FO12 Forest vegetation

>> Background information

Development

Changes in forest understorey vegetation have been analyzed three times during study period (in 1985, 1995 and 2006) in mature uncut forests and clearfelled forests. Mature uncut forests were over 55 years old in 1985 and no fellings have been done after 1975. Crearfelled forests have been cut between first and second study round. Analyzes have been carried out separately in herb-rich and moist forests and in dry forests.

In clearfelled forests bilberry (Vaccinium myrtillus) suffered more than cowberry (Vaccinium vitis-idaea). Both in moist and dry forests the cover of bilberry fell more than 80 % after fellings and had not recovered at all during the twenty year study period. The cover of cowberry fell about 50 % after clearfellings but had recovered back to the pre-felling level in 2006. In mature uncut forests the cover of bilberry has not varied much in 1985?2006 but that of cowberry has slightly decreased in moist and grown in dry forests.

Reindeer lichens form most of the lichen cover in Finland. The lichens suffered a great deal in clearfellings, especially in dry forests where the cover fell over 70 %. Lichen cover began to grow back during the twenty year study period but the recovery was very slow. In mature uncut forests the lichen cover has diminished significantly. In dry forests the lichen cover has more than halved in twenty years and the trend is similar in moist forests.

After clearfellings the cover of bryophytes both in moist and dry forests fell more than 60 %. In the third survey year 2006 the bryophytes had recovered a little but the cover was still only half of the pre-felling level. In mature moist forests the cover of bryophytes has remained at the same level during the study period 1985?2006. In dry mature forests the cover has grown 25 % since 1985. In dry forests especially Pleurozium schreberi and fork mosses (Dicranum) grew more abundant.

After clearfellings the cover of graminoids and herbs increased, but as competition grew it started to thin out again. Nonetheless, in 2006 the amount of graminoid and herb species still remained high in logging areas cut between 1985 and 1995. In mature uncut forests the cover of graminoids and herbs is a couple of per cents for moist forests, in dry forests the cover is mostly less than 1%. 

Forest vegetation

The forest understorey vegetation consists of tree seedlings and shrubs, dwarf shrubs, graminoids, herbs, bryophytes (moss) and lichens. The chosen indicator species or groups are bilberry, cowberry, lichens and bryophytes. Bilberry is very common species in Finnish forests and it has a great significance for forests? ecosystem structure, function and for other species. Bilberry is important source of nutrition for grouses, elks, hares and voles, amongst others. The extent of lichen cover on the other hand indicates the state of dry habitats and the circumstances for species depending on them (e.g. lichens, bryophytes, fungi and invertebrates).

Fellings and soil preparation alter growing circumstances and thus cause changes in the understorey vegetation. After fellings the amount of light and the temperature range increase, humidity decreases and nutrients are released from the soil and logging waste. The cover of graminoids and herbs tends to increase and that of other plant groups decrease. The clearfellings have the most intensive effect as most trees are cut and removed and the soil is heavily managed.

In clearfelled forests the bilberry suffered more than cowberry because it doesn?t tolerate so well the drought and abundance of light. The most of bilberry and cowberry biomass is underground in rhizomes, which are major nutrient stocks and important for reproduction. Most of rhizomes are destroyed by fellings and soil preparation and the recovery to the pre-felling level is very slow. Clearfellings affected profoundly also the cover of lichens and bryophytes. Especially glittering wood-moss (Hylocomium splendens) recovered slowly for it needs a shady habitat. The more light bearing bryophytes Pleurozium schreberi and Fork mosses (Dicranum) recovered faster. Lichens suffered especially from mechanical destruction and soil exposure.

In mature uncut forests the cover of dwarf shrubs, graminoids and herbs did not alter much during the twenty year study period. The most significant changes were the declining lichen cover and increasing cover of bryophytes. In Northern Finland the lichen cover has decreased mainly because of reindeer herding. In Southern Finland the probable causes are increased shading and more severe competition, lack of forest fires and the nitrogen fallout that fertilizes the ground. In mature forests the increased shading improves circumstances for bryophytes as light and moisture conditions alter. Cover of some dwarf shrubs, crowberry (Empetrum nigrum) and heather (Calluna vulgaris), decreased in old growth forests. This is most probably due to natural succession and increasing between-species competition.