capping materials. After three years, reclamation sites are compositionally distinct from post-fire and mature natural stands, with more non-native species in reclamation treatments than in natural stands. Communities developing on FFMM are more similar to post-fire successional communities than those on PMM, with high species richness and diversity on FFMM comparable with post-fire stands. Cover soil had a stronger impact on plant community development than fertilization, with fertilization effects dependent on cover soil. A standard dose of fertilizer lowered richness and diversity on FFMM and is not recommended for use with that soil.

Different Root and Shoot Responses to Mowing and Fertility in Native and Invaded Grassland

Abstract Grassland root responses to mowing and fertility are less well known than shoot responses, even though as much as 90% of productivity in semiarid grasslands occurs belowground. Thus, understanding root responses may aid the management of invasive grassland species such as Agropyron cristatum (L.) Gaerth (crested wheatgrass). We asked whether root responses reflect shoot responses to mowing and fertility in native grassland with and without a major component of crested wheatgrass. We subjected grasslands in northern Montana to 5 yr of mowing at two nitrogen (N) levels and followed root responses with minirhizotrons. Surprisingly, the roots of both native and invaded grasslands were unaffected by mowing and N addition, despite significant changes in shoot mass across both vegetation types. Root length was significantly greater beneath areas heavily occupied by crested wheatgrass (363 m · m−2 image ± 200, mean ± standard deviation [SD]) than areas comprising largely native grassland (168 m · m−2 image ± 128 SD). Also, no interactions occurred between year and any other factor, indicating that there were no changes in belowground responses over the 5 yr examined. In contrast, shoot mass was significantly reduced by mowing (not mowed, 612 g · m−2 ± 235 SD; mowed, 239 g · m−2 ± 81 SD) and was significantly increased by N addition (no added N, 380 g · m−2 ± 215 SD; added N, 488 g · m−2 ± 287 SD). In conclusion, 5 yr of mowing decreased shoot mass, but not root mass. On the other hand, 5 yr of N addition increased shoot mass, but not root mass. Given that most production and competition in grasslands occurs belowground, this suggests that mowing may not be a successful tool for reducing crested wheatgrass root length, regardless of soil fertility.

Ecosystem carbon changes with woody encroachment of grassland in the northern Great Plains

Abstract: Woody encroachment of grasslands is a common phenomenon worldwide, but the consequences of this encroachment for ecosystem carbon storage, particularly belowground are not clear. We quantified total ecosystem carbon in the 3 major natural upland vegetation communities (grassland, shrubland, and forest) at the northern edge of the North American Great Plains. Total ecosystem carbon storage was significantly greater in forest (125.3 mg C·ha-1) than in shrubland (92.4 mg C·ha-1) or grassland (80.7 mg C·ha-1), and this difference was due mainly to greater aboveground biomass, coarse root biomass, and the presence of a humus layer in the forest. Fine and total root biomass were also greater in forest than shrubland or grassland. In contrast, soil carbon was significantly greater in shrubland (80.6 mg C·ha-1) and grassland (75.4 mg C·ha-1) than in forest (48.6 mg C·ha-1). We also investigated whether aboveground variables could be used to predict belowground carbon pools. Soil carbon increased significantly with aboveground herbaceous biomass, while fine root biomass increased with foliar biomass, but the strongest relationship was between total root biomass and total aboveground biomass (r 2 = 0.785). These are simple and effective predictors of belowground carbon pools. The rapid shift in carbon storage with forest encroachment, from being dominated by soil carbon in grassland to woody vegetation in forest, represents a significant change in ecosystem structure with implications for the carbon budget.

Fine root response to soil resource heterogeneity differs between grassland and forest

Soil resource heterogeneity has clear effects on plant root development and overall plant performance. Here we test whether contrasting vegetation types have similar or different responses to soil patches of differing resource availability. We examined the fine root responses of grassland and forest vegetation at the northern edge of the Great Plains to transplanted patches of resource-poor and resource-rich soils, using rhizotron imaging. Every aspect of measured root behavior, including root length, production, mortality, turnover, variability and size distribution, varied significantly between patch types, and most aspects also varied between vegetation types. Most importantly, differential responses to patches between grassland and forest were shown by significant interactions between patch type and vegetation for two response variables. First, root length variability was significantly lower in resource-rich compared to resource-poor patches in forest but not grassland. Second, the proportion of very fine roots was significantly greater in resource-rich than resource-poor patches in forests but not grassland. Thus, compared to grassland, forest more fully occupied resource-rich patches relative to resource-poor patches by allocating more growth to very fine roots. We report the first example of significant differences between vegetation types (grassland and forest) in root responses to soil resource heterogeneity measured in a field experiment. The relatively high ability of forest roots to more fully occupy resource-rich patches is consistent with the global expansion of woody vegetation and associated increases in soil heterogeneity.

Estimating trembling aspen productivity in the boreal transition ecoregion of Saskatchewan using site and soil variables

Pinno, B. D. and Bélanger, N. 2011. Estimating trembling aspen productivity in the boreal transition ecoregion of Saskatchewan using site and soil variables. Can. J. Soil Sci. 91: 661-669. The productivity of trembling aspen, as expressed by site quality index (SQI), in natural stands growing on three different soil parent material types (fluvial, lacustrine and glacial till) in the boreal transition ecoregion of Saskatchewan was evaluated by using soil and site variables. The soil and site variables used were either general categorical variables, such as parent material and ecosite, or continuous variables, such as soil texture (percent sand or clay), pH, carbon, nitrogen, C:N ratios, and elemental composition. It was not possible to reliably estimate SQI using only categorical site variables or continuous soil variables when all plots were grouped together. However, when plots were grouped by parent material type, over 45% of the variability in trembling aspen productivity was explained using the common soil measurements of texture and pH. In estimating SQI, there was an interaction between both pH and soil texture with parent material. On fluvial and lacustrine parent materials, increased clay content was positively correlated with SQI, but was negatively correlated with SQI on till, while pH was positively correlated with SQI on fluvial parent material, but negatively on lacustrine. Including more sophisticated measures of soil nutrient availability in the forest floor and BC horizons did not improve the SQI prediction. This study indicates that it is possible to estimate trembling aspen productivity using simple site and soil variables, provided that differences in soil properties within parent material groupings are considered in the analysis.

Nitrogen translocation between clonal mother and daughter trees at a grassland–forest boundary

There is abundant evidence from short-term experiments using herbs that nutrients can be translocated from mother ramets to daughter ramets, but there is little long-term evidence from woody plants. Here, we examine translocation in field populations of a clonal tree over two growing seasons. We applied 15N to mothers or daughters in clones of Populus tremuloides at the northern edge of the North American Great Plains, where mother ramets form closed-canopy stands on relatively nutrient-rich soils, and daughter ramets occur nearby in relatively nutrient-poor grasslands. Unlabeled daughters in clones with labeled mothers had δ15N values significantly greater than those in unlabeled clones, confirming translocation from mothers to daughters. However, unlabeled mothers in clones with labeled daughters also had δ15N values significantly greater than those in unlabeled clones, indicating translocation from daughters to mothers. Further, the total foliage accumulation of added 15N was significantly (c. 10×) greater in mothers than in daughters, suggesting that more N was translocated from daughters to mothers, than from mothers to daughters. Thus, 15N moved both from mothers to daughters and from daughters to mothers, with net flow toward mothers. Because long-lived woody ramets in the field face nutrient competition from other ramets, interspecific neighbors, and soil microbes, the environmental availability of nutrients for uptake may be low for both mother and daughter ramets, causing translocation within a clone to be toward larger ramets with greater demand.

Reclaimed soils, fertilizer, and bioavailable nutrients: Determining similarity with natural benchmarks over time

Abstract: Comparing functional similarity in reconstructed ecosystems with natural benchmarks can provide ecologically meaningful information to measure reclamation success. We examined nutrient supply rate using ion-exchange resins as a measure of ecosystem function in two oil sands reclaimed soils, viz. peat mineral mix (PMM) and forest floor mineral mix (FFMM), and measured fertilization effect on nutrient supply rates in these soils for three consecutive years contrasted with young-fire-disturbed and mature forest stands. Results indicated that nutrient profiles of reclaimed soils were significantly different than natural benchmarks. Phosphorus and potassium supply rates in reclaimed soils were up to 91% lower, whereas S, Ca, and Mg were, respectively, up to 95%, 62%, and 74% higher than in benchmark soils. The expected nutrient flush postfertilization was only apparent in N and P, but the transient effect levelled off the year after fertilization in most cases. Fertilization aligned the temporal trajectory of the nutrient profile in PMM similar to benchmark conditions indicating greater ecological benefit of fertilization than in FFMM. The findings from this study suggest that fertilization focusing on P and K is likely more ecologically appropriate for establishing natural ecosystem function on reclaimed soils in this region of the boreal forest.

Inconsistent Growth Response to Fertilization and Thinning of Lodgepole Pine in the Rocky Mountain Foothills Is Linked to Site Index

Fertilization of conifers often results in highly variable growth responses across sites which are difficult to predict. The goal of this study was to predict the growth response of lodgepole pine (Pinus contorta var. latifolia) crop trees to thinning and fertilization using basic site and foliar characteristics. Fifteen harvest-origin stands along the foothills of the Rocky Mountains of Alberta were subjected to six treatments including two levels of thinning (thinning to 2500 stems per hectare and a control) and three types of fertilization (nitrogen-only fertilization, complete fertilization including nitrogen with added P, K, S, Mg, and B, and no fertilization). After three growing seasons, the growth response and foliar status of the crop trees were examined and this response was related to site and foliar characteristics. There was a small and highly variable additive response to fertilization and thinning; diameter growth of crop trees increased relative to the controls an average of 0.3 cm with thinning, 0.3 cm with either N-only or complete fertilization and 0.6 cm when thinned and fertilized. The increase in diameter growth with thinning and nitrogen-only fertilization was positively related to site index but not to any other site factors or pretreatment foliar variables such as nutrient concentrations, ratios, or thresholds.