Kevin R. Thiele

Identifying ecological barriers to restoration in temperate grassy woodlands: soil changes associated with different degradation states

Temperate grassy woodlands were once the dominant vegetation across many agricultural regions of south-eastern Australia, but most of these are now highly degraded and fragmented. Adequate conservation of these woodlands is dependent on successful ecological restoration; however, ecological barriers often limit ecosystem recovery once degrading processes are removed. To help identify these barriers, we used a state and transition framework to compare topsoils of little-disturbed (reference) and variously degraded remnants of grassy Eucalyptus albens Benth. and E. melliodora Cunn. ex Schauer woodlands. Topsoils of degraded remnants showed a repeated pattern, with the most compacted, most acidic and most depleted topsoils occurring in remnants dominated by Aristida ramosa R.Br. or Austrodanthonia H.P.Linder and Austrostipa scabra (Lindl.) S.W.L.Jacobs & J.Everett; the least compacted and most nutrient rich topsoils in remnants dominated by annual exotics; and generally intermediate topsoils in remnants dominated by Bothriochloa macra (Steud.) S.T.Blake or Austrostipa bigeniculata (Hughes) S.W.L.Jacobs & J.Everett. Surprisingly, topsoils beneath trees in reference sites (supporting Poa sieberiana Spreng.) were similar to topsoils supporting annual exotics for most soil properties. Chemical properties of topsoils from open areas of reference sites [supporting Themeda australis (R.Br.) Stapf] were usually intermediate and similar to Bothriochloa macra and Austrostipa bigeniculata topsoils. The most striking exception to these trends was for soil nitrate, which was extremely low in all reference topsoils and showed a high correlation with annual exotic abundance. We discuss the potential for positive feedbacks between soil nitrogen cycling and understorey composition and the need for intervention to assist possible nitrate-dependent transitions between annual and perennial understorey states. Dominant grasses, trees and annual weed abundance may be useful indicators of soil conditions and could inform selection of target sites, species and techniques for restoration projects.

Determining reference conditions for management and restoration of temperate grassy woodlands: relationships among trees, topsoils and understorey flora in little-grazed remnants

Temperate grassy woodlands were once widespread and dominant in many agricultural regions of south-eastern Australia. Most are now highly degraded and fragmented and exist within a context of broadscale landscape degradation. Greater understanding of natural processes in these woodlands is needed to benchmark management and restoration efforts that are now critical for their ongoing survival. We studied physical and chemical properties of topsoils from rare, little-grazed remnants of grassy Eucalyptus albens Benth. and E. melliodora Cunn. ex Schauer woodlands in central New South Wales and examined natural patterns in topsoil properties and understorey flora in relation to trees and canopy gaps. Topsoils were generally low in available macronutrients (nitrogen, phosphorus and sulfur), but were favourable for plant growth in most other measured characteristics. Topsoils beneath trees were notably more fertile than in open areas, particularly in total carbon, total nitrogen, available phosphorus, available potassium and salinity. Higher nutrient concentrations, particularly of available phosphorus, may have contributed to patterns in understorey dominants, with Themeda australis (R.Br.) Stapf predominating in open areas and Poa sieberiana Spreng. beneath trees. Trees were also associated with a higher native-plant richness, possibly resulting from their influence on the competitive dynamics of the dominant grasses. We discuss the implications of these interactions for the use of burning, grazing and slashing in woodland management and re-establishment of native grasses and trees in restoration efforts.

Effects of fire frequency and mowing on a temperate, derived grassland soil in south-eastern Australia

Frequent disturbances such as fire are widely considered important drivers of plant composition and diversity in productive grassy ecosystems. Effects of fire frequency on grassland soils, however, are less well understood. We established replicated disturbance regimes in a high-quality, representative Themeda australis-Poa sieberiana-derived grassland in south-eastern Australia that had historically been burnt every 4-8 years. Effects on soil chemical, physical and biological properties were measured after 10 years of application of 2-, 4-, and 8-yearly burning, 2-yearly mowing and an undisturbed treatment. Contrary to other grassy ecosystems, there were no detectable effects of disturbance regime on total soil nitrogen and carbon, or a range of other soil chemical properties in the top 10 cm. However, a cumulative effect of burning on the grassland soil was evident from a suite of changes to soil surface properties, available nutrients and biological activity. In particular, on biennially burnt plots, reduced litter and plant protective cover were associated with increased soil surface compaction, decreased infiltration and decreased soil biological activity, which in turn were related to poor sward recovery after fire and drought. These relationships indicate potential for positive feedbacks whereby repeated removal of soil protective cover and changes to soil surface chemistry through very frequent burning ultimately lead to further reduction in soil protective cover through reduced productivity. However, this is only likely in extreme cases: data from unburnt plots indicated that soils that had historically been burnt every 4-8 years had not passed a threshold beyond which such soil changes were irreversible or damaging. Contrary to other predictions, cessation of burning for 13 years did not lead to detectable soil nutrient release through senescence of dominant grasses. Biennial mowing with slash retention was an effective alternative disturbance for maintaining sward vigour while avoiding soil surface damage.

Management legacies shape decadal‐scale responses of plant diversity to experimental disturbance regimes in fragmented grassy woodlands

Summary Understanding multiple ecological determinants of plant diversity and composition underpins good vegetation management. In mesic ecosystems, ecological theory and empirical data predict that moderate to high disturbance promotes native plant diversity, but relationships between disturbance and other drivers of diversity are poorly understood. We examined local determinants of native plant diversity and composition through 12-year fire, mowing and grazing experiments in two mesic grassy woodland remnants in fragmented agricultural landscapes of south-eastern Australia. Remnants were representative of diverse woodlands, but had contrasting management histories. We hypothesized that (1) disturbance is a dominant driver of plant diversity and composition and (2) moderate to high disturbance promotes diversity independent of other drivers or disturbance agent. Contrary to our first hypothesis, rainfall explained an overwhelming 31–60% of variation in native plant richness and native forb cover (hereafter diversity), while aspects of disturbance regime accounted for a significant but moderate 3–8%. The magnitude of disturbance effects was often rainfall dependent, and similar to that of other local determinants such as spatial heterogeneity. Disturbance also influenced native forb composition at one site. The direction of disturbance effects on diversity did not depend on disturbance agent, but differed markedly between sites in accordance with their management history. At the cleared site with a history of frequent burning, diversity declined significantly with time since burning or mowing. By contrast, at the long-unburnt, wooded site, diversity declined with frequent fire and with lagomorph and macropod grazing. These contrasting responses indicate that moderate to high disturbance is not consistently beneficial for diversity in mesic grassy ecosystems, contradicting our second hypothesis. Instead, disturbance responses are dependent on interactions with other drivers, potentially including assemblage filtering associated with historical fire regime and increased understorey productivity associated with tree clearing. Synthesis and applications: The magnitude and direction of disturbance effects on diversity depend on interactions with other drivers, hence a single prescription for disturbance regime across different remnants of fragmented grassy ecosystems is not appropriate. Decadal-scale responses of diversity to disturbance may be shaped by historical disturbances, suggesting instead that management be guided by historical regime.

Untangling a species complex of arid zone grasses (Triodia) reveals patterns congruent with co-occurring animals.

The vast Australian arid zone formed over the last 15million years, and gradual aridification as well as more extreme Pliocene and Pleistocene climate shifts have impacted the evolution of its biota. Understanding the evolutionary history of groups of organisms or regional biotas such as the Australian arid biota requires clear delimitation of the units of biodiversity (taxa). Here we integrate evidence from nuclear (ETS and ITS) and chloroplast (rps16-trnK spacer) regions and morphology to clarify taxonomic boundaries in a species complex of Australian hummock grasses (Triodia) to better understand the evolution of Australian arid zone plants and to evaluate congruence in distribution patterns with co-occurring organisms. We find evidence for multiple new taxa in the T. basedowii species complex, but also incongruence between data sets and indications of hybridization that complicate delimitation. We find that the T. basedowii complex has high lineage diversity and endemism in the biologically important Pilbara region of Western Australia, consistent with the region acting as a refugium. Taxa show strong geographic structure in the Pilbara, congruent with recent work on co-occurring animals and suggesting common evolutionary drivers across the biota. Our findings confirm recognition of the Pilbara as an important centre of biodiversity in the Australian arid zone, and provide a basis for future taxonomic revision of the T. basedowii complex and more detailed study of its evolutionary history and that of arid Australia.

Morphological and molecular evidence supports the recognition of a new subspecies of the critically endangered Pityrodia scabra (Lamiaceae)

Abstract. Taxonomic delineation of closely related taxa can be difficult, particularly in regions such as southern Western Australia where a highly diverse flora exhibits complex patterns of subtle morphological variation and genetic structuring and where some taxa have highly disjunct populations. A combined approach utilising highly variable, non-coding chloroplast gene regions and morphological data is used here to help delimit cryptic taxa in the rare Western Australian species Pityrodia scabra A.S.George. The species comprises disjunct populations over 400 km of the Western Australian wheatbelt from near Wyalkatchem, Southern Cross and Lake Lefroy. Morphological features such as leaf phyllotaxy, calyx size and indumentum vary among the populations and provide some evidence for cryptic taxa. Phylogenetic analyses based on cpDNA psbA–trnH and psbD–trnT and nuclear external transcribed spacer (ETS) sequences revealed genetic distinctiveness between the Wyalkatchem (type) population and the Southern Cross and Lake Lefroy populations. This evidence, when used in conjunction with the morphological differences, provides support for the recognition of the new subspecies described herein as Pityrodia scabra subsp. dendrotricha K.A.Sheph. subsp. nov. This new subspecies is of conservation concern because it is currently known only from a few, isolated populations; the typical subspecies remains Critically Endangered because it comprises one extant population. A description of both subspecies, a key and images are provided.

A rare, new species of Atriplex (Chenopodiaceae) comprising two genetically distinct but morphologically cryptic populations in arid Western Australia: implications for taxonomy and conservation

Abstract. A rare, new tetraploid Atriplex, restricted to two populations ∼30 km apart in arid Western Australia, is supported as a distinct species by morphological and molecular evidence. Genetic analyses using amplified fragment length polymorphisms (AFLPs) showed significant genetic divergence between the two populations. In contrast, an ordination based on elliptic Fourier descriptors for leaf and bracteole shape did not identify any consistent morphological differentiation. Although the level of genetic differentiation is similar to that previously reported between subspecies in other Atriplex, the populations of the new taxon are described herein as A. yeelirrie K.A.Sheph. & K.R.Thiele, without taxonomic recognition at the intraspecific level. We outline our reasoning for this decision and discuss the implications for appropriate conservation management of the species, structured into two genetically distinct populations.

Polianthion, a new genus of Rhamnaceae (Pomaderreae) from Western Australia and Queensland

Recent phylogenetic studies have revealed that four species of Australian Rhamnaceae, tribe Pomaderreae Reissek ex Endl., should be assigned to a new genus. This paper describes Polianthion K.R.Thiele, including one new species, P. collinum Rye, and makes the relevant combinations for P. bilocularis (A.S.George) Kellermann, P. wichurae (Nees ex Reissek) K.R.Thiele and P. minutiflorum (E.M.Ross) K.R.Thiele. The genus is defined by having two carpels, a characteristic dense stellate indumentum on both vegetative and floral parts of the plant, free stipules, long-pedicellate flowers and fruitlets dehiscent for their full length. Three species are found in the south-west of Western Australia and one in eastern Queensland.

Genotyping-by-Sequencing in a Species Complex of Australian Hummock Grasses (Triodia): Methodological Insights and Phylogenetic Resolution

Next-generation sequencing is becoming increasingly accessible to researchers asking biosystematic questions, but current best practice in both choosing a specific approach and effectively analysing the resulting data set is still being explored. We present a case study for the use of genotyping-by-sequencing (GBS) to resolve relationships in a species complex of Australian arid and semi-arid grasses (Triodia R.Br.), highlighting our solutions to methodological challenges in the use of GBS data. We merged overlapping paired-end reads then optimised locus assembly in the program PyRAD to generate GBS data sets for phylogenetic and distance-based analyses. In addition to traditional concatenation analyses in RAxML, we also demonstrate the novel use of summary species tree analyses (taking gene trees as input) with GBS loci. We found that while species tree analyses were relatively robust to variation in PyRAD assembly parameters, our RAxML analyses resulted in well-supported but conflicting topologies under different assembly settings. Despite this conflict, multiple clades in the complex were consistently supported as distinct across analyses. Our GBS data assembly and analyses improve the resolution of taxa and phylogenetic relationships in the Triodia basedowii complex compared to our previous study based on Sanger sequencing of nuclear (ITS/ETS) and chloroplast (rps16-trnK spacer) markers. The genomic results also partly support previous evidence for hybridization between species in the complex. Our methodological insights for analysing GBS data will assist researchers using similar data to resolve phylogenetic relationships within species complexes.

(286) Proposal to replace division iii of the international code of nomenclature for algae, fungi, and plants

Special Committee on By-laws for the Nomenclature Section Members of the Special Committee: Sandra Knapp (Secretary),1 Nicholas J. Turland (Convener),2 Mary E. Barkworth,3 Fred R. Barrie,4 Renée H. Fortunato,5 Kanchi Gandhi,6 Roy E. Gereau,7 Werner Greuter,8 Patrick S. Herendeen,9 Leslie R. Landrum,10 David J. Mabberley,11 Karol Marhold,12 Tom W. May,13 Gerry Moore,14 Lourdes Rico Arce,15 Gideon F. Smith,16 Kevin Thiele17 & Li Zhang18