Effects Of Soil Disturbance Research Articles

The effects of mechanical disturbance and burn intensity on the floristic composition of two-year old aggregated retention coupes in Tasmanian wet eucalypt forests

Due to concerns about the ecological impacts of clearfelling in Tasmanian wet eucalypt forests, aggregated retention (ARN) was developed as an alternative harvesting method. It is predicted that, compared to clearfelling, ARN will have ecological benefits such as preservation of old-growth structures and improved regeneration of late successional species in harvested areas. However, early studies have indicated that ARN requires lower intensity regeneration burns and results in greater levels of mechanical soil disturbance than clearfelling. This study therefore aimed to assess the impacts of both soil disturbance and burn intensity on floristic composition, species dominance and species richness following harvesting in ARN coupes. Floristic surveys were conducted on six seedbed classes that reflected the combined effects of both burn intensity and soil disturbance in six two-year-old ARN coupes in southern Tasmania. The results showed that both factors had a significant influence on floristic composition. Higher burn intensities generally favoured colonising species such as eucalypts and Senecio minimus and resulted in lower species richness, while lower fire intensities favoured species regenerating from the seedbank and resulted in higher species richness. In contrast, mechanically disturbed seedbed generally had a high cover of the sedge Gahnia grandis but a low overall species richness due to reduced regeneration of eucalypts and understorey species. The prevalence of the six seedbed classes, and corresponding plant species composition, varied among four general harvesting-related disturbance categories; firebreaks, snigtracks, windrows of piled logging debris and the general harvested area. Maintaining a variety of burn intensities is likely to maximise plant biodiversity within ARN coupes, and soil disturbance should be minimised, with an emphasis on reducing the total area of firebreaks.

Driving factors of forest growth: a reply to Ferry et al. (2012)

Summary1. In a recent paper, we analysed the effects of climate, soil and logging disturbance on tree and forest growth (Toledo et al. 2011a). We took advantage of one of the largest data sets in the Neotropics, consisting of 165 1‐ha plots and over 62 000 trees distributed over an area of c. 160 000 km2, across large environmental gradients in lowland Bolivia. The main findings were that climate was the strongest driver of spatial variation in tree growth, whereas soils had only a modest effect on growth and that the effect of logging disappeared after a few years.2. Ferry et al. (2012) suggest that we underestimated the disturbance effects on growth because of a supposedly wrong coding of Time After Logging (TAL) for unlogged plots. Although we have good biological reasons why we coded TAL like we did, we checked Ferry et al.’s suggestions for recoding and found no differences in variables that significantly explained tree and forest growth. We agree, however, that for future research, it is important to go beyond simple descriptors such as time after logging and basal area logged, to better describe the variation in logging impact found in areas under forest management.3. Ferry et al. claim that we did not define basal area growth properly. We believe this is a semantic issue, as we clearly defined basal area growth as the net change in basal area. This net basal area change in Bolivian forests is indeed relatively high compared to other studies, which may be attributed to the higher soil fertility and biogeographic differences in species composition and their traits.4. Synthesis. Many apparent discrepancies in the ecological literature arise because tropical forest ecologists tend to see the world from the perspective of their ‘own’ forest (despite clear biogeographic differences) and try to capture the same ecological processes using different variables and measurement protocols. To advance our understanding and go beyond single‐case studies, we need to assemble large databases, quantify forest dynamics and disturbances in similar ways, be aware of differences among forests and analyse environmental dose–response curves.

Methane emission from soil under long-term no-till cropping systems

Methane (CH4) emission from agricultural soils increases dramatically as a result of deleterious effect of soil disturbance and nitrogen fertilization on methanotrophic organisms; however, few studies have attempted to evaluate the potential of long-term conservation management systems to mitigate CH4 emissions in tropical and subtropical soils. This study aimed to evaluate the long-term effect (>19 years) of no-till grass- and legume-based cropping systems on annual soil CH4 fluxes in a formerly degraded Acrisol in Southern Brazil. Air sampling was carried out using static chambers and CH4 analysis by gas chromatography. Analysis of historical data set of the experiment evidenced a remarkable effect of high C- and N-input cropping systems on the improvement of biological, chemical, and physical characteristics of this no-tilled soil. Soil CH4 fluxes, which represent a net balance between consumption (−) and production (+) of CH4 in soil, varied from −40±2 to +62±78μg Cm−2h−1. Mean weighted contents of ammonium (NH4+–N) and dissolved organic carbon (DOC) in soil had a positive relationship with accumulated soil CH4 fluxes in the post-management period (r2=0.95, p=0.05), suggesting an additive effect of these nutrients in suppressing CH4 oxidation and stimulating methanogenesis, respectively, in legume-based cropping systems with high biomass input. Annual CH4 fluxes ranged from −50±610 to +994±105g Cha−1, which were inversely related to annual biomass-C input (r2=0.99, p=0.003), with the exception of the cropping system containing pigeon pea, a summer legume that had the highest biologically fixed N input (>300kgha−1yr−1). Our results evidenced a small effect of conservation management systems on decreasing CH4 emissions from soil, despite their significant effect restoring soil quality. We hypothesized that soil CH4 uptake strength has been off-set by an injurious effect of biologically fixed N in legume-based cropping systems on soil methanotrophic microbiota, and by the methanogenesis increase as a result of the O2 depletion in niches of high biological activity in the surface layer of the no-tillage soil.

Wild Pigs (Sus scrofa) Mediate Large-Scale Edge Effects in a Lowland Tropical Rainforest in Peninsular Malaysia

Edge-effects greatly extend the area of tropical forests degraded through human activities. At Pasoh, Peninsular Malaysia, it has been suggested that soil disturbance by highly abundant wild pigs (Sus scrofa), which feed in adjacent Oil Palm plantations, may have mediated the invasion of Clidemia hirta (Melastomataceae) into the diverse tropical lowland rain forest. To investigate this hypothesis, we established three 1 km transects from the forest/Oil Palm plantation boundary into the forest interior. We recorded the distribution of soil disturbance by wild pigs, C. hirta abundance, and environmental variables. These data were analyzed using a hierarchical Bayesian model that incorporated spatial auto-correlation in the environmental variables. As predicted, soil disturbance by wild pigs declined with distance from forest edge and C. hirta abundance was correlated with the level of soil disturbance. Importantly there was no effect of distance on C. hirta abundance, after controlling for the effect of soil disturbance. Clidemia hirta abundance was also correlated with the presence of canopy openings, but there was no significant association between the occurrence of canopy openings and distance from the edge. Increased levels of soil disturbance and C. hirta abundance were still detectable approximately 1 km from the edge, demonstrating the potential for exceptionally large-scale animal mediated edge effects.

Impact of land use patterns and agricultural practices on water quality in the Calapooia River Basin of western Oregon

Agricultural practices, including tillage, fertilization, and residue management, can affect surface runoff, soil erosion, and nutrient cycling. These processes, in turn, may adversely affect (1) quality of aquatic resources as habitat for amphibians, fish, and invertebrates, (2) costs of treating surface and ground water to meet drinking water standards, and (3) large-scale biogeochemistry. This study characterized the surface water sources of nitrogen (N) (total, nitrate [NO₃⁻], ammonium [NH₄⁺], and dissolved organic N) and sediment active within 40 subbasins of the Calapooia River Basin in western Oregon in monthly samples over three cropping years. The subbasins included both independent and nested drainages, with wide ranges in tree cover, agricultural practices, slopes, and soils. Sediment and N form concentrations were tested against weather and agricultural practice variables. Subbasin land use ranged from 96% forest to 100% agriculture. Average slopes varied from 1.3% to 18.9%, and surface water quality ranged from 0.5 to 43 mg L⁻¹ (ppm) total N maxima and 29 to 249 mg L⁻¹ suspended sediment maxima. Total N during the winter was positively related to percentage landcover of seven common agricultural crops (nongrass seed summer annuals, established seed crops of perennial ryegrass [<i>Lolium perenne</i> L.], tall fescue [<i>Schedonorus phoenix</i> {Scop.} Holub], orchardgrass [<i>Dactylis glomerata</i> L.], clover [<i>Trifolium</i> spp.], and newly planted stands of perennial ryegrass and clover) and negatively related to cover by trees and one seed crop, Italian (annual) ryegrass (<i>Lolium multiflorum</i>). Results for NO₃⁻ and total N were highly similar. Sediment concentrations were most strongly related to rainfall totals during periods of 4 and 14 days prior to sampling, with smaller effects of soil disturbance. Fourier analysis of total N over time identified four prominent groups of subbasins: those with (1) low, (2) medium, and (3) high impacts of N (up to 2, 8, and 21 mg L⁻¹, respectively) and a strong cyclical signal peaking in December and (4) those with very high impact of N (up to 43 mg L⁻¹) and a weak time series signal. Preponderance of N in streams draining agriculturally dominated subbasins was in the form of the NO₃⁻ ion, implying mineralization of N that had been incorporated within plant tissue following its initial application in the spring as urea-based fertilizer. Since mineralization is driven by seasonal rainfall and temperature patterns, changes in agronomic practices designed to reduce prompt runoff of fertilizer are unlikely to achieve to more than ~24% reduction in N export to streams.

THE STATUS OF VESICULAR ARBUSCULAR MYCORRHIZAL ASSOCIATIONSWITH MEDICINAL PLANTS IN MIHINTALE SANCTUARY

Sri Lanka has an enormous diversity of medicinal plants, and most are in dry zone forests. Mihintale sanctuary has some of the widely used medicinal plants in our ayurvedic system. Vesicular Arbuscularmycorrhiza (VAM) is the most abundant form of mycorrhiza and, plays a very important role in enhancing plant growth by increased nutrient uptake. This study investigates the presence of VAM colonization in several selected medicinal plants in disturbed and undisturbed sties in the Mihintale sanctuary. The results may be used to conserve those medicinal plants from destruction due to over exploitation. Root Samples were taken randomly from fourteen plant species in both disturbed and undisturbed sites in order to determine the effect of soil disturbance due to human activities on VAM colonization. Sub samples of fine roots of each species were quantified for VAM colonization by performing standard procedures. All the species had VAM colonization but was relatively higher with the plants in undisturbed site than in disturbed site. . Results indicate that the soil disturbances cause a decrease in VAM colonization in the study species.

Soil disturbance by a native rodent drives microhabitat expansion of an alien plant

The “niche opportunity” hypothesis proposes that alien plant establishment is generally driven by the integrated effects of environmental conditions, changes in resource availability and reduced herbivory pressure, but there is yet little evidence supporting such a complex interaction in nature. We evaluated the interactive effects of soil disturbance by the native fossorial mammal Spalacopus cyanus, microhabitat (beneath shrubs and open areas), and introduced herbivores (rabbit, Oryctolagus cuniculus) on the establishment (seedling emergence, adult abundance, aboveground biomass, and reproductive effort) of the alien annual plant Fumaria capreolata in a coastal matorral of central Chile. In the absence of disturbance, seedling emergence and plant establishment of F. capreolata was largely restricted to understory microhabitats. Soil disturbance by S. cyanus significantly increased seedling emergence and establishment, both beneath shrubs and in open areas. There was no effect of herbivore exclusion on the abundance, biomass and reproductive effort of F. capreolata, although the biomass of other co-existing species was reduced. Overall, these results suggest that native fossorial mammals may favor the invasion of F. capreolata by allowing microhabitat expansion into open areas and by increasing its performance in those microhabitats already occupied. We show how the interplay between soil disturbance, microhabitat, and reduced herbivory may explain invasion patterns at the local scale in natural communities.

The influence of a long-term black medic (Medicago lupulina cv. George) cover crop on arbuscular mycorrhizal fungal colonization and nutrient uptake in flax (Linum usitatissimum) under zero-tillage management

Turmel, M. S., Entz, M. H., Tenuta, H., May, W. E. and LaFond, G. P. 2011. The influence of a long-term black medic ( Medicago lupulina cv. George) cover crop on arbuscular mycorrhizal fungal colonization and nutrient uptake in flax ( Linum usitatissimum ) under zero-tillage management. Can. J. Plant Sci. 91: 1071–1076. Leguminous cover crops are becoming a popular way to increase the sustainability of agricultural systems. Previously, cover crops have been found to increase colonization by arbuscular mycorrhizal fungi (AMF) and phosphorus and micronutrient uptake. Long-term field studies were conducted to test the hypothesis that self-regenerating black medic (Medicago lupulina cv. George) cover crops increase AMF colonization and early nutrient uptake in flax (Linum usitatissimum). Field experiments were established in 2000 (Manitoba) and 2002 (Saskatchewan) using a flax–wheat (Triticum aestivum)–oat (Avena sativa) rotation. In a second experiment, intact soil cores were harvested from the plots in spring and tested for soil disturbance and cover crop effects under controlled environment conditions (CEC). Both seedling flax crops sampled from the field in 2005 and 2006 and flax growth in CEC showed high levels of AMF root colonization, but no significant influence of the cover crop on AMF colonization by arbuscules or hyphal structures was detected. The AMF enhancing practices used in the experiments (i.e., zero-tillage and inclusion of mycorrhizal crops) may have contributed to the lack of cover crop effect on AMF colonization. The cover crop had no effect on macro- or micronutrient uptake by flax except during drought conditions (Winnipeg 2006), where flax biomass was reduced by 38% and the total uptake of N, P, Zn and Cu was decreased by 34, 30, 31 and 35%, respectively, in the medic treatment.

Greenhouse gas balance of harvesting stumps and logging residues for energy in Sweden

In this case study, forest fuel procurement chains of stumps and logging residues were evaluated using a Life Cycle Assessment perspective. Direct emissions from combustion were not included, but soil organic carbon change was included as changes in carbon stocks in litter and soil. The results showed that primary forest biomass for energy has a climate impact which is time dependent. However, in long-time perspectives, there are large greenhouse gas (GHG) savings. In a short-term (20 years), there were no GHG savings when natural gas or coal was replaced. This is due to the fact that the harvest lead to decreased input of organic matter to the soil which is compared to a reference where biomass are left to decompose. The reduction in soil organic carbon may have been underestimated in the stump harvest systems studied, as the effect of soil disturbance per se was not included. Important factors when assessing GHG balance of forest fuels, besides the time horizon used, were site productivity, geographical position and forest fuel resource (stumps or logging residues). When assessing the greenhouse gas savings, efficiency of the end-use, allocation method between heat and power and type of fossil fuel replaced were also important.

Quantitative assessment of the piping erosion susceptibility of loess-derived soil horizons using the pinhole test

The pinhole test is an empirical test based on the qualitative evaluation of the dispersivity (colloidal erodibility) of compacted fined-grained soils. This paper evaluates the pinhole test device for the quantitative assessment of the susceptibility of soil horizons to piping, assesses the effects of hydraulic head, water quality, antecedent soil moisture content and soil disturbance on the hydrological and erosion response during pipeflow, and formulates recommendations for the application of the pinhole test to study piping erosion processes. In total, 255 pinhole test experiments were conducted. The results obtained from disturbed soil samples (A p horizon) indicate: (i) a significant positive linear increase in pipeflow discharge ( Q w) and sediment discharge ( Q s) with increasing hydraulic head, (ii) no relationship between Q w and antecedent soil moisture content ( ASM), but significant and negative relationship between Q s and ASM, and (iii) significantly higher Q s for distilled water than for tap water. The use of disturbed soil samples resulted in significantly more rapid flow responses and lower sediment discharges than for undisturbed soil samples. The pinhole test experiments performed on different loess-derived soil horizons show that the plowed topsoil (A p) and the underlying clay-enriched horizon (B t) are at least two times less susceptible to piping than the decalcified (C 1) and the calcareous horizons (C 2). This confirms field observations indicating that loess-derived soil horizons are very susceptible for piping erosion, especially when the C horizon crops out. This study demonstrates that the pinhole test is suitable for assessing the susceptibility of soil horizons to piping in a quantitative way (i.e. Q w, Q s, the time to outflow and the cross-section of the pipe after the test). We recommend the use of: (i) two different hydraulic heads (i.e. 180 and 1020 mm), (ii) distilled water, (iii) contrasting antecedent soil moisture contents of the soil samples to be tested, and (iv) different soil sampling methods to investigate the effect of soil disturbance, and particularly to obtain a better understanding of the sediment response during pipeflow.

Introducing irrigation efficiencies: prospects for flood-dependent biodiversity in a rice agro-ecosystem

SUMMARYWorldwide, irrigation development has affected pre-existing natural habitats and created novel aquatic habitats, and future changes in management will continue to influence flood-dependent vegetation and fauna. Irrigated agriculture has had a profound influence on native biodiversity in the Riverina region of temperate Australia. Current irrigation practices provide large amounts of water to the landscape in the form of constructed wetland habitats: irrigation channels, impoundments and flooded crop-growing areas. Flooded rice bays support many species of native wetland plants, and 12 of the 14 species of frog recorded in the region. All constructed habitats provide a food resource for waterbirds, but not breeding habitat. While a species of tortoise benefits from the provision of constructed habitats, terrestrial reptiles and mammals are most abundant in remaining native vegetation. The climate is predicted to become increasingly hot and dry, with a reduced and more variable supply of irrigation water, thus placing increasing stress on farming and on natural ecosystems. The predicted reduction of constructed aquatic habitats may affect the native species using them, but may not have a major adverse impact on biodiversity regionally because the species recorded in constructed habitats tend be abundant and widespread, and such species also occur in natural wetland habitats. Sensitive species that depend on native vegetation persisting in reasonable amounts and in good condition are at greater risk. In the Riverina, the remaining native vegetation should be managed to protect and improve its condition, including appropriate managed inundation events for flood-dependent communities. The landscape should be managed to provide the best context for the function and health of existing vegetation including moderating the effects of soil disturbance, fertilizers and herbicides. The impacts of changed irrigation practices should be mitigated through managed flooding of remnant vegetation. In countries with more evolved, traditional rice-growing systems than the Riverina, there will be greater emphasis on biodiversity coexistence with cultivation. Nonetheless, in all settings there is value in jointly considering the role of both natural and constructed habitats in biodiversity research and conservation.

Responses of native and non-native Mojave Desert winter annuals to soil disturbance and water additions

Habitat modification (i.e., disturbance) and resource availability have been identified as possible mechanisms that may influence the invasibility of plant communities. In the Mojave Desert, habitat disturbance has increased dramatically over the last 50 years due to increased human activities. Additionally, water availability is considered to be a main limiting resource for plant production. To elucidate the effects of soil disturbance and water availability on plant invasions, we created experimental patches where we varied the levels of soil disturbance and water availability in a fully crossed factorial experiment at five replicated field sites, and documented responses of native and non-native winter annuals. The treatments did not significantly affect the density (seedlings m−2) of the non-native forb, Brassica tournefortii. However, the relationship between silique production and plant height differed among treatments, with greater silique production in disturbed plots. In contrast to Brassica, density of the non-native Schismus spp. increased in soil disturbed and watered plots, and was greatest in disturbed plots during 2009 (the second year of the study). Species composition of the native annual community was not affected by treatments in 2008 but was influenced by treatments in 2009. The native forb Eriophyllum sp. was most dense on water-addition plots, while density of Chaenactis freemontii was highest in disturbed plots. Results illustrate that habitat invasibility in arid systems can be influenced by dynamics in disturbance regimes and water availability, and suggest that invasiveness can differ between non-native annual species and among native annuals in habitats undergoing changing disturbance and precipitation regimes. Understanding the mechanistic relationships between water availability and non-native plant responses will be important for understanding the effects of shifting precipitation and vegetation patterns under predicted climate change in arid ecosystems.

Deer browsing and soil disturbance induce cascading effects on plant communities: a multilevel path analysis

Understanding how large herbivores shape plant diversity patterns is an important challenge in community ecology, especially because many ungulate populations in the northern hemisphere have recently expanded. Because species within plant communities can exhibit strong interactions (e.g., competition, facilitation), selective foraging by large herbivores is likely not only to affect the abundance of palatable species, but also to induce cascading effects across entire plant communities. To investigate these possibilities, we first tested the effects of deer browsing and soil disturbance on herbaceous plant diversity patterns in boreal forest, using standard analyses of variance. Second, we evaluated direct and indirect effects of deer browsing and soil disturbance on the small-scale richness of herbaceous taxa using a multilevel path analysis approach. The first set of analyses showed that deer browsing and soil disturbance influenced herb richness. Path analyses revealed that deer browsing and soil disturbance influenced richness via complex chains of interactions, involving dominant (i.e., the most abundant) browsing-tolerant (DBT) taxa and white birch (Betula papyrifera), a species highly preferred by white-tailed deer (Odocoileus virginianus). We found no evidence that an increase of white birch in fenced quadrats was the direct cause of a decrease in herb richness. However, we found strong evidence that a higher abundance of DBT taxa (i.e., graminoids and Circium arvense), both in fenced and unfenced quadrats, increased herb layer richness. We propose an empirical model in which competitive interactions between white birch and DBT taxa regulate the strength of facilitative relationships between the abundance of DBT taxa and herb richness. In this model, deer browsing and the intensity of soil disturbance initiate a complex chain of cascading effects in boreal plant communities by controlling the abundance of white birch.

Post-disturbance dynamics of plant communities in a Mediterranean temporary pool (Western Morocco): Effects of disturbance size

Mediterranean temporary pools are frequently visited habitats where domestic livestock and wild herbivores generate numerous physical soil disturbances. Using two sizes of experimental plots (large, 1.20 m × 1.20 m; small, 0.3 m × 0.3 m), the effects of soil disturbances on vegetation dynamics and the vertical distribution of seeds were studied in one Moroccan temporary pool. Results show a very rapid regeneration of temporary wetland vegetation in disturbed plots. The speed of regeneration depends on the size of disturbance and hydrology. There was an almost complete return of vegetation to the reference state in the small disturbed plots by the end of the 1st year. This fast restoration was mainly due to seed banks, which play a key role in the resilience of pools to the different sizes of disturbances frequently generated by herbivores, but also to lateral colonization by perennials.

Effect of soil disturbance and biocides on nematode communities and extracellular enzyme activity in soybean cyst nematode suppressive soil

AbstractSoybean cyst nematode (SCN), Heterodera glycines, remains a major yield-limiting pathogen of soybean. Natural suppression of SCN exists and becomes increasingly attractive; however, ecological mechanisms leading to the suppressive state are rarely studied. A glasshouse experiment was performed to determine the effects of soil disturbance and biocides on nematode community and extracellular enzyme activities in the SCN-suppressive soil collected in 2007 and 2008. Soil disturbance was simulated by passing soil through a sieve (aperture 5 mm) and compared with no-disturbance (non-sieve) treatment. Composition of microbial communities was manipulated by applying captan (fungicide), streptomycin (bactericide), captan plus streptomycin, or no biocide. SCN egg population density, proportion of second-stage juveniles (J2) parasitised by fungi, nematode communities in the soil, and plant weight in each pot were determined 70 days after planting soybean. In addition, the activities of six selected hydrolytic and oxidative extracellular enzymes representing cellulase, chitinase, serine protease, collagenase and peroxidase were measured. Soil disturbance resulted in an increase in SCN egg population density and reduction in the proportion of J2 parasitised by fungi. Biocide treatments increased SCN egg population density and the proportion of J2 parasitised by fungi at the end of experiment. Values of nematode community diversity index decreased and dominance and maturity indices increased in the disturbed soil compared with the no-disturbance treatment. Biocide treatments reduced maturity index values exclusively. With soil disturbance, the activity of extracellular enzyme L-proline aminopeptidase activity declined to less than half of that under no-disturbance in 2007. This experiment showed that both bacteria and fungi were potentially involved in the soil suppressiveness to SCN: soil disturbance and biocide application may reduce natural soil suppressiveness that was potentially associated with soil nematode community diversity and microbial enzyme activities.

Intensity, extent and persistence of soil disturbance caused by timber harvesting in jarrah (Eucalyptus marginata) forest on FORESTCHECK monitoring sites

Summary The intensity and extent of soil compaction caused by timber harvesting was examined in the jarrah (Eucalyptus marginata) forest of south-west Western Australia. The extent of soil compaction was determined by mapping soil disturbance categories. The intensity of compaction was determined from the bulk density of these disturbance categories. Bulk density of surface soil (0–100 mm) was measured across monitoring grids established for the FORESTCHECK project on eleven harvested sites and seven sites that had never been harvested. Surface soils on sites that had never been harvested had a mean fine earth bulk density of 0.71 g cm−3. Timber harvesting increased the bulk density of surface soils by a mean of 0.15 g cm−3. Compaction was greatest on log landings and primary and secondary extraction tracks where fine earth bulk density was increased by 0.27 g cm−3 compared to never-harvested forest. Compaction on the general harvested area (0.13 g cm−3), which excludes the extraction tracks, was about half that of log landings and extraction tracks. The intensity of soil compaction was consistent with increases observed as a result of timber harvesting in a range of other forests. Although the intensity of harvesting activity and the volume of logs removed is typically greater in gap release than in shelterwood treatments, there was no significant difference in soil compaction between these treatments. Soil compaction did decline as the intensity of individual disturbance activities inside harvested areas declined. Given the potential and demonstrated effects of soil compaction and disturbance on jarrah forest ecosystems, and the potentially long time periods indicated for the amelioration of soil compaction in these forests, ongoing operational management and monitoring of this disturbance is required to limit long-term effects on the productive capacity of jarrah forest.

A strategy in searching for stress tolerance-correlated characteristics in nematodes while accounting for phylogenetic interdependence

Biological indicators are highly relevant for assessing the condition of a soil as they are integrative; they reflect the overall impact of physical, chemical and biological changes. Indigenous soil organisms are preferable to other test organisms because the diversity and condition of indigenous soil organisms reflect both acute and chronic effects of soil disturbances. Nematodes are ubiquitous, speciose, easily extractable and present in extremely high numbers. Given the ever increasing amount of sequence data, DNA barcode-based community analysis will soon be possible and a next step would be to define objective criteria for the ecological grouping of soil nematodes. Here, we present a framework to ascertain which traits are correlated with a tolerance to stress. For this, a field study on the effects of pH and copper on nematode communities was re-analysed. Changes in abundances of individual genera were correlated with a number of potentially stress tolerance-related characteristics. The generalised least squares (GLS) method was used to account for the phylogenetic dependence of the data. Only the relationship between the ability to enter a survival stage and tolerance to copper at pH 6.1 was found to be significant, but the quantity of missing data probably had a negative impact on the analyses. This study did, however, clearly demonstrate the importance of accounting for the effects of phylogenetic dependence in the data. When the phylogeny was taken into account, we observed an average change in P value of 0.196 (and in some cases as much as 0.6) for the correlations of possible stress-related characteristics and Cu or pH tolerance. This research constitutes a proof-of-principle for a transparent method to relate stress tolerance to (ecological) characteristics. The usefulness of this powerful method should become even clearer when substantially higher numbers of individuals are analysed (as facilitated by using DNA barcodes) and when missing data are filled in

Differential effects of soil disturbance and plant residue retention on function of arbuscular mycorrhizal (AM) symbiosis are not reflected in colonization of roots or hyphal development in soil

The effects of soil disturbance and residue retention on the functionality of the symbiosis between medic ( Medicago truncatula L.) and arbuscular mycorrhizal fungi (AMF) were assessed in a two-stage experiment simulating a crop rotation of wheat ( Triticum aestivum L.) followed by medic. Plants were inoculated or not with the AMF, Glomus intraradices and Gigaspora margarita , separately or together. The contribution of the arbuscular mycorrhizal (AM) pathway for P uptake was determined using 32 P-labeled soil in a small hyphal compartment accessible only to hyphae of AMF. In general AM colonization was not affected by soil disturbance or residue application and disturbance did not affect hyphal length densities (HLDs) in soil. At 4 weeks disturbance had a negative effect on growth and phosphorus (P) uptake of plants inoculated with G. margarita , but not G. intraradices . By 7 weeks disturbance reduced growth of plants inoculated with G. margarita or AMF mix and total P uptake in all inoculated plants. With the exception of plants inoculated with G. margarita in disturbed soil at 4 weeks, the AM pathway made a significant contribution to P uptake in all AM plants at both harvests. Inoculation with both AMF together eliminated the negative effects of disturbance on AM P uptake and growth, showing that a fungus insensitive to disturbance can compensate for loss of contribution of a sensitive one. Application of residue increased growth and total P uptake of plants but decreased 32 P in plants inoculated with the AMF mix in disturbed soil, compared with plants receiving no residue. The AMF responded differently to disturbance and G. intraradices , which was insensitive to disturbance, compensated for lack of contribution by the sensitive G. margarita when they were inoculated together. Colonization of roots and HLDs in soil were not good predictors of the outcomes of AM symbioses on plant growth, P uptake or P delivery via the AM pathway. ► Soil disturbance did not affect AM colonization of medic or hyphal lengths in soil. ► AM P uptake contributed significantly to total P in all undisturbed treatments. ► Disturbance reduced P delivery via G. margarita , but not via G. intraradices . ► Inoculation with both AM fungi together eliminated negative effects of disturbance. ► Percent colonization was not a good predictor of symbiotic outcomes.

Effects of soil disturbance on plant diversity of calcareous grasslands

A soil disturbance experiment was performed during two seasons in degraded, calcareous sandy grassland in southern Sweden. pH, extractable phosphorus, plant species richness and vegetation composition were analyzed. Mechanical soil disturbance had no effect on pH, and caused only a minor increase in extractable phosphorus. Positive effects compared to control plots were seen on plot scale (360m2) in species richness and Shannon index 2 years after treatment, while on a smaller scale (1m2), species richness increased only in rotavated plots. Plant community differences were mainly found between disturbed and control plots, and some positive effects were detected on early establishing species, but the two disturbance techniques favored different species. It is concluded that mechanical soil disturbance, and a variation in techniques and intensities, may be an important measure for preserving diversity in grasslands that have a history of mechanical soil disturbance.

Analysis of PVD-enhanced consolidation with soil disturbance

Soil disturbance caused by the installation of prefabricated vertical drains (PVDs) in soft soil deposits has a detrimental effect on the rate of consolidation. The current practice of accelerating consolidation using PVDs captures the effect of soil disturbance typically by reducing the in situ hydraulic conductivity in the disturbed zone, and by assuming that the hydraulic conductivity is spatially constant over the entire disturbed zone and that preloading is instantaneous. Through recent laboratory and field studies it has been shown that the hydraulic conductivity varies spatially in the disturbed zone surrounding a PVD. Based on the data available in the literature, four possible profiles were identified for the spatial variation of the hydraulic conductivity in the disturbed zone. Analytical solutions were developed for the rate of consolidation considering these hydraulic conductivity profiles for instantaneous and time-dependent preloading. This paper shows that the consolidation rate depends not only on the hydraulic conductivity profile in the disturbed zone but also on the preloading rate.