Allelopathic interference of
Kalmia angustifolia (Ericaceae) to the growth and establishment of black spruce (
Picea mariana) has been suggested by several authors. The greenhouse studies suggested ...that
Kalmia has potential for nutrient interference. However, these studies do not eliminate probable involvement of allelopathy. Field studies indicate that soils associated with
Kalmia were nutrient-poor particularly for nitrogen, phosphorus, iron, and manganese, and support the hypothesis that
Kalmia has dominated microsites that were nutrient-poor prior to its colonization. The questions addressed in this paper are (i) Is
Kalmia interference to black spruce growth explained by allelopathy? (ii) Can
Kalmia–black spruce allelochemical interactions be better explained by ecosystem-level approach to allelochemicals rather than disturbance-related regeneration ecology of
Kalmia? At present, we do not have compelling direct evidence to support allelopathy as a mechanism of
Kalmia interference to black spruce. However, organic molecules released from
Kalmia into the environment may influence soil mineralization, mycorrhizae, nutrient dynamics, and soil microbial ecology. We hypothesize that synergistic interaction of ecological factors may better explain the interference mechanism of
Kalmia.
Post-fire nutrient flushes are an important precursor to secondary succession in fire-driven boreal forest. We studied the magnitude of changes in post-fire soil nutrient status across a ...chronosequence of ericaceous shrub-dominated boreal forest stands in eastern Newfoundland, Canada. The chronosequence comprised nine stands burned between 1 and 38 years prior to the study. These sites have resisted tree reestablishment following forest fire-induced mortality of black spruce and a concomitant increase in dominance of the ericaceous dwarf shrub Kalmia angustifolia L. Our objectives were: (1) to identify the factors driving soil nutrient status in these post-fire stands dominated by ericaceous plants, and (2) to test hypotheses that specific relationships exist among environmental factors, dominant vegetation and indicators of soil nutrient status. Macronutrients such as NH ₄ ⁺ , total organic N and mineral soil P concentrations showed non-linear declines with time since fire. These parameters were also negatively associated with cover of ericaceous plants. Potential phytotoxins such as total phenolics and aluminium concentrations increased with increasing cover of K. angustifolia. Variability in net ammonification, total P and total phenolic acids in organic soils were strongly related to ericaceous dominance even when the effect of time since fire was partialled out using regression analysis. These findings suggest a strong capacity for ericaceous vegetation to have top-down effects on soil chemical property particularly in the organic horizon with the increase in its post-fire dominance.
Disturbance regimes in much of the boreal forest have shifted from wildfire to clearcutting over the last century, resulting in concerns for biodiversity. Because the boreal forest has evolved under ...a natural fire regimes, we hypothesized that application of prescribed burning (PB) after clearcutting would result in plant communities more similar to wildfire than clearcut only. However, because clearcutting + PB involves multiple disturbances in a short interval, we proposed an alternate hypothesis that clearcutting + PB would result in a species composition and trait assemblage that differ from those that develop after a single wildfire or clearcutting event. We determined species composition, diversity, and trait composition of 17 clearcut, 17 clearcut + PB, and 15 wildfire sites of jack pine (Pinus banksiana) dominated forests in northwestern Ontario, Canada 15—37 years after disturbance. Contrary to our primary hypothesis we found that clearcut + PB formed communities different from wildfire and clearcut, the latter two being similar. Clearcut + PB harbored more early successional species associated with seed banking, wind dispersal, deciduous foliage, and alien origin than wildfire or clearcut sites, which showed no specific trait associations. Taxonomic and trait analysis of clearcut + PB sites exhibited effects of compound disturbances, as observed after short-interval fires, supporting our alternate hypothesis. We concluded that PB after clearcutting formed plant communities significantly different from those developed either after clearcutting or wildfire alone. We attribute this community divergence to the compounding effects associated with the addition of prescribed fire to these previously disturbed forests.
1. Although anthropogenic edges are an important consequence of timber harvesting, edges due to natural disturbances or landscape heterogeneity are also common. Forest edges have been well studied in ...temperate and tropical forests, but less so in less productive, disturbance-adapted boreal forests. 2. We synthesized data on forest vegetation at edges of boreal forests and compared edge influence among edge types (fire, cut, lake/wetland; old vs. young), forest types (broadleaf vs. coniferous) and geographic regions. Our objectives were to quantify vegetation responses at edges of all types and to compare the strength and extent of edge influence among different types of edges and forests. 3. Research was conducted using the same general sampling design in Alberta, Ontario and Quebec in Canada, and in Sweden and Finland. We conducted a meta-analysis for a variety of response variables including forest structure, deadwood abundance, regeneration, understorey abundance and diversity, and non-vascular plant cover. We also determined the magnitude and distance of edge influence (DEI) using randomization tests. 4. Some edge responses (lower tree basal area, tree canopy and bryophyte cover; more logs; higher regeneration) were significant overall across studies. Edge influence on ground vegetation in boreal forests was generally weak, not very extensive (DEI usually < 20 m) and decreased with time. We found more extensive edge influence at natural edges, at younger edges and in broadleaf forests. The comparison among regions revealed weaker edge influence in Fennoscandian forests. 5. Synthesis. Edges created by forest harvesting do not appear to have as strong, extensive or persistent influence on vegetation in boreal as in tropical or temperate forested ecosystems. We attribute this apparent resistance to shorter canopy heights, inherent heterogeneity in boreal forests and their adaptation to frequent natural disturbance. Nevertheless, notable differences between forest structure responses to natural (fire) and anthropogenic (cut) edges raise concerns about biodiversity implications of extensive creation of anthropogenic edges. By highlighting universal responses to edge influence in boreal forests that are significant irrespective of edge or forest type, and those which vary by edge type, we provide a context for the conservation of boreal forests.
Question
In Eastern Canada, wildfires turn Picea mariana forests into Kalmia angustifolia dominated heath or P. mariana forest depending on burn severity. These alternate end‐points of succession ...provide an opportunity to test assumptions concerning alternate successional trajectories dominated by distinct plant functional groups. Disturbance effects on functional diversity (FD) have been studied largely in single post‐disturbance communities, but rarely applied to alternate successional pathways. Do post‐fire Kalmia heaths have lower FD than forest communities, and does heath formation select for a narrow range of traits leading to biotic homogenization?
Location
Terra Nova National Park, Newfoundland, Canada.
Methods
Based on five functional traits (specific leaf area, leaf dry matter content, seed mass, height, specific root length), we measured functional trait dispersion within (alpha FD) and between sites (beta FD). We calculated overall FD metrics in nine heath and four forest sites as well as metrics for three functional groups (trees, shrubs, and herbs) in each site. We also performed a complementary taxonomic diversity (TD) analysis to establish links between FD and TD.
Results
We could not detect a difference in overall alpha TD between the two successional communities but found significant loss of alpha and beta FD in heaths and within tree and herb groups. Overall beta FD was lower in heaths than forests. It was also lower for trees and herbs, indicating an increase in functional similarity (functional homogenization) of the majority of life forms.
Conclusions
Between the two successional pathways, trait space occupancy was lower in heaths than forests. Heath formation in post‐fire communities consistently restricts functional dispersion (low alpha FD) of tree and herb traits leading to functional homogenization (low beta FD). When a successional trajectory leads to heath formation, it is accompanied by a loss of functional diversity.
Mean taxonomic and functional diversity values for dominant three life forms in forest and heath sites (n = 13). Shannon's diversity represents taxonomic α diversity, Bray–Curtis dissimilarity represents taxonomic β diversity, functional dispersion (FDis) represents functional α diversity, and mean pairwise distance (Dpw) represents functional β diversity. Asterisks indicate a significantly higher value at ** p < 0.05 and *** p < 0.01.
•We examined tree regeneration in gaps created by partial harvesting in riparian buffers.•Tree regeneration in small, medium and large gaps were compared and contrasted with uncut buffers.•We found ...dense tree regeneration in medium to large gaps with favorable light and temperature.•Partial harvesting creates desirable habitat complexity by increased seedling growth in gaps.
Partial harvesting in boreal forest riparian buffers has been proposed as a management tool to emulate natural disturbance (END) along streams and lakes to increase shoreline habitat complexity through ensuing forest regeneration. We investigated the effect of partial harvesting in stream-side riparian buffers on regeneration of canopy species (Abies balsamea, Betula papyrifera, Picea glauca, Picea mariana and Populus tremuloides) by testing the hypothesis that juvenile trees would be more abundant, species-rich, and larger in gaps than in non-harvested buffers, and that those differences would be proportional to gap size. Our main objective was to determine what gaps sizes are conducive to promote tree and woody shrub regeneration in stream-side riparian areas of boreal mixedwood forests. We compared woody plant regeneration among harvest gaps varying in size (small, 10–20m2; medium, 21–100m2; and large, >100m2), and contrasted with regeneration under closed canopy in unharvested buffers and undisturbed reference forests. We found that woody plant communities in partial harvesting gaps were denser and more diverse than unharvested buffers. They were more so in medium to large gaps and consisted of shade-intolerant and early successional species. Favorable light and soil temperature in the large gaps appear to be responsible for this. We concluded that intentional shoreline disturbance aiming to achieve increased riparian habitat complexity and early successional forest community is possible by partial harvesting at up to 50% basal area removal. However, as END principles are increasingly applied to riparian forest management, it will be necessary to test and monitor the effectiveness and longer-term ecological responses of riparian communities to such management at catchment and landscape levels.
1. Clearcutting and wildfire are the two major edge-creating disturbances in boreal forests. While clearcutting retains at least a 30 m buffer, wildfires burn close to streams killing most of the ...trees and potentially creating a different edge structure. Different edge structures are likely to support different plant assemblages. The riparian buffer and fire edge structures and their effects on plant assemblages are unknown, but they have implications for forest management that aims to harvest trees and conserve biodiversity by emulating natural disturbance. 2. We hypothesized that environmental filters created by post-fire residual structures at the fire edge will support a different plant assemblage than the buffer edge. We further hypothesized that the fire edge with a weaker environmental filter because of post-fire residual structures and proximity to streams will result in lower depth of edge effects (DEEs) and magnitude of edge effects (MEEs) than buffer edges. 3. We determined the structure of canopy trees, understorey cover and the near-ground microclimate by sampling 576 (5 × 10 m) and 1820 (1 × 1 m) quadrats along 96 transects beside 24 streams near Thunder Bay, Canada. We determined DEEs and MEEs by comparing edge variables with reference forests. We used repeated measures/factorial ANOVAS with Tukey's post hoc tests to determine DEEs and MANO VA for MEEs. 4. The average microclimatic DEEs extended 8 m into the buffer but only 2·5 m from the fire edge.Similarly, the DEEs for plant life-forms extended 20 m from the buffer edge and 5 m from the fire edge. At the fire edge, the structural MEEs were significantly higher, but the microclimatic MEEs were lower than the buffer edge. We found no significant difference in the overall life-form MEEs, but shrubs, shade-tolerant herbs and grasses were increased at the buffer edge and decreased at the fire edge. 5. Synthesis and applications. We discovered that the ecological structure at buffer and fire edges in boreal forests creates different environmental filters supporting different plant assemblages. Lower structural and microclimatic DEEs and MEEs at the fire edge result from (i) edge location, (ii) intact shrub layer and (iii) disturbance-resilient riparian vegetation. We suggest that replacing the conventional sharp edges of the riparian clear-cut buffer with ' feathered' edges by selective harvesting of trees will create wider edges mimicking wildfire legacy and will help to emulate natural disturbance for conserving biodiversity.
BACKGROUND AND AIMS: Belowground competition and allelopathic interference of neighbouring plants play important roles in shaping plant performance. We assessed the effect of belowground interactions ...involving root competition, root exudates and ectomycorrhizal (ECM) association between Kalmia and black spruce on above- and belowground biomass increment and foliar nutrient content of black spruce seedlings. We predicted that root competition and root exudates of Kalmia would exert a negative impact on black spruce performance, while ECM in black spruce would exert positive impacts on its performance. METHODS: In a greenhouse experiment, using the neutral growth medium of peat-vermiculite, we planted Kalmia and black spruce seedling in pairs. We controlled root competition by placing fine wire mesh between the seedlings and applied benomyl fungicide to control ectomycorrhizae. We used activated charcoal to neutralize the potential allelopathic effects associated with root exudates. After 8 months, we evaluated the performance of black spruce seedlings in terms of biomass, abundance of ectomycorrhizal short roots and foliar nutrient concentrations. To determine treatment effects on soil processes, we also analysed soil pH, total phenols, C:N ratio and bioavailable nitrogen (NO₃− and NH₄+) at the end of the experiment. RESULTS: We found a significant effect of root competition on root-shoot ratio and biomass increment in black spruce seedlings, which achieved the highest root-shoot ratio and biomass increment when major root competition was controlled. Kalmia produced twice the root biomass than black spruce. Surprisingly, charcoal and benomyl treatments—which remove the effects of Kalmia allelopathy on black spruce and suppress ECM growth, respectively—had little or no significant effect on overall biomass of black spruce. In contrast, Kalmia biomass increment and root-shoot ratio were maximized in benomyl treatment. Soil pH and C:N ratio were significantly higher in free competition than root exclusion and benomyl treatments and with activated charcoal. CONCLUSIONS: Kalmia root competition mediated by high root biomass is the predominant driver shaping neighbourhood interactions between Kalmia and black spruce, which in turn shape the performance of black spruce seedlings. Root exudates of Kalmia have a very weak effect on black spruce seedling growth.
Dominant understorey shrubs can interfere with tree recruitment and affect forest succession. In boreal forests of eastern Canada, Kalmia angustifolia grows vigorously dominating post-harvest black ...spruce (Picea mariana (Mill.) BSP) forests and interferes with tree regeneration. Kalmia is a dominant understorey in all stages of forest development, but its response to canopy light level is unknown. We studied the morphological and physiological responses of Kalmia in open sun (control) and experimentally low, medium and high shades allowing 100, 60, 32 and 19 per cent of full sunlight representing 0, 40, 68, and 81 per cent shade, respectively. We tested the hypothesis that Kalmia responds positively to moderate shade by adapting morphologically with larger leaf area and fewer flowering shoots and physiologically by increased stomatal conductance, photosynthesis and foliar nitrogen than low or high shade. We found significantly increased leaf area, specific leaf area and decreased flowering shoots with increasing shade. Kalmia aboveground biomass was 31 per cent higher in low shade and 22 per cent lower in high shade compared with control. The highest maximum photosynthetic capacity (A max) of Kalmia (9 µmol CO2 m−2 s−1) was found in control (full sunlight) and the lowest (5 µmol CO2 m−2 s−1) in the medium-shade treatment. We concluded that Kalmia adapts to moderate shade by morphological plasticity, reproductive trade-off (avoiding sexual reproduction) and physiological acclimation to low light.
The objective of this study was to analyze the cardioprotective roles of 3 wild blueberry genotypes and one commercial blueberry genotype by measuring markers of oxidative stress and cell death in ...H9c2 cardiac cells exposed to doxorubicin. Ripe berries of the 3 wild blueberry genotypes were collected from a 10-year-old clear-cut forest near Nipigon, Ontario, Canada (49degrees1'39"N, 87degrees52'21"W), whereas the commercial blueberries were purchased from a local grocery store. H9c2 cardiac cells were incubated with 15 microg gallic acid equivalent/mL blueberry extract for 4 h followed by 5 microM doxorubicin for 4 h, and oxidative stress and active caspase 3/7 were analyzed. The surface area as well as total phenolic content was significantly higher in all 3 wild blueberry genotypes compared with the commercial species. Increase in oxidative stress due to doxorubicin exposure was attenuated by pre-treatment with all 3 types of wild blueberries but not by commercial berries. Furthermore, increase in caspase 3/7 activity was also attenuated by all 3 wild genotypes as well. These data demonstrate that wild blueberry extracts can attenuate doxorubicin-induced damage to H9c2 cardiomyocytes through reduction in oxidative stress and apoptosis, whereas the commercial blueberry had little effect.
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