Long Term Project - Oak woodland deadwood

Deadwood terminology 

I live in an area of Britain that has a relatively high coverage of woodland and the Forest of Dean is renowned for its historic production of oak timber. I was curious to know what happens to oak deadwood, something happens otherwise the woods would be choked with deadwood. So back in 2006 I compiled a list of 5 desirable oak deadwood subjects each one underpinned by a compelling narrative. In hindsight it looks very much like a wish list compiled by someone completely ignorant of reality. Which is why this post is more of an update than anything approaching a coherent body of work.

A wind blown oak readjusting growth to its horizontal position

No 1 of the Oak Woodland Deadwood list was a photogenic native mature tree snapped by a storm that would provide a pollarded trunk to regenerate from and a wind thrown crown to decay.  Mature oak trees, at least in the woodlands I visit, appear to require winds associated with a major significant storm event to snap a mature tree. That major significant storm event has yet to happen, so what actually happens is that the trees are blown over and more often than not, enough root system remains in the ground to keep the tree alive.

A storm damaged native tree ~ Ballochbuie Forest, May 2014

A mere 8 years after writing that I finally chanced upon a group of storm snapped mature native trees: Scot's pines in Ballochbuie forest in Scotland after a particularly stormy winter 2013/2014. One damaged tree trunk had a single remaining trunk branch that may be enough to sustain the the tree, in which case it might grow into a pollard or it may die, a future visit will confirm its fate

Harvested oak, Forest of Dean ~ March 2007

No 2 on the wishlist were the stumps and brashwood left from a harvesting operation. Fortune played its part as in March 2007 oak timber was harvested from one area of the Forest of Dean and the branches left for biodiversity, a decade on the twigs and smaller diameter branches have decayed, the larger diameter branches are still 'firm' to touch. Browsing herbivores eventually killed off any regrowth from the tree stumps and aside from colonisation by bryophytes there's no dramatic evidence of decomposition of the oak stumps. I subsequently learnt that oak stumps take up to a century to rot down and wild boar will expend no little energy in uprooting a sizeable oak stump in the quest for an as yet unknown desirable foodstuff, that I am guessing might be truffles. Making a photographing record of an oak tree stump decomposing has been abandoned.

Oak branches from March 2007 harvesting operation showing Class 2 and 3 decomposition stages ~ October 2016

Hopes of photographing a branch in situ in open access woodland have been dashed by the fallen wood being moved to build shelters, bike jumps, disappeared (perhaps sawn up for firewood?) or moved by some unknown agency for some unknown purpose (wild boar rooting around?).  So instead there has been a record made of fungi that have appeared on the 2007 harvesting debris.

Pluteaceae fungi on March 2007 felled oak branch~ December 2016

No 3 A snag or standing dead tree with a narrative. That narrative has proved elusive mostly due to my ignorance of pathogens or able to confidently assign a cause of death.  Nonetheless the 2006 heatwave might be a contributory factor for the oak mortality on the heavy clay soils. I have also discovered that a dead tree anywhere near power lines, telephone lines, public road, forestry track, cycle track, footpath path or in any location with a conceivable chance of falling on someone would be cut down for health and safety reasons. The snag really needs to be in a remote location or a nature reserve.

Stage 4 decay - loose bark on an oak snag.  

I can say with some confidence that an oak snag can stand for a surprising number of years before falling.

Decay Class 5 oak snag October 2007 it finally fell winter 2013/14

No 4 was for a naturally shed branch. Having learnt the lessons of well managed open access woodland, suitable subjects were searched for in less visited woodlands and nature reserves. Tŷ Canol National Nature Reserve provided the desired subject matter.  I have no idea when the branch fell, but when I first photographed it was class 3 decomposition and in 7 years it doesn't appear to have changed much.

April 2010 

October 2011

March 2015

May 2017

No 5 on the wish list was a dead branch still attached to a living tree. If an oak branch takes a long time to decompose on the ground then a dead branch takes a much longer time to decay away from the ground. One section of branch that died in 2010 there was still some bark attached in Nov 2014. The dead branch was still attached in autumn 2017.

Dead branch ~ November 2014 

At the time it seemed like a good idea, photograph some fallen oak trees, tree stumps and branches then return every so often to record the stages of decay as they unfolded. It's been an interesting journey so far and the oak deadwood project is probably 2/3 way through after 12 years. The management regime of woodland is soon determined by the presence of standing and lying deadwood.

Deadwood in oak woodland ~ December 2013

The importance of deadwood as a habitat resource continues to surprise:

Brussels, 5 March 2018 (IUCN) – Almost a fifth (18%) of European saproxylic beetles assessed so far are at risk of extinction due to ongoing decline in large veteran trees across Europe, a new IUCN report has found.

Due to their dependence on dead or decaying wood, the loss of trees across Europe is the main driver of decline in saproxylic beetle populations. Loss of ancient and veteran trees, tree age structure gaps, degraded landscapes that are unfriendly to tree growth, and indiscriminate felling for spurious health and safety reasons all contribute to the loss and degradation of suitable saproxylic beetle habitat. 

Saproxylic beetles depend on dead and decaying wood for at least part of their lifecycle, and are involved in decomposition processes and the recycling of nutrients in natural ecosystems. They also provide an important food source for birds and mammals, and some species are even involved in pollination.

The Black Wood of Rannoch - October 2016

I had briefly visited the Black Wood of Rannoch, back in May and decided then, that it warranted a return visit(s). Events conspired to present an opportunity to further explore the woodland, during a weeks stay in Kinloch Rannoch, in late October with the potential for autumnal colour.

Surprisingly for a woodland, there is plenty of literature on the Black Wood of Rannoch and the surrounding area. Through documents, surveys and maps, woodland historians have pieced together a history of the wood, identifying major timber felling events and periods of regeneration. Archaeologists have recorded iron working sites, charcoal platforms, lime kilns, saw pits, saw mills and occupation sites, to provide an indication of the level of natural resource exploitation. Scientists have published papers and reports on numerous aspects of the ecology and species that inhabit the woodland. Judging by the number of old painted stakes, marker posts denoting transect lines and new orange spray painted stakes, the Black Wood is an area of ongoing scientific research and monitoring activities.

Granny Pines and regeneration, in the Black Wood

Geology, Glaciation, Climate and Soils

The geology underlying the Black Wood is predominantly Dalradian metasedimentary rocks, though away from streams, bedrock exposures are limited.  The area has been repeatedly inundated by glacial ice during the Quatenary, the last time during the Loch Lomond stadial. The littoral of Loch Rannoch provides evidence for the origin of glacial debris, as amongst the metasedimentary rocks of local origin, are pale speckled granite rocks that originate from the Moor of Rannoch granite pluton to the west of Loch Rannoch. Analysis of glacial landforms has allowed Geomorphologist to hypothesise that an Ice Cap ~1 Km thick, formed over Rannoch Moor during the Loch Lomond stadial, with outlet glaciers spreading out across the landscape. The study of glacial landforms has led some to hypothesise that there were areas of cold and warm based Ice and that the cold based Ice may have preserved relict landforms from previous episodes of glaciation.  When the climate ameliorated, the Loch Lomond stadial glaciers retreated and the Ice Cap down wasted, leaving behind an extensive assemblage of glacial till, morainic debris and glaciofluvial deposits, mantling the land.

Stream exposure of inclined bedrock and riparian woodland

The metamorphic bedrock underlying the woodland is relatively impermeable and rainfall drains through the superficial deposits and soil layers. The Loch Rannoch area receives a mean annual rainfall of ~1.5 metres and higher amounts over adjacent elevated ground. Away from forestry tracks and wandering along animal track ways that contour the slopes, there are a surprising number of spring lines and flushes encountered.

Flush mosses 

The nature and topography of the woodland floor has generated a range of soils: mainly podzols, gleys and peats. The diverse nature of the ground topography and soils has created a mosaic of micro-habitats within the Black Wood of Rannoch, exploited by flora to produce vegetation communities in ground and field layers of: mosses, rushes, sedges, grasses, herbs, shrubs and bracken.

Woodland history

The general consensus amongst woodland historians is that once upon a time the Black Wood extended further west, east and south. The combination of over grazing and unsustainable tree felling, reduced the wood to a core area, with Gaelic place names, Old maps, remnant Scots Pines, hinting at the former extent of the wood. Matters could be far worse, if it wasn't for enlightened individuals in times past, initiating programs of woodland regeneration, but on the whole it has been a case of gradual decline. From 1947 the Black Wood, has been managed by the Forestry Commission and what exists today reflects the good and not so good aspects of the Forestry Commissions management of the woodland, that they in turn took ownership of. Conservation areas, regeneration and expansion of the Caledonian Forest are the good aspects and Management plans are in place to underpin a number of objectives and ambitions.

Scots Pines and Birch

The not so good aspects of the FC's management are being revisited, non native trees removed and native trees of local provenance planted. A significant area of the Black Wood has also been designated as a Special Area of Conservation and Site of Special Scientific Interest, legally protected and specific management plans cover these areas.


Granny Pines

Granny Pine and Birch

The Granny Pines define the special nature of the Caledonian Forest, their size and morphology, adding presence and a visual indicator of a woods age. The Granny Pines in the Black Wood have been dated by dendrochronology to the late 17th C. To my eyes, some of the Granny Pines have a form akin to pollarded Oaks, with large spreading crowns and as with Oak woodlands there is also Wood Sorrel growing beneath then amongst the needle litter. The survival of Granny Pines has been attributed to their unsuitability for timber.

Woodland floor under a Granny Pine

Hummocks

Anyone wandering 'off piste' in native Pinewoods will encounter 'hummocks' and the Black Wood of Rannoch is no exception, with 'Hummocks' covered in bilberry and heather, sometimes with a Scots Pine or Birch tree growing on them. Some hummocks are of a substantial size, others are in an embryonic state, with a blaeberry/moss cushion colonising a pine stump.

Hummock forming on pine stump

As far as I could tell, the majority of 'hummocks' in the Black Wood, do not appear to be erratic boulders blanketed in vegetation and instead are most likely formed from relict pine tree stumps, although a case could be made for wood ants nests also making a contribution. Conventional wisdom suggests the formation of a 'hummock' takes some time and they are a feature of Caledonian Pine woods with a long history of continuous woodland cover.

Hummocks

Bones of the Forest and windthrow

Foresters indoctrinated in 'modern' forestry at the old Forest schools, would no doubt be aghast at the scruffy nature of the Black Wood, there are a visible number of snags and fallen deadwood in the conservation areas within the Black Wood. The snags and windblow are a positive development for biodiversity and the organisms who are dependent on deadwood for habitat. Standing deadwood is a particularly important resource as the decay rate is slower than fallen material on the ground. The slower decay rate in standing deadwood is exploited by different organisms, to those that breakdown fallen wood on the ground, which in turn means increased biodiversity.

The deciduous woodland

A feature of the Black Wood is the prevalence of Birch, Rowan and Willow trees, that add diversity and a welcome splash of autumnal colour. Whilst Birch dominate some woodland areas, it seems that the Rowan trees are good indicators of the grazing level, in one enclosure where deer have been excluded for some while, it is now dominated by Rowan, in stark contrast to the numbers of Rowan trees in the wider woodland. Having typed that there are numbers of Rowan seedlings on the ground under trees where birds have roosted and this might indicate a further reduction in grazing animals/pressure. With very little imagination, it is easy to extrapolate how Highlands woods and the wider landscape might appear with a reduction in grazing of herbivores, to conservation levels.

During the visits, significant numbers of Fieldfares were seen feeding on Rowan berries and blaeberries, plants that rely on avian dispersal and the reason why Rowan saplings, Blaeberry and Cowberry. can be seen growing as epiphytes on Granny Pines.

Fungi

I had anticipated some native Pine woodland specialists and was not disappointed.

Scaly Tooth fungus (Sarcodon squamosus)

Gypsy mushroom (Cortinarius caperatus) and Ostrich-plume Feather-moss (Ptilium crista-castrensis)

Fly agaric (Amanita muscaria)

Unidentified solitary Amanita fungus and Five-ranked Bog-moss (Sphagnum quinquefarium)

I thoroughly enjoyed my visits to the Black Wood of Rannoch, although only exploring a small fraction of its extent, there was still plenty of subject matter to photograph, much to ponder and the unique atmosphere of a native Pinewood in autumn to savour. Definitely a place to return to again.