remote sensing Article Intra-Annual Variabilities of Rubus caesius L. Discrimination on Hyperspectral and LiDAR Data Anna Jaroci ´nska 1,* , Dominik Kope´c 2,3 , Barbara Tokarska-Guzik 4 and Edwin Raczko 1 1 Department of Geoinformatics, Cartography and Remote Sensing, Chair of Geomatics and Information Systems, Faculty of Geography and Regional Studies, University of Warsaw, 00-927 Warsaw, Poland; [email protected] 2 Department of Biogeography, Paleoecology and Nature Conservation, Faculty of Biology and Environmental, University of Lodz, 90-237 Łód´z,Poland; [email protected] 3 MGGP Aero sp. z o.o., 33-100 Tarnów, Poland 4 Research Team of Botany and Nature Protection, Institute of Biology, Biotechnology and Environmental Protection, Faculty of Natural Sciences, University of Silesia in Katowice, 40-032 Katowice, Poland; [email protected] * Correspondence: [email protected]; Tel.: +48-606491444 Abstract: The study was focused on a plant native to Poland, the European dewberry Rubus caesius L., which is a species with the ability to become excessively abundant within its original range, potentially causing significant changes in ecosystems, including biodiversity loss. Monitoring plant distributions over large areas requires mapping that is fast, reliable, and repeatable. For Rubus, different types of data were successfully used for classification, but most of the studies used data with a very high spectral resolution. The aim of this study was to indicate, using hyperspectral and Light Detection and Ranging (LiDAR) data, the main functional trait crucial for R. caesius differentiation from non-Rubus. This analysis was carried out with consideration of the seasonal variability and different percentages of R. caesius in the vegetation patches. The analysis was based on hyperspectral HySpex images and Airborne Laser Scanning (ALS) products. Data were acquired during three campaigns: early summer, summer, and autumn. Differentiation based on Linear Discriminate Citation: Jaroci´nska,A.; Kope´c,D.; Analysis (LDA) and Non-Parametric Multivariate Analysis of Variance (NPMANOVA) analysis was Tokarska-Guzik, B.; Raczko, E. Intra-Annual Variabilities of Rubus successful for each of the analysed campaigns using optical data, but the ALS data were less useful caesius L. Discrimination on for identification. The analysis indicated that selected spectral ranges (VIS, red-edge, and parts of Hyperspectral and LiDAR Data. the NIR and possibly SWIR ranges) can be useful for differentiating R. caesius from non-Rubus. The Remote Sens. 2021, 13, 107. most useful indices were ARI1, CRI1, ARVI, GDVI, CAI, NDNI, and MRESR. The obtained results https://doi.org/10.3390/rs13010107 indicate that it is possible to classify R. caesius using images with lower spectral resolution than hyperspectral data. Received: 13 November 2020 Accepted: 28 December 2020 Keywords: dewberry; HySpex; imaging spectroscopy; vegetation indices; airborne laser scanning; Published: 31 December 2020 non-parametric multivariate analysis of variance; linear discriminant analysis Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional clai- ms in published maps and institutio- 1. Introduction nal affiliations. Growing global phenomena such as land-use changes or habitat fragmentation, and the accompanying climate change yielding changes in the ecological and geographical ranges of species, lead to biodiversity loss [1–5]. Plant species that spread on a massive scale Copyright: © 2020 by the authors. Li- beyond their original geographical ranges and native species becoming excessively abun- censee MDPI, Basel, Switzerland. dant within their original ranges often cause significant changes in ecosystems, including This article is an open access article biodiversity loss [6–8]. distributed under the terms and con- The present study is focused on a Rubus caesius L. species from the brambles genus ditions of the Creative Commons At- (Rubus), which has traits that favour spreading, such as low trophic requirements and quick tribution (CC BY) license (https:// adaptation to changing habitat conditions. In addition, by competing with other resident creativecommons.org/licenses/by/ species, brambles limit the populations of other species by competition and strongly modu- 4.0/). Remote Sens. 2021, 13, 107. https://doi.org/10.3390/rs13010107 https://www.mdpi.com/journal/remotesensing Remote Sens. 2021, 13, x FOR PEER REVIEW 2 of 23 Remote Sens. 2021, 13, 107 2 of 22 strongly modulate species interactions and community composition, leading to a decline inlate biodiversity species interactions in the affected and community habitats [9– composition,12], including leading protected to a in decline Europe in Natura biodiversity 2000 habitats.in the affected habitats [9–12], including protected in Europe Natura 2000 habitats. RubusRubus caesius L. (European(European dewberry,dewberry,R. R. caesius caesius) belongs) belongs to to the the large large and and diverse diverse genus ge- nusof Rubus of Rubus(bramble) (bramble) within within the Rosaceaethe Rosaceae family, family, covering covering about about 430 and430 and 750 species750 species [13]. [13].Numerous Numerous species species and and infrageneric infrageneric taxa taxa have have been been subsequently subsequently recognised,recognised, recently reachingreaching about about 1500 1500 species species worldwide [14], [14], depending on the taxonomic approach. This plant is aa half-bushhalf-bush reaching reaching a heighta height of of 0.5–2 0.5–2 m withm with shoots shoots lying lying on the on ground. the ground. The main The mainidentification identification features features of this of species this species include include the morphology the morphology of its stems of its (usually stems (usually slender slenderand pruinose, and pruinose, with short, with slender,short, slender, and needle-like and needle-like prickles), prickles), leaves leaves (three-foliate (three-foliate with withbroad-based, broad-based, gibbous gibbous lateral lateral leaflets; leaflets; the stipulesthe stipules are broadlyare broadly lanceolate) lanceolate) and and generative gener- ativeorgans: organs: flowers flowers (white (white flowers, flowers, appearing appear bothing onboth previous-year on previous-year and current-year and current-year twigs, twigs,gathered gathered in corymbose in corymbose inflorescences) inflorescences) and fruit and (ripe fruit black (ripe drupelesblack drupeles pruinose) pruinose) [15]. [15]. RubusRubus caesius caesius growsgrows in forest and shrub communities with natural features (mostly inin riverside riverside riparian riparian woodland), woodland), as as well well as as at at the the edges edges ofof forests forests but but much much more more often often in meadowsin meadows (formed (formed in inthe the habitats habitats of of ancient ancient riparian riparian forests) forests) and and ruderal ruderal communities (Figure(Figure 11))[ [15–17].15–17]. Dewberry Dewberry is is also also a a threat to non-forest natural habitats [16]. [16]. In many cases,cases, the the plant plant creates creates large, large, homogeneous homogeneous patc patches.hes. It also also may may cause cause problems problems as as a a weed, weed, e.g.,e.g., in in maize maize and and winter wheat [18,19] [18,19] or other cereal crops (own observations). Figure 1. ImagesImages of of RubusRubus caesius caesius takentaken at at the the study study area area acquired in summer (second campaign, C2). R.R. caesius caesius dependsdepends mainly mainly on on vegetative vegetative reproduction reproduction using the buds on its roots and creepingcreeping stems andand lessless onon itsits seeds.seeds. Its Its developmental developmental phases phases correspond correspond to to the the seasons seasons of ofthe the year, year, but butR. caesiusR. caesiustends tends to flower to flower throughout throughout much much of the of growing the growing season season [20]. Thus,[20]. Thus,vegetative vegetative growth growth occurs occurs from early from spring, early sp withring, the with flowering the flowering and fruiting and fruiting phase ranging phase rangingfrom May from to September. May to September. The first-year The first-year canes or shoots canes oforR. shoots caesius ofare R. pedunculated,caesius are peduncu- round, lated,straight, round, thin, straight, glabrous, thin, or slightlyglabrous, pubescent, or slightly waxy pubescent, frosted, waxy herbaceous frosted, bluish,herbaceous glaucous, blu- ish,and glaucous, tinged red and where tinged exposed red towhere sun. Two-year-oldexposed to sun. shoots Two-year-o are partlyld woodyshoots atare the partly base, woodybranched, at the bloom base, andbranched, bear fruit, bloom and and usually bear fruit, die afterand usually two seasons. die after The two leaves seasons. contain The leavestannins, contain flavonoids, tannins, anthocyanin flavonoids, dyes,anthocyanin organic dyes, acids, organic vitamin acids, C, vitamin C, B, vitamin vitamin B, P, vitamininositol, P, and inositol, pectin [and21]; pectin moreover, [21];Rubus moreover, caesius Rubusleaf extracts caesius haveleaf extracts medicinal have value medicinal [22,23]. valueA detailed [22,23]. description A detailed of description species variability of species during variability the growing during seasonthe growing is described season inis describedSection 3.2 in. Section 3.2. RubusRubus caesius isis widespreadwidespread throughout throughout Europe Europe and and Western Western and and Central Central Asia Asia