continuous cover forestry

Arnold Chamove A.S.Chamove at
Wed May 15 23:41:12 EST 1996

Thought you all might find this interesting:


---------- Forwarded message ----------
Date: Tue, 14 May 1996 08:44:17 +0100
From: Gary Clarke <g.c.clarke at ABERDEEN.AC.UK>
Reply-To: FOREST Mailing list on forest research and studies
To: Multiple recipients of list FOREST <FOREST at LISTSERV.FUNET.FI>
Subject: Any experiences with continuous cover Sitka spruce ?

Hi Giles

On May 13th you wrote:


Perpetual Sitka Spruce Silvicultural System

I would be grateful if anyone could provide information on perpetual or
continuous cover sivicultural systems for Sitka spruce that may be
viable in the United Kingdom.

Continuous cover forestry is currently the "buzz" word in the UK
Forestry Industry, but there are few real examples of successful

Does anyone have any experience of the following theoretical system (if
it has ever been tried) either abroad or in the UK ? If so, I would be
most grateful if you could provide information or links to information
on any related systems. I am especially interested in "commercially
tried and tested"  perpetual silvicultural systems for Sitka spruce with
details of costs, revenue, cash flows (if possible), problems, benefits
and methods.


Typical situation: 18-20 year old Sitka spruce on fairly
windfirm (WHC 3) and moderately fertile site in upland Britain. Adequate
rainfall and favourable climate. Initially planted at 2.1m spacing.

Objectives are primarily commercial timber production.

Thinned at say year 18-20, removing approx 35% of crop to leave as wide
a range as possible of tree sizes (from small to large) rather than
conventionally favouring purely larger and better stems by removing
smaller trees.

After 5 years or so the largest stems are removed and marketed as higher
grade roundwood such as sawlogs. This would then leave the remaining
medium sized and smaller trees. After another 5 or so years  the largest
trees are again removed and so on. The theory is that after each
harvesting operation the meduim and smaller sized trees grow on to
replace those larger trees already removed. The gaps created from the
thinning operation (which become progressively letting more
light to forest floor) will allow natural regeneration and so the forest
is regenerated and the cycle is started over again.

The forest is never clear felled or restocked because it perpetually
regenerates and produces a range of age and size classes of which the
largest trees are harvested at regular intervals.

Possible benefits may be:

- Revenue at regular intervals (every 5 years ?) improving cash flow

- No high costs of restocking (such as after a clearcut system) which
attracts poor grants in the UK

- No lengthy and expensive consultation processes to seek approval for
felling plans.

- Improved timber quality due to protective and self pruning structure
of forest ?

- Capital value of forest maintained at all times

Possible disavantages may be:

- High and costly management input

- High harvesting costs

I would be grateful for any views on the above subject and scenario.

Giles Thompson
Tilhill Economic Forestry       Tel: +44 (15242) 72249
NW England, UK                  Fax: +44 (15242) 72246
Home Tel: +44 (1539) 729174"

If I could make a few observations...

1/ Continuous Cover Forestry is indeed a "buzz" word in British forestry at
the moment. However, there is (as usual) some debate about the definition of
the term. My understanding is that CCF encompasses the classic silvicultural
systems of single-tree selection, group selection, irregular shelterwood
(with a long regeneration period) and small group working where clearfelled
patches are perhaps no bigger than 0.2ha. It therefore excludes uniform
shelterwood (with relatively short regeneration periods), strip systems and,
of course, large-scale clearfelling. Having said that, I think it's
important that we don't get bogged down in terminology - silvicultural
systems are not discrete but rather exist on a spectrum. They are a guide on
which to base a locally adapted system.

2/ There are examples of CCF in Britain though the practice is not
widespread. I would refer you to "McIver, H. 1992. Forests of irregular
structure in Britain. ICF, Edinburgh, UK" for a compendium of examples.

3/ The only example of CCF with pure Sitka spruce is that of Shotton Forest
Management in north Wales. I believe they started some 5 years ago to
experiment with both an irregular strip shelterwood system and a single-tree
selection system. I believe that regeneration is progressing well - the
Continuous Cover Forestry Group (I can provide a contact for those
interested) could supply more information.

4/ Research on CCF in Britain is in its infancy - it is a long term business
investigating a silvicultural system! We at the University here have
intiatated several projects concerned with CCF including an extensive
literature review of, mainly, continental and North American work and the
micro-climatic requirements for regeneration of Sitka spruce, Scots pine and
birch. Hard data will be some time coming, however.

5/ The lack of facts and figures should not stop us attemptimg CCF, even for
a commercial objective. My impression is that such parameters as ideal
stocking, residual basal area and the diminution quotient, q, are either not
considered at all in the management of CCF or used as a rough guide
secondary to the silvicultural requirements of any particular stand.

6/ The scenario you describe could be defined as some form of shelterwood.
My feeling is that this is the right way to proceed for the management of
Sitka under CCF.
There may be some probles as you describe it, though. The key to CCF is the
regeneration of the stand. Though Sitka begins to produce seed at around 20
years of age, sufficient amounts to provide adequate regeneration are
probably not produced regularly until 30+.
Sitka spruce is able to germinate under fairly deep shade BUT to survive and
develop it requires quite high light levels - the unifrom heavy thinning you
propose may not provide this once the remaining trees begin to close canopy.
If canopy trees are removed at regular intervals over the whole stand there
is a danger that a regular structure will be perpetuated - c.f. uniform
I would suggest that a fairly heavy but spatially irregular thinning should
be the first intervention in the transformation - perhaps at a later age
than 20. If the canopy is too open before heavy seed production, dense
ground vegetation will be allowed.
Thereafter, interventions (removing "target" diameter trees) should be
arranged around existing (hopefully) patches of regeneration. The
regeneration period aimed for should be long (50+ years?) to ensure true
irregularity of the subsequent stand structure. Extraction is carried out
along a system of permanent racks.

7/ The possible benefits of such a system that you outlined are likely but
as yet unproven. Harvesting may well be more expensive but I do not think
that managemnt needs to be as intensive as you fear. Certainly, where these
systems are practised (Black Forest in Germany for example) management
appears less intensive than with clearfell systems as generally currently
practised in Britain.

Happy to continue discussion.


| Gary Clarke                                          |
| Lecturer, Department of Forestry, Aberdeen University|
| Aberdeen, AB24 5UA, Scotland, UK                     |
| TEL: +1224 272 667    FAX: +1224 272 685             |
| e-mail: g.c.clarke at                        |

Arnold Chamove; Massey University Psychology Dept; Palmerston North; N.Z.
E-mail: A.S.Chamove at; FAX: +(64)63505673; Phone: +(64)25460092
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