The dendrochronological potential of lime ( Tilia spp.) from trees at Hampton Court Palace, UK

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  • This article was downloaded by: [The University Of Melbourne Libraries]On: 12 May 2013, At: 10:59Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

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    The dendrochronological potential oflime (Tilia spp.) from trees at HamptonCourt Palace, UKAndy K. Moir a b & Suzanne A.G. Leroy ba Tree-Ring Services, Hungerford, Berkshire, UKb Institute for the Environment, Brunel University, Uxbridge,London, UKPublished online: 13 Apr 2013.

    To cite this article: Andy K. Moir & Suzanne A.G. Leroy (2013): The dendrochronologicalpotential of lime (Tilia spp.) from trees at Hampton Court Palace, UK, Arboricultural Journal: TheInternational Journal of Urban Forestry, DOI:10.1080/03071375.2013.783173

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  • The dendrochronological potential of lime (Tilia spp.) from treesat Hampton Court Palace, UK

    Andy K. Moira,b* and Suzanne A.G. Leroyb

    aTree-Ring Services, Hungerford, Berkshire, UK; bInstitute for the Environment, Brunel University,Uxbridge, London, UK

    Common lime (Tilia europaea L.) and large-leaved lime (Tilia platyphyllos Scop.)are dendrochronologically and dendroclimatologically analysed for the first time. Limeis thought to be sensitive to climate change. Once a dominant species in Europe, it hasbeen in general decline from 3100 BC, but recently it has been found to be increasingthe northern limits of its range. Twenty-five trees from Hampton Court Palace (UK) arecross-matched to form a 138-year chronology spanning from AD 1866 to AD 2003.The relationships with climate were investigated using monthly instrumental records ofprecipitation and temperature from Kew between AD 1872 and AD 1997. The age ofthe lime trees was found to correlate well with girth (r 0.87). The annual resolutionof the chronology is robustly supported by regional cross-dating against established oakand yew chronologies. Summer precipitation (May, June and August) was shown to bea time-stable determinant of annual variation in radial growth. Problems of indistinctboundaries and missing rings, which become more prevalent in trees over 100 years ofage, may limit the dendrochronological potential of lime.

    Keywords: climate change; dendrochronology; dendroclimatology; lime trees; Tilia;Hampton Court

    Introduction

    In arboriculture and urban forestry, the determination of tree age is useful to identify the

    chronology of parks and gardens, to forecast future tree size and threats associated with

    increasing age and to identify individuals of particular conservation value. Dendroclima-

    tology, one of the sub-disciplines of dendrochronology, enables the identification of both

    tree age and relationships between ring width and climatic variables. In areas where a

    particular tree species is suitably responsive and long-lived and/or where past wood is

    recoverable, the discipline may enable climate records to be reconstructed at annual

    resolution, centuries before instrumental data are available. In the British Isles, the climatic

    relationships of few tree species other than oak (Kelly, Leuschner, Briffa, & Harris, 2002),

    Scots Pine (Briffa et al., 2001; Moir, Leroy, & Helama, 2011), yew (Moir, 1999) and elm

    (Brett, 1978) have been examined. All these genera have well-defined rings suitable for

    tree-ring analysis. Lime (Tilia spp.) has not been previously dendroclimatologically

    analysed. This is possibly because it is only rarely found in old buildings and it has a

    tendency to decay rapidly if damp. Furthermore, lime trees over 350400 years of age are

    typically hollow (Pigott, 1989).

    At the northern limits of its range in theLakeDistrict ofEngland, limehasbeenconsidered

    a relict species, due to its limited production of fertile seeds and pollen evidence of decline

    after 3100 year BC (Pigott &Huntley, 1980). The small-leaved lime (Tilia cordataMill.) and

    q 2013 Taylor & Francis and Aboricultural Association

    *Corresponding author. Email: akmoir@tree-ring.co.uk

    Arboricultural Journal: The International Journal of Urban Forestry, 2013

    http://dx.doi.org/10.1080/03071375.2013.783173

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  • large-leaved lime (Tilia platyphyllos Scop.) species are both native to the UK but are near the

    northern limits of their European ranges. Small-leaved lime is essentially a continental species

    known to require summer temperatures$208C at flowering for several consecutive days toproduce viable seed (Pigott & Huntley, 1981). It has had difficulty growing from seed in the

    UK under contemporary climatic conditions, but suitable conditions to permit fertilization

    may have been more prevalent during the medieval warm period (Pigott, 1989). Recently,

    Gray andGrist (2000) reported the natural regeneration of lime as far north as Perth, Scotland.

    Large-leaved lime is nationally a scarce tree (Newlands, 1999).Where both small- and large-

    leaved limes occur they can hybridise, resulting in common lime (Tilia europaeaL.),whichis also a widely planted ornamental tree.

    Limes (Tilia spp.) are one of the tallest broad-leaved trees inmost areas of Great Britain.

    They can achieve a height of 3540m, a diameter of 100300 cm and live up to 1000 years

    (Mayer, 1977). Multi-stemmed self-coppicing limes can live much longer (Pigott, 1993).

    Lime trees have played a major role as an architectural element in gardens in many

    European countries since the late seventeenth century. Owing to their aesthetic value, lime

    trees have become increasingly important in urban and open landscape in recent decades.

    The avenues of a double row of lime trees on both sides of the Long Water at Hampton

    Court Palace, UK, form the central feature of a great baroque patte doie layout (Figures 1

    and 2). This was originally commissioned by King Charles II soon after his restoration in

    AD1660. It is the finest surviving example of its kind inGreat Britain. The following history

    of the lime trees at Hampton Court is summarised from a report by Gough (2000). Adrian

    May, a royal gardener, purchased a consignment of 758 common limes fromHolland, which

    were planted in AD 1661. The average life expectancy of a European lime tree is 200250

    years, so the LongWater avenuewas in its prime at the beginning ofQueenVictorias reign.

    A policy of gapping up those trees in the avenue, which had perished, was largely

    unsuccessful due to competition with older trees. Many trees used in gaps were also a

    different species of lime, or planted in the wrong positions, which resulted in a gap-toothed

    canopy. The 1987 hurricane in Southern England affected the LongWater avenue badly. By

    2000, the original population of 544 trees had dwindled to 300, with only 7 original tree

    specimens remaining. The original trees were also a cause of problems as disease

    (particularly several types of bracket fungus) and old age had left them in a dangerous

    condition.

    In 2003, the lime trees of the royal palace park in Hampton Court were felled (Figure 2)

    to allow the replanting and restoration of the avenues, which presented a useful opportunity

    for dendroclimatological and dendrochronological analysis. Indeed, on one hand, lime

    should be considered if it has the potential to become a new proxy for estimating global

    change; on the other hand, the dating of old lime trees will contribute to the corpus of

    knowledge on gardens of a historically significant place. The aims of this research were (1)

    to establish the ages of the trees sampled, (2) to establish relationships between the radial

    growth and meteorological climate records, (3) to identify whether lime might be a useful

    species in dendrochronology and (4) to interpret the ages of the sampled trees into the

    cultural landscape of Hampton Court.

    Materials and methods

    Sampling and chronology building

    Full trunk sections were sawn by operators at Hampton Court, typically from 20 to 30 cm

    above the ground level. For practical reasons, V-section samples were cut across the widest

    diameter to provide two radii for measurement (Figure 3). Standard dendrochronological

    2 A.K. Moir and S.A.G. Leroy

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  • techniques were then utilised for sample preparation, measurement, cross-matching and

    dating (Stokes & Smiley, 1968). Cross-matches are reported using raw ring-width data and

    the standard Students t-value statistic. Those t-values in excess of 3.5 are accepted as

    significant where supported by visual comparison.

    Growth rates

    Tree-ring series commonly contain age trend, caused by the general reduction in the ring

    width as trees get progressively older and pass through the formative, mature and senescent

    phases of growth (White, 1998). For useful visual comparison between tree growth rates,

    cumulative plots were produced to help emphasise the underlying biological age growth

    trend (Figure 4).

    Figure 1. Map of Western Europe showing the location of Hampton Court.

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  • Dendroclimatic analysis

    The series were standardised (a process to remove age trends) using ARSTAN software

    (Cook, Briffa, Shiyatov,&Mazepa, 1990), andwere detrended using a negative exponential

    curve or linear regression with power transformation (Cook & Peters, 1997) to reduce

    potential end-effect inflation of resultant indices. The chronology statistics generated from

    the standardised series are described in Table 1. Mean sensitivity is a measure of the mean

    relative change between adjacent ring widths (Fritts, 1976). Values over 0.30 are high and

    indicate that the tree-ring series are highly responsive to environmental factors, while low

    Figure 3. A V-section sample cut from a full section.

    Figure 2. A standing and felled lime tree along the Long Water at Hampton Court Palace, UK.

    4 A.K. Moir and S.A.G. Leroy

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  • values indicate weak inter-annual variance. The expressed population signal (EPS)

    (Wigley, Briffa, & Jones, 1984) measures the degree to which the chronology correlates (or

    agrees) with a theoretical population chronology. The value of EPS ranges from 0 to 1, with

    1 being the best possible value (the hypothetically perfect chronology).

    Growthclimate relationships were examined using correlation functions as a

    statistical model to compute coefficients between tree-ring chronologies and monthly

    climatic variables (Blasing, Solomon, & Duvick, 1984). These coefficients are univariate

    estimates of Pearsons product moment correlation. Correlation function analyses and

    moving interval correlation function analysis were carried out using DENDROCLIM2002

    software (Biondi & Waikul, 2004), which tests significance at the 0.05% level. A 14-

    month analysis period extending from September in the year before growth to October of

    the year of growth was selected. Residual tree-ring chronologies (which have proved to

    Figure 4. Cumulative plot tree rings.

    Table 1. General statistics of lime chronologies from the arstan standard chronology.

    File name MS AR1 R(bt) SNR EPS

    HPLIME 0.33 0.29 0.67 15.99 0.94

    Note: Common interval 19101990. MS, mean sensitivity; AR1, first-order autocorrelation; R(bt), betweenseries correlation; SNR, signal to noise ratio; EPS, expressed population signal.

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  • yield more climatic information and minimise autocorrelation) were used with monthly

    maximum temperature, minimum temperature and precipitation as predictors. Monthly

    temperature and rainfall series for Kew (a meteorological station 9.5 km south west of

    Hampton Court) were used in this analysis (Wales-Smith, 1980). Temperature and rainfall

    can be intercorrelated causing an apparent negative association between temperature and

    ring width when using correlation to examine climategrowth relationships, as

    highlighted by Fritts (1976). To help resolve this problem, response function analysis

    (which transforms the predictor variables into uncorrelated principal components) was

    also carried out using DENDROCLIM2002. However, as response coefficients tend to be

    lower than correlation coefficients the results are only summarised.

    Results

    Chronology

    The results of the cross-matching between 25 samples against both oak and yew reference

    chronologies are described below. The trees sections were generally quite circular in form

    and showed no signs of hollowing. Pith was recovered in all cases. Twenty-five out of the

    30 samples (83%) were successfully measured and cross-matched. Nineteen series were

    from common lime and four from large-leaved lime. Two samples were labelled with the

    same number, and therefore, could only be established as Tilia spp. The 25 cross-matched

    together were used to form a chronology called HPLIME, which spans 18662003. The

    annual resolution of this tree-ring series is confirmed by cross-matching against both oak

    and yew existing reference chronologies (Table 2). The rings in years 1949/1950, 1964

    and 1985 were the narrowest rings and most commonly missing. Instances of missing rings

    were more frequent in older trees, i.e. after the first 80 years of growth. In five series where

    the rings to bark could not be reliably measured, it was calculated that a missing ring

    occurred on average once every 12 years, suggesting a 12% underestimation of tree age

    from ring counts in lime trees over 50 years of age.

    Growth rates and age

    The ages and girths of the 25 cross-matched trees (Figure 4), together with five ring

    counted trees, are plotted in Figure 5, and the following regression equation is calculated

    as follows:

    AGE 105:77 GIRTH in m2 11...

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