Lisa Smallbone

Changes in Bird Functional Diversity across Multiple Land Uses: Interpretations of Functional Redundancy Depend on Functional Group Identity

Examinations of the impact of land-use change on functional diversity link changes in ecological community structure driven by land modification with the consequences for ecosystem function. Yet, most studies have been small-scale, experimental analyses and primarily focussed on plants. There is a lack of research on fauna communities and at large-scales across multiple land uses. We assessed changes in the functional diversity of bird communities across 24 land uses aligned along an intensification gradient. We tested the hypothesis that functional diversity is higher in less intensively used landscapes, documented changes in diversity using four diversity metrics, and examined how functional diversity varied with species richness to identify levels of functional redundancy. Functional diversity, measured using a dendogram-based metric, increased from high to low intensity land uses, but observed values did not differ significantly from randomly-generated expected values. Values for functional evenness and functional divergence did not vary consistently with land-use intensification, although higher than expected values were mostly recorded in high intensity land uses. A total of 16 land uses had lower than expected values for functional dispersion and these were mostly low intensity native vegetation sites. Relations between functional diversity and bird species richness yielded strikingly different patterns for the entire bird community vs. particular functional groups. For all birds and insectivores, functional evenness, divergence and dispersion showed a linear decline with increasing species richness suggesting substantial functional redundancy across communities. However, for nectarivores, frugivores and carnivores, there was a significant hump-shaped or non-significant positive linear relationship between these functional measures and species richness indicating less redundancy. Hump-shaped relationships signify that the most functionally diverse communities occur at intermediate levels of species richness. Interpretations of redundancy thus vary for different functional groups and related ecosystem functions (e.g. pollination), and can be substantially different to relationships involving entire ecological communities.

Restoration treatments enhance early establishment of native forbs in a degraded temperate grassy woodland.

We investigated effects of three understorey restoration treatments, carbon (sugar) addition, spring burning and re-establishment of the perennial native grass Themeda australis (R.Br.) Stapf, on early establishment of eight species of native forbs in a degraded white box (Eucalyptus albens Benth.) woodland dominated by exotic annuals, in central New South Wales, Australia. Forb seeds and seedlings were introduced to treatments in a randomised, irrigated field trial and monitored for 4–8 months. Treatments significantly altered vegetation structure and composition, resulting in higher native grass and lower exotic grass cover on sugar and burnt plots (especially if seeded with Themeda), a proliferation of broadleaf exotic annuals on burnt plots, and continued high cover of exotic annual grasses and broadleaf annuals on control plots. Forb germination was largely confined to three large-seeded forbs, Bulbine bulbosa (R.Br.) Haw., Dichopogon fimbriatus (R.Br.) J.F.Macbr. and Microseris lanceolata (Walp.) Schultz-Bip., and few germinants of three small-seeded forbs were observed. Overall, germination (% emergence, and seedling numbers after 4 months) was significantly greater on sugar than burnt and control plots, while transplant survival was significantly enhanced by both sugar and burning treatments for up to 8 months after planting. Re-introduced Themeda swards significantly promoted seedling germination and transplant survival in burnt plots. While long-term seedling survival was extremely low owing to severe drought, we concluded that (i) the applied restoration treatments (especially carbon addition) have considerable potential for promoting forb establishment in degraded woodlands, (ii) reduced competition with exotic annuals associated with carbon addition outweighed potential disadvantages of reduced nutrient levels, (iii) competition with broadleaf annuals and/or exposure to more extreme environments associated with burning may be problematic for forb germination and (iv) Themeda swards may be more conducive to establishment of native forbs than swards of exotic annuals, owing to their contrasting growth strategies.

A hybrid genetic algorithm with local optimiser improves calibration of a vegetation change cellular automata model

ABSTRACT Cellular automata (CA) models are commonly used to model vegetation dynamics, with the genetic algorithm (GA) being one method of calibration. This article investigates different GA settings, as well as the combination of a GA with a local optimiser to improve the calibration effort. The case study is a pattern-calibrated CA to model vegetation regrowth in central Victoria, Australia. We tested 16 GA models, varying population size, mutation rate, and level of allowable mutation. We also investigated the effect of applying a local optimiser, the Nelder‒Mead Downhill Simplex (NMDS) at GA convergence. We found that using a decreasing mutation rate can reduce computational cost while avoiding premature GA convergence, while increasing population size does not make the GA more efficient. The hybrid GA-NMDS can also reduce computational cost compared to a GA alone, while also improving the calibration metric. We conclude that careful consideration of GA settings, including population size and mutation rate, and in particular the addition of a local optimiser, can positively impact the efficiency and success of the GA algorithm, which can in turn lead to improved simulations using a well-calibrated CA model.

Using growth-form attributes to identify pre-settlement woodland trees in central NSW, Australia

Old-growth woodland trees perform many important ecological functions, by providing critical fauna habitat and in sustaining biological diversity. Australian woodlands are dominated by box Eucalyptus species, which are difficult to age accurately using dendrochronology and other well-practiced methods. We aimed to develop a simple field method for identifying pre-settlement (old growth) Eucalyptus trees in south-eastern Australia, using measurements of tree growth-form attributes. We used TwoStep cluster analysis to classify and independently assess trees, and logistic regression analyses to develop models to identify pre-settlement trees in the field based on recorded attributes. Post-settlement (regrowth) trees tended to have a very uniform appearance, whereas the growth-form of older pre-settlement trees greatly varied, in terms of the number of stem and pipe hollows, and number of primary and secondary branches. This clear discrimination between cohorts of trees is discussed in terms of historic changes to disturbance regimes, and resultant impacts on remnant woodland structures. Our results provide a robust method for reliably identifying pre-settlement Eucalyptus trees in the field using tree growth-form measurements, and have broader implications for identifying age cohorts of forest and woodland trees elsewhere.

Uncertainty in a cellular automata model for vegetation change

When farmland is abandoned pasture is rapidly taken over by woody vegetation. As tree dispersal depends on the presence of a seed source nearby and other local conditions, and can be measured in discrete annual time steps, a Cellular Automata model (CA) is a natural fit for modelling this phenomenon. The model presented here is a stochastic CA, with a relaxed definition of neighbourhood. The aim is to explore sources of uncertainty in the model, and techniques for handling and visualising uncertainty. The results show that it is possible to realistically model vegetation change using CA, acknowledging and incorporating uncertainty.