The aspen trees at RSPB Scotland Insh Marshes Nature Reserve have joined many across Scotland in flowering. This is the first mass flowering of aspen in 23 years.
Aspen (Populus tremula) trees are native to the UK but they rarely flower in this country. The last time there was a major flowering event in Scotland was in 1996, following the hot summer of 1995. These trees will generally only flower and set seed here following a hot summer, just like the one we had last year.
This sporadic flowering makes aspen extremely vulnerable in Scotland, occurring mostly as small stands of trees and sometimes individual trees. It is thought that aspen has suffered more from deforestation than any other native tree in Scotland, largely because of its sporadic flowering, relatively short lifespan and being very palatable to grazing. Once aspen woods have been lost from an area, it is unlikely to be able to return on its own.
Aspen is most common in the Scottish Highlands but, even here, it occurs in small and isolated populations. There are only a few aspen dominated woodlands left here and one of those is at RSPB Scotland Insh Marshes Nature Reserve.
Unlike most trees, where male and female flowers are present on one tree, aspen have both male and female trees. When conditions are right, the trees flower in March and April before the leaves appear. Both male and female trees produce catkins. If the female catkins are successfully pollinated, they will ripen in early summer and release tiny seeds which will grow into new trees.
When conditions aren’t right, it doesn’t mean that the trees do nothing. They can also reproduce asexually by sending up shoots (called suckers) from their roots. These shoots grow into trees that are clones of the parent tree. This is the most common way for aspen to reproduce in this country. So, when you look at an aspen wood here in the Scottish Highlands, genetically it could all be made up of the same tree.
Aspen supports a wide range of animal and plant species, some very rare and many only found associated with aspen, like the aspen hoverfly. The aspen hoverfly is one of the UK’s rarest hoverflies and it is found at only a few sites, all of which are in Scotland. One of those sites is the aspen wood at our Insh Marshes Nature Reserve. Aspen hoverflies have been present at Insh Marshes for possibly thousands of years and they are regularly recorded on the reserve. Their larvae require decaying aspen wood to feed.
Aspen is also very important for many rare mosses and lichens, like the aspen bristle moss. This rare moss was thought to be extinct in the UK until it was rediscovered in Rothiemurchus in the 1990s.
Catherine Owen-Pam, assistant warden at RSPB Scotland Insh Marshes, said: “One of the factors affecting aspen woodlands from regenerating is the way in which it predominantly spreads vegetatively (by sending suckers out), and not by seed which would be dispersed widely. The suckers can be vulnerable to browsing deer which could result in preventing these woodlands from expanding. We monitor aspen regeneration in the woodland regularly to help ensure that this rare and ecologically important native tree continues to thrive. This flowering event could be an excellent opportunity for us to collect some seed to help with this work.”
If you would like to experience the magic of a rare aspen woodland, join one of our guided walks this spring and summer. More information can be found here: https://www.rspb.org.uk/reserves-and-events/reserves-a-z/insh-marshes/