Tasmanian Wet Eucalypt Forest Research Articles

DNA metabarcoding captures subtle differences in forest beetle communities following disturbance

DNA metabarcoding is an emerging approach for monitoring biodiversity, but uncertainties remain about its capacity to detect subtle differences in invertebrate community composition comparable to those achievable based on conventional morphological identification. In this study, DNA metabarcoding and morphology‐based approaches were compared as tools for investigating whether logging history impacted beetle communities in Tasmanian wet eucalypt forests. We compared 12 unlogged mature forest sites with 12 neighboring regeneration sites that had been logged approximately 55 years previously. The number of species identified based on morphology (173) was close to the number of zero‐radius operational taxonomic units (ZOTUs) identified by DNA metabarcoding of cytochrome c oxidase subunit I (COI, 176) and 16S ribosomal RNA (16S, 156) markers. Subtle but significant differences in beetle species composition between regeneration and unlogged mature forests were captured by both morphology‐based and COI DNA metabarcoding approaches, but not by 16S DNA metabarcoding. Our results support the suitability of mitochondrial COI for studying invertebrate biodiversity. A slight loss of signal compared to the morphology‐based approach may be resolved by developing more comprehensive DNA reference databases. While confirming forest recovery of 48–58 years did not fully restore mature forest beetle communities, we suggest that DNA metabarcoding can be used for monitoring biodiversity and probing subtle differences in community composition.

Forest succession where trees become smaller and wood carbon stocks reduce

As Tasmania’s wet forests transition from mixed forest (eucalypt overstory with a rainforest understory) to rainforest they can be expected to lose more than half their total (live+dead, standing+downed) bole wood volume and biomass. On average rainforest sites contained 205MgCha−1, or 708m3ha−1 less wood (live+dead, standing+downed) than mixed forests. This occurs as smaller dimension rainforest trees replace the larger eucalypts. On the fertile study sites, the largest rainforest trees were 20m shorter and 113cm smaller in breast height diameter than the mature eucalypts in mixed forests. Tasmanian wet forests do not attain the highest site level C-stocks possible in late succession, as is expected for many other forests. Rather, the maxima is attained for a short period several centuries after disturbance and regeneration of a eucalypt cohort. Hence, the maintenance of the highest C-density stands in the landscape, and potentially that largest landscape level C-stocks among Tasmania’s wet forests ironically requires the periodic killing of all, or part, of the large C-dense eucalypt overstory by intense wildfire to allow these large eucalypts to regenerate and persist on these sites. This creates challenges when modeling forest carbon in Tasmanian wet forests, as not only is the area of forest that has progressed sufficiently toward rainforest to be emitting C is unknown, but the rate of C emission and the amount that will be lost over time across the various site fertility types is also unknown. Certainly, setting aside Tasmanian wet eucalypt forest to store C will not deliver the usual long term C accumulation benefits common to forests elsewhere. Maximizing landscape level C-stocks is likely to require periodic disturbance to maintain the C-dense eucalypts in the landscape.

Bird assemblages in Tasmanian clearcuts are influenced by the age of eucalypt regeneration but not by distance from mature forest

Many species of birds are adversely affected by clearcutting of Australian eucalypt forests for timber. However, recolonisation of harvested areas may be enhanced if mature forest is retained nearby (forest influence).We test the benefits of proximity to mature Tasmanian wet eucalypt forest on birds in adjacent regenerating clearcuts. We hypothesised that bird assemblages in silvicultural regeneration would become more similar to those in adjacent mature forest with increasing proximity to the mature forest. To test this, we sampled birds in regenerating clearcuts using 25 m radius point counts centred 35, 120, and 200 m from mature forest. We also hypothesised that the magnitude of forest influence would decrease with time since harvest, across three age classes of approximately 7, 27 and 45 years-old, because the assemblages in older regeneration would be more similar to those in the mature forest.We found that distance from mature forest had no significant effects on bird assemblage composition, native species richness per sample, or the incidences of any species. This result was apparent across all three age classes of silvicultural regeneration, despite significant changes in the assemblage composition, native species richness, and incidence of 10 species, with time since harvest.

Variation in stream organic matter processing among years and benthic habitats in response to forest clearfelling

We assessed rates of organic matter (OM) processing in coarse gravel and fine benthic sediment, along with water temperature, in four clearfell harvested and two undisturbed headwater streams flowing through wet eucalypt forest in southern Tasmania, Australia. Clearfell forestry in Tasmanian wet eucalypt forest involves felling of all timber followed by a high intensity regeneration burn to provide a receptive mineral seedbed for seedling growth. Bacterial carbon production and cellulose decomposition potential (together referred to as OM processing) were measured seasonally 3–5years before and 2–4years after harvesting in each stream. We employed a staircase design (staggered harvesting treatments) within a multiple before–after control–impact design to distinguish harvesting effects from natural variation. Clearfell harvesting raised the yearly mean water temperature by between 0.25°C and 0.94°C, and raised the maximum water temperature by between 0.84 and 1.6°C. Rates of cellulose decomposition were not significantly correlated with sediment temperature but bacterial carbon production showed weak, significant correlations with temperature in fine (r=0.20, P=0.01, n=137) and coarse gravel sediment (r=0.39, P<0.001, n=137). The response in OM processing to clearfell harvesting differed between years and among benthic habitats. In coarse gravel habitat, there was a significant decrease in rates of cellulose decomposition potential in the 2nd and 4th year after harvesting, and a significant decrease in bacterial carbon production in the 3rd year after harvesting. However, we found a significant increase in rates of bacterial carbon production of fine sediment habitat in the 2nd and 4th year after harvesting. The contrasting response of OM processing between habitats indicates that habitat-specific changes occur after clearfell harvesting, which inhibit attempts to quantitatively predict downstream cumulative effects. Scaling up the habitat-specific responses will not only require estimates of the relative abundances of the distinct habitats, but may also require research into how different spatial configurations of habitats may affect reach- and catchment-scale estimates of OM processing.

Impact of distance to mature forest on the recolonisation of bryophytes in a regenerating Tasmanian wet eucalypt forest

Forest influence is a type of edge effect that occurs when mature forests affect the recolonisation of adjacent disturbed areas. This can be driven by changes in microclimate conditions near the edge or by an increase in establishment ability with proximity to a propagule source. Bryophyte recolonisation is sensitive to both microclimate and dispersal distance, therefore they are an ideal group to examine how strong forest influence is and over what distance it operates. Responses to forest influence are known to be highly species dependent; therefore, we tested whether distance affects the recolonisation ability of a range of bryophytes. As well as examining a range of species, we tested whether forest influence operated differently on two types of substrate used by bryophytes (logs and ground). For most of the species examined, establishment rates in disturbed forest diminished further away from the mature edge. The influence of unlogged mature forest on bryophyte establishment in harvested forest occurred up to 50 m. Species varied in their response to distance, and the relationships with distance were stronger on the ground compared with log substrates. These results support the concept of forest influence, with areas closer to mature forest experiencing more substantial re-establishment. These findings are relevant to conservation of bryophytes in managed native forests.

The effects of mechanical disturbance and burn intensity on the floristic composition of two-year old aggregated retention coupes in Tasmanian wet eucalypt forests

Due to concerns about the ecological impacts of clearfelling in Tasmanian wet eucalypt forests, aggregated retention (ARN) was developed as an alternative harvesting method. It is predicted that, compared to clearfelling, ARN will have ecological benefits such as preservation of old-growth structures and improved regeneration of late successional species in harvested areas. However, early studies have indicated that ARN requires lower intensity regeneration burns and results in greater levels of mechanical soil disturbance than clearfelling. This study therefore aimed to assess the impacts of both soil disturbance and burn intensity on floristic composition, species dominance and species richness following harvesting in ARN coupes. Floristic surveys were conducted on six seedbed classes that reflected the combined effects of both burn intensity and soil disturbance in six two-year-old ARN coupes in southern Tasmania. The results showed that both factors had a significant influence on floristic composition. Higher burn intensities generally favoured colonising species such as eucalypts and Senecio minimus and resulted in lower species richness, while lower fire intensities favoured species regenerating from the seedbank and resulted in higher species richness. In contrast, mechanically disturbed seedbed generally had a high cover of the sedge Gahnia grandis but a low overall species richness due to reduced regeneration of eucalypts and understorey species. The prevalence of the six seedbed classes, and corresponding plant species composition, varied among four general harvesting-related disturbance categories; firebreaks, snigtracks, windrows of piled logging debris and the general harvested area. Maintaining a variety of burn intensities is likely to maximise plant biodiversity within ARN coupes, and soil disturbance should be minimised, with an emphasis on reducing the total area of firebreaks.

Succession of mosses, liverworts and ferns on coarse woody debris, in relation to forest age and log decay in Tasmanian wet eucalypt forest

In managed forest landscapes, understanding successional processes is critical to management for sustainable biodiversity. Coarse woody debris is a key substrate for forest biodiversity, particularly because it undergoes complex succession reflecting the effects of changes in both forest structure and substrate characteristics. The present study used a chronosequence approach to investigate succession of mosses, liverworts and ferns on coarse woody debris following clearfell, burn, sow native forest silviculture in wet eucalypt forest in Tasmania, focussing on discriminating between the effects of forest age and log decay. It also compared successional processes following wildfire with those following clearfell, burn, sow silviculture. Forest regenerating after the latter form of regeneration showed clear ecological succession up to 43 years (the limit of available sites), characterised by increasing diversity and cover, and clearly delineated specialisation among species with regard to successional stage. Analyses of subsets of the full data-set indicated that the effects of forest age dominated this succession, with minimal effects of substrate change independent of forest age. Analysis of within forest microenvironments were consistent with the inference that microenvironmental changes related to forest age drive major successional changes in these forests. Comparative analysis indicated similarity between successional states in post-wildfire and post- clearfell, burn, sow regeneration after 43 years for logs of the same decay stages, and continuing succession on post-wildfire sites to at least 110 years. Overall, these data suggest that management to sustain fern and bryophyte diversity should ensure that areas of forest beyond 110 years are represented in the landscape at appropriate spatial scales.

Do wildlife habitat strips act as refuges for mature-forest carabid beetle assemblages? A case-study in Tasmanian wet eucalypt forest, Australia

Carabid beetles (Insecta: Coleoptera: Carabidae) were sampled with pitfall traps in central Tasmania to assess the conservation utility of wildlife habitat strips (WHS) in native high-altitude wet eucalypt forest. Sampling followed a Before-After, Control-Impact design, with replicated samples being collected at one control site and two treatment sites, both before harvesting and then again seven to eight years after the harvest that established the WHS. Catches of carabid beetles decreased in harvested areas, but there were great increases in species richness and gross changes in assemblage composition — largely attributable to the colonisation of young-forest specialist species. Assemblages in the control site remained essentially unchanged, and were dominated by mature-forest specialist species. Assemblages in the WHS changed little compared to their pre-harvest condition, but assemblage structure was slightly affected. In this particular landscape, WHS appear to effectively maintain carabid assemblages typical of intact mature native forest, at least in the short-term. A broader and longer-term assessment of the ecological performance of WHS across Tasmania would be required to assess the long-term viability of WHS as a conservation strategy for carabids and other species requiring mature forest.

Litter retention in Tasmanian headwater streams after clear-fell logging

Clear-fell logging around small headwater streams in Tasmanian wet eucalypt forests was predicted to affect both the retention of leaf litter and the composition and size of leaf packs. Retention structures were surveyed in six natural streams and six streams in forest regenerated 3–5 years after clear-fell and burn logging. Logged streams had more wood, but retained less leaves than natural streams, and consequently had fewer and smaller leaf packs. Leaf packs from natural streams contained 200% more leaves, bark and twigs than packs from logged streams. The effect of buoyancy on leaf retention was assessed with release and recapture of marked Eucalyptus obliqua and Nothofagus cunninghamii leaves. Eucalypt leaves were more likely to be trapped by retention structures on the bed of the stream, while smaller, more buoyant N. cunninghamii leaves were mainly trapped by leaf packs. Leaf packs in natural streams were formed on a matrix of small twigs and long strips of bark, shed from the upper branches of mature stringybark eucalypts, while leaf retention was reduced in logged streams because there are no mature trees to provide effective retention structures. Changes to the channel form increase both discharge and sedimentation. These factors have strong implications for downstream nutrient processing and riverine food webs.

Stand-replacing wildfires?: The incidence of multi-cohort and single-cohort Eucalyptus regnans and E. obliqua forests in southern Tasmania

The natural age structure of wet eucalypt forest has important implications for biodiversity conservation and the mode of wood production. Southern Tasmanian wet eucalypt forests were sampled to describe age class variation and to test the following hypotheses that relate to it: (1) Eucalyptus regnans stands are more likely to be single-cohort than Eucalyptus obliqua and mixed stands; (2) old-growth trees are associated with multi-cohort wet eucalypt forests; (3) the E. regnans stands are more multi-cohort than Victorian E. regnans stands. Data from 762 stands, all with either E. obliqua or E. regnans were analysed to determine how stand characteristics related to forest type and to the presence of old-growth trees. Over half the stands studied were multi-cohort. Stands with E. regnans had a lesser tendency towards multi-cohortness than stands lacking this species, although most old-growth stands, including those dominated by E. regnans, were multi-cohort. In contrast, most regrowth stands of all species combinations were single-cohort. The proportions of E. regnans stands that were multi-cohort were similar to some estimates from the same type of forest in Victoria. Modifications of forestry regimes in wet eucalypt forests could help to maintain the existence of these biodiverse multi-cohort forests in the landscape.

Short-term responses of ground-active beetles to alternative silvicultural systems in the Warra Silvicultural Systems Trial, Tasmania, Australia

The Warra Silvicultural Systems Trial (SST) in Tasmania, Australia provides a framework for investigating the responses of beetles (Order: Coleoptera) to three alternative systems in lowland wet eucalypt forest: aggregated retention; dispersed retention; and understorey islands retained in clearfelled areas. Beetles from three families known to be sensitive to forest management, the families Carabidae (ground-beetles), Curculionidae (weevils) and Leiodidae (fungus-beetles), were collected with pitfall traps prior to harvest, and in the first and third years post-harvest. The retained aggregates in the aggregated retention system maintained beetle assemblages reasonably typical of mature forests, at least in these early years following harvesting. These aggregates appear to provide a stable habitat, with similar species composition in the first and third years post-harvest. In contrast, the harvested areas of the aggregated retention system contained low numbers of beetle species affiliated with mature forest, as did the understorey islands and the dispersed retention system. Relative to clearfelling, all alternative silvicultural systems appeared to be of some benefit to beetles affiliated with mature forest, but aggregated retention retained far greater numbers of these beetles compared to the other systems in Tasmanian wet eucalypt forest.

Public judgements of the social acceptability of silvicultural alternatives in Tasmanian wet eucalypt forests

Summary This research compared individual's social acceptability ratings of six harvest and regeneration systems that could be applied in wet eucalypt forests: the clearfell, burn and sow system and five alternatives. A smaller calibration study also tested the effect of providing participants with a wider range of alternative systems including a no-harvest option and conversion to blue gum plantation. A survey method was complemented by qualitative follow-up interviews. About 300 Tasmanians with different affiliations in relation to forest harvesting were asked to judge the acceptability of the harvest systems. These were presented to them in two ways: as still images showing the forest in the first year after harvest and as animated sequences showing the forest regenerating over time. On average, non-affiliated and conservation-affiliated people rated the clearfell system least acceptable and a selective logging system most acceptable. For these two groups, as a general trend, acceptability increased with the proportion of forest retained at the first harvest. Aggregated harvest patterns were more acceptable than dispersed. Follow-up interviews provided examples of aesthetic and more thought—based responses leading to these trends. The trend for large-scale timber-industry-affiliated participants was opposite: the more forest retained on the site, the less acceptable the result. In the calibration study, which included a wider range of systems and mostly non-affiliated participants, a no-harvest option was rated most acceptable and the selective-harvest system was rated significantly less acceptable than when the no-harvest option was not available. Viewing animated sequences led to higher ratings of the more intensive harvest systems and lower ratings of the selective harvest system than those based on still images. While significant, these differences were small.

Uptake of nitrate, ammonium and glycine by plants of Tasmanian wet eucalypt forests

A central assumption of ecosystem N cycling has been that organic N must be converted to inorganic N to be available for plant uptake, but this has been questioned by recent studies. We examined uptake of nitrate, ammonium and the amino acid glycine in three species from Eucalyptus obliqua L'Her. wet forest in Tasmania, south-eastern Australia, to test the hypothesis that all three species can take up glycine, and to compare rates of glycine uptake with rates of uptake of nitrate and ammonium uptake. The alternative hypothesis that species vary in their preference for nitrate, ammonium and glycine ("niche differentiation") was also examined. Measurements were made on the canopy dominant Eucalyptus obliqua, and two rain forest tree species found in the understory or as sub-dominants of the canopy, Nothofagus cunninghamii (Hook.) Oerst. and Phyllocladus aspleniifolius (Labill.) Hook.f. Nitrogen uptake was examined in situ with attached roots placed in uptake solutions containing equimolar concentrations (100 micromol l(-1)) of (15)N-nitrate, (15)N-ammonium and 2-(13)C(2) (15)N-glycine. Species did not differ in their preference for different forms of N (species x N form interaction, P > 0.05), and thus there was no evidence of niche differentiation. In all species, rates of uptake were highest for ammonium (11 +/- 5 micromol g(DM) (-1) h(-1); mean +/- SD, n = 108), uptake of glycine occurred at less than half this rate (4.4 +/- 2.6 micromol g(DM) (-1) h(-1)), whereas uptake of nitrate occurred at one-tenth of this rate (0.9 +/- 1.2 micromol g(DM) (-1) h(-1)). The strong positive relationship between (15)N and (13)C uptake indicated that at least 72% of glycine-N was taken up intact. These findings indicate the potential for considerable uptake of organic N in the field.

Estimating edge effects on ground-dwelling beetles at clearfelled non-riparian stand edges in Tasmanian wet eucalypt forest

Edge effects potentially have negative consequences for biodiversity in logging areas. In Tasmanian wet eucalypt forest, ground-dwelling beetle assemblages responded to habitat edges between mature unlogged forest and young regeneration following clearfelling. Transects of pitfall traps extended 100 m into unlogged forest and 10 m into the felled area firebreaks at four study sites (4 sites × 3 transects × 8 traps/transect = 96 traps). The depth of edge influence extended between 10 m and 25 m into mature forest, and the beetle assemblage was estimated to be 95% similar to interior forest at approximately 22 m from the edge. The species composition of beetles changed gradually with distance from the edge, but for practical purposes we distinguished three zones of edge response: mature forest interior extending ≥22 m into unlogged forest, firebreak habitat at the edge of the coupe that extends 1 m into unlogged forest, and an edge-affected mature forest zone in between. Individual species known to be characteristic of mature and young forest were of greatest indicator value in mature forest interior and firebreak habitat, respectively. Choleva TFIC sp 01 (Leiodidae), Decilaus nigronotatus, D. lateralis and D. striatus (all Curculionidae) were identified as indicator species characteristic of mature forest interior. No species were found to be characteristic of the habitat edges. These results are relevant to current management practices in Tasmanian wet eucalypt forest, in particular to the efficacy of linear reserve networks. One hundred metre wide wildlife habitat strips, when bounded by recently harvested forest, are estimated to contain a little over 50% of interior habitat not compromised by edge effects. Small patches of forest (<1 ha) retained in variable retention harvesting are predicted to contain little or no uncompromised interior habitat for ground-dwelling beetles.

Coarse woody debris, biodiversity and management: a review with particular reference to Tasmanian wet eucalypt forests

Summary This paper reviews the biodiversity conservation issues relating to management of coarse woody debris (CWD) in the wet eucalypt production forests of Tasmania, with particular emphasis on clearfell, burn and sow (CBS) silviculture and on fuelwood harvesting. CBS is the standard silvicultural system in these forests, while fuelwood harvesting, as currently proposed, would involve the recovery of a higher proportion of felled biomass than standard CBS, as well as some pre-existing CWD. Studies and practices from around the world are considered that have relevance to the temperate Australian forestry situation in general, and the Tasmanian situation in particular. The paper considers the ecological roles of CWD in natural forest ecosystems, emphasising its value as a key structural component and as habitat for biodiversity (especially invertebrates). Temporal continuity and spatial connectivity in supply of CWD, and presence of larger-diameter CWD, emerge as key factors determining community richness and composition. Whilst levels of CWD naturally fluctuate spatially and temporally in wet eucalypt forests, studies from northern temperate and boreal forests with similar dynamics demonstrate that, historically, management of native forests has tended to result in a gradual diminution of the CWD resource. Larger-diameter material is readily diminished through management, with potential consequences for dependent biodiversity. Suggested mitigation measures (landscape-level and coupe-level), to accommodate biodiversity concerns and avoid a long-term conservation management problem for forest managers in Tasmania, centre on two main concerns. One is the likelihood that current standard rotation lengths used in CBS are probably too short to allow for the recruitment of sufficient CWD to replace that which is lost through harvesting, regeneration burning and natural decomposition. The other concern is that fuelwood harvesting may significantly increase the impacts of CBS on biodiversity in general and on threatened species in particular.