Undisturbed Control Plots Research Articles

Effects of fire on CO2, CH4, and N2O exchange in a well‐drained Arctic heath ecosystem

Wildfire frequency and expanse in the Arctic have increased in recent years and are projected to increase further with changes in climatic conditions due to warmer and drier summers. Yet, there is a lack of knowledge about the impacts such events may have on the net greenhouse gas (GHG) balances in Arctic ecosystems. We investigated in situ effects of an experimental fire in 2017 on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) surface fluxes in the most abundant tundra ecosystem in West Greenland in ambient and warmer conditions. Measurements from the growing seasons 2017 to 2019 showed that burnt areas became significant net CO2 sources for the entire study period, driven by increased ecosystem respiration (ER) immediately after the fire and decreased gross ecosystem production (GEP). Warming by open‐top chambers significantly increased both ER and GEP in control, but not in burnt plots. In contrast to CO2, measurements suggest that the overall sink capacity of atmospheric CH4, as well as net N2O emissions, were not affected by fire in the short term, but only immediately after the fire. The minor effects on CH4 and N2O, which was surprising given the significantly higher nitrate availability observed in burnt plots. However, the minor effects are aligned with the lack of significant effects of fire on soil moisture and soil temperature. Net uptake and emissions of all three GHG from burnt soils were less temperature‐sensitive than in the undisturbed control plots. Overall, this study highlights that wildfires in a typical tundra ecosystem in Greenland may not lead to markedly increased net GHG emissions other than CO2. Additional investigations are needed to assess the consequences of more severe fires.

Phenotypic Plasticity of Drought Tolerance Traits in a Widespread Eucalypt (Eucalyptus obliqua)

Long-term studies of tree responses to drought stress help us to understand the capacity of species to adapt to their environment. In this study, we investigated how Eucalyptus obliqua adjusts physiological and morphological traits in response to seasonal and multi-year droughts. We monitored physiological and morphological traits over multiple years in undisturbed control and throughfall reduction plots in a eucalypt forest in south-eastern Australia. The throughfall reduction treatment did not induce significantly lower soil moisture in the throughfall reduction plots compared with the control plots. However, natural variability in precipitation and evaporative demand induced drought stress of varying intensity each summer in all plots. We observed a significant relationship between seasonal precipitation and leaf pre-dawn water potential (ΨPD), with less precipitation over summer, resulting in a decline in ΨPD and drought stress when ΨPD fell below −0.75 MPa. Eucalyptus obliqua responded to short-term summer drought through rapid leaf osmotic adjustment which lowered the leaf water potential at the turgor loss point beyond the minimum leaf water potential. Morphological adjustments, such as the reduction of leaf area to sapwood area (higher Huber Value) were moderate during the measurement period and only occurred under severe drought stress (pre-dawn water potential < −1.2 MPa). Overall, E. obliqua responded to short-term mild drought stress through physiological trait plasticity, while morphological adjustment only occurred under a more severe water deficit.

Does stump removal reduce pine weevil and other damage in Norway spruce regenerations? – Results of a 12-year monitoring period

Although impacts of intensive forest harvesting practices such as removing logging residue and stumps for bioenergy on forest ecosystem has been extensively studied, no information is available about the long-term effects of stump harvesting on the health status of young Norway spruce stands. In the present study, we surveyed damage caused by the large pine weevil (Hylobius abietis L.) and other causal agents as well as the height growth of the Norway spruce seedlings for 12 years in stump-harvested and non-harvested experimental plots. The overall effect of stump harvesting combined with mounding on the health and survival of spruces was positive: 70% of spruce seedlings in stump-harvested plots were spared any damage, while 58% of seedlings remained undamaged in undisturbed control plots. The positive effect of stump removal and mounding on tree health was mainly due to reduced pine weevil damage. In all, 14.8 and 24.6% of spruce seedlings were gnawed by pine weevil in stump-harvested and control plots, respectively. In stump-harvested plots, pine weevil damage was slighter and lasted for a shorter time than in control plots. In addition, damage caused by Hylastes spp., black root beetles, was significantly less on stump-harvested plots. By contrast, vole damage was most frequent in stump-harvested plots during the population peak when the vole density was exceptionally high. Irrespective of whether stumps were harvested or not, stump roots provided a source of Heterobasidion inoculum in the next spruce regeneration. During this early stage of stand development only a few spruce seedlings were killed by Heterobasidion root rot and there were neither temporal nor quantitative treatment-related differences between the treatments. From the third year onwards the height growth of undamaged seedlings was more rapid in stump-harvested than non-harvested plots. Our results suggest that the overall risk of damage in young Norway spruce stands can be reduced by stump harvesting. Thus, stump harvesting and mounding seem to decrease the need for supplementary planting, which reduces regeneration costs that represent a considerable financial investment for a forest owner.

A reintroduced ecosystem engineer provides a germination niche for native plant species

Grasslands and grassy woodlands worldwide have experienced declines in extent and condition, with substantial changes to their ground-layer biodiversity. In Australia, this decline has coincided with the extinction of many digging mammals that may have once created regeneration niches for native ground layer plants. These digging mammals are widely recognised as ‘ecosystem engineers’, due to their influence on biopedturbation and resultant soil functions. Yet there is uncertainty as to the benefits of digging in restoring grassland diversity with current levels of modification and the presence of exotic plants. We investigated the effect of digging by the reintroduced eastern bettong (Bettongia gaimardi) on seedling germination in a temperate grassy woodland in south-eastern Australia. We marked fresh bettong foraging pits and undisturbed control plots in dense and open grassland. We added seeds of seven native forb species and monitored germination and establishment over 2 years. We found significantly more seedlings in bettong pits than controls, particularly in dense grassland. This effect persisted beyond 1 year, suggesting that pits may have increased seedling survival in dry conditions. Surprisingly, native species displayed a stronger positive response to pits than exotic species, particularly in a wet year. There was an initial reduction in exotic species, but this was followed by their increase in 1-year-old pits, suggesting that the disturbance created by digging could eventually lead to an increase in weed abundance. Our results demonstrate that while bettong pits provide a germination niche for native forbs, reintroducing digging animals will not necessarily result in the desired restoration outcomes. Ongoing persistence of exotic species is to be expected, and seed addition may be required for species that are seed-limited.

Anthropogenic disturbance facilitates a non‐native species on offshore oil platforms

Abstract Anthropogenic practices that facilitate species introductions must be identified and modified to improve management and control the spread of non‐native taxa in many environments. Maintenance practices that remove dense epifaunal invertebrates attached to offshore structures create a disturbance that may facilitate the establishment of non‐native species. We evaluated the effect of disturbance on the abundance (percent cover) of a non‐native bryozoan, Watersipora subatra, on an offshore oil platform in the Santa Barbara Channel, USA by removing the existing epifaunal community in experimental plots and comparing Watersipora cover in these plots to that in undisturbed control plots over a 15‐month period. We explored the importance of larval supply and the epifaunal community in driving observed patterns, using measurements of Watersipora larval availability and colony recruitment and growth in the disturbed and control plots. We also examined the effect of disturbance on Watersipora establishment at the larger, platform‐scale over c. 18 months with comparative surveys of cleaned and uncleaned portions of another oil platform. Both the experimental disturbance and the larger platform cleaning facilitated Watersipora establishment, with cover increasing from c. 5% to 20–60% at shallower (≤12 m) depths within 15 to 18 months following disturbance. Initial Watersipora recruitment to the disturbed plots occurred during a period of elevated larval availability, as indicated by recruitment onto settlement plates. However, 1 year after the experimental disturbance, sessile invertebrates occupied all available settlement space, and there was little recruitment of Watersipora into disturbed plots despite the availability of larvae. Synthesis and applications. Maintenance operations for offshore structures can include the manual removal of subtidal epibenthic invertebrates attached to the structure. Our study at offshore oil platforms found that this anthropogenic disturbance enhanced the establishment of the non‐native invertebrate Watersipora subatra. The timing of disturbance relative to Watersipora's reproductive season was an important driver of this pattern. Scheduling maintenance practices to occur soon after the reproductive period of Watersipora could allow adequate time for native species to recruit and occupy the available bare space, thereby reducing the potential for establishment of this non‐native species.

The European ground squirrel increases diversity and structural complexity of grasslands in the Western Carpathians

Disturbances are important natural factors affecting biological diversity, community composition, and ecosystem structure. The European ground squirrel is a semi-fossorial organism, and through disturbances caused by burrowing activities, it can play an important role as an ecosystem engineer of grasslands in central and south-eastern Europe. The aim of this study was to assess the response of grassland vegetation to disturbances by the European ground squirrel. We conducted a pairwise survey within a 1-ha study site with homogenous environmental conditions. We compared the vegetation characteristics of 2 × 2-m plots placed on 30 mounds, with paired control plots situated at a distance of 10 m from each mound. The results showed that plots disturbed by the European ground squirrel achieved a higher species richness and diversity and a distinct species composition compared to the undisturbed control plots. Vertical structure of vegetation was also significantly different with a higher proportion of the high and medium vegetation layers on the mounds. Shifts in the composition of plant life forms and life strategies were reflected by the reduction of graminoids and plant competitors, and support of forbs on the mounds. These findings suggest that the European ground squirrel helps to maintain heterogeneity in grassland ecosystems and creates patches of higher diversity and higher structural complexity in the relatively homogenous grassland vegetation of the Western Carpathians.

Selecting fungal disturbance indicators to compare forest soil profile re-construction regimes

Physical disturbance of soil profiles, even at shallow depths, is a ubiquitous consequence of anthropogenic landscape modification, with short-term impacts on important ecological guilds of fungi. DNA-based methods for surveying community composition are widely incorporated into studies attempting to explain fungal responses to forest ecosystem disturbances. Here we compare fungal community composition between three distinct soil profile manipulations (20cm depth) and undisturbed control plots in a sub-boreal spruce forest in the Central Interior region of British Columbia, Canada. Fungal community composition differences were tracked by internal transcribed spacer 2 (ITS2) amplicon sequencing, with comparisons drawn using genus-level annotations. Non-metric multidimensional scaling (NMDS) analysis indicated that disturbed-sample community compositions were similar to controls at 0-months and distinct from controls at 5- and 12-months post disturbance, but did not indicate clustering of samples according to disturbance regime. We used Linear Discriminant Effect Size (LEfSe) analysis to identify fungal genera that consistently indicate disturbed or undisturbed (control) treatments across 5- and 12-month sampling times. Four fungal genera (Exophiala, Hyphodontiella, Mastigobasidium, and Umbelopsis) were detected with higher ranges of relative abundance in all disturbance regimes when compared to control plots. Deliberate mixing of LFH into mineral horizon soils stimulated multiple genera that were more frequently detectable in replicate plots at 12 months, when compared to undisturbed and immediately re-assembled plots. Four ectomycorrhizal genera (Amphinema, Cortinarius, Piloderma, and Russula) were identified as strong indicators of control plot soils. A single genus, Capronia, was identified as differentially abundant between stockpiled LFH and immediately replaced LFH. Our results are consistent with declines in ectomycorrhizal fungal abundance and increases in saprotroph abundance previously reported in DNA-based community profiling studies of forest soil disturbance. This investigation demonstrates that bulk soil sampling can be used to evaluate soil-handling regimens to understand fungal community disruption/recovery and highlights LEfSe as an approach to indicator selection in DNA-dependent biodiversity surveys.

Restoration of peatland by spontaneous revegetation after road construction

AbstractQuestionsSpontaneous revegetation from indigenous soil was used as a restoration method for peatlands degraded during road construction in northern Norway. We examined how plant community properties responded to the restoration, and which environmental factors affected the restoration success.LocationRestored peatlands along roadsides at E10, mainland connection to the Lofoten islands, northern Norway.MethodsThe restored area originally consisted of poor to intermediate Sphagnum‐dominated natural peatlands. Restoration consisted of stripping and stockpiling the topmost (30 cm) peat. The peat was stored for 1–2 yr before redistribution, with no further hydrological management. We conducted first time analyses of plant community properties 8 and 9 yr after restoration. We recorded vegetation and environmental variables in 108 plots distributed between 18 transects running from the road edge over the restored area to the undisturbed peatland. Undisturbed peatland was used as target for successful restoration. We used CCA and ANOVA to test the effect of restoration on species composition and richness.ResultsThe ordination showed that species composition still differed significantly between restored and undisturbed plots, indicating incomplete restoration after 8 and 9 yr. Soil moisture, pH, slope and microtopography were the most important environmental factors for species composition. Polytrichum mosses had a high percentage cover in restored (30%) compared to undisturbed control plots (1%). Linear regression showed that peatland species decreased in abundance with increasing depth of Polytrichum cushions.ConclusionThe low soil moisture level in the restored areas is most likely limiting the establishment of Sphagnum mosses, considered as key species of the typical peatland environment. Thus, the restoration method studied here must be improved to increase the soil moisture by raising the water table or reducing drainage. This should be done through reducing storage time of the peat before redistribution, and minimizing slopes and heterogeneity of the microtopography of the restored area.

Experimental evidence of human recreational disturbance effects on bird-territory establishment.

The worldwide increase in human outdoor activities raises concerns for wildlife. Human disturbances, even at low levels, are likely to impact species during sensitive periods of the annual cycle. However, experimental studies during the putative sensitive period of territory establishment of birds which not only investigate low disturbance levels, but which also exclude the effect of habitat modification (e.g. walking trails) are lacking. Here, we experimentally disturbed birds in forest plots by walking through twice a day during territory establishment. Later we compared the breeding bird community of experimentally disturbed plots with that of undisturbed control plots. We discovered that the number of territories (-15.0%) and species richness (-15.2%) in disturbed plots were substantially reduced compared with control plots. Species most affected included those sensitive to human presence (assessed by flight-initiation distances), open-cup nesters and above-ground foragers. Long-distance migrants, however, were unaffected due to their arrival after experimental disturbance took place. These findings highlight how territory establishment is a sensitive period for birds, when even low levels of human recreation may be perceived as threatening, and alter settlement decisions. This can have important implications for the conservation of species, which might go unnoticed when focusing only on already established birds.

Biotic constraints on the establishment and performance of native, naturalized, and invasive plants in Pacific Northwest (USA) steppe and forest

Factors that cause differential establishment among naturalized, invasive, and native species are inadequately documented, much less often quantified among different communities. We evaluated the effects of seed addition and disturbance (i.e., understory canopy removal) on the establishment and seedling biomass among two naturalized, two invasive, and two native species (1 forb, 1 grass in each group) within steppe and low elevation forest communities in eastern Washington, USA. Establishment within each plant immigrant class was enhanced by seed addition: naturalized species showed the greatest difference in establishment between seed addition and no seed addition plots, native and invasive species establishment also increased following seed addition but not to the same magnitude as naturalized species. Within seed addition plots, understory canopy disturbance resulted in significant increases in plant establishment (regardless of plant immigration class) relative to undisturbed plots and the magnitude of this effect was comparable between steppe and adjacent forest. However, regardless of disturbance treatment fewer invasive plants established in the forest than in the steppe, whereas native and naturalized plant establishment did not differ between the habitats. Individual biomass of naturalized species were consistently greater in disturbed (canopy removed) versus undisturbed control plots and naturalized species were also larger in the steppe than in the forest at the time of harvest. Similar trends in plant size were observed for the native and invasive species, but the differences in biomass for these two immigration classes between disturbance treatments and between habitats were not significant. We found that strong limitations of non-native species is correlated with intact canopy cover within the forest understory, likely driven by the direct or indirect consequences of low light transmittance through the arboreal and understory canopy. Considered collectively, our results demonstrate how seed limitation and intact plant ground cover can limit the abundance and performance of naturalized species in Pacific Northwest steppe and low elevation forest, suggesting that local disturbance in both habitats creates microsites for these species to establish and survive. Future studies evaluating interactions between multiple barriers to establishment using more representatives from each immigration class will further reveal how biotic interactions ultimately influence the demography and distribution of non-native plants within these communities.

Regeneration dynamics of woody vegetation in a Mediterranean landscape under different disturbance‐based management treatments

AbstractQuestionMediterranean landscapes have been affected for millennia by agro‐pastoral disturbances such as grazing and vegetation clearing. Increased levels of fine‐scale habitat heterogeneity that resulted from these disturbances contribute to reduced wildfire risk and increased species diversity. Disturbance‐based management tools utilize disturbances in order to promote biodiversity and reduce fire risk, but are complicated to apply effectively due to the natural regeneration ability of many woody species following disturbances. Therefore, their successful application requires a better understanding of woody regeneration dynamics. Here, we asked how disturbance‐based management treatments affected the spatiotemporal dynamics of woody vegetation across 11 yrs in a Mediterranean landscape.LocationRamat HaNadiv LTER, northern Israel.MethodsWe analysed vegetation dynamics in a field experiment comprising five treatments: cattle grazing, goat grazing, shrub clearing, shrub clearing followed by goat grazing and undisturbed control. We used image analysis of high‐resolution aerial photographs to map woody patches in our study plots. We then quantified the spatial pattern of woody vegetation using multiple landscape indices, and conducted a comparative analysis of woody regeneration rates under different management treatments.ResultsCattle grazing did not inhibit woody regeneration, as regeneration rates were similar to those found in undisturbed control plots. Shrub clearing led to rapid woody regeneration (7% yr−1), while a combination of shrub clearing and intense goat grazing halted woody regeneration completely. Finally, intense goat grazing not only prevented woody regeneration but led to significant decline in woody cover (1% yr−1).ConclusionsOur results highlight the rapid regenerative response of woody vegetation to severe disturbances, and the growth rates we found can serve as guidelines for long‐term management regimes aimed at maintaining low woody cover and biomass in fuel breaks and buffer zones.

Convergent high diversity in naturally colonized experimental grasslands is not related to increased productivity

Initial plant diversity might control subsequent community assembly processes and plant productivity. To study these effects, we used a biodiversity experiment (Jena Experiment) with subplots of different sown diversity that were never weeded and spontaneously colonized control plots of different size (3.5×3.5m, 20×20m) with and without mowing in an 8-year study. On non-sown bare plots without mowing, colonizer accumulation depended on plot size resulting in a loss of diversity in large, undisturbed (unmown) control plots after initial colonization. On sown plots that were mown, species richness converged to high levels due to the accumulation of internal colonists (species belonging to the experimental pool of sown species), while initially high species richness of external colonists (species not belonging to the experimental pool) and residents (species sown on the plot) declined over time. The convergence of total species richness at higher levels was paralleled by increased taxonomic (Simpson index, QSimp), phylogenetic (QPhylo) and trait (FDQ) diversity, whereby FDQ was greatest on plots with low resident species richness after several years. Rates of change in terms of species colonization and extinction decelerated over time irrespective of resident species richness, mowing or plot size. While the contribution of residents declined and that of colonists increased, community biomass production did not change over time. The biomasses of residents and colonists were greatest at higher levels of species richness, partial QPhylo and FDQ of the respective species group, but community biomass was consistently weakly related to total species richness and diversity indices. Our study shows that in contrast to the period of succession, “mature” plant communities resulting from natural assembly processes, favouring the coexistence of multiple species and thus high biodiversity, do no longer show significant relationships between species richness and variables related to ecosystem functioning such as primary productivity.

Twelve years of repeated wild hog activity promotes population maintenance of an invasive clonal plant in a coastal dune ecosystem.

Invasive animals can facilitate the success of invasive plant populations through disturbance. We examined the relationship between the repeated foraging disturbance of an invasive animal and the population maintenance of an invasive plant in a coastal dune ecosystem. We hypothesized that feral wild hog (Sus scrofa) populations repeatedly utilized tubers of the clonal perennial, yellow nutsedge (Cyperus esculentus) as a food source and evaluated whether hog activity promoted the long‐term maintenance of yellow nutsedge populations on St. Catherine's Island, Georgia, United States. Using generalized linear mixed models, we tested the effect of wild hog disturbance on permanent sites for yellow nutsedge culm density, tuber density, and percent cover of native plant species over a 12‐year period. We found that disturbance plots had a higher number of culms and tubers and a lower percentage of native live plant cover than undisturbed control plots. Wild hogs redisturbed the disturbed plots approximately every 5 years. Our research provides demographic evidence that repeated foraging disturbances by an invasive animal promote the long‐term population maintenance of an invasive clonal plant. Opportunistic facultative interactions such as we demonstrate in this study are likely to become more commonplace as greater numbers of introduced species are integrated into ecological communities around the world.

Diverse Effects of a Seven-Year Experimental Grassland Fragmentation on Major Invertebrate Groups.

Habitat fragmentation is a major driver of biodiversity loss, but observed effects vary and may depend on the group examined. Time since fragmentation may explain some differences between taxonomical groups, as some species and thus species composition respond with a delay to changes in their environment. Impacts of drivers of global change may thus be underestimated in short-term studies. In our study we experimentally fragmented nutrient-poor dry calcareous grasslands and studied the response of species richness, individual density and species composition of various groups of invertebrates (gastropods, ants, ground beetles, rove beetles, orthoptera, spiders, woodlice) in 12 small (1.5 m * 1.5 m) and 12 large (4.5 m * 4.5 m) fragments and their corresponding control plots after 7 years. We further examined responses to fragmentation in relation to body size and habitat preferences. Responses to fragmentation varied between taxonomical groups. While spider species richness and individual density were lower in fragments, the opposite was true for an orthopteran species and woodlice. Species composition and β-diversity differed between fragments and control plots for some groups. However, the interaction treatment*plot size was rarely significant. Species with high occupancy rates in undisturbed control plots responded more negatively to the fragmentation, while species with large body size were relatively more abundant in fragments in some groups. No effect of the fragmentation was found for ants, which may have the longest lag times because of long-lived colonies. However, relationships between abundance and the species’ preferences for environmental factors affected by edge effects indicate that ant diversity too may be affected in the longer-term. Our results show the importance of considering different groups in conservation management in times of widespread fragmentation of landscapes. While species richness may respond slowly, changes in abundance related to habitat preferences or morphology may allow insights into likely long-term changes.

Canopy structure of woody landscape modulators determines herbaceous species richness along a rainfall gradient

Landscape modulators are ecosystem engineers that create distinct patches that differ from their surroundings in abiotic conditions and species composition. Woody plants are principal landscape modulators in many terrestrial ecosystems. The effects of woody landscape modulators on herbaceous species richness have been studied at the site level in Israel. Here we examine the effect of woody landscape modulators on the general pattern of herbaceous species richness over a large spatial scale along a rainfall gradient, and develop a novel quantitative model to explain that pattern. A uniform experimental design was implemented at five sites along a rainfall gradient in Israel. Herbaceous species richness was determined in woody (modulated) patches and in their surrounding (unmodulated) areas, both in undisturbed (control) plots and in plots in which the canopies of the woody plants had been removed. Herbaceous species richness increased asymptotically with increasing rainfall in the unmodulated areas, but not in the modulated patches of the no-removal plots. Removal of woody plant canopies resulted in a similar pattern of herbaceous species richness to that of the unmodulated areas. Woody landscape modulators modify the pattern of herbaceous species richness along rainfall gradients by creating a biotically induced gradient of abiotic conditions, mainly via their canopy structure. The proportion of species in the site-level species pool that are filtered into the modulated patches declines in strong negative correlation with increasing LAI of the landscape modulator. The combination of climatic and biotically induced gradients determines the overall pattern of herbaceous species richness in two-phase landscape mosaics.

Response of bird assemblages to windstorm and salvage logging — Insights from analyses of functional guild and indicator species

Natural disturbances, such as fire, windstorms and insect outbreaks, are important drivers of biodiversity in forest ecosystems, but at the same time cause large economic losses. Among the natural disturbances in Europe, windstorms cause the highest economic loss. After such storms, damaged forest stands are commonly salvage logged to restore economic value. However, such interventions could affect species assemblages of various taxonomic groups, including breeding birds. Despite these potential effects, investigations of the impacts of post-storm logging are largely lacking. We thus investigated assemblages of breeding birds in 21 logged and 21 unlogged windstorm-disturbed forest plots and 18 undisturbed, control forest plots using fixed-radius point-stop counts three, five and seven years after a windstorm within the Bavarian Forest National Park as part of the European Long-Term Ecosystem Research Network. We recorded 2100 bird individuals of 55 bird species. Bird assemblages were predominantly altered by the consequences of the windstorm and affected only to a minor degree by subsequent logging of storm-felled trees. Nevertheless, bird species richness was significantly reduced by post-storm logging within the first season. In general, the windstorm led to a shift in bird assemblage composition from typical forest species towards open- and shrub-land species. Assemblages of logged and unlogged disturbed plots consisted mainly of long-distance migrants and ground-foraging bird species, whereas assemblages of undisturbed control plots consisted of resident species that forage within vegetation. Both unlogged and logged storm-felled coniferous forest stands were inhabited by endangered or declining bird species, such as Water Pipit (Anthus spinoletta) on logged plots and Eurasian Redstart (Phoenicurus phoenicurus) on unlogged plots. Indicator species analyses suggested that species of unlogged storm disturbed plots depended on storm-created legacies, such as pits and snags, for foraging and nesting. Hence, we recommend reducing post-storm logging of these legacies to support species restricted to unlogged disturbed forest. To increase the diversity of breeding birds on the landscape scale, diverse logged and unlogged post-disturbance stands should be provided, which could be gained by a partial benign neglect strategy of storm disturbed forest stands.

Site impact after motor-manual and mechanised thinning in Mediterranean pine plantations

The study determined the site impacts of motor-manual and fully mechanised whole tree harvesting, as applied in the thinning of young pine plantations on the Tuscan coastline. The thinning was applied with selection criteria, removing between 36 and 39% of the tree number. The frequency of tree wounding was 1.5 and 5%, respectively for the mechanised and the motor-manual treatment. Wounds inflicted by the mechanised system were also four times smaller than those inflicted by the motor-manual system. The superior performance of the mechanised system was ascribed to its better capacity for handling cut trees. Soil bulk density increased by 3% and 6% after motor-manual and mechanised harvesting, respectively. The increase was small but significant, whereas the difference between treatments was not significant. Machine traffic resulted in a significant increase of CO2 concentration in the soil air, which was 0.4% in the undisturbed control plots and 0.8% in the machine tracks. No significant difference was found between the treatments. The CO2 concentration in the machine tracks was very near to the 1% critical threshold, beyond which biological activity is so constrained that soil recovery may be significantly delayed. When repeated entries are necessary, it is best to avoid creating new tracks by restricting traffic to designated permanent tracks. Properly applied mechanised harvesting does not cause heavier soil impacts than traditional motor-manual harvesting, but it results in a much lower stand damage. Foresters may support the introduction of mechanised harvesting, to the advantage of productivity, economics and work safety.

How does plant species composition change from year to year? A case study from the herbaceous layer of a submediterranean oak woodland

Over millions of years there is a long-term increase in species richness, accompanied by substantial turnover in species composition. However, little is known about species temporal turnover over shorter, ecologically relevant time periods, such as years. In the present study, we examine the inter-annual temporal turnover in species composition in 100 m2 plots of the herbaceous layer in a submediterranean oak woodland over six years. We found that approximately half of the accumulated number of species over the six years is accommodated as temporal turnover. We also found that species temporal turnover in undisturbed control plots was not significantly different from that in plots where vegetation was recovering naturally without assistance, i.e., plots undergoing ecological succession. Only in the most disturbed (continuously overgrazed) plots temporal turnover was low to non-existent. We therefore suggest that diversity estimates based on a single year of observations may seriously underestimate species richness or the detrimental effects of disturbance, at least at the 100 m2 scale. Furthermore, we found that, with the exception of the heavily grazed plots, short-lived species (annuals and biennials) did not display significantly greater temporal turnover than long-lived (perennial) species. Our analysis also supports that the space for time substitution applies in the patterns of species turnover. Spatial species turnover was comparable to temporal turnover. Species that are observed in many plots are also present in many years, and vice versa. Also, the similarity in species composition decreased as the time period between observations increased, as is the case with distance decay. Overall we conclude that the patterns of species turnover in time resemble those in space, and thus temporal turnover makes an important contribution to total biodiversity that should not be ignored.

Subtropical plantations are large carbon sinks: Evidence from two monoculture plantations in South China

Quantifying the net carbon (C) storage of forest plantations is required to assess their potential to offset fossil fuel emissions. In this study, a biometric approach was used to estimate net ecosystem productivity (NEP) for two monoculture plantations in South China: Acacia crassicarpa and Eucalyptus urophylla. This approach was based on stand-level net primary productivity (NPP, based on direct biometric inventory) and heterotrophic respiration ( R h). In comparisons of R h determination based on trenching vs. tree girdling, both trenching and tree girdling changed soil temperature and soil moisture relative to undisturbed control plots, and we assess the effects of corrections for disturbances of soil moisture and soil moisture on the estimation of soil CO 2 efflux partitioning. Soil microbial biomass and dissolved organic carbon were significantly lower in trenched plots than in tree girdled plots for both plantations. Annual soil CO 2 flux in trenched plots ( R h-t) was significantly lower than in tree-girdled plots ( R h-g) in both plantations. The estimates of R h-t and R h-g, expressed as a percentage of total soil respiration, were 58 ± 4% and 74 ± 6%, respectively, for A. crassicarpa, and 64 ± 3% and 78 ± 5%, respectively, for E. urophylla. By the end of experiment, the difference in soil CO 2 efflux between the trenched plots and tree-girdled plots had become small for both plantations. Annual R h (mean of the annual R h-t and R h-g) and net primary production (NPP) were 470 ± 25 and 800 ± 118 g C m −2 yr −1, respectively, for A. crassicarpa, and 420 ± 35 and 2380 ± 187 g C m −2 yr −2, respectively, for E. urophylla. The two plantations in the developmental stage were large carbon sinks: NEP was 330 ± 76 C m −2 yr −1 for A. crassicarpa and 1960 ± 178 g C m −2 yr −1 for E. urophylla.

Shrub expansion may reduce summer permafrost thaw in Siberian tundra

AbstractClimate change is expected to cause extensive vegetation changes in the Arctic: deciduous shrubs are already expanding, in response to climate warming. The results from transect studies suggest that increasing shrub cover will impact significantly on the surface energy balance. However, little is known about the direct effects of shrub cover on permafrost thaw during summer. We experimentally quantified the influence of Betula nana cover on permafrost thaw in a moist tundra site in northeast Siberia with continuous permafrost. We measured the thaw depth of the soil, also called the active layer thickness (ALT), ground heat flux and net radiation in 10 m diameter plots with natural B. nana cover (control plots) and in plots in which B. nana was removed (removal plots). Removal of B. nana increased ALT by 9% on average late in the growing season, compared with control plots. Differences in ALT correlated well with differences in ground heat flux between the control plots and B. nana removal plots. In the undisturbed control plots, we found an inverse correlation between B. nana cover and late growing season ALT. These results suggest that the expected expansion of deciduous shrubs in the Arctic region, triggered by climate warming, may reduce summer permafrost thaw. Increased shrub growth may thus partially offset further permafrost degradation by future temperature increases. Permafrost models need to include a dynamic vegetation component to accurately predict future permafrost thaw.