School Microclimates

Outdoor school environments need to be safe, stimulate physical and cognitive development of children and encourage learning. These key requirements are jeopardised by increasing summer heat. Summer heat limits outdoor activities and has adverse effects on physical wellbeing of school children and teachers. Children are particularly vulnerable to heat as they regulate their core temperature through convection, which becomes less effective when it is hot. Based on empirical data collections, this report provides more than 20 practical recommendations on how to reduce the impacts of outdoor heat. Although these recommendations were devised based on work around a public school in Western Sydney, their universal character allows applying them to any school or other urban build infrastructure. Avoiding the use of artificial grass in unshaded spaces, shading black asphalt, allowing natural air flows and using shade materials with highly reflective upper surfaces should be fundamental principles in design and building guidelines for heat-smart schools

Impacts of key threatening processes on grass-dominated ecosystems in a high CO₂ world: a case study of Cumberland Plain woodland

Thesis by publication.Includes bibliographical references.Chapter 1. Introduction -- Chapter 2. Leaf area index drives soil water availability and extreme drought-related mortality under elevated CO₂ levels in a model temperate grassland system -- Chapter 3. Extreme drought associated reductions in native grass biomass facilitates the invasion of an exotic grass into a temperate model grassland system -- Chapter 4. Competitive interactions between established grasses and woody plant seedlings under elevated CO₂ levels are mediated by soil water availability -- Chapter 5. Leaf flammability and fuel load accumulation increase under elevated CO₂ levels in a model grassland system -- Chapter 6. Discussion.Rising atmospheric CO₂ concentration is one of the best documented global changes of the past half century and may have a profound effect on the structure and functions of ecosystems globally. Grass-dominated ecosystems (hereon referred to as grasslands) may be particularly vulnerable to this increase in atmospheric CO₂ concentration due to their highly dynamic nature. Historically, the major threat to grasslands was their conversion to an agricultural landscape. Although this conversion continues today, grasslands face a number of other threatening processes whose impacts may be exacerbated by rising atmospheric CO₂ concentration. This thesis explores how these threatening processes interact with elevated CO₂ levels and each other to impact the structure and function of grasslands. Four threatening processes to grasslands that may be substantially modified under elevated CO₂ levels were identified and examined in this thesis. These threatening processes were extreme climatic events, exotic plant invasion, woody plant encroachment and changes to fire regime. Data for all chapters were obtained by carrying out manipulative CO₂ glasshouse experiments using Cumberland Plain Woodland, an open grassy woodland community of western Sydney, as the model grassland system. Chapter 2 and 4 test the vulnerability of grasslands to extreme drought and woody plant encroachment under elevated CO₂ levels. Chapter 3 investigates the interaction between extreme drought and elevated CO2 levels and how this may facilitate exotic plant invasion. Chapter 5 examines the changes in leaf flammability and fuel load accumulation of grassland species under elevated CO₂ levels.Mode of access: World wide web1 online resource (174 page ) graphs, table

Leaf area index drives soil water availability and extreme drought-related mortality under elevated CO2 in a temperate grassland model system.

The magnitude and frequency of climatic extremes, such as drought, are predicted to increase under future climate change conditions. However, little is known about how other factors such as CO2 concentration will modify plant community responses to these extreme climatic events, even though such modifications are highly likely. We asked whether the response of grasslands to repeat extreme drought events is modified by elevated CO2, and if so, what are the underlying mechanisms? We grew grassland mesocosms consisting of 10 co-occurring grass species common to the Cumberland Plain Woodland of western Sydney under ambient and elevated CO2 and subjected them to repeated extreme drought treatments. The 10 species included a mix of C3, C4, native and exotic species. We hypothesized that a reduction in the stomatal conductance of the grasses under elevated CO2 would be offset by increases in the leaf area index thus the retention of soil water and the consequent vulnerability of the grasses to extreme drought would not differ between the CO2 treatments. Our results did not support this hypothesis: soil water content was significantly lower in the mesocosms grown under elevated CO2 and extreme drought-related mortality of the grasses was greater. The C4 and native grasses had significantly higher leaf area index under elevated CO2 levels. This offset the reduction in the stomatal conductance of the exotic grasses as well as increased rainfall interception, resulting in reduced soil water content in the elevated CO2 mesocosms. Our results suggest that projected increases in net primary productivity globally of grasslands in a high CO2 world may be limited by reduced soil water availability in the future

Competitive interactions between native and invasive exotic plant species are altered under elevated carbon dioxide

We hypothesized that the greater competitive ability of invasive exotic plants relative to native plants would increase under elevated CO2 because they typically have traits that confer the ability for fast growth when resources are not limiting and thus are likely to be more responsive to elevated CO2. A series of competition experiments under ambient and elevated CO2 glasshouse conditions were conducted to determine an index of relative competition intensity for 14 native-invasive exotic species-pairs. Traits including specific leaf area, leaf mass ratio, leaf area ratio, relative growth rate, net assimilation rate and root weight ratio were measured. Competitive rankings within species-pairs were not affected by CO2 concentration: invasive exotic species were more competitive in 9 of the 14 species-pairs and native species were more competitive in the remaining 5 species-pairs, regardless of CO2 concentration. However, there was a significant interaction between plant type and CO2 treatment due to reduced competitive response of native species under elevated compared with ambient CO2 conditions. Native species had significantly lower specific leaf area and leaf area ratio under elevated compared with ambient CO2. We also compared traits of more-competitive with less-competitive species, regardless of plant type, under both CO2 treatments. More-competitive species had smaller leaf weight ratio and leaf area ratio, and larger relative growth rate and net assimilation rate under both ambient and elevated CO2 conditions. These results suggest that growth and allocation traits can be useful predictors of the outcome of competitive interactions under both ambient and elevated CO2 conditions. Under predicted future atmospheric CO2 conditions, competitive rankings among species may not change substantially, but the relative success of invasive exotic species may be increased. Thus, under future atmospheric CO2 conditions, the ecological and economic impact of some invasive exotic plants may be even greater than under current conditions.10 page(s

Leaf flammability and fuel load increase under elevated CO₂ levels in a model grassland

Fire is a common process that shapes the structure of grasslands globally. Rising atmospheric CO₂ concentration may have a profound influence on grassland fire regimes. In this study, we asked (1) does CO₂ and soil P availability alter leaf flammability (ignitibility and fire sustainability); (2) are leaf tissue chemistry traits drivers of leaf flammability, and are they modified by CO₂ and soil P availability?; (3) does CO₂ and soil P availability alter fuel load accumulation in grasslands; and (4) does CO₂ and soil P availability alter the resprouting ability of grassland species? We found that leaf flammability increased under elevated CO₂ levels owing to decreased leaf moisture content and foliar N, whereas fuel load accumulation increased owing to decreased foliar N (slower decomposition rates) and increased aboveground biomass production. These plant responses to elevated CO₂ levels were not modified by soil P availability. The increase in leaf flammability and fuel load accumulation under elevated CO₂ levels may alter grassland fire regimes by facilitating fire ignition as well as shorter fire intervals. However, the increased root biomass of grasses under elevated CO₂ levels may enhance their resprouting capacity relative to woody plants, resulting in a shift in the vegetation structure of grasslands.9 page(s

Soil water content across all mesocosms under ambient and elevated CO₂ levels.

<p>Mean soil water content across all mesocosms under ambient and elevated CO₂ levels over the 30 days prior to the extreme drought treatment and the drought/recovery cycles. The letters on the x-axis represent different phases of the experiment with I = the 30 day initial period prior to the extreme drought treatment, D = drought period and R = recovery period. Error bars represent one standard error.</p

Are fire resprouters more carbon limited than non-resprouters? Effects of elevated CO₂ on biomass, storage and allocation of woody species

Resprouting ability is a key functional trait determining plant responses and vegetation dynamics after disturbances such as fire that shape most global biomes. It is likely that rising atmospheric CO₂ concentrations will alter resource allocation patterns in plants which in turn will alter resprouting responses. In this study, we asked: (1) do resprouters have greater allocation to storage than non-resprouters?; (2) if so, do resprouters account for this negative carbon balance by having reduced growth?; and (3) do resprouters have a relatively weaker growth response compared to non-resprouters under elevated CO₂ levels due to their increased allocation to storage? To address these questions, we grew congeneric species-pairs of shrubs common to south-eastern Australia with contrasting resprouting abilities under ambient and elevated CO₂ levels. We found that resprouters in general allocated more resources to storage (root non-structural carbohydrates and biomass) and had less total biomass than non-resprouters. Under elevated CO₂ levels both sprouting types increased biomass production, suggesting they were carbon limited. Surprisingly, the resprouters allocated this additional carbon to biomass rather than to storage. This suggests that although elevated CO₂ levels may not affect resprouting ability directly in resprouters, it may enhance other aspects of persistence such as escapability and bud protection. Furthermore, non-resprouters may also benefit from the additional carbon by being able to set seed more quickly and increase seed production thus enhancing their recruitment after fire. Thus, the relative benefits of elevated CO₂ levels on resprouters versus non-resprouters remain equivocal.9 page(s

Rapid field assessments of impacts of plant fungal pathogen Austropuccinia psidii on five high priority Myrtaceae species in New South Wales, Australia

In 2010, the plant fungal pathogen Austropuccinia psidii was detected in Australia. It has since spread rapidly through the eastern states of Australia causing significant population declines in a number of susceptible species. However, there are still a number of potentially vulnerable species that lack the necessary field observations that are needed to accurately gauge the risk Austropuccinia psidii poses to them. Because of this, rapid field assessments of these species have been given the utmost priority. In the spring of 2018 (October) we carried out rapid field assessments for five high priority species. We did not observe active Austropuccinia psidii infection on any of the species at the time of assessment despite the majority of individuals having susceptible new flush. However, we did find evidence of significant previous infection (branch dieback) in the largest Archirhodomyrtus beckleri population we assessed. Therefore, to confirm our observations, it is necessary to re-assess this population when environmental conditions are more favourable for infection to occur in order

Reductions in native grass biomass associated with drought facilitates the invasion of an exotic grass into a model grassland system

The invasion success of exotic plant species is often dependent on resource availability. Aspects of climate change such as rising atmospheric CO₂ concentration and extreme climatic events will directly and indirectly alter resource availability in ecological communities. Understanding how these climate change-associated changes in resource availability will interact with one another to influence the invasion success of exotic plant species is complex. The aim of the study was to assess the establishment success of an invasive exotic species in response to climate change-associated changes in resource availability (CO₂ levels and soil water availability) as a result of extreme drought. We grew grassland mesocosms consisting of four co-occurring native grass species common to the Cumberland Plain Woodland of western Sydney, Australia, under ambient and elevated CO₂ levels and subjected them to an extreme drought treatment. We then added seeds of a highly invasive C₃ grass, Ehrharta erecta, and assessed its establishment success (biomass production and reproductive output). We found that reduced biomass production of the native grasses in response to the extreme drought treatment enhanced the establishment success of E. erecta by creating resource pulses in light and space. Surprisingly, CO₂ level did not affect the establishment success of E. erecta. Our results suggest that the invasion risk of grasslands in the future may be coupled to soil water availability and the subsequent response of resident native vegetation therefore making it strongly context-dependent.9 page(s

Leaf area index across all grass species for each CO₂×plant type combination.

<p>Mean leaf area index across all grass species for each CO₂×physiology and CO₂×origin combination. Error bars represent one standard error. Letters indicate significant differences at p<0.05.</p