Disturbance Type and Plant Successional Communities in Bahamian Dry Forests

Different disturbances in similar habitats can produce unique successional assemblages of plants. We collected plant species composition and cover data to investigate the effects of three common types of disturbances—fire, anthropogenic clearing (‘cleared’), and clearing followed by goat grazing (‘cleared‐and‐grazed’)—on early‐successional coppice (dry forest) community structure and development on Eleuthera, Bahamas. For each disturbance type, both the ground layer (<0.5 m height) and shrub layer (>0.5 m height) were sampled in eight patches (>1 ha) of varying age (1–28 yr) since large‐scale mature coppice disturbance. Overall, plant communities differed among disturbance types; several common species had significantly higher cover in the shrub layer of fire patches, and cleared‐and‐grazed patches exhibited higher woody ground cover. Total percent cover in the shrub layer increased in a similar linear fashion along the investigated chronosequence of each disturbance type; however, cover of the common tree species, Bursera simaruba, increased at a notably slower rate in cleared‐and‐grazed patches. The pattern of increase and subsequent decrease in cover of Lantana spp. and Zanthoxylum fagara in the shrub layer was characterized by longer persistence and higher covers, respectively, in cleared‐and‐grazed patches, which also exhibited low peak cover and fast decline of nonwoody ground cover. Our results suggest that goats may accelerate some aspects of succession (e.g., quickly removing nonwoody ground cover) and retard other aspects (e.g., inhibiting growth of tree species and maintaining early‐successional shrubs in the shrub layer). These effects may lead to different successional trajectories, and have important conservation implications.     

Changes in woody vegetation abundance and diversity after natural disturbances causing different levels of mortality

Questions: How does woody vegetation abundance and diversity differ after natural disturbances causing different levels of mortality? Location: Abies balsamea–Betula papyrifera boreal mixed‐wood stands of southeast Quebec, Canada. Methods: Woody vegetation abundance and diversity were quantified and compared among three disturbance‐caused mortality classes, canopy gap, moderate‐severity disturbances, and catastrophic fire, using redundancy analysis, a constrained linear ordination technique, and diversity indices. Results: Substantial changes in canopy tree species abundance and diversity only occurred after catastrophic fire. Shade‐tolerant, late‐successional conifer species remained dominant after canopy gap and moderate‐severity disturbances, whereas shade‐intolerant, early‐successional colonizers dominated canopy tree regeneration after catastrophic fire. Density and diversity of mid‐tolerant and shade‐intolerant understory tree and shrub species increased as the impact of disturbance increased. Highest species richness estimates were observed after catastrophic fire, with several species establishing exclusively under these conditions. Relative abundance of canopy tree regeneration was most similar after canopy gap and moderate‐severity disturbances. For the sub‐canopy tree and shrub community, relative species abundances were most similar after moderate‐severity disturbances and catastrophic fire. Vegetation responses to moderate‐severity disturbances thus had commonalities with both extremes of the disturbance‐caused mortality gradient, but for different regeneration layers. Conclusions: Current spatio‐temporal parameters of natural disturbances causing varying degrees of mortality promote the development of a complex, multi‐cohort forest condition throughout the landscape. The projected increase in time intervals between catastrophic fires may lead to reduced diversity within the system.     

The age of Calluna stands moderates post‐fire regeneration rate and trends in northern Calluna heathlands

Questions: Does stand age influence the direction and rate of post‐fire successional dynamics in coastal Calluna heaths and can old degraded heath vegetation be restored through reintroduction of fire? Location: Coastal heaths in the Tarva archipelago, central Norway. Methods: We investigated revegetation dynamics after experimental fires set in young (8 years since last fire) and old (>50 years since last fire) grazed heath stands. A repeated measures design was used, with floristic data recorded in permanent plots in the post‐fire successions (n=12) over a 7‐year period. The data were analysed using multivariate ordination techniques (PCA, RDA and PRC) and mixed effects models. Results: The age of Calluna stands strongly influenced post‐fire succession, different trends due to age explained 10.4% of variation in floristic data. Young heath showed faster succession towards pre‐fire community composition than old heath, and this could partially be explained by succession‐related factors: young heath had lower cover of mosses and lichens in the pre‐burned vegetation, and lower cover of litter early in succession. Young heath had a less pronounced overall community response to fire than old heath. Vegetative regeneration of C. vulgaris was absent in both old and young heath, but Calluna still re‐established as the dominant species within 5–7 years in both young and old stands. Regeneration dynamics were also affected by habitat conditions, different trends due to habitat explained 6% of variation. Conclusions: Our study demonstrates that old stands do develop characteristic heathland vegetation and structure after fire, and while potential invasives into the system such as trees and rhizomatous species are present, they do not impair Calluna regeneration or vegetation development towards the target heathland community composition and structure. Further, as our young stands are only in their second fire rotation after restoration, we suggest that characteristic dynamics of managed heathlands can re‐establish relatively rapidly, even in severely degenerated sites (>50 years since last fire). Site‐specific factors also need to be considered. We conclude that there is restoration potential in old heaths, despite slow dynamics in the first rotation.     

Human disturbance and environmental factors as drivers of long‐term post‐fire regeneration patterns in Mediterranean forests

Question: What are the main forces driving natural regeneration in burned mature Mediterranean forests in the medium‐long term and what are the likely successional trajectories of unmanaged vegetation? Location: Valencia Region, eastern Spain. Methods: A wildfire burned 33 000 ha of Pinus halepensis and P. pinaster forest in 1979, and subsequent smaller wildfires took place between 1984 and 1996. The study was designed to sample the range of environmental and disturbance (fire recurrence and land use) conditions. The territory was classified into 17 different geomorphological and fire‐recurrence units. Vegetation cover and floristic composition were measured on a total of 113 plots (1000 m² each) randomly selected within these units. Results: The results show that 23 years after the fire the regenerated vegetation consists of successional shrublands, and that forest ecosystem resilience can be very low. The vegetation presents a strong correlation with most of the environmental variables, but fire (one or two fires), soil type and land use (in that order) are the main drivers of vegetation composition. Quercus coccifera shrublands persist on limestone soils while diverse types of other shrublands (dominated by seeder species) are found on marl soils. Conclusions: The results of this study indicate that disturbance factors strongly coupled to human activities, such as land use and fire, play a critical role in the current state of vegetation. Fire creates vegetation patches in different successional states while land use and soil type define the different types of shrubland in terms of their specific composition.     

Forest responses to the large-scale east coast fires in Korea

The east coast forest fires of April 2000 were Koreas largest recorded fires. This, along with the fact that they took place in the region most frequently affected by fire, attracted a great deal of attention. Due to the variations in wind, topography and pre-fire forest stands, a heterogeneous landscape mosaic of burn severity was created across the region. It turned out to be an excellent opportunity to study various landscape-scale impacts of fires on forest dynamics. Therefore, we investigated stands in the 23794ha of burned forest region, in terms of burn severity, vegetation regeneration and forested landscape change as a measure of community stability. Using the geographic information system technique, we analyzed the differential severity and post-fire recovery of pre-fire forest types of different stand age both at stand and species level. Analysis showed that pre-fire vegetation was composed of mainly pine (Pinus densiflora) stands that occupied 70% of the whole forested area, while pine-hardwood and hardwood stands occupied only 28% and 3%, respectively. In addition, two-thirds of all stands were less than 30-years-old. Pine stands were the most severely burned, while conversely pine-hardwood and hardwood stands were less vulnerable. This implied that pine forests had fire-prone characteristics. Vegetation recovery went the opposite way; that is, the regenerating vegetation cover was 71% at pre-fire hardwood stands, and 65% and 53% at pine-hardwood and pine stands, respectively. However, these recovery rates were strikingly fast, considering that investigation took place about 3months after the fires. Fire did not initiate successional processes, but tended to accelerate the predicted successional changes by releasing pre-fire understory species that survived the fires and regenerated by sprouting. The dominant pre-fire tree species (P. densiflora) was susceptible to fire and not resilient enough to reestablish in competition with oak species. Contrary to pines, the abilities of oak species, mainly Quercus mongolica and Q. variabilis, to survive fires and to resprout vigorously made them dominant at most post-fire stands. These shifts in species abundance caused drastic changes to the landscape: from pine-dominated to oak-dominated stands without any notable change in species composition. The patterns in forest regeneration that we observed in Korea may be representative of forest responses to any long-term repeated disturbances, including fire.     

Post-fire bryophyte dynamics in Mediterranean vegetation

Abstract. Bryophyte dynamics after fire in the Mediterranean macchia of Southern Italy was studied both by diachronic and synchronic approaches. Changes of bryophyte cover and species composition were found in relation to both age and fire intensity. During the first 2 yr after fire, bryophytes dominated the plots which had experienced the highest fire intensity while herbs were dominant in plots affected by lighter fires. Pioneer species, such as Funaria hygrometrica, Barbula convoluta and Bryum dunense, characterized recent intense fires, whereas Bryum torquescens, B. radiculosum and B. ruderale were dominant after less intense burning. Pleurochaete squarrosa, Tortula ruraliformis and Tortella flavovirens dominated intermediate successional stages. Pleurocarpous mosses were dominant only in the older closed stands. Different patterns of regeneration strategies were described: spores dominated early stages of intense fire, while vegetative propagules characterized later successional stages and less severely burned areas. Although bryophytes usually have a low abundance in Mediterranean vegetation, their role in post-fire vegetation dynamics may be locally enhanced according to burning conditions.     

Effects of re‐introducing fire to a central Florida sandhill community

Abstract. A southern ridge sandhill site in central Florida, USA, was burned in 1989, 1991, and 1995 after 63 years of fire‐suppression to simulate a pre‐settlement fire regime. Fire changed species abundance and vegetation structure but caused only minimal changes in species turnover and diversity. There was a general trend for an increase in the cover of herbs following fire but this was a statistically significant effect for only one species, Liatris tenuifolia var. tenuifolia. Aristida beyrichiana increased, litter cover and litter depth were significantly reduced, and ground lichens were eliminated in response to burning. Scrub oaks and palmettos in the ground cover and small shrub layers (height ≤ 1 m) either increased or did not respond to burning, reflecting strong post‐fire resprouting. Diversity in the ground cover and small shrub layers were not affected by fire. Scrub oaks and palmettos in the large shrub and overstorey layers (height > 1 m) were reduced in density, basal area, and longest canopy measurements in response to fire. Species diversity also decreased within these layers following fire. Some Pinus elliottii var. densa survived fire, but their density was reduced. All Pinus clausa were eliminated by fire. Periodic burning can suppress the dominance of shrubs (Quercus spp.) while increasing the cover of grasses and herbs in southern ridge sandhill vegetation.     

Vegetation establishment, succession and microsite frost disturbance on glacier forelands within patterned ground chronosequences

Aim The impact of microscale frost disturbance on vegetation colonization and successionary trends was examined within patterned ground features of Little Ice Age chronosequences. The goal was to investigate and compare vegetation response to micro‐site frost disturbance with that of previous studies done at a coarser landscape scale. Location The study sites occur on Little Ice Age glacier forelands within Jotunheimen, Norway (61°–62° N). The forelands of the glaciers Slettmarkbreen, Styggedalsbreen and Vestre Memurubreen have been well studied providing chronological controls for landscape studies. Sorted patterned ground features are found within the chronosequences, typically declining with frost intensity and disturbance with increasing terrain age. Methods Micro‐plots (8.3 × 8.3 cm) were placed at the inner borders and centres of patterned ground features. Species were identified and per cent species cover and per cent cover of life‐form category were noted. Nonparametric Kruskal–Wallis and Mann–Whitney U‐tests were used to test for differences between percent cover of life‐form categories within patterned ground features as well as to identify thresholds of successional change across the chronosequences. Results Significant relationships between life‐from groups and patterned ground positions of varying ages were deduced using nonparametric statistics. Findings were then used to discuss trends of succession within patterned ground features and across the chronosequences. Vegetation establishment occurs at the border positions of young (< 30 years) patterned ground features. With time and distance from the ice margin, vegetation encroaches inwards toward the disturbed centres. Succession within patterned ground exhibits several stages: (1) bryophytes/crusts and lichens, (2) grasses/sedges and (3) woody shrubs. The occurrence of forbs was sporadic and generally non‐significant. Main conclusions Frost disturbance in patterned ground appears to delay successional trends of vegetation communities when compared with previous studies on ‘stable’ terrain, producing micro‐site lag effects. These small patches of disturbed ground are therefore important regarding vegetation assemblages across the landscape and are unlikely to be detected at the landscape scale.     

Long‐term seed bank dynamics in a temperate forest under conversion from coppice‐with‐standards to high forest management

Questions: How do changes in forest management, i.e. in disturbance type and frequency, influence species diversity, abundance and composition of the seed bank? How does the relationship between seed bank and vegetation change? What are the implications for seed bank dynamics? Location: An ancient Quercus petraea — Carpinus betulus forest in conversion from coppice‐with‐standards to regular Quercus high forest near Montargis, France. Methods: Seed bank and vegetation were sampled in six replicated stand types, forming a chronosequence along the conversion pathway. The stand types represented mid‐successional stages of stands in transition from coppice‐with‐standards (to high forest (16 plots) and early‐ and mid‐successional high forest stands (32 plots). Results: Seed bank density and species richness decreased with time since last disturbance. Adjusting for seed density effects obscured species richness differences between stand types, but species of later seres were nested subsets of earlier seres, implying concomitant shifts in species richness and composition with time since disturbance. Later seres were characterized by species with low seed weight and high seed longevity. Seed banks of early seres were more similar to vegetation than to later seres. Conclusions: Abandonment of the coppice‐with‐standards regime altered the seed bank characteristics, as well as its relationship with vegetation. Longer management cycles under high forest yield impoverished seed banks. For their persistence, seed bank species will increasingly rely on management of permanently open areas in the forest landscape. Thus, revegetation at the beginning of new high‐forest cycles may increasingly depend on inflow from seed sources.     

Demographic structure of California chaparral in the long-term absence of fire

Abstract. Demographic structure of 12 chaparral sites unburned for 56 to 120 years was investigated. All sites were dominated by vigorous shrub populations and, although there was colonization by seedlings of woodland tree species in several stands, successional replacement of chaparral was not imminent. Although successional changes in community composition were evident, there was no indication of a decline in species diversity. Non-sprouting species of Ceanothus suffered the greatest mortality at most, but not all, sites. Sprouting shrubs, such as Quercus and Heteromeles had very little mortality, even in stands more than a century old. All postfire resprouting species had multiple stems of different ages indicating these shrubs were capable of continuously regenerating their canopy from basal sprouts. Ceanothus populations were highly clumped and there was a significant correlation across all sites between variance/mean ratio and percentage mortality. As Ceanothus populations thinned, they became less clumped. In mixed chaparral stands, Quercus and Heteromeles were significantly taller than associated Ceanothus shrubs and overtopped the Ceanothus; at two sites, the density of live Quercus per plot was correlated with the density of dead Ceanothus. Thus, mortality of Ceanothus stems is likely related to both intra and interspecific interations. Seedling recruitment was observed for most shrub species that regenerate after fire by resprouting; seedling and sapling densities ranging from 1000–36 500 ha^-1 were recorded for Quercus dumosa, Rhamnus crocea, Prunus ilicifolia, Heteromeles arbutifolia and Cercocarpus betuloides. For all but the last species, seedlings and saplings were most abundant beneath the canopy cover and not in gaps. Across all sites, recruitment was significantly correlated with depth and bio-mass of the litter layer. Cercocarpus betuloides was present in several stands, but seedling establishment was found only in one very open, disturbed stand. Regardless of stand age, taxa such as Adenostoma, Arctostaphylos and Ceanothus, which recruit seedlings after fire, had no significant seedling production.     

Afforestation causes changes in post‐fire regeneration in native shrubland communities of northwestern Patagonia,Argentina

Question: What are the effects of fire in native shrubland communities and in pine plantations established in these shrublands? Location: Northern Patagonia, Argentina. Methods: We surveyed four sites in Chall‐Huaco valley, located in northwest Patagonia. Each site was a vegetation mosaic composed of an unburned Pinus ponderosa plantation, a plantation burned in 1996, and an unburned matorral and a matorral burned by the same fire. We recorded the cover of all vascular plant species. We also analysed species richness, total cover, proportion of exotic species, abundance of woody species and herb species, cover of exotic species, abundance of woody and herb species and differences in composition of species. For both shrubs and tree species we recorded the main strategy of regeneration (by resprouting or by seed). Results: We found that fire had different effects on native matorral and pine plantations. Five years after fire, plantations came to be dominated by herbs and exotic species, showing differences in floristic composition. In contrast, matorral communities remained very similar to unburned matorral in terms of species richness, proportion of woody species, and herb species and proportion of exotics. Also, pine plantations were primarily colonized by seedlings, while matorrals were primarily colonized by resprouting. Conclusions: Matorrals are highly fire resilient communities, and the practice of establishing plantations on matorrals produces a strong reduction in the capacity of matorral to return to its original state. The elimination of shrubs owing to the effect of plantations can hinder regeneration of native ecosystems. Burned plantations may slowly develop into ecosystems similar to the native ones, or they may produce a new ecosystem dominated by exotic herbs. This study shows that plantations of exotic conifers affect native vegetation even after they have been removed, as in this case by fire.     

Limited Edge Effects Along a Burned‐Unburned Bornean Forest Boundary Seven Years after Disturbance

Large parts of the everwet tropics have been burned, leaving many unburned–burned forest edges. Here we studied a Bornean forest edge to determine: (1) how unburned and burned forest differ in vegetation structure, diversity, composition and plant functional traits 7 yr after fire, and (2) if these variables showed significant edge effects. Environmental and inventory data from 120 plots (0.01 ha each), covering both sides of a ～1.3 km forest boundary were sampled. Differences in vegetation structure, diversity, composition and plant functional traits were analyzed in relation to disturbance type (Mann–Whitney tests) and edge distance (partial correlation analysis that controlled for confounding effects of elevation, slope and fire intensity). Seven years after fire, burned forest differed significantly from unburned forest in most measured variables while few significant edge effects were detected, i.e., there existed a sharp delimitation between the two forest types. The regeneration of the burned forest depended almost entirely on in situ recruitment with little input of late successional species from the neighboring old growth forest. On the other hand, old growth forest showed few signs of edge degradation. A possible explanation for these results might be related to the absence of a mast fruiting event during these first 7 yr of forest recovery, resulting in low levels of late successional species seed input into the burned forest, combined with the quick development of a closed canopy in the burned forest by early successional species that shielded the unburned forest from adverse edge effects.     

Successional trends in standing dead biomass in Mediterranean basin species

Question: Landscape models of fire occurrence in ecosystems assume that the time since the last fire determines vegetation flammability by enabling the accumulation of dead biomass. In this study we ask if Mediterranean basin shrublands respond to these models or, on the contrary, if initial successional stages in these ecosystems could be more flammable than later stages. Location: Mediterranean shrubland in the Valencia region, eastern Spain. Methods: Using different stages of vegetation development (5, 9, 14 and 26 years since the last fire), we first study the structural comiosition of the above‐ground biomass in 375 individuals of nine woody species. Then, we measure how the standing dead biomass varies during succession, taking into account the surface cover of each species and the quantity of total dead biomass accumulated in different successional stages (3, 9, 14 and 26 years since the last fire). Results: The largest amount of standing dead biomass at the plant community level is observed in the middle stages of the succession. Early successional species, such as Cistus spp., Ulex parviflorus and Pinus halepensis, have a higher percentage of standing dead biomass at earlier stages in the succession than species typical of later successional stages, e.g. Juniperus oxycedrus, Quercus coccifera and Quercus ilex. Conclusions: The results suggest that monotonic increase in fire hazard with increasing stand age is not necessarily the rule in Mediterranean basin shrublands, since early successional species may accumulate large amounts of standing dead biomass and thus promote fire at early successional stages.     

The relationship between fire history and an exotic fungal disease in a deciduous forest

Exotic diseases have fundamentally altered the structure and function of forest ecosystems. Controlling exotic diseases across large expanses of forest has proven difficult, but fire may reduce the levels of diseases that are sensitive to environmental conditions. We examined Cornus florida populations in burned and unburned Quercus–Carya stands to determine if burning prior to anthracnose infection has reduced the impacts of an exotic fungal disease, dogwood anthracnose, caused by Discula destructiva. We hypothesized that fire has altered stand structure and created open conditions less conducive to dogwood anthracnose. We compared C. florida density, C. florida health, and species composition and density among four sampling categories: unburned stands, and stands that had burned once, twice, and 3 times over a 20-year period (late 1960s to late 1980s). Double burn stands contained the greatest density of C. florida stems (770 stems ha⁻¹) followed by triple burn stands (233 stems ha⁻¹), single burn stands (225 stems ha⁻¹) and unburned stands (70 stems ha⁻¹; P < 0.01). We observed less crown dieback in small C. florida trees (<5 cm diameter at breast height) in burned stands than in unburned stands (P < 0.05). Indicator species analysis showed that burning favored species historically associated with Quercus–Carya forests and excluded species associated with secondary succession following nearly a century of fire suppression. Our results suggest that fire may mitigate the decline of C. florida populations under attack by an exotic pathogen by altering forest structure and composition. Further, our results suggest that the burns we sampled have had an overall restorative effect on forest communities and were within the fire return interval of the historic fire regime. Consequently, prescribed fire may offer a management tool to reduce the impacts of fungal disease in forest ecosystems that developed under historic burning regimes.     

Relative influence of habitat structure,species interactions and rainfall on the post‐fire population dynamics of ground‐dwelling vertebrates

The long‐term impacts of wildfires on animal populations are largely unknown. We used time‐series data based on a tracking index, from coastal NSW spanning 28 years after a wildfire, to investigate the relative influence of habitat structure, species interactions and climate on post‐fire animal population dynamics. The fire had an immediate impact on habitat structure, reducing and simplifying vegetation cover, which then underwent post‐fire successional change including an increase and plateau in tree canopy cover; an increase, stabilization and then decline in shrub cover; and an increase in ground litter cover. Population changes of different animal species were influenced by different components of successional change, but there was also evidence that species interactions were important. For example, bandicoots (Isoodon obesulus and Perameles nasuta combined) increased concurrent with an increase in shrub cover then declined at a faster rate than a direct association with senescing shrub cover would suggest, while the feral cat (Felis catus) population changed with the bandicoot population, suggesting a link between these species. Potoroos (Potorous tridactylus) increased 10 years after the fire concurrent with the closing tree canopy, but there was also evidence of a negative association with feral foxes (Vulpes vulpes). Variation in rainfall did not have significant effects on the population dynamics of any species. Our results suggest that changes in habitat structure play a key role in the post‐fire dynamics of many ground‐dwelling animals and hence different fire regimes are likely to influence animal dynamics through their effects on habitat structure. However, the role of predator–prey interactions, particularly with feral predators, is less clear and further study will require manipulative experiments of predators in conjunction with fire treatments to determine whether feral predator control should be integrated with fire management to improve outcomes for some native species.     

Old-field secondary succession in SE Spain: can fire divert it?

In the Mediterranean Basin, most cultivated areas were abandoned in the last century and are now in various stages of old-field succession. The aim of this work was to analyse the successional trajectories of these ecosystems, and to assess possible deviations in these pathways due to fire occurrence at high or low recurrence levels. Old-fields abandoned either about 50 or about 100 years ago were selected in SE Spain. Within the 50-year-old abandoned fields, plots were established which had been burned by 1, 2 and 3 fires in the last 25 years. Cover values of vascular species were sampled and then analysed by means of multivariate analysis. Euclidean distances between resulting communities were used as an indicator of the possible deviation from the unburned successional pathway. Our results pointed to the possibility that different successional pathways may exist depending on fire occurrence and recurrence. In the absence of fire, the vegetation is dominated by pioneer species, mainly Pinus. With the passage of time this vegetation will become dominated by later successional tree species (Quercus). However, when early-successional communities are affected by fire, the succession can be diverted. A single fire is enough to change Pinus forests into alternative stable states dominated by Rosmarinus officinalis shrub communities, where the colonisation of species in later successional stages is arrested. This deviation increases in high fire recurrence regimes where the vegetation changes to dwarf shrubs and herbs.     

Conifer seedling recruitment in a southeastern Canadian boreal forest: the importance of substrate

Abstract. In order to explain conifer species recruitment in Canada's southeastern boreal forest, we characterized conifer regeneration microsites and determined how these microsites vary in abundance during succession. Microsite abundance was evaluated in deciduous, mixed and coniferous stands along a 234-yr postfire chronosequence. Conifers were most often found in relatively well-illuminated microsites, devoid of litter, especially broad-leaf litter, and with a reduced cover of lower vegetation (< 50 cm tall). Although associated with moss-rich forest floor substrates, Abies balsamea was the most ubiquitously distributed species. Picea glauca and especially Thuja occidentalis seedlings were frequently found on rotten logs. Light measurements did not show differences among seedling species nor between stand types. The percentage cover of broad-leaf litter decreased significantly during succession. Also, rotten logs covered with moss occupied a significantly larger area in the mid-successionnal stands than in early successional deciduous or late successional coniferous stands. The results suggest that the presence of specific forest floor substrate types is a factor explaining low conifer recruitment under deciduous stands, conifer codominance in the mid-successional stage, and delayed Thuja recolonization after fire. Results also suggest that some facilitation mechanism is responsible for the observed directional succession.     

Managing open habitats by wild ungulate browsing and grazing: A case‐study in North‐Eastern Germany

Question: Can wild ungulates efficiently maintain and restore open habitats? Location: Brandenburg, NE Germany. Methods: The effect of wild ungulate grazing and browsing was studied in three successional stages: (1) Corynephorus canescens‐dominated grassland; (2) ruderal tall forb vegetation dominated by Tanacetum vulgare; and (3) Pinus sylvestris‐pioneer forest. The study was conducted over 3 yr. In each successional stage, six paired 4 m²‐monitoring plots of permanently grazed versus ungrazed plots were arranged in three random blocks. Removal of grazing was introduced de novo for the study. In each plot, percentage cover of each plant and lichen species and total cover of woody plants was recorded. Results: Wild ungulates considerably affected successional pathways and species composition in open habitats but this influence became evident in alteration of abundances of only a few species. Grazing effects differed considerably between successional stages: species richness was higher in grazed versus ungrazed ruderal and pioneer forest plots, but not in the Corynephorus sites. Herbivory affected woody plant cover only in the Pioneer forest sites. Although the study period was too short to observe drastic changes in species richness and woody plant cover, notable changes in species composition were still detected in all successional stages. Conclusion: Wild ungulate browsing is a useful tool to inhibit encroachment of woody vegetation and to conserve a species‐rich, open landscape.     

Effects of high‐severity fire drove the population collapse of the subalpine Tasmanian endemic conifer Athrotaxis cupressoides

Athrotaxis cupressoides is a slow‐growing and long‐lived conifer that occurs in the subalpine temperate forests of Tasmania, a continental island to the south of Australia. In 1960–1961, human‐ignited wildfires occurred during an extremely dry summer that killed many A. cupressoides stands on the high plateau in the center of Tasmania. That fire year, coupled with subsequent regeneration failure, caused a loss of ca. 10% of the geographic extent of this endemic Tasmanian forest type. To provide historical context for these large‐scale fire events, we (i) collected dendroecological, floristic, and structural data, (ii) documented the postfire survival and regeneration of A. cupressoides and co‐occurring understory species, and (iii) assessed postfire understory plant community composition and flammability. We found that fire frequency did not vary following the arrival of European settlers, and that A. cupressoides populations were able to persist under a regime of low‐to‐mid severity fires prior to the 1960 fires. Our data indicate that the 1960 fires were (i) of greater severity than previous fires, (ii) herbivory by native marsupials may limit seedling survival in both burned and unburned A. cupressoides stands, and (iii) the loss of A. cupressoides populations is largely irreversible given the relatively high fuel loads of postfire vegetation communities that are dominated by resprouting shrubs. We suggest that the feedback between regeneration failure and increased flammability will be further exacerbated by a warmer and drier climate causing A. cupressoides to contract to the most fire‐proof landscape settings.     

Fire severity mediates climate‐driven shifts in understorey community composition of black spruce stands of interior Alaska

Question: How do pre‐fire conditions (community composition and environmental characteristics) and climate‐driven disturbance characteristics (fire severity) affect post‐fire community composition in black spruce stands? Location: Northern boreal forest, interior Alaska. Methods: We compared plant community composition and environmental stand characteristics in 14 black spruce stands before and after multiple, naturally occurring wildfires. We used a combination of vegetation table sorting, univariate (ANOVA, paired t‐tests), and multivariate (detrended correspondence analysis) statistics to determine the impact of fire severity and site moisture on community composition, dominant species and growth forms. Results: Severe wildfires caused a 50% reduction in number of plant species in our study sites. The largest species loss, and therefore the greatest change in species composition, occurred in severely burned sites. This was due mostly to loss of non‐vascular species (mosses and lichens) and evergreen shrubs. New species recruited most abundantly to severely burned sites, contributing to high species turnover on these sites. As well as the strong effect of fire severity, pre‐fire and post‐fire mineral soil pH had an effect on post‐fire vegetation patterns, suggesting a legacy effect of site acidity. In contrast, pre‐fire site moisture, which was a strong determinant of pre‐fire community composition, showed no relationship with post‐fire community composition. Site moisture was altered by fire, due to changes in permafrost, and therefore post‐fire site moisture overrode pre‐fire site moisture as a strong correlate. Conclusions: In the rapidly warming climate of interior Alaska, changes in fire severity had more effect on post‐fire community composition than did environmental factors (moisture and pH) that govern landscape patterns of unburned vegetation. This suggests that climate change effects on future community composition of black spruce forests may be mediated more strongly by fire severity than by current landscape patterns. Hence, models that represent the effects of climate change on boreal forests could improve their accuracy by including dynamic responses to fire disturbance.