Rainforests in northern climes - yes, they exist!
When we think of rainforests we don't usually think of extreme northern climes, but in reality rainforests are also found in northern regions where temperatures are far cooler than in the equatorial zone where their tropical counterparts can be found.
And while you might be hard pushed to spot a brightly coloured bird or a monkey swinging through the trees, these forests are every bit as diverse as their southern cousins and are also worryingly endangered.
Now, a new study from Norwegian researchers, published in the journal Molecular Genetics, explores this genetic diversity that is protected in the remaining fragments of these northern rainforests.
Biologist Olga Hilmo from the Norwegian University of Science and Technology (NTNU) says that this fantastic diversity is 'hidden in plain sight' and can be spotted in the organisms that drape tree branches in long tendrils of green or grow on bark and rocks in crusty or leafy patches of green or grey.
These organisms, called lichens, are actually two or more species living together in a symbiotic relationship, where a fungus provides the structure and an alga provides nutrients. The study shows that there exists an extremely high genetic diversity for individuals of one lichen species, Lobaria pulmonaria, that grow on the same tree. Lobaria pulmonaria is in decline and is considered an endangered species in many parts of Europe.
The implications of the study are that genetic diversity can persist, even if the species in question is found only in tiny fragments of once plentiful habitat, like northern rainforests.
The lichen most often reproduces vegetatively, which means that it spreads via small fragments. Each fragment, if it blows or falls to a favourable spot, is capable of starting a new plant, genetically identical to its 'mother' plant.
As these little fragments, about the size of a coarse sugar grain, are relatively heavy, you wouldn't expect them to spread very far and you would expect the lichens growing on the same tree to be genetically very similar. But the team has found that they are not, meaning that populations of Lobaria are either extremely old or that in some way or another the species is very good at spreading.
Conversely, their findings also show that Lobaria populations in neighbouring rainforest fragments are fairly similar. Even though these fragments of boreal rainforest may be somewhat far apart, there is clearly some kind of connection between them that enables Lobaria to share genetic material with its neighbours.
'There appears to be limited genetic differentiation between the different populations of Lobaria, which means that there has been some genetic exchange between the different fragments of rainforest,' Olga Hilmo says.
Norway's boreal rainforests are like small islands in a sea of tree plantations and harvested areas. Less than 1% of the productive forest area in Namdalen, an area in central Norway with some of the world's most northerly boreal rainforests, is still home to this rare habitat. Here, annual precipitation can top 1,350 mm per year, and it rains on average about 230 days of the year. As a result, humidities are always very high and the forest canopy rarely dries out - making for a wholly unique habitat for humidity loving species such as Lobaria.
Despite these favourable growing conditions, there are essentially no untouched boreal rainforests in Norway and changes in logging practices in Norway after World War Two reduced the area covered by natural boreal rainforests.
'All these forests are affected by logging in one way or another. Before World War Two there was selective logging, but after World War Two they went to clear-cutting. Most natural stands have been left in ravines where it is too hard to log,' Olga Hilmo says.
The good news is that species like Lobaria have managed to maintain high genetic diversity in these small fragments, and that logging around them does not appear to be having a negative effect on the rainforest fragments. Because of this, Hilmo and her colleagues hope that foresters and loggers in Norway can find ways to protect these remaining bits of forest, which are important reservoirs of diversity.
'We need to know a lot more about the species that grow in these forests, particularly rare species such as Lobaria. If we want to establish targeted measures to protect these species, we need to know much more about them, both in terms of their ecology and population biology,' says Olga Hilmo. 'These forests are fantastic, there are moss-covered logs all over the ground, and lichens draping tree trunks and branches, and pendulous lichens hanging down from the trees. It's fascinating and beautiful. Everyone should get to experience being in a rainforest like this, especially in the rain.'
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Document Reference: Hilmo, O., et al. 'Genetic structure in a fragmented Northern Hemisphere rainforest: large effective sizes and high connectivity among populations of the epiphytic lichen Lobaria pulmonaria', Molecular Ecology, 2012. doi:10.1111/j.1365-294X
Subject Index: Climate change & Carbon cycle research; Coordination, Cooperation; Environmental Protection; Scientific Research; Social Aspects