Dry Ecosystems Research Articles

Sequence of plant responses to droughts of different timescales: lessons from holm oak (Quercus ilex) forests

The functional traits of plants in regions of the world with a Mediterranean climate have been shaped to tolerate periods of water deficit. These species are adapted to summer droughts but may not be able to cope with future increases in drought intensity, duration, and/or frequency. Here, we review the mechanisms and traits of drought resistance and recovery of the well-studied holm oak (Quercus ilex), which we propose as a model species for Mediterranean-type ecosystems. Our aim was to understand the differences and links between the responses of Q. ilex to summer droughts, extreme droughts, and long-term drought experiments. A main goal was to provide an integral picture of drought responses across organisational and temporal scales for identifying the most relevant processes that are likely to contribute to determining the future of Mediterranean vegetation. Evidence from long-term drought experiments showed that acclimation processes from the molecular (e.g. epigenetic changes) to the ecosystem level (e.g. reductions in stand density) mitigate the effects of drought. Changes in leaf morphology and hydraulics, leaf-to-shoot allometry, and root functioning are among the key mechanisms for overcoming increasing drought. The duration of drought determines its severity in terms of canopy loss and stem mortality. Although Q. ilex can vigorously resprout after such episodes, its resilience may be subsequently reduced. In the future, higher frequency of return of extreme droughts will challenge thus the capacity of these forests to recover. The insights provided by this review of the complex interplay of processes that determine the response of trees to droughts of different duration, intensity, and frequency will also help us to understand the likely responses of other resprouting angiosperms in seasonally dry ecosystems that share similar functional traits with Q. ilex.

Seasonal water relations in four co-existing native shrub species from Northeastern Mexico

ABSTRACTSeasonal xylem water potentials (Ψ, MPa) and their relationship to soil water content and evaporative demand components were studied in the shrub species Acacia amentacea, Celtis ehrenbergiana, Forestiera angustifolia, and Parkinsonia texana var. macra. Predawn (Ψpd) and midday (Ψmd) water potentials were estimated at 15 days intervals, between January 15 and October 30, 2009 using a Scholander pressure bomb at 06:00 h (predawn) and 14:00 h (midday), respectively. During the humid period, Ψpd ranged from −0.30 MPa (C. ehrenbergiana), to −0.90 MPa (P. texana). In contrast, over the driest period, Ψpd varied between −2.18 (P. texana) and −3.94 MPa (F. angustifolia). At midday, P. texana and F. angustifolia showed the highest (−1.14 MPa) and lowest (−3.38 MPa) Ψ values, respectively. Average soil water content accounted for 35 to 70% of the variation in predawn Ψ. Furthermore, both Ψ reflected the environmental conditions, as indicated by typical correlations observed. The studied shrub species exhibited what seem to be different strategies to avoid damage caused by drought. Thus, P. texana behaved rather as an isohydric plant able to deal well with severe, but short periods of drought. Under exceptionally dry environmental conditions, Ψpd undercut Ψmd values. Similar observations have been made by researchers studying plants in dry ecosystems. All studied native species are recommended for reforestation of the Tamaulipan shrublands, although C. ehrenbergiana and F. angustifolia seem to have limited tolerances for extreme water stress.

The dry season intensity as a key driver of NPP trends

AbstractWe analyze the impacts of changing dry season length and intensity on vegetation productivity and biomass. Our results show a wetness asymmetry in dry ecosystems, with dry seasons becoming drier and wet seasons becoming wetter, likely caused by climate change. The increasingly intense dry seasons were consistently correlated with a decreasing trend in net primary productivity (NPP) and biomass from different products and could potentially mean a reduction of 10–13% in NPP by 2100. We found that annual NPP in dry ecosystems is particularly sensitive to the intensity of the dry season, whereas an increase in precipitation during the wet season has a smaller effect. We conclude that changes in water availability over the dry season affect vegetation throughout the whole year, driving changes in regional NPP. Moreover, these results suggest that usage of seasonal water fluxes is necessary to improve our understanding of the link between water availability and the land carbon cycle.

Warming increases isoprene emissions from an arctic fen

Emissions of biogenic volatile organic compounds (BVOCs) from dry ecosystems at high latitudes respond strongly to small increases in temperature, and warm canopy surface temperatures drive emissions to higher levels than expected. However, it is not known whether emissions from wetlands, cooled by through-flowing water and higher evapotranspiration show similar response to warming as in drier ecosystems. Climate change will cause parts of the Arctic to experience increased snow fall, which delays the start of the growing season, insulates soil from low temperatures in winter, and increases soil moisture and possibly nutrient availability. Currently the effects of increasing snow depth on BVOC emissions are unknown. BVOC emissions were measured in situ across the growing season in a climate experiment, which used open top chambers to increase temperature and snow fences to increase winter snow depth. The treatments were arranged in a full factorial design. Measurements took place during two growing seasons in a fen ecosystem in west Greenland. BVOC samples collected by an enclosure technique in adsorbent cartridges were analysed using gas chromatography–mass spectrometry. Gross ecosystem production (GEP) was measured with a closed chamber technique, to reveal any immediate effect of treatments on photosynthesis, which could further influence BVOC emissions. Isoprene made up 84–92% of the emitted BVOCs. Isoprene emission increased 240 and 340% due to an increase in temperature of 1.3 and 1.6°C in 2014 and 2015, respectively. Isoprene emissions were 25 times higher in 2015 than in 2014 most likely due to a 2.4°C higher canopy air temperature during sampling in 2015. Snow addition had no significant effect on isoprene emissions even though GEP was increased by 24%. Arctic BVOC emissions respond strongly to rising temperatures in wet ecosystems, suggesting a large increase in arctic emissions in a future warmer climate.

Plant versus microbial controls on soil aggregate stability in a seasonally dry ecosystem

The formation of water-stable macroaggregates in soil is beneficial for many reasons, including carbon (C) sequestration, nutrient retention, and erosion control. A mix of biotic (e.g., plant C input, microbial activity) and abiotic factors (e.g., water, mineral interactions) contribute to form macroaggregates. However, in order to better model and manage soil macroaggregates, we need to know more about the relative contributions of these mechanisms. Previous experiments to separate microbial and abiotic mechanisms have been hampered by the need to add sterilant dissolved in water, thus limiting our ability to draw conclusions about the role of soil moisture in controlling aggregation and preventing conclusions about dry soil. Our first goal was to quantify the contribution of plant growth (and fresh plant C inputs) by continuously removing plants for 2years in a seasonally dry grassland. Our second goal was to quantify microbial vs. abiotic contributions to macroaggregate formation under a range of soil moisture conditions by using chloroform vapor to sterilize soil without adding water or destroying soil structure. In the field, regardless of dry season length, removing plants reduced the average size of soil aggregates by 22–33%, which was primarily driven by a shift from large macroaggregates (2–9mm diameter) to small macroaggregates (0.25–2mm). In the laboratory, in sterile soils macroaggregate production increased with the moisture content. The resulting physicogenic aggregates appeared planar and angular at both macro- and micro-scales. In contrast, biogenic aggregates were formed most at intermediate moisture levels and were spherical. Our results suggest that—even in dry climates—soil macroaggregates are preserved by the presence of even dead plant roots, but are engineered by live microbes.

Denitrification in a subtropical, semi-arid North American savanna: field measurements and intact soil core incubations

Information on denitrification (particularly N2) losses from dry ecosystems is limited despite their large area. Here, we present the first direct denitrification measurements for a northern hemisphere savanna, a Prosopis-dominated grassland/grove matrix in south Texas. We used the gas-flow intact soil core method to quantify N2, N2O and CO2 losses and compared these with field measurements of N2O, NOy, NH3 and CO2. Under field-realistic soil moisture and O2 conditions (average 17.5–20 % O2, minimum 15 %) incubated soils produced no measurable N2 flux (detection limit 52.2 µg N m−2 h−1). Only in a subset of grove soils were fluxes of 70–75 µg N m−2 h−1 recorded after 102 h of incubation at 5–10 % O2 following wetting of very dry soils. Making the assumption that potential N2 production falls just below the detection limit (likely an overestimate given the conditions needed to generate measurable fluxes), N2 flux rates would fall on the low end of that recorded for a tropical Australian savanna (45–110 µg N m−2 h−1) under comparable abiotic conditions. Assuming maximum possible production rates, N2 could comprise <32–76 % of total soil N gas flux following soil wetting in summer. Lack of flux response to soil wetting in winter suggests that cold-season N2 fluxes are negligible. N2O fluxes for core incubations were significantly higher than for field chambers; thus it is likely that incubations may overestimate N2O flux by reducing soil column consumption. Overall, results indicate that soil N2 fluxes are less dominant in this savanna than in other ecosystems investigated.

Effects of disturbance on understory succession in upland and lowland boreal forests and implications for woodland caribou (Rangifer tarandus caribou)

Boreal forest development is influenced by both natural and anthropogenic disturbances that alter stand structure and nutrient cycling over decadal timescales. The effects of disturbance on boreal forests is likely to be modified by soil moisture, given that disturbance severity, vegetation structure and plant productivity vary between upland and lowland forest stands. Future changes in boreal vegetation dynamics are predicted to have consequences for a range of ecosystem services including climate feedbacks and wildlife management. Here, as part of a broader study on habitat use and forage of woodland caribou, we investigated the effects of soil drainage class (upland vs. lowland), disturbance (wildfire vs. timber harvest), and stand age on understory plant species richness, cover, biomass, productivity, and foliar C/N. Due to faster nutrient turnover rates in upland soils, we predicted that understory vegetation in uplands would be more productive, biodiverse and nutrient-rich than in lowlands. We also expected disturbance to lead to greater changes in understory vegetation in uplands, given that both fire and timber harvesting tend to be more severe in drier ecosystems. Our results showed that plant understory characteristics varied primarily between soil drainage classes, with few differences between stands recovering from wildfire or timber harvesting. Contrary to our predictions, lowland understory vegetation had greater total understory plant species richness, aboveground net primary productivity, and foliar C/N compared to upland understory vegetation. We also found no difference in total understory vegetation percent cover, productivity or foliar C/N between burned and harvested stands. Understory net primary productivity decreased with time following disturbance in uplands but increased nonlinearly with stand age in lowlands. Greater productivity in lowlands was attributed primarily to evergreen shrubs, though graminoids also were more productive in lowlands than in uplands. Our study has implications for the threatened woodland caribou with respect to the nutritional aspects of their habitat selection. Our results suggest that the commonly held assertion that, by selecting lowlands, caribou face a trade-off between lower predation risk and lower forage quality may be incorrect and requires further examination.

Direct and indirect effects of climatic variations on the interannual variability in net ecosystem exchange across terrestrial ecosystems

Climatic variables not only directly affect the interannual variability (IAV) in net ecosystem exchange of CO2 (NEE) but also indirectly drive it by changing the physiological parameters. Identifying these direct and indirect paths can reveal the underlying mechanisms of carbon (C) dynamics. In this study, we applied a path analysis using flux data from 65 sites to quantify the direct and indirect climatic effects on IAV in NEE and to evaluate the potential relationships among the climatic variables and physiological parameters that represent physiology and phenology of ecosystems. We found that the maximum photosynthetic rate was the most important factor for the IAV in gross primary productivity (GPP), which was mainly induced by the variation in vapour pressure deficit. For ecosystem respiration (RE), the most important drivers were GPP and the reference respiratory rate. The biome type regulated the direct and indirect paths, with distinctive differences between forests and non-forests, evergreen needleleaf forests and deciduous broadleaf forests, and between grasslands and croplands. Different paths were also found among wet, moist and dry ecosystems. However, the climatic variables can only partly explain the IAV in physiological parameters, suggesting that the latter may also result from other biotic and disturbance factors. In addition, the climatic variables related to NEE were not necessarily the same as those related to GPP and RE, indicating the emerging difficulty encountered when studying the IAV in NEE. Overall, our results highlight the contribution of certain physiological parameters to the IAV in C fluxes and the importance of biome type and multi-year water conditions, which should receive more attention in future experimental and modelling research.

Оценка динамики аридных экосистем на основе временных рядов космических снимков

Оценка динамики аридных экосистем на основе временных рядов космических снимков

Dry season streamflow persistence in seasonal climates

AbstractSeasonally dry ecosystems exhibit periods of high water availability followed by extended intervals during which rainfall is negligible and streamflows decline. Eventually, such declining flows will fall below the minimum values required to support ecosystem functions or services. The time at which dry season flows drop below these minimum values (Q*), relative to the start of the dry season, is termed the “persistence time” ( ). The persistence time determines how long seasonal streams can support various human or ecological functions during the dry season. In this study, we extended recent work in the stochastic hydrology of seasonally dry climates to develop an analytical model for the probability distribution function (PDF) of the persistence time. The proposed model accurately captures the mean of the persistence time distribution, but underestimates its variance. We demonstrate that this underestimation arises in part due to correlation between the parameters used to describe the dry season recession, but that this correlation can be removed by rescaling the flow variables. The mean persistence time predictions form one example of the broader class of streamflow statistics known as crossing properties, which could feasibly be combined with simple ecological models to form a basis for rapid risk assessment under different climate or management scenarios.

Global patterns and climate drivers of water‐use efficiency in terrestrial ecosystems deduced from satellite‐based datasets and carbon cycle models

AbstractAimTo investigate how ecosystem water‐use efficiency (WUE) varies spatially under different climate conditions, and how spatial variations in WUE differ from those of transpiration‐based water‐use efficiency (WUEt) and transpiration‐based inherent water‐use efficiency (IWUEt).LocationGlobal terrestrial ecosystems.MethodsWe investigated spatial patterns of WUE using two datasets of gross primary productivity (GPP) and evapotranspiration (ET) and four biosphere model estimates of GPP and ET. Spatial relationships between WUE and climate variables were further explored through regression analyses.ResultsGlobal WUE estimated by two satellite‐based datasets is 1.9 ± 0.1 and 1.8 ± 0.6 g C m−2 mm−1 lower than the simulations from four process‐based models (2.0 ± 0.3 g C m−2 mm−1) but comparable within the uncertainty of both approaches. In both satellite‐based datasets and process models, precipitation is more strongly associated with spatial gradients of WUE for temperate and tropical regions, but temperature dominates north of 50° N. WUE also increases with increasing solar radiation at high latitudes. The values of WUE from datasets and process‐based models are systematically higher in wet regions (with higher GPP) than in dry regions. WUEt shows a lower precipitation sensitivity than WUE, which is contrary to leaf‐ and plant‐level observations. IWUEt, the product of WUEt and water vapour deficit, is found to be rather conservative with spatially increasing precipitation, in agreement with leaf‐ and plant‐level measurements.Main conclusionsWUE, WUEt and IWUEt produce different spatial relationships with climate variables. In dry ecosystems, water losses from evaporation from bare soil, uncorrelated with productivity, tend to make WUE lower than in wetter regions. Yet canopy conductance is intrinsically efficient in those ecosystems and maintains a higher IWUEt. This suggests that the responses of each component flux of evapotranspiration should be analysed separately when investigating regional gradients in WUE, its temporal variability and its trends.

Generic delimitations, biogeography and evolution in the tribe Coleeae (Bignoniaceae), endemic to Madagascar and the smaller islands of the western Indian Ocean

This study presents the most complete generic phylogenetic framework to date for the tribe Coleeae (Bignoniaceae), which is endemic to Madagascar and the other smaller islands in the western part of the Indian Ocean. The study is based on plastid and nuclear DNA regions and includes 47 species representing the five currently recognized genera (including all the species occurring in the western Indian Ocean region). Bayesian and maximum likelihood analyses supported (i) the monophyly of the tribe, (ii) the monophyly of Phylloctenium, Phyllarthron and Rhodocolea and (iii) the paraphyly of Colea due to the inclusion of species of Ophiocolea. The latter genus was also recovered paraphyletic due to the inclusion of two species of Colea (C. decora and C. labatii). The taxonomic implications of the mutual paraphyly of these two genera are discussed in light of morphological evidence, and it is concluded that the two genera should be merged, and the necessary new nomenclatural combinations are provided. The phylogenetic framework shows Phylloctenium, which is endemic to Madagascar and restricted to dry ecosystems, as basal and sister to the rest of the tribe, suggesting Madagascar to be the centre of origin of this clade. The remaining genera are diversified mostly in humid ecosystems, with evidence of multiple dispersals to the neighboring islands, including at least two to the Comoros, one to Mauritius and one to the Seychelles. Finally, we hypothesize that the ecological success of this tribe might have been triggered by a shift of fruit-dispersal mode from wind to lemur.

Seed predation and removal from faeces in a dry ecosystem

The fate of dispersed seeds from mammal faeces depends both on the animal that finds the seeds and environmental conditions. We explored the simultaneous influence of microhabitat and food availability on seed predation and removal from faeces by different animals in a protected Prosopis flexuosa open woodland site of the central Monte desert (Argentina). Using exclusion trials on simulated cattle faeces, we quantified seed predation in situ (within cages) and seed removal from faeces by rodents and ants in two different microhabitats (under shrub cover and on bare soil). This was done for two levels of availability of P. flexuosa fruits (during the fruiting season of P. flexuosa and when there are no fruits on the ground). We found that 67.9% of seeds remained in faeces, 28.9% were removed, and 3.2% were depredated in situ. Rodents removed more seeds under shrub cover than on bare soil, and during the non-fruiting period than during the fruiting period, whereas ants removed similar proportions of seeds in different microhabitats but almost exclusively during the fruiting season. This work acknowledges the complexity of dispersal processes and identifies the relative importance of some environmental factors for seed fate.

Photodegradation effects on CO2 emissions from litter and SOM and photo-facilitation of microbial decomposition in a California grassland

Decomposition of soil organic matter (SOM) and plant litter has been shown to be affected by high solar radiation; this could partly explain why biogeochemical models underestimate decomposition in arid and semi-arid ecosystems. We set out to test the effect of using traditional PVC chambers for measuring soil gas fluxes versus quartz chambers that allowed passage of light during field measurements in a dry-land field in Davis, CA. Results showed that fluxes from quartz-top chambers were on average 29% higher than from opaque chambers. We also studied the effect of solar light exposure on decomposition of native grass litter and SOM in a field experiment where plots were shaded or left exposed for 157 days during summer; litter did not seem to be affected by exposure to light. However, we concluded that SOM decomposition was affected by light exposure since shaded soil had similar respiration to sunlight-exposed soil indicating that microbial respiration occurred under the shade while photo-degradation likely occurred under the sun. Additionally, 15N-labeled grass was placed in litter bags in the field with either clear filters to allow light or aluminum covers to block light; 3-month exposure caused a change in lignin degradability as indicated by the change in the Ad/Al ratio. Incubation of that litter showed 9.3% more CO2 produced from litter in clear and aluminum bags than unexposed litter. This showed that photo-facilitation occurred although to a small degree and was a result of light exposure and/or heat degradation. We attributed the similar respiration from clear- and aluminum-exposed litter to heat degradation of the aluminum-exposed litter. In conclusion, our results show that in hot dry ecosystems conventional PVC chambers underestimate measured CO2 flux rates; sunlight exposure changes litter chemistry and appears to affect the degradation of soil organic matter, but the magnitude of degradation depends on an interaction of factors such as soil temperature and moisture.

Leguminosae na APA do Cariri, Estado da Paraíba, Brasil

RESUMO Leguminosae Juss. é uma família amplamente distribuída, sendo dominante em alguns ecossistemas, como na Caatinga. Este trabalho trata do levantamento taxonômico de Leguminosae na Área de Proteção Ambiental (APA) do Cariri, semiárido paraibano, nordeste do Brasil. Foram encontradas ao todo 31 espécies, 22,6 % das quais acreditadas como endêmicas da Caatinga. O gênero mais diverso taxonomicamente foi Senna, com cinco espécies. Sete espécies foram referidas pela primeira vez para o Estado da Paraíba (C. belemii var. belemii, D. violacea, I. blanchetiana, P. microphilla, V. halophila, Z. echinocarpa e Z. myriadena). O hábito arbustivo foi o mais representativo, com 45,2% do total de espécies registradas, seguido pelos hábitos herbáceo e arbóreo, com 22,6 e 16,1% respectivamente. As trepadeiras e lianas perfizeram respectivamente 9,7 e 6,5% das espécies. O tratamento taxonômico inclui chaves de identificação para subfamílias e respectivas espécies, dados de distribuição geográfica e ilustrações.

다변량 환경 공간변수 주성분 분석을 통한 남·북 생태계 차이

The objectives of this study are to analyze the quantitative ecological principal components of Korean Peninsula using the multivariate spatial environmental datasets and to compare the ecological difference between South and North Korea. Ecological maps with GIS(Geographical Information System) are constructed by PCA(Principal Component Analysis) based on seventeen raster(cell based) variables at 1km resolution. Ecological differences between South and North Korea are extracted by Factor Analysis using ecosystem maps masked from Korean ones. Spatial data include SRTM(Shuttle Radar Topography Mission), Temperature, Precipitation, SWC(Soil Water Content), fPAR(Fraction of Photosynthetically Active Radiation) representing for a productivity, and SR(Solar Radiation), which all cover Korean peninsula. When it performed PCA, the first three scores were assigned to red, green, and blue color. This color triplet indicates the relative mixture of the seventeen environmental conditions inside each ecological region. The first red one represents for 'physiographic conditions' worked by high elevation and solar radiation and low temperature. The second green one stands for 'seasonality' caused by seasonal variations of temperature, precipitation, and productivity. The third blue one means 'wetness condition' worked by high value such as precipitation and soil water contents. FA extraction shows that South Korea has relatively warm and humid ecosystem affected by high temperature, precipitation, and soil water contents whereas North Korea has relatively cold and dry ecosystem due to the high elevation, low temperature and precipitation. Results would be useful at environmental planning on inaccessible land of North Korea.

Zoogeography of South American Forest-Dwelling Bats: Disjunct Distributions or Sampling Deficiencies?

Many forest-dwelling bats are purported to be widespread in South America, although records are scant from the vast diagonal belt of dry ecosystems that straddles the continent, implying possible sampling deficiencies. Here, we investigate this possibility in the case of four species of bat (Centronycteris maximiliani, Lampronycteris brachyotis, Peropteryx kappleri and Trinycteris nicefori), evaluating whether their disjunct present-day distributions reflect their true zoogeographic characteristics or the subsampling of intermediate zones. We use environmental niche modelling (ENM) in an ensemble approach, combining four different modeling techniques, and using niche descriptors based on climatic and remote sensing data, to estimate the potential distribution of the four species. The models indicate that all four species have disjunct distributions in the Amazon and Atlantic forest biomes. The one possible exception is P. kappleri, which the models indicated might potentially occur in humid forest enclaves in western Brazil and eastern Bolivia. The present-day distribution of the species may date back to the Plio-Pleistocene, when the forested biomes of South America were more extensive and connected. Further studies of different chiropteran lineages may provide additional insights into the historic processes of faunal interchange between the Amazon and Atlantic forest biomes.

Diversity and conservation of plant species in dry valleys, southwest China

The dry valleys in southwest China harbor a highly varied concentration of endemic plant species. To date, the conservation of the unique ecosystem has been paid attention, whereas conservation for the regional endemic plant species has not been much focused. The dry valleys own approximately 1707 plant species among which, 37.42 % are endemic. The plant species in that dry ecosystem are currently challenged by the climate change and anthropogenic activity. To give insight into the current (and past) status of threatened species and the population conservation management strategies, we investigated the genetic diversities of endemic and endangered plant species in the dry valleys in the last decade, using nuclear or plastid molecular markers. Our data revealed that the plant species in this region have low levels of genetic diversity within populations and strong genetic structure. We thus concluded that strong geography patterns are mainly shaped by complex topography as well as their local habitats. We pointed that it is of importance to incorporate neutral and non-neutral genetic diversity when assessing the status of the endangered species. We suggest more research findings are needed to well understand and ensure regional effective conservation on the plant species occurred in the dry valleys.

Vulnerability of native savanna trees and exotic Khaya senegalensis to seasonal drought.

Seasonally dry ecosystems present a challenge to plants to maintain water relations. While native vegetation in seasonally dry ecosystems have evolved specific adaptations to the long dry season, there are risks to introduced exotic species. African mahogany, Khaya senegalensis Desr. (A. Juss.), is an exotic plantation species that has been introduced widely in Asia and northern Australia, but it is unknown if it has the physiological or phenotypic plasticity to cope with the strongly seasonal patterns of water availability in the tropical savanna climate of northern Australia. We investigated the gas exchange and water relations traits and adjustments to seasonal drought in K. senegalensis and native eucalypts (Eucalyptus tetrodonta F. Muell. and Corymbia latifolia F. Muell.) in a savanna ecosystem in northern Australia. The native eucalypts did not exhibit any signs of drought stress after 3 months of no rainfall and probably had access to deeper soil moisture late into the dry season. Leaf water potential, stomatal conductance, transpiration and photosynthesis all remained high in the dry season but osmotic adjustment was not observed. Overstorey leaf area index (LAI) was 0.6 in the native eucalypt savanna and did not change between wet and dry seasons. In contrast, the K. senegalensis plantation in the wet season was characterized by a high water potential, high stomatal conductance and transpiration and a high LAI of 2.4. In the dry season, K. senegalensis experienced mild drought stress with a predawn water potential -0.6 MPa. Overstorey LAI was halved, and stomatal conductance and transpiration drastically reduced, while minimum leaf water potentials did not change (-2 MPa) and no osmotic adjustment occurred. Khaya senegalensis exhibited an isohydric behaviour and also had a lower hydraulic vulnerability to cavitation in leaves, with a P50 of -2.3 MPa. The native eucalypts had twice the maximum leaf hydraulic conductance but a much higher P50 of -1.5 MPa. Khaya senegalensis has evolved in a wet-dry tropical climate in West Africa (600-800 mm) and appears to be well suited to the seasonal savanna climate of northern Australia. The species exhibited a large phenotypic plasticity through leaf area adjustments and conservative isohydric behaviour in the 6 months dry season while operating well above its critical hydraulic threshold.

Establishing the ecological restoration network in Argentina: from Rio1992 to SIACRE2015

The development of the science and practice of restoration ecology in Argentina can be divided into three periods. The first was 1992–2004, characterized by isolated restoration efforts, mostly in arid and dry ecosystems, and engaging specific people in the academic, agro‐technological, and private sectors as partially required by national regulations, but also inspired by the 1992 Earth Summit, the 1994 Amendments of the Constitutional Law, and environmental guidelines from investment entities. The second period of 2005–2010 showed significantly greater involvement in international networking and conference contributions. The current period from 2011‐present has witnessed rapid advances and national integration. The country's network Red de Restauración Ecológica de Argentina (REA) was founded in 2012, with seven subnational nodes. In 2014, the 2nd REA symposium was held to determine priority areas for restoration and to generate a National Plan. Public agencies, NGOs and volunteer groups are now actively engaged stakeholders. In 2013 Argentina became a founder member of SIACRE (Sociedad Ibero‐Americana y del Caribe para la Restauración Ecológica) and is organizing SIACRE's 4th international conference (April 2015; Buenos Aires). Restoration ecology in Argentina is ascendant because of long‐term efforts related to strengthening democracy, people initiatives, and strong support from SIACRE, SER (Society for Ecological Restoration), SER‐Europe, and the national networks of Colombia, Brazil, Mexico, and Chile. Moreover, Argentina is now the first country to have updated its Civil Code by integrating the environment as a “legal good,” which reinforces the citizens' rights to demand the implementation of degradation prevention and/or ecosystem restoration measures.