Sclerophyllous Vegetation Research Articles

Fossil evidence for open, Proteaceae-dominated heathlands and fire in the Late Cretaceous of Australia.

The origin of biomes is of great interest globally. Molecular phylogenetic and pollen evidence suggest that several plant lineages that now characterize open, burnt habitats of the sclerophyll biome, became established during the Late Cretaceous of Australia. However, whether this biome itself dates to that time is problematic, fundamentally because of the near-absence of relevant, appropriately aged, terrestrial plant macro- or mesofossils. We recovered, identified, and interpreted the ecological significance of fossil pollen, foliar and other remains from a section of core drilled in central Australia, which we dated as Late Campanian-Maastrichtian. The sediments contain plant fossils that indicate nutrient-limited, open, sclerophyllous vegetation and abundant charcoal as evidence of fire. Most interestingly, >30 pollen taxa and at least 12 foliage taxa are attributable to the important Gondwanan family Proteaceae, including several minute, amphistomatic, and sclerophyllous foliage forms consistent with subfamily Proteoideae. Microfossils, including an abundance of Sphagnales and other wetland taxa, provided strong evidence of a fenland setting. The local vegetation also included diverse Ericaceae and Liliales, as well as a range of ferns and gymnosperms. The fossils provide strong evidence in support of hypotheses of great antiquity for fire and open vegetation in Australia, point to extraordinary persistence of Proteaceae that are now emblematic of the Mediterranean-type climate southwestern Australian biodiversity hotspot and raise the profile of open habitats as centers of ancient lineages.

Ecological Modelling of the Distribution of the Lanner FalconFalco biarmicus feldeggiiin Sicily at Two Spatial Scales

Summary. The presence of the lanner falcon Falco biarmicus feldeggi in Sicily was modelled by generalized linear models using climatic, topographic, ecological and land-use variables at both the landscape (UTM cells of 10 × 10 km) and the home range (12.56 km2) spatial scales. At the landscape scale, a significant spatial autocorrelation of the lanner population, corresponding to the longitudinal distribution of sites, was found, with the species occurring within the most xeric UTM cells. There was also a negative relationship between falcon presence and potential evapo-transpiration values, either in the coldest months or throughout the year. The same negative relationship was also seen with the surfaces of CORINE artificial areas, thus showing that the species has a low tolerance to any anthropogenic landscape. At home range scale, our predictive models revealed a preference for territories with steep slopes surrounded by natural grassland, sclerophyll vegetation, arable land and agricultural land. The ...

Estimating belowground biomass and root/shoot ratio of Phillyrea latifolia L. in the Mediterranean forest landscapes

This study developed and tested models to predict the belowground biomass and root/shoot ratio using aboveground field measures. The predictive power of such indirect measurement is useful for a rapid and reliable assessment of the biomass of the Mediterranean species. Forest biomass estimation has been simplified by the availability of indirect methodologies for automatic measuring. However, most of the information on forest root systems is largely unexplored due to the difficulty in estimating belowground biomass (BGB) at large scale. A plausible approach to investigating forest BGB is to establish a relationship between a number of dendrometric parameters related to the aboveground vegetation (AGB) (e.g., tree diameter and height) and the belowground component of the total biomass. This work presents findings for indirect measurements of BGB in the typical Mediterranean landscapes focusing on sclerophyllous vegetation, specifically Phillyrea latifolia L. The purpose of the present study is twofold: (a) to develop a model explaining the BGB distribution of P. latifolia based on field data for dendrometric parameters, and (b) to understand how the ratio between BGB and AGB varies according to stem diameter as a proxy of plant growth. A total of 50 P. latifolia plants were randomly selected in the study areas and considered for excavation. Individual plants were analyzed to determine AGB and BGB development. A number of models were developed and tested to predict the BGB and root/shoot ratio using aboveground field measures. Allometric equations were employed to predict the AGB and BGB and relative partitioning in the Phillyrea community. Models for P. latifolia AGB and BGB estimation that include crown diameter and stem height measures augment the models’ predictive power. When used alone, the predictive power of the root collar diameter appears to be overestimated, while its effect is stronger for a subset of observations with larger crown diameter and stem height. The root/shoot ratio values of plant species typically related to the Mediterranean context seem to be largely superior to the ratio values of trees and forests. The model is ideally suited to incorporate indirectly measured tree height for a rapid and reliable assessment of the biomass of single Mediterranean species. Further research might include replication of the same studies in different geographic areas of the Mediterranean and in-depth analyses of AGB.

Fires in the Cenozoic: a late flowering of flammable ecosystems.

Modern flammable ecosystems include tropical and subtropical savannas, steppe grasslands, boreal forests, and temperate sclerophyll shrublands. Despite the apparent fiery nature of much contemporary vegetation, terrestrial fossil evidence would suggest we live in a time of low fire activity relative to the deep past. The inertinite content of coal, fossil charcoal, is strikingly low from the Eocene to the Pleistocene and no charcoalified mesofossils have been reported for the Cenozoic. Marine cores have been analyzed for charcoal in the North Pacific, the north and south Atlantic off Africa, and the south China sea. These tell a different story with the oldest records indicating low levels of fire activity from the Eocene but a surge of fire from the late Miocene (~7 Ma). Phylogenetic studies of woody plants adapted to frequent savanna fires show them beginning to appear from the Late Miocene with peak origins in the late Pliocene in both South American and African lineages. Phylogenetic studies indicate ancient origins (60 Ma+) for clades characteristic of flammable sclerophyll vegetation from Australia and the Cape region of South Africa. However, as for savannas, there was a surge of speciation from the Late Miocene associated with the retreat of closed fire-intolerant forests. The wide geographic spread of increased fire activity in the last few million years suggests a global cause. However, none of the potential global factors (oxygen, rainfall seasonality, CO2, novel flammable growth forms) provides an adequate explanation as yet. The global patterns and processes of fire and flammable vegetation in the Cenozoic, especially since the Late Miocene, deserve much more attention to better understand fire in the earth system.

Soil pyrogenic organic matter characterisation by spectroscopic analysis: a study on combustion and pyrolysis residues

Pyrogenic organic matter (PyOM) in the soil of a maritime pine forest in Central Italy, formed during a fire of high severity, was characterised by Fourier transform infrared (FT-IR) and 13C nuclear magnetic resonance (NMR). Furthermore, soil samples from burnt and unburnt sampling sites and natural charcoal collected from the ground were characterised after progressive heating under air and nitrogen atmosphere. The aim was to better understand the role fire plays on PyOM formation and oxidation. The top 10 cm of mineral soil and the above-lying charcoal particles were collected soon after the fire. Sampling was also performed on an adjacent unburnt portion of the forest. The bulk soil organic matter (SOM), its extractable fraction and charcoal particles were investigated by FT-IR and 13C NMR spectroscopies. They also underwent thermogravimetric analysis under air or N2, stopping the thermal reactions at the end of the first exothermic reaction in the range 350–500 °C. The NMR investigation clearly revealed a significant enrichment in aromatic and alkyl C in the burnt soil compared to the unburnt one. Several clues led to hypothesise that SOM was not exposed to extreme heating during the fire, notwithstanding the high fire severity estimated by a vegetation-based visual scale. In the thermal treatment mimicking fire, charcoal lost much of its mass and carbon content. However, at 500 °C, it still maintained a significant recalcitrant fraction. Nitrogen concentration in the bulk soil increased after heating, particularly under air condition. This phenomenon could be due to the formation of heterocyclic nitrogen compounds in the charred material. In the study area, PyOM is rich in aliphatic compounds presumably because of the understory sclerophyllous vegetation typically found in Mediterranean environments. A large fraction of the charcoal released to the soil during the fire is sensitive to oxidation by subsequent fires. On the other hand, charcoal preserves a significant fraction of C, the most recalcitrant one, with expected long residence time in soil. PyOM formed under high oxygen availability is richer in N than that formed in inert atmosphere, which might make PyOM more susceptible to biochemical degradation.

Contribution of organic matter molecular proxies to interpretation of the last 55 ka of the Lynch's Crater record (NE Australia)

The Lynch's Crater (NE Australia) deposit is a key information source on Late-Quaternary palaeoenvironmental change, including human-induced deforestation since the arrival of Aboriginals, megaherbivore extinction and southern hemisphere tropical climate dynamics. This study adds to the important dataset available for the site by assessing the molecular composition of organic matter in the record using pyrolysis–GC–MS to elucidate ecological and hydrological conditions since 55ka BP.Pyrolysates were dominated by methylene chain compounds (MCCs) and lignin products (methoxyphenols). Concomitant increases in MCCs and aquatic source indicators (biogenic opaline silica, Si:Al ratio, SEM-visible debris of sponges and diatoms and aquatic pollen taxa), which roughly coincide with abrupt climate events in GISP2 δ18O (Heinrich event H3, H1, 8.2ka and oscillations at 33–36ka BP), reflect transitions from peat (dominated by lignin from terrestrial plants) to lacustrine (MCCs from aquatic plants) conditions. The evidence points towards wet conditions causing the accumulation of layers rich in inorganic sediment during H events, favouring the hypothesis of a southward ITCZ shift, rather than an ENSO-induced northward shift, as the underlying mechanism. This contradicts previous studies using the “degree of peat humification” index (DPH). We measured DPH and the extracts and residues by PY–GC–MS, to better understand the validity of this surface moisture proxy. Paradoxically, high DPH corresponds to the relatively young (<15ka) ombrotrophic peat environment, as DPH relies on the proportion of extractable carbohydrates concentrated in this part of the core, while deeper and unarguably more evolved layers are comprised of alkali-inextricable lignin and MCCs. Therefore, DPH does not accurately reflect humidity-controlled degradation/preservation dynamics and its use for studying climate change in complex records, such as Lynch's Crater, is cautioned. Finally, the decoupling of humidity conditions from changes in regional arboreal vegetation supports the hypothesis of an anthropogenic- rather than climate-driven shift towards sclerophyllous vegetation since 45ka, but the hydroseral complexity of the system demands caution on this matter.

Young clades in an old family: Major evolutionary transitions and diversification of the eucalypt-feeding pergid sawflies in Australia (Insecta, Hymenoptera, Pergidae)

A calibrated phylogeny of the family Pergidae indicates that the major lineages within the family evolved during the fragmentation of the Gondwanan supercontinent. The split between the Pergidae and its sister group Argidae is estimated at about 153Myr ago. No central dichotomous division between Australian and South American pergid sawflies was observed, showing that the major lineages within this group had already evolved by the time Australia had become completely isolated from Antarctica. The molecular dating analysis strongly indicates a co-radiation of Australian pergid sawflies with their Myrtaceae hosts and suggest that the two eucalypt-feeding clades, pergines and pterygophorines, colonised their eucalypt host plants independently during the Palaeocene, at the time when their hosts appear to have started radiating.The present analysis includes representatives of 13 of the 14 currently recognised subfamilies of Pergidae, almost all of which are supported by the molecular data presented here. Exceptions include the Euryinae (paraphyletic in respect to Perreyiinae), Acordulecerinae (paraphyletic to the Perginae), and the Australian Phylacteophaginae (placed within the Neotropical Acordulecerinae).The break-up of Gondwana and the timing of the subsequent climatic change in Australia, leading from vegetation adapted to a seasonal-wet conditions to the arid-adapted sclerophyll vegetation typical of Australia, suggest that the species-poor subfamilies occurring in rainforests represent remnants of more diverse groups that were decimated through loss of habitat or host species.

The challenge of Mediterranean sclerophyllous vegetation under climate change: From acclimation to adaptation

Forecasting models for climate change in southern Europe differ from those proposed for central and northern regions mainly with regard to precipitation. In fact, a strong reduction in average rainfall, mainly caused by decrease frequency of rainy events, is believe to occur in the Mediterranean basin in the forthcoming hundred years. Increased frequency of drought events will be paralleled and exacerbated by warming. Differently from areas where plant growth is limited by sub-optimal temperature (i.e. boreal and most temperate forests) and where warming has been reported to increase carbon assimilation and growth, plants growing in the Mediterranean basin are currently near their temperature optimum, and warming may contribute (e.g. with drought) to impair photosynthesis and depress growth and survival. Rising atmospheric CO2 has been found to increase growth, photosynthesis water use efficiency, and may partially alleviate the deleterious effects of warming and drought. However, in areas where severe and prolonged drought episodes occur, severe photoinhibition and metabolic limitation to photosynthesis may prevent Mediterranean sclerophylls to take advantage of higher atmospheric CO2, and may slow down recovery after the end of the dry season. The most sensitive forest types consist in tree species which are, in the Mediterranean basin, at the southernmost limit of their distribution range. In contrast, thermophilous trees are expected to have a greater diffusion both in southern and central Europe, as winter cold stress will be reduced by warming. Yet due to great variability of ecological features, the alleged substitution of tree species can follow a natural pattern from south to north and from low to high altitudes, without considering obstacles deriving from urbanization. For these reasons, research on the performance and ecologic plasticity of different genotypes, on species selection, and on planting and management techniques can have strategic importance for adaptive forest management.

Major Clades of Australasian Rutoideae (Rutaceae) Based on rbcL and atpB Sequences

BackgroundRutaceae subfamily Rutoideae (46 genera, c. 660 species) is diverse in both rainforests and sclerophyll vegetation of Australasia. Australia and New Caledonia are centres of endemism with a number of genera and species distributed disjunctly between the two regions. Our aim was to generate a high-level molecular phylogeny for the Australasian Rutoideae and identify major clades as a framework for assessing morphological and biogeographic patterns and taxonomy.Methodology/Principal FindingsPhylogenetic analyses were based on chloroplast genes, rbcL and atpB, for 108 samples (78 new here), including 38 of 46 Australasian genera. Results were integrated with those from other molecular studies to produce a supertree for Rutaceae worldwide, including 115 of 154 genera. Australasian clades are poorly matched with existing tribal classifications, and genera Philotheca and Boronia are not monophyletic. Major sclerophyll lineages in Australia belong to two separate clades, each with an early divergence between rainforest and sclerophyll taxa. Dehiscent fruits with seeds ejected at maturity (often associated with myrmecochory) are inferred as ancestral; derived states include woody capsules with winged seeds, samaras, fleshy drupes, and retention and display of seeds in dehisced fruits (the last two states adaptations to bird dispersal, with multiple origins among rainforest genera). Patterns of relationship and levels of sequence divergence in some taxa, mostly species, with bird-dispersed (Acronychia, Sarcomelicope, Halfordia and Melicope) or winged (Flindersia) seeds are consistent with recent long-distance dispersal between Australia and New Caledonia. Other deeper Australian/New Caledonian divergences, some involving ant-dispersed taxa (e.g., Neoschmidia), suggest older vicariance.Conclusions/SignificanceThis comprehensive molecular phylogeny of the Australasian Rutoideae gives a broad overview of the group’s evolutionary and biogeographic history. Deficiencies of infrafamilial classifications of Rutoideae have long been recognised, and our results provide a basis for taxonomic revision and a necessary framework for more focused studies of genera and species.

Root system investigation in sclerophyllous vegetation: an overview

Sclerophyllous vegetation contributes to the formation of forest resources in the Mediterranean biome that in turn provides an important resource in terms of ecosystem services. Despite this, scientific knowledge of sclerophyllous vegetation, in particular with regard to their root systems, is fragmented. This review takes into account the research on below-ground sclerophyllous biomass in different contexts where there is a Mediterranean climate. In particular, the authors analyse the different investigative approaches used in studying roots, the main topics covered by research, and the relationships between root and shoot biomass. The review shows that there is a paucity of research on the root systems of sclerophyllous vegetation although there are examples of innovative technologies being applied to research questions. This review considers some key works in the literature, and provides useful information to address re-vegetation and reforestation programmes in the context of Mediterranean ecosystems.

An update of the world survey of myrmecochorous dispersal distances

We update the global assessment of seed dispersal by ants and test the hypothesis that the body size of seed‐dispersing ant species varies with latitude in the same way as dispersal distance. We compiled all published data about seed dispersal distance by myrmecochory through March, 2011. We then broke the data down by vegetation type, geography and taxonomy. We also compiled data on body size (body length) of the seed‐dispersing ant species from the studies consulted. Based on 7889 observations, the mean dispersal distance was 1.99 m, although the curve has a long tail extending to 180 m. Considering the mean dispersal distance by ant species and study as independent data, the mean dispersal distance was 2.24 ± 7.19 m (n = 183). Shorter distances are associated with smaller ant species, while the tail of the dispersal curve is due to larger ant species. The mean dispersal distance of myrmecochorous seeds dispersed by ants decreased with increasing latitude, but there was no significant relationship between the body size of dispersing ant species and latitude (i.e. myrmecochorous seed‐dispersing ant species do not follow Bergmann's rule). In 1998 we made three predictions: 1) the dispersal distances of the Southern Hemisphere will decrease with as more data from mesophyllous vegetation are obtained; 2) assuming that ant nest density is higher at lower latitudes, the differences in distances between hemispheres would probably decrease with more data; and 3) numerical differences between dispersal distances in mesophyllous and sclerophyllous vegetation zones would increase with more data. The results obtained since 1998 support the only the third prediction. The dispersal distances in mesophyllous vegetation zones are shorter than in the sclerophyllous vegetation zones, and the difference between 1998 have increased. The differences in dispersal distances between hemispheres are consistent with the avoidance of parent–offspring competition (escape hypothesis).

A Broad Approach to Abrupt Boundaries: Looking Beyond the Boundary at Soil Attributes within and Across Tropical Vegetation Types

Most research on boundaries between vegetation types emphasizes the contrasts and similarities between conditions on either side of a boundary, but does not compare boundary to non-boundary vegetation. That is, most previous studies lack suitable controls, and may therefore overlook underlying aspects of landscape variability at a regional scale and underestimate the effects that the vegetation itself has on the soil. We compared 25 soil chemistry variables in rainforest, sclerophyll vegetation and across rainforest-sclerophyll boundaries in north-eastern Queensland, Australia. Like previous studies, we did find some contrasts in soil chemistry across vegetation boundaries. However we did not find greater variation in chemical parameters across boundary transects than in transects set in either rainforest or woodland. We also found that soil on both sides of the boundary is more similar to “rainforest soil” than to “woodland soil”. Transects in wet sclerophyll forests with increasing degrees of rainforest invasion showed that as rainforest invades wet sclerophyll forest, the soil beneath wet sclerophyll forest becomes increasingly similar to rainforest soil. Our results have implications for understanding regional vegetation dynamics. Considering soil-vegetation feedbacks and the differences between soil at boundaries and in non-boundary sites may hold clues to some of the processes that occur across and between vegetation types in a wide range of ecosystems. Finally, we suggest that including appropriate controls should become standard practice for studies of vegetation boundaries and edge effects worldwide.

Physico-chemical impacts of terrestrial alien vegetation on temporary wetlands in a sclerophyllous Sand fynbos ecosystem

Temporary depression wetlands form a characteristic feature of the wet-season landscape in the south-western Cape region of South Africa, yet they remain largely unstudied. We hypothesized that the loss of sclerophyllous Sand fynbos habitat around these temporary wetlands causes in-wetland physico-chemical changes. We expected to observe a decrease in the concentration of humic substances in wetlands and a corresponding rise in surface water pH as fynbos cover decreases around wetlands, in this case owing to alien vegetation invasion. A set of 12 differentially invaded temporary depression wetlands within a Sand fynbos ecosystem in Cape Town were repeatedly sampled during the 2009 wet season. Multivariate gradient analysis techniques revealed associations between fynbos cover bordering wetlands and various physico-chemical and biotope constituents within wetlands. Univariate linear regression models reported strong and temporally consistent negative relationships between terrestrial fynbos vegetation cover and wetland pH and positive relationships with humic content. Results indicate that replacement of Sand fynbos with alien vegetation causes a reduction of humic input to wetlands, which in turn has knock-on effects on other wetland environmental constituents such as pH. These findings are expected to be applicable to any wetland where surrounding humic-rich sclerophyllous vegetation is replaced by a non-sclerophyllous agent.

Supplemental feeding drives endoparasite infection in wild boar in Western Spain

Wildlife population management is thought to destabilize existing host–parasite equilibriums in opposing directions, that is, it may increase parasite success or host resilience once infection takes place. This process is of special importance for species such as the wild boar (Sus scrofa) that are managed for game purposes throughout much of Europe. However, little is known about how this practices influcences either gastrointestinal or pulmonary parasitism in the wild boar. Twelve hunting estates were chosen in order to study the relationship of management measures (feeder density, wild boar abundance, the ratio of wild boar per feeder and the percentage of sclerophyllous vegetation) and host factors (age and sex) with gastrointestinal and pulmonary parasite aggregation, richness, infection probability and intensity of infection. Parasitological analyses from 300 wild boar gastrointestinal and 269 respiratory tracts were performed for this purpose. A set of general linear models with combinations of the explanatory variables was built and the model with the smallest Akaike Information Criterion was selected as the best. The feeder density increased gastrointestinal parasite traits (richness, infection probability and intensity of infection), probably due to the contamination of feeding sites with infective parasite forms. Pulmonary parasite traits, on the other hand, were only influenced by host sex and age class, and parasite aggregation was as expected for a wild population. Managers should be aware of the consequences on parasitism when implementing supplemental feeding in hunting estates.

Land cover and land use change in the Central Spanish-Portuguese Border Region

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Enhanced seasonality of precipitation in the Mediterranean during the early part of the Last Interglacial

The deposition of sapropels in the eastern Mediterranean Sea is thought to occur during intervals of intensified African monsoon and increased precipitation in the Mediterranean borderlands. Speleothem and pollen records, however, reveal conflicting evidence for a Mediterranean-wide precipitation increase, suggesting that seasonal changes in the hydrological regime may be important. Using a multiproxy record, we present the first independent evidence for seasonality of precipitation during the early Last Interglacial (ca. 130–119 ka) from the Tenaghi Philippon peatland in northeast Greece. During the early part of the interglacial, mineralogical, macrofossil, and pollen records from the same core show a shift from mire to lacustrine conditions simultaneous with an expansion of sclerophyllous vegetation and the presence of acicular aragonite, indicating the onset of highly evaporative summer conditions. This indicates enhanced seasonality of precipitation and reconciles the apparent incongruity between Mediterranean pollen and speleothem records. It also provides evidence for significantly increased winter precipitation coeval with the deposition of sapropel S5, one of the most prominent sapropels of the Pleistocene. We suggest that in addition to the summer African monsoon component, increased winter precipitation from the northern Mediterranean borderlands may have contributed to maintaining reduced surface-water salinities in the Mediterranean Sea over the entire year.

The mid‐Holocene vegetation of the Mediterranean region and southern Europe, and comparison with the present day

AbstractAim To contribute to the intense debate surrounding the relative influence of climate and humans on Mediterranean‐region land cover over the past 6000 years, we assess the Holocene biogeography and vegetation history of southern Europe by means of an extensive pollen record dataset.Location The Mediterranean biogeographical zone and neighbouring parts of Iberia, the Alps and Anatolia, between 30° N, 48° N, 10° W and 45° E.Methods We compiled a southern European pollen record dataset using available pollen databases (124 sites) and other sources (74 sites), with improved spatial coverage and dating control compared with earlier studies. We used only those sites that had pollen data for both 0 ka and 6 ka. We reconstructed mid‐Holocene and present‐day biomes, arboreal pollen percentages and distribution and relative abundance of 11 key woody taxa, with anomaly maps.Results Northern temperate forest biomes extended further south at the mid‐Holocene than at present, but not as far as earlier studies suggested. Sclerophyllous vegetation occurred along the Mediterranean coast throughout the region at 6 ka. Arboreal pollen percentages were up to 50% higher than at present. At 6 ka, Olea, Fagus and Juniperus had smaller distributions and/or abundances; Abies, Cedrus and both deciduous and evergreen Quercus had larger distributions and/or abundances; Phillyrea, Pistacia and Cistus showed minimal difference; and Pinus showed a cosmopolitan distribution with variable abundance.Main conclusions Temporal difference analysis is more meaningful when only sites containing samples for all time slices are analysed. During the mid‐Holocene, southern Europe was more heavily forested with temperate vegetation than it is at present, but drought‐tolerant xeric vegetation was still widespread along the southern margins of the region. Although human land use may have caused the degradation of land between the mid‐Holocene and the present, the mere presence of xeric vegetation in the Mediterranean region does not require human impact. This challenges the commonly held belief that modern Mediterranean vegetation represents a ‘degraded’ state.

Island ecosystem and biodiversity dynamics in northeastern Australia during the Holocene: Unravelling short-term impacts and long-term drivers

Vegetation changes of tropical Lizard Island (Great Barrier Reef World Heritage Area, Australia) over the last 8000 years are derived from palaeoenvironmental analysis of a 475 cm long sediment core. During early-Holocene sea-level rise, flooding of the continental shelf and thus isolation of Lizard Island, the pollen record shows the gradual establishment of a mangrove forest paralleled by contraction of the near-coastal palm and grass-dominated vegetation. Subsequently, mid-Holocene relative environmental stability supported a diverse, Rhizophora-dominated mangrove and open, mixed sclerophyll vegetation inland. Around 6000 years ago, a profound disturbance of the mangrove is recorded by a siliciclastic layer and we hypothesise that this deposit documents the impact of a storm or cyclone. Postevent environmental conditions were strongly altered with enhanced estuarine conditions supporting a Sonneratia and Bruguiera-dominated mangrove forest. During late-Holocene sea-level fall and stabilisation, progradation and contraction of the mangrove forest was paralleled by the expansion of a palm-dominated swamp. Freshwater taxa continued to dominate the record, however, a distinct disturbance signal from anthropogenic activity is recorded in the last century. Although Sonneratia dominated the post-event mangrove, late-Holocene environmental instability led to the extinction of this genus on the island. Local environmental changes in the freshwater swamp and rainforest also led to the loss of Arenga and Ilex from the island’s ecosystems. Our record implies that long-term ecosystem and biodiversity change on Lizard Island is: (a) primarily reflected in the spatial extent of the island’s vegetation communities and the species dominance within them and (b) driven by an interplay between climate, sea-level and potentially human activity. In addition, a short-term impact provoked the reconfiguration of the mangrove, potentially causing long-term ecosystem instability and thus impacting on mangrove biodiversity development on the Great Barrier Reef islands.

Commentary: Towards an efficient management of biological invasions

ISSN 1948-6596 news and update commentary Towards an efficient management of biological invasions Biological invasions are a current conundrum for the management of worldwide biodiversity. Inter- national transportation networks have facilitated the connection of distant regions, and eased the movement of exotic species historically confined to their native areas by natural barriers and dis- persal constraints. Some of these species have the capacity to establish and spread successfully in newly occupied biogeographic regions, becoming a real problem for the hosting ecosystems and the humans that depend on them. They compete with native species and alter the functioning of ecosys- tems, threatening the services provided by these ecosystems and in some cases having direct ef- fects on human health. The management of biological invasions and/or ecosystems hosting them is becoming ever more relevant, as the number of exotic plant and animal species increases worldwide. Management actions range from preventive measures to avoid the introduction of exotic species, to control op- erations of entire ecosystems after establishment of invasive organisms. To facilitate the manage- ment of these novel ecosystems (sensu Hobbs et al. 2006), it is necessary to expose and develop appropriate data on the ecology and distribution of invasive species, as well as tools to assist in pri- oritizing actions for control of alien plants. In this vein, two papers have been published recently that shed some light into these issues. The first study was conducted by several plant ecologists from Europe, and has been pub- lished in Diversity and Distributions under the leadership of Milan Chytrý from the Masaryk Uni- versity (Czech Republic). Chytrý et al. (2009) pro- vide the first spatially explicit quantification of the level of alien plant invasion at a regional level for Europe. Combining quantitative data on the pro- portion of alien species that invade different habi- tat types with a land-cover map, they produced a map that estimates the levels of invasion across Europe. Their utilization of habitats as a basis for mapping levels of invasion was justified by a previ- ous study (Chytrý et al, 2008), in which habitat types were shown to be better predictions of inva- sion levels than other variables, such as environ- mental characteristics or propagule pressure. Their results predict that the highest levels of alien plant invasions occur among arable land, urban and industrial areas, whereas the lowest levels occur in sclerophyllous vegetation, peat- bogs and heathlands. The spatial distribution of the level of invasion suggests that the highest lev- els of invasion are in lowland areas of western Europe and in agricultural regions in central and eastern Europe. In contrast, low levels are pre- dicted in boreal regions and mountainous zones, except along coastlines, irrigated agricultural land, and rivers of the Mediterranean region. Even though the approach used to elaborate the map is coarse and although there is potential for further improvements, this study provides a first look at the level of plant invasion in Europe and permits the identification of areas susceptible to donate/ receive exotic species. In parallel with this study mapping levels of invasion, Andrew J. Tatem from the University of Florida (USA) examined the potential dispersal of exotic species in a new study published in Ecogra- phy. Tatem (2009) provides a framework to pre- dict biological invasion risks through the world- wide airline network, and assesses future changes due to human and environmental variations. The growth of air travel increases the propagule pres- sure and rate of exotic species introductions, but the establishment of such organisms in new re- gions will depend upon whether they find climatic conditions similar to those at their origin. Build upon a previous study (Tatem and Hay 2007), he examines the spatial and seasonal distribution of incoming traffic volume to individual airports, and combines this information with climate scenarios for the period 2007-2010 to identify potential in- vasion risk routes. His results suggest that changes in global climate will be relatively small during the near fu- ture, but increases in incoming traffic from China, India, Russia and eastern Europe are expected to frontiers of biogeography 1.1, 2009 — © 2009 the authors; journal compilation © 2009 The International Biogeography Society

Nucleated regeneration of semiarid sclerophyllous forests close to remnant vegetation

Natural regeneration of mediterranean plant communities has proved difficult in all continents. In this paper we assess whether regeneration of sclerophyllous forests shows nucleated patterns indicative of a positive effect of vegetation remnants at the landscape level and compare the regeneration patterns between sites with distinctive climate conditions. We studied the spatial patterns of vegetation change during 52years in central Chile using remotely-sensed images to test the predictions that (1) regeneration of sclerophyllous vegetation expands from patches of remnant vegetation; and (2) regeneration is more dependent on remnant vegetation in drier sites. Our results show that the regeneration of the sclerophyllous vegetation in central Chile is a slow process that may be possible under certain conditions. We found that the fraction of regenerated vegetation increases with the proximity to remnant sclerophyllous forest in an aggregated pattern. Especially in drier sites, vegetation remnants have a facilitative role on the regeneration of mediterranean-type ecosystems. These results have important implications for the management and conservation of these ecosystems.