Abstract
Urban trees grow under adverse conditions, governed by the combinatorial effect of mul- tiple natural and anthropogenic factors. Global climate change adds new challenges regarding urban green management that should be taken into account when designing future green urban policies. The development of a smart Information and Communications Technology (ICT) system and the establishment of a continu- ously up to date information system regarding urban trees is a key issue for future manage- ment which aims at:
– climate change adaptation, by providing an instrument for measuring the cities CO2 emis- sion offsets by CO2 sequestration of the tree biomasses;
– efficient utilization of resources that are spent for urban tree management in order to decrease the cities’ environmental footprint;
– enhancement of the cities’ social fabric by pro- moting citizen participation during the deci- sion making process regarding urban trees.
The project was selected for funding after a competitive process by the General Secretary of Research and Development. The Municipal- ity of Thessaloniki was selected as the key study area. The core of the project is the development of a software suite named GreenTree. Through the GreenTree client Android application, 105 different sets of data are collected for each urban tree. The urban tree inventory includes 37,328 tree sites on the pavements, from which we found 1,239 dead trees, 2,787 empty sites and 937 trees which had to be removed because they had been planted in inappropriate loca- tion and they disturbed the circulation of cars or pedestrians. The numbers above clearly show the significant need for the establishment of a reliable and smart monitoring system for urban tree management. This system could also help manage the decision making process. Finally, the numbers show that urban environment can be easily improved by applying fast and cheap measures of tree replanting and replacement.
for Governance in Urban MTEs and
for Adapting Cities to Climate Change:
Preliminary Results
Création d’un modèle intégré pour la gouvernance
des écosystèmes méditerranéens urbains et pour adapter les villes aux changements climatiques : premiers résultats
Thekla TSITSONI1*, Nikolaos GOUNARIS2, Aimilia B. KONTOGIANNI1, Valia XANTHOPOULOU-TSITSONI3 1. School of Forestry & Natural Environment, Laboratory of Silviculture,
Aristotle University of Thessaloniki, University Campus, P.O. Box: 262, 54124 Thessaloniki, Greece.
2. CEO of Homeotech Co Company, Grigoriou Lampraki 210, 54352 Thessaloniki, Greece.
3. School of Economics, Department of Development and Planning, Aristotle University of Thessaloniki, University Campus, P. O. Box: 178, 541 24 Thessaloniki, Greece
*Corresponding author: tsitsoni@for.auth.gr
Received: 20 January, 2015; First decision: 30 April, 2015; Revised: 4 December, 2015; Second decision: 14 December, 2015
Keywords: urban forestry, green spaces, urban tree management, street trees, GreenTree Software.
Résumé
Les arbres urbains se développent dans des conditions difficiles, régies par l’effet combiné de multiples facteurs naturels et anthropiques.
Le changement climatique mondial ajoute de nouveaux défis en matière de gestion urbaine
“verte” qui devrait être prise en compte lors de l’élaboration des futures politiques urbaines écologiques. Le développement d’un système intelligent en Technologie de l’Information et de la Communications (TIC) et la mise en place d’un système d’information, mis à jour en continu, concernant les arbres urbains est un enjeu clé pour la gestion future qui vise à : – l’adaptation au changement climatique, en
fournissant un instrument pour mesurer les émissions de CO2 que les villes compensent par la séquestration du CO2 dans la biomasse des arbres ;
– l’utilisation efficace des ressources qui sont dépensées pour la gestion des arbres en milieu urbain afin de réduire l’empreinte environne- mentale des villes ;
– le renforcement des liens sociaux dans les villes en favorisant la participation des citoyens pendant le processus de prise de décisions concernant les arbres urbains.
Le projet a été sélectionné pour financement après un processus compétitif organisé par le Secrétaire Général de la Recherche et du Déve- loppement. La municipalité de Thessalonique a été choisie comme zone d’étude principale. Le cœur du projet est le développement d’une suite de logiciels nommée GreenTree. Via l’applica- tion android GreenTree, 105 ensembles distincts de données ont été collectés pour chaque arbre urbain. L’inventaire des arbres en milieu urbain comprend 37 328 sites de plantation d’arbres sur les trottoirs, parmi lesquels ont été trouvés 1 239 arbres morts, 2 787 absents de leur site (trous vides sur les trottoirs) et 937 arbres devant être retirés. Les chiffres ci-dessus montrent clai- rement la nécessité de la mise en place d’un système de suivi fiable et intelligent pour la gestion des arbres urbains. Ce système pourrait aussi faciliter la gestion du processus de prise de décisions. Enfin, les chiffres montrent que l’environnement urbain peut être facilement amélioré par l’application de mesures rapides et bon marché pour la replantation et le rem- placement des arbres.
Introduction
The world is undergoing the largest wave of urban growth in history, as it is calculated that above half of the world population lives in urban regions while by 2030 the urban popu- lation is expected to be twice as large as the
corresponding rural (Samara & Tsitsoni 2010, Lang 1999, Sandberg 1999, OECD-ECMT 1995, Lambert & Vallet 1994). Increasingly, urban green space is seen as an integral part of cities, providing a range of services to both the people and the wildlife living in urban areas (James et al. 2009, Wolf 2004, Nowak & Dwyer 2000). So, for the last 50 years there has been a growing realization that the solutions to most of environmental prob- lems reside in making cities more efficient in their consumption of energy and materials and disposing of waste products, and in altering patterns of urban development to reduce the amount of impervious “grey” infrastructure and to increase the amount of “green” infra- structure, particularly trees (Carreiro 2006).
With this recognition and resulting from the simultaneous provision of different services, there is a real need to identify a research framework in which to develop multidiscipli- nary and interdisciplinary research on urban green space (James et al. 2009). This realiza- tion has been expressed in the concepts of the eco-cities movement, adopted by many envi- ronmentalists and urban designers throughout the world (Register 2002).
A major problem that globally has to be faced is the climate change and mostly what deals with global warming. The definition of climate change refers to any significant change in the measures of climate lasting for an extended period of time (EPA 2015). Climate change is caused by factors, such as biotic processes, variations in solar or volcanic eruptions etc., but the main threat, mostly because of human activity is referred to as global warming and that is the recent and ongoing global average increase in temperature near the Earth’s sur- face. According to NASA, the global tempera- ture increased by 0.77 oC since 1880 while nine of the ten warmest summers on record have occurred the last 15 years (NASA 2015).
Natural and human factors cause changes in Earth’s energy balance, leading, among other things to increased greenhouse effects. Within this context, urban green spaces can play a central role in both climate-proofing cities and in reducing the impacts of cities on climate (Gill et al. 2007). Urban vegetation through its physiological features could provide potential help to the cities’ adaptation and mitigation strategies for climate change. Global climate change adds new challenges regarding urban green management that should be taken into account when designing future green urban policies.
Mots clés : foresterie urbaine, espaces verts, gestion des arbres en milieu urbain, arbres de rue.
Adaptation deals with preparing for inevitable climate change while mitigation is the act of limiting further climate change, for example by reducing emissions of greenhouse gases.
Urban green spaces can help to alleviate the consequences of climate change mostly by cooling. Trees, especially when located close to buildings can reduce temperatures, acting as natural air conditioners through their evapotranspiration and providing shade with their foliage, therefore reducing energy consumption required to maintain comfort- able climatic conditions. Even small green spaces can have a cooling effect – parks of 1 or 2 hectares only have been found to be 2 oC cooler than surrounding areas (Shashua-Bar
& Hoffman 2000). The extent of the cooling effect is greatest when temperatures beyond the park are highest (Handley & Carter 2006).
At the same time, urban trees and green spaces can mitigate the impacts of climate change through the absorption of the CO2 that takes part in greenhouse gases and act as carbon sinks. Additionally trees that are placed close to buildings lead to lower consumption of energy for mechanical cooling and heating, decreasing CO2 emissions.
All green spaces help urban areas adapt to the impact of climatic change regardless of whether they are park, private garden or street trees, with location, structure, compo- sition and spatial configuration of them to influence their ecological qualities and func- tions (Turner et al. 2005). At the same time vegetation type that is characterized by the plant species, the size of the trees and the mixture of the species and the proportion of urban tree canopy as well influence the impact level. The challenge is to find functional and as low budget as it is possible ways for adapta- tion and mitigation solutions based on urban greening providing the total of physiological, sociological, economic and aesthetic benefits.
Identifying and describing the benefits of urban trees to a community is the first step in gaining support for an urban forestry program of tree planting, maintenance and replace- ment. An urban tree inventory is essential because the information about the quantity and quality of the existing vegetation and its characteristics are important for urban green- ing management. Nevertheless, there is a lack of urban tree inventory and monitoring pro- tocols and standards. These protocols could detect change over time and across cities, while providing flexibility required by diverse users.
A great proportion of the urban infrastructure consist of urban streets where people walk, shop, meet and generally participate in many social and recreational activities that make urban living enjoyable (Wolf 2004). The use of trees as an element of the landscape is an important design concept that has been used throughout the world, and continues to shape the aesthetics and function of the streets (Gezer & Gül 2009).
Street trees are one of the most important com- ponents of urban green space and they play an important role in city’s aesthetics as people’s first impression of a city comes from its street landscape (Jacobs 1993). Street trees are com- plex to study because this entails technical, aesthetical, biological and ecological knowl- edge (Küçük & Gül 2005). Moreover there is no homogeneous urban environment or site, as it is a conglomeration of soils, microclimates and other site conditions. Street trees should possess strong apical growth, strong branch- ing angles, overall high aesthetic values, pre- dictable growth rates and, in general, have a potential for a long life span (Gezer & Gül 2009), although they also sometimes grow in adverse environments. Over recent decades, a growing proportion of the commonly used species have shown increasing difficulties in coping with the conditions at urban paved sites (Sjöman et al. 2010). Overall, trees in these environments tend to be greatly exposed to heat, low air humidity, periods of critical water stress, high lime content and high soil pH, limited soil volume, pollutants and de- icing salts (Pauleit 2003, Sieghardt et al. 2005) Under this perspective a project has been com- piled using as a study case the metropolitan area of Thessaloniki in northern Greece. The project was selected for funding by the Gen- eral Secretary of Research and Development after a competitive process. The main goal of the project is to create a standard system for the exercise of governmental and decision making in the practice of urban forestry in a holistic and integrated way. The concept of holistic lays in a comprehensive manner, examining the needs and problems of urban green infrastructures taking into consideration as many factors as possible, anthropogenic or not, each of which has different weight. This integrated system includes all processes, ser- vices and products considered necessary for the existence of the holistic approach to the exercise of urban forestry.
The policy that is followed for the goal to be achieved contains the following objectives:
1) to create the appropriate guidelines for the management of urban greening, through the proper treatment of the wooden species;
2) adaptation strategies for the inevitable cli- mate change and mitigation of the factors that lead to climate change;
3) to provide an efficient appliance for meas- uring the city CO2 emission offsets by CO2 sequestration of the tree biomasses;
4) to provide an efficient utilization of resources that are spent for urban tree man- agement in order to decrease the cities’ envi- ronmental footprint; and
5) to enhance the cities’ social fabric by pro- moting citizen participation during the deci- sion making process regarding urban trees.
The main tool that is used is a smart Informa- tion and Communications Technology (ITC) system that had been developed for that pur- pose and the establishment of a continuously up to date information system regarding urban greening. The aim of this paper is to show the preliminary results of this research and try to make an estimation of the sufficiency and the functionality of the existing urban greening of Thessaloniki.
Methods
Study area
The area where the specific project is taking place is the whole territory of the municipality of Thessaloniki, the second-largest city of the country and the capital of central Macedonia, in northern Greece. According to the prelimi- nary results of the 2011 census, the municipal- ity of Thessaloniki today has a population of 322,240, while its urban area has a population of 790,824.
Thessaloniki lies on the northern fringe of the Thermaic Gulf on its eastern coast and is bound by Mount Chortiatis on its southeast.
Its proximity to imposing mountain ranges, hills and fault lines, especially towards its southeast have historically made the city prone to geological changes.
Thessaloniki’s climate is directly affected by the sea it is situated on. The city lies in a transitional climatic zone, so its climate displays characteristics of a mosaic of micro- climates. As reported by Hellenic National
Meteorological Service, the total character of the climate is humid subtropical climate (Cfa) that borders on a semi-arid climate (BSk) – according to Köppen climate classification.
The total annual precipitation is 458.4 milli- metres due to the Pindus rain shadow drying the westerly winds. However, the city has a summer precipitation between 21 to 31 mil- limeters – with August the driest month and November the wettest – which borders it close to a hot-summer Mediterranean climate (Csa).
The mean annual temperature in Thessaloniki is 15.6 °C. During the coldest winters, tem- peratures can drop to -10 °C, while the mini- mum temperature ever recorded is -14 °C. On average, Thessaloniki experiences frost for about 30 days per year. The coldest month of the year is January. Thessaloniki’s summers are hot with rather humid nights. Maximum temperatures usually rise above 30 °C and sometimes over 40 °C. The maximum tem- perature ever recorded is 42 °C. On average, Thessaloniki experiences hot waves for about 30 days per year. The hottest month of the year is July. The average wind speed for June and July is 20 km/h while in winter the average wind speed is about 26 km/h (Samara & Tsit- soni 2014). Papakostas et al. (2014) represent the variation of temperature and annual aver- age temperature during the period from 1983 to 2012 as it is shown to the Figures 1a and 1b. The same authors conclude that the total increase in the annual average temperature from the first to the third decade was 1.1 °C with an upward trend.
Experimental design
From August 2013 to October 2014 and dur- ing two growing seasons, every single street tree of the municipality of Thessaloniki was recorded in order to build an integrated street tree inventory. In the inventory qualitative and quantitative information was included.
Hence every above-ground characteristic of each individual as well as site features were estimated or measured (Table 1).
The development of a smart Information and Communications Technology (ITC) system and the establishment of a continuously up to date information system regarding urban trees is a key issue for future management. The core of the project is the development of a software suite named GreenTree. Its use makes it easy to collect data and make a tree inventory that is based on field measurements and estimations
for both trees and their site features. Through the GreenTree client Android application, 105 different sets of data were collected as men- tioned above.
Breast height diameter and tree height data were measured directly in situ using cal- lipers and laser measurement instruments.
Tree crown projection extracted using ellipse equation and four radii from the tree trunk R1 and R2 along and R3 and R4 vertically the sidewalk. The crown volume derived using standard geometry shapes equations (Troxel et al. 2013).
Table 1 – Set of tree measurements and evaluation.
Tree Species Tree Location Height
Crown height Crown diameters Breast height diameter
Tree health data Soil data Proposed future measurements
Existence of Utilities’ elements Tree importance
(i.e. historical, monumental tree etc) Maintenance data
(i.e. existence of grade, irrigation etc) Figure 1a – Variation of temperature for the period from 1983 to 2012 (Papakostas et al. 2014).
Month Jan
30
1983-1992 1993-2002 2003-2012 25
20 15 10 5
0 Fer Mar Apr Mai Jun Jyl Aug Sep Okt Nov Dec
Ambient Temperature [°C]
Figure 1b – Annual average temperature for the period from 1983 to 2012 (Papakostas et al. 2014).
Year 1983
18
Average per year Fitter curve 17
16
15 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011
Ambient Temperature [°C]
Results
Street tree characteristics
The preliminary analysis of the project data showed that the area of total green spaces under the jurisdiction of the municipality services covers about 906,000 m2, less than 5% of the total city’s area, as analytically it is represented to the Table 2.
The total number of tree sites of the pavements that were surveyed is 41,672 belonging on
76 different species. To facilitate data process- ing, the species with population less than 50 individuals did not participate to the calcula- tions, thus they eliminated from this exhaus- tive inventory. The revised inventory includes 37,328 tree sites of the pavements. They rep- resented 45 wooden species from 24 families – with the majority of them being forest spe- cies. 74.34% of the individuals belonged to 12 species, while 25.66% belonged to 33 species (Tables 3 and 4). From these 33 species, 25 species were not much represented (< 1%).
At the family level, from the total number of
Table 3 – Species occurrence proportion.
Species Presence % Species Presence % Species Presence %
Sophora japonica 15.52 Cercis siliquastrum 1.91 Alnus glutinosa 0.41
Robinia pseudoacacia 12.78 Albizia julibrissin 1.88 Paulownia tomentosa 0.40
Acer negundo 9.62 Fraxinus sp. 1.83 Ficus carica 0.39
Ligustrum japonicum 7.62 Olea europaea 1.68 Pinus nigra 0.35
Koelreuteria paniculata 6.20 Aesculus hippocastanum 1.34 Broussonetia papyrifera 0.33
Platanus prientalis 4.72 Acer pseudoplatanus 0.91 Ginkgo biloba 0.29
Citrus x aurantium 4.31 Cupressus sp. 0.89 Pinus brutia 0.27
Celtis australis 2.81 Morus sp. 0.81 Magnolia grandiflora 0.25
Liquidambar orientalis 2.81 Catalpa bignonioides 0.77 Quercus sp. 0.24
Tilia sp. 2.73 Prunus cerasifera
var. pissardii 0.70 Pittosporum tobira 0.23
Populus x canadensis 2.63 Nerium oleander 0.69 Pinus sp. 0.17
Ulmus sp. 2.59 Chamaerops humilis 0.66 Prunus domestica 0.16
Populus alba 2.22 Populus nigra
subsp. thevestina 0.54 Eriobotrya japonica 0.15
Acer campestre 1.99 Laurus nobilis 0.50 Thuja plicata 0.14
Hibiscus syriacus 1.97 Ailanthus altissima 0.43 Acacia sp. 0.13
Table 2 – Urban green area per category and per resident for the territory of the municipality of Thessaloniki.
Urban greening Categories Area (m2) m2 / resident % of Municipality’s
Total area
Municipality’s urban green spaces Parks, road islets 527,475 1.64 2.85%
Street trees 378,480 1.17 2.05%
Total 905,955 2.81 4.90%
Urban green spaces under special management status
University Campus 132,551 0.41 0.72%
Military basis 93,321 0.29 0.50%
Hospitals 28,378 0.09 0.15%
Open spaces 43,193 0.13 0.23%
Streams 216,593 0.67 1.17%
Stadiums 63,278 0.20 0.34%
Cemeteries 8,898 0.03 0.05%
Churches 15,000 0.05 0.08%
Total 601,212 1.87 3.25%
Private green spaces (yards, gardens) 970,940 3.01 5.25%
Total green area of the municipality of Thessaloniki 2,478,107 7.69 13.40%
24, 3 of them hold 56.1% of individuals (12 species), 91% of individuals belonged to 10 families, and 11 families had a representation lower than 1%. The 45 species consisted of 5 gymnosperms and 40 angiosperms – 64.5%
deciduous and 22.3% evergreen. Approxi- mately 50% of the planted species were large and medium sized trees (Table 5). Finally, 44.5% were introduced species – mainly from Asia – while 48.9% were native to Mediter- ranean region, Balkan Peninsula or generally to Europe (Table 6).
The cumulative crown volume that came from 378,480 m2 of urban street trees equalled 2,633,959 m3. For all 45 species, population diagrams of height, breast height diameter (dbh), crown projection and crown volume created are shown on Figures 2, 3, 4 and 5.
Breast height diameter (Figure 2) and crown projection area (Figure 3) followed an ascend- ing trend, showing that tree growth in diame- ter was not affected by pruning and that crown projection areas were less affected than the other two silvicultural characteristics meas- ured (i.e. tree height and crown volume).
Tree height and crown volume diagrams showed an abrupt reduction in number of existing trees in the 3rd class in comparison with the 3rd of dbh class, 7.203 vs. 15.401. This result can easily be explained by the intense height reduction interventions on street trees and hence on the crown volume. It is com- monly known that these interventions are not always appropriate; the actions of pruning are greatly exaggerated and inappropriate but happen because of lack of personnel exper- tise and low maintenance cost needs. On the other hand the greenhouse gases sequestration is directly related to total leaf surface and thus directly to the volume of the crown.
Table 4 – Number of species and individuals on each family.
Family Species Individuals % Family Species Individuals %
Fabaceae 6 12,115 32.46 Cupressaceae 2 384 1.03
Aceraceae 3 4,672 12.52 Rosaceae 3 379 1.02
Oleaceae 3 4,154 11.13 Pinaceae 3 294 0.79
Sapindaceae 2 2,814 7.54 Bignoniaceae 1 286 0.77
Ulmaceae 2 2,016 5.40 Apocynaceae 1 259 0.69
Salicaceae 3 2,011 5.39 Arecaceae 1 248 0.66
Platanaceae 1 1,763 4.72 Lauraceae 1 188 0.50
Malvaceae 2 1,757 4.71 Simaroubaceae 1 162 0.43
Rutaceae 1 1,609 4.31 Betulaceae 1 154 0.41
Altingiaceae 1 1,050 2.81 Paulowniaceae 1 150 0.40
Moraceae 3 574 1.54 Gingoaceae 1 108 0.29
Table 5 – Number of species in life form categories.
Life form Number of
Species %
Large Tree 10 22.22
Large – Medium tree 10 22.22
Medium tree 3 6.67
Medium – Small tree 8 17.78
Small tree 5 11.11
Small tree – Shrub 6 13.33
Shrub 1 2.22
Depend on species 2 4.44
Table 6 – Species origin.
Origin Species Origin Species
Mediterranean region 13 Europe, Asia, Africa 1
Asia 13 Australia 1
Northern America 5 Balkans 1
Europe, Asia 3 Northern hemisphere 4
Europe, Asia and North America. 1 Hybrids 2
When only the genre is known
depend on species 1
Estimation of CO2 sequestration At this point an effort was made to obtain a coarse image about the potential augmenta- tion of CO2 sequestration that the replacement of approximately 12,000 trees would provide;
this concerns the dead individuals and the empty pavement tree sites. This theoretical study examined the effect that these 12,000 trees would play in greenhouse gases seques- tration through a correlation of crown volume distribution with the existing distribution of dbh. A wide range of tolerance of ± 20% was used to cover the great variety of conditions prevailing in city trees. By using complex My SQL queries in database of 36,089 liv- ing trees it was found the cases where crown volume distribution of each species deviates from the dbh diameter distribution more than
± 20%. As a result 22 of the 40 tree species showed discrepancies greater than ± 20%.
A theoretical model was developed where a virtual transfer from volume categories that show surplus, to them of deficit crown volume categories was performed following species dbh distribution. If there were no surplus cat- egories, the transfer occurred proportionally from the other categories in volume deficit, provided that this should not be exceeded ± 20%. As a result a theoretical increased in crown volume equal of 375,388 m3 or 14.56%
of the current crown volume of those 40 spe- cies derived (Figure 6). Even if this result is not a spectacular increase in the total urban trees crown volume, it gives an idea of what is achievable by applying low cost managerial measures. For this analysis, My SQL queries and PHP programming language are used.
Figure 2 – F requency in diameter classes. Figure 3 – Frequency in crown area classes.
Figure 4 – Frequency in height classes. Figure 5 – Frequency in crown volume classes.
Additionally, tree health was to be excellent to moderate for 68% of the trees, 10% of the tree needed to be replaced immediately, while there are 2,787 empty pits (Table 7). Finally, in situ management recommendations were proposed (Table 8).
Discussion
Every community tree planting program coor- dinates several processes in order successfully manage public trees. To support a vigorous population of trees, these programs plan and design planting areas, select species for indi- vidual sites, coordinate planting activity, per- form regular maintenance and pest manage- ment, and remove hazardous trees in a timely manner (Burcham 2009).
GreenTree specifications
The specific ongoing project involves the col- lection of reliable and accurate information for each tree managed by the municipality of Thessaloniki, the organization of this infor- mation in a functional geospatial database, which will be updated and will be editable for completion of new data fields, if neces- sary. This database will be analyzed to derive statistics and indicators to 1) identify prob- lematic individuals requiring urgent inter- vention, for example pruning, removal, etc., 2) assess the health situation and the goal achievement level in a management period and to plan maintenance works, supplement- ing or replacing individuals and calculating the corresponding cost, 3) compare work cost and quality that has to be done by private con- tractors, and 4) examine alternative scenarios for the distribution of the annual municipal resources by prioritizing the importance of the planned projects according to their contribu- tion to achieving the objectives of the strategic management plan. The project will also take place actions to inform the public and publi- cize the results of the project.
In order to implement all the above acts, GreenTree has been developed, as a special software to be a basic tool in urban green- ing management, scheduled to enter into pilot operation at the end of the project. The purpose of this tool is to help municipality services to manage their urban greening specifically in relation to the potential CO2 sequestration and the regulation of temperatures.
As referred above, each entry in GreenTree contains information for each individual like:
tree record number, species code and name, health status and management needs, dbh, height, crown measurements and site fea- tures, etc. The data provided by the inventory will lead to the evaluation of the silvicultural characteristics that describe the tree as carbon sink. A number of different kinds of tables can be printed that will help the visualization of the data and summarize the results. The soft- ware is not designed only for professionals but also for beginners or unskilled workers;
as skill levels improve the quality of the input and output increases as well.
Table 8 – Preliminary management recommendations.
Conservation Maintenance Removal Replacement 9,849 (23.63) 18,974 (45.53) 937 (2.25) 11,912 (28.60) Table 7 – General view of street tree health condition.
Excellent
Condition Good Condition Moderate
Condition Bad Condition Worst
Condition Dead Empty pavement
tree site 5,554 (13.32%) 13,068
(31.35%)
9,537 (22.88%)
6,236 (14.96%)
3,257 (7.82%)
1,239 (2.98%)
2,785 (6.68%)
Figure 6 – Frequency in potential crown volume classes.
GreenTree stages of implementation During our collaboration with the municipal- ity services, we were faced with 1) a disap- pointing lack of data and 2) disorganization of the operations related to urban forestry, both due to the absence of proper staff numbers and financial resources. The gap of this procedure is expected to be solved by GreenTree system, as it will make data collecting process much easier.
So, the first step that had to be done was to put a set of guiding principles of urban greening management, starting by standardizing the monitoring protocols and the construction of the tree inventory. The challenge was to make protocols as simple as possible and at the same time flexible enough for different situations.
These technical guidelines for long-term data collection and urban tree inventory develop- ment followed Miller (1997): management planning for street tree population involves an inventory of trees and community values;
then, this inventory is used to develop man- agement goals, the next step is to develop a management plan to achieve these goals (selection, establishment and maintenance of street trees), and finally a feedback allows monitoring the entire process. Additionally, guidelines for urban green planning and management under the perception of climate change will be provided, including a national network of public and private organizations as well that deal with urban forestry.
General considerations
One practical concern faced by all commu- nity tree planting programs is the need for biological diversity. The heavy, often exclu- sive, reliance on a small number of species contributed to the proliferation of species- specific landscape pests (Burcham 2009).
In the case of Thessaloniki, there are more than 70 tree species participate in urban veg- etation. Nevertheless, on the one hand there is an uncontrolled distribution and on the other hand about 30 species are represented with population less than 50 individuals and 11 families have rare appearance, less than 1% of the total population of street trees. So, even though species diversity enhances land- scape ecological balance and value, it makes it difficult to organize the spatial and temporal planning of management treatments.
Additionally, after in situ observation, there were evidence of inadequate tree species
selection for particular features of a site, like damages to pavements or other infrastructure:
the size of the mature plant had not been taken into consideration in relation with the size of the available growth space. The life form of approximately 50% of the planted trees in the streets of Thessaloniki belongs to the category of large tree, making the individual inappro- priate in the most cases. The large proportion of introduced species shows that no ecological properties and their relations with the environ- mental conditions were taking into considera- tion when the selection was made.
The inadequate plant selection for urban use also cause health problems to the citizens as the pollen of specific species such as poplar, pines, olive and plane trees can have an aller- gic effect (Papageorgiou 2003).
The existence of power and telephone lines in urban areas is indisputable. Planting trees that are expected to grow high in their maturity leads to inevitable trimming and pruning, that in most of the case is inadequate and without any spatial and temporal planning. Topping and lopping is very often with irreversible impact on tree health.
Conclusion
In Thessaloniki the basic rules took into account as Miller’s (1997) proposed model for selecting species for urban uses were never applied. The main factors to take into account are site conditions, such as cultural and environmental elements, economic fac- tors like planting and maintenance costs and social factors as functional utility, landscape enhancement and public safety. So, the basic properties of the trees must be: 1) climate adaptation, 2) resistance to diseases, 3) large phenotypic plasticity in the plant materials, 4) root quality, 5) growth potential and form at maturity phase, 6) wind and snow resistance, 7) drought resistance and 8) tolerance of air pollution (Sæbø et al., 2003).
Species selection, planting location, and cultural practices all have an impact on the ultimate visual quality, health, and cost of street tree maintaining. The use of appropri- ate species, the proper location of plantings, and the implementation of a program of pre- ventative maintenance of the street trees, will allow a cost effective tree management sys- tem. Action programs related to trees in the
urban are: (I) policy making, planning and designing, (II) technical focus, such as selec- tion programs and establishment techniques and (III) management aspects (Konijnendijk
& Randrup 2002).
Apparently the ecological and functional spe- cies selection is of utmost importance but the general point is how to apply an efficient man- agement plan with the lower ecological and social cost. Urban greening, when sustainably managed, can have a central role in climate change mitigation and adaptation.
Specifically, from the preliminary results of this project can be concluded that:
–the potential crown volume of the existing trees can be increased to 14.5%;
–the replacement of dead individuals will increase the number of trees within 3%;
–the filling of the empty pavement spaces will increase the number of trees at 6.7%.
The numbers above clearly show the signifi- cant need for the establishment of a reliable and smart monitoring system for urban tree management. This system could also help in managing the decision making process.
Finally, the numbers show that urban envi- ronment can be easily improved by applying fast and cheap measures of tree replanting and replacement.
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