Tim Wardlaw

A latitudinal cline in disease resistance of a host tree

The possible drivers and implications of an observed latitudinal cline in disease resistance of a host tree were examined. Mycosphaerella leaf disease (MLD) damage, caused by Teratosphaeria species, was assessed in five Eucalyptus globulus (Tasmanian blue gum) common garden trials containing open-pollinated progeny from 13 native-forest populations. Significant population and family within population variation in MLD resistance was detected, which was relatively stable across different combinations of trial sites, ages, seasons and epidemics. A distinct genetic-based latitudinal cline in MLD damage among host populations was evident. Two lines of evidence argue that the observed genetic-based latitudinal trend was the result of direct pathogen-imposed selection for MLD resistance. First, MLD damage was positively associated with temperature and negatively associated with a prediction of disease risk in the native environment of these populations; and, second, the quantitative inbreeding coefficient (QST) significantly exceeded neutral marker FST at the trial that exhibited the greatest MLD damage, suggesting that diversifying selection contributed to differentiation in MLD resistance among populations. This study highlights the potential for spatial variation in pathogen risk to drive adaptive differentiation across the geographic range of a foundation host tree species.

Do artificial and natural defoliation have similar effects on physiology of Eucalyptus globulus Labill. seedlings

Abstract• Artificial defoliation is often used to simulate defoliation by herbivory and is usually considered a good indication of a plant’s response to a given type of damage. However, the findings of studies directly comparing the two defoliation types are inconsistent.• Here, the short term effects of artificial and insect defoliation by larvae of Paropsisterna agricola on growth, biomass allocation and photosynthetic capacity of Eucalyptus globulus seedlings were compared in a glasshouse experiment. The artificial defoliation was carried out to closely resemble the spatial patterns observed for insect defoliation.• Height and diameter increments were reduced as a result of insect defoliation, whereas artificial defoliation had no significant effect on height. Increased photosynthetic capacity was observed in response to both treatments, but the magnitude of this increase was larger in insect-than in artificially-defoliated seedlings. Significant reductions in foliar carbohydrate content and total biomass were noticeable in artificially-defoliated seedlings. Although the foliar carbohydrate levels also decreased across the crown zones following insect defoliation treatment, seedlings allocated a large amount of their biomass in the branches of the damaged zone.• Despite our best endeavours to simulate insect defoliation in the artificial treatment, the latter may not reflect accurately the full strength of the effects. However, artificial and insect defoliation were similar in their direction of the responses they caused in E. globulus seedlings.Résumé• La défoliation artificielle est couramment employée pour simuler la défoliation par les insectes herbivores et elle est généralement considérée comme un bon indicateur de la réponse des plantes pour un type de dommage donné. Cependant, les résultats d’études comparant directement les deux types de défoliation sont inconsistants.• Ici, les effets court terme des défoliations artificielles et naturelles par la larve de Paropsisterna agricola ont été comparés au plan de la croissance, de l’allocation de la biomasse et de la capacité de photosynthèse dans une expérimentation conduite en serre. La défoliation artificielle a été menée pour ressembler étroitement aux modèles spatiaux observés avec la défoliation par les insectes.• À la suite de la défoliation par les insectes, les accroissements en hauteur et en diamètre ont été réduits, alors que la défoliation artificielle n’a eu aucun effet significatif sur la hauteur. L’augmentation de la capacité de photosynthèse a été observée en réponses aux deux traitements, mais l’ampleur de cette augmentation a été plus forte pour les plants défoliés par les insectes que pour les plants artificiellement défoliés. Des réductions significatives de la teneur foliaire en glucides et de la biomasse totale ont été notées chez les plants artificiellement défoliés. Malgré la réduction générale de la teneur en glucides à la suite de la défoliation par les insectes, les jeunes plants assignèrent une importante partie de la biomasse aux branches de la zone endommagée.• Malgré nos meilleures tentatives pour simuler la défoliation par les insectes dans le traitement artificiel, ce dernier ne reflète pas avec exactitude toute l’ampleur de l’impact engendré. Cependant, les défoliations artificielles et naturelles ont entraîné chez les jeunes plants d’E. globulus des réponses qui allaient dans le même sens.

Harmonisation of methods for the assessment and reporting of forest health in Australia — a starting point

Summary The harmonisation of a sub-set of forest health attributes suitable for aggregating, through scales ranging from individual trees to the operational forest management unit and up to the national level, has been achieved in countries such as the USA and Canada. In Australia, however, data collected on forest health is currently obtained on an ad hoc basis with only a small proportion of the national forest estate actually having been assessed. National guidelines are required for the objective assessment of a set of indices relating to forest health before Australia is in a position to report adequately on forest ecosystem health and vitality as recommended by the (Australian) Montreal Process Implementation Group. Obtaining these indices must be an affordable process that fulfills forest health reporting requirements for a range of national, state and regional reporting commitments such as the State of the Forests Reports and for the Regional Forest Agreements review process. In addition, it is envisaged that the indices will contribute to the verification process for the forest health and vitality criterion described in the Australian Forestry Standard for certification of sustainable forest management practices. Tree crown condition is proposed as a key attribute of forest health and it is amenable to rapid standardised assessment. Four measures are proposed which have the potential to provide consistent core data on tree crown condition. Adoption of these indices will depend on the assessments being cost effective and consistent, and the results being meaningful for a range of applications. To facilitate this process an illustrated field manual has been published, providing guidance for standardised assessment methods. Initially the scope of the manual is limited, focusing on the assessment of eucalypt tree crown damage. If it proves successful, the number of indicators relating to forest health monitoring could be increased.

Living near the edge: Being close to mature forest increases the rate of succession in beetle communities

In increasingly fragmented landscapes, it is important to understand how mature forest affects adjacent secondary forest (forest influence). Forest influence on ecological succession of beetle communities is largely unknown. We investigated succession and forest influence using 235 m long transects across boundaries between mature and secondary forest at 15 sites, sampling a chronosequence of three forest age classes (5-10, 23- 29, and 42-46 years since clear-cutting) in tall eucalypt forest in Tasmania, Australia. Our results showed that ground-dwelling beetle communities showed strong successional changes, and in the oldest secondary forests, species considered indicators of mature forest had recolonized to abundance levels similar to those observed within adjacent mature forest stands. However, species composition also showed forest influence gradients in all age classes. Forest influence was estimated to extend 13 m and 20 m in the youngest and intermediate-aged secondary forests, respectively. However, the estimated effect extended to at least 176 m in the oldest secondary forest. Our environmental modeling suggests that leaf litter, microclimate, and soil variables were all important in explaining the spatial variation in beetle assemblages, and the relative importance of factors varied between secondary forest age classes. Mature-forest beetle communities can recolonize successfully from the edge, and our results provide a basis for land managers to build mature habitat connectivity into forest mosaics typical of production forests. Our results also indicate the importance of forest influence in determining potential conservation value of older secondary forest for beetles.

Solid-wood production from temperate eucalypt plantations: a Tasmanian case study

Since 1988, there has been a major focus in Tasmania on research for the management of temperate eucalypt plantations for solid wood. This coincided with the formal transfer of large areas of native forest that had previously been part of the production forest estate into reserves, a decision that triggered the establishment of eucalypt plantations for solid wood. This review summarises research on several key areas: silvicultural requirements for solid-wood production; wood properties of plantation-grown eucalypts and the influence of silviculture and genetics on these properties; factors influencing stem defect and decay; balancing silvicultural requirements with maintenance of tree vigour; and issues concerning wood processing and products. We conclude that there are still operational challenges to be confronted in the production of solid wood from plantations. If these can be overcome in the medium term, temperate plantation eucalypts have the potential to provide wood products that meet the requirements for appearance-grade material and that can compete in the same markets as wood from native forests. The bigger challenge at the national level will be to provide the log volumes of suitable material to meet the anticipated demand 25 to 30 years from now.

The genetic variation in the timing of heteroblastic transition in Eucalyptus globulus is stable across environments

Eucalyptus globulus is one of the best known examples of a heteroblastic plant. It exhibits a dramatic phase change from distinctive juvenile to adult leaves, but the timing of this transition varies markedly. We examined the genetic variation in the timing of heteroblastic transition using five large open-pollinated progeny trials established in north-western Tasmania. We used univariate and multi-variate mixed models to analyse data on the presence/absence of adult or intermediate foliage at age 2 years from a total of 14 860 trees across five trials, as well as height to heteroblastic phase change from one trial. Up to 566 families and 15 geographic subraces of E. globulus were represented in the trials. The timing of the heteroblastic transition was genetically variable and under strong genetic control at the subrace and within-subrace level, with single-trial narrow-sense heritability estimates for the binary trait averaging 0.50 (range 0.44–0.65). The degree of quantitative trait differentiation in the timing of heteroblastic transition among subraces, as measured by QST, exceeded the published level of neutral molecular marker (FST) differentiation in all cases, arguing that diversifying selection has contributed to shaping broad-scale patterns of genetic differentiation. Most inter-trial genetic correlations were close to one at the subrace and additive genetic levels, indicating that the genetic variation in this important developmental change is expressed in a stable manner and that genotype-by-environment interaction is minimal across the environments studied.

A cross‐continental comparison of plant and beetle responses to retention of forest patches during timber harvest

Timber harvest can adversely affect forest biota. Recent research and application suggest that retention of mature forest elements (retention forestry), including unharvested patches (or aggregates) within larger harvested units, can benefit biodiversity compared to clearcutting. However, it is unclear whether these benefits can be generalized among the diverse taxa and biomes in which retention forestry is practiced. Lack of comparability in methods for sampling and analyzing responses to timber harvest and edge creation presents a challenge to synthesis. We used a consistent methodology (similarly spaced plots or traps along transects) to investigate responses of vascular plants and ground-active beetles to aggregated retention at replicate sites in each of four temperate and boreal forest types on three continents: Douglas-fir forests in Washington, USA; aspen forests in Minnesota, USA; spruce forests in Sweden; and wet eucalypt forests in Tasmania, Australia. We assessed (1) differences in local (plot-scale) species richness and composition between mature (intact) and regenerating (previously harvested) forest; (2) the lifeboating function of aggregates (capacity to retain species of unharvested forest); and whether intact forests and aggregates (3) are susceptible to edge effects and (4) influence the adjacent regenerating forest. Intact and harvested forests differed in composition but not richness of plants and beetles. The magnitude of this difference was generally similar among regions, but there was considerable heterogeneity of composition within and among replicate sites. Aggregates within harvest units were effective at lifeboating for both plant and beetle communities. Edge effects were uncommon even within the aggregates. In contrast, effects of forest influence on adjacent harvested areas were common and as strong for aggregates as for larger blocks of intact forest. Our results provide strong support for the widespread application of aggregated retention in boreal and temperate forests. The consistency of pattern in four very different regions of the world suggests that, for forest plants and beetles, responses to aggregated retention are likely to apply more widely. Our results suggest that through strategic placement of aggregates, it is possible to maintain the natural heterogeneity and biodiversity of mature forests managed for multiple objectives.

The Australian SuperSite Network: A continental, long-term terrestrial ecosystem observatory

Ecosystem monitoring networks aim to collect data on physical, chemical and biological systems and their interactions that shape the biosphere. Here we introduce the Australian SuperSite Network that, along with complementary facilities of Australias Terrestrial Ecosystem Research Network (TERN), delivers field infrastructure and diverse, ecosystem-related datasets for use by researchers, educators and policy makers. The SuperSite Network uses infrastructure replicated across research sites in different biomes, to allow comparisons across ecosystems and improve scalability of findings to regional, continental and global scales. This conforms with the approaches of other ecosystem monitoring networks such as Critical Zone Observatories, the U.S. National Ecological Observatory Network; Analysis and Experimentation on Ecosystems, Europe; Chinese Ecosystem Research Network; International Long Term Ecological Research network and the United States Long Term Ecological Research Network. The Australian SuperSite Network currently involves 10 SuperSites across a diverse range of biomes, including tropical rainforest, grassland and savanna; wet and dry sclerophyll forest and woodland; and semi-arid grassland, woodland and savanna. The focus of the SuperSite Network is on using vegetation, faunal and biophysical monitoring to develop a process-based understanding of ecosystem function and change in Australian biomes; and to link this with data streams provided by the series of flux towers across the network. The Australian SuperSite Network is also intended to support a range of auxiliary researchers who contribute to the growing body of knowledge within and across the SuperSite Network, public outreach and education to promote environmental awareness and the role of ecosystem monitoring in the management of Australian environments.

A review of the outcomes of a decade of forest health surveillance of state forests in Tasmania

Summary Forest health surveillance, involving annual inspection of pine and eucalypt plantations by trained health observers, commenced in Tasmania in 1997. In the ten years since its introduction, forest health surveillance has become fully integrated into Forestry Tasmanias plantation management program. Importantly, forest health surveillance has provided value extending beyond the detection of pest and disease problems and has become a key element of the solutions for the management of health problems. The use of forest health surveillance to assist in the management of health problems at strategic, tactical and operational levels is discussed and illustrated with examples including establishing priorities for research, informing deployment strategies for managing pests or diseases, incursion responses and management in direct response to detection of pests or diseases.

Options for managing chrysomelid leaf beetles in Australian eucalypt plantations: reducing the chemical footprint

In Australia, eucalypt plantations require management to prevent economic damage by native chrysomelid leaf beetles, generally by aerially spraying a broad‐spectrum insecticide. These beetles also pose a serious threat to plantations in other countries. Various alternatives, both ‘landscape’ and ‘control’ options, for managing leaf beetles were reviewed and evaluated by a panel of experts. Options were scored on effectiveness, feasibility for use, impact on the environment, perceived social acceptability (including by certification bodies) and perceived cost. None of the options were scored as well as broad‐spectrum insecticide for effectiveness, feasibility and perceived cost, although virtually all of the other options scored better for environmental and social outcomes. The highest ranked options were the ‘landscape’ option of tree improvement to reduce susceptibility to insect attack, and the ‘control’ option of attract‐and‐kill traps. The next three ranks were two ‘landscape’ options aimed at enhancing the effectiveness of natural enemy populations by conserving their overwintering sites and their alternative food and hosts, and then silvicultural management. The best strategy for an Integrated Pest Management programme would be a combination of ‘landscape’ options to reduce the frequency of pest outbreaks and, if outbreaks occur, spraying with biological insecticides until attract‐and‐kill traps become available, possibly in combination with repellent sprays in a push–pull strategy. If control measures fail to prevent damaging defoliation, plantations could be fertilized to encourage recovery. Because most of the alternative options are not yet available, many research directions were identified, with the highest priorities being to develop plantation stock that is less susceptible to defoliation and to develop attractants for leaf beetles.