Cristina Antunes

Evaluating green infrastructure in urban environments using a multi-taxa and functional diversity approach.

Forested areas within cities host a large number of species, responsible for many ecosystem services in urban areas. The biodiversity in these areas is influenced by human disturbances such as atmospheric pollution and urban heat island effect. To ameliorate the effects of these factors, an increase in urban green areas is often considered sufficient. However, this approach assumes that all types of green cover have the same importance for species. Our aim was to show that not all forested green areas are equal in importance for species, but that based on a multi-taxa and functional diversity approach it is possible to value green infrastructure in urban environments. After evaluating the diversity of lichens, butterflies and other-arthropods, birds and mammals in 31 Mediterranean urban forests in south-west Europe (Almada, Portugal), bird and lichen functional groups responsive to urbanization were found. A community shift (tolerant species replacing sensitive ones) along the urbanization gradient was found, and this must be considered when using these groups as indicators of the effect of urbanization. Bird and lichen functional groups were then analyzed together with the characteristics of the forests and their surroundings. Our results showed that, contrary to previous assumptions, vegetation density and more importantly the amount of urban areas around the forest (matrix), are more important for biodiversity than forest quantity alone. This indicated that not all types of forested green areas have the same importance for biodiversity. An index of forest functional diversity was then calculated for all sampled forests of the area. This could help decision-makers to improve the management of urban green infrastructures with the goal of increasing functionality and ultimately ecosystem services in urban areas.

Do climatic and habitat conditions affect the reproductive success of an invasive tree species? An assessment of the phenology of Acacia longifolia in Portugal

Plant phenological events are some of the most sensitive indicators of how plant species respond to favourable or stressful conditions. The evaluation of the flowering phenology of invasive plant species is particularly relevant, mainly due to its crucial importance in determining plant reproductive success and the outcome of invasion. We studied the phenology of Acacia longifolia, an aggressive, invasive plant species in the Mediterranean basin. We measured its vegetative growth and reproductive traits, specifically flowering phenophases and fruit production, under different climatic conditions (mesic and xeric Mediterranean climates), and in two different habitats (pine forest and open area). All the measured phenological phases began earlier at the xeric site than at the mesic site; this was particularly evident when comparing reproductive phenophases. Flowering dates were significantly associated with air temperature, with early peak flowering dates linked to increases in air temperature. The number of fruiting flowers per inflorescence in A. longifolia trees was higher at the mesic site, mainly in the pine forest plot, and the number of aborted fruits was notably lower than in the xeric plots. The presence of a pine forest at the mesic site strongly influenced the flowering phenology of A. longifolia and resulted in the highest reproductive success and the lowest branch growth rate. Our results demonstrate that a combination of climate and forest structure can cause pronounced differences in phenology and reproductive success of A. longifolia. These data can help to understand the variations in invasive rates of A. longifolia across the Mediterranean basin.

Understanding plant drought resistance in a Mediterranean coastal sand dune ecosystem: differences between native and exotic invasive species

Mediterranean coastal dunes are habitats of great conservation interest, with a distinctive and rich flora. In the last century, Acacia spp., native from Australia, have been introduced in Portugal, with the objective of stabilizing sand dunes, and since have become dominant in numerous sand dune habitats. This invasion process led to the reduction of native plant species richness, changed soil characteristics and modified habitat’s microclimatic characteristics. The aim of this research was to typify and compare, in Mediterranean sand dune ecosystems, the ecophysiological responses to drought of Helichrysum italicum and Corema album, two native species, and Acacia longifolia, an exotic invasive species. We addressed the following specific objectives: (i) to compare water relations and water use efficiencies, (ii) to evaluate water stress, (iii) to assess water use strategies and water sources used by plants and (iv) to evaluate the morphological adaptations at leaf and phyllode level. In order to obtain an integrative view of ecophysiological patterns, water relations and performance measuring methods have been applied: predawn (ψPD) and midday (ψMD) water potential, chlorophyll a fluorescence, oxygen isotopic composition of xylem, rain and groundwater (δ¹⁸O) and leaf carbon isotopic discrimination (Δ¹³C). The leaf characteristics of the three species, as well as the histochemistry of non-glandular trichome cell walls, were also studied to identify morpho-traits related to drought resistance. The results support our initial hypothesis: although A. longifolia clearly possesses a degree of resistance to water stress, such ability is provided by a different water strategy, when compared to native species. Natives relied on morphological adaptations to restrict water loss, whereas the invasive species adjusted the water uptake as a way to balance their limited ability of restricting water loss. We corroborate that woody native species (i) have a conservative water-saving strategy and minor seasonal variations relative to invasive species, (ii) use enriched water sources during drought periods, indicating different water sources and root systems comparing with invasive species and (iii) present drought leaf morpho-functional adaptations related with limiting water loss. Comparing the physiological performance of invasive and native species can offer causal explanations for the relative success of alien plant invasions on sand dunes ecosystems.

Groundwater drawdown drives ecophysiological adjustments of woody vegetation in a semi-arid coastal ecosystem

Predicted droughts and anthropogenic water use will increase groundwater lowering rates and intensify groundwater limitation, particularly for Mediterranean semi-arid ecosystems. These hydrological changes may be expected to elicit differential functional responses of vegetation either belowground or aboveground. Yet, our ability to predict the impacts of groundwater changes on these ecosystems is still poor. Thus, we sought to better understand the impact of falling water table on the physiology of woody vegetation. We specifically ask (a) how is woody vegetation ecophysiological performance affected by water table depth during the dry season? and (b) does the vegetation response to increasing depth to groundwater differ among water-use functional types? We examined a suite of physiological parameters and water-uptake depths of the dominant, functionally distinct woody vegetation along a water-table depth gradient in a Mediterranean semi-arid coastal ecosystem that is currently experiencing anthropogenic groundwater extraction pressure. We found that groundwater drawdown did negatively affect the ecophysiological performance of the woody vegetation. Across all studied environmental factors, depth to groundwater was the most important driver of ecophysiological adjustments. Plant functional types, independent of groundwater dependence, showed consistent declines in water content and generally reduced C and N acquisition with increasing depths to groundwater. Functional types showed distinct operating physiological ranges, but common physiological sensitivity to greater water table depth. Thus, although differences in water-source use exist, a physiological convergence appeared to happen among different functional types. These results strongly suggest that hydrological drought has an important impact on fundamental physiological processes, constraining the performance of woody vegetation under semi-arid conditions. By disentangling the functional responses and vulnerability of woody vegetation to groundwater limitation, our study establishes the basis for predicting the physiological responses of woody vegetation in semi-arid coastal ecosystems to groundwater drawdown.

Water source partitioning among plant functional types in a semi-arid dune ecosystem

Co-ordinating Editor: José Paruelo Abstract Question(s): The aim of this work was to characterize the main water sources used by the woody plant community of a semiarid coastal dune ecosystem. We ask: Do the seasonal water sources used by plants differ between functional types? Does the seasonal drought promote shifts towards deeper soil layers in all plants? Does greater use of deep soil water enables the maintenance of a more favorable plant water status? Do watersourcesuse strategies mirror overall drought strategies? Location: Semiarid coastal dune system in Doñana Biological Reserve, southwest Spain. Methods: We analyzed the oxygen isotope composition of xylem water of fourteen coexisting woody species and compared it to water sources (soil water at different depths, rain and groundwater), both in spring and dry summer. Bayesian isotope mixing models were used to estimate the proportion of each water source used by plants. We tested the influence of different (categorical) traits on plants’ watersourceuse. We evaluated the relationships between the use of deep soil water and ecophysiological parameters related to water economy (leaf δ13C and reflectance waterindex). Results: A greater similarity between species was found in periods of higher water availability (spring). Contrastingly, during the dry period the traits considered showed a significant effect on the water sources used and a high interspecific differentiation was observed. Accordingly, species clustered in five wateruse functional groups, exploring water from shallower to deeper soil layers. Greater use of deep soil layers in the dry season was linked to a better seasonal maintenance of plant water status. Conclusions: Coexisting plant functional types segregated along a spectrum of watersourceuse under extremely dry conditions, evidencing great soil water partitioning. Relevant seasonal wateruse shifts towards deeper soil layers were observed, but not in all species. Furthermore, we confirmed that the watersourceuse behavior accompanied broader strategies of drought resistance.