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CONTINUOUS COVER FORESTRY
Gain expertise in the development of healthier, more sustainable forests with this indispensable guide
Continuous Cover Forestry (CCF) is an approach to forest management with over a century of history, one which applies ecological principles to the project of developing biologically diverse, structurally complex forests. Long used as the standard forest management method in Central Europe, CCF is generating renewed interest globally for its potential to develop and sustain forests that can withstand climate change impacts, maintain forest biodiversity in the face of major ecological challenges and offer better recreation experience. There is an increasingly urgent need for forest scientists and policymakers to be familiar with the toolkit provided by CCF.
Continuous Cover Forestry: Theories, Concepts, and Implementation provides a thorough, up-to-date introduction to the theory and practice of CCF. Beginning with an overview of the method’s history and its foundational principles, the book provides detailed guidance for applying CCF methods to a range of ecological scenarios and forest types. The result is a clear, comprehensive portrait of this increasingly effective set of forestry tools.
Continuous Cover Forestry readers will also find:
- Case studies throughout showing CCF at work in real-world forests
- Detailed discussion of topics such as forest structure, transformation, silvicultural systems, training, carbon forestry, conservation and more
- R code ready to take and apply
- Simple, adaptable models for deriving quantitative guidelines for CCF woodlands
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Table of Contents
Cover
Table of Contents
Title Page
Copyright
Dedication
Foreword
Preface
1 Introduction
1.1 When Is a Forest a Forest?
1.2 The Nature of Forestry and Forest Management
1.3 Silvicultural Regimes and Types of Forest Management
1.4 Silvicultural Analysis and Planning
1.5 Continuous Cover Forestry – Definitions, Terms and Semi-synonyms
1.6 Common Misconceptions Dispelled
1.7 The Societies that Shape Us: Contrasting History of Forestry
1.8 Ensuring Sustainability: Area Control Versus Size Control
1.9 CCF in a Changing World
1.10 How to Introduce CCF to a New Region or a Country?
2 How Do I get Started with CCF?
2.1 Introduction
2.2 Identifying Land Suitable for CCF
2.3 Starting from Scratch – Instant New CCF
2.4 The Mission of Transformation and Conversion
2.5 Keeping it Going: The Maintenance of CCF
2.6 Biological Automation and Rationalisation
3 Individual-Based Forest Management
3.1 Introduction
3.2 Definition and Terms of Individual-Based Forest Management
3.3 History of Individual-Based Forest Management
3.4 How and When Frame Trees Are Selected
3.5 How Frame Trees Are Managed
3.6 Individual-Based Forest Management for Restructuring and Transforming Forests
4 Forest Structure – The Key to CCF
4.1 Introduction
4.2 Crown Classes
4.3 Mixing Species – But How and When?
4.4 Non-spatial Measures of Forest Structure
5 Interacting with Forest Structure
5.1 Introduction
5.2 Thinnings
5.3 Regenerating Forest Stands with Silvicultural Systems
5.4 Selection System
5.5 Continuous Two-Storeyed High Forest
6 Demographic Equilibrium and Guidance Modelling
6.1 Introduction
6.2 History
6.3 Static Equilibrium Models
6.4 Dynamic Equilibrium Models
6.5 Quantifying Deviations
6.6 Critique and Concluding Remarks
Notes
7 Putting it All Together: Implementing CCF for Different Management Purposes
7.1 Introduction
7.2 Forest Development Types
7.3 Specialised CCF Management
8 Training for CCF
8.1 Introduction
8.2 Training Requirements
8.3 Marteloscopes
Appendix A: Overview of the Most Common Principles of CCF
Appendix B: Light Demand of Tree Species
References
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Characteristics for agronomy (agriculture) and silviculture (fores...
Table 1.2 Synonyms and semi-synonyms used in connection with near-natural fo...
Table 1.3 The GB CCF trial areas.
Chapter 2
Table 2.1 Interpreting height–diameter ratios.
Table 2.2 Interpreting crown ratios.
Table 2.3 Tree numbers and ages in the nine plots of a unit according to the...
Table 2.4 Attributes associated with simple and complex forest structures (P...
Table 2.5 Variable-density thinning patch types.
Chapter 3
Table 3.1 Regional guidelines for target diameters of important species in N...
Chapter 4
Table 4.1 Examples of specific objectives for adding species to an existing ...
Table 4.2 Species proportions (abundances) in terms of basal area and the nu...
Table 4.3 Possible tree height bands. The definition relates to individual-t...
Table 4.4 Simple but useful dispersion measures quantifying size diversity a...
Table 4.5 Simple example for the calculation of the Lorenz curve.
Table 4.6 Example height curve functions. , and are regression coeffici...
Chapter 5
Table 5.1 Methods of tending forest stands according to Burschel and Huss (1...
Table 5.2 Guidelines for residual basal area [] in Central European thinn...
Table 5.3 Approximate ranges of appropriate residual basal area, after thinn...
Table 5.4 Regeneration methods traditionally used with tree genera and speci...
Table 5.5 Stand monitoring data relating to the
Picea abies
(L.) H. KARST.
s...
Chapter 6
Table 6.1 Normative definition of the proportions of standing volume of a se...
Table 6.2 Revised Méthode du Controle with ideal volume proportions in diffe...
Table 6.3 Tree-number and basal-area characteristics of an observed hypothet...
Table 6.4 Model parameters of Susmel's factor model relating to different ...
Table 6.5 Demographic equilibrium provisional and final numbers of trees per...
Table 6.6 Hypothetical example of a small tree arrangement of ten trees with...
Table 6.7 Tree-number (), basal-area () and BAL per hectare by stem diamet...
Table 6.8 Equations used for the equilibrium guide curves relating to the mi...
Table 6.9 Example of varying factor for different ranges of the empirical ...
Table 6.10 Marking guide for Plashetts Wood (England, UK).
Chapter 7
Table 7.1 Main British FDT categories.
Table 7.2 Example of a complete individual-based treatment guideline for mix...
Table 7.3 Examples of management objectives and corresponding sivicultural s...
Table 7.4 The most common European tree and shrub species used in stand impr...
Chapter 8
Table 8.1 Design of a typical, basic tree-marking sheet for use in martelosc...
Appendix B
Table B.1 Light demand of selected tree species.
List of Illustrations
Chapter 1
Figure 1.1 The relationship between silvicultural regimes and basic silvicul...
Figure 1.2 Resprouting of
Catanea sativa
MILL.
trees from coppiced stools in...
Figure 1.3 Traditional coppice with standards with
Catanea sativa
MILL.
tree...
Figure 1.4 Biomass development in different management approaches. Plantatio...
Figure 1.5 Examples of broadleaved plantations involving native tree species...
Figure 1.6 The general process of silvicultural planning.
Figure 1.7 Retention forestry/green tree retention is often only but a small...
Figure 1.8 The main components or tenets of the contemporary international c...
Figure 1.9 Example of the marking of a permanent extraction rack on the stem...
Figure 1.10 The continuum of continuous cover forestry stretching from maxim...
Figure 1.11 Illustrations of the two extremes of the continuum of continuous...
Figure 1.12 Memorial stone erected in honour of CCF pioneer Henry Biolley in...
Figure 1.13 Contrasting British and Central European history of forestry.
Figure 1.14 Spatio-temporal separation of regenerating (R), thinning (T) and...
Figure 1.15 Current diameters sprayed (in blue paint) onto the stem surface ...
Chapter 2
Figure 2.1 The three basic CCF situations.
Figure 2.2 Flow chart for judging on stand resilience based on the mean an...
Figure 2.3 (a) and (b) ratios over stem diameter
d
in three forest plots...
Figure 2.4 Artist's Wood – a lowland single tree selection system with mainl...
Figure 2.5
P. sitchensis
(BONG.) CARR.
and
P. abies
(L.) H. KARST.
natural r...
Figure 2.6 Accidental mixed
P. sitchensis
(BONG.) CARR.
–
Betula
spp. woodla...
Figure 2.7 The concept and functions of a nurse crop/artificial shelterwood ...
Figure 2.8 Early stage of an instant CCF mixed broadleaved woodland (mainly
Figure 2.9 Late stage of an instant CCF mixed broadleaved and conifer woodla...
Figure 2.10 Layout of how the trees and plots are arranged in units accordin...
Figure 2.11 Schematic representation of units, plots, extraction racks and r...
Figure 2.12 Layout of a hypothetical forest stand according to the Anderson ...
Figure 2.13 Transformations of plantations to CCF can go wrong, particularly...
Figure 2.14 The four phases of transforming a mixed-species conifer RFM to a...
Figure 2.15
Simple
and
complex
CCF
structure
according to Mason and Kerr (20...
Figure 2.16 Flow chart illustrating the decision-making process when transfo...
Figure 2.17 Forest restoration through conversion based on the concept of an...
Figure 2.18 Diversifying
Picea
spp. stands and enhancing resilience through ...
Figure 2.19 The basic principle of the nest or cluster planting (Ogijewski m...
Figure 2.20 The circular nest or cluster planting design suggested by Gockel...
Figure 2.21 Graduated density thinning (GDT) simulated for a hypothetical pl...
Figure 2.22 An example of a first graduated density thinning (GDT) in an app...
Figure 2.23 Alternative representation of Figure 2.21. At the bottom in brac...
Figure 2.24 Tree locations (brown) of a simulated pattern after variable-den...
Figure 2.25
Juglans regia
L.
frame trees (trees with light bark) in a matrix...
Chapter 3
Figure 3.1 Envisaged dispersion and development of frame trees shortly after...
Figure 3.2 Sketch of an imaginary single-species conifer forest. The frame t...
Figure 3.3 A mixed-species and low-density woodland with
Pinus pinea
L.
in t...
Figure 3.4 Number of frame trees per hectare approximated from crown diamete...
Figure 3.5 Sketch of an imaginary mixed-species forest where frame trees wer...
Figure 3.6 Schematic representation of how frame trees (filled circles) form...
Figure 3.7 Three-dimensional sketch of the local management units in an imag...
Figure 3.8 Two different simulated patterns of frame-tree dispersion at Embr...
Figure 3.9 Crown classes according to Rittershofer (1999) and result of a se...
Figure 3.10 The relationship between the stem diameter at breast height, , ...
Figure 3.11 A worked example of the -thinning index involving a frame tree,...
Figure 3.12 Frame tree realisation space (within the grey boundary lines) de...
Figure 3.13 (a): Schematic illustration of the frame-tree method for promoti...
Figure 3.14 Impressions from the forest structure at the Schlägl forest esta...
Chapter 4
Figure 4.1 Selection of ecosystem functions, goods and services connected to...
Figure 4.2 The three major characteristics of forest structure and -diversi...
Figure 4.3 Tree reactions to changing growing space. The red dots symbolise ...
Figure 4.4 Crown classes according to Kraft (1884). The numbers and letters ...
Figure 4.5 Native
Fagus sylvatica
L.
saplings planted under non-native matur...
Figure 4.6 Equivalent (genuine) tree species mixture (a). Gap tree species m...
Figure 4.7 A mixed-species woodland including
F. sylvatica
L.
and
Fraxinus e
...
Figure 4.8 Temporary tree species mixture in the same canopy storey but diff...
Figure 4.9 Permanent tree species between different canopy storeys (a). Perm...
Figure 4.10 Top height development over age for four species taken from the ...
Figure 4.11 Visualisation of the relative abundance proportions of Table 4.2...
Figure 4.12 The relationship between the relative abundance proportions, , ...
Figure 4.13 Shannon (blue, in Eq. (4.1)) and Simpson indices (red, in Eq...
Figure 4.14 Typical stem-diameter () distributions of (a) an even-aged pure...
Figure 4.15 Total stand (a) and species-specific (b) stem-diameter distribut...
Figure 4.16 Population pyramids for visualising the stem-diameter distributi...
Figure 4.17 Skewness indicated by the relationship between median, , and me...
Figure 4.18 A bimodal empirical stem-diameter distribution (
d
) and the corre...
Figure 4.19 Lorenz curve corresponding to the example of Table 4.5. Variable...
Figure 4.20 Lorenz curve, Gini indices (, ) and stem-diameter coefficient ...
Figure 4.21 Comparison of Gini index (), standardised Gini index () and co...
Figure 4.22 Conceptual model of how growth dominance indicates four phases o...
Figure 4.23 Growth dominance curves and growth dominance indices (, Eq. (4....
Figure 4.24 Growth dominance index (, Eq. (4.9)) monitored in the Hirschlac...
Figure 4.25 Vertical structure of the stand Pen yr Allt Ganol indicated by s...
Figure 4.26 Vertical structure of the stand Pen yr Allt Ganol indicated by s...
Chapter 5
Figure 5.1
Pseudotsuga menziesii
MIRB.
Franco woodland in the Sellhorn Fores...
Figure 5.2 The relationship between thinning regimes and thinning types.
Figure 5.3 The principles of thinning from below (a) and crown thinning (b) ...
Figure 5.4 The principles of negative (a) and positive (b) tree selection ap...
Figure 5.5 The effect of different thinning types on the stem-diameter (
d
) d...
Figure 5.6 Tree number guide curves depending on the crown spread ratio (ass...
Figure 5.7 Using a hypothetical ‘sawtooth’ curve of stand basal over time to...
Figure 5.8 Visual impression of the structure involved in basic silvicultura...
Figure 5.9 Silvicultural or regeneration systems using natural processes....
Figure 5.10 Relationship between spatial and temporal scale of natural tree ...
Figure 5.11 Typical shelterwood system involving
F. sylvatica
L.
, the specie...
Figure 5.12 Residual basal area and percentage light intensity at the forest...
Figure 5.13 Schematic representation of a concentric spatio-temporal gap enl...
Figure 5.14 Schematic representation of a crescenting spatio-temporal gap en...
Figure 5.15 Distribution of light and shade in a gap with South-North exposi...
Figure 5.16 An emerging
F. sylvatica
L.
regeneration cone in a mixed
F. sylv
...
Figure 5.17 Schematic overview of elliptic, ‘slit-shaped’ canopy openings ar...
Figure 5.18 In a mixed
Picea abies
(L.) H. KARST.
and
P. sylvestris
L.
fores...
Figure 5.19 Schematic overview of a basic strip system with the first three ...
Figure 5.20 Schematic example of a wedge system with a spatial orientation t...
Figure 5.21 Example of a group-strip shelterwood system with Sitka spruce (
P
...
Figure 5.22 Schematic overview of a forest stand situated between two forest...
Figure 5.23 Severely bent
P. sylvestris
L.
trees, windbreak and windthrow ca...
Figure 5.24 Wind damage in stands of
Picea abies
in relation to stand height...
Figure 5.25 (a): When pulling even-aged stands representing different age cl...
Figure 5.26 Mostly monospecies
Picea abies
(L.) H. KARST.
selection forest i...
Figure 5.27 Temporal development of the empirical stem-diameter distribution...
Figure 5.28 Differences in mean annual stem-diameter
absolute growth rate
(A...
Chapter 6
Figure 6.1 Tree-number (white) and stem-volume (grey) proportions in balance...
Figure 6.2 (a) Decreasing exponential function according to de Liocourt (189...
Figure 6.3 Main processes of a dynamic stem-diameter distribution and the co...
Figure 6.4 Observed stem-diameter (
d
) distribution of a hypothetical forest ...
Figure 6.5 Equilibrium curves for five different values of produced using ...
Figure 6.6 Typical example of observed and simulated annual ingrowth and mor...
Figure 6.7 The relationship between BAL and stem-diameter AGR in a 56-years ...
Figure 6.8 Observed (red) and simulated (blue) relationships between tree nu...
Figure 6.9 Models of mean absolute growth (a) and mortality (b) rates re...
Figure 6.10 Equilibrium guide curves for the mixed
Pseudotsuga menziesii
(MI
...
Figure 6.11 Differences between a Schütz (orange) and a -adapted Schütz (bl...
Figure 6.12 Example of an adjustment of allowable cut based on the data prov...
Figure 6.13 Equilibrium guide curve for the mixed
Pseudotsuga menziesii
(MIR
...
Chapter 7
Figure 7.1 Basic principle of defining silvicultural prescriptions as part o...
Figure 7.2 Ecogram of forest development types based on the Ellenberg vegeta...
Figure 7.3 Example of a schematic visualisation of a typical vertical profil...
Figure 7.4 ‘Structural arrow’ indicating a range of possible stand structure...
Figure 7.5
Quercus robur
L.
underplanted with
P. abies
(L.) H. KARST.
for pr...
Figure 7.6 Schematic representation of a
wood vault
that is partially above ...
Figure 7.7 Blowdown and associated processes that occur along an edge are pa...
Figure 7.8 Schematic structure of outer forest margins where forests border ...
Figure 7.9 Almost perfect mature forest margins enveloping a small mixed
Que
...
Figure 7.10 Schematic structure of an outer forest margin with inlets and ad...
Figure 7.11 Small stream running down from Mecklenbruch bog in the Solling M...
Figure 7.12 Advance regeneration of
P. abies
(L.) H. KARST.
enveloping and c...
Figure 7.13 Cover and inside of the leaflet explaining management at the CCF...
Figure 7.14 Grave-marker tree at the burial site of the author's mentor Prof...
Figure 7.15 Naturally established seedlings and saplings of
P. abies
(L.) H.
...
Chapter 8
Figure 8.1 Number of trees classified separately by two forest managers (sho...
Figure 8.2 The principle of the thinning-event analysis: Human marking behav...
Figure 8.3 Map (a) and proportions (b) of the frame (black) and competitor t...
Figure 8.4 (a) Students of Göttingen University selecting trees in a martelo...
Figure 8.5 Empirical distribution of the Fleiss kappa characteristic, , fro...
Figure 8.6 (a) Mean ratio of the proportion of number of trees selected by t...
Figure 8.7 Trainees selecting trees for a local crown thinning in the mixed
Guide
Cover
Title Page
Copyright
Dedication
Foreword
Preface
Table of Contents
Begin Reading
Appendix A Overview of the Most Common Principles of CCF
Appendix B Light Demand of Tree Species
References
Index
End User License Agreement
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Continuous Cover Forestry
Theories, Concepts, and Implementation
Arne Pommerening
Swedish University of Agricultural SciencesUmea, Sweden
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Library of Congress Cataloging-in-Publication Data
Names: Pommerening, Arne, author.
Title: Continuous cover forestry : theories, concepts, and implementation / Arne Pommerening.
Description: First edition | Hoboken, NJ : Wiley, 2024 | Includes index.
Identifiers: LCCN 2023023698 (print) | LCCN 2023023699 (ebook) | ISBN 9781119895305 (cloth) | ISBN 9781119895312 (adobe pdf) | ISBN 9781119895329 (epub)
Subjects: LCSH: Continuous cover forestry. | Forest management.
Classification: LCC SD387.C67 P66 2023 (print) | LCC SD387.C67 (ebook) | DDC 634.9/2–dc23/eng/20230711
LC record available at https://lccn.loc.gov/2023023698
LC ebook record available at https://lccn.loc.gov/2023023699
Cover Design: WileyCover Images: © feipco/Adobe Stock Photos; Cover image courtesy of Joss Everett
To my parents who provided me with a privileged start in life and to the whole Pommerening-Küter forestry family whose lives inspired me to choose what is a truly wonderful profession.
Foreword
When I first learned about this textbook project I immediately thought it was really high time that someone wrote a consistent, systematic English language textbook on continuous cover forestry (CCF), since we have been lacking this for quite a while. Therefore I am keen to endorse this fine accomplishment.
One of the most remarkable properties of forest ecosystems is the ability to autonomously prevail over other plant formations so that most areas in the world that are suitable for plant growth would naturally be occupied by forests without human aid. This is owed to the trees' ability to escape competition at ground level by growing tall, to their resilience and longevity. Forest ecosystems apparently have self-organisation capabilities allowing them to form stable states of equilibrium without our assistance.
Instead of maximising the production of certain ecosystem goods through genetically engineered species selection and other technical inputs in plantation forests, the processes in semi-natural forest ecosystems are regulated by making use of mechanisms of self-organisation. This is the fundamental change of paradigm that CCF or nature-based forest management, as it is also known, is based on. This concept is a low-cost alternative form of forestry ensuring ecological sustainability whilst fulfilling the expectations of modern societies. CCF began to develop more than a century ago in different parts of the world, and as a consequence much experience and silvicultural knowledge is now available. One of the most common concerns in this context is how highly artificial forests can be transformed without trade-offs to an equilibrium state of sorts and how to maintain such a steady state.
For successful implementation, CCF requires more pre-requisites than plantation forest management, namely a sufficient understanding of the natural principles of self-organisation, a good knowledge of the ecological requirements of native and introduced tree species, and particularly the ability to judge environmental conditions including soil properties correctly, since the successful development of forest ecosystems much depends on them. In addition, a good knowledge of how the trees involved respond to silvicultural interventions is required, e.g. the ability to successfully initiate processes of natural regeneration and make use of other ecosystem benefits without additional costs.
With ongoing climate change, energy crisis and increasing spare time, our societies are taking much greater interest in forests and forestry than in previous decades and are rightly concerned about long-term environmental sustainability. CCF is the best form of forest management to meet all these diverse expectations and simultaneously delivers a maximum of very different ecosystem goods and services across large landscapes.
Crucial to the success of CCF is the clever application of a solid silvicultural skill set including methods of biological rationalisation rather than an exclusive reliance on mechano-technical inputs and advances. Education and experience of silvicultural specialists play a central role in the successful implementation of nature-based forest management, but also the organisational freedom granted to forest managers for working directly with the forest stands that are put into their care. I am certain that this textbook will greatly contribute to building the necessary skills and knowledge for a successful uptake of CCF and its many variants.
Jean-Philippe Schütz
Zürich, Switzerland
February 2023
Preface
Творческая задача лесовода - суметь законы жизни леса превратить в прин- ципы хозяйственной деятельности. Г. Ф. Mорозов
It is the creative task of a silviculturist to figure out how to turn the laws of forest life into the principles of forest management. G. F. Morozov
‘A spectre is haunting Europe – the spectre of continuous cover forestry. All the traditional powers of forestry have entered into a holy alliance to exorcise this spectre.’ Borrowing and only slightly modifying these words of The Communist Manifesto published by K. Marx and F. Engels in 1848 surprisingly well describes the situation at the end of the nineteenth and beginning of the twentieth century, when continuous cover forestry (CCF) was first proposed in publications. Since then forestry has come a long way and CCF has even become mainstream in quite many countries, although the quote still applies in others.
In recent years, CCF has received much attention for its potential to help mitigate climate change, for its usefulness in the context of forest conservation and for the increasing resistance of society to industrialised plantation forest management. Worldwide forestry students feel enthusiastic about courses and field trips related to CCF. Ironically, this is contrasted by a steady decrease of research funds in the core fields of silviculture and forest management. Hardly any national research council is prepared to fund the development of methods in forest management and the associated scientific experiments whilst forest industries often do not have sufficient means to invest in research. This situation leads to a continued decline of silvicultural research staff at universities and as a result, teaching of silviculture including CCF is in steady decline as well. Therefore, this book unwillingly acts as a lantern bearer of sorts but hopefully also as an eye opener at a time that is difficult for academic silviculture when the knowledge in this field is bizarrely more needed than ever.
Since the beginning silviculture and forest management were dominated by commercial forestry. Other objectives such as nature conservation and biodiversity were considered by-products or welcome side effects, if they were considered at all. This has fundamentally changed in the twenty-first century when other objectives of forestry have become at least as prominent as commercial forestry if not more important. This book is the first attempt to present a central part of silviculture, continuous cover forestry, in a neutral and balanced way so that commercial forestry is just one purpose of forest management among others but has no supremacy.
The contents of this book are based on more than 20 years of teaching in CCF in the United Kingdom, Switzerland, and Sweden. I had the good fortune to be educated in CCF as part of my own degree programmes at Göttingen University (Germany). When I took up my first faculty position in the United Kingdom, CCF was being introduced to the country and I was asked to contribute to CCF teaching, training of practitioners and setting up CCF research experiments. This provided me with invaluable experience of a kind I could never have achieved in my own country. During this time, I organised quite a few CCF field trips for British forestry students and practitioners. These academic activities I continued in Switzerland and there I had the opportunity to deepen my knowledge in the cradle of CCF. At the time of writing, CCF is being considered for introduction in Sweden, my current academic home, so the subject keeps following me around.
Chapter 1 sets the scene, gives vital definitions and context. Methods and options for getting started with CCF are discussed in Chapter 2. This is followed by an explanation of the principles of individual-based forest management in Chapter 3, which forms an important part of CCF. Forest structure is the key to understanding ecological processes and delivers CCF. These key relationships are explained in Chapter 4. Following on from Chapter 4, thinnings and silvicultural systems as the main methods of manipulating forest structure are introduced in Chapter 5. Demographic equilibrium and guidance models for identifying steady-state conditions of CCF woodlands are reviewed in Chapter 6. These modelling approaches were originally developed in the CCF research community. In Chapter 7, I discuss how general CCF management needs to be adapted to deliver different ecosystem goods and services. Finally, Chapter 8 is dedicated to the important topic of training for CCF management. Where appropriate, R source code is provided and a brief introduction to R can be found in Appendix C of Pommerening and Grabarnik (2019).
I particularly thank the members of my former Tyfiant Coed research team, Sharron Bosley, Dr. Owen Davies, Dr. Jens Haufe, Gareth Johnson, Dr. Steve Murphy, Mark Rogowski and Björn Welle for their support and cooperation when we made a humble contribution to the introduction of CCF in Wales. It has been fun to co-organise the annual one-week CCF field trips to Denmark and Germany together with my friend and colleague Professor Douglas Godbold (BOKU University, Vienna). These field trips have been a tremendous source of inspiration and together with my students I learnt a lot from the Danish and German CCF practitioners who kindly showed us around. I am also much indebted to my silvicultural mentors, Professors Hanns H. Höfle, Burghard von Lüpke (both Göttingen University, Germany) and Jean-Philippe Schütz (ETH Zürich, Switzerland). Dr. Thomas Campagnaro (Padova University, Italy) helped me with understanding the Susmel model (Chapter 6). Professor Hubert Sterba (BOKU University, Austria) engaged in many helpful discussions and kindly made photos and the Hirschlacke data available. I much enjoyed the discussions on biological rationalisation and silvicultural training I had with Dr. Peter Ammann (Fachstelle Waldbau, Switzerland). Dr. Lucie Vítková (Czech University of Life Sciences, Czech Republic) kindly shared her experience in graduated density thinning and thus contributed to Section 2.4.2. Professor Jorge Cancino (University of Concepción, Chile) joined a helpful discussion on the BDq approach (Section 6.3.1.1). Dr. Xiaohong Zhang (Chinese Academy of Forestry, Beijing) kindly made data collected at the Tazigou Experimental Forest Farm (Jilin Province, China) available. For some illustrations in this book, data were gratefully received from Andreas Zingg (Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland). Professor Áine Ní Dhubháin (University Colleague Dublin, Ireland) undertook the enormous task of proofreading and commenting on the text of the whole manuscript, for which I am most grateful. Professor Dan Binkley (Northern Arizona University, US) has kindly encouraged and advised me in the proposal phase of this book project. Zeliang Han and Dr. Gongqiao Zhang (Beijing, China) tremendously enriched the book project by preparing illustrations, often at short notice, for which I am very grateful. Any remaining errors and shortcomings in this work are mine alone.
Looking back and contemplating the long history of forestry one cannot help but think that there is some similarity between the evolution of civilisation in general and forestry in particular: Humankind has always strived to improve the constitutions of states up to the point when (social) justice and democracy finally were sufficiently developed so that even unprivileged members of society have a good chance to thrive and to live a full life. This evolution has taken a long time, taken many wrong turns and is by no means complete nor are current achievements secured forever. In a similar way, CCF is undoubtedly among the great achievements of humankind. With CCF, forestry has come a long way starting with agricultural practices that marked its beginnings and has now eventually arrived at a point where a type of land use is pursued that attempts to be fair to the forest ecosystems and landscapes we humans have inherited and will pass on.
Arne Pommerening
Umea, Sweden
February 2023
1Introduction
Abstract
The terms ‘forest management’ and ‘silviculture’ refer to deliberate, professional human interaction with forest ecosystems, i.e. the direct hands-on human interference with tree vegetation for particular purposes – which, in one way or another, is almost as old as mankind. Over the last 200 years, a wide range of different techniques have been developed, refined, and formalised in forest practice and science with the objective to modify forest structure and thus to steer forest development into certain desired directions.
This chapter outlines the basic concepts and techniques of forest management and silviculture in a changing world. The text provides non-specialists with an easy access to this field of forest ecosystem management by explaining basic terms and definitions. The concept of continuous cover forestry (CCF) is introduced, and how the history of different societies has contributed to its shaping is described. Common misconceptions are explored, and important sustainability concepts are explained. Finally, the place of CCF in a changing world is outlined, and suggestions are made as to how to introduce CCF to a new region or country.
1.1 When Is a Forest a Forest?
Despite their very different plant compositions forests form very characteristic plant communities which set them aside from other vegetation forms (such as grasslands, shrublands, bog vegetation) not only in terms of visual appearance but also in terms of ecology. Trees, as large woody plants, are the most significant element of wooded landscapes. Forest trees are, unlike fruit trees, for example, only rarely genetically modified organisms, whether native to their sites or introduced from another, ecologically similar region. In order to form a forest, trees have to be so close to each other in a sufficiently large land area that they form a common crown canopy which shades the forest floor to a large extent. Only under these circumstances can life conditions be sustained which are very different from any other plant formation. After afforestation or replanting, it takes time for the elements which form the typical characteristics of a forest to appear. Such typical elements are the size of the forest area, canopy closure, forest soils and woodland microclimate and a specific vegetation of vascular plants on the forest floor which only occurs in forests. Natural disturbances and human interventions can destroy some of these elements. But as long as the tree vegetation is sustained and can again develop a more or less closed formation, the corresponding land area remains a forest (Burschel and Huss, 1997).
‘In the United Kingdom, a woodland or forest is defined as land with a minimum area of 0.1 ha under stands of trees with, or with the potential to achieve, tree crown cover of more than 20%. Areas of open space integral to the woodlands are also included. Orchards and urban woodland between 0.1 and 2 ha are excluded. Intervening land-classes such as roads, rivers or pipelines are disregarded if less than 50 m in extent’.
National Inventory of Woodland & Trees – Wales
There is no world-wide unique definition of forests. In developed countries, the lower limit in older forest stands is a crown canopy closure of more than 20%, while in many developing countries, only 10% is required. This affects the estimation of deforested areas around the world (Bartsch et al., 2020).
The IUFRO (International Union of Forest Research Organisations) terminology of forest management (Nieuwenhuis, 2000) provided an ecology and a management motivated definition:
Forest (ecology perspective)
‘Generally an ecosystem characterised by a more or less dense and extensive tree cover. More particularly, a plant community predominantly of trees and other woody vegetation, growing more or less closely together’.
Forest (silviculture/forest management perspective)
‘An area managed for the production of timber and other forest produce, or maintained under woody vegetation for such indirect benefits as protection of catchment areas or recreation’.
Helms (1998) in his dictionary of forestry put forward the following definition of a forest:
‘An ecosystem characterised by a more or less dense and extensive tree cover, often consisting of stands varying in characteristics such as species composition, structure, age class, and associated processes, and commonly including meadows, streams, fish, and wildlife […]’.
Finally, Thomasius (1990) characterised forests as ecosystems, in which life forms dominate, which
reach such a height,
are so close together,
occupy a sufficiently large area,
so that the spatial occupation by living and dead biomass leads to
a specific microclimate,
characteristic soil conditions and
interactions between the different organisms that influence their onto-, auxo- and morphogenesis.
Consequently, three conditions need to be fulfilled to deserve the status of a forest:
The dominant life form must be trees which reach a total height of at least 7 m in their adult stage (under extreme environmental conditions 3 m is often also acceptable).
The trees must form stands which shade at least 20% of the soil surface.
Stands of trees have to occupy an area with a radius which with full crown closure corresponds at least to their height.
These features create a habitat for plants and animals which require the specific microclimatic and/or soil conditions of a forest or which are dependent on other life forms that occur in forest ecosystems (Thomasius, 1990). A forest is a highly interactive community of organisms with the tree life form dominating among the energy-capturing green plants. These plants generate the cascade of energy that supports food webs composed of thousands of species (Franklin et al., 2018).
From the standpoint of forest management, the term ‘forest’ has a special meaning and denotes a collection of stands administered as an integrated unit, usually under one ownership. This division of forests into stands is especially important in regulating timber harvests as well as managing wildlife populations and large watersheds. One objective of stand management for timber products is usually the achievement of sustained yield. However, the forest (estate or district), and not the stand, usually is the unit from which this sustained yield is sought. Management studies of prospective growth and yield determine the volume of timber to be removed from the whole forest in a given period (Smith et al., 1997).
Thomas and Packham (2007) and Helms (1998) noted that the terms ‘forest’ and ‘woodland’ are commonly used almost interchangeably. In agreement with public perception, they suggested that a woodland is a small area of trees with an open canopy (often defined as having 40% canopy closure or less) such that plenty of light reaches the ground, encouraging other vegetation to grow beneath the trees. Since the trees are well spaced, they tend to be short-trunked with large canopies. The term ‘forest’, Thomas and Packham (2007) asserted, by contrast, is usually reserved for a relatively large area of trees forming for the most part a closed, dense canopy. Since the terms ‘woodland’ and ‘forest’ overlap, we have used them as synonyms in this book. A forest is made up of a series of more or less homogeneous stands, and the main focus of silviculture is on these forest stands with trees as their main components.
A forest stand is a contiguous community of trees sufficiently uniform in species composition, density, structure and/or age-class distribution, and growing on a site of sufficiently uniform site conditions and site quality, of a sufficient size to be a distinguishable planning and management unit (Thomasius, 1990; Helms, 1998; Nieuwenhuis, 2000; Franklin et al., 2018; Smith et al., 1997).
In continuous cover forestry (CCF), forest managers commonly deal with stands that can be quite diverse in terms of tree species, sizes and dispersal. Consequently, in this book, we used the term ‘stand’ in its broadest interpretation often denoting a distinctive population of trees (Franklin et al., 2018). In many countries, forest stands usually coincide with sub-compartments, as these administrative units were chosen to reflect the forest stand definition. Tree canopies or crowns of a forest stand can usually be found in one or more canopy levels. The uppermost canopy level is referred to as overstorey, the lowest layer of vegetation is the understorey and tree canopies in between over- and understorey form the mid-storey (Helms, 1998). For a possible quantitative definition of these forest canopy levels see Table 4.3. The vertical tree canopy structure of forest stands plays an important role in CCF, see, for example, Figure 2.15.
1.2 The Nature of Forestry and Forest Management
Nyland (2002) stated that forestry involves the science, business and practice of purposefully organising, managing and using forests and their resources to benefit people. Many authors adopted the anthropocentric view that it is the prime objective of forestry to satisfy the forest-related demands of society in a sustainable way with minimum input of scarce resources, e.g. energy and money (Köstler, 1956; Bartsch et al., 2020). These demands include the provision of various goods and services, namely of raw materials, environmental conservation and the conservation of aesthetical and spiritual properties (see Section 7.3.3). For a long time, the production of timber has been the only or at least the dominant objective of forestry. This has changed significantly in the last few decades in many parts of the world, although timber production will undoubtedly continue to be important. Even many academic educational programmes lag a little behind in this emancipation of forestry.
To achieve the general objectives of forestry, there are a number of academic and practical fields that help deliver them. The most central one is forest management or silviculture. Köstler (1956) wrote that silviculture is the kernel of forestry and forest science, for it includes direct action in the forest, and in it, all objectives and all technical considerations ultimately converge. Silviculture today is still the main academic discipline providing methods and techniques for goal-oriented management of forest vegetation for a wide range of ecosystem goods and services, i.e. the science of deliberate human–tree interaction. This is the main reason why this field is very attractive to students and largely contributes to their decision to enrol on a forest science rather than an ecology or nature conservation degree programme. Similar to the use of the terms ‘ecosystem management’ and ‘conservation management’, forest management is often used as a synonym of silviculture and sometimes even of forestry as a whole (Helms, 1998). In this book, both terms are used as synonyms. Silviculture has a long history and is the oldest and possibly most traditional subject of forest science and education. As such it also carries much traditional, inherited ‘baggage’ that sometimes is more a hindrance rather than a help (see Section 8.3) and hard to leave behind.
The purely natural forest is governed by no purpose unless it be the unceasing struggle of all the component plant and animal species to perpetuate themselves. Human intervention (be it, for example, for timber production or conservation) is characterised by preference for certain tree species, stand structures, or processes of stand development that have desirable characteristics for the purpose in mind. In silviculture, natural processes are deliberately manipulated to create forests that a majority of humans of a given society perceives as more useful than natural ones and to do so in as short a time as possible (Smith et al., 1997; Nyland, 2002). Given the lifetime of humans compared to that of trees, the acceleration effect achieved by silviculture is not unimportant. The primary objective of silviculture is therefore not necessarily the reconstruction of natural forests but, rather, the establishment and management of forests that can satisfy societary needs. This still requires, however, the retention of a forest's functioning as a viable ecosystem.
Silviculture, and particularly CCF, have gradually developed to use natural processes to a large extent in order to meet societary needs. The ability to utilise the forces of nature has improved during the history of mankind through an increased knowledge of natural laws (Thomasius, 1990). The gradual emancipation from agriculture has made room for employing natural processes in forest management. As a result, it is now entirely possible to conduct forestry indefinitely without the degradation of soils that is almost inevitable in most agriculture and in other ‘higher’ uses of land.
The Roman writer Pliny used the term silvicultura for the first time (Mayer, 1984). The German equivalent Waldbau was coined around 1764 in a time when large-scale forest restoration took place following long-term devastation (Hasel and Schwartz, 2006). A literal translation would be ‘forest building’, ‘forest construction’ or ‘forest design’. This rather strange term was used in the Germany of the eighteenth century to label a new discipline, which was initially thought to be the forestry equivalent to Feldbau, i.e. agronomy (Cotta, 1816). The strong legacy of agriculture in forestry is still evident in the agricultural term ‘crop’ that is often used by foresters to refer to a forest stand or to a plantation grown for commercial purposes, whilst using the expression ‘crop trees’ to distinguish desired trees from less desired trees (Puettmann et al., 2009, see Chapter 3). Early concepts of ensuring sustainability such as the ‘normal forest’ (see Section 1.8) owe much to agriculture, and this legacy lives still on in plantation forestry (Heger, 1955).
Only gradually it became evident that silviculture had to follow very different lines than agronomy, since long production periods of 100 years (and more) and the limited possibilities of influencing production processes set forestry apart from agriculture (see Table 1.1). In agronomy, with its short production periods and with plenty of opportunities for technical manipulation of production, biological processes are part of an industrial framework. On the other hand, agricultural production is influenced much more by short-term weather fluctuations and extremes than forestry. The same applies to changes in the timber market: A forest company can choose to cut less in one year or even over the course of several years. When the market is ready to take larger quantities of certain timber assortments again, these timber reserves can then be reduced. Such flexibility is difficult to achieve in agriculture.
Successful long-term forest management has to be based on biological–ecological requirements, because there is little scope for technical manipulation which is also increasingly being restricted by law in many countries. Therefore, silviculturists by definition are bound to understand and to employ natural processes to meet economic objectives. Economic objectives have to be based on ecological and environmental site limitations rather than keeping highly artificial, industrial and risky crops alive by tending symptoms through chemical forest protection, fertilisation and weeding (Mayer, 1984).
Table 1.1 Characteristics for agronomy (agriculture) and silviculture (forestry).
Source: Adapted from Mayer (1984).
Criteria
Agronomy (agriculture)
Silviculture (forestry)
Target plants
Short-lived grass, herb and perennial species
Long-lived trees
Production period
1 year
40–350 (120) years
Objectives
Meeting current well known demand
Speculative anticipation of future unknown demand
Amortisation of investments
Short with average interest rates
Long-term with low interest rates
Production risk
Low (insurance)
High (owner has to take the risk)
Scope for increasing yield
Larger
Smaller
Fertilisation
Standard. Short-term effect, increased yield rapidly available
Uncommon or prevented by law. Short-term effect with little influence on long-term production
Breeding results
Applicable after few years of testing
Applicable only after 1–2 forest generations (130–300 years)
Production
Cultivation, harvesting and processing mostly within one year
Harvest – management result of past forester generations, processing at present time, replanting for future generations, 4–6 generations of foresters in total
Historical aspects
Only present-day conditions matter
Past management has a long-lasting influence (forest development history)
Initial biological conditions
Artificial plant community with short life expectancy (4–6 months), which is kept alive artificially through soil preparation, fertilisation and chemicals. Maximum production expected
Near-natural to semi-natural biocenosis with long life expectancy (80–120 years). Only stable structures are able to provide long-term production, stands far removed from natural conditions can be at a very high risk
The German term, more than the English word, reflects the main task of silviculture – the active building and development of forests following a plan, which is largely determined by societary needs or preferences. Even forest conservation is anthropocentric, as it satisfies a particular societary need for protecting and sustaining nature. Morosov (1959) pointed out that silviculture bizarrely enough owes its existence to large-scale forest degradation and a painful lack of timber resources. Without this cataclysmic forest degradation and timber shortage, which came to the Europeans as a shock and turned into a long-term trauma, there would not have been a need to consider silviculture and to address sustainability. Dengler (1944) noted that silviculture is concerned with the building and design of forests by arranging their individual components, the forest stands, which significantly influence production, health and utilisation of the forest. In Central Europe, Schädelin, Leibundgut, Abetz and Pollanschütz made the next logical step and extended this idea by breaking these individual components even further down to the level of individual trees (Pommerening et al., 2021a, see Chapter 3).
Silviculture as we know it today is a process of forest engineering aimed at creating structures or developmental sequences that eventually serve the intended purposes, whilst being in harmony with the environment and withstanding the loads imposed by environmental influences. Because forests grow and considerably change with time, their design is more sophisticated and difficult to envision than that of static buildings. This complexity and the fact that considerable costs were involved have made foresters uneasy about their investments in the past and, as an expression of this, natural disturbances have often been labelled as ‘calamities’ and ‘risks’ (Puettmann et al., 2009).
Furthermore, forest stands alter their own environment sufficiently that the forester is partly creating a new ecosystem and partly adapting to the one that already exists (Smith et al., 1997). Based on Helms (1998) and Nyland (2002), we can summarise these aspects in the following definition:
The term ‘silviculture’ or ‘forest management’ denotes the main activity of forestry to establish new forests and the management and regeneration of existing ones as healthy communities of trees and other vegetation. Silvicultural activities should aim to maintain and improve site quality and growth, resilience, quality and diversity of forest vegetation to meet the targeted diverse needs and values of landowners and other members of society on a sustainable basis.
Silviculture is the oldest conscious application of the science of ecology and is a field that was recognised even before the term ‘ecology’ was coined. It is concerned with the technology of growing tree vegetation. Silviculture is also a major part of the biological technology that carries ecosystem management into action (Smith et al., 1997) and silvicultural activities reflect the forester's efforts to imitate natural succession and disturbance. As such silviculture is fundamental to sustainable forestry (Nyland, 2002).
Silviculture and forest management heavily draw on a wide range of basic sciences as does practical silviculture carried out by forest managers in the field. These basic sciences include soil science, climatology, geology, dendrology, hydrology, ecophysiology and many more. When talking about silviculture, it can be practical to distinguish different hierarchical levels. These are
Tree,
Stand,
Forest,
Landscape.
For planning purposes, public and private forest services have other or additional hierarchical levels such as for example sub-compartment, compartment, local area and district.
1.3 Silvicultural Regimes and Types of Forest Management
Silvicultural regimes are technically different methods which give whole forests their specific character (Köstler, 1956). In the Anglo-American literature, both silvicultural regimes and forest regeneration methods are usually lumped together by the term ‘silvicultural systems’ (see, for example, Matthews, 1991; Nyland, 2002). In this tradition, silvicultural systems are perceived as ‘plans for management’ (Nyland, 2002) or ‘planned programmes of silvicultural treatment’ (Smith et al., 1997) including and fully integrating the three main domains of silviculture, i.e. establishment, thinning and harvesting, and extending throughout the life of a forest stand or its present generation. This concept differs from the European view where most silvicultural systems are purely seen as regeneration methods, whilst coppice, coppice with standards and high forest are fundamental silvicultural regimes operating at a higher conceptional level than silvicultural systems, see, for example, Burschel and Huss (1997) and Bartsch et al. (2020). Particularly in the central parts of Europe, it was felt that silvicultural regimes are structural and management archetypes that give all stands subjected to the same regime a similar, general appearance and long-term character. This difference in long-term fundamental appearance sets them apart from the short-term silvicultural systems that they were separated from as a matter of principle (Köstler, 1956; Figure 1.1).
One of the oldest silvicultural regimes is coppice or low forest (in some of the European terminologies like, for example, in German and Spanish), because they were perceived as being limited in stand height due to vegetative reproduction and short rotation (Smith et al., 1997), i.e. a short production period, cf. Figure 1.4. It is believed that this silvicultural regime was first discovered in the Neolithic as a natural consequence of clearing forest vegetation for settlements (Matthews, 1991). When felled near ground level, some of the trees re-sprouted from dormant, adventitious buds in the cambial layer of the remaining tree stumps (also termed stools) or at the roots (root suckers) and these shoots gave rise to a secondary forest that eventually developed into a coppice forest. Layering of trees is another, but rare, technique of coppicing. It naturally occurs in peat bogs where Sphagnum spp. moss tends to overgrow the lower branches of trees in open stands so that roots start to form on them with time. Artificial layering is one of the techniques of inducing branches to form roots while they are still firmly attached to the trees. Later, they can be severed and left in situ or planted elsewhere (Smith et al., 1997). These processes of vegetative regeneration are collectively referred to as coppicing (Nyland, 2002).
Figure 1.1 The relationship between silvicultural regimes and basic silvicultural systems.
Source: Adapted from Pommerening and Grabarnik (2019).
Coppicing was well developed in Roman times and often coupled with the introduction of the species Castanea sativaMILL.. The method was perfected towards the High Middle Ages (Hasel and Schwartz, 2006). Coppice forests (sometimes also referred to as copses) typically have a short rotation length, i.e. all trees are cut every 15 to 25 years because the sprouting ability of trees decreases with age and because traditionally the focus was on small-sized timber assortments (Rittershofer, 1999; Bartsch et al., 2020). New trees of seedling origin occasionally replace worn-out stools. In England, hazel (Corylus avellanaL.) grown in coppice forests for thatching spars is cut every five to seven years which suggests that many other shrub species may be suitable as well. After coppicing, which essentially is a clearfelling operation, the forest then regenerates from stool shoots and root suckers (Figure 1.2). Coppice woodlands are rarely thinned, but on occasion there may be some merit in removing abundant shoots, thereby improving the growth of the remaining stems (Hart, 1995). It is likely that first concepts of rotation and timber sustainability were developed for coppice forests before they were applied to other silvicultural regimes (Hasel and Schwartz, 2006). Due to their fairly short lifetime, the tree diameters involved remain small. In contrast to trees in high forests, each tree of a low forest typically tends to have multiple stems. These stems form vegetation clusters and share similarities with the basitonic growth pattern of shrubs.
In coppice forests, broadleaved species are predominantly used not least for their prolific resprouting ability. In Europe, tree genera included in coppice forests are Acer, Alnus, Betula, Castanea, Carpinus, Corylus, Fraxinus, Populus, Prunus, Quercus, Robinia, Salus, Sorbus, Tilia and Ulmus. Some species of Eucalyptus apparently show phenomenal coppicing potential (Matthews, 1991; Nyland, 2002). The resprouting ability typically decreases with repeated coppicing. Regionally different types of coppice forest exist that favour different species, are managed in different
