Trunk invertebrate faunas of Western Australian forests and woodlands: Influence of tree species and season

Abstract Trunk–associated invertebrates were sampled on two rough‐barked tree species (jarrah, Eucalyptus marginata and marri, E. calophylla) at Karragullen, in the hills near Perth, Western Australia, and on these two species plus two smooth‐barked species (wandoo, E. wandoo, and powderbark wandoo, E. accedens) at Dryandra, a drier site situated 150 km to the south‐east. Invertebrates were sampled by intercept traps, which collect animals that attempt to land on the trunks, and photo‐eclector bark traps, which collect invertebrates that move, or live, on the trunk. The range and abundance of invertebrates sampled was generally greater in the intercept than the bark traps. Invertebrate abundance and activity (but not biomass) on bark was strongly seasonal, with greater numbers being found during the moister periods. The two smooth‐barked species supported, and were visited by, more invertebrates than the two rough‐barked species. There was some evidence that jarrah supported more invertebrates than marri at both Karragullen and Dryandra, although the results were equivocal. Within the two smooth‐barked species, wandoo tended to support more invertebrates than powderbark wandoo. These trends are discussed in terms of the characteristics of the bark of these trees and the environments in which they occur.     

Invertebrate communities on Western Australian eucalypts: A comparison of branch clipping and chemical knockdown procedures

Chemical knockdown and branch clipping procedures were used in wandoo (Eucalyptus wandoo) woodland and jarrah (E. marginata)/marri (E. calophylla) open-forest to sample arboreal invertebrate faunas on three species of Western Australian eucalypts. Jarrah was sampled in both habitats and had significantly lower invertebrate populations and a less diverse fauna than either wandoo or marri. The two procedures provided similar results with respect to the relative abundance of invertebrates on each plant species but the knockdowns sampled a more diverse fauna, including species sheltering in or on bark. Chemical knockdowns underestimated the abundance of sessile invertebrates, such as psyllids. Branch clipping sampled insufficient numbers of large, mobile, or cryptic invertebrates to estimate abundances, but provided a more accurate estimate of the abundance of sessile, leaf-dwelling organisms. Neither procedure provides a complete sample of arboreal invertebrates, but they are complementary. When used in conjunction with each other a more complete estimate of arboreal invertebrate abundance and diversity is obtained. Both procedures can be used concurrently with only a small increase in field time.     

New evidence of unexpectedly high animal density and diet diversity will benefit the conservation of the Critically Endangered western ringtail possum

A comprehensive and contemporary understanding of habitat and resource requirements has been critical to the conservation of multiple taxa and ecosystems globally. Until recently, much of the ecological knowledge that contributes to conservation priorities and strategies for the Critically Endangered western ringtail possum (Pseudocheirus occidentalis) was largely derived from decades‐old observations in peppermint (Agonis flexuosa) and marri‐jarrah (Corymbia calophylla and Eucalyptus marginanta) woodlands in the northern parts of the species range. These observations do not account for more recent evidence of their flexible use of habitat resources in other regions of its range. This may represent a significant conservation opportunity for the species through the identification of additional habitats that warrant protection. In a region where knowledge of their ecology is scarce, we used scat analysis and quantitative spotlighting to determine the diet and density of western ringtail possums in three vegetation types: peppermint, sheoak (Allocasuarina fraseriana) and marri‐eucalypt (C. calophylla, E. marginanta and Eucalyptus staerii) woodlands. Given the species’ reported dependence on peppermint woodlands and dominant canopy species for food sources, we hypothesised that western ringtail possums would be most abundant in this habitat type and that their diet would comprise the foliage of few (≤2 species) canopy species. We found western ringtail possums consumed a higher diversity of plant species than expected (8–14), exhibited dietary preference for non‐dominant canopy species and were present in all sampled vegetation types at substantially higher densities than previously recorded for the region (as high as 17 possums ha^?1). Our results confirm (i) the western ringtail possum is flexible in its use of habitat resources and (ii) the significant conservation value of sheoak and marri‐eucalypt woodlands in the southernmost portion of its distribution.     

The effects of sheep-grazing on the subterranean termite fauna (Isoptera) of the Western Australian wheatbelt

Abstract The majority of existing remnants of wandoo Eucalyptus capillosa woodland in the Western Australian wheatbelt have been grazed by sheep for several decades and are often visibly degraded. A pilot survey was conducted into the effects of sheep on vegetation and soil variables, and the abundance, diversity and species frequency of occurrence of subterranean termite communities. Ten 1/4 ha study plots were used for paired grazed/ungrazed comparisons. Ungrazed plots had more litter mass (dry weight), leaf and woody litter, canopy cover (%) and soil moisture (moisture content <1.2% across study plots); grazed plots had a higher percentage of bare ground. Termites were as abundant, and as diverse, in grazed as in ungrazed plots, and were equally often sampled in the soil and surface wood. Termite species eating sound wood, decayed wood/debris and grass were sampled equally often, and were of equal diversity in sheep-grazed as in ungrazed plots. The mounds of Drepanotermes tamminensis were more abundant in grazed plots. These findings indicate that prolonged sheep grazing in remnants of wandoo woodland of the Western Australian wheatbelt has had no detrimental or beneficial effect on its subterranean termites.     

Variation in foliar nutrients in Eucalyptus trees in eastern and Western Australia

Abstract Levels of nitrogen, phosphorus and potassium were measured for the foliage of two co-dominant eucalypts at each of two sites, one in eastern Australia and the other in Western Australia. In eastern Australia, foliage was sampled in the canopy and subcanopy for narrow-leaved ironbark Eucalyptus crebra and grey box E. mollucana and in Western Australia, for jarrah E. marginata and marri E. calophylla. The Western Australian trees were also sampled for ‘young’ and ‘old’ leaves. Both eucalypts in eastern Australia had greater nitrogen and phosphorus levels, but lower potassium, than E. marginata or E. calophylla. Eucalyptus calophylla foliage had greater levels of all three nutrients than E. marginata foliage as did E. crebra relative to E. mollucana. At both sites, foliar nutrient levels were greater in the canopy than subcanopy foliage, and, at least in Western Australia, the younger leaves had greater nutrient levels than the older leaves. The observed differences in foliar nutrient levels are consistent with observed trends in the abundance and diversity of foliage arthropods and the use of the trees as foraging substrates by birds.     

Diversity patterns of eucalypt canopy arthropods in eastern and western Australia

1. As part of a larger study on canopy arthropods and birds, a 1‐year chemical knockdown study was carried out in one Western Australian forest, where jarrah Eucalyptus marginata and marri E. (Corymbia) calophylla were sampled, and one eastern Australian (New South Wales) forest, where narrow‐leaved ironbark E. crebra and grey box E. moluccana were sampled. 2. Ten trees of each species were sampled during each of the four seasons and the arthropods were sorted to morphospecies level. This paper documents the foliage‐associated component of arboreal arthropod communities and compares arthropod species richness within orders and families, between tree species, and between the two forest types. 3. Hymenoptera, Coleoptera, Diptera, and Araneae were the richest in species. Nine hundred and seventy‐six species in 173 families were found in the eastern Australian forest, while 687 species in 176 families were found in the western Australian forest. Only 53% of families were common to both forests, but almost half the families recorded were represented by fewer than five species. Species overlap between tree species in each region was 40–53%. 4. Analysis using nonparametric bootstrapping procedures showed that sampling of foliage was comprehensive and that only 4–9% more species would be expected with more intensive sampling of the canopy. Absolute richness, as well as differences between tree species and regions, therefore appear to be real and not the result of sampling errors. As a consequence, arthropod species richness in Australian eucalypt forests is shown to be substantially greater than previous estimates.     

A comparison of two methods for sampling assemblages of subterranean,wood-eating termites (Isoptera)

Abstract Within a 50 × 50 m area of wandoo Eucalyptus capillosa woodland in the Western Australian wheatbelt, the diversity and frequency of occurrence of wood-eating termite species was assessed at two food types. Over a 12 month period, monthly termite activity was determined: (i) at sound/undecayed artificial baits (seasoned wooden stakes of Jarrah, Karri, Pine, Batu, Oregon; Jarrah sawdust; paper rolls); and (li) at naturally occurring timber, fallen logs and branches of wandoo, in varying stages of decay. Termite diversity was 11 species at baits, 18 species at wandoo out of an overall site richness of 21 species. Karri attracted the most species (9); sawdust attracted none. At wandoo, Nasutitermes exitiosus, Coptotermes acinaciformis and Occasitermes occasus accounted for 59% of samples where termites were recorded. At baits, Heterotermes occiduus accounted for a mean of 80% of samples across bait types, but was rarely sampled at wandoo (5% of samples). Only H. occiduus, C. acinaciformis and Amitermes neogermanus ate bait. Pine, Oregon and paper rolls were most effective in attracting foraging termites in terms of highest per cent of replicates showing bait consumption and highest consumption rates. Jarrah and Batu were least attractive to foraging termites. Samples from wandoo underestimated the relative frequency of occurrence of H. occiduus within the study site. Coptotermes acinaciformis, which attack large food items, and certain species of Amitermes, which forage on subterranean food, may have been underestimated by both sampling methods. These findings indicate that a proper understanding of the structure of wood-eating termite assemblages within a given area requires a composite sampling strategy which addresses termites that eat sound or decayed wood, as well as surface and subsurface foragers.     

Phosphorus nutrition of jarrah (Eucalyptus marginata) seedlings

Summary Effects of calcium phosphate supply on plant dry matter and phosphorus concentrations of parts of jarrah (Eucalyptus marginata) seedlings grown in a lateritic topsoil from the jarrah forest were examined in two glasshouse trials. Phosphorus deficiency depressed root and shoot dry weights and severely deficient leaves were smal and purple with prominent red major veins. Phosphorus deficiency severely reduced stem phosphorus levels (0.5% to 0.02%, experiment 1). Phosphorus concentrations were higher in bark than wood and the amount of phosphorus in the bark was sensitive to stem age and phosphate supply. Phosphorus adequate plants had bark phosphorus concentrations in the range 0.2–0.9% compared to <0.1% in deficient plants (experiment 2). Jarrah leaves accumulated dry matter up to 80 days after expansion and some leaves exported phosphorus during this period. Bark analysis may therefore be preferable to leaf analysis for detecting phosphorus deficiency in this species.     

Seasonality of canopy invertebrate communities in eucalypt forests of eastern and western Australia

Abstract Chemical knockdown procedures were used to sample canopy arthropods at 3 month intervals over 1 year at two sites, one in eastern Australia and the other in western Australia. Samples were taken from narrow-leaved ironbark, Eucalyptus crebra, and grey box, Eucalyptus moluccana, in the east and from jarrah, Eucalyptus marginata, and marri, Eucalyptus calophylla, in the west. Arthropods were more abundant on trees in eastern Australia and exhibited different seasonal patterns from those in the west. Members of different functional groups exhibited different seasonal patterns, with some herbivorous groups responding to times of leaf production, decomposers and fungus feeders responding to high moisture availability, and predators/parasites responding to the abundance of food items. Seasonal variability was slightly higher in the west, possibly reflecting the greater seasonal amplitude in rainfall. In the eastern forest, proportionately more taxa peaked in spring or summer and declined to minimum numbers in winter. In the western forest several taxa attained peak numbers in autumn, winter or spring, while others declined to minimum values in winter or summer. The phenological patterns of canopy arthropods appear to be linked to the condition of the host plant and/or to climatic factors. Comparison of the western Australian data to those from a second year of sampling at a time when rainfall was greater and fell later into the season indicated that variability in arthropod numbers between years can be as great as that between seasons. Implications of the variability in seasonal and annual patterns of canopy invertebrate communities are discussed in relation to the need for long-term sampling and in relation to evaluating the impact of disturbance on forest communities.     

Food and density limitations of the Seychelles Magpie Robin,Copsychus sechellarum,on Cousine Island

The critically endangered Seychelles Magpie Robin, Copsychus sechellarum, is one of the rarest birds in the world. At the end of December 1999, there were 88 individuals distributed on four small granite islands: Fregate, Aride, Cousin and Cousine. Little is known of Magpie Robin ecology in its natural habitat. Studies carried out on Aride, Cousin and Cousine are therefore valuable as each island is dominated by native woodland. The composition of Magpie Robin diet was compared between Fregate and Cousine. An exotic species of cockroach, Pycnoscelus indicus, and dropped fish were found to be considerably more important prey items on Cousine. Observations of chick food provisioning indicated habitat quality differences between the territories. Invertebrate and vertebrate food resources available to the Magpie Robin were sampled on Cousine between 1997 and 1998. Fourteen sites were sampled for invertebrates and fifty-two species from fifteen taxa were identified. There were significant differences between the mean number of species recorded per site and the mean number of animals found at each site. Skink density was estimated at between 1219-1516/ha and 354-538/ha for Mabuya sechellensis and Mabuya wrightii respectively. Invertebrate diversity and abundance was greatest in areas dominated by closed-canopy woodland on or near the coastal plain. These results explained the current distribution of Magpie Robin territories. The invertebrate abundance data were used to estimate the carrying capacity of the island for the Magpie Robin. Cousine could theoretically support up to six breeding pairs but it is questionable that a population of this size could be self-sustaining in the long-term.     

The foraging profile of a wandoo woodland avifauna in early spring

Abstract This study reports on the foraging profile of a wandoo woodland avifauna at Dryandra in Western Australia, Australia. Despite its geographical isolation, wandoo woodland shares a large number of species with woodland bird communities in eastern Australia and there are broad similarities in community foraging profiles. Insect-eating birds using ground, bark, foliage, and aerial substrates dominate eucalypt bird communities. Nectar-feeding and seed/fruit-eating guilds are important components of the Australian avifauna, but have fewer species, and vary in composition and abundance as nectar, seed, and fruit availability changes seasonally and from year to year, and from one locality to another. Despite similarities, there are also differences between the foraging profile of the wandoo avifauna and those in eastern Australia. Specifically, the wandoo avifauna is characterized by a high proportion of ground-foraging species. In addition, many wandoo woodland birds appear to spread their foraging over a wider range of substrates (i.e., ground, bark, and foliage) than eastern species. Differences in habitat structure do not explain these differences in community foraging profiles, and there may be differences in the abundance, kind, and spatial distribution of resources between different eucalypt ecosystems. Possibly the eastern communities have lost ground-dwelling components of their avifauna since European settlement, while the woodlands at Dryandra retain a more intact avifauna. The reasons why some species and not others are lost from woodlands as a result of European land management practices are discussed.     

Climate and landscape drivers of tree decline in a Mediterranean ecoregion

Climate change and anthropogenic land use are increasingly affecting the resilience of natural ecosystems. In Mediterranean ecoregions, forests and woodlands have shown progressive declines in health. This study focuses on the decline of an endemic woodland tree species, Eucalyptus wandoo (wandoo), occurring in the biodiversity hotspot of southwest Western Australia. We determined the change in health of wandoo stands between 2002 and 2008 across its geographic and climatic range, and associated this change in health with non‐biotic variables focusing on: (1) fragment metrics; (2) topography; (3) soil characteristics; and (4) climate. Only fragment metrics and climate variables were found to be significantly related to the observed change in health. Stands that were small with high perimeter/area ratios were found to be most sensitive to health declines. Recent increases in autumn temperatures and decreases in annual rainfall were negatively affecting health of wandoo most prominently in the low rainfall zone of its climatic range. Together, these results suggest the onset of range contraction for this ecologically important species, which is likely to be exacerbated by projected future changes in climate. Our results emphasize the importance of establishing monitoring programs to identify changes in health and decline trends early to inform management strategies, particularly in the sensitive Mediterranean ecoregions.     

Decomposition of litter from three major plant species of jarrah (Eucalyptus marginata Donn ex Sm.) forest in relation to site fire history and soil type

Rates of weight loss and release of N, P, K, S, Ca, Mg, Na, and Cl from litter of several species in jarrah (E. marginata Donn ex Sm.) forest were measured in relation to site fire history and soil type. Weight loss from leaf litter decreased in the order jarrah > marri (E. calophylla R. Br. ex Lindl.) > Banksia grandis Willd. After 18 months on the forest floor senesced leaves of jarrah, marri and Banksia had lost 45%, 42% and 19%, respectively, of their original weight. Although greatest rates of decomposition occurred on a site burnt 3 y previously by an intense autumn fire and slowest rates on a site which had not been burnt for 8 y, the differences between burn sites were small in comparison with the total weight loss from decomposing litter. The order of release of nutrients from decomposing eucalypt litter was P<N<Ca<S<Mg<Cl<K<Na. There appears to be only slow release of N and P from the litter layer of these forests in the period between successive control burns. Fresh jarrah leaves, which are similar in chemical composition to leaf litter falling after crowns have been scorched by intense fire, decompose rapidly in comparison with senescent leaf tissue. Release of nutrients, particularly N and P, is also more rapid from fresh leaves than from leaf litter. Rates of decomposition of green leaves differed between soil types in the order reddish gravels > dark sandy duplex soil > yellow gravels. These differences may be related to the higher nutrient status of the reddish gravel soils.     

The influence of tree species and edge effects on pheromone trap catches of oak processionary moth Thaumetopoea processionea (L.) in the U.K.

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Plant species richness in the mallee region of Western Australia

Sixteen sites (area 1000 m²) within the mallee region of southern Western Australia were sampled for vascular plant species richness. Species richness ranged from 17 species per 1000m² in a Halosarcia syncarpa salt-complex site and a Eucalyptus occidentalis tree mallee site, up to 48 species per 1000 m² in a Eucalyptus angulosa-Eucalyptus tetragona shrub mallee site. Woodland, woodland/mallee and mallee sites consisted mainly of perennial species while shrubland sites and salt-complex sites had a higher percentage of ephemeral species. Sites with the highest species richness occurred on soils with the lowest nutrient content. Sites with lowest species numbers were those with severe habitat conditions or where better nutrient conditions may have provided the dominants with a competitive advantage to suppress associated species.     

Arthropod fauna of jarrah (Eucalyptus marginata) foliage in Mediterranean forest of Western Australia: Spatial and temporal variation in abundance,biomass, guild structure and species composition

Abstract A 2 year study (using a branch-clipping technique) of the arthropod fauna of jarrah crowns (14 m above ground level) in a 7500km² area centred on Manjimup, Western Australia, yielded 7461 individuals belonging to 396 species. Lepidoptera, Hemiptera and Araneae dominated the fauna in abundance and biomass but Lepidoptera less so in number of species. Consequently, leaf chewers, sapsuckers and predators were the dominant guilds. Most species showed great spatial and temporal variation in their occurrence, with some 73% being recorded on only one or two of the nine sampling occasions. In addition 77% of species were recorded on four or fewer of the 45 trees sampled. Crowns of these trees tended to have highly dissimilar assemblages of arthropods. Dissimilarity between trees was not predictable from the distance between them. Total species richness was greatest in samples collected in summer. Predators and sapsuckers tended to be the most speciose guilds. Within-stand differences were much less pronounced than between-stand differences: ants were more abundant on jarrah foliage within 2 m of ground level and the pest defoliator Uraba lugens (Lepidoptera, Noc-tuidae) was more abundant on foliage of jarrah pole crowns 14 m above ground. The most abundant arthropod, U. lugens, did not reduce appreciably the biomass or abundance of other arthropod groups present in jarrah pole crowns. This is consistent with the paradigm that competition between species of herbivorous insects is infrequent. After comparison with other studies in jarrah forest, we tentatively conclude that there is no single fixed pattern of organization or predictable assemblage of invertebrates on jarrah foliage.     

Response of ants and spiders to prescribed fire in oak woodlands of California

Conservation managers of oak woodlands have been reintroducing fire both as an ecological process per se and to assist in restoring native plant communities. To increase our understanding of the impacts of reintroduced fire on ground-dwelling invertebrates we examined the response of ants and spiders to a late season (autumn) prescribed fire conducted in a blue oak (Quercus douglasii) woodland ecosystem in northern California. Twelve 100 m × 100 m plots were established, six plots received a burn treatment and the remaining six plots were unburned controls. Ants and spiders were sampled using pitfall traps left open continuously and collected approximately every 32 days. Sampling was conducted over a year, consisting of four pre-burn and nine post-burn collections. Abundance was analyzed using a repeated measures ANOVA, which showed seed-harvester ants decreased significantly in the two months following the fire. Total spider abundance also showed a significant decrease in two months, although this did not occur immediately after the burn. One spider hunting guild, the ‘diurnal ambush’ group (Thomisidae) remained suppressed for up to nine months. Correspondence analysis measures of ant species abundance with environmental and vegetation variables (percent rock, bare ground, plant species richness and height of herbaceous vegetation) were higher than expected by chance, which assists in explaining some of the responses. Findings from this study revealed that the reintroduction of autumn burns has modest and short-term effect on the invertebrates sampled, suggesting that late season fires are compatible with other conservation goals for oak woodland ecosystems.     

The effects of a single hot summer fire on soil fauna and on litter decomposition in jarrah (Eucalyptus marginata) forest in Western Australia

An area of jarrah (Eucalyptus marginata Sm) forest was burnt with a hot fire (ca 600 kw/ha) in March 1975. The meso- and microarthropod faunas were sampled in May, June and July 1976 and the decomposer activity of the soil and litter was estimated using buried cotton strips. The growth of jarrah seedlings in pots was measured under different litter and nutrient regimes. Feeding experiments with Eucalyptus, Banksia and Bossiaea litter were carried out on Podykipus sp., a litter millipede common at the site of the fire. Burning reduced the numbers of arthropods, the proportion of juveniles and the proportion of fungal feeders in the micro-arthropod population. The rate of decomposition was also reduced. The seedlings grew most under leaf Utter and millipede faeces and least under leaf ash. Podykipus sp. preferred Bossiaea litter (high nutrient content) to either Eucalyptus or Banksia litter (low nutrient content).     

Response of plant species and life form diversity to variable fire histories and biomass in the jarrah forest of south‐west Australia

Frequent fires reduce the abundance of woody plant species and favour herbaceous species. Plant species richness also tends to increase with decreasing vegetation biomass and cover due to reduced competition for light. We assessed the influence of variable fire histories and site biomass on the following diversity measures: woody and herbaceous species richness, overall species richness and evenness, and life form evenness (i.e. the relative abundance or dominance among six herbaceous and six woody plant life forms), across 16 mixed jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) forest stands in south‐west Australia. Fire frequency was defined as the total number of fires over a 30‐year period. Overall species richness and species evenness did not vary with fire frequency or biomass. However, there were more herbaceous species (particularly rushes, geophytes and herbs) where there were fewer shrubs and low biomass, suggesting that more herbaceous species coexist where dominance by shrubs is low. Frequently burnt plots also had lower number and abundance of shrub species. Life form evenness was also higher at both high fire frequency and low biomass sites. These results suggest that the impact of fire frequency and biomass on vegetation composition is mediated by local interactions among different life forms rather than among individual species. Our results demonstrate that measuring the variation in the relative diversity of different woody and herbaceous life forms is crucial to understanding the compositional response of forests and other structurally complex vegetation communities to changes in disturbance regime such as increased fire frequency.