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ŠUMARSKI LIST 11-12/2019 str. 56     <-- 56 -->        PDF

The only unified and integrated forest monitoring system that is currently in use is the International Co-operative Programme on the Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests), which was established in 1985 by the Convention on Long-range Transboundary Air Pollution under the United Nations Economic Commission for Europe (Lorenz, 2010). ICP Forests was developed in response to the widespread concern that air pollution could affect forest condition. At present, 41 European countries, as well as the United States of America and Canada, are participating in the Programme, which includes assessments according to harmonized methods following the ICP Forests Manual and which has developed into an important platform for the exchange of expert knowledge.
ICP Forest health monitoring is implemented at two levels: Level I, large-scale monitoring, and Level II, intensive site monitoring (ISM). Approximately 7,000 Level I plots have been established across Europe on a 16 × 16 km grid. The data taken in Level I plots include annual crown defoliation visible on a total of 10–24 trees. The sample plots and trees are selected using a statistically sound procedure (Ferretti et al., 2010). Many authors have questioned and criticized the use of crown condition as a main indicator of forest health (e.g., Innes, 1993; Ferretti, 1997; Ferretti and Chiarucci, 2003; Seidling, 2004). Crown defoliation may be a good indicator of tree stress, but measuring it accurately requires extensive training of field personnel. Nevertheless, estimates can still vary considerably. Furthermore, the spatial coverage and spatial specificity of the systematic grid are inadequate when we want to focus on urban forest health problems along walking paths and roads, and on sparse but important damaging factors. Monitoring is an essential activity for management planning; however, we do not know if inventories are being utilized to their full potential in terms of producing management plans (Keller and Konijnendijk, 2012).
We argue that the ICP Forests method shows poor performance in assessing urban forest health: The economic performance is poor, and the number of direct management measures that can be acquired from the monitoring results is low. Therefore, one of the goals of this study was to develop an economically feasible method for surveying urban forest health that will result in more direct management measures.
Many of the functions of urban forests are recreational activities, such as walking, jogging, and biking, which depend on green infrastructure, such as roads, walking paths, parks, and playgrounds (Arnberger, 2006). The paths are surrounded by trees, which may represent an immediate security risk to a visitor in the form of damaged trees and falling branches. Surveying urban forest health should also include walking paths and roads. However, ICP Forests is based on a systematic grid that covers only a small portion of these highly important areas in urban forests. Therefore, another approach is needed to survey these areas, e.g. non-linear transects that correspond to the nature of walking paths, roads and forest edges, which are all essentially line elements.
Forest tree diseases and other damaging agents are numerous, and their distribution is often limited to a small area, even to a single tree. It is difficult to glean information on sparsely distributed damaging factors with a systematic grid. To cover more area, transects could be an alternative. However, cutting straight line transects through dense forest is time consuming and expensive when large areas need to be surveyed for rare or highly clustered damaging agents. Existing forest paths and roads may be suitable as line transects even though they do not, in general, run straight. Furthermore, roads and trails are not established randomly within an area but are generally found in areas with suitable terrain. There may well be a correlation between terrain and site factors that can influence tree response to insects and pathogens. More importantly, roads and trails receive much higher levels of public use than elsewhere within an urban forest, and consequently trees in the vicinity of roads and trails are more likely to be damaged or stressed as a result. Therefore, the use of existing paths involves bias resulting from the unrepresentative sampling of available green areas, and this must be weighed against the increase in coverage (Hiby and Krishna, 2001).
We developed a non-linear transect method in the frame of the EMoNFUr Project, Establishing a Monitoring Network to Assess Lowland Forest and Urban Plantations in Lombardy and Urban Forests in Slovenia (LIFE10 ENV/IT/000399), for comparison purposes and as a competitive alternative for assessing urban forest health. We named it the Urban Forest Management Oriented (UFMO) method (Ogris et al., 2013), and it is described in detail in the methods section below.
Our aim was to compare the efficiency of the ISM and UFMO methods for monitoring tree health in urban forests. We predicted that the UFMO method would record more damage that might compromise the urban forest visitor’s security because we surveyed trees within the vicinity of forest paths. The nature of line transects dictates that the surveyed trees are closer to each other, which means assessments can be conducted more efficiently, and a larger area can be covered.
The data were collected according to two methods. The first method was performed following the rules of Intensive Site Monitoring (ISM) developed by ICP Forests Expert Panel on Crown Condition and Damage Causes (Eichhorn et al.,