The biodiversity of urban and peri-urban forests and the diverse ecosystem services they provide as socio-ecological systems

Urban and peri-urban forests provide a variety of ecosystem service benefits for urban society. Recognising and understanding the many human-tree interactions that urban forests provide may be more complex but probably just as important to our urbanised society. This paper introduces four themes that link the studies from across the globe presented in this Special Issue: (1) human-tree interactions; (2) urban tree inequity; (3) carbon sequestration in our own neighbourhoods; and (4) biodiversity of urban forests themselves and the fauna they support. Urban forests can help tackle many of the "wicked problems" that confront our towns and cities and the people that live in them. For urban forests to be accepted as an effective element of any urban adaptation strategy, we need to improve the communication of these ecosystem services and disservices and provide evidence of the benefits provided to urban society and individuals, as well as the biodiversity with which we share our town and cities. © 2016 by the authors

The overlooked carbon loss due to decayed wood in urban trees

Decayed wood is a common issue in urban trees that deteriorates tree vitality over time, yet its effect on biomass yield therefore stored carbon has been overlooked. We mapped the occurrence and calculated the extent of decayed wood in standing Ulmus procera, Platanus × acerifolia and Corymbia maculata trees. The main stem of 43 trees was measured every metre from the ground to the top by two skilled arborists. All trees were micro-drilled in two to four axes at three points along the stem (0.3 m, 1.3 m, 2.3 m), and at the tree’s live crown. A total of 300 drilling profiles were assessed for decay. Simple linear regression analysis tested the correlation of decayed wood (cm²) against a vitality index and stem DBH. Decay was more frequent and extensive in U. procera, than P. acerifolia and least in C. maculata. Decay was found to be distributed in three different ways in the three different genera. For U. procera, decay did appear to be distributed as a column from the base to the live crown; whereas, decay was distributed as a cone-shape in P. acerifolia and was less likely to be located beyond 2.3 m. In C. maculata decay was distributed as pockets of variable shape and size. The vitality index showed a weak but not significant correlation with the proportion of decayed wood for P. acerifolia and C. maculata but not for U. procera. However, in U. procera, a strong and significant relationship was found between DBH and stem volume loss (R² = 0.8006, P = 0.0046, n = 15). The actual volume loss ranged from 0.17 to 0.75 m³, equivalent to 5%–25% of the stem volume. The carbon loss due to decayed wood for all species ranged between 69–110 kg per tree. Based on model’s calculation, the stem volume of U. procera trees with DBH ≥ 40 cm needs to be discounted by a factor of 13% due to decayed wood regardless of the vitality index. Decayed wood reduces significantly the tree’s standing volume and needs to be considered to better assess the carbon storage potential of urban forests

Net ecosystem carbon exchange of a dry temperate eucalypt forest

Forest ecosystems play a crucial role in the global carbon cycle by sequestering a considerable fraction of anthropogenic CO₂, thereby contributing to climate change mitigation. However, there is a gap in our understanding about the carbon dynamics of eucalypt (broadleaf evergreen) forests in temperate climates, which might differ from temperate evergreen coniferous or deciduous broadleaved forests given their fundamental differences in physiology, phenology and growth dynamics. To address this gap we undertook a 3-year study (2010–2012) of eddy covariance measurements in a dry temperate eucalypt forest in southeastern Australia. We determined the annual net carbon balance and investigated the temporal (seasonal and inter-annual) variability in and environmental controls of net ecosystem carbon exchange (NEE), gross primary productivity (GPP) and ecosystem respiration (ER). The forest was a large and constant carbon sink throughout the study period, even in winter, with an overall mean NEE of −1234 ± 109 (SE) g C m⁻² yr⁻¹. Estimated annual ER was similar for 2010 and 2011 but decreased in 2012 ranging from 1603 to 1346 g C m⁻² yr⁻¹, whereas GPP showed no significant inter-annual variability, with a mean annual estimate of 2728 ± 39 g C m⁻² yr⁻¹. All ecosystem carbon fluxes had a pronounced seasonality, with GPP being greatest during spring and summer and ER being highest during summer, whereas peaks in NEE occurred in early spring and again in summer. High NEE in spring was likely caused by a delayed increase in ER due to low temperatures. A strong seasonal pattern in environmental controls of daytime and night-time NEE was revealed. Daytime NEE was equally explained by incoming solar radiation and air temperature, whereas air temperature was the main environmental driver of night-time NEE. The forest experienced unusual above-average annual rainfall during the first 2 years of this 3-year period so that soil water content remained relatively high and the forest was not water limited. Our results show the potential of temperate eucalypt forests to sequester large amounts of carbon when not water limited. However, further studies using bottom-up approaches are needed to validate measurements from the eddy covariance flux tower and to account for a possible underestimation in ER due to advection fluxes

London Plane trees (Platanus x acerifolia) before, during and after a heatwave: Losing leaves means less cooling benefit

Platanus x acerifolia (London Plane) is a widely planted street tree throughout cities in temperate and Mediterranean climates. Heatwave intensity and frequency is likely to increase in these cities as a combined result of the urban heat island and climate change. High air temperature during heatwaves can lead to canopy leaf loss in vulnerable tree species, such as P. acerifolia. This rapid change in canopy cover may lead to subsequent reductions in ecosystem service benefits, such as shade cooling, human well-being, pollution interception and stormwater interception. This study investigates canopy leaf loss in two streets planted with P. acerifolia trees following a summer heatwave and the impacts upon street micrometeorological conditions and human thermal comfort. The plant area index of P. acerifolia, trees, and the micrometeorological conditions under and away from these trees was measured before and after a >43 °C heatwave in Melbourne, Australia. Physiological equivalent temperature was calculated from micrometeorological parameters to estimate human thermal comfort. Canopy loss was significant (30–50 %) and rapid and reduced thermal comfort benefits provided by canopy shade on two of the three warm summer days measured after the heatwave. However, the under-canopy areas of the street maintained a cooler micrometeorological conditions than areas in the open. This study suggests that as summer air temperature extremes and heatwave frequency increase in urban areas, more vulnerable urban tree species may experience sparse canopy cover throughout summer months reducing some ecosystem service benefits when they are needed most

In a heatwave, the leafy suburbs are even more advantaged

Summer brings out the heliophobe in many of us. It\u27s manageable if you live in a house that stays cool when shut up tight. It helps if you\u27re physically capable of crossing to the shadier side of a hot street. It\u27s even better if you can work from home or use public transport stops that enjoy the cover of buildings or trees. We have reason to think a lot about shade these days, especially as the heatwaves roll in. At such times, shade is our friend. On top of the existing urban heat island effect, the incidence of extreme heat events is rising. These events are also lasting longer and getting hotter. Coverage for all is a wonderful ideal, and the federal government has announced plans to set urban canopy targets. But, in the meantime, some communities and areas need trees more urgently than others. Shade is not only a matter of public health; it is a social equity issue. In a warming city like Melbourne, some of the most socially vulnerable people are in areas that are most exposed to extreme heat. Our pilot research in Melbourne suggests that integrated social and ecological data sets should be used to develop programs that reduce socioecological vulnerability

The biodiversity of urban and peri-urban forests and the diverse ecosystem services they provide as socio-ecological systems

Urban and peri-urban forests provide a variety of ecosystem service benefits for urban society. Recognising and understanding the many human-tree interactions that urban forests provide may be more complex but probably just as important to our urbanised society. This paper introduces four themes that link the studies from across the globe presented in this Special Issue: (1) human-tree interactions; (2) urban tree inequity; (3) carbon sequestration in our own neighbourhoods; and (4) biodiversity of urban forests themselves and the fauna they support. Urban forests can help tackle many of the "wicked problems" that confront our towns and cities and the people that live in them. For urban forests to be accepted as an effective element of any urban adaptation strategy, we need to improve the communication of these ecosystem services and disservices and provide evidence of the benefits provided to urban society and individuals, as well as the biodiversity with which we share our town and cities. © 2016 by the authors

The Biodiversity of Urban and Peri-Urban Forests and the Diverse Ecosystem Services They Provide as Socio-Ecological Systems

Urban and peri-urban forests provide a variety of ecosystem service benefits for urban society. Recognising and understanding the many human–tree interactions that urban forests provide may be more complex but probably just as important to our urbanised society. This paper introduces four themes that link the studies from across the globe presented in this Special Issue: (1) human–tree interactions; (2) urban tree inequity; (3) carbon sequestration in our own neighbourhoods; and (4) biodiversity of urban forests themselves and the fauna they support. Urban forests can help tackle many of the “wicked problems” that confront our towns and cities and the people that live in them. For urban forests to be accepted as an effective element of any urban adaptation strategy, we need to improve the communication of these ecosystem services and disservices and provide evidence of the benefits provided to urban society and individuals, as well as the biodiversity with which we share our town and cities

High potential, but low actual, glycine uptake of dominant plant species in three Australian land-use types with intermediate N availability

The traditional view of the nitrogen (N) cycle has been challenged since the discovery that plants can compete with microbes for low molecular weight (LMW) organic N. Despite a number of studies that have shown LMW organic N uptake by plants, there remains a debate on the overall ecological relevance of LMW organic N uptake by plants across ecosystems with different N availabilities. We here report patterns of glycine N uptake by plants from three different Australian land-use types with intermediate N availability and low inherent glycine concentrations in the soil. Using 15N labeled tracers, we tested the potential of these plants to acquire glycine in ex-situ laboratory experiments and attempted to validate these results in the field by determining actual uptake of glycine by plants directly from the soil. We found in the ex-situ experiments that plants from all three land-use types were able to take up significant amounts of glycine. In contrast, glycine uptake directly from the soil was minimal in all three land-use types and 15N tracers were largely immobilized in the soil organic N pool. Our study confirms that the potential for LMW organic N uptake by plants is a widespread phenomenon. However, our in-situ experiments show that in the three land-use types tested here plants are inferior competitors for LMW organic N and rely on NH 4 + as their main N source. In contrast to several previous studies in arctic, alpine and even temperate ecosystems, our study suggests that in ecosystems with intermediate N availability, mineral N is the plants’ main N source, while LMW organic N is of less ecological relevance to plant N nutrition

Leaf trait plasticity means green facades are a flexible nature-based solution for vertical greening under full-sun and heavy shade conditions

Climbing plants that cover building walls (indirect green façades) are a nature-based solution for urban greening in dense urban areas. Green facades can provide important ecosystem service benefits such as cooling, biodiversity habitat and visualamenity and screening. However, as new buildings are constructed the urban form changes and this can create heavy shade that impacts the growth, health and function of existing green façade climbing plants. Climbing plants may respond to increased shade through plasticity in some leaf traits (e.g. specific leaf area, photosynthetic rate or leaf chlorophyll content). However, deciduous climbing plant species are likely to be more plastic than evergreen species as they have less conservative resource strategies.In this study we measured morphological, physiological and biochemical leaf traits of seven mature climbing plant species growing in full-sun and in response to the addition of heavy shade (via shade cloth). All seven climbing plant species significantly increased specific leaf area; whilst physiological traits relating to light compensation and thermal tolerance remained unchanged in response to heavy shade. Other physiological, biochemical or morphological traits only changed in response to heavy shade for certain species. There was a very similar level of phenotypic plastic response to shade by both deciduous and evergreen climbing plant species, except for photosynthetic capacity which was significantly more plastic (greater reduction) in deciduous species.Our results suggest most climbing plant species can maintain growth and physiological function when light conditions change from full-sun to heavy shade. These green façade plants are likely to maintain building wall coverage, healthy function and delivery of ecosystem service benefits in cities. In areas experiencing densification and new building shadows, deciduous climbing plant species appear to respond slightly better to heavy shade and may be more suitable for green façades that may become shaded by future building