Alnus Glutinosa (L.) Gaertn

Alnus Glutinosa (L.) Gaertn.Author(s): D. N. McVeanSource: Journal of Ecology, Vol. 41, No. 2 (Aug., 1953), pp. 447-466Published by: British Ecological SocietyStable URL: http://www.jstor.org/stable/2257070 .

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[ 447 ]

BIOLOGICAL FLORA OF THE BRITISH ISLES

L.C. (Ed. 11) No. 1738 ALNUS Mill.

One British Species.

Alnus glutinosa (L.) Gaertn. (A. rotundifolia Stokes)

D. N. MCVEAN

Botany School, University of Cambridge*

A tree of moderate size attaining a height of 60-80 ft. (18-24 m.) in cultivation but natural specimens normally 10-40 ft. (3-12 m.) high. Habit variable from the low multiple- stemmed bush form to tall single-bole trees.

In favourable situations growth is strongly excurrent, the short main branches departing at an acute angle, which becomes a right angle with age, and forking little except at their peripheral ends. In woodland the stems are tall and thin, bearing a small, sparse crown, but the pioneer form is shorter and stouter with stronger, more irregular, open branching. Bark brown, smooth at first, becoming darker, fissured and rough.

Young twigs triangular in cross-section, green to reddish brown according to illumina- tion (both colours normally visible on opposite sides of the same shoot); lenticels prominent, yellow-brown. Long and short shoots present. Leaf buds dark purple with two stipular scales, stalked. Phyllotaxy normally 2/3.

Leaves plicate in the bud, glutinous when young, orbicular, usually emarginate, finely or coarsely serrate except at the cuneate base, often obscurely lobed or sinuate, dark green and with tufts of hairs in the angles of the principal veins beneath. Laminae 4.5 x 4-0 cm. to 8-0 x 7-0 cm. with petioles one-quarter to one-half as long and green or dark red.

Male catkins 2-5 at end of branch, long and drooping, green or purplish; female catkins 2-12 on lateral shoot of the same branch, oval, erect, dark crimson enlarging to 1-0-2-5 cm. in length and becoming green in fruit; scales persistent and blackening after the fall of the nutlets.

Fruit brown, compressed, one-seeded, with lateral corky outgrowths and two persistent styles.

British varieties have been named according to leaf and catkin size. Moss (1914) gives macrocarpa Loudon-laminae as long as broad (7-8 cm.) and with coarse serrations; pistillate catkins 3 cm. long at maturity, typica Moss-laminae 5.6 x 4-5 cm., pistillate catkins 1-7-2-0 x 1-0-1-4 cm. 'Not yet known for Wales, Scotland or Ireland', microcarpa Rouy-laminae 4-5 x 3-5-4-0 cm., with fine serrations; pistillate catkins 1-5 x 1-0 cm. 'Common form in hilly and northern localities, West Riding of Yorkshire north to Caithness. Also occurs in England as far south as Somerset and Suffolk.'

There are numerous horticultural varieties in cultivation in Britain (Loudon, 1875; * Now The Nature Conservancy, Edinburgh. This account was prepared while the author was in receipt of

research grants from the Carnegie Trust for the Universities of Scotland and from the Nature Conservancy. J. Ecol. 41 29



448 Alnus glutinosa Hemsley, 1877; Elwes & Henry, 1906). In Britain the species is certainly variable in habit and in leaf and catkin size, and the variation appears to be continuous. Leaf and catkin measurements of eighteen populations (twenty of each from five or ten trees per

12 10 8 6 4 2 0 2 4 / E 1T~~~~~~~ - h l l30 20 10 0 10 20 30'40

English Miles o0 A0 60 0 20 40 60 80 100 . .

I I I I I

Kilometres eich 30 56 0 25 50 75 100 150 "A

52 _ 58

10 8 6Longitude West 4 of Greenwich 2 OLongitudeEast 2 of Greenwich

Fig. 1. Alnus glutinosa (L.) Gaertn., vice-comital distribution in the British Isles and (inset) limits of distribution as a native species in Europe.

population) suggest that both leaf and catkin size diminish fairly regularly from south to north and from east to west, the northern and western populations being perhaps less variable (Fig. 2).

..... .......... .:

.... 86LongiWofO Lon .E.oflO G ree nwich 30

56g. 1. Ainu8 glutinosa (L.) Gaertn.; viee-eomital distribution in the British Isles and (inset) limits

of distribuion..s native secies i E urope.

population) suggest that both leaf and eatkin size diminish fairly regularly from sou.h..o north and from east o west, e northern nd western populat:ions.......... ..... ...... v ar?:?iable (F:.?.ig::::: ... )....... ....... ......... ..j:jjjj::i:::,l:5 f~~::f~;::::::::~~6~~;.... ............ .. 54 ~ ii~iiiii jji~'~ii~:~ ~ ~~ti~ ....... ...... ...... .......:::::: ............... .......:c;::::~: ~5~.??:??%:?::??:??:::?.::.: ? ;i:1::............?s~~:?:~ ,6 :::::::1:.:.:.:.?~.:.:.:.:............. ............. .......~7:i::::::::j :~i:::::;::: :::?-???:?::.;:: ?/.. ??:?::............ .......:~ ~I. ~j?.ijjjjj:r.:-?:::::jjj ;;i::j:?:?:?:?:::r;~~~~:?:?::::::: ??~~~~:~~~ti~:~i~ ~ ~l~iiij~~iii.... ....... ~~ ~~?1~~~~~::j::jjjjjjjj::?~~~~~~~~~~~~la:~~~:`j:............ !:::?:?:?:?:?:?.i?:?~~?~~?:?:?:?~C??:.:?r :::::::::?~::j:i~::::::........ ....... ~:?:?:?:?:::j::~::::::::::~%:::::::?~:?; I::::::::::::i:~::::::::5 4

i~:-i~fj~j~.j::::::........ .....:: .......... ...... . .....j::~:i~ ~ 521~i~ ~:? ... ....... . ......... ..... .?:

~~:?:?~~?~i?;?:?:?;?;?C4::?:?:?::~~~~~~1~:5 52 :l:l?:~~'TT :::2~~~~;-~~~i;:?.~~~~??:"?:-~~~~~?;j:: ?~~~~?:i j...........

variable (Fig. 2).



D. N. MCVEAN 449

A native species of stream and lake sides and on many flush soils and soils of impeded drainage throughout the British Isles.

I. Geographical and altitudinal distribution. Occurs in all the vice-counties of the British Isles, but only as a planted tree in Shetland. Noted as' not common' in Cambridge- shire and parts of Oxfordshire but abundant elsewhere, its frequency increasing towards the high-rainfall areas of the north and west (Fig. 1). From sea-level to 400 ft. (122 m.) in Arran, 1600 ft. (488 m.) in the Cairngorms (Schlich, 1925), 950 ft. (289 m.) in the north of England (Alt. range Br. P1.), 1200 ft. (366 m.) in West Inverness and Sutherland.

150

E

100

S 52 53 54 55 56 57 58 59 N. Lat.

Fig. 2. Variation of catkin length with latitude in the British Isles, the standard deviation of the population means being represented by the length of the vertical lines. (Similar figures have been prepared for variation with longitude, and for leaf size variations.)

Extends through most of Europe except the Arctic, the Mediterranean region (including Sardinia), and the Russian steppes. Also in Asia Minor and North Persia south to 37? 25'. In Sierra Morena in Spain south to 38?. Also West Siberia and North Africa (Tansley, Br. Isl., Hegi, Fl. 3, 95). Distribution classified as 'Boreomeridional Sub-montane Oceanic' by Meusel (1943). From sea-level in the Baltic and Mediterranean regions to 289 m. in Norway, 760 m. in Bavaria, 1300 m. in the Tyrol and in Greece, 1800 m. in the Oberengadin and the Caucasus (Hegi, Fl. 3, Rikli, 1943-8).

Especially abundant as pure alderwood or carr in the Norfolk Broads, and as mixed alder-birch and alder-ash wood in the region of the Great Glen of Scotland. Also in Pennine and Welsh oakwoods, Donegal woodland, Caithness birchwoods, etc. (Tansley Br. Isl.).

29.2



450 Alnus glutinosa II. (a) Climatic and topographic limitations. Boundary of its Eurasian distribution

shows close correspondence with the 20 in. (51 cm.) isohyet in south and east. There is little correlation with isotherms or seasonal rainfall. The factors limiting the northward distribution are not clear, nor are the stages of the life cycle at which the limitations operate. In Scandinavia it appears to be limited by the duration of low winter temperature, since it does not extend to those regions having a minimum of 6 months of mean daily temperature of 0? C. or less. At its most northerly station at the head of the Gulf of Bothnia the height of the tree is 12 m. and it bears viable fruit there (Kujala, 1924).

Groszman & Melzer (1933) give data on climates endured by the species in Eastern Europe.

Often described as a warmth-demanding species, but this can only be relative to the birches and A. incana. Soil moisture would seem to exercise more control over local and regional distribution than atmospheric humidity.

In west Britain and Ireland resistant to wind exposure and possibly to a moderate amount of salt spray since it is planted in coastal wind-breaks.

Not topographically limited to stream sides and low lying, badly drained areas provided rainfall is high.

Gives straight-boled trees only in moderate shelter, but exposed crowns, though gnarled, are not usually wind cut. Wind-cut forms and die-back of branches have been seen in the hills and at the coast of North Wales and in the Isle of Skye.

Many alderwoods in the Scottish Highlands are found on south- and west-facing slopes while north-facing slopes carry only stream-side trees.

Very sensitive to shading, the seedling less so but still requiring a higher light intensity than those of larger-seeded trees, so that internal regeneration of the woodland is prac- tically unknown.

(b) Substratum. Largely indifferent to the parent material of its soils. Sendtner reports that in Bavaria A. glutinosa and A. incana occur by stream margins, the former in siliceous areas, the latter in calcareous regions, but that, where A. incana is absent, A. glutinosa is 'certainly not a calcifuge' (Lebensg. 1). Alder is absent from the calcareous drifts of Caithness, its place by stream-sides being taken by Corylus avellana. It does occur on the siliceous drifts (Crampton, 1911).

Trees and saplings may exhibit chlorosis on calcareous soils, e.g. on the chalky boulder clay of East Anglia.

Restricted to the unstable soils of stream and lake margins, recent alluvia, flush soils and those of impeded drainage or seasonally wet on hill slopes and to hydromorphic meadow soils on the flat. Occurs on deep fen peat or the acid peats of, for example, Molinia-Myrica bog, but not on blanket or raised bog. Profiles are generally those of hydromorphic meadow soils and gleys with or without peat layer. Water-table may be at, or close to, the surface at all seasons, and regeneration then tends to be abundant but the trees are shrubby and badly grown. Water-table often sinks well below the surface during summer months and tree growth is then better. Seedlings will only establish on a soil surface that comes within the capillary'fringe of the water-table so that the 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 the situation in the same way.

Worms and usual soil fauna absent from the wetter soils. Soils oxidizing and with



D. N. MCVEAN 451

nitrate in summer, tending to be reducing in winter and without nitrate; pH> 38 (Pearsall, 1938). Godwin & Turner (1933) record soil surface pH of 4-6-7-0 over the range of alder growth in the succession at Calthorpe Broad.

Table 1 presents results of the analysis of some alderwood soils.

Table 1. Soil analysis (a) Conway Valley, North Wales. Data kindly supplied by R. E. Hughes; analysis by H. Hagger.

Ca (p.p.m.) mg P205/100g. K (p.p.m.) (1) Seasonally wet gley 2312-5 3-3 485-0 (2) Equably moist site 1250-0 0-2 85-0 (3) Permanently wet gley 1012-5 0-6 20-0 (4) Seasonally wet gley

0-6 in. (0-15 cm.) 1087-5 2-2 150-0 6-12 in. (15-30 cm.) 1037-5 2-1 50-0 12-15 in. (30-37-5 cm.) 662-5 2-0 25-0 C horizon 850-0 1-9 25-0

(b) Scottish sites: (i) open wood on slopes of Meall a' Bhata, Sutherland (a free-draining brown earth with seasonally wet gley in places); (ii) dense wood on alluvial fans, Glen Nevis, Inverness-shire. (Free drainage); (iii) as (ii); (iv) alder scrub on Molinia-Myrica bog, Glen Nevis. (Permanently wet peat.) All samples composite to a depth of 9 in. (17-5 cm.). Analysis by D. Thomson.

Mechanical analysis (%)

Loss on Coarse Fine pH Ex. CaO (%) ignition (%) sand sand Silt Clay

(1) 5-13 0-0360 24-64 31-52 26-96 6-79 6-09 (2) 5-14 0-0184 6-26 (3) 6-66 0-0140 9-50 (4) 5-12 0-1282 45-67 -

Table 2. Soil tests at Chippenham Fen Tests

Diphenylamine Sapling Misra-Comber Sulphide sulphate

1 Surface 0/0 0/0 0/0 30 cm. 1/4 2/4 1/4

2 Surface 0/0 0/0 0/0 30 cm. 0/4 0/4 0/4

3 Surface 0/0 0/0 0/0 30 cm. 0/4 0/4 0/4

Table 2 gives the results of some soil tests carried out at Chippenham Fen, Norfolk, in the neighbourhood of the saplings described in VI(a). The tests are as described by Pearsall & Mortimer (1939), and results show that the saplings were rooted in a reducing substratum though nutritional rootlets were confined to the oxidizing surface layers.

III. Communities. Occurs with oak, ash, birch and willow, particularly the last three, forming ash-alder wood on low-lying ground of high soil fertility and moisture, alder- willow thickets in areas liable to seasonal flooding, and alder-birch wood on higher-lying less fertile, generally acid soils in the north and west of Britain (Anderson, 1950). Pure stands are of common occurrence, but are not as extensive in Britain as, for example, in north-west Germany.

The status of the alder in Quercetum is still uncertain. Tansley (Br. Isl., p. 325) states that alder occurs scattered throughout the Welsh oakwoods. In closed oakwood, alder societies in the damper places, with scattered trees by stream-sides only, is more typical.



452 Alnus glutinosa The species of eleven representative British alder communities are listed in Table 3. First-year seedlings and 2- to 3-year-old plants of up to 5 cm. in height are frequent in

some woods but complete internal regeneration is seldom seen. Regeneration tends to be peripheral, or to occur with the formation of an even-aged stand in some suitable area adjacent to the parent trees.

Table 3. Floristic composition of alder woodland (1) Coppiced? tall alderwood on waterlogged fen peat and river alluvium, Brandon, Norfolk. (2) The same with field layer dominated by Urtica dioica. (3) Abundantly flushed south-facing slope at 400 ft. (122 m.) O.D. on boulder clay, Mugdock, Stirlingshire. (4) Seasonally wet gley, peaty in places, developed on glacial drift at 800-1000 ft. (244-305 m.) O.D. on the

south-facing slope of Moel Eilio, North Wales. (5) Shallow soil among stable block scree, continually flushed. West-facing slope of Nant Gwynant, North

Wales. (6) Brown forest soil on steep south-west-facing slope of glacial drift, head of lower Glen Nevis, Inverness-shire. (7) Gley soil, with some surface peat, on east-facing slope at 150 ft. (46 m.) O.D., Loch Lomond, Dumbarton-

shire. (8) Swamp carr, Hoveton Great Broad (Lambert, 1951). The numbers are for frequency and constancy

respectively. (9) Fen carr, do.

(10) Sweat Mere, Shropshire (Clapham in Tansley Br. Isl.). (11) Deep fen peat, Ruskin Reserve, Cothill, Berkshire (Clapham, Ibid.).

In addition to the standard symbols, s. =seedlings, m. = marginal. (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)

Acer pseudoplatanus - r. f.. - Alnus glutinosa d. d. d. d. c.d. d. d. 5-5 5-5 d. d. Betula pendula - r. B. pubescens l.f. r.s. r. - - 12 o.-f. o. Cratoegus monogyna a. - - a. f. 1 1 r. Corylus avellana a. f. o. - Frangula alnus -?? 11 - Fraxinus excelsior - - f. c.d. f. 1.1 2-2 - f. Hedera helix -a. - - Ilex aquifolium - - .a. o. - f. 11 1.1 - Ligustrum vulgare - ????f. Lonicera periclymenum ? 1.1 2-3 f. o. Prunus padus o. P. spinosa r. Quercus petraea l.a. Q. robur - - - - 11 - r. Rhamnus cathartica -- - - . 11 1 - r. Ribes nigrum f. 1.1 1.1 - R. rubrum - - -. 1.1 - Rosa canina agg. - o. - 11 1.1 - r. Rubus fruticosus agg. r. a. - f. o. R. idaeus - -f. o. f. 11 1.1 o. Salix atrocinerea - o. 5-5 4.5 o. f. S. capraea o. S. pentandra l.a. Sambucus nigra . - .. o.s. Sorbus aucuparia a. - o.s. -- r. Viburnum opulus r. o.

Agrostis stolonifera a. a. a. a. l.a. x Ajuga reptans - f. r. - o. Anthoxanthum odoratum - a. l.f. r. a. Angelica sylvestris - a. 1-2 1.1 r. Arrhenatherum elatius - - a.m. Asperula odorata .. .. x Athyrium filix-foemina f. a. a. Blechnum spicant - - - f.

x, presence; -, absence.



D. N. MCVEAN 453 Table 3 (continued)

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) Brachypodium sylvaticum -f. Bromus ramosus 0. - - Calamagrostis canescens - -- 3-2 3- 3 -Calystegia sepium . .-- 23 - Callitriche stagnalis -0. Caltha palustris a. - -a. Cardamine flexuosa- 1.f. f. C. pratensis 0. - Carex acutiformis a, a.m. --- 45 2. 3 o. C. pallescens o. C. panicea ?-- x C. paniculata 5.5 2-2 o. x C. remota a. C. rostrata - f.m. C. sylvatica o. Cerastium vulgatum- -.-f. Chrysosplenium oppositifolium a. l.a.- Circaea alpina l.a. Cirsium palustre f. f. f. l.f. r. x C. anglicum- x Conopodium majus - a. Corydalis claviculata - r. Crepis paludosa o. f. f. Cynosurus cristatus- - r. Daphne laureola__ l.a. Deschampsia caespitosa a. o., l. f. f. a. - Digitalis purpurea a. f. - o. r. Dryopteris Borreri - a.- - - D. dilatata ? ???f. D. filix-mas - f. l.a. 1-2 1-2 D. phegopteris - r. D. spinulosa 0o. r. x Epilobium hirsutum .- - 3-3 1-2 E. montanum - -?- r. E. palustre _??? x Equisetum sylvaticum f. Eupatorium cannabinum 3-4 3-4 - x Filipendula ulmaria o. a. l.f. a. a. f. 3-4 2-3 f. x Galium aparine a. G. palustre l.f. 1-- 11 .f. G. saxatile a. o. l.o. -- G. uliginosum r. - a. a- x Geranium robertianum- o.,l.a. a. f. -o. Geum urbanum -- a. f. - - Glechoma hederacea a. Glyceria fluitans - l.a. Holcus lanatus a. - a. o. H. mollis - - a. a. r. a. - Hydrocotyle vulgaris - - - - -- - - x Impatiens capensis - a.- 11- Iris pseudacorus -- - -- 2-3 1*2 l.a. Juncus acutiflorus f. a. J. effusus- a.m. l.a. f.- J. subnodulosus- - - - - - - x Lemna minor -?- --? 2-3 Lotus uliginosus - a.m. Lychnis flos-cuculi r. - Lycopus europaeus f. - Lysimachia nemorum- o. f.l. a. l.a. l.a., L. nummularium r. - L. vulgaris -- 11 11 Lythrum salicaria .-- - 1-3 - Melandrium dioicum- o. Mentha aquatica o. - a.m. .a. I-l.a. x Mercurialis perennis - l.a. l.a. - x Molinia caerulea- f.m. 0o. - Myosotis scorpioides r. - r.



454 Alnus glutinosa Table 3 (continued)

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) Myrica gale . .- 11 - Oenanthe lachenalii ... .. x Oxalis acetosella l.a. a. l.a. l.a.- Peucedanum palustre ?? 2-4 11 Phalaris arundinacea a.m. Phragmites communis . . - 3-5 3-4 Poa pratensis f. P. trivialis a. Polygonum hydropiper o. Potamogeton coloratus---- x Potentilla tormentilla f. l.a. a.- Prunella vulgaris o. - o. f.- Pteridium aquilinum l.a. l.a. l.a. l.a.- Ranunculus flammula r. R. repens a. a. f.l. l.a. Rumex acetosa a.m. R. crispus a. R. obtusifolius a. Sanicula europea a. Schoenus nigricans ..- - x Scilla non-scripta l.a. l.a.- Scrophularia nodosa o. Scutellaria galericulata r. 11 Senecio aquaticus o. - -o. - S. jacobea o. --- Solanum dulcamara ?- 2-5 1-2 f. o. Solidago virgaurea --r. Sparganium erectum - -- 2-3- Stachys sylvatica f.m. f. Stellaria holostea - f.m. S. media f. l.a. Succisa pratensis . -r. a. - x Tamus communis 0--- o. Teucrium scorodonia l.a. r. Thelypteris oleopteris .. - o.- T. palustris -- 5-5 3-4- Urtica dioica a. v.a. l.a. 1-2 1-2 l.a. Valeriana dioica -??? x V. officinalis - f. - 11 - o. Veronica chamaedrys a. -- - V. montana - - o. Viola palustris f. o. a. a. l.a. - V. riviniana - - a. f. f. - x

Bryophytes Acrocladium cuspidatum O. -o. x Atrichum undulatum f. Aulacomnium androgynum a. Brachythecium rutabulum - --- f. x Eurhynchium striatum f. a. E. swartzii---- x Fissidens adiantoides f. Hypnum cupressiforme agg. a. a. f. a. f. Mnium affine---- x M. hornum -o. -f. x M. punctatum f. --f. x M. undulatum---- x Pellia epiphylla f f.f Plagiothecium undulatum - f.- - a.- Polytrichum formosum o. o. Rhacomitrium aciculare -f. - Rhytidiadelphus loreus f. Sphagnum girgensohnii f. S. plumulosum -??? x Thuidium tamariscinum o. a. a. - Trichostomum brachydontium? -- o.



D. N. MCVEAN 455

Floristics of some of the most favourable sites for alder regeneration are shown in Table 4. Regeneration was active on all areas listed.

In Britain the alderwood flora is everywhere strongly influenced in its composition by the fen and marsh vegetation it has replaced. The communities are at their most dis- tinctive on the wetter, more basic habitats, the drier and more acid types merging with those of oak and birch. The alder-birch woods of our hill slopes do not appear to find a parallel on the Continent.

Table 4. Floristics of regeneration sites

(1) Riverside meadow with ridge and furrow, Brandon, Norfolk. pH 6.5-7.0. (2) Grazed Molinia fen, Chippenham, Norfolk. pH c. 7-0. (3) Small swinging bog on edge of Upton Broad, Norfolk. (4) Open alder scrub on land reclaimed from sea, Tremadoc, N. Wales. Seasonally flooded, grazed. (5) Marsh on raised beach, Corrie, Arran. (6) Molinia-Myrica fen marginal to alder carr, Matley Bog, Hampshire. pH c. 4-0. (7) Clear-felled alderwood on acid fen over greensand, Flitwick Moor, Bedfordshire. (8) Abandoned pond, now Sphagnum-filled, Milngavie, Glasgow. pH 4-5. (9) Sphagnum hollow above alderwood, 500 ft. O.D. Loch Lomond. pH c. 4-0.

(10) Molinia-Myrica-Sphagnum bog, Glen Nevis, Inverness-shire. pH of water expressed from Sphagnum 4-0, of surface peat 4.7.

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) Achillea ptarmica x Agrostis stolonifera x x - x x x - - Ajuga reptans - - x x Alisma plantago-aquatica x x Anagallis tenella - x Angelica sylvestris x x x x x x - Anthoxanthum odoratum x x x Bellis perennis x x x - Betula pubescens (s) - - -? x x Briza media x x Callitriche stagnalis x x Calluna vulgaris x x Caltha palustris x x x x x - Cardamine hirsuta x x C. pratensis x x x Carex appropinquata x C. curta x - - C. disticha x C. echinata x x x C. flacca x x C. hostiana x C. lepidocarpa x x C. nigra . x - - C. panicea x x x x x x - C. pulicaris x x x C. rostrata x - - C. tumidicarpa x x - Carum verticillatum x Centaurea nigra x x x Cerastium vulgatum x x - x Cirsium palustre x x x x - Cladium mariscus x Comarum palustre x x x Crepis paludosa ... x Cynosurus cristatus x x Dactylus glomerata x Deschampsia caespitosa x Drosera rotundifolia - x x x Dryopteris dilatata . . x - Eleocharis palustris x -?? x -

x, presence; -, absence.



456 Alnus glutinosa Table 4 (continued)

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) Epilobium hirsutum - - x E. montanum- x E. obscurum - - x- E. parviflorum x- E. palustre--- x- E. sp. x Epipactis palustris- x Equisetum limosum - x x x- E. palustre x x- E. sylvaticum .- - x- Erica cinerea - x E. tetralix - x x - Eriophorum angustifolium - x x Eupatorium cannabinum - - x Euphrasia officinalis agg. - - x x - Festuca ovina - - - x F. pratensis- x F. rubra- x Fraxinus excelsior (s) - - x - Filipendula ulmaria x x x x x Galium aparine - - x G. palustre x x x x - G. saxatile- x G. uliginosum x x x x Geum urbanum- x Glechoma hederacea- x Glyceria fluitans- x - x x- G. maxima x G. plicata - - x- Holcus lanatus x x x x- H. mollis--- x- Hydrocotyle vulgaris x x x x x x x Hypericum dubium - x - H. elodes x- Iris pseudacorus x x - - x- Juncus acutiflorus - x x x x x x x J. articulatus x x- J. bufonius x x x-- J. bulbosus--- x- J. conglomeratus- x J. effusus x x x x x x J. inflexus x x J. subnodulosus x x J. supinus x x x- Lathyrus palustris- x Lemna minor- x Leontodon autumnalis - x Liparis loeselii- x Lotus corniculatus- x x L. uliginosus x x x x x Ludwigia palustris-- x- Luzula multiflora- x -- x Lychnis flos-cuculix x x x x Lysimachia nummularia - x Lythrum salicaria- x x x Mentha aquatica x x x x x x Menyanthes trifoliata x x x - Molinia caerulea x x x x x x x Myosotis scorpioides- x x x x Myrica gale- x - x x x Nardus stricta- x Narthecium ossifragum - x x x Odontites rubra x Oenanthe crocata-- x- 0. fistulosa x Ophioglossum vulgatum - x Orchis ericetorum- x x x



D. N. MCVEAN 457

Table 4 (continued) (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

Orchis latifolia x - - - - 0. praetermissa- x Parnassia palustris- - x Pedicularis palustris x - x x x- P. sylvatica x Phra rmiteq communis x 'ilglie.iila vulgaris x x

Plantago lanceolata k x x-- P. media x x- Platanthera bifolia x Polygonum amphibium x Potamogeton polygonifolius x x x Potentilla anserina x x P. reptans x P. tormentilla x x x x x Primula veris x P. vulgaris x -- Prunella vulgaris x x x Prunus spinosa x Pyrola rotundifolia x Ranunculus acris x R. flammula x x x x- R. lenormandi x R. lingua x R. repens x x x x- Rhinanthus stenophyllus? x Rubus caesius x R. fruticosus agg. x x x - Rumex acetosa x x x - R. crispus x R. hydrolapathum x Sagina nodosa x S. procumbens x x Salix atrocinerea (s) x x x x- S. capraea (s)---- x S. repens x x Senecio aquaticus x x S. jacobea x Serratula tinctoria x Sieglingia decumbens- x Solanum dulcamara.. .- x- Stachys betonica - - x Stellaria palustris x - Succisa pratensis- - x x x x Taraxacum officinale agg. x - x x Thelypteris palustris - - x Trifolium repens x x x- Triglochin palustre- x --- Tussilago farfara- x Typha latifolia.. . x - Ulex europaeus - - - x Valeriana dioica- x x x- V. officinalis- - x Veronica beccabunga- x V. scutellata x Vicia sepium- x Viola palustris-- x - x

Bryophytes Acrocladium cuspidatum x x x x A. giganteum - - x Campylium stellatum x x x Climacium dendroides - - x Fissidens adiantoides x x x Hypnum cupressiforme - - - x Mnium seligeri- x



458 Alnus glutinosa

Table 4 (continued) Bryophytes

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) Pleurozium schreberi -x x x -x Polytrichum commune - -x x x - Pseudoscleropodium purum - x Rhytidiadelphus squarrosus x x x x Scorpidium scorpioides - x Sphagnum girgensohnii x S. palustre x x x x x S. plumulosum . . . x x S. teres -- x

IV. Response to biotic factors. Frequently coppiced and produces basal shoots readily. Habitats not normally subject to fires, but personal observations at Dernford Fen,

Cambridge, and in the New Forest show that the species is in fact fairly resistant, young saplings and mature trees alike sprouting readily from lengths of stem not too badly scorched.

Moderate grazing of marshland and fenland may favour the spread of the trees by reducing the shading and smothering effect of tall herb vegetation on the seedling, and

breaking any surface turf or litter mat. Cattle will keep the saplings trimmed into bushes if the grazing is heavy, and red deer

on their winter territory will nibble the young shoots. Not so sensitive to sheep grazing as birch, perhaps because of the soft ground it favours.

There is also some evidence that cattle will graze birch in preference to alder saplings. Rabbits and hares seldom ring-bark saplings as they do those of ash.

Alder tends to invade a deflected succession or biotic climax, once the biotic influence has been lessened or removed, more readily than it does the primary hydrosere.

V. (a) Gregariousness. Occurring usually in small woods or carrs, often of even age, or as linear populations by streams or standing water. Solitary trees are occasionally found some distance from parent populations.

(b) Performance. Maximum growth rate and height attained in cultivation on deep moist loams:

Av. increment At end of (cm.) (cm.) 1st year 12-29 17 2nd year 40-136 75 3rd year 112-210 72 4th year 180-454 126 (Lebensg. 1).

Cuttings, like seedlings, show greatest growth in the first 5 or 6 years, at an average of 1 m. per year. From 6 to 20 years, growth averages 2-9 m. per year. May live only 20-25 years in poor ground, attaining 3-4 m.; on good ground a 100-year-old tree may have a diameter of 1 m. Maximum age 120 years (Lebensg. 1). Maximum height 80 ft.

(24 m.) (Grigor, 1868). In Molinia-Myrica bog may attain only 1-2 m. Sets abundant seed in all habitats.

(c) Effect of frost, drought, etc. The mature tree is hardy, withstanding winter temperatures of -49? C. at the extreme north-east of its range (Groszman & Melzer, 1933). Not

usually defoliated by spring frosts though flushing early (F.C. Bull. 18). Used with Betula as a frost-hardy pioneer.



D. N. MCVEAN 459

Believed to be drought resistant once the deep tap roots have formed since these are able to penetrate to water sources under reducing conditions.

Flowering catkins resistant to at least -6? C., though high winds may damage the catkins and thus reduce the viability of the seed set.

Newly germinated seedlings susceptible to drought, and this is a main reason for the hydrophytic behaviour of the species.

Seedlings also liable to damage by late frosts and frost heaving in winter. VI. (a) Morphology. Extensive root system of both surface and deep branches with

considerable plasticity of structure which enables the tree to survive on either waterlogged soils or those of deep water-table.

No measurements available for mature trees, but the following refer to 5- to 10-year-old saplings on Chippenham Fen, Norfolk.

(1) 13 cm. loam over sandy calcareous clay. Water-table within 30 cm. of surface in winter, below 80 cm. in summer. Stem height 150 cm., basal diameter 23 mm.; diameter of surface root system 140 cm.; depth of central forked tap root 80 cm. Four structural root types:

(a) Surface nutritional system with nodules and mycorrhiza confined to loam. (b) Short fibrous roots with nodules confined to crown. (c) 'Strut roots' running diagonally to end in clay at 30-40 cm. depth as fan-shaped

cluster of stout rootlets. (d) Whip-like tap roots branching little. (2) 1 m. fen peat over calcareous clay. Water-table at surface in winter, within 15 cm.

in summer. Sapling on Molinia tussock. Stem height 120 cm., diameter 26 mm.; diameter of surface system 250 cm. Original tap root probably missing, replaced by two vertical branches of surface system penetrating to depth of 75 cm. Surface system shallow, exposed in places between the Molinia tussocks, branching into the tussocks. No strut roots, though some surface roots turned down peripherally to end in clusters of rootlets at 20-40 cm. depth.

(3) Soil as in (2). Water-table above the surface between the Molinia tussocks at all times of year. Surface gelatinous iron precipitate. Stem height 100 cm.; diameter of root system 140 cm.; depth of tap roots 80 cm. Surface system sparse, branching and bearing nodules and mycorrhiza only in tussocks above water-table. Strut roots well developed.

Roots from below water-level are always spongy and easily compressed in the fingers. If these are cut below water-level abundant gas bubbles can be expressed from all but the finest roots, apparently from the xylem cylinder. In reducing soils the roots are surrounded by a sheath of ferric iron compound. An aeration mechanism, resembling the xylem aerenchyma system of Aeschynomene aspera and Herminiera elaphoxylon (Arber, 1920), may exist.

In wet places water lenticels are freely formed along the main branches of the surface roots and for some distance up the boles of saplings. Surface of nodules may produce powdery lenticel tissue where water-table is high.

(b) Mycorrhiza (N. F. Robertson). Although the alder shows mycorrhizal roots, there have been no clear-cut demonstrations of the nature of the fungal symbionts and details of morphology are lacking. Kelley (1950) cites Lactarius lilacinus and L. cyathula as being



460 Alnus glutinosa

always associated with alder, and Gyrodon rubescens as possibly a third symbiont. Gyrodon lividus (Bull.) Sacc., which on the Continent is associated with alder, has recently been found associated with alder in Britain (E. J. Corner, personal communi- cation).

Alder roots also show well-marked nodules which have been the subject of much work. The identity of the organisms which cause them is still in doubt. Recent papers discussing the problem are those of Klecka & Vukolov (1935), Plotho (1941), Cernik (1937), Roberg (1938) and Hawker & Fraymouth (1951).*

(c) Perennation; reproduction. Meso-phanerophyte with bud covering. Root suckers are rare (Loudon, 1875), and vegetative reproduction is usually confined to the production of stool shoots, but I have seen fallen green branches beginning to take root in soft swamp mud. It is not known to what age the life of the tree may be prolonged by coppicing.

(d) Chromosome number. Diploid 2n= 28 (Mert. Cat.). I have obtained the same count on' microcarpa', 'typica' and 'macrocarpa' seedlings from Arran, Arran and Chippenham, and Chippenham respectively.

Tetraploid alders have been produced by colchicine treatment (Johnsson, 1950) and have been found in natural populations in Denmark (Ording, 1939).

(e) Physiological data. Owing to high rate of transpiration and development of small water deficits only placed by Steffanoff & Stoikoff (1932) in summer-green xerophylls. Cannot regulate transpiration to any great extent by stomatal closure (Biisgen, Minch & Thomson, 1929). No information on osmotic values.

VII. Phenology. First period of mild weather in February with temperatures ex- ceeding 50-55? F. causes anthesis and stigma extrusion. Flowering prolonged by sub- sequent low temperatures. Average date for start of leafing, 14 April (Salisbury, 1921). Root growth begins in April (Lebensg. 1). In Britain root growth appears to continue almost throughout the year. Seed shedding and leaf fall begin with the first night frosts, October-November. Leaves are shed green. Humid weather over autumn and winter causes retention of seed in catkins until the dry weather of spring. Catkins form in early July. Shoot growth ceases July-August; in saplings, September-October (Wareing, 1948). Seed germination begins in late February or early March.

VIII. (a) Floral biology. Catkins wind-pollinated, usually protogynous but about 12% protandry. I have established the existence of complete self-sterility among the trees on Chippenham Fen. Sylven (1948) reports partial self-sterility and reduced fertility in back- crosses in Sweden. Apomyxis is not known.

(b) Hybrids. It is likely that most species of the genus will prove interfertile (Richens, 1945). A. glutinosa and A. incana hybridize freely when they meet-A. pubescens Tausch. The hybrid is less common in Finland than in north Sweden and may have a wider distribution than either parent in the extreme north (Kujala, 1924). In Britain the hybrid is reported from near Horley, Surrey, by Brenan (1950).

A. glutinosa x A. rugosa-A. fiekii Callier (Hegi, Fl. 3). (c) Seed production and dispersal. Fruit nearly always contains but the one seed and

twin embryos are rare. Average number of seed per catkin is 60, and rough estimates of the number of pistillate catkins in a moderate crop give about 4000 per tree.

* Ferguson & Bond (1953) report the occurrence of extensive fixation of nitrogen in association with nodulated plants of Alnus glutinosa.



D. N. MCVEAN 461

Often included in lists of wind-disseminated species, but this method s not so effective as with other light-seeded trees, seedlings seldom being found more than 30 m. from seed parents when wind dispersal alone is at work. Fruits have lateral corky floats, and dispersal by flowing water and wind drift over standing water is very efficieInt. Dispersal by seed-eating birds is a possibility, though seeds are generally split open and the embryo consumed.

(d) Viability of seed; germination. Viability is so variable that average values mean little. Good seed has 35% germination (Schlich, 1925). Germination on fresh-water agar 5 % (Kujala, 1924), 6-10% (Lebensg. 1). The 1949 crop in Britain gave values 0-23 % at 25? C. on damp filter-paper (mean 7-5 %). The 1950 and 1951 crops gave 12-80% under the same conditions (means 41-5 and 40-0 % respectively). Optimum germination occurs at 25? C. Detmer (Lebensg. 1) gives minimum 7? C., optimum 24? C., and maximum 36? C.

Germination takes place in light or darkness and is independent of normal temperature fluctuations and pH of substrate 3-5-8-0. It is sensitive to low oxygen tension and seed will not germinate if the oxygen supply is restricted-for example, if below the surface of waterlogged soil.

The seedling is sensitive to periodic slight drying out which kills radicle tips or the complete embryos once water has been initially absorbed.

If collected before the catkins are brown, seeds require several months of after-ripening. Cold treatment moist at 0-4? C. does not improve final germination percentages, or rate of germination at the optimum temperature, but it lowers the minimum germination temperature from 17? C. to 7? C.

In the field, seeds, because of their buoyancy, generally germinate on the soil or vegetation surface. Cotyledons cannot reach the surface if the seed is buried under more than 1 cm. of soil. For successful establishment the alder seedling requires abundant moisture for at least 20-30 days after germination, i.e. high water-table or abundant rainfall, and a relatively high light intensity.

(e) Seedling morphology. Germination is epigeal. When the radicle has protruded about 5 mm. from the fruit coat the region of active growth is transferred to the hypocotyl, which elongates rapidly, carrying up the cotyledons, still enclosed by the fruit, and straightening out the plumular hook. At this stage the seedling is inclined to be top heavy if the short radicle is not securely anchored.

The cotyledons are ovate (4-6 mm. long), glabrous, dark green, and with a faint mid- nerve and prominent stomata. They are never red tinted beneath, and this helps to dis- tinguish the smaller alder seedlings from those of Betula in the field. The hypocotyl is covered with short deflexed hairs and is usually reddish towards the base. Fig. 3 shows developmenat on moist filter-paper.

(f) Effective reproduction. Almost entirely by seed (see VI (c)). IX. (a) Animal feeders and parasites. Mice sometimes store the seeds but seldom

eat seedlings. Slugs, snails, Tipulid larvae, wireworms, etc., attack the roots or cotyledons, but are seldom, if ever, responsible for the failure of regeneration. Seeds are taken by several birds, the crossbill Loxia curvirostra, finches such as the brambling Fringilla montifringilla, and. siskin Spinus spinus and tits Parus spp. (see also VIII (c)).



462 Alnus glutinosa

(. Fourth day

Third day

2 mm,

Seventh day

Seventh day

Ninth day

Fig. 3. Germination of alder seeds on moist filter-paper.

INSECTS AND MITES (0. W. RIcHARDs) The list below includes species of which alder is the only food, or one of the principal foods. The nomenclature follows Kloet and Hincks list (1945), except for the Homoptera, where the later list (China, 1950) has been used. Dr H. F. Barnes, Mr R. B. Benson, Mr C. T. Gimingham, O.B.E., Dr A. M. Massee and Dr G. T. Morison were kind enough to supply some of the information on which it is based.

ACARINA PHYTOPTIDAE: Phytoptus laevis inangulis (Nal.) (=Eriophyes axillaris of Connold,

1901), makes galls in axils of primary veins of main-rib, in pairs on upper surface. Two other species of Phytoptus and three of Epitrimerus are said to live in these galls as inquilines.

INSECTA THYSANOPTERA: Thrips alni Uzel, feeds on flowers, fruits and leaves (Surrey).



D. N. MCVEAN 463

HETEROPTERA. MIRIDAE: Lygus viridus (Fall.) (also on Quercus and some other trees); Orthotylus flavinervis (Kb.); Psallus alnicola D. & S. (also on Salix); Sthenarus rothermundi (Scholtz.) (also on Populus).

HOMOPTERA. CICADELLIDAE: Oncopsis alni (Schrk.)'; Erythroneura alneti (Dhlb.) (also on Ulmus); Typhlocyba callosa Then. var. distincta Edw.; T. jucunda H.-S.; Edward- siana geometrica (Schrk.); E. alnicola (Edw.); E. bergmanni (Tullqr.); Empoasca smarag- dula (Fall.).

CHERMIDAE (=PSYLLIDAE): Chermes alni (L.); Ch. forsteri (Floz.). APHIDIDAE (s.l.): Glyphina betulae (Kalt.); Myzocallis alni (Deg.).

COLEOPTERA CHRYSOMELIDAE: Chrysomela aenea L.; Agelastica alni (L.) (rare). CURCULIONIDAE: Deporaus betulae (L.), larva in rolled leaves (also on Betula; rarely

other trees); Phyllobius calcaratus (Fab.); Anoplus roboris Suff., larva in mines; Rhyn- chaenus testaceus (O.F.M.), larva in mines.

HYMENOPTERA XIPHYDRIIDAE: Xiphydria camelus (L.), larva in wood (also Betula). CIMBICIDAE: Cimbex connata (Schrk.). TENTHREDINIDAE: Monsoma pulverata (Retz.); Eriocampa ovata (L.); Fenusa dohrni

(Tischb.), larva mines leaves; Hemichroa crocea (Geoffz.) (also Betula; rarely Corylus or Salix); H. alni (L.) (also Betula); Platycampus luridiventris (Fall.); Croesus sepen- trionalis (L.), common but often also on Betula, Carpinus, etc.; C. varus (Villaret); Pteronidea collina (Cam.) (also Betula, etc.); P. polyspila (Forst.); Nematinus fuscipennis (Lep.); N. luteus (Panz.); N. willigkiae R. V. Stein.

DIPTERA CECIDOMYIDAE: Dasyneura alni (F. Loew), larva in somewhat reduced, puckered leaves

with swollen veins; Jaapiella clethrophila Rubs., larva in malformed leaves with swollen veins.

AGROMYZIDAE: Agromyza alnibetulae Hend., larva in leaf mines (also on Betula).

LEPIDOPTERA CARADRINIDAE: Grapholithafurcifera (Hufn.) var. suffusa Tutt. (also Betula). HYDRIOMENIDAE: Hydriomena impluviata (Schiff.); Euchoeca obliterata (Hufn.);

Hydreliaflammeolaria (Huffn.), (also Acer); H. sylvata (Schiff.) (also Salix). NOTODONTIDAE: Notodonta dromedarius (L.) (sometimes Betula); Cerura bicuspis

(Bork.) (also Betula). PHYCITIDAE: Cryptoblabes bistriga (Haw.) (also Quercus). EUCOSMIDAE: Eucosma penkleriana (Fisch. v. Rosl.), larva in catkins and buds (also

Corylus); E. demarniana (Fisch. v. Rosl.), larva in catkins (also Betula and Salix); E. triquetrana (Haw.), larva in twigs when young, later on leaves (also Betula); E. sordi- dana Hb.

SESIIDAE: Aegeria spheciformis (Schiff.), larva in stems. SCHRECHENSTEINIIDAE: Stathmopoda pedella (L.), larva in fruits. J. Ecol. 41 30



464 Alnus glutinosa COLEOPHORIDAE: Coleophora orbitella Zell. (also Betula); C. binderella Koll. (also Betula

and Corylus); C.fuscedinella Zell. (also Ulmus and Corylus); C. limosipennella (Dup.) (also Ulmus and Corylus).

GRACILARIIDAE: Lithocolletis rajella (L.), larva in blotch on underside of leaf; L. stettinensis Nic., larva in blotch on upperside; L. kleemannella (Fab.), larva in blotch on underside; L. froelichiella Zell., larva in blotch on underside; Gracilaria elongella (L.), larva in rolled leaves (also Betula); G. falconipennella (Hb.), larva in folded leaves (rare).

PLUTELLIDAE: Argyresthia brocheella (Hb.), larva in shoots and catkins (also Betula); A. goedartella (L.), larva in shoots and catkins (also Betula).

LYONETIIDAE: Bucculatrix cidarella (Zell.). HELIOZELIDAE: Heliozella resplendella (Staint.), larva in mid-rib of leaves. STIGMELLIDAE: Stigmella alnetella (Staint.), larva in leaf mine; Scoliaula quadri-

maculella (Boh.), larva probably in bark.

(b) Plant parasites (N. F. Robertson).

FUNGI ASCOMYCETES

TAPHRINALES

Taphrina Tosquinettii (Westen.) Magn. causing deformation of the leaves (Rams- bottom & Balfour-Browne, 1951).

Taphrina Sadebeckii Johans. causing discrete swollen spots on the leaves (Rams- bottom & Balfour-Browne, 1951).

?Taphrina alni-incanae (Kuhn.) Magn. affecting the cone scales of female flowers. Ramsbottom & Balfour-Browne refer the records on female catkins to T. Tos- quinettii.

Taphrina epiphylla Sadebeck is apparently not recorded but is a common cause of Witches' Brooms on the Continent (Viennot-Bourgin, 1949).

ERYSYPHALES

Phyllactinia suffulta (Rebent.) Sacc. Phyllactinia corylea (Pers.) Kars. (Blumer, 1933, List Pyrenomyc.).

Microsphaera alni (Wallr.) Wint. Widespread in Europe but not reported in Britain (Blumer, 1933).

HYPOCREALES Nectria cinnabarina (Tode) Fr. (Dennis & Foister, 1942).

SPHAERIALES A large number of Sphaeriaceous fungi belonging to genera which contain plant

parasites have been recorded on dead twigs and leaves of Alnus glutinosa but we have no evidence on the part they play in the biology of the alder.

Valsa oxystoma Rehm. There is some evidence that this fungus may be injurious (Jones, 1910).

HELOTIALES

Ciboria amentacea (Babb ex Fr.) Fuck. (Ramsbottom & Balfour-Browne). Ciboria amenti (Batsch.) Whetzel (Helotium amenti Batsch.) Fuck.



D. N. MCVEAN 465

BASIDIOMYCETES UREDINALES

Melampsoridium alni Diet. Uredo- and teleutospores on leaves of A. glutinosa. The aecidial stage on Larix europea has not yet been found in Britain (Wilson 1934).

APHYLLOPHORALES

Polyporus sulphureus (Bull.) Fr. Polyporus radiatus (Bull.) Fr. The most important cause of heart rot in Britain

(Cartwright & Findlay, 1946). Fomes igniarius (Linn.) Fr.

FUNGI IMPERFECTI SPHAEROPSIDALES

Leptothyrium alneum Sacc. Causing a leaf spot (Br. Stem and Leaf F. 2). MONILIALES

Passalora bacilligera Mont. et Fr. on fading leaves (List Hyphomyc.). Ramularia alnicola Cooke on living leaves (List Hyphomyc.).

AQUATIC HYPHOMYCETES. A large number of interesting fungi on decaying alder leaves have been described by Ingold (1942).

(c) Diseases. See Jones (1910). X. History. Macroscopic fossil remains reported for Cromer Forest Bed and other

inter-Glacial deposits (Reid, C., 1890; Reid, E. M., 1920). Firbas (1949) considers it unlikely that the species survived the maximum extent of the Pleistocene glaciation north of the Alps. In British post-Glacial deposits alder pollen is relatively scarce until the opening of Atlantic times, which is marked by a considerable increase in its frequency in the south and east. This is less well marked in Ireland (Jessen, 1949). The post-Atlantic period shows a gradual decline of the alder, accelerating with the commencement of drainage and deforestation.

Loudon (1875) records that alders from the Low Countries were planted in Scotland between 1730 and 1750. Planting and management of alder coppice in Britain never on the continental scale. At present day holds its own mainly as a riverside tree, and few stands of any extent exist except in Norfolk, Wales and west Scotland.

XI. Uses. Next to Frangula alnus yields the highest quality charcoal. Wood very resistant to decay if completely submerged in water. Also found suitable for clogs, hat blocks, herring-barrel staves and small turnery work. All parts of the plant, particularly the bark, are rich in tannins.

REFERENCES Anderson, M. L. (1950). The Selection of Tree Species. Edinburgh. Arber, A. (1920). Water Plants. Cambridge University Press. Blumer, S. (1933). Beitrdge zur Kryptogamenflora der Schweiz. Band viI, Heft I, Zurich. Brenan, J. P. M. (1950). Yearb. Bot. Soc. Brit. Isles, p. 56. Biisgen, M. & Munch, E., trans. Thomson, T. (1929). Structure and Life of Forest Trees. London. Cartwright, K. St J. & Findlay, W. P. K. (1946). Decay of Timber and its Prevention. London: H.M.S.O. Cernik, L. (1937). Krankheiten und teratologische Missbildungen an Pflanzen der Olmutzer Flora. Verh. naturf.

Ver. Brimnn, 68, 49. China, W. E. (1950). A Check-list of the British Hemiptera-Homoptera Auchenorhyncha. Ent. Mon. Mag.

86, 243. 30-2



466 Alnus glutinosa Crampton, C. B. (1911). Vegetation of Caithness considered in Relation to the Geology. Edinburgh. Dennis, R. W. G. & Foister, C. E. (1942). List of Diseases of Economic Plants recorded in Scotland.

Trans. Brit. Mycol. Soc. 25, 266. Elwes, H. J. & Henry, A. (1906). The Trees of Great Britain and Ireland, Vol. m. Edinburgh. Ferguson, T. P. & Bond, G. (1953). Observations on the formation and functions of the root nodules of

Alnus glutinosa L. (Gaertn.). Ann. Bot., N.S., 17, 65, 175-188. Firbas, F. (1949). Waldgeschichte Mitteleuropas. I. Allgemeine Waldgeschichte. Jena. Forestry Commission Bull. 18 (1937). Spring Frosts. London: H.M.S.O. Godwin, H. & Turner, J. S. (1933). Soil acidity in relation to vegetational succession in Calthorpe Broad,

Norfolk. J. Ecol. 21, 235-62. Grigor, J. (1868). Arboriculture. Edinburgh. Groszman, A. & Melzer, I. H. (1933). Die Schwarzerle in Lungau. Zbl. ges. Forstw. May-June. Hawker, L. E. & Fraymouth, J. (1951). A Reinvestigation of the Root Nodules of species of Eleagnus,

Hippophae, Alnus and Myrica, with special Reference to the Morphology and Life History of the Causative Organism. J. Gen. Microbiol. 5, 369.

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Alnus Glutinosa (L.) Gaertn