IJERD – International Journal of Environmental and Rural Development (2022) 13-2

Research article
erd

Relation between the Level of Degradation and the Wind
Speed Reduction Efficiency of Tree Windbreaks Systems inOvche Pole Region, Macedonia
OGNEN ONCHEVSKI
Graduate School of Agro-Environmental Science, Tokyo University of Agriculture, Japan
Email: ognenoncevski@hotmail.com

TERUAKI IRIE
Faculty of Regional Environment Science, Tokyo University of Agriculture, Japan

IVAN MINCHEV
Hans Em-Faculty of Forest Sciences, Landscape Architecture and Environmental Engineering,
University of Ss. Cyril and Methodius-Skopje, North Macedonia

MACHITO MIHARA*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Japan
Email: m-mihara@nodai.ac.jp
Received 16 January 2022

Accepted 20 May 2022(*Corresponding Author)

Abstract Ovche Pole is an agricultural region in Macedonia with dry climatic conditions
characterized by low precipitation and high ambient temperatures during the growing
period as well as prevailing winds that are present considerable time of the year. During the1950s series of measures have been implemented to improve the agriculture productivity inthe region. One of the measures taken was the establishment of tree windbreaks (fieldshelterbelts) aimed to reduce wind velocity and protect shelter crops. Ever since they
become essential elements for the regional landscape, performing many important
ecosystem functions. As far as authors’ knowledge, so far there are no scientific studies thatinvestigated the performance of the tree windbreaks in Ovche Pole-research area of thisstudy. To fill the gap of scientific data, this study examines the relation between wind
reduction efficiency of tree windbreaks with their level of degradation in that area. Opticalporosity is used as a proxy for quantitative description of the level of degradation of thestructure of the tree windbreaks. To this aim, field measurements for wind velocity andoptical porosity (OP) were done on 3 (three) windbreaks sections. Photogrammetry method
was used to determent the porosity at each windbreak section. Wind velocity fieldmeasurements were done with two handheld cone anemometers The windspeed reduction
efficiency was assessed by comparing the windspeed at the windward side with thewindspeed at 3 points on the leeward side. The results show that the level of degradation issignificantly related with the relative windspeed at distance of 30m and 60m from the treeline at the leeward side.
Keywords windbreaks, windspeed reduction efficiency, optical porosity,
Ovche Pole region, North Macedonia

INTRODUCTION
Ovche Pole is an agriculture region in Macedonia with dry climatic condition characterized by low
precipitation and high ambient temperatures during the growing period as well as year-roundprevailing winds. The region is part to the semi-arid agriculture zone and sub-humid agriculturezone of the country (Aksoy et al., 2020). Northern winds are most dominant, blowing throughout
the entire year, with an average frequency of 188% and an average speed of 4.6 m/sec. Northwestern winds have an average frequency of 127% and an average speed of 3.9 m/sec, blowingⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2022) 13-2

throughout the entire year, but mostly in June and August. The third most frequent are the southernwinds, with an average frequency of 66% and an average aped of 2.4 m/sec. (Evolving DOO, 2016).
During the 1950’s series of projects were taken to improve the agriculture productivity in theregion. One of the activities was the establishment of tree windbreaks. The tree windbreaks wereplanted on a surface of 555.66 ha (Forest public enterprise, 2011). The trees rows are 10 m wide
row in rectangle grid that formed agriculture parcels that are approximately 1000 m in length and
250 m width. Tree windbreaks are planted in southwest to northeast direction perpendicular todirection of the prevailing northwest winds. Today, much of the initial area is lost and certain areas
are degraded because of illegal cutting done by the local population. Depending on the level ofdegradation, different sections of the tree wind brake systems have different wind speed reductionefficiency. The ability of windbreak to fulfill its wind protection function in landscape is given by
its external and internal structure. The external structure is defined by width, height, shape, andorientation. The internal structure is given by the amount and arrangement of branches, leaves, andtrees or shrubs trunks (Brandle et al., 2004). The most used descriptor of internal structure for
artificial windbreaks has been porosity which is a simple ratio of perforated area to total area
(Heisler and Dewalle, 1988). Height of the windbreak and porosity of windbreak are main
parameters used to explain the windspeed reduction efficiency (Brandle et al., 2004; Helfer at al.,2009; Středová et al., 2012; Řeháček et al., 2017; Kučera, 2020). The windbreak porosity isclassified as real (aerodynamic) and optical.

Fig. 1 Tree windbreaks in the research area showing its width is 10 m
Note: Taken by Onchevski in August 2021

Aerodynamic porosity is defined as the ratio between the average wind speed measured on thewindward side of windbreak and the average speed in open space. Since aerodynamic porosity isdifficult to define, the parameter of optical porosity (OP) is mostly used. For the evaluation ofwindbreak efficiency, optical porosity (OP) is determined by using the photogrammetry method(Kučera, 2020). Although, there is a linear relationship between windbreak efficiency and opticalporosity; this connection can be influenced by several external characteristics of tree windbreaks(Wu et al., 2018). Therefore the objective of this study is see the relation between the level ofdegradation of the tree windbreaks and optical porosity and relate this parameter with thewindbreak efficiency to protect the agriculture land from negative effects of prevailing wind.
METHODLOGY
Study Area and Measuring of Wind Speed
Windbreak efficiency was analyzed on three windbreaks sections near the village of Erdzelija inthe region of Ovche Pole. The agricultural field are located on around 3.5 km from village withlatitude 41°51'18.45"N and longitude 22° 0'50.12"E.
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IJERD – International Journal of Environmental and Rural Development (2022) 13-2

Fig. 2 Satellite photo showing research sites and windspeed measuring points
Averagely the tree windbreak sections are 6 m high and 10 m wide, however the level ofdegradation was different. To analyze the windspeed reduction efficiency, between 18 and 26
August 2021 at each tree windbreak section wind speed was measured on one point at thewindward side and at tree points on the leeward side. Windward measuring point was set 30 mfrom the tree line and the leeward measuring points were set on 30 m, 60 m, and 90 m from the treeline. Windspeed was measured with two handheld cup anemometer type (Sato Tech AM-4257SD)
fixed 1m above the ground, measurements were taken every 5 seconds. On the windward sidewindspeed was measured continuously for 6 hours during, however on the leeward side the firsttwo hours was used for windspeed measuring at the first point (30 m distance), second two hours
for measuring at the second point (60 m distance) and the last 2 hours for measuring at the thirdpoint (90 m distance).

Fig. 3 Setting up wind speed measuring equipment
Top left corner showing the cup anemometer type used for recording the windspeed
Note: Taken by Onchevski in August 2021
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IJERD – International Journal of Environmental and Rural Development (2022) 13-2

Optical Porosity- Level of Degradation of Tree Windbreaks
In addition to the windspeed measurements, the optical porosity was analyzed for each windbreaksection. Optical porosity of windbreak was described by terrestrial photogrammetry method as thevalue of the optical porosity from the photo documentation of the windbreak at the time of fieldmeasurement. Each section was photographed with iPad Pro 12MP, ƒ/1.8 aperture camera from theleeward side of the windbreaks at a 30 m distance from the windbreak on 1.5 m ground.
Photogrammetric analysis was done using GIMP (version 2.10.28), AutoCAD and Excel software.
At first, all photos were scaled in AutoCAD and then graphically processed to black and withbinary image, where vegetation was highlighted and assigned in black against the backgroundassigned in white. Histogram tool was used to calculate the exact number of black (= vegetation)
and white(= background) pixels. The value of optical porosity was calculated as distribution of thewhite (background) pixels expressed as percent value. The higher the value of OP, the lower thevegetation distribution and windbreak effectiveness to reduce windspeed.

Fig. 4 Photos indicating tree windbreak measuring sites before and after pixel processing
Measuring site no.1 on the top, measuring site no.2 in the middle, and measuring site no.3 in the bottom

RESULTS
Optical Porosity
Analysis showed that site number 2 has the OP value of 35.8% which is highest, while site number
3 has lowest OP value of 16.57 %. Site number 1 has OP of 18.23%, value that is close to value ofsite number 3. The results of optical porosity (OP) analysis are presented in Table 1.
Table 1 Optical porosity of tree windbreak measuring sites
White (background)pixels1064042

Optical porosity

1Black (foreground)pixels4774038

23289752

183423035.80%

34751115

943361

16.57%

Site no.

18.23%

Wind Speed Reduction Efficiency
The first wind speed measurements at site no.1 (Fig. 4) showed that this tree windbreak section cansignificantly reduce the windspeed coming from the windward side. At the leeward side at 30 m
distance the there is a reduction of 54%, at 60 m distance there is a reduction of 25% and at 90 m
distance reduction of 8%. Expressed as relative windspeed, at 30 m distance the wind velocity isⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2022) 13-2

46% of wind at the windward side, at 60 m the velocity is 75% of the velocity of windward sideand at 90 m the wind speed is 92% of the windspeed at the windward side. The second
measurements show similar trend in windspeed reduction efficiency. In this time, at 30 m distancethe wind velocity is 47% relative to the windward side, at 60 m the velocity is 72% of the velocity
of windward side and at 90 m the windspeed reached the same value (100%) as the incoming wind.
Table 2 shows the relative windspeed at each site at the different measuring distances.
Table 2 Windspeed reduction related to different optical porosity and distance to tree line
Tree windbreak siteno.
1 (first measuring)
1 (second measuring)23

Optical porosity
background pixels (%)
18.23%
18.23%
35.80%
16.57%

30 m
46%
47%
74%
40%

Relative windspeed (%)
60 m
90 m
75%
92%
72%
100%
95%
98%
78%
96%

Correlation results showed that optical porosity and windspeed reduction is significantly
correlated for the measuring points at 30 m and 60 m distance from the tree windbreak, however at
90 m distance there was no correlation. For the 30 m distance measuring point the correlation
coefficient (r) is high with a value of 0.993 and with a 99% level of significance (p < 0.01). For the60 m measuring point correlation coefficient (r) is 0.95 and the level of significance of 90% (p <0.10). These results confirm other authors’ research conclusions that optical porosity is linearly
connected with wind speed reduction efficiency and can be reliable measure for evaluation ofwindbreak efficiency (Brandle et al., 2004; Helfer at al., 2009; Středová et al., 2012; Řeháček et al.,2017; Wu et al., 2018; Kučera, 2020).
Table 3 Relation between optical porosity and windspeed reduction efficiency
Anemometer position (leeward side) 1 m above ground
30 m
60 m
Measurements
44
Correlation coefficient (r)0.993
0.950P-value
0.007
0.05
Level of significancep < 0.01
p < 0.1090 m
40.2920.708
n/a

CONCLUSION
Research results presented in this chapter shows that tree windbreaks systems in the research area
play key role in buffering the negative effect of the prevailing winds. Having in mind thatsignificant windbreak area was lost and existing are under threat of degradation, it is important thatexisting tree windbreaks systems are protected from degradation, degraded areas should be restored,
and new tree windbreaks should be expanded to other areas. Another conclusion coming from theresults is that optical porosity (OP) is a reliable measurement that can describe the wind speed
reduction efficiency and level of degradation of windbreaks in the research area. This indicate that
optical porosity can be used as guidance for maintenance and management of existing tree
windbreaks as well as for guidance when establishing new windbreak areas. As recommendation
optical porosity of the windbreaks should be maintained between 15-20%. At the degradedwindbreak sections with optical porosity higher that 20%, to fill the internal voids and space,interplanting new trees is recommended. New planted trees should be species that can thrive in thelocal conditions and provide multiple functions such as: nitrogen fixation, fruits, pollen for honey,
medicines and other NTFP. Some of the possible tree species are Elaeagnus angustifolia (Eng.
Russian olive), Ziziphus jujuba (Eng. Chinese date), Quercus spp. (Eng. Oaks), Cornus mas (Eng.
Cornelian cherry), Prunus Amygdalus (Eng. Almond), Prunus cerasifera (Eng. Cherry plum) andothers.
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