Using Lidar Data to Analyse Sinkhole Characteristics Relevant for Understory Vegetation under Forest Cover\u2014Case Study of a High Karst Area in the Dinaric Mountains

In this article, we investigate the potential for detection and characterization of sinkholes under dense forest cover by using airborne laser scanning data. Laser pulse returns from the ground provide important data for the estimation of digital elevation model (DEM), which can be used for further processing. The main objectives of this study were to map and determine the geomorphometric characteristics of a large number of sinkholes and to investigate the correlations between geomorphology and vegetation in areas with such characteristics. The selected study area has very low anthropogenic influences and is particularly suitable for studying undisturbed karst sinkholes. The information extracted from this study regarding the shapes and depths of sinkholes show significant directionality for both orientation of sinkholes and their distribution over the area. Furthermore, significant differences in vegetation diversity and composition occur inside and outside the sinkholes, which indicates their presence has important ecological impacts

Rastlinska vrstna diverziteta izbranih dobovih in gradnovih gozdov v Sloveniji

In Slovenia, the plant species diversity on 225 research plots dominated by pedunculate oak (Quercus robur L.) and by sessile oak (Quercus petraea (Matt.) Liebl.) has been analysed. Plots of Q. robur are located in five, andplots of Q. petraea in four semi-natural managed forest complexes. In the tree layer, 28 species were found beside the dominant two oak species, with Carpinus betulus L., Picea abies (L.) Karst., Quercus cerris L. and Fagus sylvatica L. having significant shares of growing stock. Based on the understorey vegetation (shrub and herb layer, terricolous mosses), the Ddetrended Correspondence Analysis (DdCA) made a clear distinction between plots with dominant Q. robur and those with Q. petraea. The understorey vegetation also proved to be a valuable indicator of the site conditions and of forest management in the past. Based on ordination, lowland pedunculate oak forests of relatively long standing near to natural management have been separated from the pedunculate oak forests where spruce was favoured by the forest management, and from the man-made pedunculate oak stands on primary sites of Q. petraea. DCA clearly differentiated the sessile oak forests in warmer climate of Sub-Mediterranean region, and in warmer meso-sites of Pre-Pannonian region from other sessile oak forests. The main gradients of vegetation structure and of species diversity, as well main ecological gradients in different oak forests were obtained by ordination technique.Na 225 raziskovalnih ploskvah v dobovih (Quercus robur L.) in gradnovih (Quercus petraea (Matt.) Liebl.) gozdovih smo analizirali rastlinsko vrstno pestrost. Dobove ploskve so postavljene v petih, gradnove pa v štirih gospodarjenih gozdnih kompleksih. V drevesni plasti preučevanih gozdnih ekosistemov se poleg dominantnih vrst hrasta pojavlja še 28 vrst, med katerimi so v lesni zalogi bolj zastopani beli gaber (Carpinus betulus L.), smreka (Picea abies (L.) Karst.), cer (Quercus cerris L.) in bukev (Fagus sylvatica L.). Ordinacija DCA (Detrended Correspondence Analysis) je samo na osnovi vrst v pritalnih plasteh vegetacije (grmovna in zeliščna plast, na tleh rastoči mahovi) jasno ločila ploskve s prevladujočim dobom od ploskev z gradnom. Vrste pritalnih plasti so dober indikator rastiščnih razmer kot tudi gospodarjenja z gozdovi v preteklosti. Nna tej osnovi je ordinacija ločila nižinske dobove gozdove z razmeroma sonaravnim gospodarjenjem v daljšem obdobju od dobovih gozdov, v katerih so v preteklosti pospeševali smreko, in od umetno zasnovanega dobovega gozda na primarnih rastiščih gradna. Analiza jeločila tudi gradnov gozd, ki uspeva v toplejšem podnebju v submediteranskem območju, in gradnov gozd na toplejših rastiščih v predpanonskem območju od preostalih dveh gradnovih gozdov. Ordinacija raziskovalnih ploskev dobro odseva razlike v floristični sestavi hrastovih gozdov, nakazuje gradiente pestrosti pritalnih plasti vegetacije in glavne ekološke gradiente

The current distribution of Black locust (Robinia pseudoacacia L.) in Slovenia and predictions for the future

V raziskavi smo ugotavljali lesno zalogo robinije (Robinia pseudoacacia L.) in njen delež v gozdovih Slovenije. Poleg tega smo z uporabo empiričnega modela in scenarijev podnebnih sprememb napovedali njeno pojavljanje in delež v prihodnost. Robinija je trenutno najbolj pogosta tujerodna drevesna vrsta v naših gozdovih. Sedanja lesna zaloga robinije dosega okoli 0,6 % celotne lesne zaloge naših gozdov. Najpogostejša je v gozdovih GGO Murska Sobota in Kraškega GGO. Ob uresničitvi scenarijev podnebnih sprememb, ki vsi predvidevajo povečanje povprečnih temperatur zraka v prihodnosti, se bo delež lesne zaloge robinije postopoma še povečeval na vzhodnem in severovzhodnem ter jugozahodnem delu Slovenije. Večji delež lahko pričakujemo tudi v nižinskem in gričevnem delu osrednje Slovenije. Po napovedih modela bi se lahko lesna zaloga robinije do konca stoletja najmanj podvojila glede na današnje stanje. Ob uresničitvi scenarijev podnebnih sprememb bi se gozdarstvo srečevalo še z večjimi težavami, povezanimi s to invazivno tujerodno drevesno vrsto. Ob doslednejšem uresničevanju konceptov sonaravnega gozdarstva bomo morali na čim bolj optimalen način usklajevati med nezaželenostjo te invazivne tujerodne vrste in njenimi številnimi koristmi ter interesi lastnikov.In this study, we analyse the growing stock of black locust (Robinia pseudoacacia L.) and its share in Slovenian forests. In addition, based on empirical model and climate change scenarios, we predict its distribution and share in the future. Black locust is the commonest non-native tree species in Slovenian forests. The current growing stock of black locust is near 0.6% of the total growing stock of our forests. This tree species has the highest share in forests of the Regional Unit of Murska Sobota and Regional Karst Area Unit (Sežana). Should the recent climate change scenarios, which all predict an increase in mean air temperature in the future, proved to be true, the share of the black locustʼ growing stock will increase gradually in the eastern, north-eastern and south-western parts of Slovenia. Higher share of this species can be expected also in the lowlands and hilly area of central Slovenia. According to the forecasts of the model, the black locustʼs growing stock could at least double in comparison with its present state by the end of the century. In such situation our forestry will be faced with even more difficulties associated with this invasive tree species. Through a more consistent implementation of the concepts of sustainability in forestry, the balance between this invasive alien species, which is less desirable in our forests, and its many benefits and interests of the forest owners needs to be found

Pestrost mahovnih vrst v gozdnih ekosistemih Slovenije (program intenzivnega spremljanje stanja gozdnih ekosistemov)

As part of the Intensive Monitoring Programme (IM) of Forest Ecosystems in Slovenia, the bryophyte flora and vegetation have been studied on 11 IM plots and 64 vegetation sub-plots (10*10 m). On the IM plots, high species diversityof bryophytes has been assessed. The total number of bryophytes was 109among them 82 species belonging to the mosses (Bryophyta) and 27 species to the liverworts (Marchantiophyta). The mean number per plot was 27 species, ranging from 13 species on the Brdo plot to 36 species on the Borovec and Draga plots. The most common moss species are Hypnum cupressiforme, Ctenidium molluscum, Tortella tortuosa, Brachythecium velutinum, Isothecium alopecuroides, Dicranum scoparium, Polytrichum formosum, Fissidens taxifolius,F. dubius (Bryophyta)and liverworts are Radula complanata, Chiloscyphus profundus, Plagiochila porelloides and Metzgeria furcata (Marchantiophyta). Regarding the substrate preference, the opportunistic species that inhabit very different substrates are prevalentand the second main group are bryophytes inhabiting wood material (epiphyte, epixylic species). Using multivariate techniques (cluster analysis, DCA), the bryophytes have proved to be valuable indicator of site conditions (bedrock, surface rockiness, soil type, micro- and regional climate, vegetation) and forest stand conditions (dominant tree species, dead wood).V okviru Programa za intenzivno spremljanje gozdnih ekosistemov oz. Intenzivnimonitoring (IM) v Sloveniji smo na 11 IM ploskvah in 64 pod-ploskvah(10*10 m) preučevali tudi mahovno floro in vegetacijo. Na IM ploskvah smo ugotovili veliko pestrost mahovnih vrst. Skupaj smo popisali 109 vrst, od katerih je bilo 82 listnatih mahov (Bryophyta) in 27 vrst jetrenjakov(Marchantiophyta). V povprečju smo našli 27 vrst na ploskev, v razponu med 13 vrstami na ploskvi Brdo in 36 vrstami na ploskvah Borovec in Draga. Med najpogosteje popisanimi listnatimi mahovi so Hypnum cupressiforme, Ctenidium molluscum, Tortella tortuosa, Brachythecium velutinum, Isothecium alopecuroides, Dicranum scoparium, Polytrichum formosum, Fissidens taxifolius,F. dubius, med jetrenjaki pa Radula complanata, Chiloscyphus profundus, Plagiochila porelloides in Metzgeria furcata. V pogledu vezanosti na določeno rastno podlago prevladujejo oportunistične vrste, ki rastejo na zelo različnih podlagah. Drugo večjo skupino sestavljajo mahovi, ki naseljujejo lesnate podlage (epifitne in epiksilne vrste). S pomočjo uporabe multivariatnih tehnik (klastrska analiza, DCA) smo dokazali, da so tudi mahovidober indikator rastiščnih razmer (geološka matična podlaga, površinska skalnatost, talni tip, mikro- in regionalna klima, vegetacija) in sestojnih razmer (prevladujoča drevesna vrsta, odmrli les)

Recent trends and future directions in vertex-transitive graphs

A graph is said to be vertex-transitive if its automorphism group acts transitively on the vertex set. Some recent developments and possible future directions regarding two famous open problems, asking about existence of Hamilton paths and existence of semiregular automorphisms in vertex-transitive graphs, are discussed, together with some recent results on arc-transitive graphs and half-arc-transitive graphs, two special classes of vertex-transitive graphs that have received particular attention over the last decade