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MoraVian geographical reports 4/2010, Vol. 18 from rock fall events are decelerated by trees, so they may be stopped, or continue as rolling and bouncing stones and boulders down the slope. The bioprotective role is especially obvious on taluses, where the decelerated rock fall clasts mix with a finer material. The finer material is both autochtonous (primitive organic horizon on taluses) and alochtonous (delivered from slight slope segments above the rock cliff). Exposures on taluses displayed different activities below the rock cliff. Talus A was most active with two debris slides/ flows and sporadic herbs. Talus B was almost totally covered by herbs, while the vegetation cover of talus C was disrupted by a debris flow. The exposures alluded to the different activity in the past as well. While talus C is formed by loams and finer sediments of debris flows, taluses A and B showed a former rockfall-dominated development. The scree horizons with the open-work structure (exposures p1 and p2) indicate the former existence of a forest-free zone. Changes in geomorphic dynamics within the contact zone are represented by the subsequent movement of clasts downward to the open scree. Larger clasts are accumulated below the compact rock cliff, whereas the large clast flows occur below the taluses. As the most distinct active clast flows were present below the vegetation covered (i.e. relatively stable) taluses, other factor that could influence the occurrence of clast flows had to be taken into consideration, too. The topography analyses showed that the large clast flows are located on a down-slope concave ridge in the centre of the open scree. The occurrence of the large clast flows therefore seems to be conditioned both by the rock cliff morphology/activity, and by palaeotopography and sedimentary history. The sedimentological analyses of small clast flows indicated limited or absent influence of the frost action. The activity of clast flows is likely to be caused by rain and meltwater runoff from the source zone above and on taluses, and by biogeomorphic effects. While the clast flows spreading along the whole slope profile are most likely triggered 36 by surface runoff, small flows could be triggered by both runoff and zoodisturbances (cf. Govers and Poesen, 1998). The zoodisturbances would also explain the random spatial distribution of small clast flows on an inter-seasonal time-scale. This assumption was confirmed by the observation of mouflon hordes (Ovis musimon) in the area. The observations implied that scree slopes represent a frequent alternative habitat for this species, which is in agreement with results of other studies (Cransac and Hewison, 1997; Heroldová and Homolka, 2001). On slope segments with coarse material without clast flows, the surface dynamics is under the regime of clast rolling combined with the sieve effect (Carniel and Scheidegger, 1974). This reflects both ways of rock slope development proposed by Poesen and Lavee (1994). The previous discussion of scree slope dynamics emphasized the vegetation-control of the material transport. The sedimentary sequence in exposures indicates only a short historical record of sedimentary regime on the scree, which – in some cases (taluses A and B) – displays changes of this regime. Chronological interpretation of these changes in relation to recent environmental change is limited. Focusing on the most recent environmental change, old photographs (beg. of the 20 th century) and aerial photos (2 nd half of the 20 th century) were analysed. The analyses of aerial photos from years 1954 and 2004 (Fig. 9) showed that the open scree did not change its shape significantly. The forest edge dynamics is apparent locally (arrows a, c and b in Fig. 9), and has a character of continual forest expansion to the scree. The clast flows in the older photos are more restricted to the central part of the scree. The old photographs from the nearby surrounding of the study site depict a sparse vegetation cover on rock cliffs and rock slopes, which is in agreement with land use and land cover studies from the area (Anděl et al., 2004). The findings presented above support the concept of slow, but continual expansion of forest stands into the study site, and the Fig. 9: Vegetation pattern changes between years 1954 (A) and 2004 (B) indicated with lower case letters, and oblique photo of the locality and its surrounding (C). Source: aerial image VGHMU Dobruška and Geodis; photo author
Vol. 18, 4/2010 MoraVian geographical reports increasing – though not unique – role of vegetationcontrolled mechanisms of rock cliff disintegration and material transport. In this respect, the applications of palaeogeomorphic approaches, which traditionally emphasized the climatic factors, appear to be limited in the study of the recent geomorphology of low-altitude scree slopes in the region. References Acknowledgement The research was supported by IGA research project (2010 – 2011) funded by J. E. Purkyně University. The previous works were supported from a former project held by the Department of Geography, FS UJEP and funded by MLSA, Czech Republic. ANDĚL, J., BALEJ, M., BRZÓSKA, M. (2004): Land use changes in relation to basic natural factors with tourism effects: case study in Brná (Czech Republic). In: Michalczyk, Z. [ed.]: Badania geograficzne w poznawaniu środowiska. Wydawnictwo Uniwesytetu M. Curie-Sklodowskiej, Lublin, p. 641 – 646. BOLLSCHWEILER, M., STOFFEL, M., SCHNEUWLY, D. M. (2008): Dynamics in debris-flow activity on a forested cone – A case study using different dendroecological approaches. CATENA, Vol. 72, p. 67 – 78. CARNIEL, P., SCHEIDEGGER, A. E. (1974): Morphometry of an alpine scree cone. Rivista Italiana di Geofisica, Vol. 23, p. 95 – 100. CÍLEK, V. (2000): Scree Slopes and Boulder Fields of Northern Bohemia: Origin, Processes and Dating. In: Kubát, K. [ed.]: Stony Debris Ecosystems. Acta Universitatis Purkinianae Vol. 52, Studia Biologica IV, UJEP, Ústí nad Labem, p. 5 – 18. CORENBLIT, D., STEIGER, J. (2009): Vegetation as a major conductor of geomorphic changes on the Earth surface: toward evolutionary geomorphology. Earth Surface Processes and Landforms, Vol. 34, p. 891 – 896. CRANSAC, N., HEWISON, A. J. M. (1997): Seasonal use and selection of habitat by mouflon (Ovis gmelini): Comparison of the sexes. Behavioural Processes, Vol. 41, p. 57 – 67. CURRY, M. A., MORRIS, CH. J. (2004): Lateglacial and Holocene talus slope development and rockwall retreat on Mynydd Du, UK. Geomorphology, Vol. 58, p. 85 – 106. CZUDEK, T. (1986): Pleistocenní permafrost na území Československa. Geografický časopis, Vol. 38, p. 245 – 252. FRENCH, H. M. (2007): The Periglacial Environment. John Wiley & Sons, Inc., New York, 458 pp. GERBER, E. K., SCHEIDEGGER, A. E. (1974): On the dynamics of scree slope. Rock Mechanics, Vol. 6, p. 25 – 38. GOVERS, G., POESEN, J. (1998): Field experiments on the transport of rock fragments by animal trampling on scree slopes. Geomorphology, Vol. 23, p. 193 – 203. GRAHAM, D. J., MIDGLEY, M. G. (2000): Graphical representation of particle shape using triangular diagrams: an Excel spreadsheet method. Earth Surface Processes and Landforms, Vol. 25, p. 1473 – 1477. GUDE, M., DIETRICH, S., MÄUSBACHER, R., HAUCK, C., MOLENDA, R., RŮŽIČKA, V., ZACHARDA, M. (2003): Probable occurrence of sporadic permafrost in non-alpine scree slopes in central Europe. In: Proceedings 8th International Conference on Permafrost 2003, A. A. Balkema (Lisse, NL), Zürich, p. 331 – 336. HALES, T. C., ROERING, J. J. (2005): Climate-controlled variations in scree production, Southern Alps, New Zealand. Geology, Vol. 33, p. 701 – 704. HARRIS, S. A., CHENG, G., ZHAO, X., YONGQIN, D. (1998): Nature and dynamics of an active block stream, Kunlun Pass, Qinghai Province, People´s Republic of China. Geografiska Annaler, Vol. 80, p. 123 – 133. HEROLDOVÁ, M., HOMOLKA, M. (2001): The introduction of mouflon into forest habitats: a desirable increasing of biodiversity? In: Proceedings of the third international symposium on mouflon. Sopron, Hungary, p. 37 – 43. HÉTU, B., GRAY, J. T. (2000): Effect of environmental change on scree slope development throughout the postglacial period in the Chic-Choc Mountains in the northern Gaspe Peninsula, Quebeck. Geomorphology, Vol. 32, p. 335 – 355. HUBBARD, B., GLASSER, N. F. (2005): Field Techniques in Glaciology and Glacial Geomorphology. John Wiley & Sons, Inc., New York, 412 p. KIRCHNER, K., MÁČKA, Z., CÍLEK, V. (2007): Scree and blocky formations in Northern and Central Bohemia: Geologic and geomorphologic development. Acta Geographica Silesiana, Vol. 2, p. 19 – 26. KUBÁT, K. (1971): Ledové jámy a exhalace v Českém středohoří II. Vlastivědný sborník Litoměřicko, Vol. 8, p. 67 – 89. LAFORTUNE, M., FILION, L., HÉTU, B. (1997): Dynamics of a forest edge on an active scree slope occurring in a cold temperate climate environment (Gaspe peninsula, Quebec). Géographie Physique et Quaternaire, Vol. 51, p. 67 – 80. PAWELEC, H. (2006): Origin and palaeoclimatic significance of the Pleistocene slope covers in the Cracow Upland, southern Poland. Geomorphology, Vol. 74, p. 50 – 69. 37
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