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No. 260 November 8, 2000
aceska at victoria.tc.ca Victoria, B.C.
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Dr. A. Ceska, P.O.Box 8546, Victoria, B.C. Canada V8W 3S2
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ANEMO-OROGRAPHIC SYSTEMS AND THEIR IMPACT ON PLANT LIFE
From: Jan Jenik [jenik at natur.cuni.cz]
More than three decades ago, a preliminary paper followed by a
monograph (Jenik 1959, 1960) attempted to describe and explain
the origin and unequal distribution of biodiversity in the
Sudetes and other Hercynian/Variscan mountains in Europe. The
essence of these publications, the theory of anemo-orographic
systems (A-O systems for short), has become a reasonably
feasible model for describing and explaining large-scale ecosys-
tem patterns encountered in the summit areas of these "middle-
mountains". Some geographers positively responded to this con-
cept, which aims at integration of biogeographical knowledge and
topoclimatic and geomorphologic evidence. Many ecologists and
conservationists have utilized and even further developed this
theory (see a review in Srutek 1990) and applied it to other
European mountains (Jenik, 1990).
Essential features of the Hercynian middle-mountains
In Central Europe, the Hercynian mountains create an arch of
separate massifs situated to the NW and N of the Alps. Their
major representatives are the Vosges, Black Forest, Bohemian
Forest, the Ore Mountains and the High Sudetes, the latter with
three dominant elevations called Giant Mts. (1602 m), Snow Mts.
(1423 m) and High Jesenik Mts. (1491 m). A product of Palaeozoic
mountain-building, these massifs - despite various specificities
- are similar in age, lithology, georelief, climate and, in
their plant and animal life. They consist mostly of gneiss,
crystalline schists and granite, and the base-rich carbonate
rocks and volcanic rocks are scarce.
Due to advanced denudation in the Tertiary, their rounded
georelief lacks rugged rock-faces, precipitous cliffs and deeply
cut ravines. Seldom surpassing the altitude of 1500 m a.s.l.,
they are transformed by periglacial cryogenic processes or
glacial erosion only in their topmost areas. In contrast to
rugged landforms and glaciated valleys met with in the Alps or
Carpathians, these middle-mountains, called also "forest-
mountains" ("Waldgebirge" in German), offer only constrained
areas for treeless ecosystems and fine-grained alpine biodiver-
sity.
Contrasting distribution of biodiversity
The surface of Hercynian mountains is largely covered by con-
iferous and mixed forests. A product of Postglacial succession,
the flora and fauna consist of widely distributed "common"
European species. In the German and Czech botanical literature,
the expression "Hercynian flora" is a pejorative term indicating
species-poor and monotonous floristic composition. Zonal forest
communities consist of only a few dozens of vascular species,
and similar uniformity refers to other life forms, such as
mosses, lichens, fungi, and to many groups of vertebrate and
invertebrate animals.
There exists, however, a small number of local exceptions,
species-rich sites, which are recurrently reported in documents
of European natural history.
These species-rich sites
1. are colonised by outstanding numbers of plant and animal
populations,
2. excel in a remarkable coexistence of biogeographically and
ecologically contrasting species, e.g., glacial relics near
thermophilous populations,
3. display remarkable diversity of contrasting biotic com-
munities and ecosystems.
For example, about 500 vascular species, coexisting in 30 dif-
ferent plant communities, have been recorded from a small
valley-head called Velka Kotlina (Jenik et al. 1980). Species-
rich fauna usually accompanies the botanical wealth. Occurrence
of endemic and/or biogeographically and taxonomically isolated
populations suggests that these localities serve as (i) refuges
of retreating biota, (ii) forerunner sites of spreading biota,
and even (iii) centres of active microevolution for new species
(Jenik 1983).
Earlier explanations of outstanding biodiversity in these par-
ticular localities were rather inconsistent and confusing (Jenik
1961: 54-74). Many explanations linked the biotic wealth with a
"sheltered site", a general qualification which was seldom
described in terms of physical parameters. By many hypotheses,
mainly locally outcropping base-rich rocks were taken into
account. Detailed geological and geobotanical research did not
confirm the primary role of this factor: some species-rich
communities evidently occur within the acid parent rocks and,
vice versa, the existence of mineral-rich rocks in the subsoil
does not always support species-rich ecosystems.
In order to understand the identity of species-rich localities,
broader environs of these sites must be taken into account
(Soukupova et al., 1995). Though numerous arctic and alpine
organisms participate, their refuges do not occupy the highest
altitudes reached in particular ranges. In contrast, the
majority of diversified ecosystems occurs at lower altitudes,
often on treeless avalanche tracks below the present-day timber-
line. Remarkably, many arctic/alpine/nordic/boreal species of
the Hercynian mountains coexist in association with numerous
southern/lowland plants and animals.
A detailed analysis of the biodiversity pattern in the High
Sudetes disclosed repeated geomorphological and meteorological
components in these species-rich localities: (i) linkage to
east-facing slopes, and situation on the eastern margin of large
summit plateaux or saddles, (ii) situation on back side of an
upland plateau or saddle, with regard to a funnel-shaped valley
ascending the summit area and accelerating air currents from W,
SW or NW, (iii) coincidence with recurrent snowdrifts, cornices
and active avalanche action in winter, and (iv) coincidence
within various concave landforms, such as nivation niches and
glacial corries.
In terms of georelief, the high-biodiversity sites coincide
mostly with E-facing (NE, E, SE) concave landforms, particularly
with shallow hollows or deeply cut cirques, which are con-
tinually subjected to nivation and, in the past, were sculpted
by glaciers. Remarkably, the topmost Hercynian peaks lack
prominent glacial cirques even on their eastern flanks. If
altitude lacks importance, what is then the general setting of
the remarkable biodiversity centres? The Giant Mts., in the
Czech and Polish territory offer a particularly meaningful
picture: 15 cirques with botanical and zoological sanctuaries
situated to the east of large upland plateaux. In the High
Jesenik Mts. and in Black Forest two large funnel-shaped valleys
join in the topmost area, and the famous cirques and species-
rich habitats are situated at the eastern side of these junc-
tions. In a range stretched from north to south, such as the
Vosges, understandably, a variety of nivation hollows and
cirques is developed along the long E-facing flank of the ridge.
A generalized model called anemo-orographic system
Existing interplay of landforms and meteorological/ecological
effects in culminating areas of the Hercynian mountains have
been summarized in a generalized model called the Anemo-
Orographic System.
According to the above quoted monograph (Jenik 1961), this model
consists of a
1. funnel-shaped windward section,
2. wind-accelerating summit section, and
3. leeward turbulent section.
Summary of the individual sections of A-O systems:
Funnel-shaped windward section
Landforms: large valley, gradually ascending
Wind action: laminar air currents, prevailing local wind
Precipitation: enhanced cloudiness, rainfall, snowfall
Snowpack: moderately deep, stratified according to weather
sequence
Temperature: according to altitudinal gradient
Soils: deeply weathered zonal soils, podzols, cambisols
Ecosystems: forests, controlled by altitude, species-poor,
coarse- grained pattern
Wind-accelerating summit section
Landforms: high elevation summit plateau, flat saddle
Wind action: high-speed, laminar air currents
Precipitation: maximum rainfall, snowfall, rime
Snowpack: shallow and short durations, reduced by eolian
ablation
Temperature: equable over flat relief due to wind and advec-
tion
Soils: azonal soils in cryo-eolian zone, partly relic soils,
organic soils
Ecosystems: treeless, controlled by wind action, upwelling
springs and mires
Leeward turbulent section
Landforms: concave hollow, niche, cirque, corrie
Wind action: turbulent currents, reduced velocity, calms in
shelter
Precipitation: fog, drizzle, dew, plenty of melt water
Snowpack, avalanches: cornices, snowdrifts, avalanche tracks,
long duration
Temperature: variable in rugged relief, due to differences in
insolation and reduced convection
Soils: variety of lithosols and rankers, locally nutrient-
rich outcropping rocks
Ecosystems: treeless, controlled by avalanche action, high
biodiversity, fine-grained pattern
A great variety of real A-O systems is encountered in different
ranges and parts of these ranges. In the above quoted monograph
(Jenik 1961: 195-196) various models have been proposed (1)
according to their distance or proximity to the generalised
model as "imperfect" or "perfect", respectively, and (2) accord-
ing to occasional combination of two or several funnel-shaped
windward valleys, as "simple" and "composed" A-O systems. Obser-
vations in the past four decades disclosed a number of less
perfect A-O systems in numerous mountains of Europe. Wherever
unilateral winds blow over suitably sculpted landforms, the
respective windward, topmost and leeward sites develop in con-
trasting ecosystems which are clearly indicated by plant life.
However, only long-term interaction of broader relief, wind
action and plant succession results in the scenery of a "per-
fect" A-O system.
Applicability of the model
The late Prof. Askell Love, University of Colorado, was the
first to indicate the potential applicability of A-O systems
outside Europe, i.e., in the area of Mount Washington, White
Mountains. This massif is marked by terminal situation in a
funnel-shaped configuration of the Presidential Range, and by
extremely unilateral western winds. Elevation, georelief with
distinctive climate, position of the timberline and vegetation
are similar to the European middle-mountains. Though covered by
an ice-sheet in the Glacial period, the famous species-rich
Alpine Garden, Tuckerman's Ravine, Huntington Ravine and Great
Gulf were very likely developed and preserved due to their
stabilised leeward position and avalanche action throughout the
Postglacial period. The A-O system model seems to fit the
spatio-temporal scale and evolutionary history of Mount
Washington more satisfactorily than the"alpine mesotopographic
gradient" described by Billings (1973) and illustrated in the
new edition of "_North American Terrestrial Vegetation_"
(reviewed in BEN No. 252).
References
Billings, W.D. 1973. Arctic and alpine vegetations:
similarities, differences, and susceptibility to disturbance.
BioScience 23: 697-704.
Jenik J. 1959. Kurzgefasste Uebersicht der Theorie der anemo-
orographischen Systeme. Preslia 31: 337-357. (In German.)
Jenik J. 1961. Alpine vegetation of the Giant Mts., Snow Mts.
and High Jesenik Mts. Theory of anemo-orographic systems.
Naklad. CSAV, Praha, 409 p. (In Czech with German summary.)
Jenik J. 1983. The evolutionary stage of the Sudetic cirques.
Biol. Listy 48: 241-248. (In Czech.)
Jenik J. 1990. Large-scale pattern of biodiversity in Hercynian
massifs. Pp. 251-259 in: F. Krahulec, A.D.Q. Agnew, S. Agnew,
J.H. Willems [eds.]: Spatial processes in plant communities.
Academia, Praha.
Jenik J. 1997. Anemo-orographic systems in the Hercynian Mts.
and their effects on biodiversity. Acta Univ. Wratislav.,
Prace Inst. Geogr., ser. C, Meteorol. i Klimatol. 4: 9-21.
Jenik J., L. Bures, & Z. Buresova. 1980. Syntaxonomic study of
vegetation in Velka Kotlina cirque, the Sudetes. Folia
Geobot. Phytotax. 14: 337-448.
Soukupova L., M. Kocianova, J. Jenik, & J. Sekyra [eds.] 1995.
Arctic-alpine tundra in the Krkonose, the Sudetes. Opera
Corcontica 32: 5-88.
Srutek M. 1990. Application of the theory of anemo-orographic
systems in natural history. Opera Corcontica 27: 47-58. (In
Czech.)
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