Temperate region

Characteristics of European temperate region
Flatlands
Floodplain and swamp forests
Montane zone
Subalpine zone

Here we briefly describe European temperate forests in their supposed natural condition. The high elevation forests of the Mediterranean region resemble the temperate mountain forests at somewhat lower elevations and are also described here.

Characteristics of European temperate region

On other continents there is no region climatically matching the temperate region of Europe. In comparison with the two other large temperate deciduous forest regions – eastern North America and East Asia – the European temperate region is more oceanic due to the west winds blowing from the Atlantic throughout the year, thus the annual temperature amplitudes are smaller. On the other hand, summer precipitation is greater than in the temperate coniferous forest region of western North America. The combination of the dry summers and oceanicity is considered the main reason that the west coast of North America is almost totally conifer dominated from sea level upwards¹. The climates of these regions are compared in the table below. The selected cities have comparable mean annual temperatures. All are located on the coast to eliminate the influence of mountains. The second figure represents oceanity/continentality, the higher value being more continental.

In the temperate zone of Europe, tree species richness is only half that in the corresponding climates in eastern North America, and four to six times lower than in eastern Asia^{2 3}. However, the number of all vascular plant species is approximately the same in these regions⁴. The photos on this website give an impression of even lower tree species diversity than is the reality because in the European temperate zone, virgin forests have remained intact particularly in sites where the tremendous competitiveness of European beech (Fagus sylvatica) allows few other species to thrive. However, the tree species diversity is remarkably higher on sites that are too wet or too dry for beech. Unfortunately, no floodplain forests or forests on dry sandy soils, for example, have survived in their natural condition. There may be approx. 20 tree species per hectare at most. As the species diversity increases, identification gets slightly more difficult, too. Nevertheless, most trees are quite easy to identify. True difficulties – even for a specialist – may be caused by hawthorns (Crataegus spp.) in eastern Europe, where their species diversity is higher. For hawthorn identification, we can recommend the book Christensen, K. I. (1992): “Revision of Crataegus Sect. Crataegus and Nothosect. Crataeguineae (Rosaceae-Maloideae) in the Old World”.

Strong winds are generally the most common natural disturbance type in Central Europe; however, storms as violent as the hurricanes and typhoons of eastern North America and East Asia, are absent⁵. Unlike boreal and Mediterranean forests, temperate forest does not burn, or burns very rarely. The forest floor is deep in leaves that remain moist due to close contact with the soil. As coarser debris decomposes rapidly and undergrowth is sparse, there is a lack of flammable material. Furthermore, beech and other large broadleaf trees form a dense, closed canopy that prevents the sun from drying the forest floor. At higher elevations precipitation is usually high, adding to the moisture content.

Flatlands

Without human impact, most of Central Europe would be dominated by mixed deciduous broadleaf forests, in which beech would have an important position. Some authors, e.g. Henschel, estimate that for example approx. 75% of German forests would be dominated by beech⁶. Beech dominates the forests in an extremely wide amplitude of elevations and soil conditions: in places it dominates from the sea shore to the alpine tree limit⁷. In extreme cases it is possible to find stands with only one plant species – beech! Reasons for its extraordinary role include its wide climatic, edaphic and shade tolerances (the minimum requirement is only 1–2% of sunlight), the heavy shade it casts, its height and longevity^{8 9}. Natural stands dominated by other tree species are restricted to extreme sites (e.g. wet, dry, cold or unstable) outside their growth optimum¹⁰, where beech is unable to form a closed canopy¹¹. Leuschner considers beech as the most successful plant species of Central Europe by the nature⁷. However, it should be noted that the spread of beech and of settlement after the last Ice Age proceeded in parallel and that humans strongly affected the forests very early on^{12 13}. A beech forest landscape neither influenced nor settled by humans probably never existed in the flatlands. Müller points out that the view of the naturally dominant beech is influenced by the managed forests since the 1960s under wet and cold conditions and extremely high game densities¹⁴. He therefore suggests speaking of temperate mixed deciduous forests instead of beech forests.

The colours of beech forest are the canopy’s light green, trunks’ light grey and leaf litter’s brownish orange. In autumn, the beech crowns also turn orange. Lofty pillars hold up a dense canopy that casts deep shade on the forest floor. Few plants can grow there. There is surprisingly little dead wood because it decomposes more rapidly than e.g. conifer wood.

Other tree species growing here and there in beech forest include sessile oak (Quercus petraea), European hornbeam (Carpinus betulus), small-leaved linden (Tilia cordata), large-leaved linden (T. platyphyllos), sycamore maple, Norway maple (A. platanoides), wych elm (Ulmus glabra) and European ash (Fraxinus excelsior). Sandy soils are dominated by pedunculate and sessile oak⁴.

However, the eastern limit of beech distribution is sharp; on the Central European flatlands it runs through central Poland, east of which late frosts or summer drought kill its flowers and young fruits⁴. Here, mixed deciduous forests grow on fertile soils, the most abundant trees being often small-leaved linden, European hornbeam and pedunculate oak; Scots pine (Pinus sylvestris) dominates on sandy soils⁴. In southeastern European “Pannonian” region from Hungary eastwards with dry late summers, the natural vegetation would likely be diverse oak forest, almost nothing of which remains¹⁵.

British Isles’ tree flora is particularly impoverished due to the combination of a long history of glaciation and insularity¹⁶. Also beech may have been introduced by man¹⁷, and natural forests would have been dominated by small-leaved linden, wych elm, pedunculate and sessile oak, and European ash¹⁸. There are no longer any virgin or near-virgin forests in the British Isles.

The tallest natural lowland tree species are beech and European ash; they may both attain approx. 50 m in height¹⁹ (photo right: the tallest known ash at 50.6 m grows in this grove in Kelheim, Germany). Trees on the flatlands are almost exclusively deciduous. This fact alone results in remarkable ecological differences to the other regions. The trees produce huge amounts of leaf litter in the autumn. The beech litter is acid, decomposing only slowly, which suppresses undergrowth, as do the efficient beech roots and the deep shadow in the summer. Mosses form only on surfaces raised above this litter layer, such as rocks and trees, standing or fallen. However, in the spring before the leaves have reached their full size, there is plenty of light on the forest floor; under other trees rich flowering herb vegetation covers the forest floor but the undergrowth in beech forest may be almost non-existent in the spring, too, the most common plant on the forest floor being… beech seedlings! In addition there may be some wood sorrel (Oxalis acetosella), wood anemone (Anemone nemorosa), white wood-rush (Luzula luzuloides) and wavy hair-grass (Deschampsia flexuosa), for example. An exception is beech forests on lime-rich soil²⁰. Their less acid brown earths are suitable for earthworms, fallen leaves decompose faster and the field layer may be quite rich, some common species being sweetscented bedstraw (Galium odoratum), dog’s mercury (Mercurialis perennis), wood anemone, hollowroot (Corydalis cava), wild garlic (Allium ursinum), lords-and-ladies (Arum maculatum), wood-barley (Hordelymus europaeus) and hard shield-fern (Polystichum aculeatum). However, beech grows better on more acid than lime-rich soils⁴.

Floodplain and swamp forests

Earlier, luxuriant alluvial forests grew on the floodplains of large rivers, today almost totally disappeared through leveeing and clearing. The floodplains are divided into three zones. Shrubby willows, like purple willow (Salix purpurea), almond willow (S. triandra) and osier (S. viminalis) grow in the first zone. The second zone is already a forest but is still inundated every year; its trees include white willow (Salix alba), crack willow (S. euxina), their hybrid S. × fragilis, almond willow, black poplar (Populus nigra, today replaced by hybrid black poplar (P. × canadensis)), white poplar (P. alba) and black alder (Alnus glutinosa). The third zone is inundated more seldom only at very high floods. The trees of this very productive and species-rich forest type include European ash, narrow-leafed ash (Fraxinus angustifolia) in the south, wych elm, European white elm (Ulmus laevis), field elm (U. minor, today practically extirpated by Dutch elm disease (Ophiostoma spp.)) and pedunculate oak. Undergrowth is luxuriant and rich. Lianas common ivy (Hedera helix) and traveller’s joy (Clematis vitalba) growing on trunks give the forest a subtropical look. The floodplain forests may be rather dry after the flooding period.⁴

Swamp forests on peat grow on the wettest soils suitable for tree growth. Much of the soil surface is generally inundated at least in early spring. Black alder grows on hummocks above the (periodically) flooded soil. On poor soils, downy birch (Betula pubescens) replaces the black alder.

Montane zone

The forests of this zone are usually mixed forests, with three species dominating: European beech, European silver fir (Abies alba) and Norway spruce (Picea abies). There are also almost pure beech forests that resemble the lowland beech forests. In drier regions, Scots pine (Pinus sylvestris) often grows on south-facing slopes.

The tallest native European trees grow in this zone. At their best these forests almost reach the majesty of some coniferous forests of western North America; however, the presence of broadleaf trees gives these European forests a unique feeling. At the moment, the height record tree is a 62.7-metre Norway spruce in Slovenia¹⁹.

In forests with abundant silver fir, undergrowth is usually richer as the fir needles are rich in calcium, resulting in less acid soil than under beech and spruce²¹. Common species include sweetscented bedstraw, wood sorrel, yellow archangel (Lamiastrum galeobdolon), sanicle (Sanicula europaea), blackberries (Rubus spp.) and ferns.

Beech and fir are very shade tolerant, making them capable of reaching the canopy even in small gaps left by a single fallen tree²². Beech usually dominate the smallest size classes of the tree regeneration. However, its shade tolerance decreases when it grows taller, thus fir being able to maintain its co-dominance if the herbivore pressure is low enough²². Recent studies indicate that in addition to the small-scale gap dynamics, periodic intermediate-severity damage from wind disturbances up to several thousand square metres in size is an important component of the disturbance regime²³. These larger gaps give less shade-tolerant species (like sycamore maple, wych elm and European ash) a chance to regenerate²².

In southeastern Bulgaria and northwestern Turkey there are oriental beech (Fagus orientalis) forests with an evergreen shrub layer with pontic rhododendron (Rhododendron ponticum) and cherry laurel (Prunus laurocerasus) ²⁴. This same forest type exists more richly on lower slopes in the western Caucasus (see Caucasus–Northern Iran).

Subalpine zone

The lower subalpine zone is usually almost pure Norway spruce forest, in southeastern Europe with Macedonian pine (Pinus peuce) (in the Pyrenees, spruce is lacking). In the Pyrenees, Alps and western Carpathians, a zone of European larch (Larix decidua) and Swiss pine (Pinus cembra) ⁴ occurs above the Norway spruce forest. The larch and Swiss pine are lacking from the mountains of southeastern Europe. Instead, there is a zone of Macedonian pine, Bosnian pine (P. heldreichii) and Norway spruce. Above these forests, there are dwarf mountain pine (P. mugo) thickets. In the western Alps and in the Pyrenees, tree-like mountain pine (P. uncinata) replaces the dwarf mountain pine. Nevertheless, in some areas there are, up to the forest limit, almost pure forests of – you guessed it – European beech!

The subalpine forests have some common features with boreal forests but as the precipitation is generally high at high elevations, these forests rarely burn. As in the boreal forests, there are often plentiful bilberry (Vaccinium myrtillus) and moss on the forest floor.

KR & TM

References:

1. Franklin, J. F. & Dyrness, C. T. (1988): Natural Vegetation of Oregon and Washington. Oregon State University Press.
2. http://www.ents-bbs.org/viewtopic.php?f=144&t=6804
3. Latham & Ricklefs (1993): Continental Comparisons of Temperate-Zone Tree Species Diversity. In Species Diversity in Ecological Communities: Historical and Geographical Perspectives. University of Chicago Press.
4. Ellenberg, H. (1996): Vegetation Mitteleuropas mit den Alpen. Ulmer.
5. Fischer, A., Marshall, P. & Camp, A. (2013): Disturbances in deciduous temperate forest ecosystems of the northern hemisphere: their effects on both recent and future forest development. Biodivers Conserv 22:1863–1893.
6. Henschel, U. & Stephan, T. (2012): Grünes Wunder: Wälder in Deutschland. Grubbe.
7. Leuschner, C. (1998): Mechanismen der Konkurrenzüberlegenheit der Rotbuche. Ber. d. Reinh.-Tüxen-Ges., 10, 5–18.
8. Jahn, G. (1991): Temperate deciduous forests of Europe. In Röhrig, E. & Ulrich, B.: Temperate Deciduous Forests. Elsevier.
9. Körner, C. (2005): An introduction to the functional diversity of temperate forest trees. In Scherer-Lorenzen, M., Körner, C. & Schulze, E.-D. (eds.): Forest diversity and function. Temperate and boreal systems. Ecological Studies 176, pp. 13–37. Springer Verlag.
10. Härdtle, Ewald & Hölzel (2004): Wälder des Tieflandes und der Mittelgebirge. Ulmer.
11. Felbermeier, B. & Mosandl, R. (2006): Fagus sylvatica. In Schütt, P. et al.: Enzyklopädie der Laubbäume, pp. 241–260. Nikol.
12. Grove, S. (2002): Saproxylic Insect Ecology and the Sustainable Management of Forests. Annu. Rev. Ecol. Syst.: 33: 1–23.
13. Kaplan, J. (2009): The prehistoric and preindustrial deforestation of Europe. Quaternary Science Reviews 28: 3016–3034.
14. Müller, J. (2019): Was macht Buchenwälder artenreich?
15. Polunin, O. & Walters, M. (1985): A guide to the vegetation of Britain and Europe. Oxford.
16. Ingourille, M. (1995): Historical ecology of the British flora. Kluwer.
17. Harris, E. (2002): Goodbye to Beech? Farewell to Fagus? Quarterly Journal of Forestry 96(2): 97.
18. Rackham, O. (1990): Trees & Woodland in the British Landscape. Weidenfeld & Nicolson.
19. https://www.monumentaltrees.com/en/
20. Willner, W., Moser, D. & Grabherr, G. (2004): Alpha and Beta Diversity in Central European Beech Forests. Fitosociologia 41 (1).
21. Schütt, P. (1991): Tannenarten Europas und Kleinasiens. Birkhäuser.
22. Nagel, T. A. et al. (2010): Gap regeneration and replacement patterns in an old-growth Fagus–Abies forest of Bosnia-Herzegovina. Plant Ecol 208:307–318.
23. Nagel, T. A., Svoboda, M. & Kobal, M. (2014): Disturbance, life history traits, and dynamics in an old-growth forest landscape of southeastern Europe. Ecological Applications 24(4), 2014, pp. 663–679.
24. Mayer, H. (1986): Europäische Wälder. Gustav Fischer.