Suomen Luonto
English summaries 4/2000

Climate change is choking the Baltic
by Markku Lappalainen

page 18

From time to time, saline sea water penetrates into the Baltic through the Straits of Denmark. In conjunction with a high tide and a south-westerly or westerly storm, water surges in through the natural channel formed by Denmark's Skagerrak and Kattegat between Norway and Denmark, and Denmark and Sweden. Several cubic kilometres of this water pours into the Baltic basin.

However, the Baltic gets most of its water from rivers and rain. Mixing with this fresh water, salty ocean water turns the Baltic into an enormous brackish water basin, in which the salinity varies from over one percent in the south to 0.2-0.4 percent in the northern corners.

In addition to salt, sea water also contains oxygen. Being denser than water of low salinity, the sea water sinks into the depths. Simultaneously, it forces out the unoxygenated water, polluted by anaerobic bacteria and environmental toxins. Pulses of this kind keep the deep waters of the Baltic functioning; they form, as it were, the lungs of the Baltic.

Now the salinity of the Baltic is falling. This phenomenon has been caused by two things happening simultaneously. Firstly, the amount of rain in the Baltic's catchment area has increased, and secondly the amount of salty water coming in from the North Sea has decreased. Researchers say that the changes are due to the climate change brought about by human activities.

Previously, almost permanent high pressure conditions reigned close to the Azores, while the neighbourhood of Iceland was characterised by low pressure conditions. Sea winds blow in the same direction as the Gulf Stream, warm up and make the winter climate mild. In Finland, instead of snowing, it rains, or sleet falls. In the past, the level of the Baltic was at a minimum in winter. Nowadays, thanks to the large amount of rain, the Baltic is full of water and salt water pulses are unable to penetrate there. This change is already apparent in the living communities of the Baltic. As salinity decreases, large-sized planktonic animals also decline. Such animals provide food for Baltic herring which, as a consequence, are far thinner than they were ten to fifteen years ago.

Hairy birch reinstated in forestry
by Seppo Vuokko

pages 24-27

Finlandís dendrology society chose the hairy birch (Betula pubescens) as the tree of the year 2000. Common everywhere in Finland, in recent times this lovely tree has been somewhat pushed into the shade by its near relative, the silver birch (B. verrucosa), although over the past few years people have begun to appreciate it again. As recently ago as the 1960s, both birches were felled in State forests and left to rot as so-called "rubbish trees" and as economically worthless competitors of "useful" trees.

Hairy birches do not grow as large as silver birches. Finlandís largest specimen is only 22 metres tall, although the bole has a circumference of 369 cm. The hairy birch grows almost anywhere , from dry heathland to wet shores and even bogs. It does so well on a moist substratum that it was at one time known here as the bog birch.

Birch came into favour as a useful wood supplying species with the development of office technology and furnishings, and the opening up of major markets for short-fibre fine papers. Pulp made from birch is admirably suited to the production of fine paper qualities. The forest industry was forced to take note of the fact that a tree which it had considered worthless had been destroyed in the forests to such an extent that there were no longer enough birch logs available in Finland to satisfy the new mill demand. So birch had to be imported from the Soviet Union. Meanwhile birch has been so extensively planted on commercial forest land that there are fears there will be too much of it by the 2050s!

Three species of birch are found in Finland. These comprise the hairy and silver birches just mentioned, and the diminutive dwarf birch (B.nana), a shrub growing on bogs and mires. A subspecies of the hairy birch is found in the fells of Lapland. The species is extremely adaptable and can grow as either a tree or a shrub, with one or more trunks; its bark may be drab brown or shining white with large black blotches.

Hello, Spring!
by Hannu Aarnio

pages 20-23

Few Lepidoptera hibernate as adults - the most well-known exceptions being some butterflies, i.e. the small tortoiseshell, brimstone, Camberwell beauty, comma and peacock. Thus, of Finlandís one hundred or so butterfly species, only five pass the winter as adults. Only ten species of Noctuids out of the three hundred found here hibernate in the adult stage; these species are on the wing in the autumn. Overwintered individuals can easily be identified when they fly again in spring by their faded colours and often rather ragged wings. However, spending the winter as an adult, or imago, confers some advantages, since it then becomes possible to make use of the nectar provided by early spring flowers and to lay eggs before other species emerge.

Most Lepidoptera pass the winter as an egg (ovum), caterpillar (larva), or chrysalis (pupa). Larvae and pupae generally overwinter in the soil, on vegetation, or in leaf litter lying on the ground. In such situations, the temperature remains low and the insectís life cycle does not continue until those species hibernating as adults have been on the wing for some time.

The time tables of butterflies overwintering as an imago in northern Europe closely resemble each other. The females lay their eggs on the foodplant(s) in spring or in early summer, after which the caterpillars feed up, grow and eventually pupate. The new generation of adults emerges in late summer. These adults collect energy to tide them over the long winter ahead. Almost all the butterflies have gone into hibernation by the end of September. Small tortoiseshells and peacocks hibernate with the assistance of mankind, i.e. in cracks or mouse holes in buildings and in similar places.

Wild animal diseases
by Alice Karlsson

pages 36-37

It is the job of the National Veterinary and Food Research Institute (NVFRI, or EELA in Finnish) to study the state of health of wild animals. Each year the institute carries out over one thousand autopsies on wild animals to determine what diseases the animals have suffered from and why they have died. However, in general it is only "cute" animals or game animals that are sent in for examination. Rarely, for instance, does a "nasty" rat or crow arrive on the morticianís slab.

Different kinds of animals tend to suffer from different diseases and parasites. Predators catch trichinosis and scabies, lagomorphs are subject to tularaemia, and birds suffer from salmonella outbreaks. Often birds of prey succumb to inflammation or parasites as a result of lowered resistance which itself can be traced to malnutrition. Many animals acquire parasites, sometimes in large quantities, but these do not usually result in the death of the animal. The most common reason for mortality in wild animals is a road accident or drowning in fishing gear such as nets and traps.

A whole contingent of diseases can be transferred from animals to humans and vice versa. Such zoonoses include trichinosis (trichiniasis), salmanellosis, rabbit plague (tularaemia), rabies and echinococcus. Each year a few cases of so-called rabbit plague (tularaemia) in hares are brought to light, varying from a handful to several dozen. In 1999, this particular disease was diagnosed in ten hares. Ten or so reindeer a year are found with trichinosis annually. This disease is particularly prevalent among racoon-dogs. No cases of rabies have been reported in Finland since 1989. However, it is feared that this dread disease may again spread into Finland from Russia at any time.