The ridgeline is a thoroughfare
The ridges surrounding the waters of Lake Petkeljärvi are part of a geological formation dozens of kilometres in length. It extends from far-away Tolvajärvi in Russian Karelia via Petkeljärvi and Putkela to Ilomantsi, south of Lake Koitere.
The ridges formed when the ice sheet melted more than 10,000 years ago. As the edge of the ice receded, low, steep ridges were exposed in the tunnels carrying the meltwater. Depressions typical of ridge landscapes were formed when large pieces of ice mixed in with the piled-up soil melted.
As the ice receded, animals and plants spread to the north west along the ridge isthmuses. The first species of trees to spread to the area were birch, followed by pine, which had adapted to dry conditions. The first animals to follow the edge of the ice were the Arctic Fox and Finnish forest reindeer, also known as petra, from which the names Petkeljärvi and Petraniemi derive. Lured by the prospect of fresh venison, stone-age humans also walked along the ridges.
The Petkeljärvi-Putkelanharju ridge area, which is 15 kilometres long, is one of Finland's most valuable natural ridge areas. More than 2,700 hectares of the area are protected, and it is part of the European Natura 2000 network of protected areas.
The esker forest is a sparse pine stand
The forests of Petkeljärvi are left to develop naturally. Most of the trees growing in in the forest today are sturdy pine trees more than 150 years old. The thick-barked pine trees that have stopped growing are more than 200 years old. The fire wounds at the bottom of the trees are evidence of forest fires that previously burned in the area. The thick bark on the pines protects them from heat. However, spruce and deciduous trees often die in forest fires. Consequently, many forests that have burned in the past are now populated by pine trees that grow sparsely.
The slopes of the ridges open in opposite directions. The different conditions can be seen in the flora. Southern and western slopes are often warm and dry. There are shrubs and lichens in the undergrowth. A northern or eastern slope is usually cooler and are home to plants other than those that thrive in drier locations.
The depressions bring small-scale differences in height to the landscape. Some of the depressions are dry, while others have a small pond or swamp at the bottom. The deepest depressions are in contact with ground water. The temperature at the bottom of a depression can be several degrees lower than that of the surroundings, because cold air flows to the bottom of the depression. For that reason, snow melts more slowly at the bottom of the depressions and vegetation can differ from what it is at higher levels.
Wilderness lakes echo with the call of the Black-throated diver
A feeling of wilderness in the summer of Petkeljärvi is brought by the black-throated diver - the official animal of the park. The black-throated diver can be found in all parts of Finland on wild lakes with clear water. An adult black-throated diver in its regal dress, with shades of black, grey, and white, with stripes, and spots, is like a graphic artist’s masterpiece.
The flat body and the feet that are located at the far end of the body make the black-throated diver a skilful swimmer. The bird prefers to do its fishing in clean waters and when it dives, it can stay submerged for distances of hundreds of metres. However, on land, its movements are clumsy. Consequently, the female black-throated diver builds its nest hear the shore, no further than 1.5 metres from the waterline.
Throughout the summer and autumn flocks of black-throated divers, sometimes numbering dozens of individuals, can be seen on the lakes. Loons also fish in these groups. In the early summer, birds without partners seek out these flocks and are joined later by pairs whose nesting has been unsuccessful. Nesting birds will also occasionally join flocks for a short time.
Petkeljärvi's most prominent mammal
North American beavers are also residents of the national park. The fruits of their labours are numerous; trees falling on routes, den and dam structures, and blocks of aspen floating in the water, with the bark removed. The beaver is the only animal in the world, besides the elephant, that can fell a full-grown tree! The techniques differ from each other: an elephant pushes trees down, while a beaver gnaws. Markings caused by the front teeth can be seen on both small and large tree stumps in Petkeljärvi. Areas flooded by beaver dams are often valuable oases where, for instance, aquatic insects and families of ducks have a good habitat for growth.
Deadwood trees are teeming with life
In protected areas pine trees can live to an old age an die slowly, standing up. It can take more than 500 years from the germination of a pine seedling for the tree to grow, die, fall down, and decompose. The wood in dead trees is close-grained, which is why it is tough for saprotrophs to eat. Fallen dead pine trees are home to specific species of specialised saprotrophs. Many of these are endangered, because there are currently much fewer trees in our forests that have died standing up than before the age of industrial forestry. In commercial forests trees are utilised before they are old and dying.
The fallen dead pine trees in Petkeljärvi National Park are home to many endangered polypores, such as Antrodia crassa, Diplomitoporus crustulinus, and Antrodia infirma. Dead trees in an advanced state of decay offer an excellent growth platform also for new pine seedlings. Before falling the holes in the trunks have served as homes for woodpeckers, tits, and flycatchers.
Feed gathered for livestock from flood meadows
Ruununsaari, an island in Petkeljärvi, and Petraluhta, a flood meadow which borders on it, are shallow sandy formations in Lake Valkiajärvi. Residents in nearby areas used to cut sedge that grows in Petraluhta as winter feed for cattle for hundreds of years. Nowadays the flood meadow is no longer harvested, but it remains open thanks to ice and flooding.
Nature management in the Putkelanharju nature conservation area
There is no need in the forests of Petkeljärvi National Park to engage in habitat restoration. However, in the Putkelanharju nature conservation area swamp and forest habitats have been restored.
Ditches in state-owned land in Putkelanharju were filled up over an area of 80 hectares in 2006. The water level rose rapidly to a more suitable level. At the same time swamp vegetation and other species have started to recover. The filled ditches are soft, and it is possible to sink in, so it is a good idea to find a higher dam location to cross one.
The forests of the Putkelanharju conservation area reveal the previous history of economic use: the trees are of the same age and there is little decayed wood in the area. In 2005 a five-hectare stand of trees was burned north of Ahvenlampi. A backhoe and chainsaws were also used to increase the amount of decaying wood to about 12 m³ a hectare. Meanwhile, the structure of living timber has become more diverse, as saplings start to grow in the small clearings that result from habitat restoration.
Esker vegetation is very fragile
The deterioration of the terrain on the ridges of the national park could prove to be a problem. The flora of the dry heath soil easily suffers when it is stepped on. The recovery of the damaged forest flora is monitored at an old camp site which was in use from 1960 - 1978.
For nature on the ridge to remain as close to the natural state as possible, visitors should favour marked trails and existing paths.
Part of the UNESCO programme
Petkeljärvi National Park is part of the North Karelia biosphere area covering the municipalities of Ilomantsi and Lieksa as well as Tuupovaara, which is part of Joensuu. Biosphere areas are aimed at promoting the diversity of nature, while developing social, economic, and ecological sustainability. Environmental education, guidance, and research are in an important role. The activities are based on voluntary agreements among municipalities, businesses, and associations. The North Karelia Biosphere Reserve Programme is maintained by the Ministry of the Environment and the North Karelia ELY Centre. Further information: www.kareliabiosphere.fi