As you pass through the ancient woods, take care to note how the scene changes: even a short walk can take you through several different forest types.
Europe has transformed most forests so as to maximise their profitability – draining their soils, logging their trees, and planting monocultures of fast-growing conifers. By contrast, Białowieża has preserved its natural landscape diversity. Wet, leafy and coniferous woodlands, the primeval woodland has them all. This post describes the forest’s three general tree communities.
What is old-growth?
You’ll need to head to the old-growth stands to see Białowieza Forest’s tree communities in all their majesty.
Old trees and dead trees are the hallmarks of an old-growth forest. In most managed forests, trees, often of a single species, are planted in rows and then cut down as they reach 80-100 years. Foresters also remove trees that happen to die, removing dead wood from the ecosystem. By contrast, in an old-growth forest, you can see trees in all stages of their lifecycle: seedlings, middle-agers, veterans and decomposers.
In natural forests, trees grow spontaneously and chaotically. What’s more, in the absence of the foresters saw, they grow past middle-age, sometimes reaching majestic ages of 300 years or more, with some nobles reaching even 500 years. When their time comes, trees die a natural death, often standing as a snag for several years, before falling to the ground. In this climate zone, trees can spend 25% of their lifespan decomposing. In this way they provide habitat for myriad dead-wood loving species, like woodpeckers and saproxylic beetles. The critical difference between natural and managed forests is that the whole cycle of life-and-death of trees happens without human intervention.
The three tree communities
Note that the same forest type in different parts of Białowieża Forest can have a different appearance. This is for a few reasons, amongst others: 1) Silviculture has homogenised large areas into plantations, 2) Natural disturbances like the bark beetle (see below) have killed most or all of the trees in some areas, 3) Local variation in relief, and soil and water conditions leads natural variation in tree composition and structure. Moreover, each general community type described here has several different sub-types, which differ from eachother often quite markedly.
1) Deciduous (Oak-lime-hornbeam) forest
This forest type is Białowieża’s most iconic. It comprises oak, lime, hornbeam and maple trees, with the occasional pine and spruce mixed in. It is particularly beautiful in spring, when the forest floor is decorated in flowers, and in Autumn, when the trees are draped in gold. This tree community dominates the strict reserve where it can be seen in model form.
Exceptionally by European standards, deciduous woods cover 50% of the Polish side of the forest. Leafy trees prefer fertile soils, which in most cases in Europe were cleared long ago en masse to make way for farmland. That’s why forests across the continent are largely coniferous, comprising tree species that prefer the unfertile soils least suitable for agriculture. Białowieża’s deciduous woods survived due to the forest’s long history of protection.
In the better preserved deciduous stands, note the old trees. Old trees have character. They wear diverse bark, they’re often hollowed out by mushrooms, and they reach prodigious sizes. Oaks attain the greatest girth and age, living up to 500 years. Its ancient specimens, reaching 6 m in diameter, form the most impressive component of the better-preserved stands. Lime, maple and hornbeam can reach 300 years or so, ages rearely reached by these species elsewhere. Look out for old hornbeams – possibly the goofiest looking trees in existence.
Masting is a strategy employed by several deciduous species in Białowieża to increase their chances of reproducing. Trees produce few seeds for several years running, before mass producing fruit during a mast year. In Białowieża, masting happens every 5-7 years. Oaks synchronise with hornbeams and limes to produce a bonanza for herbivores, like rodents, wild boar, and mice. The trees’ aim is to temporarily overwhelm the seed predators in a way that allows some offspring to survive.
These inconsistent pulses of seed production are a powerful ecosystem process, helping to control the population sizes of the herbivores. In the intervening years, a lack of seed production keeps seed predator populations low. After the mast, their populations explode, with effects that cascade through the food chain to other groups of species, like owls and weasels. Then, as food levels in the forest return to normal, their populations gradually decrease again in preparation for the next mast year.
2) Coniferous Forest
This forest type comprises the needle-leaved trees, pine and spruce, with various deciduous species mixed in. In this community, the forest floor is usually sparse, and is mostly carpeted in a thick layer of moss, often with bilberry bushes and moor grass growing on top. Much (if not most) of the coniferous stands in the ‘managed forest’ are anthropogenic, having been planted by foresters over the past 100 years. Some coniferous forest also grows in the strict reserve, but in areas inaccessible to tourists.
Spruce dominated forests are particularly charming. Intensely green year-round and very dark beneath, they exude a murky atmosphere. In recent years, a massive bark beetle infestation has ravaged Białowieża’s spruce trees. This insect drills into their bark and lays eggs. Its larvae then hatch and gorge on the tree’s soft tissue. If the tree fails to defend itself, it dies – and millions have done. It is impossible to miss the stark cemetery-like landscapes where these magical forests once stood.
A few years ago, spruce forest covered some 25% of the Polish side of the woods; foresters suggest half of Białowieża’s spruce trees are now dead. All is not lost however. Some spruce stands have survived the onslaught, and the species is regenerating well in some areas (see photo below). But it seems climate change is making conditions generally unfavourable for the species. It is likely the coming decades will see the species leave all but its most favourable habitats in the forest.
3) Bog forests
Technically speaking, bog forests comprise a great many different types. But for simplicity’s sake, the post will describe them together. They are usually dominated by ash and alder, and in rarer cases by spruce, birch or pine.
Growing along watercourses, river valleys and depressions, moisture is the hallmark of these communities. Even when they don’t have water standing on the surface, the forest-floor is usually sodden underfoot. Although nowadays these communities are increasingly drying out, due to droughts caused by climate change and historical drainage works.
In many bog forests you can see a characteristic mosaic of hollows and hummocks. On the latter grows a tree or two, whose root systems give the hummock structure. On the forest-floor usually grow a variety of ferns, nettles, and mosses. The most mysterious plants are the horsetails, species that look to have been transplanted from the distant past.
Widespread drainage works have endangered this forest type across Europe, as people have traditionally regarded wetland areas as ‘wasted’ land. In Białowieża, bog forests were largely innacessible to foresters, which saved them from the loggers saw and maintained their natural character. Although even here, ground water levels are falling fast; as the bog forests dry, deciduous forest is encroaching into areas previously too wet to support it.
Enjoy the bog forests while you still can. They’re like a time-machine into an age before man transformed the land, a portal into the carboniferous coal forests of 300 million years ago.
A more detailed description of the forest’s communities can be found in this excellent leaflet by Paweł Pawlaczyk.