Humans have changed forests to such an extent, that the majority of people have never seen, nor could even imagine, how the pristine forests covering Europe in the prehistoric times could have looked like. Fortunately enough remnants of such forests have survived in the Białowieża Forest. This allow one to travel back in time to see with one’s own eyes how such forests, which originated without man’s intervention, function free of direct human interference.

The primeval forest is very diversified: as a rule it has multiple species living in multiple layers, of uneven age, with abundant snags and fallen logs. The oak-hornbeam Tilio-Carpinetum forest type (above, photo J. Walencik) is composed of a dozen or so tree species.

Ancient, legacy trees constitute an inherent feature of primeval forest. The oldest Pedunculate Oaks Quercus robur can be 400-500 years old, 43 m tall, with trunk circumference exceeding seven meters. Norway spruces Picea abies (left) are the tallest trees in the Białowieża Forest, they can reach 55 m. Black Alders Alnus glutinosa (right) grow to 40 m and to more than three meters circumference. Thick, full of crevices bark on huge trees forms a unique microhabitat inhabited by numerous specialised fungi, lichens and invertebrates.

Broken and uprooted trees constitute a permanent and important ingredient of such forests. Fallen logs make „fences” protecting young trees against browsing animals. Entangled branches and soil covered root pads of fallen trees provide important hiding places for the nests of numerous birds species. The falling trees are momentous to processes of soil formation and succession of the ground layer plants.

Dead wood – both snags, and fallen decaying logs - constitute an indispensable ingredient of the primeval forest. Dead wood makes c. one third of the total wood volume in the oak-hornbeam forest type. A whole community of saproxylic fungi, insects, as well of specialised birds species, such as Three-toed woodpecker (Picoides tridactylus, photo G. Okołów) shown here at a hole in dead spruce, are critically dependent on this resource. The presence of dead and dying spruces is a necessary prerequisite for the Three-toed woodpecker’s presence (more here).

The primeval temperate forest is a very dynamic system, on top of regular flow of seasons and long-term successional changes one can see there spectacular irregular bursts of activity/numbers of different organisms, masting of trees, outbreaks or rodents, folivorous caterpillars or bark beetles Ips typographus. The effects of such sudden inflow of resources cascade - via trophic links – throughout the whole ecosystem. Outbreaks of Winter Moth Operophtera brumata (left), which happen every 8-10 years lead to the almost complete defoliation of trees (middle). After a few weeks, though, the defoliated trees produce a second generation of leaves. In such seasons birds feeding young with caterpillars, such as Marsh Tits (Poecile palustris, photo G. Okołów) can be swamped by food.

The primeval forest with its vast array of different microhabitats and diversified, often very rich, food resources would appear a very attractive place to live. It is however, a very dangerous place, too, where one can easily lose ones life. Pine Marten (Martes martes, left) is just one of over thirty species of birds and mammals attacking birds and their nests in this forest. Not infrequently predators destroy 70-80% of Wood Warbler (Phylloscopus sibilatrix, right) and other small birds nests.