Changes In Rainfall Regime Research Articles

Impact of climate change on maize production in Ghana. A review

Climate change is one of the challenges that human populations and the environment face. In Ghana, agricultural production is expected to be negatively affected because of the projected changes in rainfall regimes and increase in temperatures. Due to the essential role of maize in the food security of the country, numerous studies have been conducted to estimate how its production is being affected now and likely to be affected in future by current and projected changes in climate. In order to assemble the current knowledge of how maize production in Ghana will be affected, a systematic literature review was conducted for published material relating to the topic. From the review, it was apparent that climate change is already happening in Ghana. Available records indicated that temperature has increased by 1oC across the country over the last 30 years. Rainfall has decreased by 20% over the same period. The yields of maize have been affected by these climatic changes. In recent years, there has been a decline in maize yields across the country. Although other contributing factors exist, increasing temperatures and irregularity in rainfall have been cited as the primary causes of the continuous reduction in yields. For future climate projections, the common agreement amongst all the reviewed literature is that maize yields will further decline. The decline varied from 7% in 2020 to 55% by 2050 depending on crop models and emission scenarios used in the study. With a projected increase in population, Ghana is likely to face many challenges in meeting the maize demands by its habitants in the future under the projected climate scenarios. The planting of more heat and drought tolerant maize varieties, adjustments in the planting dates and increasing irrigation facilities in maize production were the commonest adaptation measures identified.

Salt tolerance of rhizobial populations from contrasting environmental conditions: understanding the implications of climate change.

It is predicted that global climate change may alter environmental parameters such as rainfall distribution which in turn may alter the salinity of soils with unpredictable effects upon soil microbial populations. In the present work the tolerance to salinity of rhizobia, isolated from locations with contrasting climatic conditions, and the potential of strains to fix nitrogen symbiotically under saline conditions were investigated. Since plasmids may encode key genes related to growth and survival under environmental stress conditions, which will reflect on protein synthesis, both the plasmid and protein profiles were analyzed. A multivariate statistical approach related salt tolerance to the origin of the isolates, identifying rainfall and water availability as a possible factor explaining the differences in salt tolerance displayed by rhizobia isolates. The classification analysis allowed the subdivision of isolates in terms of salt tolerance into extremely sensitive (≤0.15%), sensitive (0.15-0.6%), moderately tolerant (0.9-1.5%), tolerant (2.1-3.6%) and extremely tolerant (≥5.4%). Taken all together it was shown that plasmids are involved in salt tolerance and that the impact of salinity on the protein profile and nitrogen fixation varied according to the salt tolerance of the strains, evidencing the susceptibility of rhizobial communities to changes in rainfall regimes.

Increased drought impacts on temperate rainforests from southern South America: results of a process-based, dynamic forest model.

Increased droughts due to regional shifts in temperature and rainfall regimes are likely to affect forests in temperate regions in the coming decades. To assess their consequences for forest dynamics, we need predictive tools that couple hydrologic processes, soil moisture dynamics and plant productivity. Here, we developed and tested a dynamic forest model that predicts the hydrologic balance of North Patagonian rainforests on Chiloé Island, in temperate South America (42°S). The model incorporates the dynamic linkages between changing rainfall regimes, soil moisture and individual tree growth. Declining rainfall, as predicted for the study area, should mean up to 50% less summer rain by year 2100. We analysed forest responses to increased drought using the model proposed focusing on changes in evapotranspiration, soil moisture and forest structure (above-ground biomass and basal area). We compared the responses of a young stand (YS, ca. 60 years-old) and an old-growth forest (OG, >500 years-old) in the same area. Based on detailed field measurements of water fluxes, the model provides a reliable account of the hydrologic balance of these evergreen, broad-leaved rainforests. We found higher evapotranspiration in OG than YS under current climate. Increasing drought predicted for this century can reduce evapotranspiration by 15% in the OG compared to current values. Drier climate will alter forest structure, leading to decreases in above ground biomass by 27% of the current value in OG. The model presented here can be used to assess the potential impacts of climate change on forest hydrology and other threats of global change on future forests such as fragmentation, introduction of exotic tree species, and changes in fire regimes. Our study expands the applicability of forest dynamics models in remote and hitherto overlooked regions of the world, such as southern temperate rainforests.

The influence of the conservation status and changes in the rainfall regime on forest-savanna mosaic dynamics in Northern Brazilian Amazonia

Coupled carbon/climate models are predicting changes in Amazon carbon and water cycles for the near future, with conversion of forest into savanna-like vegetation. However, empirical data to support these models are still scarce for Amazon. Facing this scenario, we investigated whether conservation status and changes in rainfall regime have influenced the forest-savanna mosaic over 20 years, from 1986 to 2006, in a transitional area in Northern Amazonia. By applying a spectral linear mixture model to a Landsat-5-TM time series, we identified protected savanna enclaves within a strictly protected nature reserve (Maracá Ecological Station - MES) and non-protected forest islands at its outskirts and compared their areas among 1986/1994/2006. The protected savanna enclaves decreased 26% in the 20-years period at an average rate of 0.131 ha year-1, with a greater reduction rate observed during times of higher precipitation, whereas the non-protected forest islands remained stable throughout the period of study, balancing the encroachment of forests into the savanna during humid periods and savannization during reduced rainfall periods. Thus, keeping favorable climate conditions, the MES conservation status would continue to favor the forest encroachment upon savanna, while the non-protected outskirt areas would remain resilient to disturbance regimes. However, if the increases in the frequency of dry periods predicted by climate models for this region are confirmed, future changes in extension and directions of forest limits will be affected, disrupting ecological services as carbon storage and the maintenance of local biodiversity.

Ecosystem functions are resistant to extreme changes to rainfall regimes in a mesotrophic grassland

Major changes to rainfall regimes are predicted for the future but the effect of such changes on terrestrial ecosystem function is largely unknown. We created a rainfall manipulation experiment to investigate the effects of extreme changes in rainfall regimes on ecosystem functioning in a grassland system. We applied two rainfall regimes; a prolonged drought treatment (30 % reduction over spring and summer) and drought/downpour treatment (long periods of no rainfall interspersed with downpours), with an ambient control. Both rainfall manipulations included increased winter rainfall. We measured plant community composition, CO2 fluxes and soil nutrient availability. Plant species richness and cover were lower in the drought/downpour treatment, and showed little recovery after the treatment ceased. Ecosystem processes were less affected, possibly due to winter rainfall additions buffering reduced summer rainfall, which saw relatively small soil moisture changes. However, soil extractable P and ecosystem respiration were significantly higher in rainfall change treatments than in the control. This grassland appears fairly resistant, in the short term, to even the more extreme rainfall changes that are predicted for the region, although prolonged study is needed to measure longer-term impacts. Differences in ecosystem responses between the two treatments emphasise the variety of ecosystem responses to changes in both the size and frequency of rainfall events. Given that model predictions are inconsistent there is therefore a need to assess ecosystem function under a range of potential climate change scenarios.

Changing precipitation regimes and the water and carbon economies of trees

Climate change is predicted to affect the water balance of several ecosystems mostly through changes in the energy budget and hydrological input (rainfall frequency, intensity, and timing). Changes in rainfall patterns and cloudiness directly affect incoming radiation, atmospheric water vapor saturation deficit and soil water availability, the main variables controlling the rates of water uptake and transport along the soil–plant–atmosphere continuum (SPAC). Developing a predictive framework about vegetation responses to a changing climate is challenging because it involves complex non-linear interactions between these environmental variables and species-specific responses. By examining the hydraulic traits of functional groups within plant communities we can better predict the impacts of changes in rainfall regimes within functional groups and therefore, generate more realistic predictions of ecosystem carbon and water balance changes due to local and regional changes in precipitation regimes. In this review, we discuss several aspects of plant hydraulic functioning and then explore how predicted changes in precipitation regimes may affect tree water and carbon balance. We examine the impacts of changes in rainfall patterns on the SPAC and also explore the multiple ways that plants can absorb and transport water. Finally, we explore the diversity of hydraulic traits and potential mechanisms causing large-scale drought-induced mortality recently observed in several ecosystems.

Response of transpiration to rain pulses for two tree species in a semiarid plantation

Responses of transpiration (Ec) to rain pulses are presented for two semiarid tree species in a stand of Pinus tabulaeformis and Robinia pseudoacacia. Our objectives are to investigate (1) the environmental control over the stand transpiration after rainfall by analyzing the effect of vapor pressure deficit (VPD), soil water condition, and rainfall on the post-rainfall Ec development and recovery rate, and (2) the species responses to rain pulses and implications on vegetation coverage under a changing rainfall regime. Results showed that the sensitivity of canopy conductance (Gc) to VPD varied under different incident radiation and soil water conditions, and the two species exhibited the same hydraulic control (-dG c/dlnVPD to Gcref ratio) over transpiration. Strengthened physiological control and low sapwood area of the stand contributed to low Ec. VPD after rainfall significantly influenced the magnitude and time series of post-rainfall stand Ec. The fluctuation of post-rainfall VPD in comparison with the pre-rainfall influenced the Ec recovery. Further, the stand Ec was significantly related to monthly rainfall, but the recovery was independent of the rainfall event size. Ec enhanced with cumulative soil moisture change (ΔVWC) within each dry-wet cycle, yet still was limited in large rainfall months. The two species had different response patterns of post-rainfall Ec recovery. Ec recovery of P. tabulaeformis was influenced by the pre- and post-rainfall VPD differences and the duration of rainless interval. R. pseudoacacia showed a larger immediate post-rainfall Ec increase than P. tabulaeformis did. We, therefore, concluded that concentrated rainfall events do not trigger significant increase of transpiration unless large events penetrate the deep soil and the species differences of Ec in response to pulses of rain may shape the composition of semiarid woodlands under future rainfall regimes.

Recent trends in seasonal and annual precipitation indices in Tuscany (Italy)

Global warming alters the hydrological cycle since a rise in temperature leads to an increase in the moisture-holding capacity of the atmosphere at a rate of about 7 %/°C. This fact can influence the global, but also local characteristics of precipitation, such as total amount and intensity. Therefore, it is important to study changes in rainfall regime in regions with complex orography, like Tuscany, where there are strong spatial gradients in precipitation amounts. The aim of this study is to look for temporal change in precipitation from 1955 to 2007 searching for spatial differences. Daily data of 21 meteorological stations were analyzed to identify trends in seasonal and annual precipitation indices. Cluster analysis applied to principal components was applied to identify homogeneous groups of stations. A decrease in precipitation was observed at annual time scale, during winter and spring, especially in northwestern areas. Wet days highlighted a decrease in all of Tuscany, due to the same seasons. In northern Tuscany, the decrease in rainfall amount was mainly determined by a lower frequency of rainy events which in turn caused a decrease in the occurrence of extreme daily precipitation events (75th, 90th, and 95th percentile). In central-southern Tuscany, no significant changes were observed except for an increase in precipitation fraction, due to extreme events and in mean daily total amount for wet days. These results are consistent with recent findings for the Mediterranean area and confirm the usefulness of cluster analysis for the analysis of the spatial distribution of precipitation.

Effect of rainfall seasonality on carbon storage in tropical dry ecosystems

AbstractWhile seasonally dry conditions are typical of large areas of the tropics, their biogeochemical responses to seasonal rainfall and soil carbon (C) sequestration potential are not well characterized. Seasonal moisture availability positively affects both productivity and soil respiration, resulting in a delicate balance between C deposition as litterfall and C loss through heterotrophic respiration. To understand how rainfall seasonality (i.e., duration of the wet season and rainfall distribution) affects this balance and to provide estimates of long‐term C sequestration, we develop a minimal model linking the seasonal behavior of the ensemble soil moisture, plant productivity, related C inputs through litterfall, and soil C dynamics. A drought‐deciduous caatinga ecosystem in northeastern Brazil is used as a case study to parameterize the model. When extended to different patterns of rainfall seasonality, the results indicate that for fixed annual rainfall, both plant productivity and soil C sequestration potential are largely, and nonlinearly, dependent on wet season duration. Moreover, total annual rainfall is a critical driver of this relationship, leading at times to distinct optima in both production and C storage. These theoretical predictions are discussed in the context of parameter uncertainties and possible changes in rainfall regimes in tropical dry ecosystems.

Changes in rainfall regime over Burkina Faso under the climate change conditions simulated by 5 regional climate models

Sahelian rainfall has recorded a high variability during the last century with a significant decrease (more than 20 %) in the annual rainfall amount since 1970. Using a linear regression model, the fluctuations of the annual rainfall from the observations over Burkina Faso during 1961–2009 period are described through the changes in the characteristics of the rainy season. The methodology is then applied to simulated rainfall data produced by five regional climate models under A1B scenario over two periods: 1971–2000 as reference period and 2021–2050 as projection period. As found with other climate models, the projected change in annual rainfall for West Africa is very uncertain. However, the present study shows that some features of the impact of climate change on rainfall regime in the region are robust. The number of the low rainfall events (0.1–5 mm/d) is projected to decrease by 3 % and the number of strong rainfall events (>50 mm/d) is expected to increase by 15 % on average. In addition, the rainy season onset is projected by all models to be delayed by one week on average and a consensus exists on the lengthening of the dry spells at about 20 %. Furthermore, the simulated relationship between changed annual rainfall amounts and the number of rain days or their intensity varies strongly from one model to another and some changes do not correspond to what is observed for the rainfall variability over the last 50 years.

Rainfall regime changes and trends in Botswana Kalahari Transect’s late summer precipitation

Sixty-year-long January–March (JFM) rainfall data from four (4) stations along the Kalahari Transect were analyzed for long-term trends and abrupt changes in rainfall regimes. On average, JFM rainfall accounts for more than 50 % of annual rainfall in the region. Mann–Kendall trend test has shown an insignificant heterogeneous trend in the seasonal rainfall of −1.097, 0.029, −0.407, and −1.327 mm/year for Maun, Ghanzi, Tsabong, and Tshane, respectively. An abrupt change in rainfall regimes in these areas was investigated and was found to occur in the year 1982 for all stations. The change is related to large-scale atmospheric circulations. Analysis of large-scale atmospheric circulations before 1982 over the region has shown the formation of a tropical low pressure convective system over the Kalahari Transect. The tropical system shifted eastward after 1982 to be centered over southeastern southern Africa with a significant reduction in rainfall over the Kalahari. A direct impact of this is the livestock-induced overgrazing which has lead to excessive removal of palatable herbaceous species thereby giving woody species, such as Accacia mellifera and Grewia flava, a competitive edge for dominance in the ecosystems. Seed production of A. mellifera depends on rainfall; therefore, abrupt changes in rainfall regimes impact livelihood and eco-tourism industry. The correlation studies between rainfall anomalies and NINO3.4 indices show a reduction in the influence of El-Nino Southern Oscillation on the Kalahari Transect rainfall after 1982.

The natural and social history of the indigenous lands and protected areas corridor of the Xingu River basin

The 280,000 km² Xingu indigenous lands and protected areas (ILPAs) corridor, inhabited by 24 indigenous peoples and about 215 riverine (ribeirinho) families, lies across active agriculture frontiers in some of the historically highest-deforestation regions of the Amazon. Much of the Xingu is anthropogenic landscape, densely inhabited and managed by indigenous populations over the past millennium. Indigenous and riverine peoples' historical management and use of these landscapes have enabled their long-term occupation and ultimately their protection. The corridor vividly demonstrates how ILPAs halt deforestation and why they may account for a large part of the 70 per cent reduction in Amazon deforestation below the 1996-2005 average since 2005. However, ongoing and planned dams, road paving, logging and mining, together with increasing demand for agricultural commodities, continued degradation of upper headwaters outside ILPA borders and climate change impacts may render these gains ephemeral. Local peoples will need new, bottom-up, forms of governance to gain recognition for the high social and biological diversity of these territories in development policy and planning, and finance commensurate with the value of their ecosystem services. Indigenous groups' reports of changing fire and rainfall regimes may themselves evidence climate change impacts, a new and serious threat.

Fusarium crown rot disease: biology, interactions, management and function as a possible sensor of global climate change

E.A. Moya-Elizondo. 2013. Fusarium crown rot disease: biology, interactions, management and function as a possible sensor of global climate change. Cien. Inv. Agr. 40(2):235-252. Wheat crops are commonly affected by the dryland root rot complex (DLRRC) under dry and semiarid conditions. This complex is associated with seedling blight, and rotting of roots, crowns and stems of wheat plants. Several pathogens are associated with this complex, but Fusarium crown rot disease (FCR) is the most common and is of worldwide importance. Increased drought frequency and changes in rainfall regimes associated with global climate change may increase the prevalence of this complex of diseases, especially of FCR, in wheat crop areas. This review discusses the characteristics of the pathogen species involved in DLRRC, the known interactions between the pathogens, and information regarding management strategies. We also discuss the possibility that the activity of FCR pathogens could act as a sensor of global climate change.

Trait-based approaches to conservation physiology: forecasting environmental change risks from the bottom up

Trait-based approaches have long been a feature of physiology and of ecology. While the latter fields drifted apart in the twentieth century, they are converging owing at least partly to growing similarities in their trait-based approaches, which have much to offer conservation biology. The convergence of spatially explicit approaches to understanding trait variation and its ecological implications, such as encapsulated in community assembly and macrophysiology, provides a significant illustration of the similarity of these areas. Both adopt trait-based informatics approaches which are not only providing fundamental biological insights, but are also delivering new information on how environmental change is affecting diversity and how such change may perhaps be mitigated. Such trait-based conservation physiology is illustrated here for each of the major environmental change drivers, specifically: the consequences of overexploitation for body size and physiological variation; the impacts of vegetation change on thermal safety margins; the consequences of changing net primary productivity and human use thereof for physiological variation and ecosystem functioning; the impacts of rising temperatures on water loss in ectotherms; how hemisphere-related variation in traits may affect responses to changing rainfall regimes and pollution; and how trait-based approaches may enable interactions between climate change and biological invasions to be elucidated.

Global desertification: Drivers and feedbacks

Desertification is a change in soil properties, vegetation or climate, which results in a persistent loss of ecosystem services that are fundamental to sustaining life. Desertification affects large dryland areas around the world and is a major cause of stress in human societies. Here we review recent research on the drivers, feedbacks, and impacts of desertification. A multidisciplinary approach to understanding the drivers and feedbacks of global desertification is motivated by our increasing need to improve global food production and to sustainably manage ecosystems in the context of climate change. Classic desertification theories look at this process as a transition between stable states in bistable ecosystem dynamics. Climate change (i.e., aridification) and land use dynamics are the major drivers of an ecosystem shift to a “desertified” (or “degraded”) state. This shift is typically sustained by positive feedbacks, which stabilize the system in the new state. Desertification feedbacks may involve land degradation processes (e.g., nutrient loss or salinization), changes in rainfall regime resulting from land-atmosphere interactions (e.g., precipitation recycling, dust emissions), or changes in plant community composition (e.g., shrub encroachment, decrease in vegetation cover). We analyze each of these feedback mechanisms and discuss their possible enhancement by interactions with socio-economic drivers. Large scale effects of desertification include the emigration of “environmental refugees” displaced from degraded areas, climatic changes, and the alteration of global biogeochemical cycles resulting from the emission and long-range transport of fine mineral dust. Recent research has identified some possible early warning signs of desertification, which can be used as indicators of resilience loss and imminent shift to desert-like conditions. We conclude with a brief discussion on some desertification control strategies implemented in different regions around the world.

Seed bank persistence and climate change

The strong mechanistic relationship between climatic factors and seed dormancy and germination suggests that forecast climatic changes will significantly affect seed bank persistence. This review focuses on the potential impact of changing temperature, rainfall and fire regimes on the longevity of long-term persistent seed-banks. Currently, there are few studies investigating the mechanistic responses of demographic processes, such as seed-bank dynamics, to forecast climate change. However, from the work that has been published, several key points have been highlighted. First, increased air temperatures will produce significantly higher soil temperatures in open and sparsely vegetated habitats. Some evidence shows that this could accelerate the decline of seed viability and compromise bet-hedging strategies of species in dryland regions. Second, changes to rainfall season may determine the relative success of recruitment, with lower levels of success producing net losses to seed bank longevity. Finally, higher temperatures are likely to produce increased fire frequency, compromising the persistence of plant populations dependent on long-lived seed banks. Improving our understanding of both the mechanistic response and adaptive capacity of seed banks to climate change will provide a solid basis for improved predictions of future species distributions and risk of extinction, particularly in ecosystems subjected to temporally stochastic disturbances. It is necessary to develop functional groups based on key life-history trait responses to changing environmental conditions, to enable broader-scale predictions of distribution and persistence in the future.

Environmental Biotechnology Under A Changing Climate

Environmental biotechnology is when biotechnology is applied to and used to study the natural environment, and could also imply that, one try to harness biological process for commercial uses and exploitation. Environmental biotechnology can simply be described as “the optimal use of nature, in the form of plants, animals, bacteria, fungi and algae, to produce renewable energy, food and nutrients in a synergistic integrated cycle of profit making processes, where the waste of each process becomes the feedstock for another process”. Biotechnology applications in food security, agriculture and climate change, regarding climate change, the Intergovernmental Panel on Climate Change (IPCC) asserts that on an average, global temperatures will increase worldwide by 0.2 degrees per decade. There will be changes in rainfall regimes representing both an increase and decrease in precipitation, and an increased frequency of droughts and floods will result. Climate change will also have an impact on production losses, which could worsen hunger in developing countries, beyond the current one billion that are going hungry. Many of agricultural resources will become more threatened over time, as global climate change will erode genetic diversity and destabilize food ecosystems, significantly. Under these circumstances, there is a need to improve crops by means of genetic modification, for food safety and to sustain agriculture. Biotechnological contributions, to crop adaptation to climate change do not only, or even mainly, concern the placement into the crop of one or more genes, from an organism with which the crop could not normally breed (i.e. genetically modified crops). Biotechnological tools focus on providing the ability to directly detect and transfer genes of interest from other plant lines or organisms into the crop of interest, without the continuing need to use the appearance or stress response of the plant (its phenotype), as a proxy for the presence of that gene. Genes that confer a measure of abiotic stress tolerance can be obtained from germbank collections, wild relatives of the crop, or from other organisms known to perform well under water deficit/excess or high salinity or temperatures. Careful use of the molecular breeding tools have enabled a three to five-fold increase in rice yields and a fivefold increase in the yields of the best maize lines. These materials are being actively disseminated into breeding lines across Asia and Africa now, and just as importantly, they have been passed to commercial seed companies, for the production of superior hybrid lines. Biotechnology approaches have the potential to enhance crop production under different stress conditions. On the one hand, abiotic stresses are complex in nature; on the other hand, there are several challenges that have restricted the realization of the full potential of using biotechnology approaches in crop breeding, nevertheless, with current and fast emerging technologies such as RNA. Eventually, the adoption of biotech crops to mitigate abiotic stresses, that are expected to increase in frequency and intensity in coming years, will depend on public perceptions and public acceptance, as well as on cultural and institutional processes in developing countries.

Dry rainforests have a distinct and more diverse assemblage of epigaeic invertebrates than eucalypt woodlands: implications for ecosystem health monitoring.

Dry rainforests have a disproportionately higher diversity of plant species than the eucalypt woodlands that dominate Australian landscapes. While several endemic vertebrate species have been found in dry rainforests, their values for invertebrate fauna are relatively poorly known. Epigaeic invertebrates of four patches of dry rainforests in Queensland were annually compared to those of nearby eucalypt woodlands using pitfall traps between 1998 and 2002. Dry rainforests had significantly greater Order-level richness, lower dominance, fewer invertebrates and a different assemblage. Invertebrate composition was characterized by typically shelter- or moisture-requiring taxa, such as earwigs, pseudoscorpions, gastropods, millipedes, isopods, Diplura and Symphyla. This may reflect the greater prevalence of moister microhabitats in dry rainforests in comparison to woodlands. Coinciding with several years of low dry season rainfall, invertebrate abundance declined in dry rainforests but not woodlands, indicating that dry rainforest epigaeic fauna may be more sensitive to reduced soil moisture compared with woodland fauna. This may reflect differences of some taxa in evolutionary lineage or the mediation of vegetation phenology and differences in drought susceptibility of the two vegetation types. Importantly, the study provides evidence that faunal assemblages of drier rainforests may be more vulnerable to tipping points associated with droughts and changing rainfall regimes than nearby woodlands. Furthermore, it demonstrated the importance of including a range of vegetation types in any long-term monitoring programs and that an understanding of ecological responses to environmental drivers is critical to interpreting data. The relatively greater sensitivity of dry rainforest biota to droughts compared with woodlands indicates that it could provide a regional “control” for this effect.

Impact of simulated changes in rainfall regime and nutrient deposition on the relative dominance and isotopic composition of ruderal plants in anthropogenic grasslands

Plant productivity in drylands is frequently co-limited by water and nutrient availability, and thus is expected to be influenced by ongoing changes in rainfall regime and atmospheric nutrient deposition. Roadside grasslands are widespread worldwide, represent ecologically meaningful examples of highly dynamic anthropogenic ecosystems, and are well suited to investigate global change effects on plant performance. We evaluated the effects of changes in water and nutrient availability on the relative dominance and physiological performance of Bromus rubens, Carduus tenuifolius and Melilotus officinalis, which belong to contrasting functional groups (grasses, non-legume forbs and legumes, respectively). We conducted a factorial field experiment in two semiarid roadside grasslands in central Spain with the following factors: watering (no water addition vs. watering with 50% of the monthly total precipitation median) and fertilization (no fertilization vs. addition of 80 kg N ha−1 year−1). The cover of the species evaluated, was surveyed over a 2-year period. Plant isotopic composition (leaf δ13C and δ18O) and nutrient concentrations (foliar N, P and K) were used to assess plant ecophysiological performance. Carduus was able to cope with lower water availability levels through stomatal adjustments without a significant reduction in its relative dominance. The relative dominance of Bromus was negatively affected by even moderate water stress, although elevated nutrient deposition buffered the adverse impact of drought through a nutrient-mediated enhancement of plant water use efficiency. Increased nutrient availability strongly decreased the relative dominance of Melilotus, irrespective of water availability. Species-specific physiological mechanisms of adjustment to treatments suggest that plant communities in roadside grasslands will not respond as a unit to global environmental change. The characterization of species-specific responses to major global change drivers may improve predictions about the future dynamics of plant communities in novel ecosystems such as roadside slopes.

Modeling water availability for trees in tropical forests

Abstract Modeling soil water availability for tropical trees is a prerequisite to predicting the future impact of climate change on tropical forests. In this paper we develop a discrete-time deterministic water balance model adapted to tropical rainforest climates, and we validate it on a large dataset that includes micro-meteorological and soil parameters along a topographic gradient in a lowland forest of French Guiana. The model computes daily water fluxes (rainfall interception, drainage, tree transpiration and soil plus understorey evapotranspiration) and soil water content using three input variables: daily precipitation, potential evapotranspiration and solar radiation. A novel statistical approach is employed that uses Time Domain Reflectometer (TDR) soil moisture data to estimate water content at permanent wilting point and at field capacity, and root distribution. Inaccuracy of the TDR probes and other sources of uncertainty are taken into account by model calibration through a Bayesian framework. Model daily output includes relative extractable water, REW, i.e. the daily available water standardized by potential available water. The model succeeds in capturing temporal variations in REW regardless of topographic context. The low Root Mean Square Error of Predictions suggests that the model captures the most important drivers of soil water dynamics, i.e. water refilling and root water extraction. Our model thus provides a useful tool to explore the response of tropical forests to climate scenarios of changing rainfall regime and intensity.