Reduction in primary production followed by rapid recovery of plant biomass in response to repeated mid-season droughts in a semiarid shrubland

The frequency and severity of extreme weather events, including droughts, are expected to increase due to the climate change. Climate manipulation field experiments are widely used tools to study the response of key parameters like primary production to the treatments. Our study aimed to detect the effect of drought on the aboveground biomass and primary production both during the treatments as well as during the whole growing seasons in semiarid vegetation. We estimated aboveground green biomass of vascular plants in a Pannonian sand forest-steppe ecosystem in Hungary. We applied non-destructive field remote sensing method in control and drought treatments. Drought treatment was carried out by precipitation exclusion in May and June, and was repeated in each year from 2002. We measured NDVI before the drought treatment, right after the treatment, and at the end of the summer in 2011 and 2013. We found that the yearly biomass peaks, measured in control plots after the treatment periods, were decreased or absent in drought treatment plots, and consequently, the aboveground net primary production was smaller than in the control plots. At the same time, we did not find general drought effects on all biomass data. The studied ecosystem proved resilient, as the biomass in the drought-treated plots recovered by the next drought treatment. We conclude that the effect of drought treatment can be overestimated with only one measurement at the time of the peak biomass, while multiple within-year measurements better describe the response of biomass

Effects of simulated grazing on open perennial sand grassland

We studied biomass and species composition changes of open perennial sand grassland ( Festucetum vaginatae ) as response to different levels of simulated grazing pressures. We conducted a factorial micro-plot field experiment on previously grazed grassland that has been abandoned for a long time. In a two-way factorial design of 12 treatments × 8 repeats, we performed clipping (twice a year for three years) and litter treatments (removing and adding litter once at the beginning of the experiment) to simulate components of grazing, namely the biomass removal and the reduction of the litter accumulation. We used field spectroscopy and visual canopy cover estimation to measure the effects on the amount of the above-ground green biomass and on the vegetation composition

Enhancement of Ecological Field Experimental Research by Means of UAV Multispectral Sensing

Although many climate research experiments are providing valuable data, long-term measurements are not always affordable. In the last decades, several facilities have secured long-term experiments, but few studies have incorporated spatial and scale effects. Most of them have been implemented in experimental agricultural fields but none for ecological studies. Scale effects can be assessed using remote sensing images from space or airborne platforms. Unmanned aerial vehicles (UAVs) are contributing to an increased spatial resolution, as well as becoming the intermediate scale between ground measurements and satellite/airborne image data. In this paper we assess the applicability of UAV-borne multispectral images to provide complementary experimental data collected at point scale (field sampling) in a long-term rain manipulation experiment located at the Kiskun Long-Term Socio-Ecological Research (LTSER) site named ExDRain to assess the effects on grassland vegetation. Two multispectral sensors were compared at different scales, the Parrot Sequoia camera on board a UAV and the portable Cropscan spectroradiometer. The NDVI values were used to assess the effect of plastic roofs and a proportional reduction effect was found for Sequoia-derived NDVI values. Acceptable and significant positive relationships were found between both sensors at different scales, being stronger at Cropscan measurement scale. Differences found at plot scale might be due to heterogeneous responses to treatments. Spatial variability analysis pointed out a more homogeneous response for plots submitted to severe and moderate drought. More investigation is needed to address the possible effect of species abundance on NDVI at plot scale contributing to a more consistent representation of ground measurements. The feasibility of carrying out systematic UAV flights coincident or close to ground campaigns will certainly reveal the consistency of the observed spatial patterns in the long run.This research was funded by the European Union’s Horizon 2020 Research and Innovation Program under grant agreement No. 654359 (eLTER Horizon 2020 project). Gy. K-D. was supported by the National Research, Development and Innovation Fund (NRDI Fund) of Hungary (Nos. K112576, K129068)We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)Peer reviewe

Long-term weather sensitivity of open sand grasslands of the Kiskunság Sand Ridge forest-steppe mosaic after wildfires

We studied the long-term impact of wildfire on the vegetation dynamics of sand grasslands in a forest-steppe vegetation mosaic in Central Hungary (Kiskunság). Long-term permanent quadrat monitoring was carried out from 1997 to 2008. We sampled the forest-steppe mosaic both in burnt and unburnt areas in 100 patches altogether using 1 m × 1 m quadrats. The effect of fire and precipitation on vegetation dynamics was characterized by patch type transitions between years. Patch types were defined by means of Cocktail method. Nine patch types of sand grasslands were altogether identified. The least productive patch types, bare soil and cryptogam dominance, did not occur in the burnt patches, while annual dominated patch type appeared only in burnt patches. The frequencies of patch type changes were significantly higher in burnt patches than in unburnt ones, independently on time after fire. All the eight patch types found in the unburnt patches proved permanent, while in the burnt patches only four of seven were so. The relative frequency of patch type changes did not correlate with precipitation in the vegetation period in the unburnt patches, while positively correlated in the burnt patches. It was concluded that the long-term difference in grassland dynamics between the unburnt and burnt patches, i.e., the excess of the patch type transitions in the burnt grasslands, is due to increased drought sensitivity of the grassland, which is the consequence of the elimination of the woody component of the forest-steppe vegetation

Modelling of carbon cycle in grassland ecosystems of diverse water availability using Biome-BGCMuSo

Grassland ecosystems have an important role in agriculture, and at the same time, are highlysensitive to changes in land use and climate change. Simulation of the biogeochemical cycles ofmanaged grasslands may help in identifying and quantifying the main processes contributing tochanges in their productivity. In our work we used the latest version of Biome-BGCMuSo model,the modified version of the widely used biogeochemical Biome-BGC model, with structuralimprovements to simulate herbaceous ecosystem carbon and water cycles more faithfully.Our sampling areas were in diverse grasslands in the Kiskunság, Hungary. Different soil textureand changing water table level, consequently highly different water conditions are characteristicin these ecosystems, influencing the development and productivity of vegetation, and also thepotential for animal husbandry. Hence, for the meadows and the marshland ecosystems weincluded mowing management in the simulations. In order to compare the ecosystems and studytheir functions we simulated ecosystem variables, such as ecosystem respiration, standing andharvested aboveground biomass etc.We found that ecosystems with higher water availability are more sensitive to changes in waterconditions, and their productivity is more variable between years. By calibration processes usingleaf area and aboveground biomass we aim to further specify our findings.Biome-BGCMuSo is available as a standalone model, but also through virtual laboratoryenvironment and Biome-BGC Projects database (http://ecos.okologia.mta.hu/bbgcdb)developed within the BioVeL project (http://www.biovel.eu). Scientific workflow management,web service and desktop grid technology can support model optimization in the so-called"calibrated runs" within MACSUR