Fergus Cumberland, Visitor Experience Manager at Loch Garten, explores the mystery of the swathes of rowan at Abernethy.
Redwings, rowans and fieldfares, oh my!
Abernethy is best known for its amazing pine forest, old enough to have hosted wolves 400 years previously. However, there are more recent developments being made by much smaller animals. A dense section of rowan woodland that has been created within the past 30 years stands defiantly alone in a treeless expanse. Sitting close to a public footpath on the edge of Abernethy, we see a large swathe of rowan trees that have sprung up as if by magic.
Rowan is one of the most delicious trees to deer in our forest, second only to alder. To see so much of it growing out in the open, where deer would rest for an easy snack, seems quite strange. So how has this happened here?
Autumn is often associated as the season of death for many things, but for rowan, it is the beginning of life as a forest. The autumn brings with it winter migrants from Scandinavian looking for some tasty berries on their way south. The skies become alive with redwings and fieldfares jostling for position in the trees. These thrushes instigate the conditions that make forest regeneration possible.
There are two conditions that we need in balance for forest regeneration. The first is a low browsing pressure on trees. This means things like deer, mountain hare, voles or even slugs are not getting the chance in nibble on young shoots before they have a chance to establish. All of these species would prefer to eat a deciduous tree as it naturally is more palatable than our hardy scots pine trees. So if these browsers are kept at a natural level, we should see young saplings beginning to pop up. Due to this site being close to a public footpath, we might see less browsers able to access this food source.
Rowan at Abernethy. Credit: Fergus Cumberland
The second factor is a high viable seed source. Trees can produce lots and lots of seeds, but of those seeds maybe not all of them will ever develop and of the ones that will have to land in the right place to grow. Since almost all our trees in Abernethy rely on wind dispersal, rowan is quite special to rely on birds to spread far and wide. Being able to disperse out from underneath the shadow of a parent is not the only benefit these birds may be providing. Some studies have suggested that in digestion, the birds also cleanse the seed of pathogens that can dramatically increase survival when eventually pooped out! Roosting birds can create a more viable seed source that creates a forest quicker than if it the seeds were to only fall of the tree.
In both of these instances the effect overwhelms the grazing pressures. Here we see a stand of rowan that is producing trees faster than they can be browsed by animals. And the main factors helping them along the way are redwings and fieldfares pooping out the seeds of these very trees. The beautiful thing about these migrating birds, is that they have become ecosystem engineers. The positive feedback loop of having bird eating rowan berries means that over generations there have been be more birds, more berries, more roosting, more pooping. A forest made by birds, for birds.
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