The Palaeohistory of the Grey Alder (Alnus incana (L.) Moench.) and Black Alder (A. Glutinosa (L.) Gaertn.) in Fennoscandia

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  • The Palaeohistory of the Grey Alder (Alnus incana (L.) Moench.) and Black Alder (A. Glutinosa(L.) Gaertn.) in FennoscandiaAuthor(s): P. A. TallantireSource: New Phytologist, Vol. 73, No. 3 (May, 1974), pp. 529-546Published by: Wiley on behalf of the New Phytologist TrustStable URL: http://www.jstor.org/stable/2431124 .Accessed: 15/06/2014 01:43

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  • New Phytol. (i974) 73, 529-546.

    THE PALAEOHISTORY OF THE GREY ALDER (ALNUS INCANA (L.) MOENCH.) AND BLACK

    ALDER (A. GLUTINOSA (L.) GAERTN.) IN FENNOSCANDIA

    BY P. A. TALLANTIRE

    Botanical Institute, Trondheim University, N-7ooo Trondheim, Norway

    (Received I3 November I973)

    SUMMARY

    The available '4C-dated and broadly context-dated pollen and macrofossil data for the immigra- tion and spread of the two species of alder within Fennoscandia and certain adjacent countries is presented. The phases of immigration and regional spread take place during certain periods of time (e.g. 65oo, 6ooo, 5000 and 4500 14C years B.C.) and over certain restricted geographical areas. The latter yield a picture of climatic regionalism, with limits akin to that of the present day. Along its present, diffuse northern boundary Alnus glutinosa, on the evidence from Tr0n- delag in Norway, appears to have become established only in a late phase of the broad climatic optimum, after 2000 B.C., and to have lost ground again after c. 700 B.C., though the course of later events is confused by human activity. A tabulation of the postulated ecological requirements of the two species of alder at various stages of their life histories is attempted. Details of the sites mapped are included in an appendix.

    INTRODUCTION

    Sites with 14C-dated finds of macrofossils are still relatively sparse in Europe, yet they can often provide more reliable specific identification of plants whose pollen record remains at family or generic level. Such is the case for the two species of alder in northern Europe (Alnus incana and A. glutinosa); there is no evidence at present for the green alder (A. viridis (Chaix) DC) being found outside its present-day habitats in the Alps, Car- pathians and Arctic Russia earlier during the Postglacial period, with the possible exception of Poland during the Aller0d period (Szafer, I966). Recent finds of alder fruits from lake deposits in Asklundvatn in the Tr0ndelag area of Norway (site 5, Fig. 3, see Tallantire, I973) led to a comparison with other available evidence (14C-dated pollen curves on Fig. i and macrofossil finds on Fig. 2) from Fennoscandia, Britain and adjacent parts of mainland Europe, to determine whether there was evidence for climatic change or regional differentiation since c. 7000 B.C.

    My aims are threefold: to bring up to date and extend in scope the previous two sur- veys for Sweden (Andersson, I893; Wenner, I968), and to compare them with the British and European ones (Firbas, I949; Godwin, I956; Kubitzki, I96I); to indicate the need for continued, dated, macrofossil studies in those areas for which we lack data at present; and to enter a plea for a more critical attitude in the choice of sites, as well as in the appraisal of existing data, paying more attention to the equal importance of all three of the main sources of evidence in Quaternary vegetational studies, stratigraphy, macro- fossils and the pollen record, with selective 14C-dating of major changes in the first

    529

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  • 530 P. A. TALLANTIRE

    2' 0 2' 4 6 8' 10 12 14' 16' 182 20' 22 24' 26' 28' 30' 32' 34? 36'

    4 563 A300 4570- 4 78 5 5000 5050 ----...

    5 050 4998(30)

    8': 6 30 (2 1^ 1? 14 61' 0 2 2 62

    4810 2o~

    FIG. I. A, '4C-dated pollen sites. *, Dating made at or just above the main rise of the alder pollen curve. The actual percentage value shown on the left, the dating on the right (T+ - 5568). *, Datings which fall below the main rise, or about which there are qualifications.

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  • Alder in Fennoscandia 53I 24 ?W 24 4- 6. a' 10? 12' 14' 16. Is, 20" 22' 24? 26? 28? w 12, 34? 36

    Fig. 2. Sites at which macroscopic remains of alder spp. have been encountered (for details see the appendix; site numbers on map C). 0, Finds of Alnus incana remains only; ?3, finds of both A. incana and A. glutinosa, together in same deposit; *, finds of A. glutinosa only; 0 finds of A. glutinosa together with remains of other mixed-oak-forest trees; ~, sites at which the basal sediments contained remains of A. incana alone, followed above by finds of A. glutinosa, alone or with some A. incana.

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  • 532 P. A. TALLANTIRE

    1, o 2 4' 6_ 8 0 12 1' 16 18 20 22 246 26 6 8 6 6 6 6 62 6 4' 3

    68'/ / I & 2 6~/

    6

    -1

    6620 6130

    64~ ~ ~~~~~~1 4~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~4

    30

    60' .7~~~~~~~~~~~~~~~~~~~~~~~1 1 8

    66' / ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~~~~~~~~~~~~~~~~~~6

    Fig.3. ey o ste umbrs or al te steson igs an z, ogeherwit a ew npitte

    sits.Th nubes efe t te lstd rde o stesinth apenix Siesontheinetma are listed at the end of the~ apenix

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  • Alder in Fennoscandia 533 (Smith, I965) (on both sides of sharp boundaries), as well as the latter two. Regional pollen zones, or assemblages, provide too haphazard, and sometimes too metachronous (Hafsten, I970), a time-scale for studies of changes in any of the components of climate; studies which, of necessity, must compare contemporaneous events over wide geographic areas.

    In the case of the alders the objection will be raised 'are they not as much or more dependent on local groundwater levels than on any temperature limitations, summer or winter?' My view is that although the climatic background to hydrological changes can be partially obscured, or augmented, by the eustatic-isostatic interplay controlling sea- level, especially in our area, these effects are relatively slow and long-term. The hydro- logy conditions the extent of land surface available for colonization, as well as the long- term thrift or survival of established trees, but seed production, dispersal, germination and seedling establishment are under more direct control by climatic factors. The fact that we are studying sites at which plant macro- and micro-fossils have been preserved implies that groundwater has been present all along, though river valley sites are not always as well represented as one could wish for drawing firm conclusions. Suspected gaps in the fossil record due to water-level changes, with resultant erosion or corrosion, are usually detectable in one form or another.

    Alder pollen is now generally considered to be over-represented in the local pollen record (Andersen, 1970), due to high pollen production at a time when neither they nor other trees have come into leaf. However, the pollen may not be carried so very far afield in any noteworthy amount. Salmi (I962) reported pollen values of I I-34%, from A. incana trees growing on the margin of a raised bog in western Finland, in peat samples taken 200-300 m distant. Values had fallen to I-5 % at a distance of only i km across the bog. Regional transport of alder pollen, producing pollen values much> I %, seems un- likely even in unforested areas, so that the timing of the local appearance of alder in any abundance should be relatively easily detectable in a pollen diagram. The local course of events following immigration, either a steady spread, or at first restricted and only much later a general spread in the area, is complex, however, depending on vegetational suc- cessions, restriction of habitats by the spread of ombrogenous peats and, later, the direct and indirect effects of man and his animals.

    THE PRESENT-DAY DISTRIBUTIONS AND ECOLOGICAL BACKGROUND

    On a basis of the information in the available literature, I have attempted to summarize the ecological requirements, at various stages of their life histories, for the two species of alder (Table i); the references used in compiling the table have been appended there. Their climatic and edaphic requirements differ, Alnus glutinosa being the more demand- ing species, particularly as regards its mean summer tetraterm or pentaterm temperature requirement. The climatic data for the Trondheimfjord area (see Fig. 3 in Tallantire (1973)) yielded an optimum 30-year running mean, for the pentaterm May-September of i I.9? C for the period 1924-53, implying that only in individual years and in locally favourable habitats could this tree have thrived here in recent decades.

    The two alders, like many other tree genera, are singularly ill-served by the usual type of distribution map. The recent modification by Straka (Walter, I970) of Meusel's Eurasian map does at least attempt to show frequency differences, enclaves and outposts near the distributional limits, though the very scale and reduction in print preclude any opportunity of showing diffuse boundaries (see also the general map for Fennoscandia in

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  • 534 P. A. TALLANTIRE

    Table i Factor Alnus incana Alnus glutinosa

    Flowering time Feb.-Apr., C. Europe (I). Early-mid Feb.-Mar., Britain (A). Mid-Mar. to and pollination March, Poland (V). Mar.-Apr., Sweden late Apr., central Europe (H). Mid-

    (Q). Earlier than A. glutinosa in areas Apr. to May, Finland (H, J). Apr.- where both occur (I). 2-3 weeks before May, Sweden (Q). Mid-Mar.-Apr., A. glutinosa (Q). Prematurely opened Poland (V). Pollen viability 30-5O days catkins (> IOo C day max. for I4 days) according to humidity (H). Stigmas un- in mid-April, badly damaged by subse- affected by air frost before pollination quent 4 days' cold spell (

  • Alder in Fennoscandia 5.35

    Table i (contd.)

    Factor Alnus incana Alnus glutinosa

    drying-out during germination is un- favourable (B). Insensitive to light or to pH of substrate. Deep burial prevents germination due to low 02-tension; seed buoyancy helps avoidance of this fate but renders seeds more liable to subsequent drying-out (B). Cotyledons unable to reach surface if seeds buried under more than i cm of topsoil (G).

    Seedling estab- Flooding of site during first few years Germination from late-Feb. onwards in lishment and highly unfavourable (P). Rapid growth Britain, depending on degree of winter growth of roots and shoots during first and cold conditioning. Early seedlings have

    second years (P). Seedlings develop high mortality rate due to subsequent mycorrhizal roots and nodules (H), no low temperatures, rain splashing or details found. drying-out, all of which adversely

    affect radicle growth and satisfactory root anchorage (B). Timing of spring floods plays a role in preventing drying- out on free-draining soils, yet unfavour- able, by smothering, during first two years if too much sediment and/or plant debris deposited by winter or spring floods (C). Prolonged and/or repeated desiccation very unfavourable during first year, and explains why alder unable to compete with birch on such sites (C, p. I99). Alder withstands up to 5 weeks' submergence of seedlings, birch killed by only 2-3 weeks (C, p. 202). Seedling establishment only on a soil surface that comes within the capillary fringe of the water table, so that surface layers remain continuously moist for 20-30 days in the period April-June. In regions of high summer rainfall the water table does not dominate so (G). Alder will not establish at water-level unless protected from splashing and flooding, but can do so a short distance above (C, p. 204). Mycorrhizal rootlets and nodules de- veloped in all but totally anaerobic soils (C). Seedlings relatively shade tolerant within limits of small food store available, but sapling intolerance only exceeded by birch (C, pp. 2I3, 2i6). Light requirement may be only a reflection of need for root-room (H).

    Established saplings Roots capable of withstanding tem- Both surface and deep root systems well and mature trees: porary low 02-tensions, due to biotic developed, from first year onward. Can thrift and root activity in damp but not flooded ground respond to slowly rising water-levels by system extent and in summer (P). Surface root system well production of stilt-roots. Able to survive depth developed (H). Can stand appreciable temporary or slow changes in water

    periods of drought. At higher latitudes table once saplings properly established. and altitudes is found on increasingly Duration and rate of change probably drier habitats, especially if soil clay/silt more important than extent (see D and rich. No thrift in standing-water habitats K). Deep roots are capable of growth in or on peats (H, and own observations). a reducing medium; the surface nutri- Root system shallow but extensive and tional rootlets, bearing the nodules, intensive; can stand drying-out, at least require a higher 02-tension (D). Rapid on clay/silt soils (K), better than periods vertical shoot growth of seedlings and of flooding of more than a week's dura- saplings, as of coppiced stump shoots tion (P). Light requirement less than (no root suckering), gives good com- that of willows or poplars (P) or A. petitive powers over ground vegetation glutinosa (H) and less sensitive to winter (H). Growth ceases end of August, frost than latter (H). In sandy soils in Lith...

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