Abstract
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.
Highlights
Climate change effects on ecosystems are being investigated at different spatial and temporal scales
We examine the information provided by Unmanned aerial vehicles (UAVs) images and assess the effects of experimental treatments at plot scale, by which we hypothesize that effects at different scales may be different and can enhance the interpretation of the observed results
The NDVI values retrieved from Sequoia measurements were significantly related to Cropscan measurements at different scales (Table 2), being weaker at plot scale and higher at FOV scale for uncovered plots and for all measurements
Summary
Climate change effects on ecosystems are being investigated at different spatial and temporal scales. Ecological Research (LTER) networks are informing about the factors driving changes in biodiversity, the self-organizing capacity of ecosystems, the effects of rare events and disturbances, the impacts of stressors on ecosystem function and the interactions between short- and long-term trends [1]. These LTER networks rely on site-based monitoring and research by providing data and detecting. The LTER networks’ major contribution is the enlargement of temporal and spatial scales to test global research hypotheses In this case, as in the NEON [2] and GCOS [3] networks, observational approach is the dominant method
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