Posts tagged ‘ash’
Afterlife tool and spoke
Winter ash gale bend and yield
Oak a merest nodGabriel Hemery
During the recent winter gales in England I was inspired to write a Haiku poem. The amazing flexibility of the ash Fraxinus excelsior tree means that its wood is widely used in tool handles, sporting goods such as hockey sticks, and in the spokes of wooden wheels. In this short film made amidst a woodland gale, an ash tree waves and yields by amazing degrees in the gusting wind. Nearby (just visible distant far left) a stoic English oak Quercus robur tree hardly moves.
Gabriel Hemery
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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 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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Ancient ash coppice stool
I featured this ancient ash coppice stool in January.
It had been coppiced to regenerate new growth; a cycle of management that this tree may have been through perhaps a half a dozen times in its life. It attracted my interest because on one of the freshly cut faces of the stump, a member of the public had written with a marker pen:
“This was one our best loved trees. We are sad that you have cut it down” Read more …
I returned to the coppice stool last week, to search for the new growth that I had predicted so confidently in my defense of woodland management.
I was pleased, and secretly relieved, to discover its restoration to life: several tiny sprouts were emerging from the gnarled and hollow coppice stool. See the photo below. Let’s pray that the deer allow these shoots to grow.
Gabriel Hemery
I co-authored an academic paper in 2005 that summarised research undertaken to explore the relationship between a tree’s stem diameter and its crown (or canopy) diameter 1. Out of my 60 or so publications, it has been one of the most popular among forest scientists (e.g. Google Scholar citations).
It was fascinating to discover that statistically there was a very good relationship (scientists would refer to a correlation from a regression analysis) between stem diameter and crown diameter. We decided to explore this further by calculating the ratio between the two, we called it the z ratio (= crown diameter ÷ stem diameter). We then plotted this z ratio against stem size. You can see the result on the graph below for nine common European broadleaved trees.
Crown diameter: stem diameter relationship for nine broadleaved tree species. The z ratio (y axis) is crown diameter divided by stem diameter; the dbh (x axis) is stem diameter at breast height (measured at 1.3m). Click to enlarge graph
The graph highlights some very interesting growth patterns and difference between different species:
- Common walnut (Juglans regia) has the largest crown diameter at any given stage in its stem size. When a walnut stem is 15 cm in diameter its crown can be estimated to be 5m wide. Foresters can use that knowledge to design walnut plantations: e.g. if they plant their walnut trees 5m apart, their crowns will not compete until their stem diameter is 15 cm (which will take about 15 years from planting in the UK).
- Sweet chestnut (Castanea sativa), like walnut, has a very large crown while it is young (with a small stem size). Unlike walnut however, as its stem size increases, the ratio with its crown diameter decreases rapidly to the point after 35cm in diameter, when it has the smallest crown diameter for any of the nine tree species assessed.
- Sycamore (Acer pseudoplatanus) has the most consistent crown to stem ratio while it grows.
The data can be used to plan tree spacings and to calculate basal area. For example: for walnut with a stem diameter of 0.60m, its crown diameter is 13.27m, and its z ratio is 22.12. Using the equation (left) for estimating basal area per hectare (G, m2 ha-1) tells us that there would be 57 trees per hectare with a basal area of 16.1 m2 ha-1.
These findings can be used beyond tree spacings and calculating basal area; they can also be used to help in:
- planning thinning regimes (how many trees to remove in a growing plantation and when)
- planning stand density (how many trees to retain in a forest stand at any given size)
- assisting in managing mixed conifer-broadleaved stands
- estimating branchwood and woodfuel volumes
- maintaining free-growth silvicultural systems, and
- in urban tree planning by arboriculturists and landscape gardeners (e.g. designing and managing tree avenues).
Gabriel Hemery
Reference
1 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
Weatherlore says that if an oak leafs before an ash then we will have a dry summer:
If the oak before the ash,
Then we’ll only have a splash.
If the ash before the oak,
Then we’ll surely have a soak!
An oak tree (bottom left) in leaf earlier than three ash trees at different leafing stages
I wrote previously about phenology in ash and other tree species. This photograph illustrates well the natural variation within species, as well as between species. The oak tree, bottom left, is in full leaf. The neighbouring ash trees demonstrate three different stages of flushing or leafing; from almost dormant (bottom right) to almost fully leafed (top left), with the centre ash intermediately leafed. Elsewhere in this woodland there were oak trees that were less advanced in leafing than some ash trees. This natural genetic variation emphasises the importance of a large data set, such as the observation records collected by the UK Phenology Network, to gain an accurate average leafing date for species.
Every Spring ash appears to leaf before oak ever more rarely, only being earlier than oak four times in the last 50 years. Oak will leaf one day before ash with every 0.25oC increase in temperature, while ash responds more to day length in Spring. In warm Springs therefore, oak will have an advantage over ash. Long-term records, such as the celebrated Marsham record, show that the climate warmed in one local area of Britain over hundreds of years, with observer records showing corresponding earlier oak leafing dates 1.
Next time you hear the well-known “If the Oak before the ash …“, think as well about the ash before the ash before the ash ….
Gabriel Hemery
