The flammability of plant leaves influences the spread of fire through vegetation. Exotic plants invading native vegetation may increase the spread of bushfires if their leaves are more flammable than native leaves. We compared fresh-leaf and dry-leaf flammability (time to ignition) between 52 native and 27 exotic plant species inhabiting dry sclerophyll forest. We found that mean time to ignition was significantly faster in dry exotic leaves than in dry native leaves. There was no significant native-exotic difference in mean time to ignition for fresh leaves. The significantly higher fresh-leaf water content that was found in exotics, lost in the conversion from a fresh to dry state, suggests that leaf water provides an important buffering effect that leads to equivalent mean time to ignition in fresh exotic and native leaves. Exotic leaves were also significantly wider, longer and broader in area with significantly higher specific leaf area–but not thicker–than native leaves. We examined scaling relationships between leaf flammability and leaf size (leaf width, length, area, specific leaf area and thickness). While exotics occupied the comparatively larger and more flammable end of the leaf size-flammability spectrum in general, leaf flammability was significantly correlated with all measures of leaf size except leaf thickness in both native and exotic species such that larger leaves were faster to ignite. Our findings for increased flammability linked with larger leaf size in exotics demonstrate that exotic plant species have the potential to increase the spread of bushfires in dry sclerophyll forest.

Estimates of the level of invasion for a region are traditionally based on relative numbers of native and alien species. However, alien species differ dramatically in the size of their invasive ranges. Here we present the first study to quantify the level of invasion for several regions of the world in terms of the most widely distributed plant species (natives vs. aliens). Aliens accounted for 51.3% of the 120 most widely distributed plant species in North America, 43.3% in New South Wales (Australia), 34.2% in Chile, 29.7% in Argentina, and 22.5% in the Republic of South Africa. However, Europe had only 1% of alien species among the most widespread species of the flora. Across regions, alien species relative to native species were either as well-distributed (10 comparisons) or more widely distributed (5 comparisons). These striking patterns highlight the profound contribution that widespread invasive alien plants make to floristic dominance patterns across different regions. Many of the most widespread species are alien plants, and, in particular, Europe and Asia appear as major contributors to the homogenization of the floras in the Americas. We recommend that spatial extent of invasion should be explicitly incorporated in assessments of invasibility, globalization, and risk assessments

Naturalized plant species disperse their populations over considerable distances to become invasive. We tested the hypothesis that this shift from naturalization to invasion is facilitated by increased investment of resources in seed dispersal appendages, using an assemblage of naturalized plants of southeastern Australia. Compared with non-invasive species, we found in both cross-species and independent-contrasts analyses that invasive species invested more heavily in seed dispersal appendages, regardless of the structure present on the seed associated with the mode of dispersal (e.g., wings versus fleshy fruits). Invasive species such as Lonicera japonica, Hedera Helix and Acetosa sagittata were found to invest as much as 60-70% of total diaspore mass in dispersal appendages. The positive relationship between dispersal investment and invasion success was still prevalent after controlling for the effects of plant growth form, seed mass and capacity for vegetative growth. Our findings demonstrate that a plant's investment in dispersal appendages helps to overcome the dispersal barrier in the shift from naturalization to invasion.

Of the large number of exotic plant species that become naturalized in new geographic regions, only a subset make the transition to become invasive. Identifying the factors that underpin the transition from naturalization to invasion is important for our understanding of biological invasions. To determine introductionhistory correlates of invasiveness among naturalized plant species of Australia, we compared geographic origin, reason for introduction, minimum residence time and growth form between naturalized non-invasive species and naturalized invasive plant species. We found that more invasive species than expected originated from South America and North America, while fewer invasive species than expected originated from Europe and Australasia. There was no significant difference between invasive and non-invasive species with respect to reason for introduction to Australia. However, invasive species were significantly more likely to have been resident in Australia for a longer period of time than non-invasive species. Residence times of invasive species were consistently and significantly higher than residence times of non-invasive species even when each continent of origin was considered separately. Furthermore, residence times for both invasive and non-invasive species varied significantly as a function of continent of origin, with species from South America having been introduced to Australia more recently on average than species from Europe, Australasia and North America. We also found that fewer invasive species than expected were herbs and more invasive species than expected were primarily climbers. Considered together, our results indicate a high propensity for invasiveness in Australia among exotic plant species from South America, given that they appear in general capable of more rapid shifts to invasiveness than aliens from other regions. Furthermore, our findings support an emerging global generality that introduction-history traits must be statistically controlled for in comparative studies exploring life-history and ecological correlates of invasion success.

Leaf flammability is a multidimensional plant functional trait with emerging importance for wildfire risk management. Understanding relationships among leaf flammability attributes not only provides information about the properties of leaves as fuels in the wildland–urban interface (WUI), it can also offer an effective way to identify low-leaf-flammability species. We examined relationships between leaf ignitibility, sustainability and combustibility among 60 plant species of the WUI of eastern Australia. We found that leaf ignitibility and sustainability worked in opposition to each other as dimensions of flammability. Species with leaves that were slow to ignite were those with leaves that sustained burning for the longest, whereas species with leaves that were fast to ignite had leaves that burned for the shortest periods of time. Low leaf combustibility was related to short leaf burning sustainability but not to ignitibility. We created an overall leaf flammability index (OLFI) to rank species on emergent properties of ignitibility, sustainability and combustibility attributes in combination. We found that low-leaf-flammability species with low OLFI values had small leaf area, high leaf mass per area and high leaf water content. Our findings have implications for species selection for green firebreaks in the WUI.

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We examined temporal introduction patterns of 132 invasive alien plant species (IAPS) to Australia since European colonisation in 1770. Introductions of IAPS were high during 1810–1820 (10 species), 1840–1880 (51 species, 38 of these between 1840 and 1860) and 1930–1940 (9 species). Conspicuously few introductions occurred during 10-year periods directly preceding each introduction peak. Peaks during early European settlement (1810–1820) and human range expansion across the continent (1840-1860) both coincided with considerable growth in Australia’s human population. We suggest that population growth during these times increased the likelihood of introduced plant species becoming invasive as a result of increased colonization and propagule pressure. Deliberate introductions of IAPS (104 species) far outnumbered accidental introductions (28 species) and were particularly prominent during early settlement. Cosmopolitan IAPS (25 species) and those native solely to South America (53 species), Africa (27 species) and Asia (19 species) have been introduced deliberately and accidentally to Australia across a broad period of time. A small number of IAPS, native solely to Europe (5 species) and North America (2 species), were all introduced to Australia prior to 1880. These contrasting findings for native range suggest some role for habitat matching, with similar environmental conditions in Australia potentially driving the proliferation of IAPS native to southern-hemisphere regions. Shrub, tree and vine species dominated IAPS introduced prior to 1840, with no grasses or forbs introduced during early colonisation. Since 1840, all five growth forms have been introduced deliberately and accidentally in relatively large numbers across a broad period of time. In particular, a large number of grass and forb IAPS were deliberately introduced between 1840 and 1860, most likely a direct result of the introduction of legislation promoting intensive agriculture across large areas of the continent. Since the 1980s, only three IAPS have been introduced (all deliberately introduced forbs). The decline in IAPS introductions is most likely a reflection of both increased surveillance and biosecurity efforts and the likelihood that many potential IAPS are still within a pre-expansion lag period

In many parts of the world, access to groundwater is needed for domestic, agricultural and industrial uses, and global groundwater exploitation continues to increase. The significance of groundwater in maintaining the health of rivers, streams, wetlands and associated vegetation is often underestimated or ignored, resulting in a lack of scrutiny of groundwater policy and management. It is essential that management of groundwater resources considers the needs of natural ecosystems, including subterranean. We review the limited Australian literature on the ecological impacts of groundwater overdraft and place Australian information within an international context, focusing on lentic, lotic, stygobitic and hyporheic communities as well as riparian and phreatophytic vegetation, and some coastal marine ecosystems. Groundwater overdraft, defined as abstracting groundwater at a rate which prejudices ecosystem or anthropocentric values, can substantially impact natural communities which depend, exclusively or seasonally, on groundwater. Overdraft damage is often underestimated, is sometimes irreversible, and may occur over time scales at variance to those used by water management agencies in modelling, planning and regulation. Given the dangers of groundwater overdraft, we discuss policy implications in the light of the precautionary principle, and make recommendations aimed at promoting the conservation of groundwater-dependent ecosystems within a sustainable use context.