Almost one century of forest inventory data: how bright are the prospects for the Finnish forest biodiversity?

Abstract

With 73% forest cover and 26.2 million ha of forestry land, Finland is the most forested country in Europe, hence contributing significantly to its forest biodiversity. The forestry land is classified into forest land (20.3 mill. ha), poorly productive forest land (2.5 mill. ha) and unproductive land (3.2 mill. ha), depending on the potential annual increment. The majority of nature conservation areas (3/4 of the land) are located on the poorly productive and unproductive forest land, making them susceptible to fragmentation and isolation as a result of forestry-driven habitat changes on the dominant productive forest land. Here I present a detailed historical overview of ecological changes that took place in the Finnish forests within 1924-2013 and discuss their implications for biodiversity conservation.

Despite the 13% reduction in forest area in the 1940s due to the territory loss in World War II, Finland's tree growing stock has never been so high. Yet, the tree species composition, age structure and soil hydrology of the forest, three key drivers of the boreal forest biodiversity, have radically changed in just a few decades, with marked differences between the north and the south.

On the productive forest land, pine trees have become increasingly dominant at the expense of spruce forests, raising concerns for the spruce-associated biota. In Northern Finland especially, right after the war, the pine forest cover has steadily increased from 55 to 75% while the spruce cover declined from 31 to 16%. Similar changes took place in the south from the 1960s. An abrupt decline in the amount of deciduous forests is another nationwide post-war phenomenon, causing its original cover to drop from 17 to 8% by 1984. It is only recently that deciduous forests have increased again in proportion, accounting now for 11.5% of the southern forest land, although being of limited ecological value due to their younger age.

In addition to tree species composition, the simultaneous large-scale implementation of both clear-cutting and forest ditching practices that mainly took place from early 60s to late 90s, with a peak in the 70s, have caused fundamental changes in the original age structure and productivity of the forest. Today, in Northern Finland where they are mostly situated, species-rich natural forests over 120, 140 and 160 yr old only represent 17, 14 and 10% of the regional forest land. This is a pale figure compared to their 55, 45 and 36% respective coverage in the early 1920s. Based on linear regressions, the continuously declining primeval forests, despite their prime importance for the boreal biodiversity, are expected to largely vanish from the Finnish productive forest land by the beginning of the next century unless adapted new conservation measures are taken. It took at least 40 years for natural forest mires to be converted into dry production forests, demonstrating long-lasting effects of drainage on the northern ecosystem.