Demography of woody plants in relation to fire: Banksia ericifolia L.f. and Petrophile pulchella (Schrad) R.Br.

Plants of Banksia ericifolia and Petrophile pulchella are sensitive to fire. Changes in population size under different fire regimes were estimated, based on measurements of post-fire seedling emergence, seedling survival, survival and seed production in established plants of differing ages, survival of seeds held in serotinous cones and seed-release in the periods between fire. Seeds were first available at 5 years in P. pulchella and 6 years in B. ericifolia. Exact replacement would be possible when burnt at these ages, if seedling establishment were very high. Low establishment would delay replacement to 13 years of age in both species. Late summer/autumn fires of high intensity favour high establishment. Such fires at 8–10 year intervals would be tolerated without any sustained decline in numbers. Fires at 10–15 year intervals could occur regardless of season or intensity with little risk of a population decline. Large increases in numbers and density would follow fires spaced at 15–30 years. Enough seeds would be available for replacement up to about 50 years in both species. Viable seed-release in unburnt conditions was sufficient to compensate for deaths in stands over 20 years old, even with very low levels of establishment. Two variables accounted for the biggest changes in numbers and density between generations interspersed by fires; namely the age at which a stand is burned and the proportion of seeds which emerge as seedlings. A comparison with other similar species showed similarities in controls on emergence and establishment, lengths of primary juvenile periods and life spans.     

Estimating population abundance in plant species with dormant life-stages: Fire and the endangered plant Grevillea caleyi R. Br.

Summary Assessment of the conservation significance of a species at a particular site involves estimating the population size. Generally this is based on a single survey. However, where plant species vary greatly in abundance in response to disturbance regimes, there will be uncertainty associated with the use of single estimates of abundance. The interpretation of such estimates is dependent on an understanding of the ecology of the species and the disturbance regimes that impact on it. We examined the usefulness of abundance estimates in the endangered shrub Grevillea caleyi (a fire‐sensitive shrub with a persistent soil seed bank) from south‐eastern Australia, where fire is a major landscape disturbance. Comparisons of estimates of abundance before and after fire showed very large changes in the number of plants of G. caleyi above ground. Changes in abundance of over two orders of magnitude were observed. The longer the site was left unburnt, the greater the magnitude of change in abundance after the next fire. Above‐ground plants may be rare or absent at sites unburnt for over 15–20 years, but were abundant after fire, due to re‐establishment from the soil seed bank. Sites burnt by two fires in quick succession showed declines in population abundance, most likely due to the soil seed bank not being replenished between such short interval fires. Assessments of the conservation significance of remnant sites of G. caleyi and similar species based on a single sample of above‐ground plant abundance at one time are considered inappropriate. The amount of available habitat for G. caleyi, either as area of occupancy or preferably extent of available habitat, was a moderate predictor of the likely magnitude of abundance in the species after fire. However, the usefulness of these measures for species whose biology is comparable to Grevillea caleyi, will be limited due to factors relating to the degree of species‐specific habitat requirements, local site fire history and the impact of any one fire on resultant post‐fire germination levels. Any assessment of conservation significance will require the interpretation of available information in relation to the ecology of a species.     

The impact of fire,and its potential role in limiting the distribution of <Emphasis Type="Italic">Bryophyllum delagoense</Emphasis> (Crassulaceae) in southern Africa

Increasing emphasis has been placed on identifying traits of introduced species which predispose them to invade, and characteristics of ecosystems which make them susceptible to invasion. Habitat disturbance such as floods, fires and tree-falls may make ecosystems more prone to invasion. However, in this study the absence of fire was considered to be a factor in facilitating the invasion potential of a Madagascan endemic, Bryophyllum delagoense. Fire trials in South Africa killed 89 and 45% of B. delagoense plants in a high and low intensity controlled fire, respectively, with tall plants and those growing in clumps more likely to escape being killed. A reduction in the incidence and intensity of fires may therefore facilitate the invasion of B. delagoense and contribute to its invasive potential. Overgrazing, which reduces the frequency and intensity of fires probably facilitates the invasion of large and small succulent species. In South Africa, B. delagoense is still considered to be a minor weed or garden escape, despite its introduction to southern Africa 175 years earlier than in Australia, where it is extremely invasive. However, other succulents such as Opuntia species have become invasive on both continents, confounding our hypothesis that fire may be inhibiting B. delagoense from becoming invasive in southern Africa. However, closer analysis of Opuntia literature indicates that smaller species, similar in size to B. delagoense, are more likely to be killed, even by low intensity fires. We speculate that B. delagoense is more invasive in Australia because of a reduction in the frequency and intensity of fires and that fire is, amongst other factors, largely responsible for inhibiting its invasion potential in southern Africa.     

Impacts of changed fire regimes on tropical riparian vegetation invaded by an exotic vine

Abstract Riparian habitats are highly important ecosystems for tropical biodiversity, and highly threatened ecosystems through changing disturbance regimes and weed invasion. An experimental study was conducted to assess the ecosystem impacts of fire regimes introduced for the removal of the exotic woody vine, Cryptostegia grandiflora, in tropical north‐eastern Australian woodlands. Experimental sites in subcatchments of the Burdekin River, northern Queensland, Australia, were subjected to combinations of early wet‐season and dry‐season fires, and single and repeated fires, with an unburnt control. Woody vegetation was sampled using permanent quadrats to record and monitor plants species, number and size‐class. Sampling was conducted pre‐fire in 1999 and post‐fire in 2002. All fire regimes were effective in reducing the number and biomass of C. grandiflora shrubs and vines. Few woodland or riparian species were found to be fire‐sensitive and community composition did not change markedly under any fire regime. The more intense dry‐season fires impacted the structure of non‐target vegetation, with large reductions in the number of sapling trees (<5 cm d.b.h.) and reductions in the largest tree size‐class and total tree basal area. Unexpectedly, medium‐sized canopy trees (10–30 cm d.b.h.) appear to have been significantly benefited by fires, with decreases in number of trees of this size‐class in the absence of fire. Although the presence of C. grandiflora as a vine in riparian forest canopies changed the nature and intensity of crown combustion patterns, this did not lead to the initiation of a self‐perpetuating weed–fire cycle, as invaders were unable to take advantage of gaps caused by fire. Low intensity, early wet‐season burning, or early dry‐season burning, is recommended for control of C. grandiflora in order to minimize the fire intensity and risk of the loss of large habitat trees in riparian habitats.     

Accommodating scenarios of climate change and management in modelling the distribution of the invasive tree Schinus molle in South Africa

Determining the potential range of invasive alien species under current conditions is important. However, we also need to consider future distributions under scenarios of climate change and different management interventions when formulating effective long‐term intervention strategies. This paper combines niche modelling and fine‐scale process‐based modelling to define regions at high risk of invasion and simulate likely dynamics at the landscape scale. Our study species is Schinus molle (Peruvian pepper tree; Anacardiaceae), a native of central South America, introduced to South Africa in about 1850 where it was widely planted along roads. Localities of planted and naturalized trees were mapped along 5380 km of roads – a transect that effectively samples a large part of western South Africa. Correlative modelling was used to produce profiles of present and future environmental conditions characterizing its planted and naturalized ranges. A cellular‐automata simulation model was used to estimate the dynamics of S. molle under future climates and different management scenarios. The overall potential range of S. molle in the region is predicted to shrink progressively with predicted climate change. Some of the potential range of S. molle defined based on current conditions (including areas where it is currently highly invasive) is likely to become less favourable. The species could persist where it is well established long after conditions for recruitment have deteriorated. Some areas where the species is not widely naturalized now (notably the fynbos biome) are likely to become more favourable. Our modelling approach allows for the delineation of areas likely to be invaded in future by considering a range of factors at different scales that mediate the interplay of climatic variables and other drivers that define the dimensions of human intervention such as distance from planted trees and the density of planted plants, both of which affect propagule pressure.     

Selective and Non-Selective Control of Invasive Plants: The Short-Term Effects of Growing-Season Prescribed Fire, Herbicide, and Mowing in Two Texas Prairies

Conservation of North American grasslands is hampered by the impact of invasive herbaceous species. Selective control of these plants, although desirable, is complicated by the shared physiology and phenology of the invader and the native components of the invaded plant community. Fortunately, there is evidence that some management practices, such as prescribed fire, herbicide, and mowing, can cause differential responses in native and invasive grassland species. However, timing of treatment is critical, and fire has been shown to increase rates of invasion when implemented during the dormant season. Bothriochloa ischaemum, an introduced C4 Eurasian grass is an increasing problem in grasslands, particularly in southern and central regions of North America. To date, there has been little success in effective selective control. Two invaded grassland sites representative of Blackland Prairie and Edwards Plateau ecoregions were subjected to two growing‐season prescribed fire treatments, single and double herbicide applications, and single and double mowing treatments. Mowing had no effect on either B. ischaemum or other dominant species at either site one‐year posttreatment. However, growing‐season fire and herbicide were both effective at reducing the abundance of B. ischaemum, with other codominant species responding either negatively to herbicide or neutrally or positively to fire. The vulnerability of B. ischaemum to growing‐season fire may be associated with the ecology of its native range. The negative growth response to growing‐season fire, combined with its lower implementation costs, indicates that this method warrants further investigation as a selective management tool for other problematic species in invaded grasslands.     

The making of a rapid plant invader: genetic diversity and differentiation in the native and invaded range of Senecio inaequidens

To become invasive, exotic species have to succeed in the consecutive phases of introduction, naturalization, and invasion. Each of these phases leaves traces in genetic structure, which may affect the species’ success in subsequent phases. We examined this interplay of genetic structure and invasion dynamics in the South African Ragwort (Senecio inaequidens), one of Europe’s fastest plant invaders. We used AFLP and microsatellite markers to analyze 19 native African and 32 invasive European populations. In combination with historic data, we distinguished invasion routes and traced them back to the native source areas. This revealed that different introduction sites had markedly different success in the three invasion phases. Notably, an observed lag‐phase in Northern Germany was evidently not terminated by factors increasing the invasiveness of the resident population but by invasive spread from another introduction centre. The lineage invading Central Europe was introduced to sites in which winters are more benign than in the native source region. Subsequently, this lineage spread into areas in which winter temperatures match the native climate more closely. Genetic diversity clearly increases with population age in Europe and less clearly decreases with spread rate up to population establishment. This indicates that gene flow along well‐connected invasion routes counteracted losses of genetic diversity during rapid spread. In summary, this study suggests that multiple introductions, environmental preadaptation and high gene flow along invasion routes contributed to the success of this rapid invader. More generally, it demonstrates the benefit of combining genetic, historical, and climatic data for understanding biological invasions.     

Naturalization of alien plants in China

Naturalization (the establishment of a self-sustaining population for at least a decade) is a fundamental precondition for plant invasion and so compiling a complete inventory of naturalized alien species is necessary for predicting and hence preventing such invasion. However, nationwide information on naturalized plants in China is still lacking. We compiled a nationwide list of the naturalized plant species of China, based on various literature reports. The list comprised a total of 861 naturalized plant species belonging to 110 families and 465 genera. The three most dominant families were Compositae, Poaceae, and Leguminosae, accounting for 16, 13 and 12% of naturalized plants, respectively. Among genera, Euphorbia and Solanum had the most naturalized species, followed by Ipomoea, Amaranthus, Oenothera, and Trifolium. Over half of all aliens were of American origin (52%), followed by those with European (14%) and Asian (13%) origins. Annuals and perennial herbs were prevalent among naturalized species; comparison to other studies suggests however that the invasive potential is higher among plants with longer life cycles than those of annuals. The taxonomic pattern of plant naturalization in China is similar to patterns worldwide. However, the low proportion of naturalized plants within the Chinese flora overall suggests that the potential for plant invasions in China may be high. Therefore, greater attention should be focused on naturalization of alien plants in China, especially concerning species of dominant families or genera, and those with a perennial life cycle.     

The effect of fire interval on post‐fire understorey communities in Yellowstone National Park

Questions: How does the time interval between subsequent stand‐replacing fire events affect post‐fire understorey cover and composition following the recent event? How important is fire interval relative to broad‐ or local‐scale environmental variability in structuring post‐fire understorey communities? Location: Subalpine plateaus of Yellowstone National Park (USA) that burned in 1988. Methods: In 2000, we sampled understorey cover and Pinus contorta density in pairs of 12–yr old stands at 25 locations. In each pair, the previous fire interval was either short (7–100 yr) or long (100–395 yr). We analysed variation in understorey species richness, total cover, and cover of functional groups both between site pairs (using paired t‐tests) and across sites that experienced the short fire intervals (using regression and ordination). We regressed three principal components to assess the relative importance of disturbance and broad or local environmental variability on post‐fire understorey cover and richness. Results: Between paired plots, annuals were less abundant and fire‐intolerant species (mostly slow‐growing shrubs) were more abundant following long intervals between prior fires. However, mean total cover and richness did not vary between paired interval classes. Across a gradient of fire intervals ranging from 7–100 yr, total cover, species richness, and the cover of annuals and nitrogen‐fixing species all declined while the abundance of shrubs and fire‐intolerant species increased. The few exotics showed no response to fire interval. Across all sites, broad‐scale variability related to elevation influenced total cover and richness more than fire interval. Conclusions: Significant variation in fire intervals had only minor effects on post‐fire understorey communities following the 1988 fires in Yellowstone National Park.     

Reproductive potential and seedling establishment of the invasive alien tree Schinus molle (Anacardiaceae) in South Africa

Schinus molle (Peruvian pepper tree) was introduced to South Africa more than 150 years ago and was widely planted, mainly along roads. Only in the last two decades has the species become naturalized and invasive in some parts of its new range, notably in semi‐arid savannas. Research is being undertaken to predict its potential for further invasion in South Africa. We studied production, dispersal and predation of seeds, seed banks, and seedling establishment in relation to land uses at three sites, namely ungrazed savanna once used as a military training ground; a savanna grazed by native game; and an ungrazed mine dump. We found that seed production and seed rain density of S. molle varied greatly between study sites, but was high at all sites (384 864–1 233 690 seeds per tree per year; 3877–9477 seeds per square metre per year). We found seeds dispersed to distances of up to 320 m from female trees, and most seeds were deposited within 50 m of putative source trees. Annual seed rain density below canopies of Acacia tortillis, the dominant native tree at all sites, was significantly lower in grazed savanna. The quality of seed rain was much reduced by endophagous predators. Seed survival in the soil was low, with no survival recorded beyond 1 year. Propagule pressure to drive the rate of recruitment: densities of seedlings and sapling densities were higher in ungrazed savanna and the ungrazed mine dump than in grazed savanna, as reflected by large numbers of young individuals, but adult : seedling ratios did not differ between savanna sites. Frequent and abundant seed production, together with effective dispersal of viable S. molle seed by birds to suitable establishment sites below trees of other species to overcome predation effects, facilitates invasion. Disturbance enhances invasion, probably by reducing competition from native plants.     

Beating the blaze: Fire survival in the fan aloe (Kumara plicatilis), a succulent monocotyledonous tree endemic to the Cape fynbos,South Africa

Fire is central to the ecology of Mediterranean‐type climate ecosystems, but little is known about the fire ecology of succulent plants therein. This study investigated the fire ecology of an arborescent succulent monocot, Kumara plicatilis (L.) G. D. Rowley (Asphodelaceae), a Cape fynbos endemic. Habitat suitability was assessed to determine whether the species tolerates or ‘avoids’ fire, and fire survival traits (bark thickness and tissue water content) were measured. The population size structure and density of three K. plicatilis populations were assessed after natural fires, and resprouting potential was investigated. Kumara plicatilis adopts a dual fire survival strategy, occupying rocky sites to ‘avoid’ fire and possessing morphological features that afford fire tolerance, e.g. well‐protected apical meristems and thick corky bark. Bark thickness of burned individuals in situ was similar to unburned plants, suggesting that K. plicatilis bark provides effective insulation against fire. Mortality rates were 64%, 40% and 11%, and decreased as rock cover at the population level increased. All three populations showed reduced plant density post‐fire, with greater density reductions associated with lower rock cover. Small plants appear most vulnerable to fire damage due to lower absolute bark thickness and plant heights within the flame zone. Kumara plicatilis is an apical sprouter, recovering after fire or mechanical stem damage by onward growth from surviving stem apices, rather than resprouting. Post‐fire population recovery therefore likely depends on inter‐fire recruitment.     

The invasive potential of Australian banksias in South African fynbos: A comparison of the reproductive potential of Banksia ericifolia and Leucadendron laureolum

Abstract Several taxa of the Australian Proteaceae have invaded South African fynbos and require costly management programmes to bring under control. Banksia spp. have been introduced only recently to fynbos regions. The invasive potential of Banksia ericifolia (Proteaceae) was investigated by comparing its recruitment potential with that of an indigenous proteaceous shrub, Leucadendron laureolum. Both species are overstorey shrubs that are killed by fire and rely on canopy-stored seeds (serotiny) for recruitment. Eight year old B. ericifolia shrubs produced an average of 16 500 seeds per plant, which is thirty times more than the average of 570 seeds produced by 10 year old L. laureolum shrubs. The seed bank of B. ericifolia was not only larger than that of L. laureolum (1098 vs 525 viable seeds m^?2 projected canopy cover), but also considerably larger than that described for the species in its native environment (200–330 seeds m^?2 in a 9 year old stand north of Sydney). Leucadendron laureoleum released most of its seed a few days after the cones were burnt, whereas seed release in B. ericifolia was spread over 12 weeks. The seeds of B. ericifolia had lower wingloading and fall rates than L. laureolum and were dispersed over greater distances. The relative seedling growth rates of the two species were very similar (0.03 g per day), but below-ground biomass was greater and proteoid roots were more developed in B. ericifolia seedlings than in L. laureolum after 100 days. Four year old B. ericifolia plants growing in the field had attained over twice the height of indigenous pro-teoids and accumulated up to 10 times the fresh biomass of L. xanthoconus, a species which is ecologically similar to L. laureolum. The Bioclimatic Prediction System (BIOCLIM) was used to create a bioclimatic profile of B. ericifolia and identify climatically suitable areas in the Cape Province. Results show that its potential distribution covers most fynbos areas in the southwestern Cape. It is concluded that B. ericifolia has the potential to be highly invasive in fynbos.     

Ecological effects of changes in fire regimes in Pinus ponderosa ecosystems in the Colorado Front Range

Question: What is the relative importance of low‐ and high‐severity fires in shaping forest structure across the range of Pinus ponderosa in northern Colorado? Location: Colorado Front Range, USA. Methods: To assess severities of historic fires, 24 sites were sampled across an elevation range of 1800 to 2800 m for fire scars, tree establishment dates, tree mortality, and changes in tree‐ring growth. Results: Below 1950 m, the high number of fire scars, scarcity of large post‐fire cohorts, and lack of synchronous tree mortality or growth releases, indicate that historic fires were of low severity. In contrast, above 2200 m, fire severity was greater but frequency of widespread fires was substantially less. At 18 sites above 1950 m, 34 to 80% of the live trees date from establishment associated with the last moderate‐ to high‐severity fire. In these 18 sites, only 2 to 52% of the living trees pre‐date these fires suggesting that fire severities prior to any effects of fire suppression were sufficient to kill many trees. Conclusions: These findings for the P. ponderosa zone above ca. 2200 m (i.e. most of the zone) contradict the widespread perception that fire exclusion, at least at the stand scale of tens to hundreds of hectares, has resulted in unnaturally high stand densities or in an atypical abundance of shade‐tolerant species. At relatively mesic sites (e.g. higher elevation, north‐facing), the historic fire regime consisted of a variable‐severity regime, but forest structure was shaped primarily by severe fires rather than by surface fires.     

Dormant Season Prescribed Fire as a Management Tool for the Control of <Emphasis Type="Italic">Salix caroliniana</Emphasis> Michx. in a Floodplain Marsh

Expansion of woody species into herbaceous wetlands is a serious concern in wetland management. Prescribed fire is often used as a tool to manage woody species, although many species resprout after fire making control problematic. In this study, we assessed the usefulness of repeated dormant season fires for controlling Salix caroliniana (Michx.) in a floodplain marsh in Florida. Salix is a common shrub in southeastern marshes that resprouts prolifically after fire. We compared stem basal area, stem density, and cover of Salix in three adjacent sites in a floodplain marsh in east central Florida. One site was burned once in February 1997, another site was burned in February 1997 and then again in March 1999 and one site was left unburned. At the unburned site, Salix stem basal area, stem density, and cover increased over the course of the study. In the two burned sites, the first fire destroyed large diameter stems and stimulated production of sprouts. As a result, stem basal area and cover decreased but stem density remained unchanged. The second fire caused a decline in stem density and a further decline in cover. Changes in understory species composition and cover could not be attributed to the fires. Our results suggest that dormant season fires are effective in reducing Salix cover and basal area, and that repeated fires have greater effects than a single fire.     

The introduced flora of Madagascar

We provide the first comprehensive inventory of the non-native plants on Madagascar since Perrier de la Bathie’s effort 80 years ago, and evaluate the characteristics and importance of this biota. Using botanical databases (especially the Tropicos Catalogue of the Vascular Plants of Madagascar), published plant lists, field observation, and relevant literature, we inventory 546 introduced species that have naturalized, as well as 611 other introduced species that only exist in cultivation. We also list 211 species with unclear status, eight native species that have had different genetic stock introduced, and three endemics that have naturalized outside their native range. Of the naturalized species, 101 display invasive behaviour. Highly represented families include Fabaceae (224 confirmed introduced species), Myrtaceae (143), Poaceae (71), Cactaceae (52), Asteraceae (50), and Solanaceae. (33). Humans have been bringing plants to Madagascar since they colonized the island, mainly for their utility. A number of plants with native varieties but which also have long histories of human use and transport are ripe for further historical biogeographical research (including Eragrostis, Panicum, Sorghum, Dioscorea, Ziziphus, and Adansonia). The introduced flora is similar in composition to other tropical regions; its numerical size appears to confirm that poorer countries experience relatively fewer plant introductions. Madagascar’s introduced species deserve more attention, not just through the rubric of invasion biology, but as plants that build new ecologies and that sustain human communities.     

Fire frequency influences composition and structure of the shrub layer in an Australian subcoastal temperate grassy woodland

Little is known about the relationship between fire regimes and plant diversity in Australia's temperate grassy woodlands. The effect of fire frequency on shrubs in grassy woodland remnants across Western Sydney's Cumberland Plain was examined. Shrub species richness and composition were compared in sites that had experienced a high, moderate or low frequency of fire over the previous 20 years. Nine sites were surveyed, three in each fire frequency category; most sites, including all low‐fire‐frequency sites, had burnt 9–36 months prior to sampling. Fire frequency had a profound effect on the composition and structure of the shrub layer. Per cent frequency and density of the prickly shrub Bursaria spinosa (Pittosporaceae) was considerably higher in low‐fire‐frequency sites than where fires had occurred at least once a decade. In sites where fire had been absent for decades prior to a recent fire, this species dominated the landscape, while elsewhere it occurred as clumps in a grassy matrix. Per cent frequency of other native shrubs, particularly obligate seeders, was greatest at moderate fire frequencies. Exotic shrubs were recorded most often where fire had been rare. While ordination clearly separated out the low‐fire‐frequency sites, complete separation between high‐ and moderate‐fire‐frequency blocks was not achieved. The increase in Bursaria in the absence of fire mirrors the encroachment of woody plants into a range of grassy ecosystems around the world. The sensitivity of obligate seeder species, many of them short‐lived legumes with fire‐cued seeds, to both very frequent and very infrequent fire shows the vulnerability of these species to extreme fire regimes, despite the safeguards conferred by hard‐seededness. Competition from Bursaria, as well as loss of viable seed in the soil, may have contributed to the low frequency of these species after a long inter‐fire interval.     

Naturalization of ornamental plant species in public green spaces and private gardens

Ornamental horticulture is the most important pathway for alien plant introductions worldwide, and consequently, invasive spread of introduced plants often begins in urban areas. Although most introduced ornamental garden-plant species are locally not naturalized yet, many of them have shown invasion potential elsewhere in the world, and might naturalize when climate changes. We inventoried the planted flora of 50 public and 61 private gardens in Radolfzell, a small city in southern Germany, to investigate whether local naturalization success of garden plants is associated with their current planting frequency, climatic suitability (as assessed with climatic niche modelling) and known naturalization status somewhere in the world. We identified 954 introduced garden-plant species, of which 48 are already naturalized in Radolfzell and 120 in other parts of Germany. All currently naturalized garden plants in Radolfzell have a climatic suitability probability of ≥ 0.75 and are naturalized in ≥ 13 out of 843 regions globally. These values are significantly higher than those of garden plants that have not become locally naturalized yet. Current planting frequencies, however, were not related to current naturalization success. Using the identified local naturalization thresholds of climatic suitability and global naturalization frequency, and climate projections for the years 2050 and 2070, we identified 45 garden-plant species that are currently not naturalized in Radolfzell but are likely to become so in the future. Although our approach cannot replace a full risk assessment, it is well-suited and applicable as one element of a screening or horizon scanning-type approach.     

Alien plants associate with widespread generalist arbuscular mycorrhizal fungal taxa: evidence from a continental‐scale study using massively parallel 454 sequencing

Aim The biogeography of arbuscular mycorrhizal (AM) fungi is poorly understood, and consequently the potential of AM fungi to determine plant distribution has been largely overlooked. We aimed to describe AM fungal communities associating with a single host‐plant species across a wide geographical area, including the plant’s native, invasive and experimentally introduced ranges. We hypothesized that an alien AM plant associates primarily with the geographically widespread generalist AM fungal taxa present in a novel range. Location Europe, China. Methods We transplanted the palm Trachycarpus fortunei into nine European sites where it does not occur as a native species, into one site where it is naturalized (Switzerland), and into one glasshouse site. We harvested plant roots after two seasons. In addition, we sampled palms at three sites in the plant’s native range (China). Roots were subjected to DNA extraction, polymerase chain reaction (PCR) and 454 sequencing of AM fungal sequences. We analysed fungal communities with non‐metric multidimensional scaling (NMDS) ordination and cluster analysis and studied the frequency of geographically widespread fungal taxa with log‐linear analysis. We compared fungal communities in the roots of the palm with those in resident plants at one site in the introduced range (Estonia) where natural AM fungal communities had previously been studied. Results We recorded a total of 73 AM fungal taxa. AM fungal communities in the native and introduced ranges differed from one another, while those in the invasive range contained taxa present in both other ranges. Geographically widespread AM fungal taxa were over‐represented in palm roots in all regions, but especially in the introduced range. At the Estonian site, the palm was colonized by the same community of widespread AM fungal taxa as associate with resident habitat‐generalist plants; by contrast, resident forest‐specialist plants were colonized by a diverse community of widespread and other AM fungal taxa. Main conclusions AM fungal communities in the native, invasive and experimentally introduced ranges varied in taxonomic composition and richness, but they shared a pool of geographically widespread, non‐host‐specific taxa that might support the invasion of a generalist alien plant. Our dataset provides the first geographical overview of AM taxon distributions obtained using a single host‐plant species.     

Development of Brachystegia‐Julbernardia woodland after clear‐felling in central Zambia: Evidence for high resilience

Question: Does the development of Brachystegia‐Julbernardia (miombo) woodland after felling, and under a variable fire regime, occur via a serai stage of fire‐tolerant species? Location: Four sites in central Zambia, Africa. Methods: Trees in replicate plots were clear‐cut and stumps and resprouts enumerated. Species recruited into the tree layer (> 2.0 m tall) were monitored for 11 years (1991–2001) and fire occurrence and herbaceous biomass assessed annually to determine fuel loads. Results: Fire frequency was variable at the study sites and fuel loads were generally too low to suppress woodland regeneration after felling. However, at one site a change from low to high fire frequency arrested woodland development and triggered a regression towards a ‘fire‐trap’ vegetation type in which a few fire‐tolerant species survived. There was no evidence to support the hypothesis that miombo woodland regeneration is facilitated by a sere of fire‐tolerant species. All regrowth after felling was from resprouting plants present before felling. Trees with a previous history of felling sprouted more vigorously than trees that had not been felled before. Species richness in the tree layer increased with time since felling because resprout species had different height growth rates. Conclusion: The resilience of miombo trees after clear‐felling is largely due to their capacity to regenerate vegetatively from resprouts and stumps after release from frequent fires. Coppicing is therefore recommended as a suitable management technique for miombo woodland in central southern Africa.     

Stem demography and post-fire recruitment of a resprouting serotinous conifer

Abstract. The contribution of resprouts and seedling recruitment to post-fire regeneration of the South African fynbos conifer Widdringtonia nodiflora was compared eight months after wildfires in 1990. Stems on all trees were killed by fire but resprouting success was > 90 % at all but one site. A demographic study of burned skeletons revealed that prior to these fires, nearly all plants were multi-stemmed (4–9 stems/plant) and multi-aged, indicating continuous sprout production between fires. All stems were killed by these 1990 fires and at most sites > 90 % of the stems were burned to ground level. All diameter stems were susceptible to such incineration as, at most sites, there was no difference in average diameter of stems burned to ground level and those left standing. Individual genets usually had all ramets incinerated to ground level or all ramets charred, but intact, suggesting certain micro-sites burned hotter, whereas other sites were somewhat protected. Although not true of the 1990 fires, there was evidence that occasionally Widdring-tonia stems may survive fire. At one site, four of the 16 plants sampled had a burned stem twice as old as the oldest burned stem on the other 12 plants at the site, suggesting some stems had survived the previous fire (ca. 1970) and this conclusion was supported by fire-scars on these four stems that dated to ca. 1970. Based on the highly significant correlation between stem diameter and cone density left standing after the 1990 fires, we calculated that for most sites > 80 % of the initial cone crop was incinerated by fire. This is important because we observed a strong relationship between size of the canopy cone crop surviving fire and post-fire seedling recruitment. Under these conditions we hypothesize that sprouting confers a selective advantage to genets when fires cause heavy losses of seed. The infrequent occurrence of sprouting in the Cupressaceae suggests the hypothesis that resprouting is an apomorphic or derived trait in Widdringtonia. Data from this study suggests resprouting provides a selective advantage under severe fynbos fires, which are not only 'stand-replacing fires,’but also are intense enough to incinerate cone-bearing stems.