Studi Trent. Sci. Nat., Acta Geol., 82 (2005): 101-107 ISSN 0392-0534

© Museo Tridentino di Scienze Naturali, Trento 2007

Dendroecology and dendrochemistry in Trentino: the Grotta di Ernesto project

Jonathan G.A LAGEARD1, Nicola LA PORTA2, Peter A. THOMAS 3 & Neil J. LOADER4

1 Department of Environmental & Geographical Sciences, Manchester Metropolitan University, John Dalton Building,

Chester Street, Manchester M1 5GD, UK2 Istituto Agrario di San Michele all’Adige, Via E. Mach 1, 38010 San Michele all’Adige (TN), Italy3 School of Life Sciences, Keele University, Staffordshire ST5 5BG, UK4 Department of Geography, University of Wales, Swansea SA2 8PP, UK

SUMMARY - Dendroecology and dendrochemistry in Trentino: the Grotta di Ernesto project- Sampling and analyses

for dendroecological and dendrochemistry studies have been carried out in forests of Trentino, south-eastern Italian

Alps, to complement the extensive speleothem database and recognize tools for cross-correlation of the two archives.

Dendroecological data will be compared with the series of winter temperature and anthropogenic sulphate concentration

trend obtained from three stalagmites sampled at the Grotta di Ernesto cave. The main objective of the investigation

is to analyse different aspects of anthropogenic impacts recorded by the tree-ring series, such as variability in the

load of pollutants and land use changes, and discriminate them from natural phenomena. We also aim at recognizing

ecosystem storage of sulphur, which has been recognised in speleothem studies. Sampling was carried out for trees

growing within 1000 m radius around the cave. We selected trees which had a minimum of 50 and 150 annual rings, a

requirement for both computer assisted dendrochronology and isotope analysis. 85 trees belonging to the species Fagus sylvatica, Larix decidua, Picea abies and Abies alba were sampled through Pressler coring. Planned analyses included

traditional dendrochronology, dendroclimatology (measuring carbon and oxygen isotopes and blue light refl ectance)

and dendrochemistry (extraction of sulphur). The dendroecological data obtained by the study will be compared and

correlated with meteorological series from 5 permanent stations dating back to 1812. The tree-ring data will be also

compared with isotope values extracted from growth annual laminae developed from the year 1900 to the year 2000

AD in stalagmites from Grotta di Ernesto.

RIASSUNTO - Dendroecologia e dendrochimica in Trentino: il progetto Grotta di Ernesto - Un campionamento a

scopi dendroecologici e dendrochimici su anelli di accrescimento annuali degli alberi è stato effettuato in vicinanza

della Grotta di Ernesto (Grigno, TN) per confronto con serie di temperature medie invernali e di concentrazione

di solfato antropogenico ottenute da tre stalagmiti della grotta. Il principale obbiettivo dello studio era analizzare i

diversi aspetti delle trasformazioni antropogeniche registrate nelle serie degli anelli degli alberi dovute a inquinamento

ambientale o cambiamento dell’uso dei suoli, e distinguerle da fattori naturali. Di particolare interesse è riconoscere

fenomeni di immagazzinamento nell’ecosistema di zolfo da emissioni antropogeniche. All’inizio furono identifi cati

alberi che crescevano entro un raggio di 1000 m dalla Grotta di Ernesto. Tra questi furono selezionate piante con

un minimo di 50 e 150 anelli annuali, richiesti rispettivamente per analisi dendrocronologiche computerizzate e

per analisi isotopiche. Ottantacinque piante appartenenti alle specie Fagus sylvatica, Larix decidua, Picea abies e

Abies alba furono campionate con una Trivella di Pressler. Le analisi programmate includevano dendrocronologia

tradizionale, dendroclimatologia (misurando isotopi di carbonio e ossigeno) e dendrochimica (estrazione di zolfo).

I dati dendroecologici ottenuti in questo studio saranno confrontati con archivi di dati da 5 stazioni meteorologiche

permanenti, poste a diverse distanze dalla grotta. Gli anelli legnosi saranno in futuro confrontati con i valori isotopici

ottenuti dalle lamine di crescita delle stalagmiti della Grotta di Ernesto dal 1900 al 2000.

Key words: dendroecology, dendrochemistry, sulphur, Grotta di Ernesto

Parole chiave: dendroecologia, dendrochimica, zolfo, Grotta di Ernesto

102 Lageard et al. Dendroecology and dendrochemistry in Trentino: the Grotta di Ernesto project

1. AIMS OF THE DENDROECOLOGY STUDIES NEAR GROTTA DI ERNESTO SITE

The current palaeoclimate and environmental stud-ies, in particular for the past few centuries, require archives of proxy data with annual to sub-annual resolution. In the Trento Province both tree ring and speleothem proxy records have made substantial new contribution to our understanding of natural climate variability and the effects of anthropogenic forcing. In particular, the Grotta di Ernesto cave is one of the key sites for palaeoclimate and environmental research in the Alps (Frisia et al. 2003, 2005). Speleothems from this cave are temperature-sensitive in their growth rate, and encode in their chemical properties information about atmospheric sulphur load. The forest trees near Grotta di Ernesto, therefore, would allow for multi-parameter comparison of tree rings and speleothem proxy data at least over the past 150 years, which is the time interval that is better constrained in the an-nually laminated speleothems (Frisia et al. 2003). In particular, Frisia et al. (2003) not only found evidence for correlation of speleothem growth rate and tem-perature, but also identifi ed the 11-year sunspot cycle, which was related to ecosystem response to solar forc-ing. A dendroclimatological study has the potential to cast better insight on the interannual variations of climate parameters and how modes of variability have changed through time. It is important, here, to remind that while tree rings are an excellent proxy for the tem-perature in the growing season, speleothems, at Grotta di Ernesto, preferentially record the cold season.

The present study builds its rationale from the premise that tree-ring samples collected from trees in the vicinity of Grotta di Ernesto could be used to monitor tree response to climatic variables and to anthropogenic pollution over the previous 150 years and provide data complementary to speleothem data. Planned analyses included traditional dendrochronolo-gy, dendroclimatology (measuring carbon and oxygen isotopes and blue light refl ectance as climatic proxies) and dendrochemistry (extraction of sulphur).

2. SAMPLING

Sampling of tree-rings was governed by a num-ber of criteria in order to provide suitable samples for the analyses identifi ed above. Initially, it was important to identify trees species growing in the area immediately surrounding Grotta di Ernesto, which would provide ring series suitable for basic dendrochronology and, more importantly, ring series of suffi cient length to facilitate isotopic analyses. At least 50 annual rings are required for computer-as-sisted dendrochronology, and 150 rings are needed

for the isotope work envisaged here, as there is an age effect clearly discernable in the isotopic records of tree-rings. A climate signal cannot be found in young trees and therefore the isotopic records for the fi rst 40 years growth of individual trees are discounted from climatic reconstructions. In an ideal world, tree-ring records of at least 200 years are desirable for tracing environmental impacts related to changing climate and to industrial development in northern Italy. Field sampling took place between 11th and 20th July 2005 from the excellent base of the Albergo San Marco in Enego and with assistance of the Borgo Valsugana Forest District of the Forest Service of Provincia Autonoma of Trento (PAT).

An exploratory fi eld investigation in 1997 had identifi ed a number of species that might be suitable for this project: Fagus sylvatica (Beech), Larix decid-ua (European Larch), Picea abies (Norway Spruce) and Abies alba (Silver Fir). In that pilot study, larch seemed to have a good response to temperature. A search was then undertaken for mature/old trees in the area above and adjacent to Grotta di Ernesto. As can be seen in fi gure 1, the entrance to the cave is on the upper slope of Valsugana to the west of the village of Martincelli. Many dendroecological stud-ies have shown that the growth response of trees located on slopes can often mask meteorological signals (Urbinati et al. 1997; Oberhuber et al. 1998; Oberhuber & Kofl er 2000; Oberhuber 2004) and therefore another important consideration was to fi nd trees rooted on fl at or only gently sloping ground. The circle drawn in fi gure 1 describes a 1 km radius centred on the entrance to the Grotta di Ernesto and clearly illustrates why the search for suitable trees focused to the west and south of the cave.

A further restriction on sampling is the extensive area of tree-less pastures. The word “malga” is a com-mon prefi x for mountains meaning cattle-shed and can be found in many localities on the plateau within circa 6 km to the west/north-west of the cave (M. Aveati, M. Vacchetta, M. Val Capertadi Sotto, M. Campo di Sopra, M. Val d’Antenne), indicating areas that have been pasture for some considerable time.

The mixed forests in the area are predominantly of Picea abies, with Abies alba, Larix decidua and Fagus sylvatica. Mean stand density is typically 250 trees per ha and tree basal area is about 25-30 m

2 per

ha (Virgilietti 1998). Many stands over the last 40 years have been managed under a silvicultural system, “taglio di curazione”, which is similar to “naturalistic” silviculture or a selection system (Ferrari 1984).

This semi-natural conifer forest with beech under-storey is characteristic of this zone of Trentino at 1000-1500 m a.s.l. in the Valsugana (Ferrai & Mazzucchi 1974). Large old beech trees are present scattered in some parts of the forest, the remains of seed-producing trees that were present in former beech coppices (Loss

Studi Trent. Sci. Nat., Acta Geol., 82 (2005): 101-107 103

& Ferrai 1984), or some were possibly just isolated trees in the pasture. These beech growing together with larch are mostly found in private forests. Public forests are dominated by almost solely by Picea ab-ies and Abies alba. This major distinction in the forest is the result of the intensive silvicultural management that was practiced in the beech coppices and the inten-sive grazing under larch trees on private lands. There are also the remnants of charcoal pits where charcoal was made from beech wood and the waste wood from conifers.

This forest had been affected quite regularly by disturbance and signifi cant regeneration occurred only after 1920 (Motta et al. 2002). Before the war the land had been exploited as pasture, as was quite common in such regions (Backmeroff 1996; Piussi 2002), especially where the slope was not excessive. A forest management plan from the ’20s (stored in the Borgo Valsugana Forest District Archives) reveals that people exerted a large infl uence on the forest. Forest management plans for the Grigno area were useful in the interpretation of the data obtained through earlier dendroecological research, although events defi ned in the tree-rings did not always correspond with data from the management plans (yearly thinning, felling, wind-throw damage) as stand-level details were al-ways missing from the plans. These plans dealt with areas of several hectares (Motta et al. 1999).

Despite these limitations, the information included in the management plans is of crucial importance in studying stand history, and only by using all sources of information it is possible to delineate and to identify the most important natural and human features of the history and disturbance that affected the origin and subsequent growth of the forest stands.

In addition to the culture impacts discussed above, the area was also particularly affected by the First

Fig. 1 - Location of Grotta di Ernesto on the northern, upper

slopes of the Valsugana.

Fig. 1 - Ubicazione della Grotta di Ernesto, verso la sommità del fi anco settentrionale della Valsugana.

Fig. 2 - Open pasture area with evidence of sparse re-

colonization. The whole plateau was once mostly exploited

as summer grazing pastures.

Fig. 2 - Pascolo aperto con segni di giovane ricolonizzazione da parte della foresta. L’altopiano era un tempo sfruttato principalmente come pascolo estivo.

Fig. 3 - Forest re-colonisation of the plateau near Colle Dei

Meneghini.

Fig. 3 - Ricolonizzazione forestale dell’altopiano vicino al Colle dei Meneghini.

World War. Ruins of trenches are still to be seen and it is not infrequent to fi nd in tree stems with the pres-ence of splinters of bursting shells (G. Messina pers. comm.).

Today these areas, formerly kept open due to inten-sive summer grazing (Fig. 2), are still being re-colo-nised by the forest, as it is generally the case in many mountain regions in the Alps (Piussi & Pettenella 2000). As a result, large areas of the plateau are cov-ered by forest younger than 100 years (Fig. 3).

104 Lageard et al. Dendroecology and dendrochemistry in Trentino: the Grotta di Ernesto project

Fig. 4 - Location of large larch trees. Sampling a larch using

a Pressler-type increment corer.

Fig. 4 - Ubicazione dei larici con diametro del tronco largo. Campionamento di un larice con un carotiere tipo Pressler a incrementi.

Due to topographic restrictions and the generally youthful nature of the forest, detailed local knowledge of surviving older trees was essential to the success of the isotope part of the project.

Foresters from the Forest Service of PAT took the sampling team to areas where there were large larch (Fig. 4) and beech trees (Fig. 5). Even the largest larch trees, such as the one shown in fi gure 4, were gener-ally only around 90 years old. Beech trees, such as the one illustrated in fi gura 5, were either standing or dead and fallen, all with central rot making them diffi cult to core and even more diffi cult to measure. Although there was strong beech regeneration in parts of the area indicated in fi gure 5a, there was no scope for bridging the dendrochronological gap between the living and dead trees.

Attention turned to Norway spruce and Silver fi r. As with the larch, it proved very diffi cult to fi nd any living individuals over 100 years old. The forest-ers, however, knew of wood piles composed of trees thought to be old, which had been felled in the winter

Fig. 5 - Location of old beech trees. Sampling a dead

beech.

Fig. 5 - Ubicazione di vecchi faggi. Campionamento di un faggio morto.

Fig. 6 - Location of wood piles sampled at 2 km (WP1) and

4 km (WP2) from the Grotta di Ernesto.

Fig. 6 - Ubicazione delle cataste di legna campionate a 2 km (WP1) e 4 km (WP2) dalla Grotta di Ernesto.

Fig. 7a - The wood pile WP1. See fi gure 6 for its geographic

location.

Fig. 7a - La catasta di tronchi WP1. Si veda la fi gura 6 per la sua localizzazione geografi ca.

Fig. 7b. - Inspecting trunk cross-sections at WP2 to check

for century-old trees.

Fig. 7b - Ispezione delle sezioni trasversali di tronchi nella catasta WP2 per trovare tronchi centenari.

Studi Trent. Sci. Nat., Acta Geol., 82 (2005): 101-107 105

of 2004-2005. Two wood piles were inspected, one less than 2 km from the cave (WP1) and the other 4 km (WP2) (Fig. 6). Trees piled at each had not been transported far after felling and the wood piles also permitted easy viewing of stem cross sections (Fig. 7a). Quick ring counts helped to identify a number of trees of around 150 years and older. Large diameter trees were not always the old ones (Cherubini et al. 1996; Rozas 2003; Jimenez et al. 2003) so being able to see the cross-sections saved much trial and error coring. This sampling advantage was offset by the

Fig. 8a - Peter Thomas removing 5 mm and 12 mm cores using

a Pressler-type increment borer at one of the wood piles.

Fig. 8a - Peter Thomas sta campionando con un carotiere Pressler un tronco in una delle cataste.

Fig. 8b - Jonathan Lageard coring a conifer in life position.

The most critical part of the coring is hitting the centre of

the tree, which allows to obtain the age of the tree.

Fig. 8b - Jonathan Lageard mentre carota una conifera in posizione di vita. La parte più critica del campionamento è centrare l’asse di crescita dell’albero per ottenere l’età dell’individuo.

Fig. 8c and d - Peter (8c) begins coring a large trunk from

one of the woodpiles. Jonathan (8d) has reached the centre

of a smaller trunk.

Fig. 8c e d - Peter (8c) inizia a carotare un tronco piuttosto largo nella catasta. Jonathan (8d) ha raggiunto il centro di un tronco più piccolo.

impossibility of coring some trunks lodged within the centre of the wood pile. Another drawback was that bark was sometimes missing from the visible portion of the trunk and species identifi cation could only be confi rmed later by microscope examination of the wood structure. In tangential sections, the rays of spruce are seen to be comparatively small – 10-15 (25) cells high – with included resin canals while the rays of fi r are 15-25 (40) cells high without resin canals.

Increment cores, 5 mm and 12 mm diameter cyl-inders of wood, were removed using hand-operated Pressler-type corers (Figs 8a-d and Tab. 1). A few replicate disks were also removed using a chainsaw (Fig. 8e).a

b

c

d

106 Lageard et al. Dendroecology and dendrochemistry in Trentino: the Grotta di Ernesto project

Fig. 8e - Sampling with a chainsaw to obtain a whole section

of a tree.

Fig. 8e - Campionamento di una rotella di legno con una sega elettrica per ottenere l’intera rotella di legno.

Fig. 9 - Site chronologies E1_35 from wood pile WP1 and

E1_4 from WP2. a. Raw ring-widths, b. detrended.

Fig. 9 - Cronologie E1-35 da campioni provenienti dalla catasta di tronchi WP1 e E1-4 costruita da campioni provenienti dalla catasta WP2. In (a) i dati grezzi di spessore degli anelli di accrescimento degli alberi. In (b) I dati dopo elaborazione (de-trending).

Species No 5 mm cores No 12 mm cores

Fagus sylvatica 5 0

Larix decidua 16 0

Picea abies 23 10

Abies alba 24 5

Tab. 1 - Increment cores collected in 1997 and 2005.

Tab. 1 - Carote campionate nel 1997 e nel 2005.

3. LABORATORY ANALYSES

Increment cores were taken to the Dendrochronology Laboratory at Manchester Metropolitan University (UK), where they were mounted on wooden channels and sanded using coarse through to fi ne grit sandpapers to clearly reveal tree-ring wood structure and in par-ticular the boundaries between rings. Tree ring-width measurements were then made for each sample using a measuring stage, binocular microscope and specialist computer software. Measurement started with the in-nermost ring (ring closest to the centre of the tree/pith) and followed by a series of consecutive rings towards the bark edge.

4. INITIAL RESULTS

A ring-width record was made for each core and in-dividual records were crossmatched (that is compared with others for similarity). Using t-value correlations it was possible to combine contemporaneous series to form site chronologies. Chronologies were successful-

ly made for trees from both wood piles E1_35 (WP1 – 12 trees) and E1_4 (WP2 – 3 trees) – see details in fi gure 9. A comparison of these chronologies with records from living trees confi rmed that the last ring present in both chronologies was laid down in 2004.

Twelve mm diameter samples and disks were kept for isotope analyses and are currently being analysed at the University of Wales in Swansea, in the Dendrochronology Laboratory. These cores will also be subject to blue light refl ectance analysis which acts as a surrogate measurement of ring density, which is known to correlate well with climate data. Other samples are undergoing trials for sulphur extrac-tion at the Geography Department of the University of Birmingham. A successful application has been made to the European Synchrotron Facility (ESRF) in Grenoble to analyse the molecular state of sulphur via X-Ray near edge absorption spectroscopy (XANES) technique at ID 21, which allow to discriminate sul-phate and sulphide. Other elements will be also ana-lysed at ID 21 and at very high resolution by means of micro X-Ray fl uorescence spectroscopy within individual tree-rings and we expect to obtain also very detailed maps. This technique has been commonly ap-plied to archaeological wood, and will be here applied for the fi rst time for comparison with speleothem data obtained with the same method (Frisia et al. 2005).

ea

b

Studi Trent. Sci. Nat., Acta Geol., 82 (2005): 101-107 107

Tab. 2 - Meteorological data available for comparison with

tree-ring data.

Tab. 2 - Dati meteorologici disponibili per il confronto con i dati degli anelli degli alberi.

Data produced from all the afore-mentioned analy-ses will be compared to meteorological data (monthly and annual means) from meteorological stations listed in table 2 and data obtained from analyses of the spe-leothems from Grotta di Ernesto.

Meteorological Station Data coverage (years AD)

Milan 1812-2004

Trento 1875-2004

Bieno 1924-2004

Lavarone 1921-2004

Pieve Tesino 1963-2004

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Spatiotemporal growth dynamics and disturbances in a

subalpine spruce forest in the Alps: a dendroecological re-

construction. Canadian J. Forest Res., 26 (6): 991-1001.

Ferrai S. & Mazzucchi M., 1974 - Improving the forests in

Valsugana: improvement fellings in the coppice stands

and high forest. Monti e Boschi, 25 (6): 11-19.

Ferrari L., 1984 - Forests and forestry in Trento Province,

Italy. Schweizer. Zeit. Forstwesen, 135 (7): 547-612.

Frisia S., Borsato A., Preto N. & McDermott F., 2003 - Late

Holocene annual growth in three Alpine stalagmites

records the infl uence of solar activity and the North

Atlantic Oscillation on winter climate. Earth Plan. Sci. Lett., 216: 411-424

Frisia S., Borsato A., Fairchild I.J. & Susini, J., 2005 -

Variations in atmospheric sulphate recorded in stalag-

mites by synchrotron micro-XRF and XANES analyses.

Earth Plan. Sci. Lett., 235: 729-740.

Jimenez J., Kramer H. & Aguirre O., 2003 - Individual tree

growth in an uneven aged mixed coniferous stand based

on stem analysis. Allgemeine Forst- und Jagdzeitung,

174 (9): 169-175.

Loss A. & Ferrai S., 1984 - Coppice forests in Trentino:

silvicultural and management aspects. Schweizer. Zeit. Forstwesen, 135 (7): 585-597.

Motta R., Nola P. & Piussi P., 1999 - Structure and stand

development in three subalpine Norway spruce (Picea abies (L.) Karst.) stands in Paneveggio (Trento, Italy).

Global Ecol. Biogeog., 8 (6): 455-471.

Motta R., Nola P. & Piussi P., 2002 - Long-term investiga-

tions in a strict forest reserve in the eastern Italian Alps:

spatio-temporal origin and development in two multi-

layered subalpine stands. J. Ecology, 90 (3): 495-507.

Oberhuber W., 2004 - Infl uence of climate on radial growth

of Pinus cembra within the alpine timberline ecotone.

Tree Physiol., 24 (3): 291-301.

Oberhuber W. & Kofl er W., 2000 - Topographic infl uences

on radial growth of Scots pine (Pinus sylvestris L.) at

small spatial scales. Plant Ecology, 146 (2): 231-240.

Oberhuber W., Stumbock M. & Kofl er W., 1998 - Climate

tree-growth relationships of Scots pine stands (Pinus sylvestris L.) exposed to soil dryness. Trees-Structure and Function, 13 (1): 19-27.

Piussi P., 2002 - Spontaneous reforestation and post-agricul-

tural development. Monti e Boschi, 53 (3/4): 31-37.

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151-163.

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Quercus robur: testing previous and improved methods.

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5. FUTURE OBJECTIVES

There is an exciting future for sulphur analyses in tree-rings of specimens collected near a site for which increasing sulphur concentration trends have been de-tected for the past 100 years from the speleothem archive. It is envisaged that ring-width chronologies already built will be strengthened and it may also be possible to work up tree-ring chronologies for larch and for fi r. The tree-ring team is looking forward to collating the results from the range of analyses and to drawing conclusions about past climate in the hinterland of Grotta di Ernesto and about the links Sulphur forges between natural and hu-man modifi ed systems above and below ground.

ACKNOWLEDGEMENTS

This work is a part of the project AQUAPAST fi nancially supported by the Provincia Autonoma of Trento. The authors wish to thank Dr. Giorgio Messina and several other foresters of the Forest Service of the Provincia Autonoma di Trento for the very helpful as-sistance in fi nding the trees and in collecting samples, and Dr. Silvia Frisia, who coordinated the project and revised the manuscript.

We thank the UK NERC for research support (NE/C511805/1 and NE/B501504/1).

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