Vegetation History and Archaeobotany Springer-Verlag 2000
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Veget Hist Archaeobot (2000) 9 : 175-178 Vegetation History and Archaeobotany Springer-Verlag 2000 Influence of human impact and bedrock differences on the vegetational history of the Insubrian Southern Alps E. Gobet, W. Tinner, P. Hubschmid, I. Jansen, M. Wehrli, B. Ammann and L. Wick" Institute of Geobotany, Section Palaeoecology, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland Received July 5, 1999 / Accepted December 22, 1999 Abstract. Vegetation history for the study region is re- nual mean of 12~ and a July mean of 22~ This favours constructed on the basis of pollen, charcoal and AMS ~4C submediterranean trees such as Quercus pubescens, Cas- investigations of lake sediments from Lago del Segrino tanea sativa, Ostrya carpinifolia and Fraxinus ornus, (calcareous bedrock) and Lago di Muzzano (siliceous which are hardly ever abundant in forests north of the bedrock). Late-glacial forests were characterised by Alps. Together with central European tree taxa, they form Betula and Pinus sylvestris. At the beginning of the the species-rich forests of the southern Alps (Antonietti Holocene they were replaced by temperate continental 1968). Because extreme winter frosts are very rare (Mag- forest and shrub communities. A special type of temperate gini and Spinedi 1996), some scattered stands of ever- lowland forest, with Abies alba as the most important tree, green mediterranean trees and shrubs also occur at fa- was present in the period 8300 to 4500 B.P. Subsequently, voured sites, e.g. Quercus ilex, Laurus nobilis, Erica Fagus, Quercus and Alnus glutinosa were the main forest arborea and Cistus salviifolius. components and A. aIba ceased to be of importance. Cas- The intermediate position of our study area between mnea sativa and Juglans regia were probabIy introduced temperate central European and the Mediterranean is in after forest clearance by fire during the first century A.D. part also traceable in the vegetation history. Ostrya ear- On soils derived from siliceous bedrock, C. sativa was al- pinifolia and Fraxinus ornus immigrated early into the ready dominant at ca. A.D. 200 (A.D. dates are in calendar southern Alps (9000 and 7000 cal. B.P.), whereas Casta- years). In limestone areas, however, C. sativa failed to nea sativa was only introduced by the Romans 2000 years achieve a dominant role. After the introduction of C. ago (Zoller 1960; Schneider and Tobolski 1985; Tinner sativa, the main trees were initially oak (Quercus spp.) and Conedera 1995; Wick Olatunbosi 1996). Most of the and later the walnut (Juglans regia). Ostrya carpinifolia thermophilous tree taxa, such as Quercus, Tilia, Ulmus became the dominant tree around Lago del Segrino only in and Fraxinus excelsior had already spread to the southern the last 100-200 years though it had spread into the area at Alps in the Late-glacial, i.e. ca. 1000-2000 years earlier ca. 5000 cal. B.C. This recent expansion of Ostrya is con- than in the northern Alps (Schneider and Tobolski 1985; firmed at other sites and appears to be controlled by hu- Wick Olatunbosi 1996). Single pollen grains of evergreen man disturbances involving especially clearance. It is ar- and/or mediterranean species such as Quercus ilex, Olea gued that these forests should not be regarded as climax and Pistacia are regularly found after ca. 3800 cal. B.C. communities. It is suggested that under undisturbed suc- (5000 B.P.). cession they would develop into mixed deciduous forests New studies show that the vegetation of the southern consisting of Fraxinus excelsior, Tilia, Ulmus, Quercus Alps has been heavily influenced by forest fires from the and Acer. Neolithic (Tinner and Conedera 1995; Wehrli et al. 1998; Tinner et al. 1999) to the present (Delarze et al. 1992; Conedera et al. 1996a; Hofmann et al. 1998). Conedera et Key words: Vegetation history - Castanea sativa - al. (1996b) have shown that, during the 20 th century, most Juglans regia - Ostrya carpinifolia- Southern Alps forest fires start during the dry months (January-April), especially during periods with Foehn from the north, and are caused by humans. Introduction Antonietti (1968) demonstrated convincingly that the bedrock type (calcareous versus siliceous rocks) is critical In the Southern Alps from the northern Piemonte to Lake for the composition of the lnsubric vegetation. The impor- Garda the climate is mild and humid due to its southern tance of this factor in the vegetation history of the position and orographic rain. Temperatures reach an an- lnsubrian Alps has received little attention perhaps be- cause detailed modern pollen diagrams have only recently *Correspondence to: Erika Gobet; e-mail: [email protected] become available for the limestone areas (Wick Olatun- 176 bosi 1996; Gehrig 1997). The present study attempts a comparison of the vegetation in two contrasting bedrock areas by addressing the following issues: (1) The vegeta- tion history on the two types of bedrock with special refer- ence to land-use changes and the roles of Juglans and Castanea, and (2) the history of Fraxinus ornus and Ostrya carpinifolia forests. A. 9"OOE \,\ \ 'I'N W / I J 0 2 ~'~' -+ / Lugano "~==~ 46"00"N -- '~-~, m~ "'1 ~'~ f.. ;-"-'-Z.2/ ./' OCanzo "~ I, 'Como 3~#I BRIANZA i (LOMBARDY) I i 120Kin [] 1 [] 5 p Soil profile B. 2 | 6 1~ Coring point 3 r [] 4 [] 8 374 Altitude (m asl) Fig. 2. Vegetation map of area surrounding Lago del Segrino. l, Not mapped, open water (Lago del Segrino); 2, Open vegeta- tion, 3, Fraxinus excelsior dominant with Ostrya carpinifolia and Tilia cordata; 4, F. excelsior and O. earpinifolia dominant; 5, O. carpinifolia dominant with Fraxinus ornus; 6, 0 carpinifolia and Quereus pubeseens dominant; 7, O. carpinifolia and Castanea sativa dominant; 8, C. sativa domi- nant with Q. pubescens Research area, its climate and vege.tation ,:y The lakes Lago del Segrino (Brianza, Italy) and Lago di Muzzano (Sottoceneri, Switzerland) are situated in the i o E Magmatic and volcanic rocks 0 1 20 km southern Alpine foreland about 30 km apart (Fig.l). Lago Mesozoic sediments del Segrino (374 m asl) is at the northern edge of the Po plain. It is long and narrow, has a surface area of 0.38 km z ~]]] Tertiary sediments and a maximum depth of 8.6 m, and is bordered by two Lakes hills (670 m and 1241 m asl). It has no inflowing stream and is fed by groundwater and some surface water. The creek leaving the lake at the southern end enters Lago di Fig. 1. Map of A the study region showing the main lakes (par- Pusiano about 2 km away. The local bedrock is calcium allel lines) and locations of the main pollen profiles, and B the geology of the study region. I, Lago di Muzzano, 2, Lago di carbonate-rich and consists mainly of Lias and Flysch Origlio, 3, Lago del Segrino, 4, Lago di Annone, 5, Lago di (observations in the field; also Geologische Karte der Ganna. The sites for which new profiles are presented in this Schweiz 1:500 000, 2 "d ed. 1980). According to Antonietti paper are indicated by a filled-in square. The inset in A shows (1968, 1983) Fraxinus ornus, Ostrya carpinifolia, Tilia the country boundaries within the study region cordata, Ulmus glabra, Fraxinus excelsior, Quercus 177 petraea and Q. pubescens are the most important trees on history of areas around Lago di Muzzano and Lago del calcium carbonate-rich soils. Castanea sativa is the domi- Segrino were heavily influenced by natural and anthropo- nant tree on the acid soils of the western plateau (Fig. 2). genic forest fires, charcoal particles on pollen slides were Lago di Muzzano (337 m asl) occupies a glacial de- also counted. Using x200 magnification, over 100 char- pression in a hummocky landscape of the former Pleisto- coal particles > 10 gm (or 75 gm 2) were counted and, at cene Yicino glacier (Hantke 1983). Its surface area is 0.22 the same time, the added Lycopodium spores were also km 2 and its maximum water depth is 4.0 m. There are two counted. This makes possible the computation of charcoal inflowing creeks and the outflow in the south-west corner concentration. According to Tinner et al. (1998), charcoal of the lake flows into Lago di Lugano, 1 km distant. The influx values, or as an approximation charcoal concentra- geology of the catchment is characterized by Quaternary tion values, are sufficient for the reconstruction of re- deposits and siliceous rocks (Geologischer Atlas der gional fire history. The distinction of charcoal size classes Schweiz, sheet 69, No. 1353 Lugano 1976). Castanea or measurements of charcoal particles on pollen slides is sativa is the dominant tree in this area. Other important trees are Quercus petraea and Q. pubescens, Alnus not meaningful because some steps in preparation (sieving glutinosa, Fraxinus excelsior, Betula pendula, Fagus and decanting) reduce the number of particles that are sylvatica and Tilia cordata. Because of the high precipita- >20 000 ~am2 which are decisive for the reconstruction of tion Alnus glutinosa is not restricted to littoral zones in the local fire history. the Insubrian southern Alps (Zoller 1960). It can even be- come the dominant forest tree on well-drained slope soils (Steiger 1998). Lago del Segrino Both lakes are situated in the transitional zone from 0 I J ~ i ~ J climate Cfb to Cfa (K6ppen 1923). It is referred to as an too ~\ Insubric climate with mild and dry winters and with maxi- 2O0 \ 1 + I. mum precipitation in spring and autumn. The sunny sum- 3OO mers are sometimes interrupted by violent thunderstorms. 4OO At both lakes the annual mean temperature is 12~ and the "~F '~ 14Cdates i 5OO I o 14C date, rejer annual precipitation is 1600-1700 mm.