Trees
Trees ... we love them, and enjoy our time walking amongst them. Many of us have learnt their names and recognise them. It’s common knowledge that we have and accept. We also know that bees like to live in trees. But how does that work?.
If we look at a typical tree, we may struggle to see how a bee colony might find a home there - in its full and mature splendour, a tree has few holes or cavities that might seem large enough. If you’re a bee, where do you find a tree with a cavity, and how does a tree get like that in the first place? If we can understand the trees that the bees choose, how does that help us, as people who care for bees?
First of all we can deepen our understanding of trees, beyond what’s usually found in our tree ID books, beyond that which is common knowledge. Once we have this extra depth of understanding, we see why trees are so important and perfectly suited to bees, and we can learn to recognise the trees which might be home to our wild colonies.
Let’s look at how trees grow, and start with a typical mature tree (1). Its roots are strong, its trunk solid and sturdy, its branches spreading, its crown full. All being well it thrives like this for some time. The tree provides shelter in the overall environment, has flowers in the spring, and may be a place where a swarm stops as a cluster whilst a new home is found. But at this point it has nothing of interest for a colony looking for a nest site. After living as a mature tree for a while, there comes a point when the tree can’t keep increasing in girth and height. Now, different things start to happen, not necessarily in a linear order. As bee-carers, this is when it starts to get interesting.
One of the first changes to happen is that perhaps a branch will fall off or break, though this can also happen at any stage of its life. Maybe the branch is unproductive and the tree just doesn’t want it, so stops supporting it with water and nutrients. Where any twig or branch forks from the larger branch or trunk, is a branch collar, a ring of specialised cells that will slowly heal over any break, so that it’s neat and strong. This rounding over process can take years, decades or centuries, depending on how large the area of exposed trunk or branch is and on the vitality of the tree (2). Sometimes this will happen when a tree surgeon cuts the branch, just beyond the collar layer, and sometimes the branch is damaged at a point away from the trunk, and the tree decides to lose the whole branch. The area can sometimes heal right over (3).
2. Various places on the trunk of this tree, where the branch
collar is healing over. The tree doesn’t want these branches.
3. A completely healed over branch
collar, now a solid area of bark.
While this area of the tree doesn’t have the protective covering of bark, moisture enters, as well as fungus spores and insects. Sometimes a bracket fungus will appear - a sure sign that the fungus is digesting and processing something of the wood. The wood becomes soft and the branch or trunk will start to hollow. It’s here that a woodpecker might find, taking advantage of this natural strong opening with a hollow behind, perhaps excavating it more and using it for a nest (4).
4. Holes at various stages of healing and hollowing.
A blue tit was using the lower one for a nest.
Meanwhile, back to the tree, and where it’s at in its ageing process. As the tree passes its mature phase and enters what’s called a veteran phase, it starts to develop a lower crown. This is a gradual process rather than an instant thing. The tree might start by awakening dormant buds (‘epicormic buds’) in its trunk and branches (5). These points of growth are also awakened in response to any damage during the tree’s life. They will develop into twigs (6), then into small and larger branches (7 and 8), eventually becoming a main part of the tree’s structure. Branches that grow in this way look different when compared to the original growth pattern of the young or mature tree. Once you’re aware of this, you can recognise it easily.
5. Epicormic buds, just starting to develop and grow.
6. Young epicormic growth.
7 and 8. Epicormic branches.
This process of growing a lower crown is called retrenchment. It’s what trees do. Sometimes a tree looks like it’s doing two different things, but this is in fact normal, and a great example of a tree that has developed a successful lower crown (9). Over time, the tree will allow its upper branches to die off and will become proportionally more squat, with its lower crown becoming its main crown. Trees like this are often called stag headed (10).
9. Oak tree with retrenched crown.
10. A stag headed chestnut tree, with a retrenched
crown and dead upper branches still present.
So while this retrenchment is happening in the upper part of the tree, sometimes one or more large side branches will fall. The branch collar around the break will thicken and heal the edges, but if the area is too large it will gradually hollow and become an opening (11).
11. The branch that was once here fell long ago, and the
tree is becoming completely hollow.
The tree will also hollow from the top down, when its top branches have fallen. Leaves and fungus-decomposed wood will fill the cavity, perhaps mixed with insect debris and bat droppings, and the crumbly mixture becomes enriched and available to the tree again, rather than being locked up as a solid trunk of wood. This enriched substance inside a trunk is home to very specialised creatures that can only live in this ancient tree habitat (12). This habitat continues after the tree has died, with cracks in the trunk allowing more hollowing to happen.
12. Part of this dead trunk has fallen away,
revealing the rich debris inside.
Hollowing is not necessarily a bad thing. The tree only needs the outer part of the trunk for the transport of water and nutrients, and a short hollow trunk with holes is actually very stable. It’s also interesting that a tree can be both dead and alive at the same time, living for hundreds of years with changing dynamics. Consider this veteran stage from the tree’s point of view - after a fairly long phase of regular sensory input and steady activity, this phase is full and diverse, with so much going on! Personally, I think of this as a tree’s wisdom phase, living the experience of an elder. It’s only now that the tree can be what I would call an ‘apex presence’, able to support the widest variety of other life. As the veteran stage progresses and the tree becomes completely hollow, it is known as an ancient tree, and again, this phase happens over a long period of time (13).
13. This tree is now completely hollow, is both
dead and alive, and fully ancient.
The terms veteran and ancient are not about how old a tree is, but relate more to behaviour and habitat. Sometimes small young trees become veterans before reaching full maturity, while vast old trees continue in their veteran phase for centuries before even starting to hollow. It’s also worth remembering that each tree’s lifespan is different. Oaks, for example, can live for between 500 and 1000 years or more, whereas birches or beeches have much shorter lives.
Trees have been doing this for all of their time here on this earth, so this is not new to them. For those of us who are new to this knowledge, it’s more that we will have noticed these things without knowing what we’re seeing. Now that we understand, we can consider trees differently, as sentient and complex beings, living their lives in full and interesting ways.
Bees
So how does this relate to wild colonies, and the trees that bees choose? It’s clear that a veteran tree will be the tree of choice - a fully mature tree will not have developed any cavities, and the empty trunk of an ancient tree will be too vast a space. But, the veteran stage of life happens to small trees with short lifespans, as well as long lived oaks. It’s the hollow branches and trunks of large veteran trees such as oak or ash that are just right. From a bee’s perspective, it’s a good investment of resources to create a nest in something like an oak, where the tree can be home to the colony over decades, if not centuries, if needed. It’s fascinating that the Zeidler tradition of tree beekeeping emulates the habitat of a veteran tree (typically with mature pine trees), shortening the trunk and creating a cavity.
It’s quite interesting to consider how a colony’s presence might affect a veteran tree. The propolis with which the cavity is lined would halt the progress of any fungal decay in that localised area, thus perhaps prolonging the life of the tree.
There are other factors that are of interest to the bees, as well as the size of the cavity. It’s also about the size of the entrance, and to a certain extent the position of the entrance in relation to the sun, the prevailing wind, frost, fog and possible predators. Other factors that play a part include the available forage in the surrounding area, and how sheltered or exposed the tree is. Plus it’s clear that there’s a certain distance a colony can travel to find a new home, so it’s also about how far away the nearest beekeeper (or bee tree) is, and if bees from these hives are able to swarm.
When we are out and about and are keeping our eyes open for bee trees, how do we understand a tree as bees might? Even knowing about veteran trees, it’s clear that not every likely tree will house a colony. And we may see trees that have a colony which would not necessarily have seemed likely or right.
Some Examples
I seem to come across bee trees a lot whilst out recording veteran trees. Actually not all colonies are in trees - I’ve come across some in the stone walls of old churches. Somehow I seem to notice bee trees, even when the colony is high in the canopy, or I encounter a colony after being drawn to visit an area for some reason. With only one exception, I’ve found the colonies to be gentle in nature. There have even been times when I’ve measured the girth of a tree, only to then notice that a colony is living in it. Nowadays, I tend to observe trees for a while before measuring them, and contemplate what’s happening in the tree’s life. The more I stand and observe a tree, the more I understand. I approach the tree with an open heart, being there for a purpose but being open to learn.
Sometimes I ask the tree, is there anything you’d like to show me, that I might not have noticed?, and it might be then that I’m drawn to look at a particular branch where a bee colony is living.
Here, I’ll set down a few examples of veteran/bee trees, that may not be obvious ones.
There’s a field of veteran oaks in Essex, most of which died following a North Sea flood in 1953 (14). They have many cracks, hollows and holes, and many of them might seem a really likely choice as a bee tree. But the area is exposed, isolated, and with little obvious forage. There don’t appear to be any colonies here.
14. The Mundon Oaks, Essex.
Another example is of a fallen ash tree I came across, the day after a major storm in September last year (15) - it looked fairly dramatic! As I approached the tree I realised that a wild colony of bees was milling about around the base of the tree. Obviously this tree was their home, and their routine and lifestyle had been instantly disrupted. The fallen trunk revealed several types of fungus, and there was a noticeable large area of discoloured wood in the heart of the trunk (16 and 17). Obviously, it had only been a matter of time before this tree fell. I observed from afar, though what I really wanted to do was go right up to the cavities on both stump and trunk for a good close look. I wondered if the bees would survive. I thought the tree might, as it already had small points of epicormic growth on the non-fallen trunk (15), and would have had a good root system in place to support full growth. I returned to the tree this summer, glad to see that the tree was alive, and, thoroughly thrilled to see that the colony were still there! They had survived the winter, and are still living in the short trunk (18).
15. The freshly fallen ash tree.
16 and 17. The trunk, with a cavity and a
large discoloured area of rotting wood.
18. The remaining tree, still alive the year after the storm.
This tree might not seem like an obvious bee tree on first glance and it was tricky to imagine what the original entrance might have looked like. I’ll return to it over the winter to get a closer look at the entrance. The tree is in an open position, but with dense forestry plantation to the side. The entrance faces the north-west, away from the prevailing winds.
This last example is of a bee tree in a sheltered position, within a forest (19). It’s a dead oak tree, and the bees are using one of the large splits on the trunk as their main entrance. The trunk is hollow at the top, and you can actually see daylight through it. Within the trunk will be accumulated debris (12), but there’s obviously a really good cavity there. This photo was taken in the spring, which I find is the best time to notice bee trees. The leaf cover of the trees is not too dense, so doesn’t hide entrances that are tucked away somewhat.
The bees tend to be really busy as the year starts and when the sun catches them they look like dots of light.
19. A forest bee tree.
What next?
I think it’s clear that our veteran and ancient trees are of key importance as homes, or potential homes for our wild honeybee colonies. As our understanding and awareness of these trees grows, we’re starting to recognise, respect and protect them so that they’re able to live out their lives to the full. So the tree side of the situation is underway.
Some readers will have seen and perhaps will be monitoring wild bee colonies, and there are wide networks of people who look out for veteran and ancient trees. Is there a way in which we can share this knowledge, pool our resources, so that we develop a greater understanding of how widespread our wild colonies are, and actually what they are? Can this be done in a way that doesn’t put the colonies at risk, but brings about a way in which they can be recognised and protected? If there are risks linked to making the information openly available, then these should be identified and addressed. Certainly the benefits of recording our wild colonies are huge, and we have much to learn from observing bees who live in their wild and natural state.
What I’d love to see come about, is a way that we can record information about the wild colonies with information that is consistent and of good quality. If we can standardise what observations are relevant, consider guidelines for recording, and find ways to draw together our findings, then that’s a start. In the meantime, let’s visit our local veteran trees, spend time there, and have a new appreciation of them in all their wisdom and beauty. Maybe one day they’ll be a home for bees....
Helen Leaf, PhD, is a craftswoman, guided walk leader, and ancient tree verifier
for the Ancient Tree Inventory. Her ongoing time recording trees in Sherwood
Forest can be found on www.theoaksofsherwood.com/
Suggested further links:
The Ancient Tree Forum http://www.ancienttreeforum.co.uk/
The Ancient Tree Inventory https://ati.woodlandtrust.org.uk/
The Woodland Trust https://www.woodlandtrust.org.uk/
First Publish in issue 13 Natural Bee Husbandry
All photos and text copyright Helen Leaf