Elle Rajandu’s doctoral thesis studies plant and lichen species diversity in the valuable alvar forests in Estonia.
These forests grow on shallow soils (thickness up to 30 cm) with a limestone base and belong to one of the rarest forest types in Europe – they are present only in the limestone-rich areas of western Estonia and the northwest Estonian islands. Because they are concentrated in these single areas of Europe, we are responsible for preserving alvar forests as rare ecosystems.
In addition to their uniqueness, alvar forests are also very rich in species. According to a 1997 survey, approximately 13% of the endangered and preserved species of flora and fauna in Estonian forests (up to 50% of mammals and 25% of vascular plants) are associated with alvar forests.
These figures become even more pronounced when one realises that alvar forests comprise only 3.3% of all Estonian forests. The area they cover used to be significantly larger but agriculture and forestry have replaced them with wide clearings and plains that are unable to be reforested.
Steps have been taken to protect these forests: they are now protected by nature preservation laws and one of the most diverse area of alvar forests in Rapla county has been made into a nature reserve.
But how can we actually protect these forests? Despite their importance, alvar forest ecosystems remain minimally researched, especially their lichens and bryophytes (mosses, liverworts and hornworts, all of which have stems and leaves but lack true vascular tissue and roots and reproduce by spores).
A general lack of knowledge can often result in preservation methods that can sometimes make the situation even worse. For example, this happened in Vardi in 1978, where alvar forests under preservation were not cut, but standing dead trees and fallen timber were still collected.
Deadwood is important
The research performed in Rapla county showed that when compared to other substrates, decaying wood has the largest biodiversity of lichens and bryophytes. Also, dead wood had different species composition when compared to other substrates.
Deadwood has large microsite heterogeneity caused by several factors, e.g. by size of wood fragments, bark texture, nutrient composition, water-holding capacity and microclimatic conditions – this makes it a suitable habitat for a large number of species.
Research also revealed the importance of junipers in facilitating the alvar forests’ biodiversity of lichens and bryophytes. Most of these forests are coniferous and have very few or no deciduous trees. Because junipers have a more alkaline bark than other coniferous trees, they offer a growth base for a range of lichens and bryophytes that would otherwise not be present in the ecosystem.
Many bryophyte species grow on windthrow (trees uprooted by wind), where exposed ground, stones and tree roots offer various growing possibilities. Windthrows are quite common in alvar forests, where the soil is thin and tree roots cannot penetrate deep into the ground.
Different species have different requirements
My doctoral thesis compared the habitat requirements of vascular plants, lichens and bryophytes. The research showed that these groups behave very differently under the investigated environmental factors.
While vascular plant diversity was higher with better light, the ground moss species preferred the opposite: species richness was higher in the shade.
Forest management (such as thinning) was found to be directly harmful to the bryophyte diversity on wood, but lichen species diversity was more related to the overall number of different tree species in the forest.
Many questions to be answered
So, what should we do or not do with alvar forests? Since they have been occasionally used as pastures, should we therefore consider them seminatural ecosystems in which moderate human disturbance might even be beneficial? Or should we avoid all human disturbances?
As biodiversity is generally facilitated by stable environmental factors over long periods of time, perhaps we should look for answers in the older history of these forests.
And perhaps we should not only focus on protecting the biodiversity of strictly defined areas such as alvar forests. During my research, I found several rare bryophyte species (some of them had been registered before less than 5 times) near the alvar forests, in areas with a quite alkaline environment in boreo-nemoral forests. These habitats might be easily destroyed as a result of logging.