Tree reactions and dune movements: Slowinski National Park, Poland

Catena 81 (2010) 55–65

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Catena j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / c a t e n a

Tree reactions and dune movements: Slowinski National Park, Poland Marcin Koprowski a,⁎, Vanessa Winchester b, Andrzej Zielski c a b c

Laboratory of Dendrochronology, Institute of Ecology and Environment Protection, Nicolaus Copernicus University, Gagarina 9, 87-100 Torun, Poland Oxford University Centre for the Environment, School of Geography, Oxford, OX1 3QY, UK Faculty of Geology, Geophysics and Environmental Protection, University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków, Poland

a r t i c l e

i n f o

Article history: Received 8 June 2009 Received in revised form 2 January 2010 Accepted 6 January 2010 Keywords: Dune movement Ring widths Scots Pine Wood anatomical reaction Dendrochronology Dendrogeomorphology

a b s t r a c t The effects on tree growth of both climatic and non-climatic variables were investigated in relation to dune dynamics at three sites on the Czolpinska dune in the Slowinski National Park, Poland where aeolian sediments are invading a forest of Scots Pine (Pinus sylvestris L.). We found that where dune advance was relatively rapid, tree vitality declined after stem burial was over 1.9 m, but where advance was under 1 m/yr survival was remarkably increased, one tree survived, albeit with thinning needles, after an estimated 11.4 m burial. Below sand-surface stem discs, cut 0.5 m apart, from a heavily suppressed tree revealed a difference in narrow-ring reactions of up to 2 years over a 2 m burial distance; the discs also showed a time lag of 4 years before compression wood formation. Consequently, when estimating sand-movement rates we discounted compression wood reactions; we also excluded climatic events and pest infestations. The remaining data supplied a sandadvance rate at Site 1 from 2.4 to 3.5 m/yr. At Site 2, rates were from 1.2 to 2.5 m/yr, with a direct measurement of 0.3 m/yr between 2006 and 2007. At Site 3 rates were from 0.3 to 1.2 m/yr, with dune migration here virtually at a standstill over the last seven years. Direct measurement of sand movement (3.03 m/yr) at Site 1 was slower than the lowest rate (3.5 m/yr) previously recorded by Borówka (1980) for the larger dune system. © 2010 Elsevier B.V. All rights reserved.

1. Introduction 1.1. Background and aim Trees, whose growth sensitively reflects changes in the surrounding environment, have been widely used by dendrochronologists as bio-indicators to study climate change, environmental conditions and landforming processes (e.g. Shroder, 1980; Wiles et al., 1996; Schweingruber, 1996; Millar et al., 2006; Gärtner, 2007). Processes connected with dune migration in coastal areas are prime subjects for dendrogeomorphological research with woody plants growing around dune systems being living chronicles of sand-drift dynamics. However, among landforming processes those involving dune movements have received relatively little attention although initial research using dendrogeomorphological techniques has produced promising results (Alestalo, 1971, 1979; Heikkinen and Tikkanen, 1987; Marin and Filion, 1992; Cournoyer and Filion, 1994; Strunk, 1997; Maun, 1998; Wiles et al., 2003; den Ouden et al., 2007). Of particular relevance to this present study, Alestalo (1971) found that tree rings are wider above sand level than below as did Strunk (1997). Likewise, Cournoyer and Filion (1994) found a decrease of radial growth in response to stem burial. Marin and Filion (1992) also found this to be true for sub-Arctic dunes where radial growth decreases

⁎ Corresponding author. Tel.: +48 56 611 47 90; fax: +48 56 611 44 43. E-mail address: [email protected] (M. Koprowski). 0341-8162/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2010.01.004

with increasing burial depth after a delay between the initiation of sand accumulation and negative growth changes. These findings needed addressing in our study since they indicate that coring height could affect analytical results. Wood anatomical reactions of interest to dendrogeomorphologists studying dune dynamics include variations in ring widths, cell size, shape and density, eccentric rings and resin ducts, the presence of reaction wood and the date of tree death. Ring widths vary in response to climatic and environmental changes: during spring large, thin-walled earlywood cells facilitate water conductance; latewood cells are formed in summer when growth slows and cells become smaller, thickerwalled and thus darker, in addition, eccentric rings develop when trees are tilted. Response to mechanical stress or damage can be traced to the year or season by the presence of resin ducts. A further mechanicalstress marker, termed compression wood in conifers, is expressed as zones of high-density cells. And, finally, tree death can be dated by crossdating dead trees with a reference chronology. The central aim of our study was to assess whether the annual tree rings of Scots Pine (Pinus sylvestris L.) growing on the lee side of the Czolpinska dunes in the Slowinski National Park, Poland could be used to measure rates of dune advance. Our main assumption was that sand stress affects tree-ring formation soon after sand invasion (Gärtner, 2007), with affects including reduction of tree-ring width, changes in wood anatomical reactions (listed above) and, finally, tree death. The principle difficulty using tree rings as indicators of sand invasion is to separate climatic (including wind storms) and environmental events (such as vegetation changes, human or animal actions, pest

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infestations or disease) from the effects of sand movement. There will inevitably be some cross-referencing of climate/sand and other events in the dune-tree records, but for the purpose of this study we assume that the major agents other than sand most likely to affect tree growth in our study area are climate and pests. The climatic problem can be dealt with by comparison of the local meteorological records with a tree-ring reference chronology constructed from forest-floor trees allowing identification of the main climate influences on the ring widths of trees partially buried by sand. Insect infestation years are well documented (Białobok et al., 1993; Kochanowski and Bednarz, 2007) and these will appear in both the climate and sand-dune tree chronologies. Although climatic and insect events are semi-independent variables, exclusion of their main event years from analysis of dune-tree rings will reduce the possibility of false results. Further, to control our results we made direct measurements of sand advance over time in order to check rates of sand advance with rates derived indirectly from tree-ring reactions. Our research area included three sites, part of the much larger mainly arcuate Mierzeja Lebska system. The dune area is characterized by strong spatio-temporal dynamics. An earlier study by Borówka (1980) established that dune movements in the system including the most active Madwiny dunes approximately 11 km east of our study area, varied from 3.5 m to 10 m/yr, with a maximum rate of almost 15.6 m/yr at the head of the system. 1.2. Regional setting The Slowinski National Park (SNP) is a World Biosphere Reserve. It lies midway along the Polish coast edged by the Baltic, with its famous

mobile dunes on the Lebska sandbar separated from the land by several lakes. Our three study sites within the Park lie on the southern flank of the Czolpinska dune between Lebsko Lake (71.4 km2) and Gardno Lake (24.7 km2). The Park's climate is ‘transient’: the dominance of the Atlantic climate decreases from west to east due to increasing continentality, with this indicated by increasing mean annual precipitation and temperature and a decreasing vegetation growth period. The area is generally characterized by sub-Atlantic vegetation and a predominantly sub-continental maritime climate with cold, humid winters, cool and relatively dry springs and moderately warm wet summers. A rise in sea level created by a change in climate could lead to the Baltic foredunes and white-dune zones becoming exposed to erosional processes (Huis van, 1989). The vegetation and morphology of the Baltic dunes have been affected by human activities for nearly 2000 years. Since the 15th century aeolian processes caused by deforestation have been steadily increasing leading to the formation of large dunes between the 16th and 18th centuries. These began to migrate across the Leba, Vistula and Kuronska Bars finally destroying what remained of the forests and by the 17th and 18th centuries the dunes were threatening human settlements (Piotrowska and Stasiak, 1982). From the beginning of the 19th century conifers began to be planted along the whole coast to stabilize the dunes, with planting continuing throughout the first half of the 20th century. The result was the development of close-canopy woodland (Piotrowska, 1989) with only part of Leba Bar left open for dune migration. Dune slopes, gentle on their windward sides and steep to leeward, move from west to east driven by the prevailing west winds (Piotrowska, 1997).

Fig. 1. (a) Dune area (red spot) in the Slowinski National Park, Poland. (b) Red circle indicates Czolpinska Dune in the middle of the Park. (c) Research sites on the Czolpinska Dune flank.

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2. Methods 2.1. Site selection Three sites (Fig. 1) in the Slowinski National Park (SNP) were chosen for comparison of their dune dynamics: (i) Site 1 (54°43′31.7″ N 17°16′03.7″E), locally named “the VIP Dune”, with a slope angle of 31°, is near the head of the Czolpinska system; (ii) Site 2 with the same slope angle is 475 m west on a continuation of the dune flank and, (iii) Site 3, with a dune slope angle of 33°, is 25 m west of Site 2 beside a path leading from the summit of the dunes to the forest floor approximately 25 m below (54°43′20.6″N 17°15′37.8″E). There is standing water to the north and south of Site 1 where the presence of Vaccinium myrtillus, an indicator of moist coniferous forests, implies differences in moisture between sites since this species is absent from Sites 2 and 3 where the forest floor is moderately dry. Site 3 is attached, on its southern flank, to a series of tree and grass-covered stabilised dunes, with stability implied by grass cover and leaf litter.

2.2. Sampling methods and materials A total of 151 cores were taken from 71 Scots Pines (T1–T71) on the eastern flanks of the dune system, with 21 of these collected from the forest floor flanking the dunes supplying a reference chronology for comparison with the semi-buried dune trees. The cores were taken from 1.2 m above tree base and, where trees were partially buried, from about 40 cm on the down-slope side and 60 cm above sand level on the up-slope. The cores, 5 mm in diameter, were collected in July 2006 and 2007 using a 400-mm-long increment borer and notes were taken of each sampled tree, height of core above the surface, stem circumference and tilt, slope angle, tree height, crown characteristics and health (as visually defined by needle loss). The cores were prepared for measurement following standard dendrochronological procedures (Phipps, 1985; Zielski and Krąpiec, 2004).

2.3. Tree rings at different tree heights At Site 2, to obtain a detailed record of tree reactions to sand invasion at different stem heights two cores were taken in 2006 from T59 at 0.4 m and 0.65 m above the surface. In 2007, nine more cores were taken from T59 at 20 cm intervals starting 40 cm from the forest floor and ending 20 cm above the dune slope. In addition, at Site 3, five cross-section stem discs were collected from T43 at 50 cm intervals to a depth of 2 m below the dune surface. These discs were taken from a highly stressed, dying tree: only one tree was chosen due to the protected status of the SNP (Fig. 2).

2.4. Tree-ring measurements and reference chronology Basic tree-ring parameters were obtained from measurement of ring widths to the nearest 0.01 mm using CooRecorder software combined with the related CDendro programme (URL: http://www. cybis.se) providing descriptive statistics. Further checks on crossmatching were also carried out using Cofecha (Grissino-Mayer, 2001) and TSAP (URL: http://www.rinntech.com) programmes. Annual rings tend to narrow as trees age (defining a size/age trend) and thus, before growth trends can be compared, detrending, based on a modified negative exponential curve, was applied involving indexation by division. Residual chronologies, based on an autoregressive model showing the underlying annual variance for comparison with climate data, were built using CRONOL (URL:http://www.ltrr.arizona. edu/software.html). A reference chronology was also built to date dead trees and show climatic effects.

Fig. 2. Discs from tree 43: the top disc invaded by fungus, was taken at the sand surface, the other four from below ground level. The black arrows indicate 1980 onset of eccentric rings.

2.5. Direct and indirect measurements of dune movement To check real-time dune movement rates against estimated rates derived from tree rings and wood anatomical features we tied orange marker tags at measured heights in 2006 around the stems of two trees: T67 at Site 1 and T59 at Site 2. We returned in 2007 to measure sand advance 2006–2007. An Abney level and tape were used to find tree height, to construct dune profiles and to measure dune angles. Tree height estimates were based on the trigonometric function TAN 45° = 1. Thus, tree height = the measured horizontal distance from tree base (plus height to eye level) to a person standing in a position where a view of the Abney-Level angle to treetop is 45°. We calculated the horizontal locations of trees on the dune flank (and sand-movement rates, 2006–2007, on tagged trees) by constructing a right-angled triangle taking the angle of the dune surface as the hypotenuse with its length defined as the distance from stem base to dune foot. Following analysis of tree-ring widths, we divided the horizontal measurement by the number of years since abrupt growth changes in the stem to find rates for sand advance (e.g.

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horizontal measurement to dune base/number of years since reaction). Stem burial depth estimates of trees on the dunes are based on forest-floor canopy height (17.7 m), age and stem circumferences at coring height (with circumference supplying a proxy for tree age that can be checked by comparison with ring-width age) compared with canopy height, age and stem circumferences at coring height of dune trees. The assumption of a flat forest floor does not hold for Site 3 where the terrain is less uniform: here the forest floor is flanked by gently rising, grass-covered slopes intersected by a small valley. We deduced a rise in the forest floor from the height of T42, the highest tree on this dune, which has a canopy that rises 6.5 m above that of the forest floor: it is of a similar age to the trees on the forest floor and its stem circumference of 0.91 m is, given a possible 10 m increase in height above the coring-height average forest-floor circumference (1.1 m) reasonably consistent with reduction in stem size over the distance. The dune slope angle is 33° and distance down-slope to the dune foot is 28.1 m (23.5 m horizontal measurement). These values suggest a rise in the forest floor of 7 m at this point. Assuming that stem growth reaction occurs at the sand surface in the year of sand invasion (Alestalo, 1979; Strunk, 1997) and assuming that the dune slope angle has remained constant over time, horizontal rates of sand advance suggested by dating the wood anatomical features shown by T43's discs (cut below the sand surface) were calculated using trigonometry as detailed above.

visual assessment of sequences of narrow and wide ring-width patterns describing abrupt growth changes, termed event years. An event year “is characterized by its conspicuousness within a limited section of the sequence” (Schweingruber et al., 1990: 11). The required relative size of ring widths defining an event year has varied (Fantucci and McCord, 1995; Stefanini and Schweingruber, 2000). In the present study we used the Schweingruber et al. (1990) approach where event years are defined by ring widths at least 40% narrower than adjacent earlier rings. The same event year, where it appears in over 40% of the total sample is termed a pointer year with this being defined as “the summation of conspicuous cross-dated rings of several tree-ring series” (Schweingruber et al., 1990: 11). “The summation of several skeleton plots in a ‘master plot’ reveals the years significant for any given group of trees” (Schweingruber et al., 1990: 10). Furthermore, most of the pointer years in our master-skeleton plot show very thin latewood development. We obtained climate records from both the Leba Meteorological Station (Institute of Meteorology and Water Management) and the European Climate Assessment & Dataset (URL: http://eca.knmi.nl/) from which selected climate parameters and extreme weather events for selected season can be extracted (Klein Tank et al., 2002). In our study we defined drought or dry years (e.g. 2003) as those having a lower sum of precipitation compared with the average value for a longer, selected period. 3. Results

2.6. Dead trees, growth decline, event years and climate records 3.1. Reference chronology Highly stressed trees buried by sand react by creating narrow annual rings, they may die slowly or suddenly after being overwhelmed; in order to date dead trees we matched their ring-width patterns with those of the reference chronology (Wiles et al., 2003) and we compared dated growth patterns of narrow rings from the dune trees with those of the reference chronology to exclude effects other than sand movement. As well as comparing tree-ring width measurements we also applied the skeleton-plot method (Schweingruber, 1996) based on a

We constructed a 119-year-long Pine chronology (1886–2005) from 21 cores from the forest floor. This chronology proved a good match with the regional chronology from Kuyavia–Pomerania (t = 5.0, correlation = 0.43) with an overlap of 114 years. The mean ring measurement of the reference chronology was 1.57 mm, autocorrelation 0.751, standard deviation 0.694 and mean sensitivity 0.251. Fig. 3a and b respectively shows the raw ring widths and residual curves of the reference chronology; comparison of this with the dune

Fig. 3. Forest-floor reference chronology: (a) mean of the raw ring-width data, (b) residual chronology showing climate trend, with the ageing effect removed and, (c) skeleton plot highlighting negative growth pointer years (in black), 1940 cold and dry winter/spring, 1944 summer drought, 1956, 1962 cold summers, 1982/83 insect outbreaks, 1996 drought?, 2003 drought.

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Fig. 4. Site 1 showing an increase in dune surface 2006–2007 and tree identification numbers. The black trees are dead, grey trees are more or less healthy.

tree chronologies shows that they share a number of very narrow annual rings. A skeleton plot of the forest-floor chronology reveals a number of pointer years: 1940, 1944, 1956, 1962, 1983, 1996 and 2003 (Fig. 3c). We excluded these years from analysis of dune movement rates since dune-tree narrow rings could also be caused by climate or factors other than sand stress.

advance in relation to the orange tag, 2006–2007, on T59 measured 0.3 m/yr (Fig. 6; Table 2). We have no direct measurement at Site 3, since the dune there was at standstill.

3.2. Dune-movement rates: direct measurements

Site 1: the reaction years for the trees in ascending order on the dune provide the following rates: T63 2.4 m/yr; T64 3.2 m/yr and T62 3.5 m/yr, narrow ring widths for the highest tree, T61 on the profile, supply a rate of 2.9 m/yr. Thus, overall rates from the individual tree reactions vary from 2.4 to 3.5 m/yr (Fig. 4; Table 1).

A stem measurement in 2007 from the sand surface to the orange tag on T67 indicates the dune advanced 3.03 m over the forest floor 2006–2007 at Site 1 (Figs. 4 and 5; Table 1) while at Site 2 sand

3.3. Dune-movement rates: indirect measurements and tree-growth reduction

Fig. 5. Site 1: direct measurement of sand advance onto T67 at the dune foot 2006, and 2007 with stem remaining below orange tag much reduced from original 2 m high position.

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Table 1 Site 1: characteristics of buried trees and estimated sand accumulation rate. Tree ID

Estimated sand burial (%)

69 67 66 65 63 64

14.7 28.3 40.7 42.9

62

50.3

61

60.5

Ring reduction (dates)

Horizontal measurement to dune base 2006 (m)

Average annual sand movement rate (m/yr)

Remarks

None None Direct mmt 2006–2007 None None Last dated ring 2001 Very narrow rings 2001 and 2002 Regeneration 2004 to 2006 Growth reduction 2002 No growth after 2005 Growth reduction from 2000

− 7.33 0.0 3.03 4.65 8.26 11.9 12.8

0 0 3.03 ? ? 2.4 3.2

Healthy Healthy

13.8

3.5

17.4

2.9

± Dead Resin ducts in 2002 Thin needles

Site 2: the evidence for dune movement here is based on the narrow-ring reactions of 7 trees (not including reactions in the climate and insect infestation years) implying that sand movement is slightly slower than at Site 1, with rates between 0.3 and 2.5 m/yr (Fig. 6; Table 2). Site 3: dune-movement rates, ignoring the insect infestation year of 1982 and compression wood reactions (see below), are generally slower than those at Site 2, with sand advancing at a rate between 0.3 and 1.2 m/yr at an average annual rate of 0.7 m/yr (Table 3). One visible difference between this site and the first two is that none of the trees is completely dead although some were deeply buried and showed needle loss, e.g. T42 (Fig. 7).

3.4. Dune-movement rates: compression wood and eccentricity At Site 3, T43 was highly suppressed with a height above sand surface of only 2.45 m and a surface stem diameter of 2 cm (Fig. 2, Table 4). Its 5 stem discs cut at 0.5 m intervals provide a detailed record of tree reaction to sand invasion. In the lower 3 discs normal concentric ring patterns end with a very dark latewood band in 1979, followed by eccentricity in 1980 and very narrow, pale, thin latewood rings. In disc 4, eccentricity is delayed until 1986. Compression wood starts in 1984 in discs 1 and 2 lasting until 1990 then reappears in all the discs in 1994. The upper two discs both received damage in 1981, the lower disc at the beginning and the upper one at the end of the

Healthy ± Healthy ± Dead Healthy

year, suggesting that the lower disc (disc 3) was at the surface at the beginning of the year, supplying an advance rate of 0.3 m/yr in 1981– 2006. In disc 3, a very narrow ring in 2001 is packed with resin ducts. Extremely narrow or missing rings and invasion of fungi at the dune surface signal incipient tree death from 2002. 3.5. Dune-movement rates: tree rings at different tree heights The 11 cores from T59 (eight below sand surface and three above) at Site 2 show interesting similarities and differences (Fig. 8). The beetle infestation years of 1982–83 appear in all cores followed by a four-year period of recovery; the 2003 drought also shows in all cores (excepting the lowest two whose bark ends were fragmented). The 1996 year is noticeable in 10 out of the 11 cores with all but the upslope core above the dune surface taken in 2006 showing a small recovery over the next 1–2 years followed by a decline in ring width. 3.6. Sand burial and tree vitality Per cent burial of total stem and stem burial depth are known to affect tree vitality (e.g. Strunk, 1997). At Site 1 near the forefront of the Czolpinska dune system, the highest living tree (T61) is 17.4 m from the dune foot (Fig. 4, Table 1); its ring widths show moderate growth reduction after 2000. This tree, albeit in poor health as shown by needle loss, has survived sand burial up to an estimated 60.5% of its

Fig. 6. Site 2 tree identification numbers. The black trees are dead or almost dead, grey trees are more or less healthy.

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Table 2 Site 2: characteristics of buried trees and estimated sand accumulation rates. Asterisks denote climate (2003), and insect infestation years (1982–1983). Tree ID

Estimated Stem burial (%)

57

0

44

0

56

0

58

0

46 47 48

0 6.8 6.8

59

10.2

55

10.7

60 53 49

15.8 23.7 31.6

50

37.3

52

40.7

51

41.8

Ring reduction (dates)

Horizontal measurement to dune base 2006 (m)

Average annual sand movement rate (m/yr)

Remarks

Narrow ring 2001 Reduction 2003* Narrow ring 2001 Reduction 2003* Missing ring 1982* Narrow 2001 Reduction 2003* Narrow ring 2001 Reduction 2003* None None Reduction in 1983* and 2003* Reduction in 1982* and 1996* Strong reduction in 2003.* Direct mmt 2006–2007 Narrow ring in 1982*. Reduction 2004 Reduction 2002 Reduction 2003 Almost dead 2002, last ring 2003* Reduction 1998 Died 2000 Reduction 2001 2006 Reduction 2001 2004.

−4

0

Healthy

−4

0

Healthy

0

0

Healthy

0

0

Healthy

0 2.2 2.5

Healthy Healthy Healthy

12.5

0 ? 0.1* 0.8* 0.1* 0.3* 1.0* 0.3 0.1* 1.7 1.2 2.4* 2.5 3.3* 1.4 1.9 2.5

12.8

2.6

2.9 3.2

3.3 4.9 7.3 9.9 11.5

height (stem burial depth 9.8 m), assuming the tree is rooted on the forest floor as noted above. T64 remains healthy with stem burial of 42.9% (stem burial depth 7.15 m), but other trees at this site have proved less robust, with tree death for T63 occurring at 40.7% (stem burial depth 6.7 m) and for the dead T62 at 50.3% (stem burial depth 7.7 m), (Fig. 4; Tables 1 and 5). At Site 2, T49 is already dead 9.9 m from dune foot, with only 31.6% of its stem buried (burial depth 5.6 m); other even more deeply buried trees (T50, T52, T51) are also dead, 37.3%, 40.7%, and 41.8% estimated per cent stem burial and 6.6, 7.2, and 7.4 m respectively (Fig. 6, Tables 2 and 5). At Site 3, T40 shows the first signs of needle loss with stem burial of 29.4% (burial depth 5.2 m). However, T41 is healthy, stem buried to over 37% (burial depth 5.2 m) while T42, the highest tree at this site 23.5 m

Healthy

Healthy Lower crown no needles Healthy Very thin needles. Dying Dead tree Very thin needles Dead Dead

from the dune foot, shows remarkable vitality, buried to over 64% (burial depth 11.4 m), although with thinning needles (Fig. 7, Table 3). The anomalous T43 was heavily suppressed and at the point of death with stem burial of around 64.8%, (4.6 m burial) estimated tree height of 7.1 m (Fig. 7; Tables 3 and 5). For the purpose of comparison, stem burial depth, tree health and number of year's burial rather than per cent of total stem burial provide the most useful insight into tree reactions to sand burial; Table 5 reveals variations in tolerance. All the sites show trees remaining perfectly healthy for the first 1–2 years. At Site 1 there is one notable exception, T64, which after 4 years burial is still healthy. Site 2 has the highest number of dead trees due to beetle infestation; longevity here following burial is limited to 6 years. Site 3, where sand movement has been slow to stationary, has the most resilient trees with nearly all surviving, albeit

Table 3 Site 3: characteristic of buried trees and estimated sand accumulation rates. Asterisks denote climate, insect infestation and compression wood years discounted in analysis of sand movements. Tree ID

Estimated stem burial (%)

29 31 35

0 0 11.3

34 36 43

40 41 42

Ring reduction or compression wood Horizontal measurement to dune base 2006 Average annual sand movement rate Remarks (dates) (m) (m/yr)

None None Missing ring 1982* Compression 1999 18.6 Compression 1984* Strong reduction 2003* 15.8 None 64.8 (est. tree ht 7.1 m) Eccentricity 1980 Damage 1981 Compression 1984* and 1994* 29.4 Gentle reduction 1986 Compression 1997* 37.8 Compression 1988* 64.4 Compression 1987*

− 9.36 − 4.0 4.8 6.9 6.9 10.0

11.2 14.2 23.5

0 0 0.2* 0.7 0.3* ? 0.4 0.4 0.5* 0.9* 0.6 1.2* 0.8* 1.2*

Healthy Healthy Healthy Healthy but suppressed Healthy Dying

Healthy ± needle loss Healthy Healthy ± needle loss

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Fig. 7. Site 3 tree identification numbers. The black suppressed tree, T43, is almost dead, grey trees are more or less healthy.

Table 4 Site 3: years of abrupt changes at different heights in T43's tree ring sequences with arrows pointing to 1980, the onset year of sand burial. Disc

Pith age

Very narrow rings

Latewood narrow, pale

4

1977

2003–05 1991–93

2003–05 1991–92 1982 1980

3

2

1

1974

1972

1970

2003–04 2001+ Resin ducts 1990–1993 2001–03 1990–92 1982–83 1979 2001–03 1991–92 1982–83 1979

2001 (dark) 1990–93 1980–82 2001–03 1990–92 1982–83 1979 (dark) 2001–03 1991–92 1982–83 1979 (dark)

Compression wood dates

Eccentricity start date

1994–2005

1986

1994–2001

1980

1994–2000 1984–1990

1980

1994–2000 1984–1990

1980

with some needle thinning. Two remarkable trees, T34 and T41, appear to be healthy after 23 and 17 years respectively.

invasion was already slow and remained so until tree-ring reactions stopped in 1999. 4. Discussion As noted in the Introduction, the chief difficulty for this study is to separate the effects of sand advance from the effects of climate and other environmental variables on tree-ring expression. Inevitably these variables are semi-independent and dune-tree reactions will include many of these, particularly climate and insect infestation. We have dealt with these latter two variables by excluding known event years from our analysis (see below) although it is acknowledged that sand advance could have been especially active during drought years. This approach is supported by the results from the direct measurements of sand advance between 2006 and 2007 and the general consistency of the chrono-sequence shown by the results despite removal of climate and insect effects (Table 5). The exceptions in the sequence are of particular interest since they suggest variable resilience (due to genetic or environmental factors) of the sample trees due to sand burial. Furthermore, our results for sand-movement rates are consistent with those of previous studies, both in the local area and at higher latitudes (see below). 4.1. Climate and insect infestation signals

3.7. Comparison of dune movements When the average annual dune-movement rates are placed in dating order and compared, after removal of the insect infestation and climate-influenced years, differences between the three sites become clear (Table 5). At Site 1 the sampled forest trees remained unaffected by sand until the year 2000 when our data suggest that the dune started aggressively to invade this part of the forest. Invasion started two years earlier at Site 2 and sand advance was a little slower, (up to 2.6 m/yr), with marked slowing to 0.3 m/yr in the final year (2006– 2007). Sand advance into the forest at Site 3 is likely to have begun well before 1980 as indicated by the highest tree on the dune where we were only able to take cores from the crown area thus missing the earlier years of growth expressed in its lower stem. By 1980 sand

Negative annual rings in the chronology (1940, 1944, 1956, 1962, 1982, 1983, 1996 and 2003; Fig. 2c) can be linked to climatic effects: low cambium activity in 1940 displayed in Polish oak tree rings is likely to have been due to an extreme winter, with low temperatures in January and February and a precipitation deficit in the first half of the year (Ważny, 1990). Tree rings in Europe showed above average temperatures in July–August 1944 (Schweingruber, 1988). During 1956 and in 1962, summer temperatures were below average resulting in narrow tree rings across most of Europe (Schweingruber, 1988). According to Spiecker (2002) drought conditions also prevailed in the 1970s and 1990s, but only 1996, during these years, showed in the Czolpinska treering forest-floor record. A narrow ring in 2003 was caused by a precipitation deficit whose effect, in terms of tree reaction, was also

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Fig. 8. Ring-width plots (truncated in 1920) of the eleven cores from T59: these show nun moth effect on growth starting in 1982, with recovery taking 7 years and decline following sand invasion in 1996 for all cores excepting the above-surface up-slope core which only shows decline after 2003.

observed in Germany (Kahle et al., 2007). Mean summer precipitation (April to September) in 2003 was 320 mm compared with the mean for 1961–2004 when it was 360 mm. In addition, March to May 2003 was extremely dry with a mean of 72 mm while the mean for 1961–2004 was 117 mm (Klein Tank et al., 2002). Insects can have a particularly strong influence on growth. In Poland the 1978 to 1984 widespread nun moth epidemic may have been due to the forests being largely a monoculture (Białobok et al., 1993). The epidemic was observed to cause a decline in tree growth 1981–1983 (Kochanowski and Bednarz, 2007) and thus it seems highly likely that this was the cause of strong negative growth in a large number of our cores during the peak 1982-infestation year (Fig. 3a) with over 40% of the cores also showing a narrow ring in 1983. However, these years do not show up clearly in the mean index chronology (Fig. 3b) possibly because growth reaction to infestation is affecting the mean value for the year. Although the 1982–1983 anomalies are useful signature rings when cross-dating ring-width curves, we did not include them in estimates of sand-movement rates.

maintained by Alestalo (1971), a core taken at a higher point in the stem some time after sand invasion could miss earlier reactions. The mechanism behind such a reaction could be differential pressure on a steep dune flank on the up and down-slope sides of a stem, since once a stem is firmly embedded pressure around it will be approximately equal (if it were not trees would soon break under the increasing weight of sand). It follows that where sand accumulation is rapid, same-date wood anatomical features may be expressed over a stem length commensurate with the advance rate. This assumption is supported at Site 2 by the 2-m extent of stem reactions in T59's cores (defined by the up-slope core at 2.25 m showing no decline until 2003). By 1996 sand would not have reached the base of the tree (Table 5) and a small growth recovery after 1996 would be normal (Fig. 8). However after 1998, as sand began to accumulate against the stem, growth in the cores above the sand in all except the highest core (0.65 m above the surface in 2006) declines suggesting sand-stress reactions extending from ground level to over 0.2 m above the surface.

4.2. Tree rings at different stem heights

4.3. Wood anatomical reactions to sand stress

Coring height as noted in the Introduction is a further consideration since if reactions mainly occur at or near the sand surface as

Following sand burial, compression wood formation is expressed as a reduction in cell size, number and density making the stem more

64

M. Koprowski et al. / Catena 81 (2010) 55–65

Table 5 Comparative data for the three sites showing how ring reduction dates (see Tables 1–3) set out in calendar order (together with tree health, years of insect attack and climate stress, dune movement rates, stem burial depth, and estimated number of year's burial) reveal site differences both with regard to dune movement and Scots Pine resilience in the face of advancing sand. Attention is drawn to the highlighted columns generally showing progressive decline in tree health with depth of burial and time, with exceptions being of particular interest. Year 1980 1981 1982 1983 1984 " 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 " 2002 " 2003 2004 2005 2006 2007

Tree ID and Site 1 rate Burial depth Est. nos burial Tree ID and Site 2 rate Burial depth Est. nos burial Tree ID and Site 3 rate Burial depth Est. nos burial tree health (m/yr) (m) (yr) tree health (m/yr) (m) (yr) tree health (m/yr) (m) (yr) 43 D

0.4

4.6

25

34 H

0.3c

3.3

23

40 ± H 42 ± H 41 H

0.6 1.2c 0.8c

5.7 11.4 6.7

18.6 19.6 17.7

43 D

0.9

4.6

11.1

40 ± H

1.2c

5.2

9.3

35 H

0.7c

2

6.8

Effect of insect outbreak

Effect of climate 50 D 61 ± H 2.9 63 ± D 2.4 64 H 3.2 62 ± D 3.5 65 ± H *? Effect of climate

66 H 67 H

*? 3.03

9.8 6.7 7.2 7.7 4.6

2.6 –

6 4.9 4 3.9 2.7

1.5 1

1.4

6.6

6

52 ±D 51 D 60 ± H 49 ± D

2.5 2.6 1.2 2.5

7.2 7.4 2.8 5.6

5 4.9 4 3

55 H

1.7

1.9

1.9

59 H

0.3

1.8

1

*? = rate assumed 3.03 m/yr. H = healthy. ± D = more or less dead. c = compression wood. D = dead. ± H = more or less healthy.

root-like. This suggests a reciprocal process to that described by Gärtner et al. (2001) who found that on exposure root cell structures become more ‘stem-like’, numerous and regular, with earlywood-cellsizes decreasing and latewood sizes increasing and becoming thicker, with consequently darker cell walls. Evidently there are many factors influencing annual ring development with trees more or less able to tolerate or adapt to stress due to varying environmental, genetic or other factors. Larger-stemmed trees will be less prone to eccentricity than small ones with sand pressure indicated by narrow rings having large, thin-walled, pale latewood cells; these are especially marked where onset follows normal-sized cells and a wide, dark latewood band (Fig. 2). These findings support and enlarge Strunk's (1997:137) comment that for spruce ‘burial events (can be determined) by the onset of a pronounced reduction of increment in the stem wood of the affected tree’. In addition, Strunk found that death for spruce occurs when burial exceeded 1.9 m. Scots Pine at our Sites 1 and 2 where sand movement was relatively rapid, appeared to be more resistant; for this species vitality for most trees was affected after 1.9 m, but death was delayed from between 3 and 7 years (Table 5). At Site 3, slow sand advance followed by stasis appears to have extended trees vitality up to at least 7 years and over 17 years in one case. It is worth noting that our pines showed no sign of any adventitious root development (Strunk, 1997; Dech and Maun, 2006). A high incidence of compression wood at Site 3 not present at the other two may be linked, even if indirectly, to the much slower rate of sand advance. Stress reactions due to dune movement may be particularly evident when trees are young or have slender stems due to suppressed growth. We found compression reactions in the T43's stem (stem diameter 2 cm at sand surface) starting in 1984, extending over a stem length of 1.5 m. However, compression wood formation shows a delayed reaction lagging 4 years behind the onset in 1980 of

narrow, pale, thin, latewood ring widths together with eccentricity supplying a sand-advance rate of 0.4 m/yr. Narrow rings and eccentricity together suggest initial sand-displacement of this very slender stem in 1980 (Fig. 2, Table 3). 4.4. Mid to high latitude dune advance rates Similar sand-advance rates to those found by us at Site 1 (3.03 m/yr) near the forefront of the Czolpinska dune system were found in Alaska in the Tana Dune system where dead trees showed a ∼3 m/yr migration rate (Wiles et al., 2003). On the Finnish side of the Gulf of Bothnia, Heikkinen and Tikkanen (1987) estimated dune advance as 1 m a year over the last 100 years. They found one tree that despite blown sand accumulation of 3.4 m around its roots showed no burial effect. This is unsurprising compared with trees at our sites where one, possibly well adapted or otherwise advantaged, tree remained healthy after stem burial over 7 m (Table 1). Heikkinen and Tikkanen's study covered a much longer time interval than ours and they noted that dune movements on one of their profiles were faster during earlier periods. Alestalo (1979), in a similar study on a shore dune at Hailuoto Island, also noted a faster early rate (1.5 m/yr) between the 1850s and 1950s, after which their dune became virtually immobile. He found a lower rate of 0.7 m/yr from 1750 to 1905 in an earlier study in Finland at Lohtaja, south of Kalajoki, with the rate slowing to 0.1 m/yr between 1905 and 1970 (Alestalo, 1971). Our Site 1 rate is close to the lowest rate, 3.5 m/yr, found by Borówka (1980) for the Madwiny dunes 10 km to the east of Czolpinska. This suggests that dune movements here may also have been slowing over the recent period. However, evidence from the above studies is insufficient to determine whether or not dune-movement rates in

M. Koprowski et al. / Catena 81 (2010) 55–65

these latitudes have generally been slowing. There will undoubtedly have been fluctuations in rates and dune movement speeds will to some greater or lesser extent, be site specific as was clearly demonstrated by differences in rate between our three sites. 5. Conclusions The main aim of our study, which is to assess whether the annual tree rings of Scots Pine in the Slowinski National Park could be used to measure rates of dune advance, was achieved with indirect measurements confirmed by direct measurements. The steep dune flanks and speed of sand movement at Site 1 (2.4 to 3.5 m/yr) and at Site 2 (1.2 to 2.6 m/yr) resulted in rapid tree burial with needle loss after 1.9 m and death after ∼ 7 years. Whereas at Site 3 where slow sand movement (averaging 0.7 m/yr) may have ceased around 1999, tree survival in good health occurred for one tree to an estimated burial depth of ∼ 7 m, while other trees suffered needle loss after ∼ 5 years (ignoring the little suppressed tree) but survived over the longer term: 17.7+ years for the most robust tree. The assumption of sand burial causing a growth reaction soon after dune invasion was quantified based on tree health judging by needle loss reactions to 1–2 years for mature trees (Table 5); this agrees with the findings of Marin and Filion (1992). Wood anatomical analysis of the discs from T43 revealed narrow rings and eccentricity forming 4 years before compression wood suggesting that compression wood is a less accurate indicator of sand invasion. More direct measurements of tree reactions to dune advance are needed to confirm the nature and timing of stem reactions to burial events. In addition, analysis of other tree species could repay investigation; species should also include a much wider selection of woody plants having annual rings (Schweingruber and Poschlod, 2005; Winchester et al., 2006; Dech and Maun, 2006). The broader achievement of this work, apart from providing values for sandadvance rates, has been to extend the dendrogeomorphological basis for studies of dune dynamics and emphasise the range of variables requiring prior consideration. Generally, the study highlighted the innate ability of trees to reflect environmental change, an ability that makes them ideal as tools for assessing rates of change in areas where sand is invading vegetated land, an increasing problem in a warming world. Acknowledgements We thank Nicolaus Copernicus University in Torun for financial support and the Slowinski National Park Authority for allowing us to conduct research in the park. References Alestalo, J., 1971. Dendrochronological interpretation of geomorphic processes. Societas Geographica Fenniae 105, 1–140. Alestalo, J., 1979. Land uplift and development of the littoral and aeolian morphology on Hailuoto, Finland. Acta Universitatis Ouluensis A82. Geologica 3, 109–120. Białobok, S., Boratyński, A., Bugała, W., 1993. Biologia sosny zwyczajnej. Sorus, Poznań, pp. 1–624. Borowka, R.K., 1980. Present day dune processes and dune morphology in the Leba Barrier, Polish coast of the Baltic. Geografiska Annaler 62A, 75–82. Cournoyer, L., Filion, L., 1994. Variation in wood anatomy of white spruce in response to dune activity. Arctic and Alpine Research 26, 412–417. Dech, J.P., Maun, M.A., 2006. Adventitious root production and plastic resource allocation to biomass determined burial tolerance in woody plants from Central Canadian coastal dunes. Annals of Botany 98 (5), 1095–1105. den Ouden, J., Sass-Klaassen, U.G.W., Copini, P., 2007. Dendrogeomorphology — a new tool to study drift-sand dynamics. Netherlands Journal of Geosciences, Geologie en Mijnbouw 86 (4), 355–363. Fantucci, R., McCord, A., 1995. Reconstruction of landslide dynamic with dendrochronological methods. Dendrochronologia 13, 43–58. Gärtner, H., 2007. Tree roots: methodological review and new development in dating and quantifying erosive processes. Geomorphology 86, 243–251.

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