There are multiple pathogens around the world that are threatening particular tree species. In New Zealand we have thankfully come through a period of sudden decline in cabbage trees (ti kouka) but are currently very concerned about kauri dieback disease. In the Northern Hemisphere, European Ash trees are being lost as an invasive fungal pathogen effectively kills off large areas of forest.
A recent study by Asko Lõhmus and Kadri Runnel from the University of Tartu in Estonia looks at the effect of European Ash dieback on the specialised and iconic lichen Lobaria pulmonaria.
A recent study by Asko Lõhmus and Kadri Runnel from the University of Tartu in Estonia looks at the effect of European Ash dieback on the specialised and iconic lichen Lobaria pulmonaria.
European Ash leaves affected by Ash dieback. Photo: FERA
The specialised lichen Lobaria pulmonaria. Photo: Jason Hollinger.
Lobaria pulmonaria has many common names including tree lungwort, lung lichen, lung moss, lungwort lichen, oak lungs or oak lungwort. The use of "lung" reflects the fact that it looks somewhat like human lung tissue but also connects to the sensitivity of this species to air pollution. Lobaria pulmonaria populations around the world have been declining as a result of human activities and in Estonia the population is estimated to have been reduced by around 90% since the late 19th century. This species now faces the threat of host tree loss through Ash dieback.
The lung-like form of Lobaria pulmonaria. Photo: Bernd Haynold.
Lõhmus and Runnel (2014) monitored lichens in a forest remnant affected by Ash dieback from 2009 to 2013. During this time the mortality of Ash trees reached almost 60%. They found that only 6% of trees that hosted reproductive lichen populations remained healthy and thus, the survival of Lobaria pulmoaria was concluded to be at risk.
In forests with only one dominant host tree, epiphyte species will face local extinction if a species-specific pathogen affects those hosts. The authors therefore suggest that a crucial backup for epiphyte populations is the presence of different host tree species in the forest. In their study they found that large Populus and Ulmus trees, which are not affected by Ash dieback, were important refuges for epiphytic lichens.
However, the problem in many of these European forests is that a mono-culture approach is practised by silviculture managers. The authors recommend a change in forestry management that preserves natural tree diversity in hopes of minimising biodiversity loss from dieback fungi and disease.
In forests with only one dominant host tree, epiphyte species will face local extinction if a species-specific pathogen affects those hosts. The authors therefore suggest that a crucial backup for epiphyte populations is the presence of different host tree species in the forest. In their study they found that large Populus and Ulmus trees, which are not affected by Ash dieback, were important refuges for epiphytic lichens.
However, the problem in many of these European forests is that a mono-culture approach is practised by silviculture managers. The authors recommend a change in forestry management that preserves natural tree diversity in hopes of minimising biodiversity loss from dieback fungi and disease.
European Ash. Photo: soltenviva.
In New Zealand our native forests are no longer harvested (with the exception of some new, unfortunate allowances) so the natural tree diversity is in better shape. This means that we will have more host tree back ups in forests that are affected by species dieback. However, the variable characteristics of New Zealand tree species means that epiphytes with affinities for say, the bumpy bark of rewarewa, may be threatened if their 'favourite' host trees are lost.
This issue highlights the complexity of ecosystems and their many related processes. It sure gives us plenty of reason to get out there and explore these natural environments; we need to understand what we have (through observation and scientific studies) so that we can notice change and minimise biodiversity loss.
This issue highlights the complexity of ecosystems and their many related processes. It sure gives us plenty of reason to get out there and explore these natural environments; we need to understand what we have (through observation and scientific studies) so that we can notice change and minimise biodiversity loss.
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