Measurement and modelling of evapotranspiration in three fynbos vegetation types

Many studies have investigated the water relations of indigenous plants in the fynbos shrublands of the Cape, South Africa. These have mainly focused on understanding the mechanisms by which individual plant species respond to droughts, the frequency and severity of which is expected to increase due to climate change. However, comparatively little information exists on the dynamics of water use by indigenous plants in the region, and, in particular, how water use varies seasonally and between sites. In this study we determined water use by 3 fynbos vegetation types growing at 4 different sites, namely: (i) lowland Atlantis Sand Plain fynbos growing on deep sandy soils, (ii) Kogelberg Sandstone fynbos growing in a riparian zone on deep alluvial soils, (iii) dryland Kogelberg Sandstone fynbos growing on shallow sandy soils at a montane site, and (iv) alluvial Swartland fynbos growing in clayey soils. Evapotranspiration (ET) was quantified at each site during specific periods using a boundary layer scintillometer and energy balance system. A simple dual source model in which the stand ET was calculated as the algebraic sum of outputs from soil evaporation and transpiration sub-models was used to scale up the ET measurements to annual values. The data showed large differences in ET depending on site characteristics and on plant attributes. Dense stands of riparian Sandstone Fynbos had an annual ET of 1 460 mm which exceeded the reference ET of 1 346 mm. Dryland Sandstone Fynbos used only 551 mm of water per year while the Sand Plain Fynbos’ annual ET was 1 031 mm, which was similar to the reference ET of 1 059 mm. We conclude that some indigenous plant species use large volumes of water which should be accounted for in, e.g., groundwater recharge estimates, and calculations of incremental water gains after clearing alien invasive plants, among other applications.Keywords: Evapotranspiration, fynbos, scintillometer, Western Cap

Comparing two approaches for parsimonious vegetation modelling in semiarid regions using satellite data

[EN] Large portions of Earth's terrestrial surface are arid or semiarid. As in these regions, the hydrological cycle and the vegetation dynamics are tightly interconnected, a coupled modelling of these two systems is needed to fully reproduce the ecosystem behaviour. In this paper, the performance of two parsimonious dynamic vegetation models, suitable for the inclusion in operational ecohydrological models and based on well-established but different approaches, is compared in a semiarid Aleppo Pine region. The first model [water use efficiency (WUE) model] links growth to transpiration through WUE; the second model [light use efficiency (LUE) model] simulates biomass increase in relation to absorbed photosynthetically active radiation and LUE. Furthermore, an analysis of the information contained in MODIS products is presented to indicate the best vegetation indices to be used as observational verification for the models. Enhanced Vegetation Index is reported in literature to be highly correlated with leaf area index, so it is compared with modelled LAI(mod) (rWUE model = 0.45; rLUE model = 0.57). In contrast, Normalized Difference Vegetation Index appears highly linked to soil moisture, through the control exerted by this variable on chlorophyll production, and is therefore used to analyze LAI*(mod), models' output corrected by plant water stress (rWUE model = 0.62; rLUE model = 0.59). Moderate-resolution imaging spectroradiometer Leaf Area Index and evapotranspiration are found to be unrealistic in the studied area. The performance of both models in this semiarid region is found to be reasonable. However, the LUE model presents the advantages of a better performance, the possibility to be used in a wider range of climates and to have been extensively tested in literature. (C) Copyright 2014 John Wiley & Sons, Ltd.The research leading to these results has received funding from the Spanish Ministry of Economy and Competitiveness through the research projects FLOOD-MED (ref. CGL2008-06474-C02-02), SCARCE-CONSOLIDER (ref. CSD2009-00065) and ECO-TETIS (ref. CGL2011-28776-C02-01), and from the European Community's Seventh Framework Programme (FP7 2007-2013) under grant agreement no. 238366. The MODIS data were obtained through the online Data Pool at the NASA Land Processes Distributed Active Archive Centre (LP DAAC), USGS/Earth Resources Observation and Science (EROS) Centre, Sioux Falls, South Dakota (https://lpdaac.usgs.gov/get_data). The meteorological data were provided by the Spanish National Weather Agency (AEMET). The authors thank Antonio Del Campo Garcia and Maria Gonzalez Sanchis at the Universitat Politecnica de Valencia for their support and valuable comments.Pasquato, M.; Medici, C.; Friend, A.; Francés, F. (2015). Comparing two approaches for parsimonious vegetation modelling in semiarid regions using satellite data. Ecohydrology. 8(6):1024-1036. https://doi.org/10.1002/eco.1559S102410368

Synergy of extreme drought and shrub invasion reduce ecosystem functioning and resilience in water-limited climates

Extreme drought events and plant invasions are major drivers of global change that can critically affect ecosystem functioning and alter ecosystem-atmosphere exchange. Invaders are expanding worldwide and extreme drought events are projected to increase in frequency and intensity. However, very little is known on how these drivers may interact to affect the functioning and resilience of ecosystems to extreme events. Using a manipulative shrub removal experiment and the co-occurrence of an extreme drought event (2011/2012) in a Mediterranean woodland, we show that native shrub invasion and extreme drought synergistically reduced ecosystem transpiration and the resilience of key-stone oak tree species. Ecosystem transpiration was dominated by the water use of the invasive shrub Cistus ladanifer, which further increased after the extreme drought event. Meanwhile, the transpiration of key-stone tree species decreased, indicating a competitive advantage in favour of the invader. Our results suggest that in Mediterranean-type climates the invasion of water spending species and projected recurrent extreme drought events may synergistically cause critical drought tolerance thresholds of key-stone tree species to be surpassed, corroborating observed higher tree mortality in the invaded ecosystems. Ultimately, this may shift seasonally water limited ecosystems into less desirable alternative states dominated by water spending invasive shrubs

A multi-scale modelling framework to guide management of plant invasions in a transboundary context

Background Attention has recently been drawn to the issue of transboundary invasions, where species introduced and naturalized in one country cross international borders and become problematic in neighbouring countries. Robust modelling frameworks, able to identify the environmental drivers of invasion and forecast the current and future potential distribution of invasive species, are needed to study and manage invasions. Limitations due to the lack of species distribution and environmental data, or assumptions of modelling tools, often constrain the reliability of model predictions. Methods We present a multiscale spatial modelling framework for transboundary invasions, incorporating robust modelling frameworks (Multimodel Inference and Ensemble Modelling) to overcome some of the limitations. The framework is illustrated using Hakea sericea Schrad. (Proteaceae), a shrub or small tree native to Australia and invasive in several regions of the world, including the Iberian Peninsula. Two study scales were considered: regional scale (western Iberia, including mainland Portugal and Galicia) and local scale (northwest Portugal). At the regional scale, the relative importance of environmental predictors sets was evaluated and ranked to determine the main general drivers for the species distribution, while the importance of each environmental predictor was assessed at the local scale. The potential distribution of H. sericea was spatially projected for both scale areas. Results Model projections for western Iberia suggest that a large area is environmentally suitable in both Portugal and Spain. Climate and landscape composition sets were the most important determinants of this regional distribution of the species. Conversely, a geological predictor (schist lithology) was more important in explaining its local-scale distribution. Conclusions After being introduced to Portugal, H. sericea has become a transboundary invader by expanding in parts of Galicia (Spain). The fact that a larger area is predicted as environmentally suitable in Spain raises concerns regarding its potential continued expansion. This highlights the importance of transboundary cooperation in the early management of invasions. By reliably identifying drivers and providing spatial projections of invasion at multiple scales, this framework provides insights for the study and management of biological invasions, including the assessment of transboundary invasion risk.This work was funded by FEDER funds through the Operational Programme for Competitiveness Factors - COMPETE and by National Funds through FCT - Foundation for Science and Technology under the project PTDC/AAGMAA/4539/2012 / FCOMP-01-0124-FEDER-027863 (IND_CHANGE). J. Vicente is supported by POPH/FSE funds and by National Funds through FCT - Foundation for Science and Technology through Post-doctoral grant SFRH/BPD/84044/2012. D.M. Richardson acknowledges support from the DST-NRF Centre of Excellence for Invasion Biology and the National Research Foundation (grant 85417).info:eu-repo/semantics/publishedVersio

The effects of Δ9-tetrahydrocannabinol on the dopamine system

Δ(9)-tetrahydrocannabinol (THC), the main psychoactive ingredient in cannabis, is a pressing concern to global mental health. Patterns of use are changing drastically due to legalisation, availability of synthetic analogues (‘spice’), cannavaping and aggrandizements in the purported therapeutic effects of cannabis. Many of THC’s reinforcing effects are mediated by the dopamine system. Due to complex cannabinoid-dopamine interactions there is conflicting evidence from human and animal research fields. Acute THC causes increased dopamine release and neuron activity, whilst long-term use is associated with blunting of the dopamine system. Future research must examine the long-term and developmental dopaminergic effects of the drug

Critical Invasion Science: Weeds, Pests, and Aliens

The study of invasive plants and animals calls strongly for a critical approach due to the deeply social nature of invasion landscapes, the power relations affecting the science of invasions, and the differential impacts of weed or pest control on lives and landscapes. I first explore what a “critical” invasion science means. Then I investigate several aspects of invasion science ripe for critical analysis: the history of the science (to understand what the science is doing and why), the terminology and categories of analysis, and the highly contested social, political, and ethical context within which invasion management takes place. I conclude with four proposals for further work in critical invasion science and examples of the types of questions it might ask

Impact of invasive alien plants on water provision in selected catchments

We analyse the impact of failing to control invasive alien plants (IAPs) on the water supply to the Berg River and De Hoop Dams, in other words, the opportunity cost of not clearing IAPs in these two catchments. To do this we used models to assess and compare the impact of current and future invasions on inflows into the dams. Although the clearing of current invasions would only provide a modest increase in the amount of water compared to, for example, the construction of another dam, failure to clear the invasion will have a negative impact on water security in the long term. We estimated that the Berg River Dam could lose up to 51% of its mean annual inflows to IAPs over a 45-year period, and the De Hoop Dam catchment could lose up to 44%. These impacts would continue to increase over time, and the costs of control could become very high as the plants invade rugged terrain. Major infrastructural development requires Ministerial approval, supported by advice from senior officials. We suggest that such advice should substantively take sufficient account of the benefits of clearing existing invasions, or at least of preventing further invasions. Our results suggest that serious consequences arise from insufficient investment in catchment management. An integrated approach to the management of the supply of and demand for water, that ensures long-term sustainability, is essential in informed decision-making and the early control of IAPs is a key component of that approach

Water-use characteristics of Palmiet (Prionium serratum), an endemic South African wetland plant

Palmiet, Prionium serratum, is an endemic wetland plant which dominates oligotrophic wetlands throughout the Cape Floristic Region, South Africa. Palmiet is often perceived as undesirable by landowners, in part because it is thought to have high water-use, although little is known about the water-use of this important wetland species. We estimated the water-use dynamics of Palmiet at the leaf scale, using stomatal conductance measurements, and at the wetland scale, by modelling evapotranspiration using remote sensing and an energy-balance model. Factors that influenced Palmiet water-use were also considered, and seasonal variations were analysed. The aim was to estimate Palmiet wetland water-use, and to develop a set of crop factors (Kc) for use in hydrological modelling of catchments containing Palmiet wetlands. Results show that Palmiet has a comparatively low stomatal conductance (11–152 mmol∙m-2∙s-1), which was lower in summer than winter, and moderate evapotranspiration for a riparian species (1 220 mm∙a-1 compared to a local reference evapotranspiration of 1 302 mm∙a-1 and A-Pan evaporation of 2 809 mm∙a-1), which was higher in summer (more energy to drive evapotranspiration and higher vapour pressure deficits). Morphological and physiological adaptations to nutrient poverty or periodic drought are suggested theories which may explain the controls on transpiration for Palmiet