BIOLOGIJA. 2020. Vol. 66. No. 2. P. 73–79 © Lietuvos mokslų akademija, 2020

Impact of forest management on wild boar (Sus scrofa) population in south Lithuania

Tomas Barkauskas2*,

Loreta Griciuvienė1,

Olgirda Belova2,

Nomeda Bratčikovienė3

1Vytautas Magnus University, K. Donelaičio St. 58, Kaunas 44248, Lithuania

2Institute of Forestry LAMMC, Liepų St. 1, Girionys 53101, Kaunas District, Lithuania

3Vilnius Gediminas Technical University, Saulėtekio Av. 11, Vilnius 10223, Lithuania

We assessed the  effect of the  investigated felling types on the abundance of the wild boar population in south Lithuania. The study was carried out in the southern part of Prienai forest, Punia pine forest, and Kalviai forest, all located in southern Lithuania. The data on the number of the wild boar population and the hunting dynamics were gathered from six hunting seasons, from 2008 to 2014. Our results highlighted that some types of felling had negative effects on the density of the wild boar population in south Lithuania. We observed that changes in the wild boar population were not only affected by the felling of the current year, but also by that of the previous year. Further analysis of data collected over a larger area is needed to check these findings.

Keywords: Sus scrofa, forest management, south Lithuania

INTRODUCTION

The wild boar (Sus scrofa) is one of the most successful, abundant, and widespread species of wild ungulates in Europe (Apollonio et al., 2010; Lombardini et al., 2017; Lacolina et al., 2018). A high level of adaptability of this species to various environmental conditions and their successful expansion in Europe are explained by a high reproductive capacity, adaptability to a variety of habitats, dispersal potential, and high plasticity of wild boar (opportunistic, omnivorous diet) (Cahill  et  al., 2003; Gethöffer et al., 2007; Herrero et al., 2008; Ballari, Barrios-García, 2014). In most European countries, wild boar is the most widely hunted big game (Nores et al., 2008; Apollonio et al., 2010). The Central European wild boar (Sus scrofa) is considered one of the subspecies inhabiting the Baltic countries (Baleišis  et  al., 2003). Climatic trends, human impacts, and ecological factors influence the  distribution and abundance of the  ungulates (Acevedo et al., 2005). According to some authors, the  distribution of ungulate species depends on the habitat structure and suitability (Cahill et al., 2003; Acevedo  et  al., 2005, 2006). Considerable research has been conducted into the  impact of intense hunting on wild boar dispersal (Keuling et al., 2008; Tolon et al., 2009; Thurfjell et al., 2013; Massei et al., 2014), but the data on the assessment of the impact of forestry on the wild boar population are still scarce. Disturbing forest management influences habitat suitability, population density, behaviour, and movement of the ungulates (Long et al., 2008; Avgar et al., 2015; Stergar, Jerina, 2017). Investigation of demographic measurements is important in understanding how populations respond to forest management. The  purpose of this study is to analyze how changes in forest management could affect the wild boar population in Lithuania.

MATERIALS AND METHODS

The study was carried out in the southern part of Prienai forest, Punia pine forest, and Kalviai forest, all located in southern Lithuania (Fig. 1). We analysed the effects of felling intensity and felling types on the wild boar population. This research was based on two primary types of felling, which were divided into smaller categories: final felling (clear, clear salvage, shelterwood cutting, and selective felling) and intermediate felling (pre-commercial thinning, commercial thinning, selective salvage cuttings, and special felling). The data on the population number of wild boar and the hunting dynamics were gathered from six hunting seasons, from 2008 to 2014. The data on the number and abundance of animals were obtained from the official census of the Ministry of Environment and from the censuses of different hunting areas.

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Fig. 1. Map of the study area in the southern part of Lithuania

The population density of wild boar (T) was calculated by the following formula (Navasaitis and Pėtelis, 1998):

T= G P                  ( 1 )

where: G – the number of animals in the territory, individuals, P – a territory unit of 1,000 ha.

The  relationship between the  population density of wild boar and changes in forest management was analysed using Pearson product-moment correlation coefficient that measures the strength and direction of a linear association. Statistical analysis was performed using the Statistical Software R.

RESULTS AND DISCUSSION

We analyzed the effect of the investigated felling types on the  abundance of the  wild boar population in south Lithuania. Variables that affect wild boar population abundance are given in the Table.

Table. Effects of forest felling on the wild boar population in southern Lithuania

Year Monitoring of wild boars Final felling Intermediate felling Total
Abundance Density Hunting Clear felling Clear salvage Shelterwood cutting Selective felling Pre-commercial thinning Commercial thinning (1) Commercial thinning (2) Selective salvage cutting Special felling
N T N ha m3 ha m3 ha m3 ha m3 ha m3 ha m3 ha m3 ha m3 ha m3 ha m3
Kalviai forest
2009 80 61.8 47 0.9 45.8 26.2 40.1 27.1 85.9
2010 90 69.5 43 2.6 849.51 41.9 10589.05 2.5 159.33 445.2 3618.22 492.2 15216.1
2011 90 69.5 51 50 10148.61 123.4 5806.9 173.4 15955.5
2012 80 61.8 59 7.5 78.15 86.7 589.88 94.2 668.03
2013 15 11.6 46 3.3 102.97 149.6 325.66 152.9 428.63
2014 21 16.2 92 26.1 698.1 94.7 228.18 120.8 926.28
Punia pine forest
2009 84 30.4 30 3.5 243 5 361 4.5 4.5 9.9 709 84.2 414 107.1 1727
2010 53 19.2 30 2.8 136 17.2 17.2 55.5 105 75.5 241
2011 60 21.7 10 4.6 561 7.2 405 150.3 107 162.1 1073
2012 73 26.4 46 1.3 220 0.7 92 2.6 163 0.5 5 11.3 651 273.6 1511 290 2642
2013 6 2.2 66 0.9 1.69 3 309 2.2 215 3.7 3.7 3.2 68 13.4 960 95.5 1901 121.9 3454.69
2014 12 4.3 34 9.9 863 5.3 391 28.6 28.6 13.9 75 62.3 2491 47.2 1329 167.2 5149
Prienai forest
2009 42 12.2 69 8.08 2953 5.27 694 16.1 822 15.2 3.2 148 103.1 7005 490.4 979 2.2 3.8 643.55 12604.8
2010 61 17.7 44 3.8 974 23.3 6.3 221 46.9 2688 1054.8 2917 1135.1 6800
2011 63 18.3 45 5.72 1445 1.3 253 1.7 311 32.3 20.9 706 1331.7 4926 4.6 758 1398.22 8399
2012 60 17.4 62 4.7 1856 0.3 39 16.7 18.3 328 96 6063 1016.2 1077 2.2 3.8 1152.2 9363
2013 48 13.9 73 6.4 1646 13.3 2220 25.7 8.3 173 99.3 4835 1158.8 1285 1311.8 10159
2014 93 27 94 6.1 1837 0.3 78 4 1158 28.3 12.1 474 41.7 1911 1212.3 948 4.6 758 1304.8 6406

N – number of individuals; T – density, N/1000 ha; ha – hectare; m3 – cubic metre

Correlation analysis was performed to identify the  strength of relationships between wild boar abundance/density and felling types. In the  six-years observation period, a  weak positive correlation between wild boar abundance and total felling rate in hectares was observed (r  =  0.28) (Table). However, the  abundance of wild boar was strongly correlated with total felling in m3 (r = 0.59). These results illustrate that the wild boar population increases with increasing cases of felling (in hectares and in m3). We suppose that low levels of clear felling was carried out in small study areas, meanwhile selective salvage cutting in large plots has led to a positive effect in the growth of the wild boar population.

The Kalviai forest is dominated by selective salvage cutting, which is controlled by a small volume of wood over a large area (Table). This cutting does not impair the nutritional quality and does not reduce the  number of hiding places. We found that there was a weak positive relationship between wild boar abundance and selective salvage cutting (ha) (r  =  0.25); meanwhile, a  stronger positive relationship was obtained by investigating the relationship between the  measure of wood cutting in m3 (r = 0.58) (Fig. 2). The correlation coefficient of 0.59 indicates a strong positive correlation between wild boar abundance and total volume of wood cutting (m3), because in Kalviai forest, the largest amount of timber volume (m3) is felled by clear salvage felling that consists of a  relatively small area but a  large amount of wood (Fig. 3). In the interpretation of such correlations, we can conclude that clear cutting affects the soil mechanically during the felling process and after the  preparation of logging sites for planting. This improves the nutritional base of wild boars by grubbing and searching for cockchafers in the soil. Clear salvage cutting is carried out in premature and mature stands that are not attractive to wild boars. Forestry measures alter forest succession that can affect the ungulates by changing forage quantity and quality (Schrempp et al., 2019).

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Fig. 2. Estimates of correlation coefficients of the abundance of wild boars and selective salvage cutting

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Fig. 3. Estimates of correlation coefficients of the  abundance of wild boars and deforestation

A  similar situation was found in Punia pine forest, where the positive correlation between wild boar abundance and total felling (ha) was weak (r = 0.19); it might be explained by prevalent selective salvage cutting (Fig. 3). Moreover, the results indicated a strong negative correlation (r = –0.67) between the abundance of wild boar and the  volume of wood cutting (m3) (Fig. 3). In contrast to Kalviai forest, the observed negative correlation implies that the number of wild boars decreased with increasing felling intensity. The  correlation is further strengthened if a  one-year change is taken into account (r = –0.75) (Fig. 3). These results demonstrated that the  changes in the  wild boar population were affected not only by the felling of the current year, but also by that of the  previous year. Assessment of the correlation coefficient value (r = 0.46) between the abundance of wild boar and selective salvage cutting revealed that this felling type had a positive effect on the wild boar population (Fig. 2). A similar pattern is also reported by other authors (Gasperini et al., 2016). They found that that different types of forest management had strong positive effects on the density of rodent population. A sufficiently strong correlation was observed between the quantity of wild boar and total felling in m3 (r = –0.67). Contrary to the results obtained in Kalviai forest, this relationship is negative and could be explained by the  impact of increased cutting intensity on the decrease in the number of wild boars. This finding is unsurprising considering that a bigger volume of logging is realized by final cutting of shelterwood and selective felling. In these types of thinning, the  intent is to harvest a large volume of timber (m3) over a  large area, thus reducing the  stocking level of a  stand. Therefore, conditions of breeding and hiding places are affected by a reduced selection of the habitat. According to Son et al. (2017), tree affects the abundance of animals due to their preferences of the habitat. Wilson and Forsman (2013) previously demonstrated that thinning reduced the abundance of some tree-dwelling rodents.

A similar trend involving a  strong positive correlation between wild boar abundance and total felling in hectares (r = 0.54) and negative correlation with felling in m3 (r  =  –0.83) was also reported in Prienai forest (Fig. 3). Clearly, there was a weak correlation in terms of time, indicating that the felling of the current year has a  greater impact for wild boar subpopulation from Prienai forest compared to the felling of the previous year. The selective salvage cutting dominates in Prienai forest and the correlation coefficient of 0.57 indicates a  strong positive correlation (Fig. 2). These results confirmed that selective salvage cutting improved nutritional conditions for wild boar. The reason for the negative correlation of felling in m3 was similar to that in Kalviai forest. The maximum volume of timber (m3) was harvested by final cutting of shelterwood and intermediate cutting of commercial thinning (Table). These types of felling may be associated with a reduction of the stocking level of stands and activities in stands of all ages in a large area. Moreover, in this situation the  conditions of breeding and hiding places worsened, because females of wild boars choose shaded forest areas and high stocking level plots suitable for the birth of their young.

CONCLUSIONS

Our results demonstrated that some types of felling had a  negative effect on the  density of the  wild boar population in south Lithuania. Further analysis of data collected over a larger area is needed to check these findings.

Received 19 April 2020

Accepted 19 May 2020

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* Corresponding author. Email: tomas.barkauskas40@gmail.com

Tomas Barkauskas, Loreta Griciuvienė, Olgirda Belova, Nomeda Bratčikovienė

MIŠKININKAVIMO POVEIKIS ŠERNŲ POPULIACIJAI PIETŲ LIETUVOJE

Santrauka

Šio tyrimo tikslas buvo įvertinti skirtingų miško kirtimo rūšių įtaką šernų populiacijos skaitlingumui Pietų Lietuvoje. Tyrimas buvo atliktas Prienų šilo, Punios šilo ir Kalvių miško dalyje. Duomenys apie šernų populiacijos skaitlingumą ir medžioklės dinamiką buvo surinkti iš šešių medžioklės sezonų (2008–2014 m.). Rezultatai rodo, kad kai kurie kirtimų tipai turėjo neigiamą įtaką šernų populiacijos gausumui Pietinėje Lietuvos dalyje. Pastebėjome, kad šernų populiacijos pokyčius paveikė ne tik einamųjų, bet ir praėjusių metų kirtimai. Norint patvirtinti šias išvadas, reikalingi platesni tyrimai.

Raktažodžiai: Sus scrofa, miškininkavimas, Pietų Lietuva