ISO/DTS 24972

ISO/TSDTS 24972:2025(en)
ISO /TC 87/ WG 15
Secretariat: IPQ
Date: 2025-10-22xx
Cork - — Sustainable management in cork oak forests
Liège — Gestion durable des forêts de chênes-lièges

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ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Cork oak forests . 1
4.1 General. 1
4.2 Typology . 1
4.3 Management objectives . 2
4.4 Main threats to cork oak forests . 2
5 Legislation and policy. 3
5.1 General. 3
5.2 Spain . 3
5.3 Portugal . 5
5.4 France . 6
5.5 Italy . 7
6 Silvicultural treatments. 7
6.1 General. 7
6.2 Regeneration . 8
6.3 Intermediate treatments . 10
7 Cork harvest . 16
7.1 Debarking operation . 16
7.2 First debarking . 17
7.3 Debarking rotation cycle . 17
7.4 Harvest intensity . 18
7.5 Mechanization and professionalization . 19
8 Climate change . 20
8.1 Impacts of climate change on cork oak forests . 20
8.2 Contribution of cork oak forests to climate change mitigation . 21
Bibliography . 23

iii
Foreword
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iv
Introduction
Cork oak forests are the basis of cork value chain, one of the most relevant within the Mediterranean forest
area. Cork is a very important forest product whose economic activities are efficient in the use of resources
and are integrated into the Circular Economy and the Bioeconomy. Cork production constitutes a basic source
of income in these forests being their main use. However, they are also efficiently exploited for acorn
production, cattle grazing, firewood and hunting. Cork oak forests are valuable reservoirs of biodiversity and
play a key role in the maintenance of other natural resources, such as soils, air and water, as well as, contribute
significantly to the rural development of the areas, and ecosystem services such as carbon sequestration.
The ISO Technical Committee 87 (TC87TC 87) deals with the standardization of cork, both raw material and
manufactured products. According with its business plan (ISO, 2005), one of the expected benefits of the work
developed by the TC87TC 87 is to promote cork oak plantations and protect the existing cork oak forest in
order to increase cork production. Therefore, in 2010 the Working Group 15 (WG15WG 15) was created with
the main aim of tackle the topic of sustainable management of cork oak forests.
This document has been developed to inform and aid the sustainable management of cork oak forests, by
giving management guidelines for protecting cork oak forest while allowing appropriate use of the resources.
It describes practices mainly focus on cork production while promoting cork oak forest regeneration, multiple
benefits and mitigating global change. The document also points out practices which should be avoided or that
are forbidden. The information given in this document could be also used for assessing future development of
cork oak forests under different management scenarios as a guidance on how trade-offs between different
forest functions should be dealt with.
The target audience for this document are landowners and forest managers, but it can also be useful for other
stakeholders of the cork value chain. Since there could be readers without a basic knowledge of forestry, an
effort has been made for explaining the basic concepts related to forest management.
It must be highlighted that this document is not a standard. There are standards about forest management
available at international and national level developed by FSC (Forest Stewardship Council) and PEFC
(Programme for the Endorsement of Forest Certification). Regarding ISO, the related currently available
standard is the ISO 14055 (ISO, 2017)-1 about environmental management.
v
Cork — Sustainable management in cork oak forests
1 Scope
This document provides a guidanceguidances to manage cork oak forests in a sustainable way.
This document is an informative document, which provides orientation for protecting cork oak forest while
allowing appropriate use of the resources. It describes practices mainly focused on cork production while
promoting cork oak forest regeneration, multiple benefits and mitigating global change. This document also
points out practices which should be avoidedto avoid or that are forbidden. The information given in this
document can be also used for assessing future development of cork oak forests under different management
scenarios as a guidance on how trade-offs between different forest functions should be dealt with.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at http://www.electropedia.org/
4 Cork oak forests
4.1 General
Cork oak forests and woodlands can only be found in the western Mediterranean basin, mainly in the Iberian
Peninsula (Portugal and Spain), being also important in other two European countries: Italy and France, and
[ [1]]
in three northern African countries: Morocco, Algeria and Tunisia. 1. Altogether more than 2 million ha are
cover by cork oak stands, although the area is not known with exactitude and the natural distribution area of
[ [2] ]
the species is even more extent 2 . .
From an ecological point of view, the cork oak is a climax species, meaning that remain unchanged in terms of
species composition for as long as the site remains undisturbed, and its seedlings present a moderate
[ [3]]
tolerance to develop and grow in the shade of the parent trees. 3. It shares its natural distribution area with
other Mediterranean Quercus stands, mainly holm oak (Quercus ilex L.). Cork oak forests are located between
sea level and 800 m, rarely appearing at higher altitudes. They require a mild oceanic climate, with average
annual rainfall of between 600 mm and 1 000 mm, with average annual temperatures around 15 °C. The main
[ [4]]
limitation for the presence of cork oak forests is the number of days of frost and its intensity. 4. As for the
substrate, its calcifugous character characterizes the cork oak, although it can be found in basic substrates
[ [4] ]
generally washed. In addition, it prefers a sandy or loose soil texture 4 . .
4.2 Typology
Two types of forest can be distinguished in cork oak stands, fundamentally based on their density but also on
[ [5] ]
their ecological, productive and forestry characteristics: woodlands and cork oak forests 5 . .
The cork oak woodlands are savannah-type forests, with a sparse tree cover approximately 20- to 100 trees
per hectare, a 10 %-% to 50 % fraction of canopy covered, and with a well-developed herbaceous layer. In
these stands, pastoral use (acorns and/or pasture) is combined, both by domestic and wild cattle, with cork
[ [6]]
use. These two productions are made compatible and prioritized by regulating tree density. 6. This system
is located mainly in the west and southwest of the Iberian Peninsula where is called ‘montado’ in Portugal and
[ [7] ]
‘dehesa’"dehesa" in Spain, and also can be found in Sardinia 7 . .
The cork oak forests have a higher density of trees than woodlands and an important understory composed
of, among others, Arbutus unedo L., Phillyrea latifolia L., Cistus sp., Erica sp., etc. The main use is cork, so the
[ [6]]
management of these stands is aimed at optimizing cork production. 6. This system is distributed mainly in
the northeast and the very south of the Iberian Peninsula, in North Africa and in the rest of the distribution
area.
4.3 Management objectives
Cork is a renewable resource, and as such it is inexhaustible, as long as it is managed in a sustainable way.
Sustainable forest management is based on extracting income (growth) without affecting natural capital
(stocks). This means that conditions necessary to favour regeneration shoulshould be created for maintaining
an adequate number of trees per hectare.
In sustainable forest management, various ecosystem services, i.e. benefits that people obtain from forests,
need to be considered. Cork oak forests of any kind provide multiple goods and services including economic,
ecological and social benefits. Besides cork, pasture and acorns, cork oak forests can provide firewood,
hunting, mushrooms, beekeeping and understory plants. The economic activity linked to these goods
contributes significantly to rural development by generating productive fabric and employment in the
territories where cork oak grows. Furthermore, they fulfil an important ecological function by regulating
climate and water, controlling erosion, sequestering carbon and sustaining biodiversity. They also provide
cultural services being the frame for leisure activities.
The main goals of forest managements are production, protection, and/or recreation. The production- focused
management is often associated with capital investments and include treatments such as, thinning to
maximize growth, formative pruning to get a straight and smooth trunk and the treatments applied for the
establishment and tending of plantations, i.e. fertilization, irrigation, site preparation, control of competition,
and planting of genetically improved stock. The protection-focused management has lower impacts, as well as
costs and economic returns, and include treatments for preserving biodiversity and habitats, improving forest
carbon balance, promoting hydrological and soil protection and preventing from forest fires. The recreation-
focused management include treatments to accelerate the growth of large diameter trees or for developing
recreational access or infrastructures. These main goals are not exclusive and can be compatible in the same
stand by choosing specific management objectives. For example, biodiversity conservation or the
improvement of carbon balance can be compatible with cork production.
4.4 Main threats to cork oak forests
The main threats that cork oak forests face are the following, ranked by importance:
[ [8]]
— — Climate change: it is affecting the natural regeneration capacity of the cork oak forests, 8, it is less
and less frequent that a good weather year coincides with a good acorn harvest and that, moreover, the
cork oaks born from these acorns get rid of the tooth of the cattle or of other circumstance. This threat is
further treated in Clause 4Clause 4 of this document.
— — Phytosanitary problems: the main one is the disease caused by Phytophthora, an exotic pathogen that
is endangering numerous areas of cork oak forests. There are also other problems such as attacks by
cerambycids, defoliators, borers and cork shingles, which, without endangering the life of the tree,
[ [9] ]
depreciate the cork considerably 9 . .
— — Aged forests: in most of the cork oak forest territory, the youngest age classes are missing and the
[ ][ [6,10] ]
forest age class structure is skewed towards older age classes, close to the end of the rotation 6 10 . .
— — Shortage of workers: specialized in cork oak forest management and specifically in cork
[ [11]]
debarking. 11. There are fewer and fewer skilled workers for cork debarking, and few regions such as
Andalusia have training initiatives taken place in this regard, but the number of new-trained workers is
very low.
— — Forest fires: large fires are occurring with increasing frequency and sometimes affect cork oak
[ [12]]
areas. 12. Although cork oak forests are naturally adapted to fires, effective active prevention is
necessary.
— — Human pressure: on many occasions, the degradation of cork oak forests has its origin in bad
silvicultural practices that are mainly applied due to ignorance far more than bad faith. Examples of these
bad practices are harrowing with heavy machinery and pruning of adult trees. In addition, excessive
[ [13] ]
human pressure leads to degradation, for example livestock overload 13 . .
5 Legislation and policy
5.1 General
In this sectionclause a summarize of the legislation and policy of the European cork producing countries is
showed.
5.2 Spain
5.2.1 General
In Spain, the regulation of cork oak forestry, especially cork removal, is covered by regional regulations:
— — In Andalusia (AND) Order of September 26, 1988, by which instructions are given for the execution of
certain works in forests, in a private regime, populated with holm oaks and cork oaks.
— — In Extremadura (Junta de Extremadura): Law of the Dehesa of 1986 and decree 134/2019 which
regulates the performance of certain forestry actions in the area of the Autonomous Community of
Extremadura and the Registers of Cooperatives, Companies and Forest Industries and Protection Forests
of Extremadura.
— — In Catalonia (CAT): Order of May 11, 1988, on the regulation of the production of cork and the
improvement of cork oak forests.
— — In Castilla-La Mancha (CLM): Order of March 9, 2011 approving special specifications of technical-
facultative conditions, for the regulation of the execution of forest exploitation (timber and wood,
including forest biomass, and cork).
5.2.2 Mandatory regulations
— — First cork debarking: circumference at breast height > 65 cm (70 cm in EXT) and debarking coefficient
< 2 (see 7.4section 7.4 of this document for debarking coefficient definition).
— — Second cork debarking: debarking coefficient < 2,5 (all regions)).
— — Third cork debarking and onwards: debarking coefficient < 3 (all regions)).
— — Minimum branch perimeter: 65 cm for AND, CAT and CLM; 60 cm for EXT.
— — Gradual debarking: a cork oak is debarked in two or more times, several years apart. (The portion of
cork removed each time is called mesa in Spain): prohibited in AND; each debarking separated at least 3
years in EXT.
— — Partial and punctual brush clearing around the cork oak to be debarked (AND, CAT, optional
CLM)).
— — Phytosanitary precautions:
— — Cork oaks affected by external circumstances that have caused their extreme
weakening should not be debarked (EXT)).
— — After stripping the trees attacked by the fungus Biscogniauxia mediterranea, the
axes and cutting instruments used should be disinfected to avoid the transmission of the
disease to unaffected trees (AND)).
— — The trees affected by diseases will be uncorked separately from the rest and
with special attention to tools disinfection (EXT)).
— — The tools used for debarking and applying silvicultural treatments in cork oak
forests affected by fungi of the genera Biscogniauxia, Phytophtora and Diplodia, will be
disinfected with a solution of 50 % ferrous sulphate or other suitable products (CAT)).
— — Cork debarking period defined for the following periods:
— — Andalusia and CLM: June 1 -to September 1.
— — Extremadura: May 15 -to August 15.
— — Catalonia: May 15 -to October 30.
— — Minimum period of debarking rotation for one tree:
— — Andalusia: 9- years.
— — Extremadura: (9-15 to15) years.
— — Catalonia: (12- to 16 ) years.
— — Castilla-La Mancha: 10- years.
5.2.3 Prohibited operations
— — Cork debarking when is cannot be easily separated from the tree.
— — Damaging the mother-cell layer.
— — Cork debarking on rainy or windy days (AND, EXT, CLM)).
— — Leaving cork pieces in the base of the trunk above the roots (zapatas) (AND, CAT, CLM)).
— — Hitting with the reverse of the axe (AND, CLM)).
— — Cork debarking on the roots (AND, CAT, CLM)).
— — Cork debarking on trees pruned less than 3 years ago (EXT, CLM)).
5.2.4 Administrative issues
— — Prior notification to the administration (AND and EXT, usual cork debarking; CLM and CAT, cork oak
forests with management plan)).
— — Authorization request (AND and EXT, sometimes for cork debarking; CLM and CAT, cork oak forests
without management plan)).
— — Final inspection by forest agents (all regions)).
5.2.5 Other operations
— — References to mechanized uncorking (EXT)).
5.3 Portugal
5.3.1 General
Cork debarking in Portugal is regulated by Decree-Law no. 169/2001.
5.3.2 Mandatory regulations
— — First cork debarking: circumference at breast height > 70 cm and debarking coefficient < 2 (see
7.4section 7.4 of this document for debarking coefficient definition).
— — Second cork debarking: debarking coefficient < 2,5.
— — Third cork debarking and onwards: debarking coefficient< 3.
— — Minimum branch perimeter allowed for debarking: 70 cm.
— — Gradual debarking: a cork oak is debarked in two or more times, several years apart. (The portion of
cork removed each time is called "meça" in Portugal): prohibited from 2030.
— — It is mandatory to mark the tree with the last number of the year in which it was debarked.
— — Cork debarking period: when the cork is easily separated from the tree, from May to August.
— — Minimum debarking rotation allowed: 9- years.
— — Owners are responsible for maintaining cork oak forests in good vegetative conditions through active
management and proper exploitation.
5.3.3 Prohibited operations
— — Pruning is not authorized in principle, being allowed only when it improves the productive
characteristics. In this case, this operation must be carried out between November 1 and March 31, and it
cannot be done two seasons before the debarking year or in the two following ones.
— — Deep soil movements that affect trees root systems or those that cause destruction of natural
regeneration.
— — Mechanical soil mobilizations on slopes greater than 25 %%.
— — Interventions that eliminate or remove the surface soil layer.
— — It is forbidden to damage the mother-cell layer during cork debarking.
5.3.4 Administrative issues
— — It is required an authorization when cork debarking for the first time.
— — Compulsory to carry out the cork production declaration to Instituto da Conservação da Natureza e
Florestas (ICNF), broken down into three cork classes: virgin cork, secondary cork and reproduction or
mature cork (‘amadia’).("amadia").
5.4 France
5.4.1 General
In France, 100 % of public cork oak forests and numerous of private ones are PEFC certified, which has a
specific standard for cork oak forests and cork.
5.4.2 Mandatory regulation
— — First cork debarking: circumference at breast height > 70 cm and < 200 cm, and coefficient < 1,5 (see
7.4section 7.4 of this document for debarking coefficient definition).
— — Second cork debarking and onwards: debarking coefficient < 2.
— — Minimum branch perimeter allowed for debarking: 70 cm.
— — Minimum cork thickness allowed for debarking: 30 mm.
— — Cork debarking period defined from sunrise to 2:00 p.m. for the following periods:
— — For Aquitaine: from July 15 to August 31, and can be extended from June 15 to September 15,
depending on seasonal or climatic conditions.
For Corsica, Languedoc and PACA: from June 1 to August 15, and can be extended from May 15
— —
to August 31, depending on seasonal or climatic conditions.
— — Minimum period of debarking rotation for one tree:
— — 10- years in Aquitaine and Corsica.
— — 12- years in Languedoc and PACA.
5.4.3 Prohibited operations
— — It is forbidden to damage the mother-cell layer during cork debarking.
— — Cork debarking on rainy or windy days or during prolonged drought periods.
— — Leaving cork pieces in the base of the trunk above the roots.
— — For the task of scratching (making vertical and horizontal cuts in cork) is not allowed the use of a
conventional chainsaw. This task cannot be done immediately after debarking.
5.4.4 Administrative issues
Cork oak forests larger than 25 hectares ha must have a simple management plan.
5.5 Italy
5.5.1 General
Uncorking is regulated in Italy by LEGGE 18 luglio 1956, n. 759 Coltivazione, difesa e sfruttamento della
sughera.
5.5.2 Mandatory regulation
— — First cork debarking: circumference at breast height > 60 cm and coefficient < 2 (see 7.4section 7.4 of
this document for debarking coefficient definition).
— — Second cork debarking: debarking coefficient < 2,5.
— — Third cork debarking and onwards: debarking coefficient < 3.
— — Minimum neck perimeter allowed for debarking: 45 cm.
— — Cork debarking period defined May 15 -to August 31.
5.5.3 Prohibited operations
— — Cutting cork oaks without authorization.
— — Pruning when the tree can be harmed.
— — Agricultural crops and pastures without authorization.
— — Make fire between June and October.
6 Silvicultural treatments
6.1 General
Silvicultural treatments are those practices applied at the scale of forest stands to achieve the management
objectives. The key to effective forest management planning is determining a silvicultural system, which is a
scheduled program of silvicultural treatments designed to achieve specific stand structure characteristics to
[ [14]]
meet management objectives during the whole life of a stand. 14. Although these systems are typically
described by the method and organization of felling and regeneration employed, the entire silvicultural system
[ [15]]
involves also the intermediate treatments. There are four main silvicultural systems. 15. The clearcutting
system, which consists in cutting the entire stand at one time and naturally or artificially regenerate. The seed-
tree system is like clearcutting, but with some larger or mature trees left to provide seed for establishing a
new stand. These seed trees can be removed at a later date. The shelterwood systems consists in removing
most of the trees in two or more cuttings for allowing new seedling to grow up under a shelterwood of
maturing trees. The system is characterized by a preparatory cut (optional), seeding cut(s) which create gaps
for regeneration, and the final cut after regeneration is established. Finally, the selection system requires
individual or groups of trees to be harvested to make space for natural regeneration. The clearcutting, seed-
tree, and shelterwood systems produce even-aged stands of primarily one age class (assuming seed trees and
shelterwood trees are eventually removed). The selection system produces even-aged stands of several to
many age classes.
In the case of cork oak forests, besides felling, regeneration and intermediate treatments, it should be included
the organization of cork harvesting, which adds complexity to the traditional timber-oriented management
systems.
The choice of a silvicultural system would depend on the existing stands conditions, such as cork oak forest
type, trees features (age, size and health) and site conditions (site quality, slope, aspect, stand density, soil,
climate, proximity to industries and access for use), but also on the ability to make the investments needed in
each system. The term site refers to a geographic location that is considered homogeneous in terms of its
physical and biological environment. In forestry, site quality is defined as the location’s potential to sustain
[ [16]] [ ][ [17,18] ]
tree growth, 16, and it is usually measured by the site index 17 18 . .
6.2 Regeneration
The main aim of management is to ensure long term sustainability and persistence of cork oak forests by
guaranteeing regeneration. The regeneration period is the time between the initial regeneration cutting and
the successful re-establishment of a new age class by natural means, planting, or direct seeding. In order to
facilitate management and if the forest area is large, the first step would be divided the land into suitable
management units or compartments. The definition of management units should be based in variables
determinant for tree growth and forest management such as soil, topography and the site productivity. The
size of compartments should vary with the management objectives, total forest area and the diversity of forest
[ [19] ]
types, soils and topography 19 . .
6.2.1 Even-aged stands
[ [3]]
Taking into account that cork oak shows moderate shade tolerance, 3, the most appropriate silvicuture
system for producing even-aged cork oak forests is shelterwood. This system can be applied as uniform
shelterwood to the whole stand at the same time, or as group shelterwood where gaps are created in the stand.
It can be implemented for the regeneration of existing cork oak stands, or the implementation of new ones by
changing tree species composition. In both cases, the establishment of young cork oak trees takes advantage
of the adult trees shade and microsite conditions provided by them. Cuttings are carried out in the autumn-
[ [20]]
winter after cork debarking. 20. The number of cuts to carry out and the number of trees that can be cut in
each of them will depend on stand density at the beginning of the regeneration period. Thus, the preparatory
cuts will only be carried out when the density is very high. The goal after the final cut is to leave a few good
cork-producing trees. The number of years of the regeneration period should be a multiple of the duration of
the cork rotation, not only for practical reasons, but also for making coincide the first cork debarking, with the
[ [21] ]
last cork harvest carried out in the good cork-producing trees which would be cut in the following year 21 . .
6.2.2 Uneven-aged stands
Most of the cork oak forests that have not been under active management present an uneven distribution of
ages with a heterogeneous aggregation pattern from tree-by-tree mixtures to a mosaic of even-aged groups.
The most appropriate silviculture system in uneven-aged cork oak forests is tree selection, which consists in
making selective regeneration cuts during a determined period and a determined area. The duration of that
period will be the same as the cork debarking rotation. Therefore, every year after each cork harvest,
regeneration cuts will be carried out with a selective criterion in all diameter classes (DC) in an area equal to
the compartment area (or the whole area if the stand is small) multiplied by the cork debarking rotation and
[ [21]]
divided by the cutting cycle. 21. The cutting cycle is the planned interval between partial cuttings in an
[ [22] ]
uneven-aged stand 22 . .
[ [23] ]
As a general rule, the following considerations should be taken into account 23 : :
— — The number of trees that can be cut is variable according to the frequency of interventions. The
recommendation is to leave a basal area above (20- to 25) m under cork per hectare.
— — The following dimensional groups should be well represented: juveniles (DC < < 20 cm, young adults
(DC 20-30 cm to 30 cm) and adults in full production (DC> > 30 cm).
— — Given that continuous regeneration is a necessary condition, the youngest group is especially
important, since it determines recruitment and ensures the stand continuous improvement. In addition, if
a fire occurs, juveniles would allow the cork oak forest management to be restarted.
— — The proportion of trees in full production should be as large as possible without compromising the
uneven-aged character of the stand.
6.2.3 Agroforestry systems: dehesas and montados
The management to be carried out to ensure regeneration in woodlands is fundamentally based on dividing it
into equal size parts, so that there is always a part of the stand fenced to prevent livestock from accessing
[ [24]]
it. 24. The number of parts will be equal to the quotient of the number of years of the cutting cycle divided
by the regeneration period. The duration of the regeneration period will be equal to the period of time that it
takes for the cork oaks located in the fenced part to reach enough height to prevent them from losing the aerial
part due to livestock browsing. This time lapse will vary depending on livestock type and site quality.
An alternative to fencing the regeneration compartment would be to protect trees individually using
treeshelters or guards. This option has the advantages that is compatible with livestock use, understory
vegetation management could be done by grazing and trees are easier to locate. However, it could be costly
for large areas.
6.2.4 Regeneration support treatments
Due to the aforementioned particular characteristics of cork oak natural regeneration, it is necessary to carry
out treatments for guaranteeing a minimum density that ensure stand persistence and the achievement of
management objectives. These treatments are:
— — Soil scarification: this operation is done by harrowing. It aims to reduce soil compaction of the upper
layers in order to increase water infiltration and tree root development and establishment. It should only
be done occasionally, and restricted to sites with little slope and never on the line of maximum slope, and
the implements should be disinfected to prevent pathogen propagation. It is very important to highlight
that it should never be done under the canopy of adult cork oaks since when it is done only up to 20 cm
deep causes about 40 % loss of root volume, limit water absorption capacity and weaken the tree, which
[ [25]]
facilitates the entry of diseases. 25. This practice also increases the rate of soil organic matter
decomposition of the upper soil layers and for this reason showed be restricted to specific conditions.
— — Fencing for containing livestock in regeneration areas: the period would depend on livestock type and
site quality. The re-opening to grazing will be done gradually in early autumn and spring when grass is
abundant and fresh.
— — Individual protection for young plants: it is recommended the use of thorny wire mesh shelters, a
cheap adaptation of the classic tree guards wire mesh which is efficient, long-lasting and cost-efficient
because of the lower need of thermo-mechanically-treated iron bars. The use of refuges done by stacking
pruned branches can help for a couple of years, but then (if not from the beginning) the use of wire shelters
is essential. It should also be highlighted that leguminous shrubs species, like Retama sphaerocarpa, are
very efficient protecting young plants against browsers and show a positive biological facilitation of cork
[ [26] ]
oaks growth and survival 26 . .
— — Brush clearing: sometimes it is necessary to act on the brush cover, although it should always be done
taking into account the important ecological function of brush, as aforementioned (see also
6.2.3section 6.2.3 of this document).). When possible, considering shrub species and fire risk assessment,
the vegetal remains of this operation can be chipped for incorporation or cover of the top soil layer.
— — Regeneration renewal: when seedlings presents malformations due to the loss of the aerial part due
[ [21]]
to drought or grazing, it is advisable to cut the aerial part at ground level. 21. This operation will be
carried out at the same time that brush clearing.
— — Reforestation: when natural regeneration is not achieved, it will be necessary to sow or plant with
prior site preparation. Each method has advantages and disadvantages, so depending on the particular
[ [27]]
circumstances of each case, one or the other will be chosen. Montero and Cañellas 27 make a complete
description of both methods, as well as the subsequent care that should be carried out. The main aspects
that should be taken into account are: the quality of the plant or seed used, the initial density and the
protection of seedlings during the first year of reforestation. The initial planting density is usually 625 feet
per hectare (4 m x× 4 m (625 ft/ha) although it can reach densities of 1,250 feet per hectare (4 m x× 2 m
(1,250 ft/ha). The current trend is to plant lower densities per hectare to reduce or avoid thinning.
— — Irrigation is missing. In Portugal it is already accepted by forest projects and in some areas it is the
only way to have minimum number of trees surviving.
6.2.5 Rotation length: final felling
[ [22]]
Rotation is the number of years between regeneration establishment and the final felling. 22. In cork oak
forests, rotation length will depend on the period required by a cork oak, on a given site, to reach enough
diameter to be debarked for the first time (establishment and development stage), and on the period that a
cork oak can be producing cork (production stage). The first period depends on land fertility, the degree of
intensity of cultural care and the regeneration method used. Under equal ecological conditions, young trees
from planting or seeding have a faster growth in the first 15 years or 20 years than those from natural
regeneration, due to the effect of site preparation which reduces competition. If the reforestation is irrigated
the number of years could be even less. The second period depends on debarking intensity and soil fertility.
Taking into account that the age of entry into production ranges between (20- to 40) years (without
fertirrigation treatment) and the number of cork removals that a cork oak in good physiological conditions
endures, providing quality cork, is estimated at 10- to 12 removals, an indicative cutting cycle would be 150
years. Although, due to legal restrictions getting permission for cork oak felling is very difficult in most of the
cork producer countries, across those 150 years one of the regeneration techniques described above (2,1)
should be applied.
6.3 Intermediate treatments
Intermediate treatments include any silvicultural manipulation of forest vegetation occurring after
establishment of regeneration and prior to final felling.
6.3.1 Pruning
6.3.1.1 Formative pruning
The main objective of cork oak formative pruning is to facilitate the production of good quality cork by
obtaining a straight, smooth and tall trunk (more than 3 metersm) and a crown with 2- to 3 open branches at
a 30° to 45°angle with respect to vertical plane.
It should start as soon as the virgin cork appears (3- years to 5 years) and execute them with a low periodicity
(every 3- years to 5 years). It is very important to prune from top to bottom: start by eliminating the highest
branches that can lead to a too low crown height and those branches with a tendency to thicken. It is important
always to leave the main branch that is dominant over the rest, because it would help to get a straight trunk.
When up to 1/3 of the crown has been pruned, the operation should be stopped until the next intervention.
To remove more than 1/3 of the crown would be excessive and would cause regrowth of unwanted lower
branches. It should be avoided to cut branches of more than 5 cm in diameter, because thicker branches heal
slower and rot fungi can enter. For this reason, it is necessary to start pruning soon and do it with low
periodicity.
Once the cork oak has a straight and tall trunk, the branches of the lower part of the crown can be removed to
prevent second branches to growth too close from one another which could make difficult a proper cork
debarking. Figure 1Figure 1 shows a scheme of the pruning operation
Cuts should be smooth and at an angle to avoid accumulation of water that can lead to rotting. They should be
executed right above the cork, without leaving stumps, in order to promote healing.
The pruning operations should be done by qualified professionals and tools should be disinfected with suitable
products (for example, ethyl alcohol) to prevent disease transmission.
24972_ed1fig1.EPS
Key
1 First of all, eliminate those branches that compete with the main branch (double guide)
2 Remove thicker branches that may cause a lower tree crown
3 Remove any thicker branches that may cause a lower tree crown. It is not necessary to remove all lower branches
Source: Author: Raúl Lanzo
Figure 1 — Scheme of the formative pruning operation
6.3.1.2
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