Joe Fontaine

Forest die-offs associated with drought and heat have recently occurred across the globe, raising concern that associated changes in fuels and microclimate could link initial die-off disturbance to subsequent fire disturbance. Despite widespread concern, little empirical data exist. Following forest die-off in the Northern Jarrah Forest, southwestern Australia, we quantified fuel dynamics and associated microclimate for die-off and control plots. Sixteen months post-die-off, die-off plots had significantly elevated 1-hr fuels (11.8 vs. 9.8 tons ha-1) but not larger activity fuel classes (10-hr and 100-hr fuels). Due to stem mortality, die-off plots had significantly greater standing dead wood mass (100 vs. 10 tons ha-1), visible sky (hemispherical images analysis: 31% vs. 23%) and potential near-ground solar radiation input (measured as Direct Site Factor: 0.52 vs. 0.34). Supplemental, mid-summer microclimate measurements (temperature, relative humidity and wind speed) were combined with long-term climatic data and fuel load estimates to parameterize fire behaviour models. Fire spread rates were predicted to be 30% greater in die-off plots with relatively equal contributions from fuels and microclimate, highlighting need for operational consideration by fire managers. Our results underscore potential for drought-induced tree die-off to interact with subsequent fire under climate change.

Although restoration ecology has developed rapidly as a scientific discipline, there are still considerable gaps in integrating above-and belowground linkages between plants and their associated soil microbial communities into restoration efforts. However, understanding these linkages may assist in improving restoration success. The aim of this study was to assess how post-mining soil stockpile age affects plant biomass and soil microbial activity, particularly plant root symbionts such as rhizobia and arbuscular mycorrhizal fungi (AMF). We grew a legume species Acacia saligna (Fabaceae) in 1, 2, 3, 5 and 10 year old stockpile soils collected from a sand mine near Perth, Western Australia under controlled glasshouse conditions. We assessed whether plant biomass, specific root length (SRL) and root diameter (D) decrease with stockpile age. Furthermore, we investigated how stockpile age affected the distribution and the number of effective nodules, nodule biomass and AMF colonization in roots. Results revealed that plant biomass was the lowest and SRL was the highest in plants grown in oldest soils. Soil age had a negligible effect on rhizobial abundance. Colonization of AMF significantly increased with stockpile age suggesting that AMF spores and hyphae are present in old stockpiles. Thus, plants were not constrained by the absence of rhizobial and AMF propagules in old soils. However, our results revealed that plants grown in oldest soils were overall smallest but invested most into producing long and thin roots that had highest AMF colonization rates suggesting that these plants were plausibly struggling for growth in oldest stockpiles.

Projected effects of climate change across many ecosystems globally include more frequent disturbance by fire and reduced plant growth due to warmer (and especially drier) conditions. Such changes affect species–particularly fire-intolerant woody plants–by simultaneously reducing recruitment, growth, and survival. Collectively, these mechanisms may narrow the fire interval window compatible with population persistence, driving species to extirpation or extinction. We present a conceptual model of these combined effects, based on synthesis of the known impacts of climate change and altered fire regimes on plant demography, and describe a syndrome we term “interval squeeze”. This model predicts that interval squeeze will increase woody plant extinction risk and change ecosystem structure, composition, and carbon storage, especially in regions projected to become both warmer and drier. These predicted changes demand new approaches to fire management that will maximize the in situadaptive capacity of species to respond to climate change and fire regime change.

Mediterranean biomes represent five biodiversity hotspots worldwide and cover just 2% of the Earth's land area; however, they support 20% of the Earth's known plant diversity. The Jarrah forest of South West, Western Australia, represents one of these valuable biomes. Documented climate change in Western Australia shows 35 years of consistently less rainfall and higher temperatures, with an extreme drought event in 2011 resulting in mortality of 1.7% or 19,000 ha of Northern Jarrah forest. To assess drought impact on vegetation of the Northern Jarrah forest, sites were chosen with a steep gradient from areas of canopy collapse to healthy forest. This provided an opportunity to assess the forest vegetation across an ecotone using space for time substitution. Our objectives were: 1) to determine factors affecting drought /heatwave induced vegetation mortality and 2) to assess differences in species response to this event. Results from this study show mortality of species occurs in zones on sites of drought induced canopy collapse in the Northern Jarrah Forest. Midstorey mortality is determined by soil depth. Results, indicate a complex interaction between plants with differing root functional traits and soil depth, determines the collapse response in an extreme drought event. There is an ongoing shift in the species composition and structure of the forest in and around areas of drought induced canopy collapse. We anticipate the use of presence /absence of midstorey, as a proxy for soil depth, and stand composition to predict areas of forest likely to collapse in the future.

Frequency and intensity of disturbance is projected to increase for many ecosystems globally, with uncertain consequences, particularly when disturbances occur in rapid succession. Implications of these changes are most urgent in fire-prone regions undergoing warming and drying (e.g. Mediterranean type ecosystems) where increased fire (both managed and unmanaged) may interact with increasing drought leading to punctuated tree mortality and recruitment failure. We quantified tree mortality and recruitment following historic drought in Banksia-dominated woodlands surrounding Perth, Western Australia. Stands experienced drought alone (N=18), drought and wildfire (N=11) or drought and prescribed fire (N=15). We evaluated species and individual tree susceptibility to mortality and evidence for compound disturbance–whether wildfire or prescribed fire during drought increased tree mortality risk. We further quantified regeneration to understand if the drought or drought-fire event resulted in longer term shifts in stand structure and tree species composition. We observed a shift in dominance towards Eucalyptus and away from Banksia with eIevated mortality of large Banksia. Evidence of compound disturbance effects was modest. Improved understanding of disturbance interactions are critical to forecasting effects of climate change and informing fire management.

Floristically rich and ecologically complex, Mediterranean-type ecosystems are rapidly being cleared for urban, horticultural and industrial development. A prime example is Banksia woodland, an ecosystem restricted to the Swan Coastal Plain in Western Australia. In order to compensate for the clearing of Banksia woodland due to urbanization, land developers are required to attempt biodiversity offsets whereby topsoil from newly cleared landscapes can be moved to degraded land with the aim of restoring Banksia woodland. Yet the science and practice of restoration ecology is not sufficiently advanced to know for certain that this aim can be achieved. Assessing the efficacy of a spectrum of restoration techniques will provide new insights for the restoration of endangered plant communities, and critically, a test of the feasibility of biodiversity off setting. The topsoil was subjected to three site-scale treatments: altering topsoil depth, ripping & herbivore exclosures. Additionally, six plot-scale treatments were applied to explore germination effect (three smoke water-related, topsoil heating) and competition effect (herbicide & artificial shade installation) on native seedlings’ emergence and survival. Significantly fewer seedlings emerged from ripped (17.01 ±1.03 SE) than unripped plots (37.99 ±2.05 SE). Species richness was similar across all treatments with a total number of native plant species emerging from the transferred topsoil of 129 in the first year and 115 in the second year. Mean survival rates of native perennial seedlings were very low (year I = 11.1% & year II = 1.2%). The maximum average survival was recorded under artificial shade (41% ±12.2 SE).

Delayed seed release (serotiny) is a syndrome of adaptive significance in a randomly fluctuating environments such as fire-prone and arid ecosystems. Selective forces involving fire, rainfall and seed predators have been suggested as factors influencing serotiny. Callitris preissii is a conifer in the Cupressaceae found only in Australia and New Caledonia and it is regarded as “fire sensitive”. It has excellent potential for erosion control of sandy, alkaline coastal sites and has been used in revegetation in many region in Western Australia. We compared the degree of serotiny among different populations and related this to fire history, climate and seedling predators.The relative ages of cohorts of closed cones were determined on trees in populations ranging from arid interior sites to islands with much higher annual rainfall. The individuals with the greatest serotiny grow at inland sites (Kalgoorlie and Lake Grace), while the plants with the lowest serotiny were recorded at island sites. Seedling recruitment after fire at Boorabin National Park burnt in 2007 was dense and at Cape Le Grand National Park near the south coast of Western Australia a patchy fire produced many seedlings in burnt areas. However in both areas seedlings were absent from unburnt sections. The strong serotiny at these sites ensures an abundant seed rain after fire kills adult plants. The weaker serotiny at the island sites might be thought to relate to the possibility that there is interfire recruitment of the plants.

Drought and heat-induced forest dieback have recently been reported from a wide range of forest types globally. Flow-on effects of such dieback events and their interaction with subsequent processes is receiving increasing interest. One key impact may be elevated fine fuel loads, which drive increased intensity and severity of fire. In order to determine changes in the fuel complexes following a widespread, drought-induced canopy dieback event in the Northern Jarrah Forest (NJF), southwestern Australia, we quantified surface fi ne fuel loading in severely-affected and minimally-affected forest areas. Sixteen months following the dieback event, severely affected plots had significantly higher fuel loadings (1hr fuels) than areas minimally affected by the dieback event. Total fuels were greater in severely affected areas. These are expected to increase as trees fall. This study has added to the work describing the impact of drought-induced canopy dieback events by reporting changes in fuel complexes. With climate projections for many regions of the world, such as those for southwestern Australia, suggestive of increasing aridity and temperatures, it is critical that we increase our understanding of the effects of, and responses to, drought-induced canopy dieback events in forest ecosystems

Although records of forest dieback from drought are becoming increasingly common, little is known about the response of forests to this disturbance. We examined the changes in tree health, forest structure, and composition following an historic drought-induced forest dieback event on severely- and minimally-affected forest plots in the Northern Jarrah Forest of south-western Australia. Forest structure and composition were measured at 0, 16, and 26 months post-disturbance. Tree health dynamics suggest the dieback resulted from severe, acute stress. Overstory trees in severely-affected forest patches responded strongly, with 66% of trees resprouting by 16 months post-dieback. Recruitment of new individuals was higher in severely-affected plots, and living tree densities reached pre-dieback levels by 26 months following the event. On severely-affected plots, large diameter trees that died were replaced by greater numbers of small stems, decreasing the height of forest canopy and creating a dense thicket of regrowth. No direct evidence of forest composition change was detected in overstory trees. We propose that adequate rainfall following the event combined with species adaptation to drought contributed to the rapid response of affected trees. This research highlights the stabilizing properties of Mediterranean-type forests and their resilience in preventing ecosystem-type changes seen elsewhere following drought.