Introduction

There are currently two ways in which an exotic pathogen may be introduced into a country for biological control of a pest. It may enter as a ‘classical’ introduction, to be released and established for continuing control of a (usually exotic) pest, or it may enter as a formulated pesticide, either registered or in an experimental form. Either way, when released in the field, there is a likelihood of its establishment. There is a need, therefore, in both cases, to ensure that such introductions are safe to the environment, and pose acceptable risks to non-target organisms.

Introducing exotic pathogens – the classical precedent

Over the past century, the classical biological control of insect pests and weeds has been dominated by the introduction of insect control agents (see Hopper, Chapter 6; and Blossey, Chapter 8). The use of pathogens in classical biological control has been limited, but it is increasing as we come to understand more about the biology of pathogens and see the positive results from a handful of successful programmes.

Against insects pests, the success of the baculovirus of Oryctes rhinoceros on Pacific and Indian Ocean islands is well-known (Bedford, 1986). More recently, a number of exotic introductions have been made against other insect pests, including some cnew associations’. For instance, the fungus Entomophaga praxibuli has recently been introduced into the US from Australia for grasshopper control (Anon, 1989) and an isolate of Entomophaga grylli has been introduced from Australia to the US against the indigenous grasshopper, Phaulacridium vittatum (Milner, 1985).

Abstract

Between 1981 and 1990 more than 50% of the total timber yield in the Czech Republic had to be cut down due to some kind of injury, mostly windthrow or snowbreak. Most damage occurred in stands of spruce (Picea abies Karst.), a species occupying 55% of the forest area. Snow is the main damage factor in younger stands, in the period of height growth culmination. The best protective measure, proven by many experiments, is stimulation of diameter growth by wide spacing or heavy thinning in the period of canopy closure. On the other hand, wind damage starts when the top height of the stands exceeds 10–15 m, and the most reliable protection is a closed canopy and mutual shelter of individuals, with resistance to snow damage created by the previous treatment at a younger stage. A thinning regime is proposed for spruce stands suffering from both snow and wind. Heavy thinning in young stands is recommended, changing to light thinning and growth with full canopy closure in the second half of the rotation. This thinning regime is supported by the results of three long-term experiments in north-eastern Bohemia.

Introduction

Damage to forests by abiotic factors (snow, ice and especially wind) is a very frequent phenomenon in countries where forestry has been based on artificial regeneration with one prevailing species and where the relevant weather conditions are severe. This situation can be found in all Middle European countries (Germany, Switzerland, Austria, Slovakia, the Czech Republic and Poland) as well as in Great Britain and elsewhere (Australia, New Zealand and Japan).

Abstract

Wind damage is frequent in conifer plantations in the Canterbury Plains of New Zealand; 90% of all wood harvested has followed windthrow. Methods have been evolved to cope with this difficult situation. Forestry can now be carried out profitably so long as proper attention is paid to the location of stands and plantation layout, the selection of species, cultivation, tree spacing, planting pattern, thinning, pruning and harvesting. The methods used are described in relation to the prevailing climatic, edaphic and economic constraints.

Introduction

The Selwyn Plantation Board has managed forests on the plains of Canterbury since 1911. At present some 10000 ha of plantation forests are managed for both shelter and wood production. This chapter details the management experiences built up since 1911, and the strategies adopted in the light of that experience. This is reviewed against the background of the national and regional environment.

New Zealand

New Zealand lies in the south-west section of the Pacific, 1600 km to the east of Australia, 10000 km from Panama and San Francisco, and a similar distance from Tokyo and Singapore. The area of the country measures 26.9 x 106 ha. It is similar in size to the British Isles and to Japan. New Zealand is a long (1600 km) narrow country characterised by a ridge of mountains running down its north-northwest to south-south-east axis. In the North Island the mountains tend to be lower. However, high mountains still manage to occupy approximately 10% of the North Island surface.

Introduction

During the 1970s a set of powerful biochemical tools became available for the characterization and manipulation of nucleic acids and proteins. These included the ability to sequence DNA segments rapidly, to excise specific segments, to execute changes to the nucleotide sequences, if and as desired, and then to insert the modified segment elsewhere into the genome. During this period it was also demonstrated that genetic material could be transferred into the genomes of foreign organisms and, under appropriate conditions, be expressed thus leading to synthesis of RNA and protein products. For example ‘expression systems’ using eukaryote genes coding for proteins such as interferon, insulin, growth regulators, etc. could be constructed in bacteria, yeast, insect or other eukaryote tissue cultures. Expression of these foreign genes in the host represented a valuable source of such products.

In the latter part of the 1970s and for much of the 1980s, recombinant-DNA technology was largely used as a powerful and creative tool in molecular biology and genetic analysis. It was principally directed towards fundamental questions such as the improvement of our understanding of gene structure and function and for unravelling chromosome organization.

The notion that novel genetic combinations could be created with recombinant-DNA (r-DNA) technology, which would have been unlikely or impossible to arise in nature, caused molecular biologists to pause and consider the risks from inadvertent or deliberate construction of novel organisms that might cause environmental or health problems should they enter the environment by accident or design.

Mycorrhiza is widespread in all groups of higher plants (Stahl, 1900; Allen, 1991). In general mycorrhizal relationships increase the plant's access to soil resources, i.e. water and mineral ions, thereby increasing its drought tolerance and ability to grow in poor and leached soils. Ectotrophic mycorrhiza is thus strongly associated with conditions of mineral nutrient stress (Harley, 1969).

Orchid mycorrhiza differs in important respects from most other types of mycorrhiza (e.g. Smith, 1974; Harley, 1984; Allen, 1991). The green plant functions as the producer of energy in ectomycorrhizal systems, VAM and ericaceous mycorrhiza, but in the mycorrhiza of orchids the fungus is the source of energy and thus provides the plants with a separate nutrition. This may alternate with, supplement or entirely replace the phototrophic nutrition. Although gametophytes of certain pteridophytes and a few specialized groups of higher plants such as Monotropa have established a similar parasitism on fungi, Orchidaceae is the only large plant group that makes consistent use of this kind of nutrition. It is necessary for seedlings of most plants to develop leaves before the nutrient reserves in the seed are exhausted, and for the plants to remain phototrophic throughout their life. In contrast, orchid seedlings have an option of living for extended periods as heterotrophic organisms; this opens habitats and evolutionary pathways for orchids that would not otherwise have been accessible.

Ecological consequences

Importance of light

Since the orchid mycorrhiza represents an alternative source of energy, it is easy to explain how some species of orchids thrive in deep shade where few other plants will grow. This is most evidently true of the species with chlorophyll deficiency.

Introduction

Biological control by introduction and permanent establishment of exotic natural enemies of pests has been practised for over 100 years. Although a few introductions of beneficial insects had been made earlier, the introduction of an Australian ladybird (Rodolia cardinalis Mulsant) into California to control the cottony cushion scale (Icerya purchasi Maskell) on citrus in 1888–9 (Caltagirone and Doutt, 1989), is generally considered to mark the beginning of the practice of biological control as an effective pest control strategy. This operation was not only highly successful in controlling the pest but also was widely publicized with the result that economic entomologists in a number of countries were soon importing ladybirds for the control of a wide range of pests in what Lounsbury (1940) referred to as the ‘ladybird fantasy’. Few of these introductions were successful, consequently practitioners began to study the ecology and population dynamics of pest natural enemy systems and a more scientific approach to biological control developed (Waage and Greathead, 1988), with a consequent increase in the success rate. However, the introduction of natural enemies remains a largely empirical activity that depends to a large extent on the knowledge and insight of the practitioner.

There are other ways in which natural enemies can be applied as pest control agents; by augmentative or inundative releases of native or exotic agents, which includes formulation of pathogens as biological pesticides (see Huber, Chapter 18; and Waage, Chapter 9) and conservation or enhancement of the action of native species of natural enemies (see Edland, Chapter 4). Because the introduction method was the first to achieve an outstanding success, it is now referred to as ‘classical biological control’.

Abstract

New Zealand's conifer plantations have suffered at least 50000 ha of catastrophic wind damage. This is wind damage to stands over 5 years of age where most stems are either windthrown or broken. Damaged areas have ranged in size from around 1 ha to up to many thousand hectares, and where these have occurred in mature or semi-mature plantation they have usually been harvested. Also of major importance has been continuing attritional wind damage resulting from lesser winds. This is scattered endemic damage which is rarely recoverable. Quantification of the risk of wind damage is important when considering profitability, yield and cash flow projections. For 17 previously State-owned forests, where past wind damage events have been documented, risk of catastrophic wind damage was calculated as the average percentage of net stocked area lost per year. This work considered 50 years of records documenting 30 860 ha of catastrophic wind damage within the 259950 ha of softwood plantations. Estimates of attritional losses to stands over 14 years of age have been obtained from the extensive permanent growth sample plots located throughout these forests. The overall forest catastrophic and attritional levels of damage were found to be 0.38% and 0.25% of net stocked area lost per annum respectively. These data correspond to an average 12% of forest area lost over a 28 year rotation. While the least-affected forests would lose only 5–6%, the worst-affected would lose most of its stocked area. Forests subjected to high windspeeds associated with upwind mountainous terrain have had far greater levels of wind damage.

Introduction

A major attraction of the application of genetic engineering to microbial inoculant strains is the ability to create new strains with capabilities that may not be easily obtained by a process of natural selection. Such additional features may enhance the performance of an inoculant strain.

The fluorescent Pseudomonas species are an important group of bacteria that can play a beneficial role in the protection of crop plants against deleterious pathogenic micro-organisms. These bacteria produce a wide range of factors antagonistic to pathogens (particularly fungi) they include the yellow-green, fluorescent siderophores that characterize this group.

Our work has concentrated on the role of siderophores and antibiotics of fluorescent Pseudomonas in the biocontrol of ‘damping-off’ disease of sugar-beet seedlings (see Table 14.1). The biosynthesis and excretion of iron-binding siderophores are thought to decrease the pool of iron available to pathogenic fungi and other harmful micro-organisms and so contribute to the plant growth promotion effect observed when plants are inoculated with the appropriate Pseudomonas strain (Kloepper et al 1980). The producing micro-organism can use the resulting Fe3+ (ferric) siderophore complex via specific receptors located in its outer membrane (Magazin et at., 1986).

Outer membrane receptor proteins can be highly specific and only transport the appropriate ferric siderophore into the producing cell. The structures of these fluorescent (yellow-green) siderophores was reviewed by Leong (1986). Fluorescent siderophores are only produced under iron-limiting conditions, as are receptor proteins.

Abstract

A wind tunnel was used to investigate the wind regime in forest clearcuts. The model forest had a uniform height of 15 cm and a density of 500 stems m−2 to simulate an Engelmann spruce stand of height 15 cm and density 500 stems ha−1. It was found that the mean windspeed near the surface at 22 tree heights downwind of the forest edge was about 65% of the potential value obtained when no forest was upwind. From the measured mean windspeed, turbulence intensity and integral scale in the vertical direction, the vertical turbulent diffusivity was calculated. According to the spatial distribution of the vertical diffusivity at one-fifth of the tree height, a quiet zone, a wake zone and a readjustment zone were identified downwind of the forest edge.

Introduction

Despite many environmental concerns, clearcutting still remains the major timber harvesting method in British Columbia, Canada, and in many regions of the world. Forest regeneration in clearcuts is an issue of great public and scientific concern. Tree seedlings in clearcuts often experience temperature extremes, increased water loss due to exposure to the wind, and winter desiccation as a result of snow removal by wind. Blowdown along the edges of clearcuts is also a significant problem in British Columbia and little information is available to assess the effects of clearcut size and shape on wind regime. The purpose of this chapter is to provide information on the wind regime in forest openings. This information is essential to evaluate the effect of clearcut size on seedling microclimate and blowdown potential of clearcut edges.

Abstract

An experimental study was performed to test the model of buttress development proposed by Claus Mattheck: that the high rates of growth occurring along the top of the junction between the trunk and the lateral roots are stimulated by the mechanical strains set up by wind forces which are concentrated in these regions. Strain gauges were attached around the base of the trunk and the lateral roots of young rainforest trees which were developing buttresses; strains were measured during simulated wind events when the trunk was bent over using a winch. Results supported Mattheck's theory: strains were concentrated along the top of developing buttresses and on the trunk above them – the places of maximum growth – and were negligible on the sides of the buttresses and at the base of the trunk where no growth was occurring. Buttress development seems to be controlled by the mechanical environment of the tree. Once the root system, in which lateral roots are attached to the subsoil well away from the trunk by sinker roots, has formed the growth of buttresses occurs automatically. This produces a mechanically efficient anchorage system in terms of the carbon investment. Trees which do not form buttresses instead transfer forces into the ground using a tap root or sinkers positioned close to the trunk.

Introduction

Root buttresses are a characteristic feature of the trees of lowland tropical rainforest. These huge plate-like structures which are formed around the base of the trunk have been the subject of speculation by generations of biologists who have attempted to discover what function they serve and what influences their development.

Abstract

In most European countries, forests are a natural resource of timber. Neglecting information about tree growth, forestry planning and landscape modifications for construction work (e.g. for industrial areas) may result in large economic losses from damage to trees. This chapter presents a method for assessing areas of forest with an increased risk of storm damage due to a proposed landscape modification for a new motorway. The planned new road will cut through a forested mountain ridge, changing both the topography and land-use. A hierarchy of models is applied to simulate winds over hills and changing terrain properties. The first coarse-grid model is on the need to determine wind modification according to the overall topography of the area using synoptic input data. These results are then included as input data for further calculations with fine-scale models. The models are applied to a high-resolution grid which covers the area of the motorway to be built and includes the modifications of landscape and land-use. Finally, wind fields and turbulent kinetic energy are determined at a high spatial resolution for different weather regimes, topographies and land-uses. Areas with an increase or decrease in windspeed will be readily defined as a function of synoptic windspeed and wind direction. The computing facilities required are those of a 486 PC or a workstation.

Introduction

Meteorological variables such as high windspeed and precipitation are known to have an important influence on the risk of damage to trees, together with topography, silvicultural methods, species and stand structure, and the health of the trees (Mayer, 1985).