It might sound simple, but trees are without doubt one of the things which makes me happiest in this world. Their architectural limbs during winter; that joyous first flush of green in the springtime; the cacophony of life they support in the summer and the glowing hues of autumn – all through the year they can lift the spirit into their boughs. Here are a few of my favourite photographs from 2018.
Thermal imaging technology works by recording the infra-red energy emitted from surfaces – this doesn’t rely on a light source like typical infra-red photography, but instead measures the radiation given off by both living an inanimate objects. The camera can measure the temperature of these items and display a ‘thermal’ image which shows the gradation and variation between different objects within the field of view. In simple terms – it can show a hot object as white/red whilst cooler objects would be shown as green or blue.
In mid-summer, social bees produce a high density of very busy insects in the nest, so it was no surprise that they stand out a mile on a thermal camera! It was also exciting to be able to understand what individual bees had been doing – for example their temperature signature differentiated those who had recently returned to the nest from those who were standing guard and checking in new arrivals.
Wild Honey Bee Nest
We often encounter honey bees when out looking for tree roosting bats in woodland and this was a prime example! Whilst honey bees are often kept in hives, they can establish wild colonies in features such as this.
I took the following images around sunset so the tree itself was cooling but you can immediately see just how hot the inside of this tree cavity is compared with the surrounding wood. The temperature reading inside the nest was 33 degrees Celsius, whilst the surrounding tree barn dropped to around 25 degrees.
Even at sunset, honey bee workers were still returning to the nest and you can see the white-hot glow of these warmer bees compared with the much cooler bees at the entrance. What is also interesting is the pattern of heat in these recently-flown bees – the flight muscles are in the thorax where the wings are attached and this part is much hotter than the abdomen as you can see more clearly in the video below.
The thermal image gave a nice opportunity to watch guard behaviour in action – some honey bees will take the roll of guarding the nest entrance, positioning themselves on the edge and checking returning bees to ensure that they are welcome. The thermal footage clearly differentiates those bees who have recently flown from those which have not, and you can see the much cooler guard bees intercepting the warmer returning workers as they pass by.
If you’re interested in guard behaviour, you might also like this post from a couple of years ago regarding this behaviour in hornets!
These images and videos come from a bumblebee nest which was situated underneath a loose cobble in the courtyard of our office.
I think the bumblebees are either white-tailed (Bombus lucorum) or buff-tailed (Bombus terrestris) bumblebees – this photo shows one of the worker bees returning with well laden pollen baskets.
The thing that I found most surprising on the thermal footage to see just how hot this cobble got compared with those around it, even though the nest is buried beneath! I assume this is due to the heat rising with the warm air from the next and heating the stone as it passed by.
As with the honey bees, you can see how much warmer the active bumblebees are compared with their environment. Bumblebees have a good degree of control over their temperature. The hairs on their body provide some insulation and they can use their flight muscles – uncoupled temporarily from their wings – to warm themselves up before taking off. This uses the same technique as they use for buzz-pollination of some flowers. This video gives an idea of just how much heat these muscles can generate, allowing some bumblebees to remain active through the winter, flying at temperatures of just 10 degrees Celcius. You can read more about bumblebee thermoregulation here!
The different layers within a woodland are one of those classic illustrations from ecology textbooks – usually a cartoon graphic showing how the structure changes as you move from the ground up to the canopy. The distinctions are indicative – there is often plenty of overlap between the layers – but these are a useful way of thinking about the woodland in terms of its ecological function beyond what simply meets the eye. Helping you to see the wood for the trees, if you will!
We undertake tree climb and inspect surveys for bats in a variety of settings – from individual trees in gardens to well-spaced parklands and dense woodlands. Each of these gives a different insight into vertical variation but a recent climb in an oak and ash woodland gave a nice opportunity to illustrate how this changes in a typical ancient woodland habitat.
The number of ‘layers’ and their distinctions vary between sources and across countries – I’ve seen three defined layers, nine defined layers and every number in between delineated in various graphics. I’m going to keep this simple and focus on the three broad categories which are shown in these photos:
Field Layer – taken at 2m height
This photograph encapsulates what could be considered the field layer, the ground layer or the forest floor depending on which divisions you use. Broadly, this is the view from the ground – the most apparent vista for most visitors to the woodlands but the scene varies greatly as the year progresses. In secondary woodland or more botanically diminished sites, this can be a mass of ruderals such as nettles, cow parsley and bramble whilst some plantation woodlands can be head-high in bracken. In ancient woodland – such as this – springtime sees a flush of ancient woodland species which time their flowering early in the season before the canopy closes overhead. As May arrives and the trees and shrubs come into leaf, the main event on the forest floor is already coming to an end. Some species flourish later in the season but in September, the vegetation has largely died back often leaving a relatively bare floor. The dominant vegetation remaining is therefore the trunks of the trees and the shrubs which rise above the field layer to leaf and flower higher.
Scrub Layer – taken at 6m height
This could be described as the under-canopy, the scrub layer, the shrub layer or the under-storey layer. This is the level at which the shrubs flourish – those smaller woody species which often include hawthorn, blackthorn, hazel, holly, dogwood and elder, amongst others. These shrubs can often form such a dense canopy that the view to the treetops above can be quite obscured – something of an issue when you’re searching for bat roosts! In this instance, hazel and hawthorn dominate and as the photograph shows, they form a dense and highly cluttered environment some 6m above the ground.
Canopy Layer – taken at 12m height
This is up at the top of the trees, where the taller trees branch and close their canopies to claim first use of the sunlight available. I’m not right in the canopy in this photograph – the trees did not require us to climb to the peaks – but this nicely illustrates the shrub layer below with the high canopy of the oak and ash above. In some forests, the species composition includes a sub-canopy of smaller trees – such as rowan, silver birch and field maple – which form a layer between the lower shrubs and the taller climax species. This photograph nicely illustrates how much of a space can open up between distinct layers within the higher reaches of the forest structure.
Why does it matter?
An appreciation of how the character and conditions of a woodland change on a vertical plane are just as important, although a little harder to appreciate, than the variation on the ground. The illustrations above are for just one section of just one woodland and each type of species composition but they help to give a visual idea of how this works.
One example of how this type of variation is important is when considering how bats might use a habitat. Different species of bat have different hunting characteristics and habitat preferences, and this often relates to how open or cluttered a habitat is. Species such as brown long-eared are highly maneuverable and will glean insects from leaves so a reasonably cluttered woodland environment suits them perfectly. At the other end of the spectrum, a noctule hawks in open space, often flying over fields and catching its prey on the wing. Species such as pipistrelle are typically characterised as edge specialists which forage along woodland edges, hedgerows and other similar environments.
The field layer of the woodland looks ideal for a species such as brown long-eared but you might think that it would be too cluttered and enclosed for other species. However an insight into the structure above the shrub layer reveals a mosaic of open space and leaf cover which provides perfect ‘edge’ habitat for a hunting pipistrelle, and the voids between the trees would be perfectly navigable for a noctule in search of a roost. This was the subject of a talk by Ian Davidson-Watts at a recent BCT Bats and Woodland conference which you can read more about in this blog post here.
If you’re looking for tree climb and inspect surveys for bats, do check out this page for further details!
Looking back through the photographs I’ve taken in 2016, it’s striking how many trees there are! As with the small things such as wildflower ‘weeds’, it’s easy to take for granted these enormous beings which grow amongst us. The sheer scale of a mature oak or beech is far beyond our magnitude of experience, as is the timescale they can span which numbers many of our lifetimes combined.
Here are just a few of my favourite encounters from 2016.
Every week this year, with just one or two exceptions, I’ve taken part in the excellent #wildflowerhour on twitter where people across the UK share their sightings for the week between 8-9pm each Sunday – an excellent way to draw a weekend to a close.
Many of these photos made an appearance at some point but this is a run-through a few of my favourite wildflower finds or photos from 2016. The absence of orchids can be explained by a whole post all of their own from earlier this week – take a look here!
If you are interested in commissioning botanical surveys in the midlands, you can check out Landscape Science Consultancy’s website here!
On the last day of November, the decadence of summer is long gone. The flowers and leaves, butterflies and bees were so easy to take for granted until autumn and then winter take them from us. But every season has its own treasures and the wind-whipped, leaf-stripped trees are on glorious display across the countryside.
One thought which always strikes me when I see winter silhouettes, is how amazingly adept trees are at achieving their structure in an infinite number of ways. A line of trees planted together will each grow to maturity in a different form. The form will be dictated by species, by sub-species perhaps, by individual genetic variation, phenotypic plasticity to adapt to the conditions, defense responses to biotic attack or abiotic damage such as frost and wind, competition avoidance strategies and more besides. There are as many answers as there are trees to the simple question of how to be upright. And whilst the tree is growing, the process is never complete as the tree grows adaptively to maintain its balance and posture with continual interaction with their environment.
One recent 2015 study put an estimate of 3 trillion on the number of trees in the world. The mind boggles to even begin to comprehend the variety and scale which this number encompasses, but here are nine examples from my walk near Muston Meadows at dusk this evening.
I wanted to share a rather unusual video clip which I captured on a trailcam recently. I know mink to be good swimmers but I did not realise they were tree climbers! Various sources suggest this is a known behaviour, with some suggesting they climb regularly whilst others suggest rarely. One website states that they frequently climb to escape predation although there is nothing to suggest that this was the case in this video.
One of the best applications of a camera trap is when it allows you to observe something unusual or unexpected which could not otherwise be obtained without hours of watching and waiting. I think this clip is a perfect example!