Urban Tree Management E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 545

Veröffentlichungsjahr: 2015

Beschreibung

Urban tree management is the key basis for greener cities of the future. It is a practical discipline which includes tree selection, planting, care and protection and the overall management of trees as a collective resource.

Urban Tree Management aims to raise awareness for the positive impacts and benefits of city trees and for their importance to city dwellers. It describes their advantages and details their effects on quality of urban life and well-being – aspects that are increasingly important in these times of progressing urbanisation.

With this book you will learn:

• fundamentals, methods and tools of urban tree management
• state of the art in the fields of urban forestry and tree biology
• positive effects and uses of urban trees
• features, requirements and selection criteria for urban trees
• conditions and problems of urban trees
• governance and management aspects
• environmental education programs.

Edited by the leading expert Dr Andreas Roloff, Urban Tree Management is an excellent resource for plant scientists, horticulturists, dendrologists, arborists and arboriculturists, forestry scientists, city planners, parks department specialists and landscape architects. It will be an essential addition to all students and libraries where such subjects are taught.

Leseprobe

Urban Tree Management

for the Sustainable Development of Green Cities

EDITED BY

Andreas Roloff

Dresden University of Technology,Tharandt, Germany

with contributions by:

Eckhard Auch, Markus Biernath, Sten Gillner, Mathias Hofmann, Doris Krabel, Rolf Kehr, Sandra Korn, Matthias Meyer, Ulrich Pietzarka, Hubertus Pohris, Jürgen Pretzsch, Andreas Roloff, Steffen Rust, Andreas Tharang, Juliane Vogt

Dresden University of Technology, Germany

This edition first published 2016 © 2016 by John Wiley & Sons, Ltd.

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Library of Congress Cataloging-in-Publication Data

Urban tree management : for the sustainable development of green cities / edited by Andreas Roloff.  pages cm Includes index.

 ISBN 978-1-118-95458-4 (pbk.)1. Urban forestry. 2. Trees in cities. 3. Sustainable development. I. Roloff, Andreas, 1955– editor.  SB436.U736 2016 634.9–dc23

        2015031844

A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Cover image: © Andreas Roloff

List of contributors

Dr. Eckhard AuchTechnische Universität Dresden, Institute of International Forestry and Forest Products, Tharandt, GermanyDr. Markus BiernathStaatsbetrieb Sachsenforst,Forest District Dresden,Dresden,GermanyDr. Sten GillnerTechnische Universität Dresden,Institute of Forest Botany and Forest Zoology,Tharandt,GermanyDr. Mathias HofmannSwiss Federal Institute for Forest, Snow and Landscape Research WSL,Social Sciences in Landscape Research Subunit,Birmensdorf,SwitzerlandProf. Dr. Rolf Kehr HAWK Hochschule für Angewandte Wissenschaft und Kunst, Fakultät Ressourcenmanagement, Göttingen, GermanyDr. Britt KnieselTechnische Universität Dresden,Institute of Forest Botany and Forest Zoology, Tharandt,GermanyDr. Sandra KornTechnische Universität Dresden,Institute of Forest Botany and Forest Zoology,Tharandt,GermanyProf. Dr. Doris KrabelTechnische Universität Dresden,Institute of Forest Botany and Forest Zoology,Tharandt,GermanyDr. Matthias MeyerTechnische Universität Dresden,Institute of Forest Botany and Forest Zoology,Tharandt,GermanyDr. Ulrich PietzarkaTechnische Universität Dresden,Tharandt Botanic Garden & Arboretum,Tharandt,GermanyDr. Hubertus PohrisTechnische Universität Dresden,Institute of International Forestry and Forest Products,Tharandt,GermanyProf. Dr. Jürgen PretzschTechnische Universität Dresden, Institute of International Forestry and Forest Products, Tharandt,GermanyProf. Dr. Andreas RoloffTechnische Universität Dresden,Institute of Forest Botany and Forest Zoology,Tharandt,GermanyProf. Dr. Steffen RustHAWK Hochschule für angewandte Wissenschaft und Kunst, Fakultät Ressourcenmanagement, Göttingen,GermanyAndreas TharangTechnische Universität Dresden,Institute of Geodesy,Dresden,GermanyDr. Juliane VogtTechnische Universität Dresden,Institute of Forest Biometry and Systems Analysis,Tharandt,Germany

CHAPTER 1Intro: Urban trees – Importance, benefits, problems

Andreas Roloff

Technische Universität Dresden, Tharandt, Germany

1.1 Introduction

Trees often and quickly gain a bad reputation, caused by falling branches or entire trees, roots in sewage drains, neighbors fighting over fruit and leaves littering their gardens, health issues from pollen allergies, etc. The problems caused by city trees are usually more conspicuous and have greater ramifications. Their advantages can often be difficult to record and to assess. As a result, the negative impacts are much more widely discussed, whereas extensive papers about their positive aspects are rare.

This chapter, therefore, aims to raise awareness of the positive impacts and benefits of urban trees and their importance to city dwellers (Figures 1.1 and 1.2). It describes their advantages (with no claim to completeness) and details their effects on our quality of life and well-being – aspects that are increasingly important in these times of progressing urbanization.

“If I knew the world would end tomorrow, I would still plant another tree today.”

– Martin Luther

Figure 1.1

CHAPTER 2Urban trees: Features andrequirements

Andreas Roloff

Technische Universität Dresden, Tharandt, Germany

2.1 Urban tree site categories

Urban trees are subject to several special stress factors, connected to and caused by living conditions that are extreme compared to forests (Figure 2.1). Of course, this varies greatly, depending on where in a city a tree is placed. Possible site types are ordered below, in Table 2.1, by decreasing naturalness and increasing stress.

Figure 2.1

CHAPTER 3Fundamentals of tree biologyfor urban trees

Doris Krabel

Technische Universität Dresden, Tharandt, Germany

3.1 Morphological and anatomical features

3.1.1 Trunk

In comparison to woody shrubs, trees are characterized by a dominating trunk, whose lowermost part can reach a great height with age, and which is generally free of branches. In contrast, the shape of shrubs is characterized by several trunks, without a dominating stem, a height of up to ten meters, and the development of strong shoots at the basal part of the plant. Shrubs tend to rejuvenate from the bottom (Roloff, 2013). The transverse sections of a woody shoot present three major parts (Figure 3.1).

Figure 3.1Quercus stem, showing the transverse surface.

CHAPTER 4

CHAPTER 5Drought stress: Adaptation strategies

Sandra Korn

Technische Universität Dresden, Tharandt, Germany

5.1 What is stress? – Stress concepts

Classical stress concepts define “stress” as a significant deviation from optimal conditions for life. It is always induced by too little or too much of the respective factor. Schulze et al. (2005) give, as an example, the environmental factor “temperature” for two plant species – Rhododendron ferrugineum and Zea mays – which differ in their natural habitat. The rhododendron is to be found in central and southern European mountains in cold habitats, while maize is a Central American warmer climate plant. Therefore, they also differ in their perception of temperature stress. While R. ferrugineum finds optimum temperature for growth and vitality at 12–25°C, Z. mays has an optimum of 22–28°C.

Temperatures above and below these span are perceived as stress, and have a negative impact on the state of active life of the plant. Temperatures of, for example, 30°C imply more pronounced stress to cold-adapted R. ferrugineum than to maize. Thus, the optimum and stress span of any environmental factor, as well as the stress response of the plant, are highly variable and will depend on species, adaptation, combination of multiple stresses, etc. Also, the duration of the stress plays an important role on how plants can cope with it. A distinction should be made between temporary stress and permanent stress (Larcher, 1995). Temporary stress generally results in short-term impairment, since the stress response of the plant (its functional state) returns to normal after a short period of recovery. In contrast, permanent stress lowers the functional state of the plant over a long period. Even after cessation of the stressing conditions and a recovery period, the former normal functional state of life could not be sustained.

There is a large number of biotic and abiotic factors that are able to induce stress in plants (see Table 5.1). The interplay of numerous stressors and/or successive stresses may lead to enhanced or even diminished stress or, in the worst case, to a limitation of the plant’s life (Larcher, 1995).

Table 5.1 Examples for biotic and abiotic stressors (Adapted from Larcher 1995).

Stressors

Abiotic

Biotic

Radiation

Excess, shading, UV radiation

Plants

Crowding, shading, allelopathy, parasites

Temperature

Heat, cold, frost

Microorganisms

Viruses, bacteria, fungi

Water

Drought, flooding, stagnant water

Animals

Grazing, trampling, urine

Gases

Oxygen deficiency, methane-, CO

2

-enrichment

Anthropogenic

Pollution, soil compaction, soil sealing, fire, agrochemicals, waste

Damage, pruning/cutting

Minerals

Nutrient deficiency, salinity, acidity, alkalinity, heavy metals

Mechanical effects

Wind, snow cover, burial

5.2 Stress responses

Trees, like plants in general, are sessile and cannot escape stressors by moving. Trees live over many growing seasons and, therefore, have developed mechanisms to respond to environmental stressors. They have generated an array of regulatory mechanisms for maintenance of their vital processes (water uptake, photosynthesis, metabolism, etc.) and their survival. If a plant is unable to cope with a stressor (lethal stress), it is restricted to areas without this particular stress factor (e.g., trees which cannot cope with water logging situations do not grow in flood plains). In general, adaptation to stress is a relative measure describing the tree’s capability to cope with a stressor relative to other species (Niinemets, 2010).

5.2.1 Adaptation to drought stress – stress escape

For the purpose of discussing the different adaptation strategies, the focus here is on drought as a stressor. Drought may appear as short, dry periods, extended dry seasons in monsoonal climates, or even water/irrigation restrictions. It always includes limitation on water availability. However, it should be kept in mind that these stress concepts are also valid for other stressors, such as salinity, cold, pollution, and so on.

Species adapt to stress using different strategies. The strategy of escaping is very common among herbaceous plants, but is not to be found among tree species. Plants use phenological plasticity to avoid stressing periods; geophytes, bulb and tuber geophytes and annual plants survive drought periods by production of seeds or perennating (underground) organs like bulbs, rhizomes, or tubers which are protected from desiccation deep in the soil. They sprout or germinate at appropriate seasons, after rainfall events, or during rainy periods (Bresinsky et al., 2008).

A more important mechanism to cope with stress for trees is stress resistance. This adaptation to stress has numerous different characteristics at physiological, cellular, genetic, molecular, metabolic, anatomical and/or morphological levels. Based on different reactions, stress resistance is subdivided once more into tolerance and avoidance strategies (Bresinsky et al., 2008):

Avoidance mechanisms ensure that essential organs, physiological processes and cytoplasmic structures of the cells are not impaired by any water limitations.

Tolerance strategists, on the other hand, endure drought stress without damage to the aforementioned parts (Lösch, 2001).

5.2.2 Adaptation to drought stress – stress resistance by avoidance

A broad range of structural and physiological adaptations have evolved to avoid mild or severe drought stress. Tree species each possess a characteristic combination of avoidance mechanisms. The two main objectives for this strategy are:

to improve the uptake of available water; and

to reduce the transpirational water loss.

A deep tap root, in combination with a rapidly growing, extensive root system, allows the tree access to water in deeper soil layers. For example, some Acacia species in Australia are found to have roots reaching down to 12 m or more (Moore, 2013). Structural adaptations in the hydraulic architecture of the water-conducting system can also enhance water uptake. Producing more xylem with smaller vessels, enlarges the area of the water-conducting system, concurrently lowering the threat of xylem vessel cavitation (disruption of water flow by the formation of vapor cavities due to insufficient water supply).

Trees have evolved a wide variety of modified leaf characteristics, including alterations in morphology, leaf area reduction, and stomatal control, to reduce the transpirational loss of water. A reduction in leaf area can be achieved by developing pinnate or deeply lobed leaves, or needles and needle-like leaves. These leaf shapes reduce the area exposed to the sun, and have lower leaf temperatures than undivided leaves. A dense hairiness and shiny (upper) leaf surface area have the same effect (Figure 5.1).

Figure 5.1 Examples for morphological drought adaptations to avoid drought stress. Left: Pinnate and shiny leaves of Catania spec. Right: Dense hairiness of young Rhododendron spec. leaves.

An early leaf senescence, as well as leaf abscission during drought periods (e.g., dry-deciduous species from tropical dry forests), is another mechanism that allows trees to reduce their transpirational area.

Anatomical adaptations at leaf level often exhibit xeromorphic traits (Raven et al., 1988). Figure 5.2 shows a cross-section through a xeromorphic leaf of Nerium oleander. These leaves develop a thick cuticle and compacted epidermic cell walls, lowering the transpiration of the epidermic cells. The epidermis can be multi-layered. In addition, the upper leaf surface is covered with thick layers of wax, which give the leaf its characteristic sheen. Stomata are at the underside of the leaf. These are sunken stomata, at the base of pits called stomatal crypts. The stomata are hidden behind miniscule hairs in order to create a moister microclimate inside. Also, the size and distribution of stomata commonly varies with limited soil water availability; the number and size of stomata are inversely related. Plants growing under drier conditions often show smaller, but more densely distributed, stomata. This allows plants to maintain high rates of gas exchange when all stomata are open, but a more pronounced control of stomatal aperture during water-demanding periods. Moore (2013) reports a range from 28 stomata mm–2 in arid Persoonia species to 100–350 mm–2 in Eucalyptus species in Australia.

Figure 5.2 Cross-sectional illustration of drought adapted xeromorphic leaf of Nerium oleander. C – thick waxy cuticle; E – three-layered epidermis; S – stomata in SC – stomatal crypt with hairs.

A very important physiological mechanism in avoiding drought stress for trees is the stomatal regulation of the transpiration. Transpiration is the loss of water from stems and leaves, the major part of which is transpiration through stomata. Plants open the stomata to take up carbon dioxide for photosynthesis. At the same time, water vapor diffuses out of the leaf, driven by a gradient in humidity between the saturated atmosphere inside the leaf and the less humid surrounding air. Due to the cohesive character of the water molecules, this process moves water as a continuous column through the whole tree. The driving force is a water potential gradient, where “water potential” describes the energetic state of the water retained by physical and chemical forces in cells, organs, soil, etc. (simplified: their “capability for water uptake”). Water potential is negative by definition, and becomes more negative with lack of water.

CHAPTER 6

CHAPTER 7Vitality assessment, tree architecture

Andreas Roloff

Technische Universität Dresden, Tharandt, Germany

7.1 Introduction

In this chapter, general aspects of tree architecture and methods of tree vitality assessments are discussed, and existing disparities or contradictions are pointed out when assessments based on “leaf loss” and based on crown structures are compared. The necessity of considering the branching pattern is substantiated, and the methods developed to date are presented.

It is still very difficult to determine tree vitality and, thereby, the effects of stress and decline in deciduous trees. The reason for this difficulty is due to the fact that, until now, most inventories considered only parameters such as “percentage leaf loss”. Therefore, this chapter puts focus on the branching pattern and the crown structure of trees in the assessment of tree vitality.

7.2 Decline and stress symptoms of tree crowns: “leaf loss” vs. crown structure

The consideration of crown structures in the assessment of tree vitality has become increasingly important. That scientists are now aware of the problem of “leaf loss” has been shown in many studies (Roloff, 1989). The number of leaves, and above all the leaf size, is subject to considerable annual fluctuations – for example, as a result of drought and insect damage or flowering and fructification. However, leaf size can vary greatly, even within the same crown of a deciduous tree. Thus, it is difficult to show a statistical significance in values between different trees. The correlation between “leaf loss” and fructification intensity has been well demonstrated but, on the other hand, the foliage must also be considered if possible.

In this context, there is one more aspect which should be mentioned, for it has become particularly apparent in the most recent investigations. There is a great variety of tree species in which, with increasing shoot lengths (i.e., with better growth), the crown becomes more transparent. In this case, a vitality assessment on the basis of crown transparency versus crown structure is bound to produce exactly opposite results (Roloff, 1989). Finally, there are pioneer species, such as many birch and pine species, which never show a crown without any gap or transparency, because this is typical for the species strategy – the light crown.

For this reason, it is not surprising to find considerable disagreement between so-called “leaf loss” and crown structure (to be discussed in the following chapter), which occurs when vigor assessments of the same trees are compared. Assessments may differ markedly, and agreement is only achieved in about 50% of the assessed trees.

Therefore, it would be advantageous if the term “leaf loss” were to be replaced by a different, more objective term such as “crown transparency”, which does not lead to the misconception of shedded leaves. A deciduous tree showing a “leaf loss” of 30% does not mean that 30% of the leaves have been shed. These leaves often simply never existed at the beginning of the growing season because of gaps in the branches.

7.3 Tree architecture and reiterations

7.3.1 Architectural models

On the basis of so-called architectural models, woody species (trees and shrubs) all over the world can be classified into types with similar branching patterns and crown development (Hallé et al., 1978; Oldeman, 2014). Important criteria are the direction in which top shoots and lateral shoots grow, the length of the growth period and the position of the flowers. The relevant models, named after renowned botanists (e.g., Rauh), will be introduced in the following. Considering that 23 models can be differentiated and described worldwide, the number of the most important ones for trees can be reduced to five due to the following facts:

the

trunk is ramified

(this is not the case in several species of palm trees);

the

vegetative axes are differentiated

into a dominant trunk and subordinate branches (which is usually not the case in shrubs);

most woody plants

grow rhythmically

, with clearly discernible annual growth modules due to dormancy in winter or during drought periods.

The abovementioned five most important architectural models are defined by the following characteristics (see Figure 7.1):

Rauh

: All shoots are ± vertically oriented, flowers in lateral position.

Scarrone

: All shoots are ± vertically oriented, flowers in terminal position.

Massart

: Vertical trunk, ± horizontal lateral branches.

Champagnat

: All top shoots grow vertically at first; some become horizontal by turning downwards secondarily.

Troll

: All shoots grow horizontally at first; the top shoot straightens up in a secondary stage.

Figure 7.1 The five most important architectural models of broadleaved trees.

CHAPTER 8Body language of trees, tree diagnostics

Andreas Roloff

Technische Universität Dresden, Tharandt, Germany

8.1 Terms and definition

Those who are much engaged with trees will be strongly impressed by how much of a tree’s state, of its inner life and of its past/history can be deduced from its exterior appearance and symptoms. While trees cannot smile to indicate happiness, and do not look sad when they are suffering, as we humans do, events leave their marks on them for much longer – sometimes for life. We therefore also use the term “body language” for trees (Visual Tree Assessment/VTA by Mattheck and Breloer, 1997; Harris et al., 2004) to mean the interpretation of external symptoms to assess the tree’s current state, internal defects and the effects of past events.

The term “tree diagnostics” indicates that, in addition to the actual symptoms, a lot of background information and tree biology knowledge are taken into consideration, just as in human medical diagnostics (Roloff, 2015). Knowing the body language and the diagnostic characteristics is essential for tree inventory, assessment and understanding, where the primary objective is an initial evaluation of a tree’s state and potential risks or defects. Possible causes of these can be diagnosed without using technical equipment, based on a visual assessment of external symptoms alone (see Chapters 7 and 9 and ISA, 2015). Depending on the results of this inspection, it may then be decided that further examinations (with technical devices if appropriate) should be carried out (see Chapter 9).

8.2 Adaptation and optimization in trees

Trees cannot survive without adaptation. They cannot escape colds, droughts or flooding, human damage or urban site stress. They can either cope with these and other events and factors, or they have to die. No other group of organisms on earth is as dependent on optimization and adaptation as trees, whose progress through generations is extremely slow by comparison to herbaceous or low plants, or to animals.

A tree can only survive by making the use of existing resources in the best way possible, by distributing its leaves in the air space and developing roots into the ground as efficiently as possible and at a minimum effort. This is known as the survival strategy of trees. In this context, the word “strategy” does not have the same meaning as it does for people; trees do not plan or calculate things. Still, it is common usage in ecology to speak of a strategy as features which have been adopted over the course of evolution and which facilitate survival among competitors. Strategy is the total sum of all genetically fixated physiological, anatomical and morphological adaptations that serve to conquer and to defend a site by using its resources as efficiently as possible (see Chapter 16).

Also, the term “strategy” does not refer to the individual tree, but to the entire species or the life form tree in general. A strategy ensures long-term survival, because it ensures the survival both of the individual trees and of the entire species by reproduction.

Trees can be understood as masters of survival, and their strategies of adaptation and optimization are admirable (see Chapter 16). If trees are seen this way, it may awaken an interest in imitating these phenomena, with a view to improving our daily life and our social existence and making it easier. Trees can, indeed, teach us a lot in this respect. They can serve as examples, especially for technical constructions and processes – an aspect which has recently been worked on by the science of bionics. This branch of science, however, which is still very young, has not been paying much attention to trees as yet.

Particularly impressive are the various mechanisms of self-repair and self-regeneration, the biological self-optimization which is taking place in trees at all times. However, we have to interpret these symptoms of self-repair on the basis of tree biology knowledge.

8.3 Examples and explanation: branches, trunk/bark, roots

We now will look into details of tree body language symptoms in the order of branches, trunk/bark and root/root collar.

8.3.1 Branch-shedding collar