Some more tree-related books

…something something I decided to buy more books…

As you’re probably aware, I am currently reading through Vera’s book, and plan to jump straight into Hartel & Plieninger’s book on wood pasture straight afterwards (so to keep up with the very interesting wood pasture theme). The other two books in this image are the very extensive Urban Forests and Trees, and what looks like a very interesting read in the form of Trees in Urban Habitat. It looks at arboriculture in India (specifically New Delhi), and is crammed full of images alongside the text. I, for one, am keen to immerse myself in this book, to gain more of a perspective on arboriculture in other regions of the world.

book purchases trees
The four books in the flesh / paper!
Some more tree-related books

Ganoderma resinaceum on a fallen Salix (willow)

I was driving down near to a local tip site early yesterday morning, and passed a line of willow just within the tip site’s boundary. As I was driving very slowly due to the presence of speed bumps, I was able to commit a little more than just a fleeting glance at them all. Towards the end of the line, I could see a downed willow (due to windthrow), and pulled over after spotting a few fungal brackets upon the lower stem. I admit that I suspected a species of the Ganoderma genus, though hadn’t expected it to be Ganoderma resinaceum, as this is usually found on oaks (Quercus). Nonetheless, from the photos, it certainly appears to be the lacquered bracket, both from the morphology of the brackets and the colouration. Unfortunately, as there was a chain link fence between me and the willow, I could only get some shots on my camera by zooming in, so pardon the lack of closeness on the below images.

ganoderma resinaceum salix 1
We can clearly see three sporophores of the fungus Ganoderma resinaceum, and the exposed wood that has been de-lignified by the white rot the mycelium creates.
ganoderma resinaceum salix 2
A little bit closer in shows us the distinct lacquered surface atop the bracket, and the pore layer below is certainly what one would expect from Ganoderma resinaceum.
ganoderma resinaceum salix 3
Getting as far around as possible, in a bid to see more of the upper surface, we can see even more readily the lacquered surface atop.
Ganoderma resinaceum on a fallen Salix (willow)

Saproxylic organisms, old oaks, and canopy openness

In light (or the lack of, as may become evident!) of reading the first five chapters of Vera’s work in Grazing Ecology and Forest History (not yet done with the book), the recognising of oaks not regenerating under a closed canopy, because of a lack of light (and now you get the joke), is something I’d explore further. An article I found wasn’t quite aligned with this above statement directly, but sounded interesting and thus I’ll share it below. But first, a little wider context.

Often, mature oaks found in regenerating woodlands (because of the abandonment of grazing activities) will have an open-grown crown structure, with a wide-spreading crown from a low stem break, either through pollarding, or natural crown formation. Such oaks are usually very old, and of impressive size. These large trees, by virtue of their size and age, will also be host to saproxylic organisms (insects, fungi, and so on), and such a habitat may very well have also been present prior to the woodland regenerating around the old oaks. Before regeneration, these oaks may have been wholly exposed, or existed in a small scrub area, from which grazing livestock were barred from entering (to protect the tree, in order to safeguard the mast each year). Therefore, one can explore how the change in surrounds to the host trees impacts upon these saproxylic organisms, and what this may mean for future woodland management practices if conservation is a key consideration.

Generally, saproxylic organisms prefer lighter conditions. This is, of course, not true across the board, though particularly for insects, the more open conditions provide for better habitat quality. With regards to the diversity of the landscape, saproxylic organisms may also vary as diversity changes, and therefore the authors of the study being looked at in this post assess: (1) the species composition of saproxylic organisms in old oaks in regenerating thermophilic (temperate) oak woodlands in Krivoklatsko, Prague; (2) species richness in these oaks, and; (3) whether these organisms are affected by tree site conditions (solitary tree, woodland edge, open forest, dense forest). The study looked specifically at saproxylic fungi, lichens,  beetles, ants, bees, and wasps, within the Krivoklatsko area.

From the surveying of fungi and lichens and trapping of arthropods, a total of 78 species of fungi, 36 species of lichen, 153 species of beetle, and 32 species of ant, bee, and wasp, were found. Generally-speaking, open habitats supported a wider and more homogenous fungal species range than closed-canopy locations, where populations were less diverse and less homogenous (as in, the species found were not very similar across all locations). However, fungi did seem to opt more readily for denser stands and woodland edges, in place of generally more open habitats, and in woodland edges species richness was greatest. This is probably because of the moister wood and cooler temperatures, which likely suit fungi more, though woodland edges may also be host to the greatest amount of deadwood as a result of windthrown trees being more plentiful. For lichens, diversity increased alongside the level of openness. Beetles perhaps took this to the greatest extreme, showing preference for open-grown trees. The greatest richness was also found in these solitary trees, followed by woodland edges – open and closed stands were generally poor, for beetle species. The ants, bees, and wasps were shown to prefer transitonal areas where the woodland edge met scrub (an ecotone, or the mantle and fringe), and this may be due to the higher abundance of potential nectar sources associated with shrubby species and herbaceous vegetation not found in the forest. Open forest stands were also supportive of these species, to a similar degree, and probably for the same reasons. The richness of species was also positively correlated with increasing levels of openness (up to a point – not solitary trees), by-and-large. The graphs below help illustrate the above.

saproxylic organisms tree light
The size of the circles relates to the species richness at the studied locations, and the graphs in the upper right corner refer to the weighted species mean in each of the four area categories. Fungi (a), lichen (b), beetles (c), and ants, bees, and wasps (d).

In response to the above data, what can certainly be suggested is whether a non-intervenionist approach to stand management is good, with regards to preserving saproxylic organisms; of which many are endangered. Ultimately, the goals of the site will dictate management practices, though the idea of leaving stands to become high and possess a dense canopy is not necessarily going to be optimal for lichens, beetles, and ants, bees, and wasps that rely upon deadwood principally (or near exclusively). In this sense, re-introducing management practices, namely coppicing around older trees, or other good saproxylic habitats, may be of marked benefit. Such practices also ensure that actual stand diversity does not shift in favour of, in time, near exclusively (or wholly) shade-tolerant species, such as beech (Fagus sylvatica), Norway spruce (Picea abies), and European silver fir (Abies alba), and also provides scope for re-intoducing lost practices (perhaps even extensive grazing) and revive potentially dwindling economies. If a stand is large enough, this management doesn’t even need to necessarily be widespread. A good mosaic of different habitats, ranging from open ones to higher canopies, may support the greatest number of species (assuming the patches are large enough, and abundant enough), and as mentioned, also support traditional rural practices that have unfortunately been so very lost in many parts of Europe.

At the same time, attention should be given to paving the way for future old oaks, in thermophilic oak woodlands, and as oak cannot regenerate under a closed canopy, the only way to provide for future generations is to re-open the canopy in large enough areas to permit oak regeneration. Given that our large wild herbivores are largely gone, we must assume the role of those herbivores, be it through the introduction of ungulates, or woodland management practices.

This begs the question – why is a non-interventionist approach to woodland management so popular?

Source: Horak, J., Vodka, S., Kout, J., Halda, J., Bogusch, P., & Pech, P. (2014) Biodiversity of most dead wood-dependent organisms in thermophilic temperate oak woodlands thrives on diversity of open landscape structures. Forest Ecology and Management. 315 (1). p80-85.

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Saproxylic organisms, old oaks, and canopy openness

The oak apple cynipid (Biorhiza pallida)

On an oak tree right next to the pear tree I posted about earlier today, I spotted a solitary gall of the oak apple cynipid Biorhiza pallida. Evidently very fresh, it can’t have been forming for more than a few weeks. Certainly interesting to see, as usually I see them only when they’re old and no longer supporting any gall wasp larvae. Don’t pick this ‘fruit’!

Biorhiza pallida oak apple 1
In the very lowest part of the crown, sits this single apple gall.
Biorhiza pallida oak apple 2
Looking more closely, a marked glisten is observable on its structure.
Biorhiza pallida oak apple 3
The terminal buds have evidently deformed, as a result of the larvae and venom injected by the ovipositing female gall wasp (causing the oak’s tissue to mutate).
Biorhiza pallida oak apple 4
Probably the best picture of the lot. I’d say this was around 4-5cm across.
The oak apple cynipid (Biorhiza pallida)

A grand pear tree in full bloom

I was driving through a housing estate earlier on today, and a flood of colour caught my attention enough for me to pull over and have a closer look. I’m glad I did, as what drew my attention was a quite awesome pear tree (Pyrus sp.), clearly mature, and actually rather massive. Old storm damage and the open-grown setting (nothing blocks light to its south) have led to the tree becoming wider than it is tall, and it has got a serious amount of leaves and thus has great photosynthetic potential. Amenity value in ornamental cultivars is often discussed, though the huge value of this large pear tree (pre-dating the housing estate, and probably grown for fruit) in the visual sense, and ecological sense (the number of insects that must frequent this tree is most likely very high), is not even up for debate.

I hope the photos below give some sort of indication as to how lovely the tree was, and I stress that this was indeed a massive tree. For a pear, that is. Some others are dotted around, but not at all of this stature.

pear tree mature pyrus 1
Looking at the pear tree from afar, we can see it is dressed in white.
pear tree mature pyrus 2
From the opposite angle, we can appreciate its crown architecture.
pear tree mature pyrus 3
And closer still, revealing more architectural intricacies. Note the ‘harp limb’ in the foreground.
pear tree mature pyrus 4
If the first few images didn’t cut it, we can see how large the trunk is in this image.
pear tree mature pyrus 5
Thousands upon thousands of flowers!
pear tree mature pyrus 6
Zooming in on a small cluster of flowers from this pear. Very pretty!
A grand pear tree in full bloom

Palynology (pollen studies) and tree history

I’m currently engrossed in Vera’s book Grazing Ecology and Forest History, which I cannot rate high enough for its readability, lucidity, and coherency. Whilst on my holiday last week, I read through the third chapter on the study of palynology and how this relates to interpreting how treed landscapes may once have looked, and I have to be honest when I say that the entire field was somewhat (though not wholly) new to me, and what was suggested within the book certainly made me think. For this reason, I’m going to write a little bit about pollen studies and how it can effectively be used, or even ineffectively used, to determine what our landscapes once looked like, with regards to what trees existed, and in what abundance / distribution, according to Vera.

Vera begins by ‘setting the scene’, by describing how the Swedish geologist, Von Post, in 1916, produced what is considered the first pollen diagram. Prior to the utilisation of pollen, typically accumulated in peat bogs and lakes (which are regional pollen sinks), larger parts of plants were used in an attempt to understand what the landscape once looked like (up until the last Ice Age some 12,000 years ago) – leaves, fruits, tree stumps, and possibly even larger seeds were three means of how the landscape’s vegetation history was being deciphered, and again these were usually found within peat bogs. In this sense, prior to 1916, the vegetation composition of a landscape was being understood through assessing how plant macro-fossils were distributed (vertically) in peat bogs. For example, if a stump of a pine tree was found below the leaves of a willow tree, one could suggest that pine trees existed prior to willow trees in the geographical area. After 1916, pollen, which readily remains desposited in such aforementioned naturally-occurring sinks, could instead be used. Granted, pollen generally only persists for wind-pollinated species, with the exception of poplars, so one cannot, in theory, decipher the exact presence of tree (and plant – grasses, etc) species – one can instead only interpret, based on the facts gathered.

By-and-large, following Von Post’s landmark pollen diagram in 1916, studies into pollen presence had suggested that the landscape was once almost wholly covered in trees (where tree cover was possible, due to biotic and abiotic factors). This is because, when pollen studies have been undertaken, the large majority of pollen found has been from tree species (usually, non-arboreal pollen amounts for no greater than 5-20% of total pollen in the sinks). Historically, and prior to 1934, when Firbas published a paper on how one can also identify and use the pollen of grasses and shrubs to determine landscape composition, there was also a choice to ‘ignore’ the pollen of non-tree species. Because of these factors, scientific opinion was generally that grasslands and wood pastures are an advent of agriculture and man’s influence upon the landscape, in place of wild ungulates (auroch, bison, boar, deer, Przewalski’s horse, and so on) influencing upon the vegetation composition. Therefore, prior to modern man, the European and American landscape was largely void of expansive steppes and pastures, where the land was potentially habitable by trees. The wild ungulates were thus not seen as responsble for carving the landscape, and thus only existed in low numbers within treed landscapes. Instead, these wild herbivores followed the regression and regeneration of trees in the landscape.

auroch bos primigenius
An artistic depiction of the auroch (Bos primigenius). Interestingly, the breeding of cattle in an attempt to re-create the auroch is being undertaken, by breeding characteristically-similar (to the auroch) domesticated cattle and allowing them to exist in the wild. Image source: Open Up!

However, where it gets interesting is when one looks at what tree species were present in the pollen records. Before we look further at this however, we must recognise that the dense forest will generally be host only to shade tolerant tree species (beech, lime), assuming it has reached its ‘climax’ (prior to this climax, more light-demanding species will be present, initially with birch, hazel, pine, willow, and so on, and then with species such as oak). For this reason, if we assume that the historic landscapes were covered with high forest, we can assume that much of this high forest will be of climax species, as man was not historically around to carve apart such landscapes with cattle and for arable activities. Despite this, this is not what the pollen records show. In fact, hazel (Corylus avellana) and oak (Quercus robur) contribute quite significantly to pollen records, and as neither species will regenerate in high forest (because they are not shade tolerant), how is it possible that large tracts of the landscape were high forest? Unless the species were able to regenerate significantly enough in high forests to feature so readily in pollen records, which goes against the species’ understood biology and ecology, there must have existed landscapes where significant light was able to reach the floor. This is where Vera suggests that the landscape could very well have been shaped by wild grazing animals, who kept large areas adjacent to groups of trees or forests open (where there was the ‘mantle and fringe’ vegetation), and the thorny scrub that grew within such a grazed landscape enabled for hazel to grow in thickets and oak to succeed within such thickets (of hazel, and particular thorny scrub, on which ungulates would not generally graze). Oak, in particular, can in modern day be observed not to regenerate in high forest, but in grazed areas amongst thorny scrub (I myself saw this the other day at Dunwich Forest and nearby heathlands, where oak was regenerating not amongst high forest, but within the gorse and bramble scrub).

oak regeneration mantle and fringe
A young Quercus robur growing amongst gorse and bramble, and protected from the impacts of grazing as a result.

Vera also raised concerns over interpreting the high amounts of tree (arboreal) pollen in pollen records as meaning the landscape was largely comprised of trees. This is because the pollen sinks, as already stated, are generally regional (peat bogs and lakes, of which large lakes are more often used). Because tree pollen is released early in the season, and is usually released in high abundance at an elevated level in the canopy, there is a much greater chance of tree pollen travelling greater distances, where it will reach these regional pollen sinks. Conversely, grasses release pollen during the summer, and at levels just above the ground, where winds are less strong and there is a greater chance of the pollen not travelling too far (because of the lower wind speeds, and the trees and shrubs in leaf ‘trap’ the pollen in situ). As a result, a regional sink, such as a peat bog, even if large areas of land, even almost adjacent to the bog, were grassland or pasture that were bordered by trees, there is still a very high probability of non-arboreal pollen not accounting for more than 10-25% of the total pollen distribution in a sample. Not only this, but even if we assume that the landscape was wood pasture where animals grazed, the suppression of the grass by grazing herbivores and the fact that open-grown trees have much larger, fuller crowns, means that pollen ratios between arboreal and non-arboreal sources will likely register as if the area was instead a forest (for example, the total crown area of an area of wood pasture and of high forest may not be all that different). Trees in wood pasture will also have more clearance for pollen to travel great distances, and thus end up in these regional sinks at high levels. Even modern-day records suggest exactly this, and in this sense a wood pasture can be interpreted as, if assessed on pollen records alone, high, dense forest. Of course, this suggests that pollen records only tell part of the story, and it is easy to mis-interpret findings based on pollen studies.

mantle and fringe birch
What could be considered mantle and fringe vegetation (regenerating birch amongst gorse), with Dunwich Forest’s pines in the background. Bear in mind deer (at least) are found on the site, so there is some grazing pressure.

If you have found this post interesting, then please do consider buying the book. There is no way that I can give the whole picture here, and instead I have only given a fragment. Hopefully, it makes sense, and hopefully it gives an indication of why suggesting that the landscape was once comprised of massive expanses of high forest is perhaps not entirely accurate. In the modern day, there is no doubt that grazing by cattle has suppressed the regeneration of forest, and man’s conservation efforts with heathlands and grasslands has also stopped forest regeneration; as has man’s carving-up of the landscape for building and development. However, historically, when wild herbivores were still actually in existence, as man hadn’t pit-falled the last auroch to its death, the landscape may have not been covered exclusively by high forest where conditions allowed. Considering that fire is not seen as a massive driver behind the regression of forests to grassland and then back to a form of woodland at a later date, and the beaver is not considered to have been the only mammalian influence behind the loss of forest patches (again, according to Vera and the sources he immersed himself in), perhaps wild ungulates had more of a role in shaping the landscape than is generally considered. Food for thought, no doubt. Graze on that literary resource, and head out for pannage in your local library.

Source: Vera, F. (2000) Grazing Ecology and Forest History. UK: CABI Publishing.

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Palynology (pollen studies) and tree history

A collection of Kretzschmaria deusta shots from Dunwich Forest

Dunwich Forest is laden with planted pine trees that are thankfully being cleared by the Forestry Commission, in order to enable for regeneration of broadleaved woodland and heathland (would this perhaps instead be regression?), and subsequent re-wilding. Adjacent to the monocultured pine stands, which comprise large tracts of the site, reside some mixed broadleaved woodland, from which seedling regeneration will no doubt stem – beech (Fagus sylvatica), birch (Betula pendula), and oak (Quercus robur) are three species that exist in more discernible numbers, and regeneration of the light-demanding species birch and oak can already be seen amongst the gorse (which F.W.M. Vera would dub the ‘mantle and fringe’ vegetation, and something which is to be entirely expected). Heathland will also regenerate, with assistance of grazing ungulates and human management processes, to provide habitat for gorse (Ulex europaeus) and heather, amongst other species.

Anyway, the history and management of Dunwich Forest, whilst interesting, is not the point of my post. Instead, this post is to showcase a few examples of Kretzschmaria deusta, which I spotted on a few beech trees in close proximity to one another, alongside the road that cuts the Forest in half from north west to south east. The photos below are from three trees, which I am sure you’ll be able to discern apart from one another.

kretzschmaria deusta ustulina fagus 1
Look to the bottom left buttress.
kretzschmaria deusta ustulina fagus 2
As we can see, the fungus Kretzschmaria deusta can be seen to be producing sporophores within this buttress. The outwardly healthy wood atop that extends out quite markedly suggests that perhaps reaction wood has been laid down, in response to the decay.
kretzschmaria deusta ustulina fagus 3
From the other side of the stem, we can see how the root (to the right) is quite significantly jutting out from the tree’s stem.
kretzschmaria deusta ustulina fagus 4
On this beech tree, we can observe how the fungus has colonised the basal region in an area where dysfunctional wood is exposed.
kretzschmaria deusta ustulina fagus 5
A little closer in this one, and we can really spot how easy it is to recognise the fungus in its active stage (grey and white colouration).
kretzschmaria deusta ustulina fagus 6
Looking in even more closely, there appears to be a lot of ‘spent’ sporophores around the currently active ones.
kretzschmaria deusta ustulina fagus 7
The third beech is perhaps the most interesting. A large stem wound, stretching up to nearly 3m in height, is fully colonised by Kretzschmaria deusta. This is different, as in my experience I have only observed the fungus at heights of below 1m on the stem. Usually, it’s only around the butt. Not so here, of course.
kretzschmaria deusta ustulina fagus 8
The lowest part of the wound,
kretzschmaria deusta ustulina fagus 9
Moving up towards the central region.
kretzschmaria deusta ustulina fagus 10
Slightly above the central region.
kretzschmaria deusta ustulina fagus 11
Zooming in up to much nearer the top. Still, we can see active and spent sporophores.
A collection of Kretzschmaria deusta shots from Dunwich Forest