Azim U. Mallik

Conifer Regeneration Problems in Boreal and Temperate Forests with Ericaceous Understory: Role of Disturbance, Seedbed Limitation, and Keytsone Species Change

Conifer regeneration failure in the presence of dense ericaceous cover resulting from the removal of canopy trees by forest harvesting observed in boreal and temperate forest has been attributed to allelopathy, competition, and soil nutrient imbalance. Ecosystem-level alleopathic effect has been argued as a cause for conifer regeneration failure by citing examples from a species-poor boreal forest in northern Sweden with ground vegetation dominated by crowberry (Empetrum hermaphroditum, Ericales) and New Zealand dairy pastures invaded by nodding or musk thistle (Carduus nutans). This article aims to explain the phenomenon of vegetation shift from conifer forest to ericaceous heath by extending the argument of ecosystem-level impact of ericaceous plants and linking the disturbance-mediated regeneration strategies of the dominant conifer species and the understory ericaceous species with the quality of seedbed substrate that influence the direction of secondary succession. It has been argued that fire severity plays a pivotal role in controlling seedbed quality and the regeneration mechanisms of conifers, which in turn determines the direction of post-disturbance succession. The post-fire-dominated ericaceous plants and their habitat-modifying effects have been explained from the point of view of keystone species concept and their role as ecosystem engineers. In the absence of high severity natural fires the canopy keystone species (conifer) fails to regenerate successfully mainly due to limitation of favorable seedbed. On the other hand, the understory ericaceous plants regenerate vigorously by vegetative methods from the belowground components that survived the fire. Forest harvesting by clearcutting or selective cutting also create similar vigorous vegetative regrowth of ericaceous plants, but conifer regeneration suffers from the lack of a suitable seedbed. Thus in the absence of successful conifer regeneration, the vigorously growing understory ericaceous plants become the new keystone species. The new keystone ericaceous species bring about a significant long-term habitat change by rapid accumulation of plyphenol-rich humus. Ericaceous phenolic compounds have been found to inhibit seed germination and seedling growth of conifers. By forming protein-phenol complexes they cause a further reduction of available nitrogen of the already nutrient-stressed habitat. A low pH condition in the presence of phenolic compounds causes the leaching of metallic ions and forms hard iron pans that impair soil water movement. The phenolic allelochemicals of ericaceous humus are also inhibitory to many conifer ectomycorrhizae. On the other hand, ericaceous plants perpetuate in the community by their stress-tolerating strategies as well as their ability to acquire nutrients through ericoid mycorrhizae. Three mechanisms working at the ecosystem level can be suggested as the cause of vegetation shift from forest to ericaceous heath. These are (1) the absence of high severity natural fire and the limitation of suitable conifer seedbed in the presence of thick humus, (2) increased competition resulting from the rapid vegetative regeneration of understory ericaceous plants after forest canopy opening by harvesting or nonsevere fire, and (3) habitat degradation by phenolic allelochemicals of ericaceous plants causing a soil nutrient imbalance and iron pan formation. Thus, a shift in keystone species from conifer to ericaceous plant in the post-disturbance habitat may induce a retrogressive succession due to ecosystem-level engineering effects of the new keystone species. Vegetation management in conifer-ericaceous communities depends on land management objectives. If the objective is to produce timber and other forest products then the control of ericaceous plants and site preparation is necessary after forest harvesting. Ploughing and liming followed by conifer planting and repeated N fertilization has been applied successfully to promote afforestation of Calluna heathlands in Britain. However, such practice has not been proven successful in the reforestation of Kalmia-dominated sites in eastern Canada. If, on the other hand, the land management objective is to maintain heathlands for herbivore production or conservation of cultural landscape, as in the case of certain Calluna-dominated heathland in Western Europe, then moderately hot prescribed burning is useful as a management tool.

Soil respiration following site preparation treatments in boreal mixedwood forest

Abstract The effects of experimental site preparation treatments on soil respiration were studied in a boreal mixedwood forest. The treatments were: (1) intact forest (uncut); (2) clearcut without site preparation (cut); (3) clearcut followed by mixing of organic matter with mineral horizons (mixed); and (4) plots from which all organic matter was removed (screefed). Soil respiration was measured as carbon dioxide (CO2) evolution from surface soil once a month from June to October, 1994 in the field using infra-red gas analyzer (IRGA). In addition, soil temperature and moisture content were determined once a month during the 1994 growing season and soil organic matter content was determined once in July 1994. Mixed plots had the highest soil respiration rates (0.86 to 0.98 g m−2 h−1), followed by the clearcut (0.68 to 0.84 g m−2 h−1) and uncut plots (0.56 to 0.82 g m−2 h−1), with screefed plots having the lowest respiration rates (0.24 to 0.52 g m−2 h−1) from June to September. Soil respiration of the cut plots was not significantly different from that of the uncut control. The site preparation treatments reduced soil moisture and soil organic matter contents significantly. Changes in soil temperature within treatment at 0, 5 and 10 cm depths and between the treatments were not significant. Observed soil respiration patterns were attributed to changes in soil moisture and organic matter content associated with the various treatments. A laboratory incubation experiment elucidated the effects of organic matter, soil moisture, and temperature on soil respiration rates. Site preparation treatments in boreal mixedwood forests affect soil respiration by modifying the moisture and organic matter content of the soil.

Conversion of temperate forests into heaths: Role of ecosystem disturbance and ericaceous plants

Fire and logging in nutrient-poor temperate forests with certain ericaceous understory plants may convert the forests into heaths. The process of disturbance-induced heath formation is documented by using examples ofCalluna in western Europe,Kalmia in Newfoundland, andGaultheria (salal) in coastal British Columbia. In a cool, temperate climate, rapid vegetative growth ofCalluna, Kalmia, and salal following disturbance results in increasing organic accumulation (paludification), nutrient sequestration, soil acidification, and allelochemicals. These are thought to be the main reasons to conifer regeneration failure in disturbed habitats.If continuation in forest is a land-use objective, then temperate forests with an ericaceous understory should not be logged unless effective silvicultural methods are devised to control the ericaceous plants and restore forest regeneration. Preharvest vegetation control may be considered as an option. Failure to control the understory plants may lead to a long-term vegetation shift, from forest to heathland, particularly in nutrient-poor sites. Successful methods of controllingKalmia andGaultheria, however, have yet to be developed. While theKalmia- andGaultheria- dominated heathlands are undesirable in Canada and the Pacific Northwest, a wide range ofCalluna heathlands of western Europe are being conserved as natural and seminatural vegetation.

Disturbance effects on species diversity and functional diversity in riparian and upland plant communities

Understanding disturbance effects on species diversity and functional diversity is fundamental to conservation planning but remains elusive. We quantified species richness, diversity, and evenness and functional richness, diversity, and evenness of riparian and upland plants along 24 small streams subjected to a range of anthropogenic disturbances in the boreal forest of northwestern Ontario, Canada. We included a total of 36 functional traits related to productivity, competitive ability, reproduction, disturbance tolerance, life history, and tolerance to habitat instability. Using nested ANOVA, we examined the response of diversity indices to disturbance and whether it followed the intermediate disturbance hypothesis (IDH) and varied with habitat stability. We found that, like species richness and diversity, functional richness and diversity reached peaks at moderate disturbance intensity; functional diversity followed the predictions of the IDH. Second, disturbance-habitat-stability coupling has very little effect on overall species and functional diversity, but the effect on particular life forms and functions may be significant. Since species richness and diversity patterns are context and system dependent, our findings should be most applicable to similar temperate riparian systems.

Allelopathy in sustainable agriculture and forestry

History.- Historical Examples of Allelopathy and Ethnobotany from the Mediterranean Region.- Allelopathy: Advances, Challenges and Opportunities.- Allelopathy in Chinese Ancient and Modern Agriculture.- Allelochemicals and Allelopathic Mechanisms.- Allelochemicals in Plants.- Allelopathy: Full Circle from Phytotoxicity to Mechanisms of Resistance.- Allelopathic Mechanisms and Experimental Methodology.- Indirect Effects of Phenolics on Plant Performance by Altering Nitrogen Cycling: Another Mechanism of Plant-Plant Negative Interactions.- Genomic Approaches to Understanding Allelochemical Effects on Plants.- Allelopathy from a Mathematical Modeling Perspective.- Application of Allelopathy in Agriculture and Forestry.- Progress and Prospect of Rice Allelopathy Research.- Rice Allelopathy Research in China.- Recent Advances in Wheat Allelopathy.- Sorghum Allelopathy for Weed Management in Wheat.- Allelochemicals in Pre-cowing Soils of Continuous Soybean Cropping and Their Autointoxication.- Autotoxicity in Agriculture and Forestry.- Black Walnut Allelopathy: Implications for Intercropping.- Plant Growth Promoting Rhizobacteria and Mycorrhizal Fungi in Sustainable Agriculture and Forestry.- Utilization of Stress Tolerant, Weed Suppressive Groundcovers for Low Maintenance Landscape Settings.- Allelopathy in Forested Ecosystems.

Interactions betweenKalmia and black spruce: Isolation and identification of allelopathic compounds

Aqueous extracts of fresh leaves and organic soil of northern sheep laurel (Kalmia angustifolia var.angustifolia) were found to be inhibitory to the growth of black spruce (Picea mariana) germinants. Primary root growth of black spruce was more affected by the extracts than was shoot growth. The growth inhibition caused by the leaf extract was most pronounced under acidic conditions (pH 3–4). The aqueous extract ofKalmia leaves contained ferulic, vanillic, syringic, gentisic,m-coumaric,p-coumaric,o-hydroxyphenylacetic, andp-hydroxybenzoic acids as well as some other unknown compounds. These compounds were isolated from the aqueous extract ofKalmia leaves by ethyl acetate extraction and identified using thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). Bioassay indicated that the overall toxicity of the phenolic compounds to black spruce appeared to increase in the order ofo-hydroxyphenylacetic,p-hydroxybenzoic, vanillic,p-coumaric, gentisic, syringic, ferulic, andm-coumaric acids.

Regeneration of heathland plants following burning

Calluna-dominated heathlands are widespread in N. Britain, especially in the eastern and central part of Scotland. The plant communities of these heathland ecosystems are influenced by regular burning as a land management practice. In a well-controlled fire, regeneration takes place both vegetatively (from surviving stem bases or underground rhizomes) and from seed. But there is always a post-fire successon taking place even in this brief period of vegetation reoovery. In order to understand the biological mechanisms operating in the post-fire succession, the present work was carried out to examine regeneration behaviour of different species. Three ‘regenerative strategies’ were identified: I. Woody low-shrubs with slow bud development to begin with, followed by vigorous and profuse branching, becoming dominant after two years; II. Small herbaceous hemicryptophytes; sprouting not as prolific as in plants of group I, but more vigorous than in plants of group III; III. Geophytes with rapid development, important in the first 2–3 years.

BRYOPHYTE RESPONSES TO MICROCLIMATIC EDGE EFFECTS ACROSS RIPARIAN BUFFERS

Although riparian buffers are an important aspect of forest management in the boreal forest of Canada, little is known about the habitat conditions within buffers, due in part to complex edge effects in response to both the upland clearcut and the stream. We investigated microclimatic conditions and bryophyte growth and vitality in seven locations between the stream edge and 60 m into the upland undisturbed conifer forests and at the clearcut sites with riparian buffer 30 km northwest of Thunder Bay, Ontario, Canada. We hypothesized that the growth and vitality of a pleurocarpous moss, Hylocomium splendens, and an acrocarpous moss, Polytrichum commune, would be directly related to the microclimatic gradients detected. We further hypothesized that sensitivity of the bryophytes to environmental factors will vary depending on their life form type, i.e., pleurocarpous moss will respond differently than the acrocarpous moss. Both bryophyte species were transplanted in pots and placed at 10-m intervals along 60-m transects perpendicular to the stream across the buffer and undisturbed sites. Bryophyte growth, cover, and vitality, as well as microclimatic parameters and plant cover, were measured over the summer in 2003. The riparian buffers were simultaneously affected by microclimatic gradients extending from both the clearcut edge and the riparian-upland ecotonal edge. Both bryophyte species responded to changes in the microclimatic conditions. However, vapor pressure deficit (VPD) was the most important factor influencing the growth of H. splendens, whereas for P. commune growth soil moisture was most important. Our study confirms earlier findings that interior forest bryophytes such as H. splendens can be used as indicators to monitor edge effects and biodiversity recovery following forest harvesting. We demonstrate that growth and vitality of these bryophytes reflect the prevailing near-ground microclimatic conditions at the forest edges. Abundance estimates of such bryophytes can be used to determine the depth of edge effects across both ecotonal edges (e.g., riparian-upland forest edge) and anthropogenically created edges (e.g., clearcut edge). Forest management practices must consider depth of edge in determining the appropriate width of riparian buffers that would be necessary to sustain biodiversity and associated values at the land/water interface.

Effect of Phenolic Compounds on Selected Soil Properties

Abstract The effects of five phenolic compounds, catechol, protocatechuic, p-coumaric, p-hydroxybenzoic, ferulic acids and their mixture were studied on pH, organic matter, organic-nitrogen, total phenolic content and certain inorganic ions of forest mineral soils (Ae and B horizons). The Ae- and B-horizon soils, were amended with 10−4 M concentration of each phenolic compound and their mixture. In general, soil properties were affected by phenolics amendement. However, soils amended with catechol did not influence any of the soil characteristics. Contents of organic matter, nitrogen and phosphate were lower in soils amended with different phenolic compounds compared to the unamended control soil. Significance of the effects of phenolic compounds on soil properties is discussed with regard to allelopathic interactions.

Chemical ecology of plants: allelopathy in aquatic and terrestrial ecosystems.

Problems and prospects in the study of plant allelochemicals: a brief introduction.- Antifungal properties of cyanobacteria and algae: ecological and agricultural implications.- The chemistry and chemical ecology of biologically active cyanobacterial metabolites.- Compounds from Typha domingensis P..- Allelochemicals from sunflowers: chemistry, bioactivity and applications.- Feedback mechanism in the chemical ecology of plants: role of soil microorganisms.- Do allelochemicals operate independent of substratum factors?.- Ecological relevance of allelopathy: some considerations related to Mediterranean, subtropical, temperate, and boreal forest shrubs.- Linking ecosystem disturbance with changes in keystone species, humus properties and soil chemical ecology: implications for conifer regeneration with ericaceous understory.- Black walnut allelopathy: current state of the science.- Allelopathy and agroecology.- Allelochemicals phytotoxicity in explaining weed invasiveness and their function as herbicide analogues.- Shift in allelochemical functioning with selected abiotic stress factors.- Pitfalls in interpretation of allelochemical data in ecological studies: implications for plant-herbivore and allelopathic research.- Biochemical and physiological aspects of pollen allelopathy.