A long-term (1993–2016) fire experiment in the grazed semi-arid savanna of the Northern Territory was used to investigate the relative impacts of soil properties and fire history on vegetation composition and diversity in grassland and woodland habitats. Subtle variation in soil texture influenced vegetation composition and abundance independently of fire variables and was generally a more important control on floristic patterns. Total species richness, lifeform richness and the abundance and presence of many individual plant species declined with increasing clay content. Linear mixed effect models with combined habitat data, showed total richness and richness of annual and perennial forbs, annual grasses and legumes increased with more frequent fire. Perennial grass abundance and richness was not influenced by fire. Total and lifeform mean richness did not vary between two and four yearly or early and late burnt treatments. Richness and abundance was generally significantly higher on burnt blocks than unburnt blocks regardless of fire season or interval. These results suggest greater diversity after burning is a result of an increase in ephemeral species. However, the overall influence of fire on floristic patterns is relatively moderate and fire regimes may therefore be manipulated for other management imperatives, such as fauna conservation, carbon sequestration and pastoral productivity without substantial impacts on botanical values in semi-arid tropical savannas.
The project arose from field surveys across Queensland which highlighted the contrasting grazing response of indian couch and buffel grass and stimulated discussion surrounding the use of grazing in reserves to manage invasive species.
Examining how plant traits respond to and affect herbivory is a common approach to exploring plant-herbivore interactions and their impact on ecosystem processes and functioning. Despite plants being potentially exposed to both vertebrate and invertebrate herbivores simultaneously, fundamental differences in the ecology and evolution of these two herbivore guilds results in them often being studied separately. A synthesis of the literature is needed to understand the types of plant traits examined and their response to, and effect on (in terms of forage selection) vertebrate and invertebrate herbivory, and to identify associated knowledge gaps. Focusing on grassland systems and species, we found 139 articles that met our criteria: 40 invertebrate, 97 vertebrate and 2 focussed on both vertebrate and invertebrate herbivores. Invertebrate focussed research, research conducted in the Southern Hemisphere and research on non-domesticated herbivores was significantly underrepresented based on our search. Differences in study focus (trait response or trait affect), along with considerable differences in the types of traits examined, led to limited capacity for comparison between the two herbivore guilds. For both invertebrates and vertebrates however, plant traits related to growth, such as leaf nitrogen and photosynthetic capacity, were often positively associated with herbivory. Future research should prioritise understanding how invertebrates, and the combined impact of both invertebrates and vertebrates’ respond to and affect plant traits. This review can be used as a guide for future research to select plant traits which are commonly measured either within one, or across both guild/s, as to help improve comparability and the broader significance of results, while also extending research breadth and knowledge.
Questions: The impact of invasive plant species on native diversity varies with spatial scale, with some invaders leading to broad-scale diversity declines and others to only local declines. These discrepancies may reflect the invaders" capacity to reduce niche opportunities across spatial scales which can be associated with their functional traits. We investigated impact-scale relationships and trait-based mechanisms, in areas invaded by the exotic perennial grass species, Bothriochloa pertusa. We examine root traits specifically, as below-ground competition was considered particularly important to the success of this species. Location: Grassy "ironbark" woodlands of eastern Queensland, Australia. Methods: We examined plots with varying degrees of invasion by B. pertusa, at multiple spatial scales (up to 1,000 m 2) and analysed changes to the species-area relationships (SARs) with increasing invader cover. Changes to SARs were assessed in relation to the invaders" effect on rare (low patch occupancy) and common species in the community. In a separate analysis within the same habitat, we collected root cores across a gradient of invader cover and analysed changes to community root traits that were considered important correlates of competition for space and nutrients. Results: Invasion-induced reductions in diversity were pervasive at all scales investigated, and this was associated with a proportionally greater effect on rare species in the community. In the separate root analysis, changes in community root traits with increasing invader cover were potentially indicative of more intense competition for resources rather than space. Conclusions: The observed regional-scale dominance of B. pertusa and associated declines in diversity warrant serious concern for the conservation of native plant communities and species in a region already at risk from other anthropogenic threats. Intense competition for below-ground resources is likely a contributing mechanism to the success of B. pertusa in this study system. Experimental examination of this and other mechanisms would help to validate these findings.
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