Posts tagged ‘science’
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
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. 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 (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
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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.
|
dbh |
cd |
cd/dbh |
N trees per ha |
N trees per acre |
Basal Area m2 per ha |
|
0.10 |
4.47 |
44.70 |
500 |
202 |
3.9 |
|
0.15 |
5.35 |
35.67 |
349 |
141 |
6.2 |
|
0.20 |
6.23 |
31.15 |
258 |
104 |
8.1 |
|
0.25 |
7.11 |
28.44 |
198 |
80 |
9.7 |
|
0.30 |
7.99 |
26.63 |
157 |
64 |
11.1 |
|
0.35 |
8.87 |
25.34 |
127 |
51 |
12.2 |
|
0.40 |
9.75 |
24.38 |
105 |
42 |
13.2 |
|
0.45 |
10.63 |
23.62 |
88 |
36 |
14.1 |
|
0.50 |
11.51 |
23.02 |
75 |
30 |
14.8 |
|
0.55 |
12.39 |
22.53 |
65 |
26 |
15.5 |
|
0.60 |
13.27 |
22.12 |
57 |
23 |
16.1 |
|
0.65 |
14.15 |
21.77 |
50 |
20 |
16.6 |
|
0.70 |
15.03 |
21.47 |
44 |
18 |
17.0 |
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
Reference
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
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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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
I took part in the inaugural Ride for Research today; cycling 25 miles around London’s streets, visiting three schools along the way to plant trees with children and to raise money for tree research.
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We visited three London schools en route: two primary schools at Harrow and Islington, and a secondary school at Hampstead. At each school we were welcomed by the local Mayor and enthusiastic children. They learnt a little from us about Acute Oak Decline: the disease that we were raising money to support much needed research into (read more). We planted two trees at each school: either bird cherry or rowan, and an oak.
This was the inaugural Ride for Research that was supported by the UK and Ireland Chapter of the International Society of Arboriculture (ISA). The inspiration came from the ISA’s Tour des Trees in the USA, which has seen over 4 million dollars raised for tree research since it was started in 1991.
Organisers of the UK’s Ride for Research hope that the 2011 inaugural ride will be the start of an annual event in aid of tree research. I had a great time and I am already looking forward to next year’s Ride for Research. A huge thank you to organiser Russell Ball, all the corporate sponsors, my fellow riders, and last but not least to the dozens of people who sponsored me.
Gabriel Hemery
