Late-and post-glacial Vegetation immigration patterns in Switzerland

Abstract. General aspects of Swiss late- and post-glacial plant immigration patterns are briefly discussed. The following examples are mentioned: Ericaceae, Plantago alpina, Pinus cembra and Picea abies. The history of flora and Vegetation provides important palaeoecological informations. Moreover, it gives evidence to the stability and age of quaternary plant communities and serve as criteria for gene conservation in situ. Finally, the knowledge of plant immigration ways can be a valuable source of plant breeding research.

The Swiss investigation area has been divided for this purpose into the foUowing five regions: Jura.Plateau, Prealps, Central Alps and Southern Alps (including the South Alpine Valleys ofthe Simplon pass area, the Val Bregaglia, the Poschiavo valley and the Val Mustair).For this purpose the whole data of published Swiss pollen analysis and plant macrofossil analysis have been checked, i.e. a total of 612 profiles and diagrams respec- tively.This information is established in the Swiss pollen data bank ofthe Department of Geography (Biogeo¬ graphy), University of Zürich.
3. General patterns of immigration and spread GeneraUy.one can distinguish five different patterns of plant immigration and spread since the Late-Würmian (see fig.Lateand post-glacial Immigration patterns of some plant species (scheme).
2. General aspects of plan! immigration since the Lale-Würmian Plant immigration, spread and establishmentdependson a lot of complex factors or processes, i. e. diffuse biology and individual biological characteristics of plants, com¬ petition, succession, taphonomy, location ofthe glacial refugia, type of topography.role of nunataks, climate.ge¬ ology.soil development, etc. (see for example h.walter and H.straka 1970, h.j.b.birks and h.h.birks 1980, G.LANG I994).
Conradin A. Burga, Prof. Dr  The pollen data ofthe heather family (Ericaceae) show in the Prealps and the Central Alps a typical progressive de¬ velopment (El) since the Late-Würmian (see the time- space diagram, fig. 2).In Late-Würmian Sediments this plant family is represented mainly by Calluna and the Vaccinium-typt.The first pollen tetrads have been found in the Oldest Dryas.During the Bölling and mainly the Alleröd, the immigration ofthe Ericaceae has been more intensified.Calluna, Vacclnium and Rhododendron immigrated and established mainly as undershrubs of the Larix-Pinus cembra-forest in the Central Alps during the Alleröd and at the begin of the Holocene (Preboreal- Boreal).During the late Holocene, the Ericaceae shrubs often spread over a big area ofthe timberline-ecotone due to man influence (forest Clearing, farming, pasturage).Time-space diagram to the late-and post-glacial development of the Ericaceae in the Central Alps.
The opposite development pattern can be found for the Alpine plantain (Plantago alpina) in the Swiss Plateau (E2).The time-space diagram (fig.3) shows a Late-Wür¬ mian main phase from the Oldest Dryas to the Younger Dryas and a very distinct recession since the Preboreal.Plantago alpina established first very quickly light de- manding Vegetation types like grassland and non forested areas.After the establishment of dense post-glacial forest Vegetation, the area ofthe alpine plantain became very re- stricted in lower located regions, in contrast to higher elevated regions ofthe Alps (subalpine and alpine belt).
In the Central Alps, the Swiss stone pine (Pinus cembra) immigrated and established during the Alleröd and achieved its maximal extension during the early and middle Holocene.The late Holocene recession is mainly due to man's impact on the subalpine Vegetation belt (one phase development, E3).Fig. 4 shows two Central Alpine main areas of Pinus cembra, which have been established since the Boreal.One can distinguish a West¬ ern (Valais, Penninian Alps) and a Eastern (Grisons, En¬ gadine valley, Avers valley) area with more or less a gap of Pinus cembra occurrence in the Furka and Grimsel pass region.This is probably due to different immigration ways from the Northeastern European glacial refugia.
Alpen-Wegerich fP/ontago a/pinoj irr Mittel one Makro -- Time-space diagram to the late-and post-glacial development of Plantago alpina in the Swiss Plateau.
The spruce (Picea abies) shows in the Alps a progressive development (El) and a general immigration way from the Eastern to the Western Alps.Main immigration paths are areas in the Eastern and Southeastern Grisons, e.g.Lower Engadine valley, Upper Valtellina valley, Pos¬ chiavo valley and the Splügenpass area.At around 8000 BP, Picea abies immigrated from the Eastern Alps (Italy) into these areas.At 6500 BP the spruce reached the line Säntis-Glaris-Oberalppass-San Bernardino. 1000years later, the area of Picea reached the region of Lucerne and the Lake of Thoune.At 5500 BP the Sim¬ plon pass and Col de la Forclaz were crossed northwards by the spruce.In the Southwestern Jura, the spruce of Mount Risoux immigrated at around 5500 BP probably from the Savoy Alps.There are a lot of palynological evi¬ dence concerning immigration and establishment of Picea abies (c.a. burga and r perret 1997).These West¬ ern and Eastern Alpine main immigration paths of Picea have been confirmed by a complete different method.i. e. the investigation ofthe genetic Variation ofhigh elevated spruce populations in Switzerland (g.müller-starck 1995, ca.burga and g Müller-starck. in prep.).
Swiss stone pine (Pinus cembra)   Holocene sites (Preboreal-Subatlantic) with more than 5% Pinus cembra pollen Central Alpine occurrence of P<nus cembra according to pollen and macrofossil finds in Switzerland.Post-glacial immigration ways of Picea abies according to pollen and macrofossil finds in Switzerland.
5. Conclusion 6. References Flora and Vegetation history provides valuable contribu¬ tions to the development of climate and environment.The reconstruction of palaeoenvironments is connected with a lot of very complex factors (see section 2) and therefore are needed investigations based on different methods (see e.g.b.e.berglund 1986).One particular aspect is the question ofthe stability and the age of plant communities.Based on our flora history knowledge, some forest communities like the larch-Swiss stone pine forest (Larici-Pinetum cembrae), the subalpine spruce forest (Piceetum subalpinum) and the subalpine aider scrub (Ainetum viridis) seem to be very stable plant com¬ munities.
The larch-Swiss stone pine forest established in the Cen¬ tral Alps ca. 12 000 years ago (Alleröd) and is therefore one ofthe oldest forest communities ofthe Alps.The Pi¬ ceetum subalpinum developed much later between 8000 and 6000 BP.The competition between spruce and Swiss stone pine led partly to a recession of the latter in the upper subalpine belt (see ca.burga and r.perret 1997).The immigration and spread of Alnus viridis often is connected with the immigration of spruce.Atthe same time developed the typical tall herbaceous Vegetation, which occurs together with the Ainetum viridis.Furthermore, the knowledge of plant immigration ways can be an important source of breeding research (e. g.Picea abies, 1):Late-and post-glacial immigration patterns of some plants Types of development (E1-E5) -jrrrrrC^JLLL-.S" ',;&%:¦:¦