Posts tagged ‘silviculture’
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
The Christmas tree – or albero di natale, arbre de noël or sapin de noël, árbol de Navidad, árvore de natal, coeden nadolig, crann Nollag, jólatré, joulukuusi, juletre, julgran, kerstboom, Tannenbaum or Weihnachtsbaum, новогодняя елка and χριστουγεννιάτικο δέντρο – is a celebrated icon of Christmas around the world. It is perhaps the only time that most people really hug a tree as they struggle to get one through the front door!
A brief history of the Christmas tree
According to Wikipedia the first records of Christmas trees are from Northern Germany in the 15th Century. Trees were initially decorated with sweets (candies) and red paper. Tinsel was invented in Germany around 1610 using real silver. The first record of Christmas trees in America was in 1747, where a tree was provided for children in a Moravian Church settlement in Bethlehem, Pennsylvania. Prince Albert is credited with bringing the first Christmas Tree to the British royal family; an article appeared in Illustrated London News in 1848.
Top selling trees in North America
Results of one online poll, reveals that the top five ranking Christmas trees in the USA are led by Fraser Fir (33%), followed by Douglas Fir, Balsam Fir, Colorado Blue Spruce and, in fifth place, Scots Pine. The National Christmas Tree Association sell 25-30 million Christmas trees every year in North America. The trees are grown in Fifty states and in Canada, offering a green alternative to the plastic variety (of which 80% are made in China).
Perhaps the most famous Christmas tree in the US was harvested recently on 17th November, to be delivered to the White House. The US President will be receiving a 5.8m (19 foot) balsam fir, harvested from a farm near Neshkoro in Wisconsin (read story).
Find Christmas tree retailers in Canada
Find Christmas tree retailers in the USA by state
Top selling trees in Europe
Christmas tree guide from the BCTGA. Click for pdf version
In Europe the Nordman Fir is the most popular Christmas tree although recently the Fraser Fir has been increasingly available and is proving ever more popular. Denmark is the biggest European exporter of Christmas trees, and their association was famously fined in 2007 for operating a cartel (read more).
In Britain alone there are many hundreds of growers who specialise in growing Christmas trees. There are 320 members of the British Christmas Tree Growers association, who together sell 8 million trees a year (BCTGA website).
British Christmas tree growers who sell online
How to grow Christmas trees
Christmas tree growing can be a lucrative business but is unforgiving on quality, as second grade trees will not sell. Growing the trees is more like a slow agricultural crop than a fast forestry crop. A typical rotation is 5-7 years for standard sized trees, although some growers specialise in the tall trees sold for town centres and large buildings.
Site selection is important, particularly avoiding frost prone sites as buds can be damaged by severe late frosts. Soils should not be too acid, or heavy clay, chalk or very sandy. If too fertile the trees will grow too fast and be ‘leggy’, requiring expensive efforts to trim and encourage suitable form; a technique called “shearing”.
The crop must be protected from browsing mammals, whose activities will adversely affect tree form; rabbit and deer proof fencing is normally required. Sometimes insect pests will need to be controlled (Blue spruce is very prone to aphids) and specialist advice should be sought by growers.
Christmas trees are normally planted at 1x1m (10,000 per ha / 4200 per acre) or 1.2×1.2m (6900 per ha / 2900 per acre). Two or three year old trees are normally planted when dormant. Weed control is extremely important in following years, not only to ensure good tree survival and growth, but also to minimise competition that could lead to poor form on the tree’s lower branches.
Gabriel Hemery
Popular Christmas tree species
- Abies balsamea — Balsam Fir
- Abies concolor — White Fir
- Abies fraseri — Fraser Fir
- Abies procera — Noble Fir
- Cupressus arizonica — Arizona Cypress
- x Cupressocyparis leylandii —Leyland Cypress
- Juniperus virginiana — Eastern Red Cedar
- Picea abies — Norway Spruce
- Picea obovata — Siberian Spruce
- Picea pungens — Colorado Blue Spruce or Blue Spruce
- Pseudotsuga menziesii var. menziesii — Douglas Fir
- Pinus contorta — Lodgepole Pine
Saint Swithin window at York cathedral
It is Saint Swithin’s Day today, 15th July: the day on which people traditionally watch the weather. Tradition says that whatever the weather is like on St. Swithin’s Day, it will continue the same for the next forty days.
There is a well-known weather-rhyme in Britain:
St. Swithin’s day if thou dost rain
For forty days it will remain
St. Swithin’s day if thou be fair
For forty days ’twill rain nae mair.
St. Swithin’s Day is also the ideal time of the year to prune walnut trees. Pruning walnut trees in the dormant season (i.e. when the leaves are absent) is not recommended as it is for nearly all other broadleaved tree species. If a walnut is pruned when the tree is dormant, or even worse when it is actively growing, the pruned wound will bleed profusely which will weaken growth the following season, and possibly increase risk of infection. Pruning is undertaken ideally near the end of the walnut’s active growing season and St. Swithin’s Day, in mid July, provides a perfect marker.
Gabriel Hemery
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
