ABSTRACT The ability of soil microbial communities to withstand punctual disturbance or chronic s... more ABSTRACT The ability of soil microbial communities to withstand punctual disturbance or chronic stress is important for the stability of ecosystem processes. Factors controlling microbial community composition or soil resource availability should be regarded as potential determinants of this stability. Here, we explored the effects of three stand types (jack pine, aspen and mixed-wood) and two geologic parent materials (clay and till), on the stability of the microbial biomass in the forest floor. We hypothesised that microbial communities in mixed-wood stands or on the clay soil would show greater resistance to, and resilience from, a dry–wet disturbance, and a higher tolerance to incremental additions of HCl or Cu, than microbial communities in mono-specific stands or on the till soil. We also surveyed the understory vegetation, and measured chemical properties and microbial phospholipid fatty acid profiles in the forest floor, so as to gain insights into the factors regulating microbial stability. Microbial resistance to disturbance was found to be higher in mixed-wood than in mono-specific stands. Microbial communities from mixed-wood stands also showed a high tolerance to HCl and Cu stress over both geologic parent materials, as opposed to those in mono-specific stands that showed a high tolerance to stress on only one type of parent material. Some forest floor properties in mixed-wood stands (e.g. Ca on clay, mineralisable N and C/N ratio on till) were more similar to the more productive aspen, than to jack pine stands. Other properties (understory plant communities, pH, actinomycete and arbuscular mycorrhizae) of mixed-wood stands were transitional between those in aspen and jack pine stands, suggesting that both tree species contribute in structuring the forest floor microbial pool in mixed-wood stands. We put forward that this may provide a more diverse capability to resist disturbance and tolerate stress than in mono-specific stands. We found no effect of stand type on microbial resilience to disturbance, but resilience was higher on clay than on till plots. This could be due to a higher fungal/bacterial ratio on till plots, as slower fungal growth rates may hinder resilience, or to lower carbon and nutrient availability limiting the growth rate of resistant microbial cells. We conclude that plant diversity and site productivity are important drivers of forest floor microbial stability in the southern boreal forest of eastern Canada.
ABSTRACT Aims Natural disturbances leave long-term legacies that vary among landscapes and ecosys... more ABSTRACT Aims Natural disturbances leave long-term legacies that vary among landscapes and ecosystem types, and which become integral parts of successional processes at a given location. As humans change land use, not only are immediate post-disturbance patterns altered, but the processes of recovery themselves are likely altered by the disturbance. We assessed whether short-term effects on soil and vegetation that distinguish wildfire from forest harvest persist over 60 years after disturbance in boreal black spruce forests, or post-disturbance processes of recovery promote convergence of the two disturbance types. Methods Using semi-variograms and Principal Coordinates of Neighbour Matrices, we formulated precise, a priori spatial hypotheses to discriminate spatial signatures following wildfire and forest harvest both over the short- (16–18 years) and long-term (62–98 years). Results Both over the short- and the long-term, wildfire generated a wide spectrum of responses in soil and vegetation properties at different spatial scales, while logging produced simpler patterns corresponding to the regular linear pattern of harvest trails and to pre-disturbance ericaceous shrub patches that persist between trails. Conclusions Disturbance by harvest simplified spatial patterns associated with soil and vegetation properties compared to patterns associated with natural disturbance by fire. The observed differences in these patterns between disturbance types persist for over 60 years. Ecological management strategies inspired by natural disturbances should aim to increase the complexity of patterns associated with harvest interventions.
... al. 1987; Zak & Pregitzer 1990; Grigal et al. 1991), Correspondence: Dr J... more ... al. 1987; Zak & Pregitzer 1990; Grigal et al. 1991), Correspondence: Dr Joan Ehrenfeld, 126 Environment and Natural Resource Science Building, Cook College, Rut-gers University, New Brunswick, NJ 08903, USA. for ecosystems ...
ABSTRACT The practice of careful logging has been mandated in northeastern Canada’s coniferous an... more ABSTRACT The practice of careful logging has been mandated in northeastern Canada’s coniferous and mixedwood forests as a means of protecting natural regeneration while minimizing soil disturbance by machinery. This practice imposes evenly spaced, parallel trails for circulation of harvesting machinery, while most of the understory and soil is left intact in wide protection strips between the trails. The objective of this study was to examine soil physico-chemical and microbial properties, and ericaceous shrub performance (aboveground biomass) following careful logging and with or without subsequent scarification. By sampling 32 cutover forest sites (formerly black spruce-dominated) in the Abitibi-Temiscamingue region of boreal northwestern Quebec, we evaluated how (a) the presence of alternating bands of protection strips and skid trails (on non-scarified sites), and (b) a scarification treatment consisting of mixing the soil organic layer with the surface mineral soil, influenced soil and vegetation properties over time (4–15 years after careful logging). On non-scarified sites, careful logging showed a differential compaction pattern consisting of bands of disturbed zones or trails alternating with protection zones. Both soil properties and ericaceous shrub biomass estimates tracked these alternating compacted and non-compacted areas on the cutover. Soil N (Nt), soil percentage microbial C to total C (Cmic/Ct), and Kalmia angustifolia (Kalmia) and Vaccinium spp. (Vaccinium) aboveground biomass differed on strips and trails 8 and 15 years after harvest. The observed differences in ericaceous shrub biomass between strips and trails, and correlations between biomass and soil variables, suggest potential shrub interference with soil processes. These observations suggest that ericaceous species may promote differences in soil properties and plant communities that result in a long-term spatial signature perpetuating the trail pattern. Scarification reduced Kalmia and Vaccinium aboveground biomass and had a negative effect on Cmic/Nmic and Cmic/Ct, 15 years after harvest. Forest understory plants, such as ericaceous shrubs, may play a key role in driving belowground properties, forest regeneration, and long-term succession on these sites. Understanding the ecology and spatial distribution of these species may thus have important implications for ecosystem structure and function as well as timber production.
... 2.17 ± 0.13 mg C/g in the organic-surface plots and 1.44 ± 0.11 mg C/g in the substitute-surf... more ... 2.17 ± 0.13 mg C/g in the organic-surface plots and 1.44 ± 0.11 mg C/g in the substitute-surface plots (JG Ehrenfeld ... populations and that their activity is through reductions in moisture and/or available nutrients (Gadgil and Gadgil 1975, Harmer and Alexander 1985, Fisher and ...
ABSTRACT The ability of soil microbial communities to withstand punctual disturbance or chronic s... more ABSTRACT The ability of soil microbial communities to withstand punctual disturbance or chronic stress is important for the stability of ecosystem processes. Factors controlling microbial community composition or soil resource availability should be regarded as potential determinants of this stability. Here, we explored the effects of three stand types (jack pine, aspen and mixed-wood) and two geologic parent materials (clay and till), on the stability of the microbial biomass in the forest floor. We hypothesised that microbial communities in mixed-wood stands or on the clay soil would show greater resistance to, and resilience from, a dry–wet disturbance, and a higher tolerance to incremental additions of HCl or Cu, than microbial communities in mono-specific stands or on the till soil. We also surveyed the understory vegetation, and measured chemical properties and microbial phospholipid fatty acid profiles in the forest floor, so as to gain insights into the factors regulating microbial stability. Microbial resistance to disturbance was found to be higher in mixed-wood than in mono-specific stands. Microbial communities from mixed-wood stands also showed a high tolerance to HCl and Cu stress over both geologic parent materials, as opposed to those in mono-specific stands that showed a high tolerance to stress on only one type of parent material. Some forest floor properties in mixed-wood stands (e.g. Ca on clay, mineralisable N and C/N ratio on till) were more similar to the more productive aspen, than to jack pine stands. Other properties (understory plant communities, pH, actinomycete and arbuscular mycorrhizae) of mixed-wood stands were transitional between those in aspen and jack pine stands, suggesting that both tree species contribute in structuring the forest floor microbial pool in mixed-wood stands. We put forward that this may provide a more diverse capability to resist disturbance and tolerate stress than in mono-specific stands. We found no effect of stand type on microbial resilience to disturbance, but resilience was higher on clay than on till plots. This could be due to a higher fungal/bacterial ratio on till plots, as slower fungal growth rates may hinder resilience, or to lower carbon and nutrient availability limiting the growth rate of resistant microbial cells. We conclude that plant diversity and site productivity are important drivers of forest floor microbial stability in the southern boreal forest of eastern Canada.
ABSTRACT Aims Natural disturbances leave long-term legacies that vary among landscapes and ecosys... more ABSTRACT Aims Natural disturbances leave long-term legacies that vary among landscapes and ecosystem types, and which become integral parts of successional processes at a given location. As humans change land use, not only are immediate post-disturbance patterns altered, but the processes of recovery themselves are likely altered by the disturbance. We assessed whether short-term effects on soil and vegetation that distinguish wildfire from forest harvest persist over 60 years after disturbance in boreal black spruce forests, or post-disturbance processes of recovery promote convergence of the two disturbance types. Methods Using semi-variograms and Principal Coordinates of Neighbour Matrices, we formulated precise, a priori spatial hypotheses to discriminate spatial signatures following wildfire and forest harvest both over the short- (16–18 years) and long-term (62–98 years). Results Both over the short- and the long-term, wildfire generated a wide spectrum of responses in soil and vegetation properties at different spatial scales, while logging produced simpler patterns corresponding to the regular linear pattern of harvest trails and to pre-disturbance ericaceous shrub patches that persist between trails. Conclusions Disturbance by harvest simplified spatial patterns associated with soil and vegetation properties compared to patterns associated with natural disturbance by fire. The observed differences in these patterns between disturbance types persist for over 60 years. Ecological management strategies inspired by natural disturbances should aim to increase the complexity of patterns associated with harvest interventions.
... al. 1987; Zak & Pregitzer 1990; Grigal et al. 1991), Correspondence: Dr J... more ... al. 1987; Zak & Pregitzer 1990; Grigal et al. 1991), Correspondence: Dr Joan Ehrenfeld, 126 Environment and Natural Resource Science Building, Cook College, Rut-gers University, New Brunswick, NJ 08903, USA. for ecosystems ...
ABSTRACT The practice of careful logging has been mandated in northeastern Canada’s coniferous an... more ABSTRACT The practice of careful logging has been mandated in northeastern Canada’s coniferous and mixedwood forests as a means of protecting natural regeneration while minimizing soil disturbance by machinery. This practice imposes evenly spaced, parallel trails for circulation of harvesting machinery, while most of the understory and soil is left intact in wide protection strips between the trails. The objective of this study was to examine soil physico-chemical and microbial properties, and ericaceous shrub performance (aboveground biomass) following careful logging and with or without subsequent scarification. By sampling 32 cutover forest sites (formerly black spruce-dominated) in the Abitibi-Temiscamingue region of boreal northwestern Quebec, we evaluated how (a) the presence of alternating bands of protection strips and skid trails (on non-scarified sites), and (b) a scarification treatment consisting of mixing the soil organic layer with the surface mineral soil, influenced soil and vegetation properties over time (4–15 years after careful logging). On non-scarified sites, careful logging showed a differential compaction pattern consisting of bands of disturbed zones or trails alternating with protection zones. Both soil properties and ericaceous shrub biomass estimates tracked these alternating compacted and non-compacted areas on the cutover. Soil N (Nt), soil percentage microbial C to total C (Cmic/Ct), and Kalmia angustifolia (Kalmia) and Vaccinium spp. (Vaccinium) aboveground biomass differed on strips and trails 8 and 15 years after harvest. The observed differences in ericaceous shrub biomass between strips and trails, and correlations between biomass and soil variables, suggest potential shrub interference with soil processes. These observations suggest that ericaceous species may promote differences in soil properties and plant communities that result in a long-term spatial signature perpetuating the trail pattern. Scarification reduced Kalmia and Vaccinium aboveground biomass and had a negative effect on Cmic/Nmic and Cmic/Ct, 15 years after harvest. Forest understory plants, such as ericaceous shrubs, may play a key role in driving belowground properties, forest regeneration, and long-term succession on these sites. Understanding the ecology and spatial distribution of these species may thus have important implications for ecosystem structure and function as well as timber production.
... 2.17 ± 0.13 mg C/g in the organic-surface plots and 1.44 ± 0.11 mg C/g in the substitute-surf... more ... 2.17 ± 0.13 mg C/g in the organic-surface plots and 1.44 ± 0.11 mg C/g in the substitute-surface plots (JG Ehrenfeld ... populations and that their activity is through reductions in moisture and/or available nutrients (Gadgil and Gadgil 1975, Harmer and Alexander 1985, Fisher and ...
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