Amenity Trees Research Articles

Pedunculate Oaks (Quercus robur L.) Differing in Vitality as Reservoirs for Fungal Biodiversity.

Ecological significance of trees growing in urban and peri-urban settings is likely to increase in future land-use regimes, calling for better understanding of their role as potential reservoirs or stepping stones for associated biodiversity. We studied the diversity of fungal endophytes in woody tissues of asymptomatic even aged pedunculate oak trees, growing as amenity trees in a peri-urban setting. The trees were classified into three groups according to their phenotypic vitality (high, medium, and low). Endophytes were cultured on potato dextrose media from surface sterilized twigs and DNA sequencing was performed to reveal the taxonomic identity of the morphotypes. In xylem tissues, the frequency and diversity of endophytes was highest in oak trees showing reduced vitality. This difference was not found for bark samples, in which the endophyte infections were more frequent and communities more diverse than in xylem. In general, most taxa were shared across the samples with few morphotypes being recovered in unique samples. Leaf phenolic profiles were found to accurately classify the trees according to their phenotypic vitality. Our results confirm that xylem is more selective substrate for endophytes than bark and that endophyte assemblages in xylem are correlated to the degree of host vitality. Thus, high vitality of trees may be associated with reduced habitat quality to wood-associated endophytes.

CAVAT (Capital Asset Value for Amenity Trees): valuing amenity trees as public assets

Valuing amenity trees is important for calculating loss of amenity and replacement value following wilful or negligent damage, and for several aspects of urban forest management: planning, budget setting and decision-making. Capital Asset Value for Amenity Trees (CAVAT) is a tool for valuing amenity trees; it was first presented publicly in 2003. It includes two methods: the Full Method, which is used to provide a compensation replacement value for single trees; and the Quick Method, which is used to determine the value of a population of trees as an asset, for asset management purposes. CAVAT is widely adopted across the UK within local authority tree departments, and by major land-holding and transport organisations. It is also incorporated into the Joint Mitigation Protocol for use in the assessment of subsidence cases. This paper presents CAVAT for the first time in a formal publication. It describes the uses for which it has been designed, it comprehensively describes the methodology and shows where this deviates from similar valuation tools. Five case studies are presented as examples of its application and demonstration of its suitability-for-use. Finally, future potential developments that would facilitate wider use of CAVAT are also presented.

The effect of simulated trunk splits, pruning, and cabling on sways of quercus rubra L.

Cabling co-dominant stems at different heights and tensions altered neither frequency nor damping ratio, but the location and proportion of pruned crown mass significantly influenced both frequency and damping ratio. Amenity trees provide many benefits, but can damage property and injure persons. Arboricultural treatments like pruning and cabling intend to reduce the likelihood of tree failure, but the effect of such treatments on tree sways is not well known. We measured the sway response (frequency and damping ratio) of seven Quercus rubra L. before and after consecutive arboricultural treatments, including the addition a climber swaying freely or secured rigidly to the tree. We also quantified crown architecture and tree mass. Cabling two co-dominant stems did not influence sway response, but pruning increased frequency and decreased damping ratio. The effect of pruning depended on the proportion and location of pruned crown mass. Adding a climber predictably affected frequency and damping ratio in accordance with physical principles. This work adds novel insights to the understanding of tree sways, since previous studies have been limited by single trees, pruning types, or pruning severities.

Pest categorisation of Fusariumoxysporum f. sp. albedinis.

The Panel on Plant Health performed a pest categorisation of the soil‐borne fungus Fusarium oxysporum f. sp. albedinis, the causal agent of Fusarium wilt of date palm, for the EU. The identity of the pest is well established and reliable methods exist for its detection/identification. The pest is listed in Annex IIAI of Directive 2000/29/EC and is not known to occur in the EU. Fusarium oxysporum f. sp. albedinis is present in Morocco, Algeria and Mauritania. Its major host is Phoenix dactylifera, which is the only Phoenix species known to be affected by the pest. Uncertainty exists about the host status of Lawsonia inermis, Medicago sativa and Trifolium spp. cultivated as intercrops in the infested areas and reported as being symptomless carriers of the pest. The pest could potentially enter the EU on host plants and soil/growing media originating in infested Third countries. The current pest distribution and climate matching suggest that the pest could establish and spread in the EU wherever the host is present. In the infested areas, the pest causes vascular wilt resulting in yield/quality losses and plant death. It is expected that pest introduction and spread in the EU could impact date production. The pest is expected to have high environmental consequences in the Elche area (Spain), which is a UNESCO World Heritage Site, as well as other EU areas where P. dactylifera is grown as an amenity tree. Current EU phytosanitary measures are not fully effective at mitigating the risk of introduction and spread of the pest in the EU. Fusarium oxysporum f. sp. albedinis meets all the criteria assessed by EFSA for consideration as potential Union quarantine pest. As the pest is not known to occur in the EU, this criterion to consider it as Union regulated non‐quarantine pest is not met.

Can pruning help maintain vitality of ash trees affected by ash dieback in urban landscapes?

Hymenoscyphus fraxineus causes a destructive invasive tree disease known as ash dieback threatening the survival of common ash not only in the forests, but also in urban and landscape settings. Pruning is a potential management practice that could help maintain tree vitality and aesthetics in parks, gardens, alleys and recreation areas, as well as maintaining veteran trees having high heritage or cultural value, or trees with high genetic importance (e.g. located in clonal seed orchards). In this study we investigated the maximum distance proximal to the lesion margin at which H. fraxineus can be detected on individual branches infected by the fungus in order to provide recommendations for pruning. Pruning of branches was carried out on 38 trees in southern Sweden. Tissue samples including bark and wood were collected from the margin of the lesion and at 5cm intervals proximal to the lesion. Molecular analysis revealed presence of H. fraxineus in 91.3% of the investigated lesions. The proportion of lesions at which H. fraxineus could be detected declined with increasing distance from the lesion margin, with a significant reduction in the number of positive samples at 10cm proximal to the margin. At 30cm from the lesion edge the pathogen was never detected. Our results suggest that routine pruning may help maintain the vitality of younger trees. Pruning branches at least 35cm from visible, active lesions in the bark should exclude the fungus and therefore reduce the probability of stem infection by H. fraxineus, however this cultural control tactic may only be economically feasible for high value amenity trees.

Dutch elm disease in New Zealand: impacts from eradication and management programmes

Ophiostoma novo‐ulmi, the cause of the current pandemic of Dutch elm disease, is considered one of the 20 worst pests to have been introduced to New Zealand. An attempt to eradicate the pathogen came close to success, but was eventually stopped and replaced by management programmes. These programmes are slowing the spread of the pathogen. If left uncontrolled it is likely that New Zealand will lose 90% of its elm trees. Although elms are exotic trees in New Zealand, the loss of such a large number of popular amenity trees is likely to have numerous social, cultural, environmental and economic effects. It is estimated that this disease could cost public and councils over NZD $350 million in tree removal and replacement costs. Control of O. novo‐ulmi is limited, but biological control using d‐factor viruses has been proposed. Although O. novo‐ulmi was not eradicated from New Zealand, the eradication programme had many successes; in particular, the effective interaction of good management and science in the early years of the campaign. Also highlighted in this review are several tactics and steps that could be applied to eradication attempts for other species.

Can composite indices explain multidimensionality of tree risk assessment? A case study in an historical monumental complex

Urban trees are a source of ecosystem services and contribute to increase quality of life for many communities and their residents. At the same time they could also determine disservices, such as damages to structures and risk to human safety due to critical combination of tree defects and environmental factors. Although knowledge about tree structure and host–pathogen interactions has grown, the assessment of risk has not been fully explored yet. In particular, the multidimensionality of tree risk assessment as well as the concern about weighting techniques in the construction of indices to measure it need to be addressed.The aim of this paper is to develop a composite tree risk index (R) useful for the management of amenity trees, with a two-fold perspective. First, the multidimensionality issue is explored by considering three dimensions of the tree risk: the Hazard, that represents the likelihood of failure of the tree, the Contact factor, i.e. the nature and the value of the target, and the Damage factor, i.e. the potential for injury or damage. Each dimension is assessed as a function of a set of observed variables related to dendrometric attributes, health status, proximity to buildings and artifacts, tree esthetic value, derived both from field data and spatial analysis performed under GIS environment. Second, in the aggregation of variables into specific-dimension indicators we verify if and to what extent various positive and normative weighting techniques influence the construction of composite index. The R index, obtained as the product of the specific-dimension indicators, was computed for 130 trees located within the formal garden and the park of Villa Lante in Bagnaia, Viterbo (Central Italy), a well-known Renaissance monumental complex, where the needs of cultural heritage conservation and human safety have to be balanced with recreational uses. Sensitivity analyses were carried out in order to test the robustness of R with respect to the considered techniques.

Susceptibility of four Eucalyptus host species for the development of Thaumastocoris peregrinus Carpintero and Dellapé (Hemiptera: Thaumastocoridae)

Thaumastocoris peregrinus is a serious sap-sucking pest of Eucalyptus species in many important forest growing regions worldwide. This invasive insect may not only cause enormous economic losses to the eucalypt forest industry but also negatively affect urban trees in public spaces. We conducted laboratory experiments to evaluate the susceptibility of four Eucalyptus species for the development of T. peregrinus. Three of the tested Eucalyptus species are economically important for the forestry industry worldwide and the other is a popular amenity tree in New Zealand. The development of eggs, nymphs and adults was evaluated in excised leaf assays. Eucalyptus nitens and Eucalyptus nicholii were identified as suitable host plants. The adult leaf type of E. nitens was shown to be critical for successful feeding. Despite initiating feeding T. peregrinus did not survive beyond 1st instar nymph on either Eucalyptus fastigata or Eucalyptus regnans. Accordingly, our study contributes evidence that there may be a lower risk to species within the subgenus Monocalyptus from T. peregrinus damage. These are positive findings for the forestry sector as E. regnans and E. fastigata are both valued Eucalyptus species grown predominantly for pulp in commercial forestry in New Zealand and worldwide.

Amenity trees and green space structure in urban settlements of Kigali, Rwanda

According to the national policy, overall forest and agroforestry cover in Rwanda is to increase up to 30% land cover by 2020. On the other hand, demographic data reveal that Rwanda's urban areas are among the fastest-growing on the continent. Unfortunately, there is only little information of the effects of such a rapid urbanization on tree cover and green space structure, knowing that data on urban plant assemblages in the country are rather rare. The paper discusses developments in Kigali's green spaces with regard to its rapid rate of expansion. An integrated approach of research, combining results from interview sessions, desk-based investigations, walk-over and vegetation surveys, and photogrammetric analyses of remotely acquired imagery was applied. The findings suggest that the city green space network consists of plant assemblages largely dominated by alien species (75%). Tree cover fraction averaged at around 10–35%. No significant difference was observed between field-drawn and photogrammetric-based fraction of tree cover estimates; making the later a quick but cheap tool for rapid tree cover evaluation. Cultivated forests, urban woodlots and domestic garden tree stands are far the most dominant types of green spaces in terms of coverage of city surface area. Street tree communities and institutional gardens appear to be the most intensively designed green space layouts. Both distribution and species composition in domestic gardens were socioeconomic-driven. For instance, palm trees were characteristic of fortunate quarters while fruitbearing ornamental such as Psidium guajava and Persea americana were common within scattered and informal settlements. Markhamia lutea, Erythina abyssinica, Euphorbia candelabrum, Phoenix reclinata and Acacia sieberiana are among native taxa that thrive to keep a place in the city. Euphorbia tirucalli, a native tree that is widespread in home compound fences within informal settlements, is significantly declining as modern housing expands and concrete-based fences replace live enclosures.

Heritage trees and landscape design in urban areas of Rwanda

Trees play a key role in neighborhood landscapes, a belief that has been widely held for millennia in areas beyond Sub-Saharan Africa. Unfortunately, awareness of modern landscape architecture was almost absent in Rwanda until the late 20th century. Today, houses with surrounding decorative and amenity plants are a common feature in Rwanda’s neighborhood landscapes and, as the villagization of settlements progresses, new kinds of landscapes are emerging. This paper explores neighborhood tree planting around human settlements in the country. Remote sensing, photogrammetry, photo interpretation, and plant surveys were the core methods used. The average tree cover fraction ranged between 10%–35%. As the result of what is hereafter referred to as the “luxury effect,” a discrete gradient was detected along which the diversity of ornamental and amenity trees increases with the socio-economic status of neighborhoods: from rural settlements to urban residences via a series of intermediate designs, in which different levels of human-built vegetated areas alternate with non-landscaped spaces. Showy, non-productive amenity trees tend to occur more in wealthy quarters of the inner core of cities while edible ornamentals and other productive neighborhood trees prevail in rural and spontaneous settlements. In general, the practice of landscape plant design, in spite of its constant improvement, is still striving to get established as a profession in the country.

Phytophthora on Betula spp. (birch)

Birch is an important forest tree especially in colder climates. It is monoecious and wind pollinated species, and it has wind-dispersed seeds. The genus contains more than 60 taxa including trees and shrubs. B. pendula Roth (silver birch) and B pubescens Ehrh. (downy birch) have both wide distribution in Europe and are also found in northern parts of Asia (Hamet-Ahti et al., 1989, Niemisto et al., 2008). B. alleghaniensis Britton (yellow birch), B. lenta L. (sweet birch), B. papyrifera Marshall (paper birch) B. populifolia Marsh. (grey birch) and B. nigra L. (river birch) are species typical for North America (Hamet-Ahti et al., 1989; Verkasalo, 1990). In Scandinavia and northern Europe B. pendula is an important tree species for forest industry, but also used as amenity trees in parks, alleys and in gardens. B. alleghaniensis, B. lenta and B. papyrifera are also valuable for forest industry. Birches are cold tolerant pioneer species and in southern Europe they are found mainly on higher altitudes. Many Betula species such as B. nana L. (dwarf birch), B. pubescens subsp. czerepanovii (Orlova) Hamet-Ahti (arctic moor birch) and B. utilis D. Don (Himalayan birch) are typical for treeline. B. nana and it’s subspecies are shrubs native to arctic and cool temperate regions of northern Europe, northern Asia and northern North America. They are also present in Greenland as well as in mountains in Scotland and the Alps. B. utilis is growing as a shrub or tree native to the the Himalayas (Hamet-Ahti et al., 1989, http://www.discoverlife.org).

First report of lethal yellowing disease associated with subgroup 16SrIV, a phytoplasma on St. Kitts in the Lesser Antilles

Coconuts ( Cocos nucifera ) are grown as a crop and as amenity trees in many tropical countries. Caribbean countries use coconuts to enhance the aesthetics of sandy coastal beaches. Lethal yellowing (LY) as a phytoplasma disease, is the…

Biology and pest status of Uraba lugens Walker (Lepidoptera: Nolidae) in Australia and New Zealand

AbstractGumleaf skeletoniser, Uraba lugens (Lepidoptera: Nolidae), is a native Australian defoliator of many Eucalyptus and related species, and has recently established in New Zealand. Outbreaks of this species have caused significant damage to natural and commercially managed forests in Australia, and threaten plantations and amenity trees in New Zealand. With the arrival of this pest in New Zealand, research interest in U. lugens has increased. This stimulated this review and update, with previously unpublished data presented, on its taxonomy, biology, distribution, pest status and management. Host species and natural enemies are also listed, including previously unpublished records.

Variation in modulus of elasticity ( E) along Acer platanoides L. (Aceraceae) branches

Arborists and managers of amenity trees could benefit from an improved understanding of how tree canopies withstand loading events such as wind, snow or ice. Knowledge of how material properties change along tree branches is important in understanding how a branch tips can bend in the wind yet resist displacement at the base which could lead to branch failure. Limited knowledge of modulus of elasticity ( E or stiffness) in branch wood is available in the literature and is typically measured at only one location on a branch. This study investigated variation of E and density-specific E ( E/ ρ) at five locations along the axis of 20 branches from seven trees. E and E/ ρ were found to be 70% lower at the branch tips than in the proximal locations. The variation in E was negatively correlated with the percentage of tissue area composed of vessels and positively correlated with mean fiber cell wall size, suggesting a balance between the two principle functions of hydraulics and mechanics. Reaction wood was observed in the form of gelatinous layers in fibers along the branch tops, but did not result in a difference in E between the top and bottoms at each branch location. It is proposed that differences in material properties are probably related to wood development type, as juvenile wood is considered to have lower stiffness than mature wood.

CAN TREES BE DEPRECIATED LIKE (MECHANICAL) PLANT? A DEPRECIATED REPLACEMENT COST SOLUTION TO THE ADJUSTED TRUNK FORMULA ANOMALY IN CTLA'S TRUNK FORMULA METHOD

A tree cannot be depreciated like mechanical plant, because as a living organism, it will grow and increase in amenity value for most of its life. In appraisal terms though, the rate of return on a tree's increasing replacement cost will depreciate over time, as that nominal value disproportionately accelerates away from fair value. At issue, is the rectification of an accounting problem within the Council of Tree & Landscape Appraisers (CTLA) methods (making allowance for all changes in real value over time), rather than the undeniable value of aging trees. The full ecological and cultural value of ancient trees may be better considered under an alternative income approach to value, since their benefits may be partly unique and irreplaceable. Nonetheless, CTLA methods (which may be better suited to more regular urban forestry applications) will continue to provide a robust indication of their general worth. With regard to the Trunk Formula Method (TFM) of amenity tree valuation, this paper proposes an alternative procedure to that of the Adjusted Trunk Area Formula (ATAF) in consideration of large trees (>750mm stem diameter) and their replacement costs and end values. The ATAF seeks to regulate the accelerating cost of replacing larger diameter trees, by applying a quadratic equation to their area increments. The proposed alternative will be more consistent with appraisal standards: adjustments are no longer made to the cost metric, but are instead encompassed within the depreciation process by assessing the comparative age of a tree, as well as its current condition. Such a broader definition of an asset's physical deterioration is in keeping with standard appraisal practice.

Quambalaria species: increasing threat to eucalypt plantations in Australia

Spotted gum (Corymbia citriodora subsp. variegata and C. maculata) is a valuable source of commercial timber and suitable for a wide range of different soil types in eastern Australia. The main biological constraint to further expansion of spotted gum plantations is Quambalaria shoot blight caused by the fungus Quambalaria pitereka. Surveys conducted to evaluate the impact of Quambalaria shoot blight have shown that the disease is present in all spotted gum plantations and on a range of Corymbia species and hybrids in subtropical and tropical regions surveyed in eastern Australia. More recently, Q. eucalypti has also been identified from a range of Eucalyptus species in these regions. Both pathogens have also been found associated with foliage blight and die-back of amenity trees and Q. pitereka in native stands of Corymbia species, which is the probable initial infection source for plantations. Infection by Q. pitereka commonly results in the repeated destruction of the growing tips and the subsequent formation of a bushy crown or death of trees in severe cases. In comparison, Q. eucalypti causes small, limited lesions and has in some cases been associated with insect feeding. It has not been recorded as causing severe shoot and stem blight. A better understanding of factors influencing disease development and host–pathogen interactions is essential in the development of a disease management strategy for these poorly understood but important pathogens in the rapidly expanding eucalypt (Corymbia and Eucalyptus spp.) plantation industry in subtropical and tropical eastern Australia.

CAN A MORE DISCIPLINED APPROACH TO TREE APPRAISAL INFORM DEVELOPMENT SITE SURVEYS AND TREE PRESERVATION DECISIONS—AND VICE VERSA?

Some of the benefits gained from applying a rigour of process to tree valuation could be exported to wider forms of tree appraisal in the UK, such as development site surveys. Indeed, surveyors may already use depreciation methods intuitively, but unconsciously, on development sites. The advantage of unconscious usage is that practitioners have a pre-existing familiarity with these broader appraisal methods; the disadvantage of unconscious practice is that the process remains unfocussed and lacking in internal coherence—no ‘grammar’ of process. Alignment with more universal methods of quality categorisation than those currently employed in UK practice (i.e. British Standard 5837: 2005 Trees in relation to construction), could lead to a greater transparency of process and greater consistency in consultants' reports. Cross-fertilisation with more disciplined appraisal techniques, such as CTLA's Trunk Formula Method (TFM), is proposed, rather than straight substitution by them. A full TFM appraisal may be too detailed an exercise for each individual tree on a development site; nor is the financial valuation of each tree proposed. Rather, the proposal is that the TFM depreciation factors (Species, Condition, Location) inform the future review of BS5837's quality categorisation process, imparting to it, the basic grammar that is currently lacking. Tree officers could also develop this grammar to more readily justify Tree Preservation Order designations, beyond essentially visual criteria, and through the addition of the monetary factors, when seeking high-level fines. Despite 40 years of amenity tree valuation in the UK, arboriculturalists remain singularly unversed in the broader appraisal language. Familiarisation with and adaptation of CTLA methods, which draw upon this grammar, could help expose arboriculturalists to the language and allow them to communicate valuations more universally to the other professions and industries to which arboriculture must increasingly relate.

What was behind the bark? – An assessment of decay among urban <em>Tilia</em>, <em>Betula</em> and <em>Acer</em> trees felled as hazardous in the Helsinki City area

Old trees growing in urban environments are often felled due to symptoms of mechanical defects that could be hazardous to people and property. The decisions concerning these removals are justified by risk assessments carried out by tree care professionals. The major motivation for this study was to determine the most common profiles of potential hazard characteristics for the three most common urban tree genera in Helsinki City: Tilia, Betula and Acer, and in this way improve management practices and protection of old amenity trees. For this research, material from approximately 250 urban trees was collected in cooperation with the City of Helsinki Public Works Department during 2001 2004. From the total number of trees sampled, approximately 70% were defined as hazardous. The tree species had characteristic features as potential hazard profiles. For Tilia trees, hollowed heartwood with low fungal activity and advanced decay caused by Ganoderma lipsiense were the two most common profiles. In Betula spp., the primary reason for tree removal was usually lowered amenity value in terms of decline of the crown. Internal cracks, most often due to weak fork formation, were common causes of potential failure in Acer spp. Decay caused by Rigidoporus populinus often increased the risk of stem breakage in these Acer trees. Of the decay fungi observed, G. lipsiense was most often the reason for the increased risk of stem collapse. Other fungi that also caused extensive decay were R. populinus, Inonotus obliquus, Kretzschmaria deusta and Phellinus igniarius. The most common decay fungi in terms of incidence were Pholiota spp., but decay caused by these species did not have a high potential for causing stem breakage, because it rarely extended to the cambium. The various evaluations used in the study suggested contradictions in felling decisions based on trees displaying different stages of decay. For protection of old urban trees, it is crucial to develop monitoring methods so that tree care professionals could better analyse the rate of decay progression towards the sapwood and separate those trees with decreasing amounts of sound wood from those with decay that is restricted to the heartwood area.

PUTTING A VALUE ON TREES—CTLA GUIDANCE AND METHODS

Summary Arboriculturists and urban foresters frequently need to put a monetary value on amenity trees. There is interest in the UK in exploring various alternatives to currently familiar valuation methods. This paper describes the basic concepts of amenity, value, valuation and amenity value to provide a conceptual framework for valuation and a well documented context within which consider one specific valuation alternative: the CTLA guidance and methods developed for amenity tree valuation in North America. The CTLA guidance and methods are grounded in generally accepted principles of professional valuation practice, rely on readily available data and are well developed and ready to use. A Regional Plant Appraisal Committee (UKI-RPAC) has introduced supplemental guidance for the region.

PUTTING A VALUE ON TREES: AN ECONOMIST'S PERSPECTIVE

Summary Economists try to put a monetary value on trees to aid rational decisions about scarce resources. Examples exist of all the eight general methods of valuing non-market products. All methods encounter problems, to do with what is valued, by whom, from what perspective; how subjectivity influences value, and how values are scaled or partitioned according to circumstance. For a value which is so context-sensitive, an appropriate valuation protocol involves expertise drawing upon more than one method: expert aesthetic judgement calibrated by reference to the relevant population; choice experiments to establish a cardinal scale of value; and reference to data on population preferences revealed in house purchase and travel decisions. A rough indicative valuation of amenity trees in the UK was £50 000 000 000 over a 100 year period.