Ericaceous Shrubs Research Articles

Multiple-pathway succession in coastal Tsuga heterophylla, Thuja plicata, and Abies amabilis forests on northeastern Vancouver Island, British Columbia

Sustainable forest practices are often designed to mimic natural disturbance and successional processes, yet succession is poorly understood in many ecosystems. On northeastern Vancouver Island, the “disturbance hypothesis” is a widely assumed succession model asserting that shade-tolerant western redcedar (Thuja plicata Donn ex D. Don) and the ericaceous shrub salal (Gaultheria shallon Pursh) invade and colonize highly productive western hemlock (Tsuga heterophylla (Raf.) Sarg.) – Pacific silver fir (Abies amabilis Douglas ex J. Forbes) stands (HA) on zonal sites in the absence of stand-replacing wind disturbance. This leads to the development of low-productivity, low-density, uneven-aged, open-crowned redcedar–hemlock–salal stands (CH). In conflict with this model, old, apparently stable HA stands lacking redcedar can be found on such sites as well. We sought evidence for the predicted transition to CH stands by examining stand composition, crown closure, tree size class frequency distributions, salal cover, and redcedar establishment on young HA (∼90 years old), old HA (>160 years), and CH (>160 years) stands. When adjacent to a redcedar stand, young HA stands had fewer redcedar seedlings but more redcedar adult trees than old HA stands. However, redcedar abundance did not differ between young and old HA stands at distances further than 10 m from adjacent redcedar stands. This could indicate that redcedar recruits into HA stands at stand establishment and that redcedar seedling establishment is low under the thick canopy of young HA stands. The chronosequence data also suggest that both old HA and CH stands are self-replacing stand types in these forests, contrary to the disturbance hypothesis. We develop a new, multipathway model for this ecosystem that is based on the chronosequence data and life-history traits of the focal tree species and suggest that disturbance plays a role opposite to the equilibrium model.

Spatial variability of soil lipids reflects vegetation cover in a French peatland

The purpose of this study was to show how current vegetation in a peatland is imprinted on the lipid fraction of the underlying soil. La Guette is a fen peatland in Central France dominated by Sphagnum spp. and ericaceous shrubs, colonized by sedges (Molinia caerulea) and trees since the 1970s (Betula pendula and Pinus sylvestris). Lipid were identified and quantified in the most abundant plants and in samples collected at the base of M. caerulea tussocks. Among relevant biomarkers, tricyclic diterpenes and methoxy-serratenes stood out as specific for P. sylvestris, betulin derivatives as specific for B. pendula, and some pentacyclic triterpene ketones and acetates as biomarkers of Ericaceae. Multivariate analysis applied to biomarker concentration in soil samples from several sites permitted distinguishing three different types of vegetation cover: (i) closed vegetation dominated by P. sylvestris; (ii) closed vegetation dominated by B. pendula and (iii) open vegetation or semi-open vegetation (early colonization by trees) comprising mainly Ericaceae, Sphagnum and graminoids. Comparison of tree-specific biomarker concentrations with estimates of tree biomass allowed establishing of quantitative relationships that were valid over at least 80m2 around the sampling site. Although preliminary, the results are promising in attempting to relate biomarker concentrations in geological archives to paleo-biomass.

Contrasting soil fungal communities in Mediterranean pine forests subjected to different wildfire frequencies

Mediterranean forest ecosystems are characterized by various vascular plant groups with their associated mycorrhizae and free living soil fungi with various ecological functions. Fire plays a major role in Mediterranean ecosystem dynamics and impacts both above- and below-ground community structure and functioning. However, studies on the effects induced by altered disturbance regimes (associated with recent land use and climate extremes) on fire ecology and especially on its below-ground impacts are few. The objectives of this study were to evaluate the effects of different wildfire regimes on soil fungal community structure using two different molecular methods. We investigated the long-term effects of wildfire on soil fungal communities associated with Pinus pinaster forests in central Portugal, by comparing the results of denaturing gradient gel electrophoresis (DGGE)-based profiling with those obtained with 454 pyrosequencing. Four forest stands with differing fire history and fire return interval, and vegetation cover (mature forest, early successional stage of pine regeneration, and forest converted to scrubland) were sampled 6 years after the last fire event. The pyrosequencing-based approach indicated ca. eight-fold higher numbers of taxa than DGGE. However, fungal community fingerprinting data obtained for the different study stands with DGGE were congruent with those obtained with pyrosequencing. Both short (7.6 years) and long (24 years) fire return intervals (indicated by the presence of ericaceous shrubs in the understorey) induced a decrease in the abundance ratio between basidiomycetes and ascomycetes and appeared to reduce the frequency of ectomycorrhizal fungal species and saprophytes. Wildfire significantly reduced the frequency of late stage successional taxa (e.g. Atheliaceae and Cantharellales) and known or putative saprophytes belonging to the Clavulinaceae and the Archaeorhizomycetaceae. Conversely, early successional fungal species belonging to the Thelephoraceae were favoured by both fire return intervals, while the abundance of Cortinarius and Hebeloma, which include several Cistus-specific species, increased with short wildfire return intervals. This last finding highlights the relationship between post-fire vegetation composition and cover (vegetation successional stage), and fungal symbionts. We hypothesise that these changes could, in the long term, exhaust the resilience of Mediterranean pine forest vegetation and associated soil fungal communities by preventing pine regeneration.

Enigmatic Ethiopian endemic rodent Muriculus imberbis (Rüppell 1842) represents a separate lineage within genus Mus

The phylogenetic position of the Ethiopian striped mouse (Muriculus imberbis) has remained obscure since its description. Here, we report, for the first time, the phylogenetic analysis of this species using mitochondrial (cytochrome b) and nuclear (interphotoreceptor binding protein) gene sequences obtained from a specimen recently caught in the Galama Mountain in the south-central Ethiopian highland region. The recent finding of the species in ericaceous shrub in the Afroalpine habitat is remarkable, as decades of attempts to capture it in this habitat failed, probably because of inappropriate trapping methods. Our analyses strongly suggest that the Ethiopian striped mouse does not belong to a distinct monotypic genus, but to the genus Mus, as the ancient lineage of the African subgenus Nannomys

An evaluation of thinning to improve habitat for capercaillie (Tetrao urogallus)

In Scots pine (Pinus sylvestris) forests the composition of the ground flora can be affected by the amount of light reaching the forest floor, influencing the balance between the three common ericaceous shrubs bilberry (Vaccinium myrtillus), cowberry (Vacciniumvitis-idaea) and heather (Calluna vulgaris). A pinewood ground flora with more than 20% bilberry cover is considered good habitat for capercaillie (Tetrao urogallus), a large forest grouse of considerable conservation interest throughout Europe. Old, semi-natural Scots pine woodland is considered its prime habitat in Scotland, although this is limited in area compared to twentieth century planted forests. Action to manipulate environmental conditions within Scots pine plantations by altering light levels to favour bilberry through thinning and felling could potentially increase greatly the area of available capercaillie habitat in Scotland. We implemented a five year study to look at bilberry response to variable intensity thinning in two Scots pine plantations, where thinning followed management guidance for capercaillie available at the time. Bilberry was present in both forests but a positive response to thinning was not universal; although at both sites bilberry cover increased significantly over five years with levels >20% cover reached, this could only be attributed to the thinning treatment at one of the sites. A treatment of small patch clearfelling did not lead to losses in bilberry. Management guidance published after the trial had begun, identified the appropriate intensity of thinning for enhancing bilberry cover at our study sites, indicated by the relative increase of bilberry in the plots where the prescription had been followed. Although there was no significant treatment effect by year five, 42% average bilberry cover was reached at one site tested. However the format of this guidance, a range of stem density-tree height combinations, was difficult to apply using typical forest management data and we explore redefining the guidance as a post thinning stand basal area range. We suggest >22 to <31m2ha−1 basal area would be appropriate in Scots pine plantations established at normal spacing and subject to the commonest form of selective thinning regime. This range in basal area can be achieved without conflicting with management for timber production. Our results also support small patch clearfelling as a method of diversifying plantation age structure which is compatible with maintaining capercaillie brood habitat.

Is rewetting enough to recover Sphagnum and associated peat-accumulating species in traditionally exploited bogs?

When restoring ecosystems, the simple removal of stresses causing degradation may seem preferable over other more costly and time consuming approaches. However, some restoration techniques can be implemented at reasonable cost and with increased efficiency in certain cases. We examined the successional trajectories of vegetation within abandoned block-cut peatlands in a major peat-producing region of Eastern Canada to evaluate whether the use of rewetting as a restoration technique can assist in the recovery of a typical bog plant community dominated by Sphagnum compared to spontaneous recolonization alone. We surveyed a total of 55 trenches in 6 peatlands twice, ~25 and ~35 years after the cessation of peat extraction. Canonical ordinations evidenced a generalized process of afforestation during the decade studied, partially driven by agricultural drainage in the surrounding landscape. Plant communities were dominated by ericaceous shrubs that hampered the spontaneous recovery of a Sphagnum-dominated system typical of bogs in the short and medium-term. Three of the six peatlands surveyed were partially restored by blocking drainage ditches. There, we surveyed plant composition in rewetted (28) and non-rewetted (26) trenches and observed that rewetting mitigated the increase in tree dominance, decreased the dominance by ericaceous shrubs, and favored the spread of non-vascular species with a wet habitat preference (notably Sphagnum species from the Cuspidata section). We conclude that the use of low intervention restoration techniques in block-cut bogs, such as the blockage of former drainage ditches, can re-orient undesired vegetation trajectories driven by spontaneous recolonization alone.

Partitioning of soil phosphorus regulates competition between Vaccinium vitis-idaea and Deschampsia cespitosa.

It has been hypothesized that the wide range of forms and complexities of phosphorus (P) in soil may result in resource partitioning that contributes to the maintenance of plant species diversity. Here, we test whether the graminoid, Deschampsia cespitosa, and the ericaceous shrub, Vaccinium vitis-idaea, which often coexist, display preferences in utilization of P forms, and differ in their production of extracellular P-degrading enzymes. We provided plants with no additional P, or P forms with decreasing lability, namely sodium phosphate (SP), D-glucose 6 phosphate (DG6P), sodium phytate (PASS), and a combination of SP, DG6P, and PASS. We also tested if preferences for P forms affected the competitive outcomes between the two species compared between conspecifics, as indicated by shoot biomass and acquisition of nitrogen (N) and P. Both D. cespitosa and V. vitis-idaea produced the greatest biomass when supplied with a mix of all three forms of P. Of the three forms of P tested alone, shoot biomass produced by both species was least when supplied with SP. D. cespitosa performed better when grown with PASS or a mix of all P forms compared with the performance of V. vitis-idaea on these substrates. This was reflected by substantially greater phytase activity on the surface of its roots compared with V. vitis-idaea. In contrast, V. vitis-idaea produced more phosphomonoesterase to hydrolyze the simple organic P form, DG6P. Although N was kept constant in the treatments, the ability of plants to acquire it was dependent on species identity, competition, and P supply. These findings provide direct evidence for preferences toward specific forms of P and indicate a key role played by organic forms of P. The results support the idea that partitioning for soil P is one factor regulating plant competition, and ultimately, community composition. Our data also highlight the importance of the interplay between P supply and N acquisition.

Monitoring Epacris muelleri on unreachable cliffs in the Western Blue Mountains, Australia

SummaryAccurate, repeatable estimates of population densities are often desired for vegetation monitoring. However, conventional transect and quadrat field sampling methods are not always applicable to plants such as the rare shrub Epacris muelleri Sond., growing on largely inaccessible cliffs and rock faces. E. muelleri is an ericaceous shrub restricted to the Blue Mountains region in New South Wales, which is to be monitored to detect potential effects of underground coal mining. In this manuscript, we evaluated observer error associated with density estimates to assess suitability of applying the timed‐meander method to this species. The results indicate that a visual search method using binoculars can generate repeatable results among observers with very different experience levels. However, there is a large margin of error in estimating density when there are many plants growing in close association or overlapping on a cliff. Nonetheless, with a strict set of protocols and further evaluation, this method shows promise as a rapid yet robust method for carrying out repeatable surveys for quantifying changes in the population.

Ericaceae stabilize peat and foster Sphagnum majus establishment at pool margins in restored peatlands

Pools are recognized as biodiversity hotspots in natural peatlands, thus creating pools would increase the ecological value of restored peatlands. However, the peaty margins of artificial pools are unstable, as frost heave creates much surface erosion restricting establishment of vascular plant seedlings. This study evaluates the ability of heather shrubs (Ericaceae) to stabilize created pool margins in restored peatlands. Andromeda polifolia var. latifolia and Vaccinium macrocarpon plants were introduced to form a sparse cover (<25%) at pool margins. Sphagnum majus fragments were spread simultaneously between the shrubs over half the surface at a density of 50% in ground cover, and seeds of herbaceous plants typical of pool margins were sown at two distances from the low-water mark (0.5 and 3.5m). We examined the impact of Ericaceae on (1) frost heave intensity, (2) S. majus establishment and (3) herbaceous species establishment. Treatments using ericaceous shrubs or Sphagnum, both alone or in combination, all reduced frost heave by about 50%. After one year, it also increased survival of S. majus (four-fold) on the wettest soil along the banks. However, at a greater distance from the water (2 and 3.5m), the Sphagnum cover was not influenced by the presence of Ericaceae. Establishment and growth of herbaceous plants grown from seeds were not influenced by the presence of Ericaceae. This study demonstrates the potential of Ericaceae for stabilizing the peat substrate close to the water line and improving survival of S. majus introduced at the immediate edge of created pools.

Managing Understory Vegetation for Maintaining Productivity in Black Spruce Forests: A Synthesis within a Multi-Scale Research Model

Sustainable management of boreal ecosystems involves the establishment of vigorous tree regeneration after harvest. However, two groups of understory plants influence regeneration success in eastern boreal Canada. Ericaceous shrubs are recognized to rapidly dominate susceptible boreal sites after harvest. Such dominance reduces recruitment and causes stagnant conifer growth, lasting decades on some sites. Additionally, peat accumulation due to Sphagnum growth after harvest forces the roots of regenerating conifers out of the relatively nutrient rich and warm mineral soil into the relatively nutrient poor and cool organic layer, with drastic effects on growth. Shifts from once productive black spruce forests to ericaceous heaths or paludified forests affect forest productivity and biodiversity. Under natural disturbance dynamics, fires severe enough to substantially reduce the organic layer thickness and affect ground cover species are required to establish a productive regeneration layer on such sites. We succinctly review how understory vegetation influences black spruce ecosystem dynamics in eastern boreal Canada, and present a multi-scale research model to understand, limit the loss and restore productive and diverse ecosystems in this region. Our model integrates knowledge of plant-level mechanisms in the development of silvicultural tools to sustain productivity. Fundamental knowledge is integrated at stand, landscape, regional and provincial levels to understand the distribution and dynamics of ericaceous shrubs and paludification processes and to support tactical and strategic forest management. The model can be adapted and applied to other natural resource management problems, in other biomes.

Laboratory charring conditions affect black carbon properties: A case study from Quebec black spruce forests

Black carbon (BC) is an important residue of wildfires in boreal forests, but its characteristics depend on its formation conditions. The objective of this study was to characterize the chemical and physical properties of BC produced under controlled laboratory conditions, while mimicking a gradient of wildfire severity. We used fuels originating from mosses, ericaceous shrubs and spruce trees, as they constitute the major types available in boreal forests. We varied the maximum temperature (MT) from 75 to 800°C, the duration of charring from 0.5 to 24h and the abundance of O2. BC properties were analyzed using elemental analysis and proximate analysis, solid state 13C nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM) and surface area (SA) analysis. MT was the most significant factor affecting both chemical and physical changes. Results from 13C NMR spectroscopy indicated that 350°C was a threshold temperature, above which spectra became dominated by aromatic structures for all fuels. Charring duration affected BC composition at both low (250°C for 12h vs. 24h) and high (600°C for 0.5h vs. 6h) MT. The presence of O2 influenced BC composition mainly at low MT (250°C) and resulted in accelerated alkyl C degradation, accompanied with a distinct decrease in yield. Results from the SA analysis and the SEM micrographs showed that fuel type influenced BC physical properties, with moss-derived BC presenting higher surface area and microporosity than BC of woody origin.

Stephanitis blatchleyi(Hemiptera: Tingidae): First Host-Plant Association for a Rarely Collected Lace Bug

Stephanitis blatchleyi, described in 1925, is a rarely collected lace bug known only from a few localities in peninsular Florida; its host plants previously were unknown. We observed adults, nymphs, exuviae, and foliar chlorosis on the ericaceous shrub rusty lyonia (Lyonia ferruginea) at a site in Clay County, Florida, from December 2007 to October 2012. Feeding symptoms were confined to leaves of lower branches. Although the tingid was not found elsewhere in Florida on L. ferruginea (or on L. fruticosa), additional fieldwork probably will show that S. blatchleyi is more widespread than suggested by our sampling.

Can indicator species predict restoration outcomes early in the monitoring process? a case study with peatlands

Success in ecological restoration is rarely assessed rigorously due to insufficient planning for post-restoration monitoring programs, limited funding and, especially, lack of scientifically validated evaluation criteria and protocols. In this article, we propose the use of the Indicator Value Index technique (IndVal), which statistically determines the association of species to one or several particular site types, to obtain indicators of success at the early stages of the recovery process in restoration projects. Peat bogs extracted by the vacuum method, subsequently restored by a moss-transfer technique and regularly monitored for ~10 years were used as a model system to test this approach. We first identified 34 restored sectors of ~10ha from 4 to 11 years old in twelve eastern-Canadian bogs. These sectors were then classified according to their degree of success in recovering a typical sphagnum moss carpet (restoration goal). Then, we retrospectively reviewed vegetation communities recorded at the third year after restoration to identify indicator species of different categories of restoration success, using the IndVal methodology. By identifying early indicator species, our method provides a tool that guides intervention soon after restoration if a site is not on a desired successional trajectory. Typical bog species, namely the bryophytes S. rubellum and Mylia anomala and the tree Picea mariana, were indicative of successful restoration; while bare peat, lichens and one species of ericaceous shrubs (Empetrum nigrum), which cope better under drier conditions, indicated sites where restoration failed. A surprising finding was that the moss Polytrichum strictum, which is known to facilitate the colonization of sphagnum in disturbed peatlands, is an early indicator of unsuccessful restoration. This finding made us question the nursing role of P. strictum at a cover threshold above ca. 30%, when P. strictum could be outcompeting sphagnum and become dominant. We conclude that the IndVal method is an effective tool to identify early indicators of restoration success when combined with a thoughtful examination of species frequency and cover within each site type.

Heaths with dwarf ericaceous shrubs and Alpine juniper (Juniperus alpina) in the Dinaric Alps: A nomenclatorial and synsystematic re-appraisal

Abstract The ecology and phytosociology of north-western Dinaric heaths of the association Rhododendro hirsuti-Juniperetum alpinae Horvat ex Horvat et al. 1974 nom. corr. prop. as well as the syndynamics and synsystematics of heaths in the Dinaric Alps are discussed. While the structure (physiognomy) of these stands is very homogenous and dominated by few species, the flora is heterogeneous, since ecotonal areas, where heaths are most frequently developed, represent a contact zone of elements of different syntaxa. Due to an abrupt reduction in pasture activities strong encroachments of shrubs and trees have become common, which additionally contribute to the floristic heterogeneity of the heaths. Although the identification and circumscription together with synecology and synchorology of heaths in general are more or less easily understood and straightforward, their floristic affinities, in relation to structure homogeneity and syndynamics, are complicated, which led to the proposal of several synsystematic schemes depending on interpretation of the relationship between flora and structure of stands. Dinaric heaths are classified into three classes, Erico-Pinetea, Vaccinio-Piceetea and Festuco-Brometea and a classification scheme is proposed together with nomenclatorial revision of the analyzed heaths with dwarf ericaceous shrubs and Alpine juniper (Juniperus alpina) in the Dinaric Alps

Effects of two contrasting hemiparasitic plant species on biomass production and nitrogen availability

Hemiparasitic plants can substantially change plant community structure; the drainage of host resources has a direct negative effect on host biomass and, as a consequence, promotes non-host biomass production (parasitism pathway); on the other hand, hemiparasitic litter inputs can enhance nutrient cycling which may have an indirect positive effect on both host and non-host biomass production (litter pathway). We evaluated the net effect of both pathways on total shoot biomass (with and without the hemiparasite) and shoot biomass of graminoids, forbs and ericaceous shrubs using a removal experiment in three sites infested with the annual Rhinanthus angustifolius, and three sites infested with the biennial Pedicularis sylvatica. We addressed the potential importance of litter effects by determination of litter quantity and quality, as well as modeling N release during decomposition. In the second year after removing the hemiparasites, total plant biomass at Rhinanthus sites was 24 % higher in weeded plots than in control plots, while weeding had no significant effect at Pedicularis sites. The increase in total biomass following Rhinanthus removal was mainly due to a higher biomass of graminoids. The amount of litter produced by Rhinanthus was only half of that produced by Pedicularis; N contents were similar. The amount of N in the litter was 9 and 30 % of the amount removed by mowing for Rhinanthus and Pedicularis sites, respectively. Within 2 months, about 45 % of the N in both hemiparasitic litter types was released by decomposition. Our results suggest that in addition to the suppression of host biomass due to parasitism, positive litter feedbacks on host and non-host biomass-via an increase in nutrient availability-also affect plant community structure. We propose that, depending on the particular hemiparasite and/or site conditions, these positive litter feedbacks on shoot biomass can compensate for the negative effect of parasitism.

Allelopathic Exudates of Cogongrass (Imperata cylindrica): Implications for the Performance of Native Pine Savanna Plant Species in the Southeastern US

We conducted a greenhouse study to assess the effects of cogongrass (Imperata cylindrica) rhizochemicals on a suite of plants native to southeastern US pine savanna ecosystems. Our results indicated a possible allelopathic effect, although it varied by species. A ruderal grass (Andropogon arctatus) and ericaceous shrub (Lyonia ferruginea) were unaffected by irrigation with cogongrass soil "leachate" (relative to leachate from mixed native species), while a mid-successional grass (Aristida stricta Michx. var. beyrichiana) and tree (Pinus elliottii) were negatively affected. For A. stricta, we observed a 35.7% reduction in aboveground biomass, a 21.9% reduction in total root length, a 24.6% reduction in specific root length and a 23.5% reduction in total mycorrhizal root length, relative to the native leachate treatment. For P. elliottii, there was a 19.5% reduction in percent mycorrhizal colonization and a 20.1% reduction in total mycorrhizal root length. Comparisons with a DI water control in year two support the possibility that the treatment effects were due to the negative effects of cogongrass leachate, rather than a facilitative effect from the mixed natives. Chemical analyses identified 12 putative allelopathic compounds (mostly phenolics) in cogongrass leachate. The concentrations of most compounds were significantly lower, if they were present at all, in the native leachate. One compound was an alkaloid with a speculated structure of hexadecahydro-1-azachrysen-8-yl ester (C23H33NO4). This compound was not found in the native leachate. We hypothesize that the observed treatment effects may be attributable, at least partially, to these qualitative and quantitative differences in leachate chemistry.

Lichen-Spruce Woodland Early Indicators of Ecological Resilience Following Silvicultural Disturbances in Qu&amp;#233;bec’s Closed-Crown Forest Zone

Lichen woodlands (LW) located in the closed-crown boreal forest are not a successional stage moving towards a closed black spruce feathermoss stand (FM), but an alternative stable state, due to their previous forest history, and the occurrence of LWs located nearby closed-crown FM stands. Therefore, afforestation in those LWs through site preparation and plantation could shift back LW into FM stands. We implemented an experimental design with different combinations of silvicultural treatments in both site types (LW, FM). We monitored the evolution of plant diversity and the physiology of three bio-indicators (Picea mariana, Kalmia angustifolia, Rhododendron groenlandicum) in different microsites created by the silvicultural treatments. The return to the initial composition was noticed only two years after treatments, especially in the LW stands, thus indicating a higher level of early ecosystem resilience in LWs compared to FM stands. Mean species cover, especially in the FM stands, decreased the most in the skid trails created by logging, probably due to a lack of acclimation of bryophytes to open stand conditions. Conversely, ericaceous shrubs and lichens found in the LWs were already acclimated to open stand conditions, which give to LWs a restructuring advantage compared to FM plant communities after silvicultural treatments. Overall, FM and LW short-term resilience was similar, indicating equally efficient ecosystem reorganization in both stands. The comparable early resilience in managed LW and FM stands, in terms of plant biodiversity, contradicts the presumed fragility of LW stands, especially in this case where LWs are assumed to be an alternative stable state created by compound disturbances. Silvicultural treatments maintained the functional group diversity in LWs, a key element for ecosystem resilience. Therefore, this study support the idea that plantation following site preparation in LWs could be a valuable management strategy to reach several objectives, such as increasing forest carbon sinks.

Afforestation of Black Spruce Lichen Woodlands by Natural Seeding

Black spruce-lichen woodlands (LW) are naturally occurring unproductive low tree density stands within the eastern North American closed-crown boreal forest. Natural reforestation in LWs is impeded by the lichen mat and ericaceous shrubs that inhibit seedling establishment. Disk scarification is a mechanical site preparation method that creates furrows where lichens and shrubs are removed and mineral soil is exposed, which is the preferred seedbed for black spruce natural regeneration. The objective of this study was to quantify the impact of disk scarification on black spruce establishment in LWs by natural seeding. Disk scarification was performed amid scattered seed trees in six study sites located in the central area of boreal Quebec's spruce-moss bioclimatic domain. Newly established black spruce seedlings were significantly more abundant (ca. 81%; χ2 = 28.72, P < 0.001) in the furrows of scarified plots even though the proportion of disturbed soil was small (ca. 20%). Seedling establishment occurred for at least 3 years following scarification, with a peak in the first year. The distribution and density of seed trees (112‐363 stems ha−1) did not limit natural seedling establishment in this study. Five years after scarification, observed densities and stocking levels of newly established black spruce seedlings were sufficient to expect afforestation without planting in scarified LWs.

Predicting Microstegium vimineum invasion in natural plant communities of the southern Blue Ridge Mountains, USA

Shade-tolerant non-native invasive plant species may make deep incursions into natural plant communities, but detecting such species is challenging because occurrences are often sparse. We developed Bayesian models of the distribution of Microstegium vimineum in natural plant communities of the southern Blue Ridge Mountains, USA to address three objectives: (1) to assess local and landscape factors that influence the probability of presence of M. vimineum; (2) to quantify the spatial covariance error structure in occurrence that was not accounted for by the environmental variables; and (3) to synthesize our results with previous findings to make inference on the spatial attributes of the invasion process. Natural plant communities surrounded by areas with high human activity and low forest cover were at highest risk of M. vimineum invasion. The probability of M. vimineum presence also increased with increasing native species richness and soil pH, and decreasing basal area of ericaceous shrubs. After accounting for environmental covariates, evaluation of the spatial covariance error structure revealed that M. vimineum is invading the landscape by a hierarchical process. Infrequent long-distance dispersal events result in new nascent sub-populations that then spread via intermediate- and short-distance dispersal, resulting in 3-km spatial aggregation pattern of sub-populations. Containment or minimisation of its impact on native plant communities will be contingent on understanding how M. vimineum can be prevented from colonizing new suitable habitats. The hierarchical invasion process proposed here provides a framework to organise and focus research and management efforts.

A 2200-Year Record of Permafrost Dynamics and Carbon Cycling in a Collapse-Scar Bog, Interior Alaska

Recent high-latitude warming is increasing the vulnerability of permafrost to thaw, which is amplified by local disturbances such as fire. However, the long-term ecological effects and carbon dynamics are not well understood. Here we present a 2200-year record of pollen, plant macrofossils, testate amoebae, and apparent carbon (C) accumulation rates from two peat cores in a collapse-scar bog (thermokarst) near Fairbanks, Alaska. A black spruce ecosystem with low apparent C accumulation rates existed on the site during the first ~1500 years of the record. We identify two thaw events, which are linked to local fires. Permafrost aggraded rapidly following the first thaw, which we attribute to local vegetation feedbacks and a cooler climate. The second thaw event at 525 cal y BP is preceded by a stand-replacing fire, as evidenced by a drastic decline in Picea and an initial increase in Epilobium, Salix, and ericaceous shrubs, followed by a sustained increase in Populus. Locally, the forest does not recover for more than 100 years, and the site has remained permafrost-free for the last 500 years. Following thaw, average apparent C accumulation rates (60 to >100 g C m−2 y−1) are 5–6 times higher than average boreal C accumulation rates, indicating that peat C accumulation rates can remain substantially elevated for much more than a century following thaw. The low apparent C accumulation for the formerly forested, permafrost peat (<5 g C m−2 y−1) may suggest that C accumulation increases substantially following thaw, but it remains unknown whether deep peat C loss occurred immediately following thaw. Well-preserved Sphagnum peat dominates during this period of rapid accumulation, except for an interval from ~400 to 275 cal y BP which alternates between Sphagnum and vascular plant-dominated peat and wetter, minerotrophic conditions. A decline in Picea pollen during this interval and again ~100 cal y BP suggests a decrease in suitable substrate for tree growth likely attributable to thermokarst expansion on the collapse-scar margin. These findings suggest that the combined effects of fire and thermokarst will result in a long-term reduction of spruce ecosystems in interior Alaska.