Effects of open-top chambers on physical properties of air and soil at post-disturbance sites in northwestern Quebec

Ecosystem responses to current global climate change can be predicted through experimental climate simulations. One such simulation method is the open-top chamber (OTC). The effects of OTCs on environmental factors are potentially complex, and recognizing the numerous interactions among these factors is crucial for the proper use of chambers. We studied the effects of OTCs on microclimatic factors including ambient temperature, relative humidity, soil temperature, and soil moisture. Plant abundance responses were also assessed. Our study involved the construction of 20 OTCs (1 m in diameter and 0.75 m in height; made of clear acrylic plastic) and 20 control plots on substrates with and without Sphagnum moss, at post-fire and logging sites of the transitional mixedwood-boreal forest in the southern part of James Bay region, Quebec. Experimental trials were also conducted to test the effects of OTCs on snowmelt in the Montreal region. Our results suggest that OTC treatment is most evident in terms of increased daytime maximum temperatures (2°C to 3°C), and cooler (up to ～2.4°C), drier (up to 10% volumetric moisture content) soils. Advanced thawing of the insulating snow cover and exposure of soil in the OTCs to low spring temperatures appeared to prolong soil freeze and result in cooler soils. Earlier snowmelt probably also led to earlier onset and overall increased evaporation of meltwater in the OTCs, leading to drier soils. Plant abundance responses to OTC treatment differed depending on plant species. Overall, open-top chambers provide an effective and simple method of climate change simulation, but it is highly advisable that the complex interactive effects, both desired and undesired, are well understood and appreciated before using OTCs for experimental climate simulation.     

Effects of open-top passive warming chambers on soil respiration in the semi-arid steppe to taiga forest transition zone in Northern Mongolia

The response of soil respiration to warming has been poorly studied in regions at higher latitude with low precipitation. We manipulated air temperature, soil temperature and soil moisture using passive, open-top chambers (OTCs) in three different ecosystem settings in close proximity (boreal forest, riparian area, and semi-arid steppe) to investigate how environmental factors would affect soil respiration in these different ecosystems, anticipating that soil respiration would increase in response to the chamber treatment. The results indicated that OTCs significantly increased air and soil temperature in areas with open canopy and short-statured vegetation (i.e., steppe areas) but not in forest. OTCs also affected soil moisture, but the direction of change depended on the ecosystem, and the magnitude of change was highly variable. Generally, OTCs did not affect soil respiration in steppe and riparian areas. Although soil respiration was slightly greater in OTCs placed in the forest, the difference was not statistically significant. Analyses of relationships between soil respiration and environmental variables suggested that different factors controlled soil respiration in the different ecosystems. Competing effects analysis using a model selection approach and regression analyses (e.g., Q₁₀) demonstrated that soil respiration in the forest was more sensitive to warming, while soil respiration in the steppe was more sensitive to soil moisture. The differing responses and controlling factors among these neighboring forest, riparian and steppe ecosystems in Northern Mongolia highlight the importance of taking into account potential biome shifts in C cycling modeling to generate more accurate predictions of landscape-scale responses to anticipated climate change.     

Effects of benthivorous fish on biogeochemical processes in lake sediments

1. Studies of aquatic environments have shown that community organisation may strongly affect ecosystem functioning. One common phenomenon is a change in nutrient level following a shift in the fish community composition. Although several hypotheses have been suggested, there is no consensus on which mechanisms are involved. Our study evaluated indirect effects of benthivorous fish on the biogeochemical processes at the sediment–water interface separately from direct effects caused by nutrient excretion or sediment resuspension. 2. We assigned field enclosures to three treatments representing typical pond communities; without fish, addition of approximately 10 small tench or addition of one large bream. After one summer, we monitored the water chemistry, benthic invertebrates and periphyton in the enclosures and sampled sediment cores for laboratory analysis of biochemical process rates (oxygen, phosphorus and nitrogen exchange between sediment and water, and denitrification rate). 3. Fish had strong negative effects on benthic invertebrates, but weaker effects on periphyton, organic content and porosity of the sediment. Moreover, there were significant positive fish effects on both phosphorus and nitrogen concentrations in the water. However, there were no general treatment effects on sediment processes that could explain the treatment effects on water chemistry in the enclosures. 4. Hence, overall treatment effects attenuated along the chain of interactions. We conclude that the observed effect of benthic fish on water chemistry was probably because of direct effects on nutrient excretion or resuspension of sediment. The similarity between bream and tench treatments suggests large niche complementarity despite their different habitat preferences.     

Effects of global climatic warming on the boreal forest

On the basis of the predictions of the global climatic warming induced by anthropogenic activities, as provided by climatologists, current state of knowledge regarding possible ecological consequences of the warming on the boreal biome was discussed. A 600 to 700 km northward advance of the biome along with the warming was predicted. Such a shift could take place for half a century or so, which would be an unprecedentedly fast rate of progression. This might cause a serious disorder in species composition of the biome, particularly in the boundary regions. As to the carbon sink or source issues, considerable uncertainties and knowledge gaps existed. Elevated temperature and CO₂ levels would stimulate photosynthesis to result in an increase of CO₂ uptake, while the temperature increase would promote decomposition of organic matter especially that stored in the soils to release CO₂ to the atmosphere. Behaviors of northern peat bogs, whereca. 700 Gt of organic matter was thought to be accumulated, would seriously affect the balance. However, overall ecosystematic carbon balance was yet to be fully studied. It was realized that multifunctional approaches needed to be developed so as to integrate pieces of various information into a holistic picture. Need for international collaboration research efforts was also addressed.     

Postfire succession of saproxylic arthropods, with emphasis on coleoptera, in the north boreal forest of Quebec

Saproxylic succession in fire-killed black spruce [Picea mariana (Mill.) B.S.P.] coarse woody debris (CWD) in northern Quebec is estimated in this study using a 29-yr postfire chronosequence. Sampling was performed using both trunk-window traps and rearing from snag and log sections. A total of 37,312 arthropods (>220 taxa) were collected from both sampling methods. Two distinct colonization waves were identified. The onset of initial colonization occurs the year of the fire, whereas the second colonization phase begins only once debris falls to the ground. The initial colonization step is influenced by fire-associated species including subcortical predators, xylophages, and ascomycetes feeders. Abundance of most early colonizer species decline with time since fire with the disappearance of subcortical habitat. No noticeable species turnover occurred in snags thereafter. Lack of succession in snags is related to very low decomposition rates for postfire CWD because this substrate is unsuitable for species associated with highly decayed wood. Snag falling triggers fungal growth and concomitant saproxylic succession toward micro- and saprophagous species and increases accessibility for soil-dwelling organisms. Because the position of woody debris greatly influences overall physical properties of dead wood, the fall of burned CWD plays a major role in saproxylic community shift after fire.     

The use of understory species as indicators of landform ecosystem type in heavily disturbed forest: an evaluation in the Haut-Saint-Laurent,Quebec

An ecological study of the Municipalité Régionale de Comté (MRC) du Haut-Saint-Laurent area, a highly disturbed landscape located south-west of Montréal (Québec), was carried out. The aim of this study was to establish links between indicator species of ecosystems and geomorphological features in a heavily disturbed background. Analysis to obtain the ecological groups are based on the links of herbaceous plants and shrubs. This approach is defined as a sociological one where grouping is based only on the species' affinity. In order to obtain ecological groups, similarity measures using the chi-square coefficient were calculated on the relative cover values of the 150 retained species from 452 plots. An intermediate linkage cluster analysis was then performed on the similarity matrix thus created. By this procedure, 56 ecological groups were obtained. These groups were then characterized according to abiotic variables, especially the geomorphological data, by the use of binary discriminant analysis. Results indicate that 39 of these 56 groups were significantly associated specifically with one of 10 morphogenic features, while 13 of these 56 groups were associated with 2 or 3 features. The ecological groups which were associated with one specific geomorphological process showed a strong link to one texture and one specific drainage class. On the other hand, the groups which were associated with several features were linked with one drainage class, usually imperfect, and a certain topographic situation. However, ecological groups showing a strong association to more than one feature can be of cartographic use, provided soil texture is analysed to determine the origin of the deposit. Finally, the type of deposit becomes non determinant on vegetation where drainage and topographic variables indicate poorly or very poorly drained sites. Non-significant groups should be used as indicators of drainage and topographical conditions but not as indicators of geomorphological deposits. The ecological groups not associated with morphogenic features demonstrated mostly a heliophilic character. Thus, the ubiquitous character of ecological groups is not exclusive to species taking advantage of disturbances.     

Effects of fire on regional evapotranspiration in the central Canadian boreal forest

Changes in fire regimes are driving the carbon balance of much of the North American boreal forest, but few studies have examined fire‐driven changes in evapotranspiration (ET) at a regional scale. This study used a version of the Biome‐BGC process model with dynamic and competing vegetation types, and explicit spatial representation of a large (10⁶ km²) region, to simulate the effects of wildfire on ET and its components from 1948 to 2005 by comparing the fire dynamics of the 1948–1967 period with those of 1968–2005. Simulated ET averaged, over the entire temporal and spatial modeling domain, 323 mm yr⁻¹; simulation results indicated that changes in fire in recent decades decreased regional ET by 1.4% over the entire simulation, and by 3.9% in the last 10 years (1996–2005). Conifers dominated the transpiration (E_C) flux (120 mm yr⁻¹) but decreased by 18% relative to deciduous broadleaf trees in the last part of the 20th century, when increased fire resulted in increased soil evaporation, lower canopy evaporation, lower E_C, and a younger and more deciduous forest. Well‐ and poorly drained areas had similar rates of evaporation from the canopy and soil, but E_C was twice as high in the well‐drained areas. Mosses comprised a significant part of the evaporative flux to the atmosphere (22 mm yr⁻¹). Modeled annual ET was correlated with net primary production, but not with temperature or precipitation; ET and its components were consistent with previous field and modeling studies. Wildfire is driving significant changes in hydrological processes by affecting mean stand age, forest species, and energy balance. These changes, particularly in poorly drained areas, may control the future carbon balance of the boreal forest.     

Effects of forest liming on soil processes

On the basis of a field experiment in Norway spruce with acid irrigation and compensatory liming of the soil surface (Höglwald, S-Bavaria), liming effects are described as lime dissolution rate, transformation of carbonate buffer to exchange buffer, time required for deacidification of soil and drainage water, mobilization of Cu and Pb, changes in soil organisms, humus decomposition, and nitrogen turnover. It was shown that lime dissolution followed an exponentially decreasing curve. 4 t ha^-1 dolomitic lime were dissolved within 6 years. Additional acid irrigation of 4 kmol H⁺ ha^-1 yr^-1 as sulphuric acid speeded up the lime dissolution to about 4 years. After dissolution of lime about 70% of Ca and about 30% of Mg, both originating from lime dissolution, are retained in the surface humus layer, loading the exchange buffer capacity there. Liming acted as a protection against acid irrigation but the extension of soil deacidification downwards proceeded slowly due to the high base neutralizing capacity of protonated functional groups of the organic matter. The main depth effect is caused by Mg translocation. A significant increase of organic Cu complexes occurred due to mobilization of water soluble humus decomposition products. The effect of liming on litter decomposing organisms is demonstrated with microorganisms, collembolae and earthworms regarding the abundance and the structure of dominance. It was shown that liming may induce unusually large changes in biocenoses of forest soils. The decay of surface humus accounted for 7.2 t ha^-1 or 23% of the store within 7 years. Within the same time span, liming caused a loss of about 170 kg N ha^-1 or 14% of the store of the surface humus layer. The nitrate concentration in the drainage water thus increased by about 50 to 60 mg NO₃ ^- L^-1. Site-specific conditions are discussed, which produce such negative liming effects as increased nitrate concentration of seepage, humus decay and heavy metal mobilization. Redistribution of tree roots, induction of boron deficiency and root rot are also considered. It is indicated that liming may aggravate the increasing problem of nitrate contamination of forest ground water resources which is associated with deposition of atmogenous nitrogen compounds. Some recommendations are given regarding forest practice.     

Interrill erosion at disturbed alpine sites: Effects of plant functional diversity and vegetation cover

It has been hypothesized that a diverse vegetation cover with a high number of plant species and plant functional groups may be more effective at governing soil erosion processes than a vegetation cover with few species and fewer different plant functional groups.We investigated the influence of plant cover and diversity on interrill erosion on a disturbed alpine site. Rainfall simulations were conducted on micro-scale plots (25 × 25 cm) with different degrees of vegetation cover and plant functional group diversity. We selected plots with 10%, 30% and 60% of vegetation cover containing different plant functional groups: (i) grasses, (ii) forbs, (iii) cryptogams (moss and/or lichens), and all possible combinations of these three groups. On each plot a rain intensity of 375 ml min^?1 (30 mm) was applied for 5 min. The degree of vegetation cover had the largest effect on interrill erosion. At 60% vegetation cover, the sediment yield was reduced by 83% in comparison to the un-vegetated ground. In the plots with 60% vegetation cover, an increase in functional group diversity decreased the sediment yield significantly. Sediment yield was three times lower in the presence of three plant functional groups than in systems with one plant functional group. Combinations of plant functional groups including grasses reduced the sediment yield more than other combinations.The findings of this study support the view that beside the re-establishment of a closed vegetation cover, a high plant functional diversity can be a relevant factor to further reduce interrill erosion at disturbed sites in alpine ecosystems.     

树木年龄和断面积对加拿大北方林树木死亡率的影响

以加拿大北部的杨树(Populus spp.)、斑克松(Pinus banksiana)、黑云杉(Picea mariana)为对象,采用长期定位试验,对134块固定样地的活立木及枯死木进行调查,并运用线性回归的方法研究树木年龄、断面积和林分类型对3种树木死亡率的影响.结果表明:随着树龄和断面积的增加,林木的死亡率呈上升趋势.杨树在斑克松林中的死亡率较高,而在黑云杉林中死亡率较低.在黑云杉林中,树龄是影响斑克松死亡率的主要因子;而在杨树林中,断面积是影响斑克松死亡率的重要因子;不同林分类型中树龄对黑云杉死亡率的影响显著.树种组成对树种的死亡率有显著影响;树木年龄、断面积和林分类型之间的交互效应对各树种的死亡率均有显著影响;不同林分类型中同一树种的死亡状况有明显差异.     

Effects of prescribed burning and harvesting on ground-dwelling spiders in the Canadian boreal mixedwood forest

The ‘Natural Disturbance Paradigm’ for forest management seeks to meet conservation goals by modeling industrial harvest in fire-driven forest systems on patterns associated with wildfire. Fire suppression and increased forest harvesting may have detrimental effects on biodiversity, and therefore prescribed burning is suggested to retain legacies of wildfire not emulated under natural disturbance based approaches. The merits of this approach are being tested in the EMEND experiment in the Canadian boreal mixedwood forest. We compared responses of ground-dwelling spiders between sites subjected to prescribed post-harvest burning and retention harvest during three seasons during the first 7 years after disturbance. Overall, 38,661 adult spiders representing 190 species were collected. Estimated species richness was highest in undisturbed sites in all 3 years. Burning had the strongest negative effect on species richness 1–2 years after treatment; however, richness was higher in burns than in harvested sites 5–6 years post-disturbance. Species turnover was highest within controls but tended to increase over time between burned and harvested plots. Lower turnover in burned and harvested sites may reflect habitat homogenization by disturbance, suggesting a management and conservation challenge in relation to naturally disturbed and undisturbed areas. Species were grouped into disturbance-specialists, disturbance-tolerant, disturbance-generalists and generalists; 22 species were significant indicators for untreated sites, 18 for the burn and three for the harvest treatments. No major differences were observed in the spider fauna between harvested and burned areas within the first 6–7 years post-disturbance, and little evidence of recovery toward the pre-harvest fauna was evidenced. However, long term experiments may improve understanding of natural disturbance processes and improve management of boreal forests.     

The use of open-top chambers in forests for evaluating warming effects on herbaceous understorey plants

Open-top chambers (OTCs) are widely used experimental warming devices in open-field ecosystems such as tundra and alpine heath. However, knowledge of their performance in temperate deciduous forest ecosystems is largely lacking. The application of OTCs in forests might become important in the future since the effects of climate warming on growth, reproduction, and future distribution of understorey forest herbs have rarely been investigated. Therefore, polycarbonate OTCs covered with (OTCs+GF) and without permeable polypropylene GardenFleece (OTCs−GF) were installed in a temperate deciduous forest to create an experimental warming gradient. Short-term responses in phenology, growth, and reproduction of a model understorey forest herb (Anemone nemorosa L.) to OTC installation were determined. In a second growing season, an in-depth study of multiple abiotic conditions inside OTCs−GF was performed. Both OTCs+GF and OTCs−GF raised air and soil temperature in a realistic manner (ca. +0.4°C to +1.15°C), but OTCs−GF only in the leafless period (up to +1.5°C monthly average soil temperature). The early flowering forest herb A. nemorosa also showed a clear phenotypic response to OTC installation. Based on these facts and the large ecological drawbacks associated with OTCs+GF (mostly in connection with a higher relative air humidity and a lower light quantity) and very modest abiotic changes in OTCs−GF, we encourage the use of OTCs−GF in deciduous forest ecosystems for evaluating climate-warming effects on early flowering understorey forest herbs. There is also a potential to use this warming method on later flowering species, but this needs further research.     

Growth and leaf senescence in spring wheat (Triticum aestivum) grown at different ozone concentrations in open-top field chambers

The light harvesting biliprotein phycoerythrocyanin isolated from the cyanobacterium Mastigocladus laminosus Cohn was separated into its subunits by isoelectric focusing in a granulated gel in the presence of urea with subsequent renaturation. Smaller amounts of the subunits were obtained from Tolypothrix distorta Kützing var. symplocoides Hansgirg, strain IUCC 424 (now UTEX 424), by chromatography of phycoerythrocyanin on hydroxylapatite. In both cases the isolated α-subunits showed the photoreversible photochemistry characterizing phycochrome b , a photoreversibly photochromic pigment so far found only in extracts of phycoerythrocyanin-containing organisms. Light-induced absorbance changes in the β-subunit and in phycoerythrocyanin were also studied.     

Effects of roots and litter on mineralization processes in forest soil

Summary Leaf litter breakdown and fine root production, including exudation, are two major influences upon carbon and nitrogen mineralization rates in forest soil. Sieving and root removal experiments were used to examine their effects. Although carbon mineralization rates declined in smaller particle size fractions of forest litter, this trend largely disappeared when results were calculated on an ash-free basis. Nitrogen mineralization by contrast, was greatest in smaller fractions.Much of the variation in carbon mineralization rates appeared to be associated with fine roots. A rapid initial exponential decay phase noted in laboratory respiration studies was probably associated with disappearance of available carbon in the form of root exudates and/or the microorganisms dependent on them. Clear cutting caused a marked reduction in the size of available carbon pools, reflecting decreased root exudation and rhizosphere activity. A model of mineralization is proposed which represents the available and humified carbon pools.Deceased