Impact of the invasive rust Puccinia psidii (myrtle rust) on native Myrtaceae in natural ecosystems in Australia

The invasive rust Puccinia psidii (myrtle rust) was detected in Australia in 2010 and is now established along the east coast from southern New South Wales to far north Queensland. Prior to reaching Australia, severe damage from P. psidii was mainly restricted to exotic eucalypt plantations in South America, guava plantations in Brazil, allspice plantations in Jamaica, and exotic Myrtaceous tree species in the USA; the only previous record of widespread damage in native environments is of endangered Eugenia koolauensis in Hawai’i. Using two rainforest tree species as indicators of the impact of P. psidii, we report for the first time severe damage to endemic Myrtaceae in native forests in Australia, after only 4 years’ exposure to P. psidii. A 3-year disease exclusion trial in a natural stand of Rhodamnia rubescens unequivocally showed that repeated, severe infection leads to gradual crown loss and ultimately tree mortality; trees were killed in less than 4 years. Significant (p < 0.001) correlations were found between both incidence (r = 0.36) and severity (r = 0.38) of P. psidii and subsequent crown loss (crown transparency). This provided supporting evidence to conclude a causal association between P. psidii and crown loss and tree mortality in our field assessments of R. rubescens and Rhodomyrtus psidioides across their native range. Assessments revealed high levels of damage by P. psidii to immature leaves, shoots and tree crowns—averaging 76 % (R. rubescens) and 95 % (R. psidioides) crown transparency—as well as tree mortality. For R. psidioides, we saw exceptionally high levels of tree mortality, with over half the trees surveyed dead and 40 % of stands with greater than 50 % tree mortality, including two stands where all trees were dead. Tree mortality was less prevalent for R. rubescens, with only 12 % of trees surveyed dead and two sites with greater than 50 % mortality. Any alternative causal agents for this tree mortality have been discounted. The ecological implications of this are unclear, but our work clearly illustrates the potential for P. psidii to negatively affect Australia’s biodiversity

Longer-term changes in streamflow following logging and mixed species eucalypt forest regeneration: The Karuah experiment

The Karuah replicated paired catchment experiment was initiated in the 1970s to examine the hydrological effects of eucalypt-to-eucalypt forest succession in New South Wales, Australia. Treatments were conducted on 25.4-78.8% of the area of six small catchments in 1983. Five of the treated catchments experienced a significant increase in streamflow following forest disturbance, equivalent to annual water yield changes ranging from 120 mm to 319.6 mm which varied in proportion to the percentage of each catchment logged. This initial increase lasted for greater than 5 years in the logged and unburnt Bollygum (L-) catchment, but had returned to pre-treatment levels within 2.5 years in the logged and burnt (L+) Corkwood and Jackwood catchments, and within 2 years in the Kokata and Coachwood plantation catchments (P). A significant reduction in streamflow then occurred in three catchments - Corkwood (113.5 mm a⁻¹), Bollygum (72.7 mm a⁻¹) and Kokata (68.9 mm a⁻¹) - but had returned to the pre-treatment level within 7 years post-harvest in the Corkwood catchment. A continuing suppression of streamflow after 27 years is evident in two of the catchments, Bollygum and Kokata, with Kokata experiencing a further decline from 2005 onwards to a mean annual reduction of 172.4 mm. By contrast a significant increase in streamflow relative to the pre-treatment level has been recorded in the Jackwood catchment after 23 years (157.6 mm a⁻¹). Relative changes in streamflow measured in this experiment can be explained largely by changes in forest species composition, basal area and stocking rates. The eucalypt stands have variously self-thinned and in some cases forest growth appears to have been slowed by insect attack and bell miner associated dieback. Contrary to earlier published findings, while this study confirms that Mountain ash type water yield reductions can occur in other forest types, this response appears to be the exception rather than the rule. These findings have implications for the modelling and management of water yield impacts of mixed species eucalypt forest disturbance

Impact of the invasive rust Puccinia psidii (myrtle rust) on native Myrtaceae in natural ecosystems in Australia

The invasive rust Puccinia psidii (myrtle rust) was detected in Australia in 2010 and is now established along the east coast from southern New South Wales to far north Queensland. Prior to reaching Australia, severe damage from P. psidii was mainly restricted to exotic eucalypt plantations in South America, guava plantations in Brazil, allspice plantations in Jamaica, and exotic Myrtaceous tree species in the USA; the only previous record of widespread damage in native environments is of endangered Eugenia koolauensis in Hawai’i. Using two rainforest tree species as indicators of the impact of P. psidii, we report for the first time severe damage to endemic Myrtaceae in native forests in Australia, after only 4 years’ exposure to P. psidii. A 3-year disease exclusion trial in a natural stand of Rhodamnia rubescens unequivocally showed that repeated, severe infection leads to gradual crown loss and ultimately tree mortality; trees were killed in less than 4 years. Significant (p < 0.001) correlations were found between both incidence (r = 0.36) and severity (r = 0.38) of P. psidii and subsequent crown loss (crown transparency). This provided supporting evidence to conclude a causal association between P. psidii and crown loss and tree mortality in our field assessments of R. rubescens and Rhodomyrtus psidioides across their native range. Assessments revealed high levels of damage by P. psidii to immature leaves, shoots and tree crowns—averaging 76 % (R. rubescens) and 95 % (R. psidioides) crown transparency—as well as tree mortality. For R. psidioides, we saw exceptionally high levels of tree mortality, with over half the trees surveyed dead and 40 % of stands with greater than 50 % tree mortality, including two stands where all trees were dead. Tree mortality was less prevalent for R. rubescens, with only 12 % of trees surveyed dead and two sites with greater than 50 % mortality. Any alternative causal agents for this tree mortality have been discounted. The ecological implications of this are unclear, but our work clearly illustrates the potential for P. psidii to negatively affect Australia’s biodiversity

Carbon dynamics of paper, engineered wood products and bamboo in landfills: evidence from reactor studies

Abstract Background There has been growing interest in the development of waste-specific decay factors for estimation of greenhouse gas emissions from landfills in national greenhouse gas inventories. Although engineered wood products (EWPs) and paper represent a substantial component of the solid waste stream, there is limited information available on their carbon dynamics in landfills. The objective of this study was to determine the extent of carbon loss for EWPs and paper products commonly used in Australia. Experiments were conducted under laboratory conditions designed to simulate optimal anaerobic biodegradation in a landfill. Results Methane generation rates over incubations of 307–677 days ranged from zero for medium-density fibreboard (MDF) to 326 mL CH4 g−1 for copy paper. Carbon losses for particleboard and MDF ranged from 0.7 to 1.6%, consistent with previous estimates. Carbon loss for the exterior wall panel product (2.8%) was consistent with the expected value for blackbutt, the main wood type used in its manufacture. Carbon loss for bamboo (11.4%) was significantly higher than for EWPs. Carbon losses for the three types of copy paper tested ranged from 72.4 to 82.5%, and were significantly higher than for cardboard (27.3–43.8%). Cardboard that had been buried in landfill for 20 years had a carbon loss of 27.3%—indicating that environmental conditions in the landfill did not support complete decomposition of the available carbon. Thus carbon losses for paper products as measured in bioreactors clearly overestimate those in actual landfills. Carbon losses, as estimated by gas generation, were on average lower than those derived by mass balance. The low carbon loss for particleboard and MDF is consistent with carbon loss for Australian wood types described in previous studies. A factor for carbon loss for combined EWPs and wood in landfills in Australia of 1.3% and for paper of 48% is proposed. Conclusions The new suggested combined decay factor for wood and EWPs represents a significant reduction from the current factor used in the Australian greenhouse gas inventory; whereas the suggested decay factor for paper is similar to the current decay factor. Our results improve current understanding of the carbon dynamics of harvested wood products, and allow more refined estimates of methane emissions from landfills

Influence of biochars on nitrous oxide emission and nitrogen leaching from two contrasting soils

The influence of biochar on nitrogen (N) transformation processes in soil is not fully understood. This study assessed the influence of four biochars (wood and poultry manure biochars synthesized at 400°C, nonactivated, and at 550°C, activated, abbreviated as: W400, PM400, W550, PM550, respectively) on nitrous oxide (N₂O) emission and N leaching from an Alfisol and a Vertisol. Repacked soil columns were subjected to three wetting–drying (W–D) cycles to achieve a range of water-filled pore space (WFPS) over a 5-mo period. During the first two W–D cycles, W400 and W550 had inconsistent effects on N₂O emissions and the soils amended with PM400 produced higher N₂O emissions relative to the control. The initially greater N₂O emission from the PM400 soils was ascribed to its higher labile intrinsic N content than the other biochars. During the third W–D cycle, all biochar treatments consistently decreased N₂O emissions, cumulatively by 14 to 73% from the Alfisol and by 23 to 52% from the Vertisol, relative to their controls. In the first leaching event, higher nitrate leaching occurred from the PM400-amended soils compared with the other treatments. In the second event, the leaching of ammonium was reduced by 55 to 93% from the W550- and PM550-Alfisol and Vertisol, and by 87 to 94% from the W400- and PM400-Vertisol only (cf. control). We propose that the increased effectiveness of biochars in reducing N₂O emissions and ammonium leaching over time was due to increased sorption capacity of biochars through oxidative reactions on the biochar surfaces with ageing

Carbon in Mature Native Forests in Australia: The Role of Direct Weighing in the Derivation of Allometric Equations

Accurate estimates of forest biomass are essential to understand the contribution of forests to climate change mitigation efforts. In this manuscript, we report on biomass determinations for 586 directly weighed trees located in three important native forest areas in Australia. The sites were paired according to management strategy; i.e., managed for periodic cycles of harvest or conservation only. The key aim of the work was to test whether non-site specific available biomass relationships are reliable, especially in the estimation of the biomass of trees with a large diameter at breast height (DBH). The above-ground carbon (AGC) estimates for largely undisturbed forests ranged from approximately 200–400 t C ha−1. Existing allometric equations were generally poor at estimating biomass for mature trees, especially those of large DBH. Direct weighing of biomass ensured a degree of certainty in the results that cannot be associated with previous studies that relied on sub-sampling, or with studies that relied on existing allometric equations. Thus, caution should be exercised when interpreting the results of previous studies that did not rely on direct weighing of the biomass in the context of decisions around optimum forest management regimens, and the contribution of mature forest stands to the global carbon balance