Consequences of weed invasion and control on plant-bird interactions and bird communities

Introduced plants can have a variety of impacts in ecosystems in which they become invasive. These impacts can include the disruption of interactions between native plant and animal species, such as seed dispersal and pollination. Subsequently, other interactions and mutualisms can be affected, both at the site of the plant invasion and elsewhere. Interactions can also become established between the invasive plant and native and invasive animal species. The removal of an invasive plant has the potential to disrupt these newly formed interactions, thus disadvantaging some fauna and potentially affecting subsequent interactions involving these species. While control of invasive plants is typically a goal of conservation management, the consequences of control for other species are rarely fully considered or investigated. In this study, I have tested several hypotheses regarding the interaction of an invasive plant with fauna, and the effects of the plant’s invasion and control on plant-animal interactions. Bitou Bush (Chrysanthemoides monilifera ssp. rotundata) is an invasive plant in coastal New South Wales (NSW), Australia. South African in origin, it has now spread to occupy at least 80% of the NSW coastline. Fruit production in C. monilifera is prolific and fruits are consumed and dispersed by vertebrates, especially birds. In addition to other effects of C. monilifera, this plant-animal interaction has the potential to affect the seed dispersal of other vertebratedispersed plants and also the composition of the bird community, which may subsequently affect other plant-bird interactions. In order to quantify the magnitude of these possible effects, I designed this study with the following five major components: (i) comparison of the fruiting characteristics of C. monilifera with those of co-occurring birddispersed native plant species; (ii) description of the plant-bird interactions that involve flowers and fruits in vegetation that has been invaded or is at risk of invasion by C. monilifera; (iii) measurement of the rate of removal of C. monilifera fruits and those of some co-occurring bird-dispersed plant species in: habitat dominated by C. monilifera, where C. monilifera had been eliminated by the application of herbicide, and uninvaded vegetation; (iv) assessment of the effect of C. monilifera removal by herbicide application on the species composition and abundance of the bird community; and (v) assessment of the effect of dominance of the vegetation community by C. monilifera on the species composition and abundance of the bird community. I found that the fruits of C. monilifera are within the range of physical dimensions and nutrient composition of those of co-occurring native species. The greatest distinction in fruit characteristics is in phenology and the combination of phenology and morphology, as peak production of C. monilifera fruits occurs when native fruits are scarce. Consequently, C. monilifera fruits are attractive to vertebrate dispersers, especially birds. At least 25 species of birds feed on C. monilifera fruits in NSW, most of which are indigenous and are likely to disperse viable seeds. In an experimental study using feeding stations, I found that the rate of removal of fruits of native plant species was unaffected by either dense infestation of C. monilifera, or its elimination. This is likely to be due to highly facultative relationships between frugivorous birds and plants, combined with differences in phenology and, in some cases, the morphology of fruits of native plants and C. monilifera. Consequently, in this system there has been little impact of an invasive plant on this plant-bird interaction. The rate of removal of C. monilifera fruits, however, was less in herbicide-treated habitat. This has implications for long-term C. monilifera control, because herbicide treatment often leaves scattered individual plants alive, which would have poorer seed dispersal than plants in dense C. monilifera stands. The removal of C. monilifera affected the bird community, with the overall abundance of birds declining in herbicide-treated areas after the C. monilifera died. Only those birds that consume C. monilifera fruits were affected, while other groups of birds that do not directly use C. monilifera resources were unaffected. Although this impact was minor, it illustrates that removal of an invasive plant can affect bird communities, and these impacts should be considered before control programs are implemented. Dominance of the vegetation by C. monilifera also affected bird communities, with overall bird abundance, specifically that of insectivorous birds, and at some locations nectarivorous birds, being lower in C. monilifera than native habitat. The quantity of remaining native vegetation, particularly of nectar-producing plants widely used by birds, appears to be important in determining bird community composition in invaded areas. In this study, I have demonstrated that both dominance of the vegetation by an invasive plant, and the control of an invasive plant, can induce change in fauna communities, and disrupt some plant-animal interactions. These changes will need to be considered carefully in planning management actions to conserve coastal bird communities and their interactions with plants. While continued efforts to control C. monilifera are clearly justified, these should form part of a broad strategy for coastal community conservation, including consideration of other threats to native communities that act independently or in concert with C. monilifera invasion. These considerations should include the potential impacts of other invasive plant species, targeted sites and species for control efforts, and other forms of habitat loss and degradation

Using a Multi-Century Post-Fire Chronosequence to Develop Criteria to Distinguish Prior and Bowman’s (2020) Post-Fire Obligate Coloniser and Fire-Intolerant Flora

Prior and Bowman added a new dimension to existing frameworks of post-fire responses of woody plants, by including the trait of colonisation ability (C) for those taxa which neither resprout (Rf−) nor produce seedlings (Sf−) after fire. Specifically, they recognised distinctions between: (i) post-fire obligate colonisers, being species that neither resprout nor produce seedlings from persistent seed banks post-fire but are able to colonise burnt areas through dispersal from unburnt populations, and (ii) fire-intolerant, which are unable to recover after fire by either resprouting, seeding or colonisation. We use data on temporal and spatial patterns of colonisation of Rf−Sf− mistletoes from a chronosequence study with an exceptionally long span of times since fire as a practical example of the delineation of post-fire obligate coloniser and fire-intolerant species. We propose that when a population of a species is burnt, if the species is unable to regularly colonise and reach reproductive maturity in burnt areas spatially distant from fire edges within plausible and regularly-occurring maximum fire-return intervals for the now-burnt community type, it would be classified as fire-intolerant. In our examples, Lysiana meets the criteria for fire-intolerant in obligate-seeder eucalypt woodland, while Amyema is classed as a post-fire obligate coloniser

Chaining and Burning Modifies Vegetation Structure, Fuel, and Post-Disturbance Sprouting Capacity

Prescribed fire and/or mechanical methods can be used to modify the quantity, continuity, and/or spatial arrangement of flammable fuel. Yet the consequences of fuel management, both in terms of ecological outcomes and in facilitating improved fire management, often are poorly documented. In the global biodiversity hotspot of southwest Western Australia, chaining and burning is a novel technique for manipulating fuels. Vegetation first is dislodged using a chain, then after a period of curing, burnt. We tested whether combining two disturbance events in this way results in different vegetation structure postfire than only burning, and whether the postfire sprouting capacity of community-dominant Eucalyptus spp. is compromised. Both chained and burnt and only burnt treatments had much less leaf litter and vegetation >25 cm high than long-unburnt vegetation, indicating a fire management benefit of fuel modification. Chained and burnt strips had a threefold reduction in standing dead vegetation compared to only burnt samples. The stem number of Eucalyptus spp. was reduced by 20% in chained and burnt strips compared to only burnt vegetation, indicating that consecutive disturbances reduce resilience and might render sprouters vulnerable to subsequent disturbances. Balancing the fire management benefits of chaining and burning with the ecological consequences is a significant challenge facing land managers in this fire-prone landscape. The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Fire management strategies to maintain species population processes in a fragmented landscape of fire-interval extremes

Changed fire regimes have led to declines of fire-regime-adapted species and loss of biodiversity globally. Fire affects population processes of growth, reproduction, and dispersal in different ways, but there is little guidance about the best fire regime(s) to maintain species population processes in fire-prone ecosystems. We use a process-based approach to determine the best range of fire intervals for keystone plant species in a highly modified Mediterranean ecosystem in southwestern Australia where current fire regimes vary. In highly fragmented areas, fires are few due to limited ignitions and active suppression of wildfire on private land, while in highly connected protected areas fires are frequent and extensive. Using matrix population models, we predict population growth of seven Banksia species under different environmental conditions and patch connectivity, and evaluate the sensitivity of species survival to different fire management strategies and burning intervals. We discover that contrasting, complementary patterns of species life-histories with time since fire result in no single best fire regime. All strategies result in the local patch extinction of at least one species. A small number of burning strategies secure complementary species sets depending on connectivity and post-fire growing conditions. A strategy of no fire always leads to fewer species persisting than prescribed fire or random wildfire, while too-frequent or too-rare burning regimes lead to the possible local extinction of all species. In low landscape connectivity, we find a smaller range of suitable fire intervals, and strategies of prescribed or random burning result in a lower number of species with positive growth rates after 100 years on average compared with burning high connectivity patches. Prescribed fire may reduce or increase extinction risk when applied in combination with wildfire depending on patch connectivity. Poor growing conditions result in a significantly reduced number of species exhibiting positive growth rates after 100 years of management. By exploring the consequences of managing fire, we are able to identify which species are likely to disappear under a given fire regime. Identifying the appropriate complementarity of fire intervals, and their species-specific as well as community-level consequences, is crucial to reduce local extinctions of species in fragmented fire-prone landscapes

Appendix C. Alternative model forms and model statistics for relationships between time since fire and vital attributes.

Alternative model forms and model statistics for relationships between time since fire and vital attributes

Appendix A. Species sampled, their habitats, functional classification, and replicates per times since fire.

Species sampled, their habitats, functional classification, and replicates per times since fire

Appendix B. Estimating the age of long-unburnt sites.

Estimating the age of long-unburnt sites

Distribution, Biogeography and Characteristics of the Threatened and Data-Deficient Flora in the Southwest Australian Floristic Region

The Southwest Australian Floristic Region (SWAFR) supports an exceptional number of threatened and data-deficient flora. In this study, we: (i) collated statistics on the number, listing criteria and tenure of occurrence of threatened and data-deficient flora; (ii) conducted spatial and biogeographic analyses to address questions concerning patterns of diversity of threatened and data-deficient flora relative to the whole flora and evolutionary and threat drivers; and (iii) examined whether threatened and data-deficient flora richness is evenly distributed across plant lineages. We found that although threatened and data-deficient flora occurred across the breadth of the SWAFR, high richness was concentrated in a limited number of locations, which were not always strongly aligned with areas of higher land transformation. Data-deficient flora demonstrated different spatial patterns of occurrence to threatened flora. Approximately 70% of the populations of threatened and data-deficient flora occurred outside of lands managed primarily for conservation. Both evolutionary history and contemporary threats contribute to the current status and distribution of diversity of the threatened and data-deficient flora, with evolutionary history playing a significant role in predisposing a portion of the flora to having population traits that result in those flora meeting IUCN Red List criteria, along with ecological traits that predispose some to specific novel threats. An understanding of the distribution of species and threats, flora traits, and how these traits mediate susceptibility to threats, offers one potential way forward for an initial assessment of which of the 1819 data-deficient flora may be most at risk of extinction