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Posts tagged ‘science’

Talking resilient woods on BBC Radio

Gabriel Hemery being interviewed for BBC Radio 4 Farming Today, 11 September 2015

I was interviewed recently about work I am helping lead on the British Woodlands Survey with the Sylva Foundation— this year exploring adaptation to environmental change. The piece was featured this morning BBC Radio 4 Farming Today.

Gabriel Hemery being interviewed for BBC Radio 4 Farming Today, 11 September 2015

Gabriel Hemery being interviewed for BBC Radio 4 Farming Today, 11 September 2015

I had arranged to meet BBC journalist Ruth Sanderson at the University of Oxford’s Wytham Woods, perhaps one of the most studied woodlands in the UK, along with its Conservator Nigel Fisher. It was an ideal location to discuss environmental change and how woodland owners can respond, especially given the breadth of research underway in the woodland. I have supervised the work of two Oxford graduates in Wytham Woods; the first studied cord-forming fungi, and the current student is researching ash dieback.

BBC Radio 4 Farming Today

BBC Radio 4 Farming Today

You can listen to the programme again here.

If you own or manage a woodland, or work as a professional in the forestry sector, the Sylva Foundation and its partners are keen to hear your views about environmental change. Please do try to find the time (15-20 minutes) to complete the survey.

Please take the survey

Crowdsourcing questions for global project

July 16, 2014

Gabriel Hemery

Gabriel Hemery - one question for T20Q

Gabriel Hemery – one of my questions submitted to T20Q – have you submitted yours?

I am currently working on a global crowdsourcing project T20Q, which stands for Top 20 Questions for Forestry and Landscapes. T20Q encourages the forestry community to pose what they consider to be the key questions that should guide research and policy.

If you work in forestry, or have an interest as a business professional, student or retired individual, the project team are keen to hear from you. So far over 1000 questions have been received from more than 70 countries. Why not have your say? Visit the T20Q website.

I was interviewed recently by journalist Julie Mollins. Read the interview on the Global Landscapes Forum

T20Q is a project run by multiple partners. The website is hosted by the Sylva Foundation at:

Global forest cover change 2000-12

Global Forest change Earth view

This month a team of scientists published a paper in Science that quantifies global forest change, releasing a phenomenal online resource that is both beautiful and terrifying in equal measure.

The scientists from the University of Maryland used Earth observation satellite data to map global forest cover, discovering that while there had been a gain of 0.8 million square kilometers over twelve recent years (2000-12), almost three times as much forest cover had been lost (2.3 million square kilometers) in the same period.

Data on the high resolution (30m resolution) interactive map, powered by Google, are beautiful to look at, and the amount of forest, shown by green around the Earth, is awe-inspiring. The UK appears dark in colour given its sparse forest cover (read more) but zoom in and it is possible to see the relatively stable forest cover across much of the country, and even the activities of felling and replanting (shown by purple) in southern Scotland.

Elsewhere, hotspots of forest cover loss are easy to spot in red. Tropical forests exhibited a significant trend in forest loss, with rates of loss increasing by 2101 km² per year, with Boreal forests experiencing the second greatest loss of forest cover. Specific geospatial impacts can be seen on the map when zooming into some areas. One example highlighted by the authors is of Borneo, where Malaysia to the west has logged much of its land, the patterns of forest loss clearly following logging roads, while to east in Indonesia the forests look relatively stable. Another example shows loss of Boreal forest cover from man-made fires in Yakutsk.

Seen in this way, losses of forest cover are represented very powerfully. Not as much of course as when witnessed on the ground, as in the destruction of wildlife habitat, or impact on the livelihoods of indigenous people, but perhaps in a way that may help those working strategically to reduce deforestation, giving them potent visual statistics to support their vital work.

Visit the Earth engine Global Forest change map

Hansen et al. (2013) High-Resolution Global Maps of 21st-Century Forest Cover Change. Science, Vol. 342 no. 6160 pp. 850-853. View abstract

A hidden world of fungal cords

April 28, 2012

Gabriel Hemery

Fungal cords running between a rotting silver birch log and the leaf litter on the forest floor

Next time you crunch or squelch through a rich leaf litter under trees, stop and get your eyes down to the forest floor. Carefully tease apart the rotting leaves, twigs and decaying branches and you may be lucky enough to see some fungal or mycelial cords.

Fungal cords running between a rotting silver birch log and the leaf litter on the forest floor

Fungal cords running between a rotting silver birch log and the leaf litter on the forest floor

Quite a number of saprotrophic fungi, particularly the wood-decaying Basidiomycetes (e.g. including some of the stinkhorns, bracket fungi, or puffballs), can form mycelial cords. Cords are collections of  hyphae that aggregate to form long cords. These cords can create vast webs across the floors of forests, in both temperate and tropical regions, where they link nutrient resources together.

Fungal cords and hyphae on a decomposing silver birch log on the forest floor

Fungal cords and hyphae on a decomposing silver birch log on the forest floor. One cord can be seen top right linking to the leaf litter. Bottom left, visible as a network of dark strands, are probably the cords of the Honey Fungus Armillaria mellea

The cords can be visible as creamy white strands, varying in thickness from thin cotton threads to chunky spaghetti. Carefully roll over a well-rotten log (don’t forget to roll it back afterwards) and you may see cords running from the leaf litter on the forest floor, and onto and into the log . Sometimes you may find rotting leaves stuck together by tiny nets of white threads. Cords also travel at the surface of the soil, running along underneath a carpet of leaf litter, where you can track them to their source; often a substantial rotting log.

Fungal cords running along underneath the leaf litter

Fungal cords running along underneath the leaf litter (cleared away for the photograph). The cords rarely penetrate the soil.

It is thought that fungal cords play an extremely important role in recycling carbon and mineral nutrients, but little is actually known about their diversity and behaviour; for instance it is thought that fungi species that form cords can be highly competitive. Their ability to redistribute nutrients across the forest is extremely important but only just beginning to be understood and appreciated.

Gabriel Hemery

These photographs were taken during fieldwork where I was assisting the Sylva Foundation’s scholar, Kirsty Monk, in her DPhil research programme read more

Basal Areas for common walnut

December 27, 2011

Gabriel Hemery

common walnut basal areas

There are no published Yield Class tables for common walnut Juglans regia – at least that I am aware of. A search on the European Forest Yield Tables Database reveals that data are only available for black walnut Juglans nigra in Hungary.

I wrote previously about research that I undertook exploring the crown sizes of major hardwood species – Estimating tree crown size. This work provides the next best available data on managing a stand of common walnut, in the form of basal areas for common walnut ref.

The table below shows the stem diameter (dbh), crown diameter (cd), crown/stem ratio (cd/dbh), number of trees per hectare (Nha) and acre (Nac), and Basal Areas (G) in m2 per hectare. These data were collected from trees grown in open conditions, and calculated for stand densities with zero crown overlap.




N trees per ha

N trees per acre

Basal Area m2 per ha















































































common walnut basal areas

Common walnut Juglans regia basal areas with dbh.

A growth rate of 1cm per year in stem diameter can be presumed, permitting this graph and data to be used in estimating suitable basal areas at different stand ages. If real dbh data is available, then the accurate growth rates will provide accurate basal area increase projections for a given site.

Gabriel Hemery


Hemery, G.E., Savill, P. & Pryor, S.N. (2005). Applications of the crown diameter – stem diameter relationship for different species of broadleaved trees. Forest Ecology and Management 215, 285-294. View abstract

How big will this tree grow?

June 15, 2011

Gabriel Hemery

Many people are interested in how big a tree’s crown will grow. It can be important in planning gardens, managing street trees, forest silviculture and in assessing the health of ancient trees.

Estimating tree height is very imprecise as it is dependent on so many different factors.  However, I wrote recently about the very good relationship statistically between a tree’s stem diameter and its crown diameter (read more).  I have received several requests for more information, and for this to be presented in a way that could be used by those who care for and manage trees.

So I have reworked the graph to produce a simple plot of tree crown diameter and stem diameter for the following nine species: ash (Fraxinus excelsior), beech (Fagus sylvatica), silver birch (Betula pendula), wild cherry (Prunus avium), sweet chestnut (Castanea sativa), oak (Quercus robur & Q. petraea) poplar (Populus spp.), sycamore (Acer pseudoplatanus) and common walnut (Juglans regia).

tree crown diameter and stem diameter graph

Tree crown diameter and stem diameter for nine broadleaved species. Click to enlarge.

Here is a simple summary of the same data in a table, presented in 0.10m stem diameter (dbh) increments.

crown diameter (m)
dbh (m) walnut ash oak sweet chestnut wild cherry beech sycamore silver birch poplar
0.10 4.47 2.65 2.50 3.86 3.30 2.52 2.48 2.58 2.71
0.20 6.23 4.54 4.28 4.93 4.84 4.10 4.37 4.19 4.60
0.30 7.99 6.43 6.05 5.99 6.38 5.67 6.26 5.81 6.50
0.40 9.75 8.32 7.82 7.06 7.92 7.24 8.15 7.43 8.39
0.50 11.51 10.21 9.59 8.13 9.46 8.82 10.04 9.05 10.29
0.60 13.27 12.10 11.36 9.19 11.00 10.39 11.93 10.67 12.18
0.70 15.03 13.99 13.14 10.26 12.54 11.96 13.82 12.29 14.08

The data for this work was collected from open grown trees.  Note therefore that trees grown in forest conditions, where they will have been affected by light levels and other competition factors, will not follow closely the data presented here.

I hope that this data may prove useful for those who are interested in scoring the condition of ancient trees, in planning tree avenues, and in garden planning or landscape architecture. Remember that the results presented here are based on peer-reviewed scientific work: if you want a reference for this work you can find it in my previous post on this subject (click here).  Let me know if you find a use for this data.

Gabriel Hemery

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