John M. Koch

Fuel characteristics, vegetation structure and fire behaviour of 11–15 year-old rehabilitated bauxite mines in Western Australia

Summary Bauxite mines rehabilitated in the early 1980s in Western Australia have built up substantial fuel loads that may be reduced through prescription burning. Fuel characteristics, vegetation structure and fire behaviour of 11–15 year-old rehabilitated bauxite mines were examined. Fuel loads were high in all pre-burn rehabilitation areas (23.4–35.1 t ha−1) although large ranges in fuel load estimates of sample plots (6.3–49.3 t ha−1) indicated the heterogenous nature of the fuel distribution that led to heterogeneity in fire behaviour. The vegetation structure of the rehabilitated areas differed from that of the native jarrah forest due to a lower proportion of live to dead plant material and the presence of a prominent mid-storey layer composed of dead Acacia plants. This mid-storey layer contributed 45% of the total fuel load and led to increased flame heights and subsequent higher levels of crown scorch regardless of the soil and litter moisture conditions. Seven prescription burns were carried out...

Toward an optimal sampling protocol for Hemiptera on understorey plants

There are no standardised sampling protocols for inventorying Hemiptera from understorey or canopy plants. This paper proposes an optimal protocol for the understorey, after evaluating the efficiency of seven methods to maximise the richness of Hemiptera collected from plants with minimal field and laboratory time. The methods evaluated were beating, chemical knockdown, sweeping, branch clipping, hand collecting, vacuum sampling and sticky trapping. These techniques were tested at two spatial scales: 1 ha sites and individual plants. In addition, because efficiency may differ with vegetation structure, sampling of sites was conducted in three disparate understorey habitats, and sampling of individual plants was conducted across 33 plant species. No single method sampled the majority of hemipteran species in the understorey. Chemical knockdown, vacuum sampling and beating yielded speciose samples (61, 61 and 30 species, respectively, representing 53, 53 and 26% of total species collected). The four remaining methods provided species-poor samples (<18 species or <16% of total species collected). These methods also had biases towards particular taxa (e.g., branch clipping and hand collecting targeted sessile Hemiptera, and sticky trapping were dominated by five species of Psyllidae). The most time-efficient methods were beating, sweeping and hand collecting (200 minutes of field and laboratory time yielded >7 species for each technique). By comparison, vacuum sampling, sticky trapping, branch clipping and chemical knockdown yielded <5 species for the same period. Chemical knockdown had further disadvantages; high financial cost and potential spray drift. The most effective methods for a standardised sampling protocol to inventory Hemiptera from the understorey are beating and vacuum sampling. If used in combination, these methods optimise the catch of understorey hemipteran species, as their samples have high complementarity.

Orchid species succession in rehabilitated bauxite mines in Western Australia

Twenty-three orchid species were recorded in Alcoas permanent vegetation-monitoring plots in unmined and rehabilitated jarrah forest. Of these, 22 were identified in the unmined jarrah forest and 20 were recorded in rehabilitated areas of between 1 and 31 years old. Three species (Cyrtostylis ovata, Lyperanthus serratus and Prasophyllum elatum) were only recorded in the unmined forest and one species was only recorded in rehabilitated areas (Diuris carinata). The overall density of native orchids in the forest was 13 755 plants ha–1, 10 times greater than the density in rehabilitated areas (1381 plants ha–1). The most abundant species in the forest were Cyrtostylis robusta, Caladenia flava, Pterostylis nana and Thelymitra crinita, all with densities greater than 1000 plants ha–1. The most abundant species in the rehabilitated areas were Microtis media, Disa bracteata (an introduced species), Caladenia flava, Pterostylis nana, Diuris longifolia and Pterostylis vittata, all with densities greater than 60 plants ha–1. In rehabilitation older than 10 years, the density of orchids increased to 2685 plants ha–1. Burning in rehabilitated areas resulted in large increases in orchid densities. It is believed that orchid colonisation of rehabilitated bauxite mines is dependent on symbiotic mycorrhiza, which are in turn dependent on development of an organic litter component in the soil.

Contrasting physiological responses of two co-occurring eucalypts to seasonal drought at restored bauxite mine sites

This study describes the physiological response of two co-occurring tree species (Eucalyptus marginata and Corymbia calophylla) to seasonal drought at low- and high-quality restored bauxite mine sites in south-western Australia. Seasonal changes in photosynthesis (A), stomatal conductance (g(s)), leaf water potential (ψ), leaf osmotic potential (ψ), leaf relative water content (RWC) and pressure-volume analysis were captured over an 18-month field study to (i) determine the nature and severity of physiological stress in relation to site quality and (ii) identify any physiological differences between the two species. Root system restriction at the low-quality site reduced maximum rates of gas exchange (g(s) and A) and increased water stress (midday ψ and daily RWC) in both species during drought. Both species showed high stomatal sensitivity during drought; however, E. marginata demonstrated a higher dehydration tolerance where ψ and RWC fell to -3.2 MPa and 73% compared with -2.4 MPa and 80% for C. calophylla. Corymbia calophylla showed lower g(s) and higher ψ and RWC during drought, indicating higher drought tolerance. Pressure-volume curves showed that cell-wall elasticity of E. marginata leaves increased in response to drought, while C. calophylla leaves showed lower osmotic potential at zero turgor in summer than in winter, indicating osmotic adjustment. Both species are clearly able to tolerate seasonal drought at hostile sites; however, by C. calophylla closing stomata earlier in the drought cycle, maintaining a higher water status during drought and having the additional mechanism of osmotic adjustment, it may have a greater capacity to survive extended periods of drought.

Tree species response to prescribed burns in rehabilitated bauxite mines in Western Australia.

Summary The response of fourteen tree species to autumn and spring prescribed burns was assessed in 11 to 13-year-old rehabilitated bauxite mines. Of the 578 trees recorded, 2.8% were killed, a further 14.7% resprouted basally (no resprouts above 2 m) while the remainder resprouted aerially (73.2%) or were not scorched (8.5%). This is indicative of the high tolerance to fire of all species recorded in this study. The most fire tolerant species were Eucalyptus calophylla, E. patens, E. botryiodes and E. maculata. The most susceptible species were E. accedens and E. wandoo. Increased fire tolerance was related to increased bark thickness and larger stem diameter. Rough-barked species were more resistant to fire than smooth-barked species. Tree mortality and the incidence of basal resprouting was higher following autumn burning than spring burning. Based on these findings, it would appear that spring burns are more favourable than autumn burns to the survival and growth of tree species in rehabilitated areas.

Optimising smoke treatments for jarrah (Eucalyptus marginata) forest rehabilitation

Alcoa is undertaking rehabilitation in the jarrah (Eucalyptus marginata D.Don ex Sm.) forest of Western Australia, following bauxite mining. One of the methods used in the rehabilitation program is broadcasting seeds; however, about two-thirds of species require seed-dormancy-breaking treatments. Smoke overcomes dormancy and enhances the germination of many jarrah forest species. Smoke-application methods were investigated to find the best seed treatment for 64 jarrah forest species. The optimum duration of seed imbibition in aqueous smoke and dilution of the aqueous smoke product were also investigated. The method of smoke application was important. Smoke water enhanced the germination of 12% of species, whereas aerosol smoke enhanced the germination of 6% of species. Both Grevillea pilulifera (Lindl.) Druce and Velleia trinervis Labill. had germination enhanced by both smoke-application methods. Aerosol smoke inhibited the germination of Clematis pubescens Endl. and Hypocalymma angustifolium (Endl.) Schauer. A total of 78% of species did not exhibit significantly enhanced germination when smoke treated, including the two species inhibited by smoke treatment. Germination was equivalent following 1- and 12-h imbibition in the aqueous smoke extract. Dilutions of the aqueous extract Regen 2000 Smokemaster from 1 to 3% were optimal for the germination of Marianthus bicolor (Putt.) F.Muell and Stylidium amoenum R.Br., even after subsequent washing with water, demonstrating the irreversible nature of smoke treatments. For species that did not exhibit smoke-enhanced germination, other dormancy-breaking treatments may be required before a response to smoke is elicited. These results have application to a wide variety of natural managed lands, disturbed and designed landscapes.

Thirteen-year growth of jarrah (Eucalyptus marginata) on rehabilitated bauxite mines in south-western Australia

Summary Alcoas objective is to restore its bauxite mines in south-western Australia to a productive self-sustaining jarrah forest. This paper describes the growth and form of 13-y-old jarrah (Eucalyptus marginata) trees established from seed and planted seedlings, and subject to various fertiliser, understorey seed and spacing treatments. Seeded jarrah had a mean establishment density of 2662 stems ha−1 and a density of 2300 stems ha−1 after 13 y, a survival rate of 86%. Sixty-two per cent of the seeded trees developed into saplings (> 1.5 m tall). The saplings had a mean height of 9.0 m and dbhob of 14.4 cm after 13 y. The mean density of potential sawlogs (trees with a single stem to at least 2 m) was 1297 stems ha−1 after 13 y. The presence of tall native legumes (acacias) decreased the percentage of trees that became saplings from 72% to 53%. When N fertiliser was not provided the legumes had a suppressive effect on the basal area and bole volume of potential sawlogs, reducing them to 60% and 57%, respectively, of the values without legumes. Planted jarrah trees had a mean survival rate over all treatments of 84% after 13 y. Closer tree spacing (particularly 1 m × 1 m) resulted in significantly lower survival (77%) than the wider spacings. Inclusion of tall native legumes with closer tree spacing reduced survival even more (69% at 1 m × 1 m). The mean sapling height across all planted treatments was 9.1 m. The mean dbhob was 15.2 cm with 67% becoming saplings. Closer tree spacing had the strongest effect in significantly reducing all of these parameters. Tall native legumes reduced the dbhob of the jarrah trees and reduced the overall mean height of all jarrah by limiting the proportion of jarrah that became saplings. Absence of added N fertiliser also significantly reduced these measures. Basal areas were similar in rehabilitated and unmined forest after 13 y. Mean annual growth increments (1.52 m2 ha−1 seeded, 2.72 m2 ha−1 planted) were similar to those reported for similar aged regrowth forest (2.62 m2 ha−1) and higher than older thinned (0.45 m2 ha−1) or unthinned (0.19 m2 ha−1) unmined forest. Basal area increments were higher from 8–13 y than 0–8 y, indicating that growth rates were not slowing down over this period. The optimum stocking rate for jarrah in rehabilitated bauxite mines will be a balance between growth rate, tree form, other environmental factors and cost considerations. The current rehabilitation prescription aims to establish 1300 stems ha−1 of ‘total eucalypts’ by broadcast seeding (jarrah and marri — Corymbia calophylla). This study indicates that an initial stocking of 1300 stems ha−1 is optimum and meets Alcoas mine rehabilitation completion criterion of providing at least 300 potential sawlogs ha−1 at 15 y of age.

Multi-scale patterns in the host specificity of plant-dwelling arthropods: the influence of host plant and temporal variation on species richness and assemblage composition of true bugs (Hemiptera)

The influence of temporal variation in the host specificity of invertebrates to estimates of biodiversity is rarely considered. While patterns at large spatial scales have stimulated much attention, such comparisons are constrained for southern-hemisphere biomes because the patterning of invertebrates on plants is largely unknown. Here, we analyse variation of plant-dwelling Hemiptera from 15 understorey plant species over 18 months in the south-west Australian biodiversity hotspot. Analyses showed significant interactions in species composition between sampling period and plant species. Fauna that were “effectively specialized” (host-specificity index) to plants changed with season, although this was also related to the number of singletons and overall species richness. Sampling from a single season also overestimated the degree of host specificity by 52% and underestimated the perception of species richness when an outbreak of a particular herbivore occurred. High host-specificity values (12.7 hemipteran species per plant) support the case for high estimates of global arthropod richness.

The effect of burning, soil scarification and seeding on the understorey composition of 12 year-old rehabilitated bauxite mines in Western Australia

Summary The effect of burning, soil scarification and seeding on 11 to 13-year-old rehabilitated bauxite mines was examined to assist the development of a prescription for increasing establishment of native tree and understorey species. Scarified and non-scarified treatments were investigated following burning in autumn and spring, and in no burn areas. All treatments were seeded with a mix containing jarrah (Eucalyptus marginata), the native overstorey dominant, and 37 understorey species. Plant response was measured as the density of all plants, weeds, eastern Australian eucalypts, acacias and jarrah as well as native species numbers and the Shannon-Weiner diversity index. Nearly all of these measures were significantly higher in the burnt compared to the unburnt treatments. Species numbers, total plant density. Acacia density and jarrah density were higher following autumn burning than spring burning. However, the density of eastern Australian eucalypt seedlings was also significantly increased by autu...

The effect of in situ seed burial on dormancy break in three woody-fruited species (Ericaceae and Proteaceae) endemic to Western Australia

The woody-fruited species Leucopogon propinquus R.Br., Styphelia tenuiflora Lindl. (Ericaceae) and Persoonia longifolia R.Br. (Proteaceae) need to be returned to restored mines in Western Australia. All species have physiological seed dormancy, however germination has been observed following the application of smoke to native habitats. We recorded seed viability, permeability to water, endocarp strength, morphology and germination ± gibberellic acid (GA3) every 3 months for 24 months of in-situ burial in the jarrah forest to determine the time of dormancy release and corresponding seed changes. The term ‘seed’ refers to the woody endocarp, plus the true seed. Persoonia longifolia reached 37% germination after burial in soil for 21 months, followed by chipping the endocarp and GA3 application. A minimum of 15 months soil burial was necessary for unchipped seeds to germinate; 22% germination was achieved after 18 months burial in soil followed by GA3 application. Viability of fresh seeds of all three species was 96–100% and remained unchanged for P. longifolia, but declined to 5 and 0% following 24 months of soil burial for L. propinquus and S. tenuiflora, respectively. Germination of the two Ericaceae species was negligible, despite the presence of viable seeds (30–63%, depending on the species) after 12 months of soil burial and substantial deterioration of the endocarp. To germinate large quantities of P. longifolia, for use in land restoration, drupes should be buried in-situ in forest soil for 18 months immediately following seed fall (early spring) and GA3 treated, following exhumation.