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Influence of human impact and bedrock differences on the vegetational history of the Insubrian Southern Alps

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Vegetation History

and Archaeobotany

9 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- constructed on the basis of pollen, charcoal and AMS ~4C investigations of lake sediments from Lago del Segrino (calcareous bedrock) and Lago di Muzzano (siliceous bedrock). Late-glacial forests were characterised by Betula and Pinus sylvestris. At the beginning o f the Holocene they were replaced by temperate continental forest and shrub communities. A special type of temperate lowland forest, with Abies alba as the most important tree, was present in the period 8300 to 4500 B.P. Subsequently, Fagus, Quercus and Alnus glutinosa were the main forest components and A. aIba ceased to be o f importance. Cas- mnea sativa and Juglans regia were probabIy introduced after forest clearance by fire during the first century A.D. On soils derived from siliceous bedrock, C. sativa was al- ready dominant at ca. A.D. 200 (A.D. dates are in calendar years). In limestone areas, however, C. sativa failed to achieve a dominant role. After the introduction o f C. sativa, the main trees were initially oak (Quercus spp.) and later the walnut (Juglans regia). Ostrya carpinifolia became the dominant tree around Lago del Segrino only in the last 100-200 years though it had spread into the area at ca. 5000 cal. B.C. This recent expansion of Ostrya is con- firmed at other sites and appears to be controlled by hu- man disturbances involving especially clearance. It is ar- gued that these forests should not be regarded as climax communities. It is suggested that under undisturbed suc- cession they would develop into mixed deciduous forests consisting o f Fraxinus excelsior, Tilia, Ulmus, Quercus and Acer.

Key words: Vegetation history - Castanea sativa - Juglans regia - Ostrya carpinifolia- Southern Alps

Introduction

In the Southern Alps from the northern Piemonte to Lake Garda the climate is mild and humid due to its southern position and orographic rain. Temperatures reach an an- *Correspondence to: Erika Gobet; e-mail: gobet@sgi.unibe.ch

nual mean of 12~ and a July mean of 22~ This favours submediterranean trees such as Quercus pubescens, Cas- tanea sativa, Ostrya carpinifolia and Fraxinus ornus, which are hardly ever abundant in forests north o f the Alps. Together with central European tree taxa, they form the species-rich forests of the southern Alps (Antonietti 1968). Because extreme winter frosts are very rare (Mag- gini and Spinedi 1996), some scattered stands of ever- green mediterranean trees and shrubs also occur at fa- voured sites, e.g. Quercus ilex, Laurus nobilis, Erica arborea and Cistus salviifolius.

The intermediate position of our study area between temperate central European and the Mediterranean is in part also traceable in the vegetation history. Ostrya ear- pinifolia and Fraxinus ornus immigrated early into the southern Alps (9000 and 7000 cal. B.P.), whereas Casta- nea sativa was only introduced by the Romans 2000 years ago (Zoller 1960; Schneider and Tobolski 1985; Tinner and Conedera 1995; Wick Olatunbosi 1996). Most of the thermophilous tree taxa, such as Quercus, Tilia, Ulmus and Fraxinus excelsior had already spread to the southern Alps in the Late-glacial, i.e. ca. 1000-2000 years earlier than in the northern Alps (Schneider and Tobolski 1985; Wick Olatunbosi 1996). Single pollen grains of evergreen and/or mediterranean species such as Quercus ilex, Olea and Pistacia are regularly found after ca. 3800 cal. B.C. (5000 B.P.).

New studies show that the vegetation of the southern Alps has been heavily influenced by forest fires from the 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 al. (1996b) have shown that, during the 20 th century, most forest fires start during the dry months (January-April), especially during periods with Foehn from the north, a n d are caused by humans.

Antonietti (1968) demonstrated convincingly that the bedrock type (calcareous versus siliceous rocks) is critical for the composition o f the lnsubric vegetation. The impor- tance o f this factor in the vegetation history of the lnsubrian Alps has received little attention perhaps be- cause detailed modern pollen diagrams have only recently become available for the limestone areas (Wick Olatun-

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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 o f Fraxinus ornus and Ostrya carpinifolia forests.

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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

R e s e a r c h a r e a , its c l i m a t e a n d v e g e . t a t i o n

The lakes Lago del Segrino (Brianza, Italy) and Lago di Muzzano (Sottoceneri, Switzerland) are situated in the southern Alpine foreland about 30 km apart (Fig.l). Lago del Segrino (374 m asl) is at the northern edge o f the Po plain. It is long and narrow, has a surface area of 0.38 km z and a maximum depth of 8.6 m, and is bordered by two 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 Pusiano about 2 km away. The local bedrock is calcium carbonate-rich and consists mainly of Lias and Flysch (observations in the field; also Geologische Karte der Schweiz 1:500 000, 2 "d ed. 1980). According to Antonietti (1968, 1983) Fraxinus ornus, Ostrya carpinifolia, Tilia cordata, Ulmus glabra, Fraxinus excelsior, Quercus

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petraea and Q. pubescens are the most important trees on calcium carbonate-rich soils. Castanea sativa is the domi- nant tree on the acid soils of the western plateau (Fig. 2). Lago di Muzzano (337 m asl) occupies a glacial de- pression in a hummocky landscape o f the former Pleisto- cene Yicino glacier (Hantke 1983). Its surface area is 0.22 km 2 and its maximum water depth is 4.0 m. There are two inflowing creeks and the outflow in the south-west corner of the lake flows into Lago di Lugano, 1 km distant. The geology of the catchment is characterized by Quaternary deposits and siliceous rocks (Geologischer Atlas der Schweiz, sheet 69, No. 1353 Lugano 1976). Castanea

sativa is the dominant tree in this area. Other important

trees are Quercus petraea and Q. pubescens, Alnus glutinosa, Fraxinus excelsior, Betula pendula, Fagus

sylvatica and Tilia cordata. Because o f the high precipita-

tion Alnus glutinosa is not restricted to littoral zones in the Insubrian southern Alps (Zoller 1960). It can even be- come the dominant forest tree on well-drained slope soils (Steiger 1998).

Both lakes are situated in the transitional zone from climate Cfb to Cfa (K6ppen 1923). It is referred to as an Insubric climate with mild and dry winters and with maxi- mum precipitation in spring and autumn. The sunny sum- mers are sometimes interrupted by violent thunderstorms. At both lakes the annual mean temperature is 12~ and the annual precipitation is 1600-1700 mm. As Antonietti (1968) points out in contrast to Oberdorfer (1964), it is the bedrock (siliceous versus calcareous) and not the cli- mate that determines the various lowland vegetation types o f the southern Alps.

M e t h o d s

Coring, and analysis of pollen and charcoal

history of areas around Lago di Muzzano and Lago del Segrino were heavily influenced by natural and anthropo- genic forest fires, charcoal particles on pollen slides were also counted. Using x200 magnification, over 100 char- coal particles > 10 gm (or 75 gm 2) were counted and, at the same time, the added Lycopodium spores were also counted. This makes possible the computation o f charcoal concentration. According to Tinner et al. (1998), charcoal influx values, or as an approximation charcoal concentra- tion values, are sufficient for the reconstruction o f re- gional fire history. The distinction of charcoal size classes or measurements o f charcoal particles on pollen slides is not meaningful because some steps in preparation (sieving and decanting) reduce the number o f particles that are >20 000 ~am 2 which are decisive for the reconstruction o f the local fire history.

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A modified Livingstone piston corer (Merkt and Streif 1970) was used to obtain core LS-3a in Lago del Segrino in 6.0 m water depth, and core MUZZ III in Lago di Muzzano at 2.8 m water depth. Both cores are from the profundal part o f the basin. The core sections studied con- sist throughout o f calcareous gyttja and marl in LS-3a and silty fine-detritus gyttja in MUZZ II1.

The sediment was prepared using standard physico- chemical methods and with the addition o f Lycopodium

tablets for the estimation o f pollen concentration (Stock- mart 1971). Pollen identification was carried out under x400 or x l 0 0 0 magnification. Aids to pollen identifica- tion included the pollen reference collection at the Insti- tute o f Geobotany, and keys by F~egri and Iversen (1989), Punt (1976), Punt and Clarke (1980, 1981, 1984), Punt et al. (1988, 1995), Punt and Blackmore (1991), Moore et al. (1991) and the photomicrograph volumes by Reille (1992, 1995). In Holocene and Late-glacial samples ca. 1000 and ca. 800 pollen were counted, respectively. A total terres- trial pollen sum was used from which was excluded pteridophytes, aquatics, indeterminata and Cannabis-

type. The results are presented as TILIA pollen diagrams (Grimm 1992).

Charcoal particles in lake sediments are indicators o f past fire events (e.g. Swain 1973; 1978; Wright 1974; Clark et al. 1989). On the assumption that the vegetational

200 400 o E 600 800 Q 1000 1200 1400 1600 0 Lago

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Fig. 3. Radiocarbon and pollen dating of the sediments from Lago del Segrino and Lago di Muzzano. Unbroken line indi- cates curve fitted by locally weighted regression; a broken line

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Table 1. AMS-radiocarbon dates from Lago del Segrino (LS-3a) and Lago di Muzzano (MUZ II1)

14C Lab. No. Depth Age

(cm) (~4C y B.P., non-cal.) Lago delSegrino UTC-5240 233 - 235 1310 • 40 UTC-5241 262- 264 1580 • 70 UTC-5242 283 - 284 1810 • 45 UTC-5243 391- 395 2280 • 40 UTC-5244 450- 453 2520 • 35 UTC-5245 517- 519 3050 • 35 UTC-5246 550- 552 3160 • 35 *UTC-5247 641- 643 5420 • 40 UTC-5248 716- 719 5040 • 70 UTC-5249 787- 789 5730 • 45 Ua-12533 841- 843 6630 • 70 Lago di Muzzano *UTC-4976 224.5 - 227.0 -40 • 35 UTC-5620 237.0 1000 • 60 UTC-4977 471.0- 472.5 2010 • 40 UTC-4978 597.0 - 598.0 2800 • 40 UTC-5271 762.0 - 763.0 3820 • 35 UTC-4979 963.5 - 965.0 4600 • 60 UTC-4980 1177.5 -1178.5 5960 • 60 UTC-5092 1260.0 -1262.0 7410 • 70 UTC-5274 1329.0 -1330.0 8310 =L 60 UTC-5272 1354.0 -1355.0 8230 • 80 UTC-4981 1392.5 -1394.5 . 10140 • 70 UTC-5093 1429.5 -1430.5 11620 • 50 UTC-5273 1447.0 -1448.0 12780 • 80

* Dates regarded as unreliable and not used in construction of chronology

Radiocarbon dating

From the two cores LS-3a and MUZ III, 23 samples o f terrestrial plant macrofossils were dated by the AMS method at the R.J. Van de G r a f t Laboratorium, University of Utrecht and one sample at the Svedberg Laboratorium, University o f Uppsala. The ~4C results are reported ac- cording to Stuiver and Polach (1977; Table 1) and cali- brated by the program CALIB Version 3.0.3c (Stuiver and Reimer 1993).

The radiocarbon ages were smoothed by locally weighted regression and the results are presented in depth-age diagrams (Fig. 3). Two dates were excluded from the regression. The date UTC-5247 is certainly too old, probably a hardwater error caused by the Mesozoic sediments o f the catchment of Lago del Segrino. The date UTC-4976 is modern perhaps due to contamination (the sample was taken from the upper end of a core segment). Relative dating using pollen data (Fig. 3) was carried out by biostratigraphic correlation with radiocarbon-dated diagrams in the region (Schneider 1978; Schneider and Tobolski 1985; Wick 1989; Wick Olatunbosi 1996; Tinner et al. 1999).

Soil descriptions and vegetation mapping at Lago del Segrino

In the Castanea forests and their surroundings, three soil profiles were described in the field by horizon, depth, pH, skeletal content, colours and structure. The soils were classified according to the FAO-UNESCO classification. The modern woodland vegetation around Lago del Segrino was mapped. In this exercise, only the main trees or shrubs were taken into account (Fig. 2).

R e s u l t s

Soil descriptions and vegetation mapping at Lago del Segrino

Soil investigations in the Castanea forests were described in an attempt to explain why this tree was present on cal- careous bedrock. The soils, which may be classified as dystic cambisols, have a pH range of 4.5-5. The soils are therefore more acid than expected. The morainic and Mesozoic Flysch parent material has probably favoured the formation o f acid brown earths. This explains the pres- ence of Castanea-dominated forests, which normally oc- cur only on siliceous soils.

Figure 2 gives an overview of the woodland vegetation at Lago del Segrino. On calcareous bedrock the dominant tree is Ostrya carpinifolia, followed by Fraxinus

excelsior, Quercus pubescens, Fraxinus ornus and Tilia

cordata. Robinia pseudoacacia is present in each o f the

m a p p e d woodland types and in higher amounts where there is much disturbance.

Vegetation history

In total 180 and 187 pollen and spore types were identi- fied from Lago del Segrino and Lago di Muzzano, respec- tively. In the percentage pollen diagrams (Figs. 4-7) the main pollen curves are shown. In Fig. 8 concentration val- ues for selected pollen groups are plotted. A summary of the vegetation history is presented in Table 2. The correla- tion o f the two sites is based on radiocarbon dates (Table 1, Fig. 3) and on their vegetational histories which are broadly similar though there are also some differences.

At Lago di Muzzano the record starts in the Late Gla- cial at ca. 14 200 cal. B.C. (13 500 B.P.) with Betula as the dominant tree in an open forest (pollen data not shown). This phase is not recorded in the pollen profile from Lago del Segrino, but an earlier study o f the Late- glacial at this site shows that reforestation started at ca. 14 500 cal. B.C. (13 700 B.P.; Wick Olantunbosi 1996). After ca. 12 400 cal. B.C. (12 300 B.P.) Pinus was more abundant at both sites. At Lago del Segrino (Fig. 4 ) and at other localities in the southern Alps (e.g. Schneider and Tobolski 1985; Wick Olatunbosi 1996, Tinner et al. 1999), the expansion of several thermophilous mixed-oak taxa had already started during the Allerod (ca. 12 000-11 000 cal. B.C., 12 000-11 000 B.P.). At ca. 9300 cal. B.C. (10 000 B.P.), Late-glacial forests with Pinus sylvestris

and Betula were replaced by temperate continental forests

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Corylus avellana, Tilia, Ulmus, Betula, P. sylvestris and Fraxinus excelsior. Insubrian forests with Abies alba as an important tree dominated in the lowlands between 7300-3200 cal. B.C. (8300-4500 B.P.). This period is characterised by fluctuations of the important woodland species at both sites and there are also differences in abun- dance of particular trees in the two localities. A. alba ex- panded more successfully and was more abundant at Lago di Muzzano, whereas C. avellana was more common at Lago del Segrino. This period ended with the local extinc- tion ofA. alba. It disappeared from the lowlands probably on account o f high fire frequency which gradually fa- voured the establishment of fire-tolerant alder-oak forests (Tinner et al. 1999). At the end of the late Insubrian forest period, which is characterised by a replacement of Abies by Fagus and increasing Alnus glutinosa-type and

Quercus (deciduous) pollen percentages, the mixed oak forest species represented by Tilia, F. excelsior and Ulmus decreased substantially. At Lago del Segrino, the expansion o f Fagus started earlier than at Lago di Muzzano. In general, Corylus was more abundant at Lago del Segrino than at Lago di Muzzano, where A. glutinosa- type was more important. This trend continued during the so-called 'oak-alder forests and farming' phase between 1800 cal. B.C. and A.D. 1 (3500-2000 B.P.; Table 2). In this phase, continuous agriculture is indicated by high val- ues of anthropogenic indicators that continue into the present. The introduction ofJuglans regia and Castanea sativa in Roman times initiated a phase of tree introduc- tion and intensive farming. There are marked discrepan- cies between the two localities as regards abundance o f plant taxa as well as an increasing floristic divergence to- wards the present, e.g. Ostrya (Figs. 4-7).

Table 2. Comparision of vegetation history at Lago del Segrino and Lago di Muzzano

Age 1 Age2 LPAZs Vegetation/land use

Segrino Muzzano

Important taxa Agree-

ment

Present- Present- LS17-14 M17-13 A.D. 1 2000

A.D. 2000- LSI3-10 MI3-(10)

1-1800 B.C. 3500

Tree introduction and intensive farming (Segrino: since c. A.D. 1850 Ostrya-forests)

Oak-alder forests and farming

1800- 3500- LS9-8 M(10) L~eInsubrianlbrests

3200 B.C. 4500

3200- 4500- LS7-(4) M9-6 lnsubrianforests

7300 B.C. 8300

7300- 8300- LS(4)-3 M5-4 Temperate continental forests

9300? B . C . 10000 and shrublands

9300?- 10000- LS2-1 M3-2 Lae-glacialforests

12400? B.C. 12300

12400?- 12300- MI

14400? B.C. 13600?

Open Late-glacial forests

Castanea sativa, Juglans regia, Quercus (deciduous), Alnus glutinosa, Ostrya carpinifolia, herbs, cultivated plants and neophytes

A. glutinosa, Quercus (deciduous), Pteridium aquilinum, Fagus silvatica, Betula, Calluna vulgaris,

herbs, cultivated plants A. glutinosa, F. sylvatica,

Tilia, Quercus (deciduous), Cotylus avellana, Fraxinus excelsior, Ulmus

Abies alba, Tilia, Quercus (deciduous), C. avellana, A. glutinosa, F. excelsior, Ulmus, Hedera helix

Quercus (deciduous), C avellana, Tilia, Ulmus, Betula, Pinus sylvestris, F. excelsior P. ~ylvestris, Betula

Betula, P. sylvestris

§ 1 7 7

+ ~

Agel, Cal. B.C./A.D.; Age2, B.P. (non-cal.)

LPAZs, local pollen assemblage zones; LS, Lago del Segrino, M, Lago di Muzzano Vegetation types after Tinner et al. (1999)

Agreement between the two sites is indicated as follows: Increasing floristic disagreement towards present + Floristic agreement

++ Floristic agreement and comparable abundance of plant taxa Uncertain

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Discussion

Three main phases of pre-Roman human impact

In the percentage pollen diagrams o f Lago del Segrino (Figs. 4, 5) and Lago di Muzzano (Figs. 6, 7), three corn-

mort pre-Roman phases o f human impact with high non- arboreal pollen (NAP) values can be recognised as fol- lows:

From ca. 3300 to 2700 cal. B.C. (4600-4100 B.P.), N A P at Lago del Segrino have very high percentage and concentration values which presumably reflect late-

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Fig. 5. Percemage non-arboreal pollen (NAP) diagram from Lago del Segrino (selected taxa). Exaggeration xl0 is indicated by stippling9 Cannabis-type and the group AQ (aquatics) and SP (spores) are excluded from the pollen sum. Analysts: Erika Gobet and Ingrid Jansen, 1996

Neolithic settlement near the lake (Castelletti, per- sonal communication) 9 A minor increase in NAP (per- centages and concentrations) is also recognised at Lago di Muzzano at ca. 3200 cal. B.C. (4500 B.P.). At ca. 1300 cal. B.C. (3100 B.P.), NAP (percentage and

concentration values) increased at both loca[ities.

Plantago lanceolata-type, Pteridium aquilinum (and

at Lago del Segrino also Cerealia) indicate major hu- man activities during the Bronze Age.

At about 450 cal. B.C. (2400 B.P.) Poaceae and several anthropogcnic indicators have high percentage and concentration values at Lago di Muzzano and Lago del

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_J .J LU > Ul .A >- C~ o t~ ~ ~ > - - O r 9 "J -J (n(n . > z = ~ e ~ = ~ i i i i : ! i i i l i : : : : : 9 ~ : i i i i I . . . , : : ! i i

i lii!

? i : i : : : ! i i i i ! I 4 0 4 0 2 0 2 0 4 0 f f l D ll:t- I-4 b J - I I1. ~.}Q. . j :i M - | 6 ii M- t5 ::i M-14

~.i3 I

M-!2' M-11

I '

i ,o!

M-6 M-5

M-4 1

I I M - 3 1 I I M-Z1 iM-1 %

Fig. 6. Percentage arboreal pollen (AP) diagram from Lago di Muzzano selected taxa). Exaggeration xl0 is indicated by stippling. Analysts: Priska Hubschmid and Michael Wehrli, 1997

Segrino. This suggests substantial deforestation and farming activity during the Iron Age (Figs. 5, 7). The woodlands subsequently regenerate but the presence of Cerealia pollen and P. lanceolata-type indicate that there was still considerable human impact. High values

of Quercus pollen could indicate that oak was fa-

voured by the inhabitants probably on account of its mast. The Greek historian Polybios (ca. 2 0 0 - 1 2 0

B.C.), for instance, mentioned .the importance of acorns for pigs in the Po plain (Polybios II 15).

Introduction of Juglans, Castanea and Secale." chrono- logical considerations

Zoller (1960) has already shown, using ]4C dates, that the main expansion of Castanea and Juglans in the Ticino re-

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ou!a6a S lap os,eq 1,e uomtuoa aJOUd atu,eoaq Uallod s~! spJ,e~auo ('d'~3 09 6I) OL "(]'V ',ea moJj pu,e '( 'd 's OgIg) "D'~] "F ~ 00~: ",eam pm~p ~! alDaas.;o Uallod alSU!S lsJU aqJ, '(%~<) uo~su,edxa ss,euJ paAo]qo,e 1[ sJ'eo/[ 00~ lsottlle Jo:lJV "spJ,e~tlo ('d'~ 00 6[ ) 00I '(I'V tuojj aAJna snonu!luoo all; ~q poa,eo]pu! S~ 'Jal,e I +~ . ... ... v,~ ,~ ,~ ,~ o.u ~a up .iv uu ua np oa lu ! a ql "(.6 "s!:I h! tu !I leUOp, eJ '% [< ) pa pu ed xa ]! spJe~auo ('d '~ O00Z:) gl "G'V "l ea "eo tuo~j pue '('Eft 0~0ZT) "D'fl 'l go 0# ",ea 1,e palJ,els (l!tu![ lea!a!duaa) ahJna snonu!luoa aql SUVlgn s J O d '('d'~l 0ggZ;) "~)'fl "Fa 06 gJ o a$,e pal,elodaolu ] u,e a,e poa,ead -d,e (l!UJ!l alnlosq,e ) ,eJaua9 qloq jo su~,eJ9 alSU!S lsJ!J aql ou!J~a S lap o~,eq aV "satu!l u,etUO,d ~u!anp paaanaao uo~$ COO I !HHVA~ [~U~lU!l/~ puu p!tuqasqn H m, ls!a d :slsaFu v

'tuns "~u!lddp, s D ods pup dnoJ~ oql C3F pu~ (so]~,~nbe) (saaods) dS' popnlaxa oJ~ aql tuoaj ]allOd

s pol~o[pu] s! 01 x uo !! ~J a~ x 3 (~xm paloalaS ) ou~zznlaI [p o~ q tuoJj tu~J~!p (dVN) Uallod FaaoqJ~-UOU o~muaaaOd "L "~!~l 'Jr., UU l U~ U~ UV Ur --i O-f1 ~Ol g %Og OOL og Og It. "fl Iz- f~l

t

L'W ~ i~ -~ 0~-w

i:.[i!i:

t~ ]

_

i :.::

i1 !i

:!:

:::::: :i:!:! 4- ., - - ~ i7 .. l i i ~ z ~ I.-V~ :: :::: 1~: ~ '"'" ,,,) --~ ~ "00 ..~ ..( ...( -.(~rrr- > .r ~ ~ Z m'0 t- CO r- Ur-m ~ c _~-_z " L dS s or -/

~ ~ ~

~o~ ~-~O--~2~.~-~r~-

~ "D~"--I::~.'~ ,, r- ,, ~:DZ('~ , -n : X~ : ~I: ~ ,-- X 0 0 ~ rrl c m-..~=:OO~Z~_'-N--cn~o .m - ' "o-o H _ Sm r-Fr -_ o~ -~ r~ __ ~ ' ~ .< _~ ; -~ 9 ~- ~c -x ~_ m ~" m~ ~-i~ r-~ ~ OM " _q ~ _m 2.~ ~.4 C~-~. "~--C} ~D " '' ~L '~ rrl u~ ~ m i: ~ " -.4 N o U) t "1 -'4 1 r---4 SB83~ ONV-lan 0

g

m -.4 ..4 m -090s ~- .OOgZ!. iOggZ| - -i 1

-i

. rO01,l - 0 0s l

I

O0 1 -001 | :-0001

--006

ooo~ -OQQZ- ~ooa " -': OgOi~ - "

oo~

loggy-

+oo~

ooo~; -OQOL- :0 09

OOg2 ~-Ogg-

~-00~

ooo~...-- og -

oo~ -:-ogv oog I

: poo~ 0001 .-096 ~-OOZ DOg ~Ogl, I ~- O01 -066L LO m m "D -q f'l

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o . . . . ~o~] 5 | ~-i6 ~00 500 .5-15 I 2O0 200 1000 10 9 M-15 ,500 k_~ . ~ 400 ~oo 15 ~ . - M-14 400 2500 6 0 0 3 0 k4-'~- 500 3000 700 35 5500 - - M- tO 500 4000 BOO 4 0 9 0 0 45 4500 ~ U-g 5500 1,oo ~ jr"

~.;

800 6000 1200 6 0 65 6500 70 M-5 7000 75 7500 / 1300 80 8500 90 M-5 9000 95 9500 ; L$-5 t00 M-4 1400 105 lO00 10000 10500 LS-2 110 11000 115 r . 5 o o I ~s-, 1~o, ~- I~000 120 M 1

xlO0000 (r#Nns/'cr xlO0000 (groins/ccrn)

Fig. 8. Pollen concentration curves (main groups) from Lago de[ Segrino and Lago di Muzzano. Analysts: Erika Gobet, lngrid Jansen, Priska Hubschmid and Michael Wehrli

Table 3. Introduction and spread of Castanea sativa in Sottoceneri and two regions within Lombardy

Locality Introduction Mass

(continuous expansion curve) (>5%)

Age (A.D.) Age (A.D.) Sottoceneri

Lago di Origlio, 416 m asl

(Tinner et al. 1999) 70 120

Lago di Muzzano, 337 m asl 1 80

Brianza

Lago di Annone, 226 m asl

(Wick unpubl.) 170 290

Lago del Segrino, 374 m asl 100 290

Valganna

Lago di Ganna 452 m (Schneider and Tobolski 1985;

Drescher-Schneider 1994)

120 450-600

Dates given are the best available estimates At Lago di Muzzano, where for this period there is

only one ~4C date (Fig. 10), the first Secale pollen record is dated at ca. 390 cal. B,C. (2350 B.P.), followed by sin- gle grains o f Castanea at ca. 370 -300 cal. B.C. (2300- 2250 B.P.). Before the onset of a continuous Castanea curve, the first Juglans pollen is recorded and its curve is continuous from the beginning. Castanea is continuously recorded since the beginning of the first century AD. The onset o f a continuous Secale curve is dated to ca. A.D. 60 (1960 B.P.). The mass expansion of chestnut (Castanea) occurred at ca. A.D. 80 (1940 B.P.).

In Table 3 the calculated and calibrated dates for intro- duction (defined as the empirical limit) and mass expan- sion (defined as the rational limit, >5%) for Castanea at

f

Z$ I

"

1310146, 140Q- 1500 I550170, 1600 1810~45- ]700- 1800- 1900 2000- 2100 Z Z 0 0 - 2280~40| ~300- 2400- 2500- O'

/

/

s

% x I~ (Nr~leS/ecm)

five sites in the ]nsubrian region (Tieino and northern Italy) are given. Mass expansion in the Sottoceneri region was ca. 200 years earlier than in the Brianza region (also Figs. 9, 10). According to Schneider and Tobolski (1985) and Drescher-Schneider (1994), the rise o f the Castanea curve and thereby the period of intensive planting of chestnut started at Lago di Ganna (ca. 20 km south-west of Lago di Muzzano) at ca. A.D. 450-600 (1600-1500 B.P.). The expansion of chestnut seems thus to be distinctly later at Lago di Ganna than in the nearby Sottoceneri (ca. 400 years, 10 km apart) and in Brianza (200 years, 40 km apart). Whether this is a local phenomenon or a dating problem is difficult to assess.

The introduction o f Castanea and Juglans in the Brianza but also in the Sottoceneri can be related chrono- logically to Roman settlements (Figs. 9, 10). Como be- came a Latin colony in 89 B.C. but archeological investi- gations show that Roman cultural iinpact began to in- crease only at about 30 B.C. at the beginning of the reign o f Augustus (27 B.C.-A.D. 14) (Sti3ckli 1975; Martin- Kilcher 1998). The introduction of Castanea and Juglans was probably facilitated by forest clearance involving fire, a view supported by the charcoal particle data (Figs. 9, 10).

It is likely that Castanea and Juglans survived the last Ice Age in Italy (Huntley and Birks 1983; Paganelli and Miola 1991; Birks and Line 1993), but were not able to spread spontaneously to the lnsubrian region during the Holocene. However, during the pre-Roman Holocene, Castanea and Juglans pollen are known for other regions o f Italy (Huntley and Birks 1983; Cruise 1990; Kelly and Huntley 1991; Brugiapaglia and de Beaulieu 1995). Differential vegetation development on calcareous and siliceous rocks - a palaeoecologieal perspective

Fig. 9. Selected pollen percentage curves and charcoal particle concentration curve from Lago del Segrino. Analyst: Erika Gobet

A major part of the pollen catchment of Lago del Segrino and Lago di Annone is characterized by calcareous bed- rock (Wick Olatunbosi 1996). In contrast, Lago di

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Muzzano and Lago di Origlio (Tinner et al. 1999) have pollen catchments dominated by acid soils (Fig. 1).

Casta-

nea

is considered to avoid calcareous soils whereas such soils are favourable to

Juglans

(e.g. Durand and Chau- meton 1991; Ellenberg et al. 1992).

Around Lago del Segrino

Juglans

was the dominant fruit tree and at ca. A.D. 1400 it achieved 19% in the pol- len record. Schneider and Tobolski (1985), Drescher- Schneider (1994) and Wick Olatunbosi (1996) state that planting of

Juglans

began before

Castanea.

Also in the Ticino, this trend is visible although the time difference is smaller and, furthermore,

Juglans

percentage values are here distinctly lower.

Conditions for

Castanea

are better in the Ticino than in the Brianza because of the siliceous bedrock (Fig.l). A total of 14 AMS 14C dates on terrestrial macrofossils from Lago di Annone (Wick unpublished), Lago di Origlio (Tinner et al. 1999), Lago di Muzzano and Lago del Segrino lie in the period 650 cal. B.C.-A.D. 760 (2500- 1250 B.P.). These dates prove that the mass expansion of

Castanea

where there was siliceous bedrock was earlier, faster and more successful than where calcareous rock prevailed. On the other hand,

Juglans

was favoured and more easily introduced on the calcareous soils o f the Brianza. It is possible that also in Brianza - j u s t as in the Ticino - people attempted to plant both trees in the areas cleared by fire (Figs. 9, 10) but chestnut, which performs poorly on calcareous soils, was soon replaced by

Quercus

petraea

and

Q. pubescens

(LPAZ LS-14).

Castanea

was then able to grow successfully only on favourable habi- tats, such as acid brown earths (e.g. on Monte Scioscia near the soil profiles PI-P3, Fig. 2) and also provided that

Q. petraea, Q. pubescens

and possibly also

Corylus

were regularly cut.

Other taxa also provide evidence that different bed- rock and hence soil types control long-term differential vegetation development. For instance,

Calluna vulgaris

and

Pteridium aquilinum,

which indicate acid soils (Ellenberg et al. 1992) are distinctly more common at

o ~

S

1400 ~,~ 6=0 1500 ~/'~ 1600 441 ~700 3 ~ 1800 ~4. f 9 0 0 I ~ ~J 2000 2100 .isw 2200 2 5 0 0 ~A-13

)

I 0 2 0 30 x ~ o o ~ (p~relestr162

Fig. 10. Selected pollen percentage curves and charcoal particle concentration curve from Lago di Muzzano. Pollen analyst: Priska Hubschmid; charcoal analyst: Willy Tinner

Lago di Muzzano than at Lago del Segrino. In contrast, at Lago del Segrino calciphilous species such as

Myriophyl-

lum spicatum

(cf. Ellenberg et al. 1992) or

Ostrya carpi-

nifolia

(cf. Durand and Chaumeton 1991) have high repre- sentation.

Ostrya-dominated

woodlands

in

the

light

of

palaeoecological studies

Most ecologists consider

Ostrya-dominated

woodlands as typical of calcareous soils in our study region and assume that succession under natural conditions leads to

Ostrya-

dominated stands (e.g. Oberdorfer 1964; Ellenberg and Kl6tzli 1972; Mayer 1984; Reisigl 1996).

New palynological studies confirm that

Ostrya-type

has been present in small quantities in our study region since at least 9000 cal. B.P. but that it did not expand around Lago di Annone (Wick Olatunbosi 1996), Lago di Origlio (Tinner and Conedera 1995; Tinner et al. 1999), Lago di Muzzano and Lago del Segrino until the last cen- tury. The very high values of

Ostrya-type

pollen reported by Lt~di (1944) from Lago di Muzzano could not be con- firmed by our new investigations. The strong increase in

Ostrya-type

especially in the Brianza, and also the minor values in the Ticino (Tinner et al. 1998), obviously reflect recent developments.

During the 19th century

Ostrya

began to expand at Lago del Segrino. Around 1960 the regional trend towards reforestation, dated by Yinner et al. (1998) using 21~ is a conspicuous feature. At Lago del Segrino

Ostrya-type,

which reaches 14% (LPAZ LS-17, Fig. 4), becomes the most important AP taxon. Studies of the present-day veg- etation around Lago del Segrino verified this

Ostrya

earpinifolia

dominance.

Fraxinus excelsior, Corylus

avellana, Quercus pubescens, Fraxinus ornus,

and (on acid soils)

Castanea sativa

are important as well (see Fig. 2). From comparison of pollen percentages from the youngest sediment and the vegetation map we can con- clude that

Ostrya carpinifolia

is well represented in sediments.

At the eastern border of the Insubrian region at Lago di Gaiano (ca. 60 km east of Lago del Segrino), it was shown that

Ostrya-type

was already present at the beginning of the Holocene. Between 100 cal. B.C. and A.D. 350 (2100- 1700 B.P.), its representation increased to 5-6% and re- mained at about this low level (Gehrig 1997). However, pre-Roman expansions are documented only for sites east and south of the Insubrian region (e.g. Beug 1964, 1965; Kral 1982; Huntley and Birks 1983; Grtiger 1996).

As shown by the comparison between the vegetation map and its presence in surface sediments,

Fraxinus

ornus,

an important diagnostic species of syntaxa with

Ostrya

at association level, is probabl.y under-represented in pollen diagrams. Pollen production and dispersal are probably limited as this tree is insect pollinated. It spread to our study region at ca. 5400 cal. B.C. (6500 B.P.) but did not achieve a major expansion (remains <2%). Around Lago del Segrino it started expanding at ca. A.D. 1100 (900 B.P.), whereas on the siliceous soils of the northern Sottoceneri it was never important. In the case of

Carpinus betulus,

a continuous curve began much later, i.e. at ca. 2500 cal. B.C. (4000 B.P.), but then pollen of

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Carpinus-type was present in higher amounts than that of

Ostrya-type until ca. A.D. 1000 (1000 B.P.), when Carpi-

nus-type declined (Fig. 4). During the last 100-200 years

it expanded slightly, together with Ostrya,

A possible explanation for the palynological sequence o f events may be found in the vegetation analysis carried out by Antonietti (1968). He described two forest types on calcareous rocks: (1) mixed deciduous broad-leaved for- est with Fraxinus excelsior, Acer pseudoplatanus, Tilia

cordata and T. platyphyllos, as well as Ulmus glabra

(Erisithalo-Ulmetum aegopodietosum prov.), and (2) a

woodland type in which Ostrya is dominant and Quercus

pubescens and Fraxinus ornus as important components

(Helleboro-Ornetum prov.). Between these two main for-

est types is a transitional association. We argue that the mixed deciduous broad-leaved forest type (Erisithalo- Ulmetum aegopodietosum =_ Asperulo taurinae-Tilietum

o f Eltenberg and Kl6tzli 1972; see Antonietti 1983) repre- sents the vegetation type that is least disturbed. Gradual human disturbance may have triggered a compositional shift in the forests, first in favour o f Castanea and

Juglans, and later in favour o f Ostrya. The character o f

modern forests with Ostrya as coppiced stands (especially Carpinio-Ostryetum) has been referred to by several au- thors (Ellenberg and Kl{Stzli 1972; Mayer 1984; Steiger 1998), but yet Ostrya is usually considered to be naturally dominant (e.g. Oberdorfer 1964; Mayer 1984; Reisigl 1996).

On the basis o f our palynological results we suggest that the strong expansion o f Ostrya is a very recent phe- nomenon on calcareous soils in the Insubric region and that it should certainly not be regarded as a climax com- munity. Earlier authors (Bettelini 1904; Geilinger 1908, cited by Antonietti 1968) and also Antonietti (1968) rec- ognized that Ostrya in the lnsubric region is a woody spe- cies that was heavily favoured by human impact (mainly wood cutting) in much the same way as Corylus. In more recent times the abandonment o f forest and meadow ex- ploitation may also have favoured Ostrya.

Taking into consideration both the palaeoecological and present-day phytosociological data, we conclude that forests in the Insubric region, that are dominated by

Ostrya (Carpino betuli-Ostryetum and Fraxino orni-

Ostryetum, Ellenberg and Kl/3tzli 1972), cannot be con-

sidered as climax forests. Under undisturbed succession these forests would probably develop into mixed decidu- ous forests with the components (in slightly decreasing abundance) Fraxinus excelsior, TiIia, Ulmus, Quercus

and Acer. In these forests, Ostrya carpinifolia, Fraxinus

ornus and Carpinus betulus would only have played a

marginal role. A new palaeobotanical study (Tinner et al. 1999) suggests that under natural conditions Abies alba

would also be co-dominant in the Insubrian region but be- cause o f anthropogenic pressure (mainly forest fires and browsing) it is sparsely present today and only at altitudes higher than 900 m asl. However, if seed sources would be available in the region, A. alba would p r o b a b l y enter again in the calcareous part o f woodlands, although in smaller quantities than on siliceous soils.

Acknowledgments. We are grateful to A. Antonietti, M.

Conedera, M. Kummer, J. van Leeuwen, I. Ogliari, C. Ravazzi, W.E. St6ckli, and H. Zoller for support and fruitful discussions.

We thank K. van der Borg and G. Possnert for radiocarbon dates, H.E. Wright Jr. and M. O'Connell for improvements to the manuscript. Helpful suggestions by J.-L. de Beaulieu, K.-E. Behre and R. Drescher-Schneider are gratefully acknowledged.

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Figure

Fig.  1. Map of A the study region  showing the  main  lakes (par-  allel lines)  and  locations of the  main  pollen  profiles,  and  B the  geology  of the  study  region
Fig.  3.  Radiocarbon  and  pollen  dating  of the  sediments  from  Lago  del  Segrino  and  Lago  di  Muzzano
Table  1.  AMS-radiocarbon  dates  from  Lago  del  Segrino  (LS-3a)  and  Lago di  Muzzano  (MUZ  II1)
Table  2.  Comparision  of vegetation  history at  Lago del  Segrino  and  Lago di  Muzzano
+6

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