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Article

Microclimate of Pedunculate Oak (Quercus robur L.) Sustainable Managed Forest Stands—A Study of Air and Soil Temperatures in Shelterwood Cutting

by
Krešimir Popić
1,
Azra Tafro
2,
Dario Baričević
3,
Irena Šapić
3,*,
Ivica Tikvić
3 and
Damir Ugarković
3
1
Croatian Forests Ltd., Forest Department Vinkovci, Forest Office Lipovac, M. Gupca 5, 32246 Lipovac, Croatia
2
Department of Processes Engineering, Faculty of Forestry and Wood Technology, University of Zagreb, Svetošimunska Cesta 23, 10000 Zagreb, Croatia
3
Department of Ecology and Silviculture, Faculty of Forestry and Wood Technology, University of Zagreb, Svetošimunska Cesta 23, 10000 Zagreb, Croatia
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(11), 5106; https://doi.org/10.3390/su17115106
Submission received: 8 May 2025 / Revised: 31 May 2025 / Accepted: 31 May 2025 / Published: 2 June 2025
(This article belongs to the Special Issue Research on Sustainable Forest Management in the Context of Climate Change)
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Abstract

:
Forest management and tree felling in the stand change the structural characteristics, which causes changes in the microclimate conditions. The microclimate is a key in sustainable forest management because soil temperature and moisture regimes regulate nutrient cycling in forest ecosystems. The aim of this research was to determine the changes in air and soil temperatures in pedunculate oak forest stands in different stages of shelterwood that stimulate natural regeneration. The research was conducted in pedunculated oak forests in Spačva area. The microclimatic parameters were measured in a mature old forest stand without shelterwood cutting and in stands with preparatory cut, seed cut, and final cut. The intensity of shelterwood had an impact on the amplitudes and values of air and soil temperatures. The highest average air temperature was in the stand with a preparatory cut. Extreme values of air and soil temperatures were measured in the stands with a final cut. The highest air and soil temperature amplitudes were in the stand with a final cut, with the exception of most of the winter, when the highest soil temperature amplitude was in the stand with a seed cut. The highest number of icy, cold, and hot days was in the stand with a final cut. SARIMA models establish that the difference between microclimatic parameters is not accidental.

1. Introduction

Pedunculate oak forests are widespread in lowland areas, especially along rivers. In Croatia, the most beautiful stands are along the Sava, Drava, Danube, and their tributaries and make up about 7% (approximately 200,000 ha) of the total forest area [1]. Regular or even-aged management has proven to be the optimal way to direct the development of pedunculate oak forests. This approach includes the establishment of a young forest stand, its care during its life cycle, and the final regeneration in which the old stand is removed and the space is left to the new generation [2].
Natural regeneration takes place over a sufficiently long period of time, during which gradual felling in two to three (maximum five) phases stimulates forest rejuvenation while at the same time exploiting its accumulated wood volume.
Each forest ecosystem creates unique and specific microclimatic conditions under the tree canopy. Forest trees shape the microclimate [3,4], and members of the forest ecosystem have adapted to these specific microclimatic conditions that differ significantly from neighboring non-forest habitats [5,6,7]. Microclimate affects key ecological processes, such as photosynthesis, food chains, nutrient cycling, and organic matter decomposition. These processes are crucial for the stability and productivity of forest ecosystems [8]. Microclimate refers to the local climatic conditions to which organisms and ecosystems are exposed. In terrestrial ecosystems, microclimate often differs significantly from the macroclimate, or climate characteristic of a wider geographical area. Microclimate is mainly shaped by topography, vegetation, and soil, and it represents a combination of local temperature, water, solar radiation, clouds, wind, and evaporation conditions [9].
Among the most important factors determining microclimate are forest structure and composition. The density of the canopy, the vertical stratification of vegetation, and the proportion of individual tree species directly affect the penetration of light and the movement of air within the forest. Denser forests and more layered structures create cooler and more humid microclimatic conditions [10]. Tree crowns and their structure, in a way, represent a buffer of a certain forest ecosystem [11]. However, the tree crown structure can be changed by forestry interventions in the stand [12,13]. Forestry interventions in the stand that thin out the tree crown assembly, that is, create openings in the crown assembly, and generate microclimatic conditions that are significantly different from those in stands with a complete crown assembly [11]. Therefore, it is important to know how felling as a cultivation procedure in the forest induces changes in the forest climate and how certain members of the ecosystem react to these changes [14].
Forest soil also has a specific microclimate, including soil temperature, moisture, and the presence of microorganisms and nutrients. It can also be observed that soil temperature is influenced by the crown structure and cover density. Soil microclimate is essential for the decomposition of organic materials and the cycling of nutrients, which is vital for plant growth. Also, lower temperatures slow down the decomposition of organic matter and increase the content of humus in the soil [15]. This improves the physical and chemical properties of the soil, which has a positive effect on plant growth and survival [16].
Although the oak forests are ecologically very important, relatively little attention has been given to the study of their microclimate so far. The location and time of clearing play an important role in the dynamics of regeneration. Studies on the influence of canopy opening size on microclimate were conducted by Tranquillini [17] and Denslow [18]. They found that increasing canopy openness increases the amount of solar radiation and air temperature in the ground layer of the forest. Reducing canopy density also increases wind speed. Potter et al. [19] researched the relationship between temperature, microclimate, and forest structure. In the largest pedunculate oak forest complex in Croatia and Europe, in Spačva, the microclimate was researched in 1972 [20], then in the lowland forests near Lipovljani in 1974 and again in the same year in Spačva [21], and the Česma River basin from 1992 to 1995 [22].
Previous research suggests that pedunculate oak forests create specific microclimates that differ from surrounding open habitats and other forest ecosystems. These forests are characterized by lower air temperatures, higher humidity, and less light, with pronounced vertical gradients of these parameters. However, systematic studies of the microclimate of pedunculate oak forests during different seasons are still lacking in order to gain more detailed knowledge. Studies by Bréda et al. [23] and Deshayes et al. [24] focus on the impact of climate change on the microclimate and biodiversity of pedunculate oak forests. The importance of knowing microclimate conditions for understanding physiological and ecological processes in forest ecosystems is emphasized.
We still lack sufficient climate data on forest climate, which would be crucial for climate predictions and for modeling species distribution [14]. Therefore, all data on forest climate are important for understanding the ecology of forest species and the relationships within the forest ecosystem.
Despite the broad influence of microclimate on forest ecosystem members, our knowledge of changes and impacts of microclimate on individual forest ecosystem members, as well as how microclimate shapes biotic responses to global change, is still insufficient and limited [7,25]. This is one of the reasons why we conducted this research on the impact of shelterwood cutting on microclimatic and microbiological changes in the forest ecosystem.
The aim of the research is to determine changes in air and soil temperatures in forest stands of different phases of shelterwood cutting. Our hypothesis is that the air and soil temperatures of forest stands change significantly depending on the cutting intensity. We analyzed and compared air and soil temperatures in a mature old forest stand without shelterwood cutting and in stands in different phases of shelterwood. We assumed the following:
1. Air temperatures increase with the sequence of shelterwood phases, that is, with cutting intensity in all treatments.
2. Soil temperatures also increase with the intensity of felling.
3. Extreme values of air and soil temperature, as well as the greatest number of warm and hot days, will be in the last phase of shelterwood (final cut). In addition to the intensity of shelterwood, air, and soil temperatures are also affected by the local climate.

2. Materials and Methods

2.1. Research Area

The research was conducted in the Spačva area, the largest complex of pedunculate oak forests in Europe. This entire forest complex, with a total area of about 51.000 ha, extends over the territory of Croatia and Serbia, in the basin of the Spačva and Studva rivers. About 40,000 ha of the forest complex is located in the territory of Croatia, where the research was conducted (Figure 1). Pedunculate oak covers over 95% of the complex as the dominant species. There are two main types of pedunculate oak forest communities in Spačva, one on lower terrains within the reach of flood waters and the other on micro-elevations outside the flood zone [26,27]. On lower terrains where periodic floods of short duration are frequent, it forms the community Genisto elate-Quercetum roboris Horvat 1938. On higher terrains outside the flood zone, it forms a community with common hornbeam Carpino betuli-Quercetum roboris (Anić 1959) Rauš 1971. The experiment was set up in a community of pedunculate oak with common hornbeam, in locations beyond the reach of flood waters but still under the influence of high groundwater levels. It is a climazonal community of a planar vegetation belt, created by natural succession from the Genisto elatae-Quercetum roboris floodplain forest. The community has a wide pedological amplitude, occurring on hydromorphic (hypogley, semigley, pseudogley, rarely amphigley) and automorphic soils. The average groundwater level is outside the root system zone of the common hornbeam (Carpinus betulus L.) but regularly within the root system zone of the pedunculate oak (Quercus robur L.). In addition to the pedunculate and hornbeam in the tree layer, there are also field ash (Fraxinus angustifolia Vahl), field maple (Acer campestre L.), small-leaved lime (Tilia codrata Mill.), wild cherry (Prunus avium (L.) L.), field elm (Ulmus minor Mill.), and black alder (Alnus glutinosa (L.) Gaertn). In the shrub layer, in addition to species from the tree layer, common hazelnut (Corylus avellana L.), wild pear (Pyrus pyraster (L.) Burgsd.), wild apple (Malus sylvestris (L.) Mill.), elder (Sambucus nigra L.), blackthorn (Prunus spinosa L.), dogwood (Cornus sanguinea L.), common spindle (Euonimus europaeus L.), hawthorn (Crataegus monogyna Jacq., Crataegus laevigata (Poir.) DC.), guelder rose (Viburnum opulus L.), and wild privet (Ligustrum vulgare L.) is common. The ground vegetation layer well reflects the habitat conditions of the community. The largest share of the floral composition is thus made up of mesophilic species of higher terrain: Stellaria holostea L., Vinca minor L., Anemone nemorosa L., Hedera helix L., Symphytum tuberosum L., Pulmonaria officinalis L., Carex sylvatica Huds., Polygonatum multiflorum (L.) All., Sanicula europea L., Galium odoratum (L.) Scop., Lamium galeobdolon (L.) Crantz, Dryopteris filix-mas (L.) Schott, Viola reichenbachana Jord. ex Boreau, and others. However, this community also includes species of wet and marshland habitats, the most common of which are Carex remota L., Lysimachia nummularia L., Carex brizoides L., Rucus caesius L., Festuca gigantea (L.) Vill., Ranunculus repens L., Lycopus europaeus L., Polygonum hidropiper L., and others [1]. The average annual air temperature in the study area is 11.8 °C, and the total annual precipitation is 665.09 mm. The highest amount of precipitation falls in the warmer part of the year during the growing season. During winter, there are on average 22 days of snow (≥1 cm), and the maximum snow cover was 53 cm (https://meteo.hr/, accessed on 6 February 2025). In the year of microclimate research, the average annual air temperature was 12.5 °C, and the amount of precipitation was 704 mm. In total, there were only 11 days of snow (≥1 cm), and the maximum snow cover depth was 4 cm. Synoptic monthly air temperature data (°C) for weather stations Gradište (lat: 45.15, lon: 18.7) and Vinkovci (lat: 45.28, lon: 18.81) from March 2021 to March 2022 were obtained from the State Meteorological Service. The soil is a light clayey luvisol in which carbonates of loess and loamy texture occur at a depth of 90 cm. The soils of the study area are partially hydromeliorated by a canal network for flood protection. The soil reaction is neutral and slightly alkaline to alkaline, and the parent substrate is “swamp” loess [28].
The research sites are in stands of different stages of shelterwood cutting or regeneration (Table 1). For this type of research, it would be ideal if the same stand were studied over time, but due to time constraints, we replaced time with different spaces (stands) representing different situations (preparatory, seed, final cut). In doing so, care was taken to ensure that the habitat conditions were approximately the same, that they were in the same habitat type and forest community, and that the stands were approximately the same age. The mutual air distances between the investigated surfaces are as follows: OF—PC 14.2 km, OF—SC 10.1 km, OF—FC 0.95 km, PC—SC 13.0 km, PC—FC 13.2 km, SC—FC 9.9 km. The whole research area is plain with no inclination of inclination. The experiment to analyze air and soil temperatures during the stand renewal processes was set up in old, mature stands aged from 130 to 150 years.

2.2. Microclimatic Measurements

Microclimatic research was conducted from March 2021 to March 2022. The microclimate of forest stands was measured using Spectrum WatchDog 2800 meteorological stations. Parameters measured were air temperature (°C) and soil temperature (°C). Air temperature measurements were taken at a height of 1.5 m, and forest soil temperature measurements were taken at a depth of 10 cm. Descriptive statistics of air and soil temperatures were analyzed by season, vegetation period, and for the whole year. The vegetation period is considered to be from the beginning of April to the end of September [22]. Microclimatic measurements were performed on 12 locations, 3 repetitions for each forest stand at a time interval of 1 h. All microclimatic data were processed using the SpecWare 9.0 software package [29].

2.3. Statistical Processing of the Data

Descriptive statistics of air and soil temperatures were created for measurements per hour and per season. Daily amplitudes (the difference between the highest and lowest hourly values in a day) were calculated, and the results are shown by season. Amplitudes are shown to emphasize the differences more clearly. For other descriptive statistical analyses and the SARIMA model, we analyzed the original measurements.
For seasons, the analysis was made for spring: 25.3. (at 12:00)–20.6. (at 23:00), for summer: 21.6. (at midnight)–22.9. (23:00), for autumn: 23.9. (midnight)–20.12. (23:00) and for winter: 21.12. (midnight)–20.3. (23:00). The number of icy days (Tmin ≤ −10.0 °C), cold days (Tmin < 0.0 °C), warm days (Tmax ≥ 25.0 °C), and hot days (Tmax ≥ 30.0 °C) was analyzed [30]. At some locations, a certain number of measurements is missing. Out of the total 8916 data points, there are 671 missing soil measurements in the preparatory cut, mostly May 1st–May 21st, and some in the summer. There are also 271 missing air measurements in the old forest stand, mostly throughout April. These occurred due to technical difficulties with the equipment. Apart from those, there are at most 6 missing measurements per stand. The number of missing values is generally small and scattered enough that there is no reason to think that the measurements are missing for any specific reason, or we assume that they are “missing at random” and do not have to be excluded from the analysis. All descriptive statistics were calculated on the available data. Since the SARIMA model estimation does not handle missing data, the missing values were substituted with linear interpolations from the available surrounding data.
To determine whether there is a statistically significant difference between areas, we observed the differences between locations (preparatory cut–old forest, seed cut–preparatory cut, final cut–seed cut). The observed time series were analyzed to determine whether the difference is random (i.e., white noise) or if there is a statistically significant difference. To allow for maximum flexibility, Seasonal AutoRegressive Integrated Moving Average (SARIMA) models were fitted to these time series. They extend the ARIMA model by explicitly accounting for seasonal patterns, which are expected here both at daily and yearly intervals. The model combines differencing to remove trends and seasonality with autoregressive and moving average components to capture dependencies in the data. The coefficients of a SARIMA model represent the strength and direction of the relationships between current values in the time series and past observations or past forecast errors. The autoregressive (AR) coefficients measure how much past values influence the current value, while the moving average (MA) coefficients reflect how past errors affect the current prediction. Seasonal AR and MA coefficients do the same but at seasonal lags. This analysis was performed in R analytics software (v4.5.0) using the forecast package [31].

3. Results

3.1. Air Temperature

Descriptive statistics of air temperature are shown in Table 2. The absolute minimum was −15.90 °C, and the absolute maximum was 40.20 °C, both in the stand with the final cut.
Figure 2 shows the daily air temperature amplitudes in pedunculate oak forest stands. In spring, the stand with a final cut had higher daily air temperature amplitudes, while the old forest stand had the lowest daily amplitudes. During summer, the daily air temperature amplitudes were highest in the stand with a final cut, while the stands with preparatory, seed, and old forest stands had lower daily amplitudes. During autumn, the highest daily air temperature amplitudes were in the stand with a final cut. The minimum daily air temperature amplitudes overlapped between the studied forest stands. The maximum daily air temperature amplitudes were in the stand with a final cut. The minimum daily air temperature amplitudes overlapped between the studied forest stands (Figure 2).
Regarding daily air temperatures, Table 3 shows the number of icy, cold, warm, and hot days. Looking at the temperature values, most of the cold days (as many as 139) and the least icy days occurred in the stands. The highest number of icy days (14), cold days (139), and hot days (69) occurred in a stand with a final cut.
The best estimated SARIMA model for differences in air temperatures between the preparatory cut and old forest was ARIMA (1,0,0)(2,1,0){24}, indicating a seasonal component in the differences. The AR1, SAR1, and SAR2 coefficients were statistically significant (p-value < 1%); therefore, there is a statistically significant difference between air temperatures at these two locations (Figure 3). For the stand in the old forest, a certain number of data points, or measurements, are missing during the spring of 2021, as can be seen in Figure 2.
For differences in air temperatures between seed and preparatory cut, the best estimated SARIMA model was ARIMA(5,1,0)(2,0,0){24} with six statistically significant coefficients (AR2, AR3, AR4, AR5, SAR1, SAR2, p-value < 1%), indicating that the difference between areas is statistically significant.
The best estimated SARIMA model for differences in air temperatures between final cut and seed cut areas was ARIMA(0,1,2)(0,0,2){24}. Again, we have 4 significant coefficients (MA1, MA2, SMA1, SMA2, p-value < 1%), which means that the difference in temperatures is statistically significant and not random.

3.2. Soil Temperature

On average, the highest soil temperature values in the warmer part of the year (spring, summer) were in stands with a final cut. In the colder part of the year (autumn, winter), the highest soil temperature values were in stands with a preparatory cut (Table 2).
During spring, daily soil temperature amplitudes were highest in the stand with a final cut, and lowest mainly in the old stand (Figure 4). During summer, soil temperature amplitudes were highest in the stand with a final cut, while the old forest stand and the stand with a seed cut had the lowest daily amplitudes. During autumn, the highest daily soil temperature amplitudes were in the stand with a final cut, while the values of the lowest amplitudes overlapped between the studied forest stands. During most of the winter, the highest daily soil temperature amplitudes were in the stand with a seed cut.
The best estimated SARIMA model for differences in soil temperatures between the preparatory cut and the old forest was ARIMA(5,1,2)(2,0,0){24}. All coefficients (AR1-AR5, MA1, MA2, SAR1, SAR2) were statistically significant (p-value < 1%), indicating there is a statistically significant difference in temperatures between these locations. For the stand in the preparatory cut, a certain number of data points, or measurements, are missing during the spring of 2021, as can be seen in Figure 4.
For the difference of soil temperatures in areas with seed and preparatory cuts, the best SARIMA model was ARIMA(5,1,2)(2,0,0){24}. All coefficients (AR1-AR5, MA1, MA2, SAR1, SAR2) were statistically significant (p-value < 1%), indicating there is a statistically significant difference in temperatures between these locations. As for differences in soil temperatures between final cut and seed cut areas, the best SARIMA model was ARIMA(3,0,2)(2,1,0){24}. All coefficients (AR1-AR3, MA1, MA2, SAR1, SAR2) were statistically significant (p-value < 1%), indicating there is a statistically significant difference in temperatures between these locations (Figure 5).

4. Discussion

Microclimatic conditions in pedunculate oak forests are influenced by several factors, including the general climate of the area, geographical location, structure and composition of the forest stand, and surrounding habitats. In general, the local climate of an area is considered a key factor that determines the basic characteristics of the microclimate in the forests of that area [32]. The diversity of tree species, forest structure, and forest management methods, i.e., felling intensity and distance from the forest edge, also affect the forest microclimate [33].
The change in forest climate, microclimate, is influenced by a number of factors. Felling causes microclimatic changes in the forest stand. That is, by cutting trees in the forest stand, we affect the amount of light, heat, and air temperature [34]. The effect of silviculture treatments on the forest microclimate also depends on the macroclimate, especially air temperature, and precipitation, as well as on the topography, location of the forest, type of forest stand, and tree species composition and structure of the stand itself [8,35,36].
In addition to the phases of shelterwood, the microclimate of the studied stands was influenced by the type of forest soil and the position of the forest stands in the forest complex.
Microclimatic conditions in the oak forests show significant seasonal and daily variations. In general, the largest temperature differences between old-forest stands and final-cut stands were recorded in this research during the warmer months (June–August), while these differences were less pronounced in winter. For example, a study in Belgium found that during summer the air temperature in pedunculate oak forests was on average 2 °C lower than that in grassland, while in winter the difference was 0.3 °C [37]. Comparing air temperatures in forest stands with data from weather stations, absolute minimum air temperatures were higher in the forest. Absolute maximum air temperatures were the same, with the exception of final cut stands, where they were lower by 2.5 to 3.1 °C (Table S1). Average air temperatures were lower in the forest compared to weather stations. These seasonal variations are a consequence of the more pronounced effect of the shade of the pedunculate oak canopy during sunny and warm periods. Also, during the summer months, there is a greater diurnal temperature range, with lower minimum and higher maximum daily values, as in the study [32]. In winter, these variations are less pronounced.
Several studies have shown that pedunculate oak forests create different microclimatic conditions compared to the surrounding open habitats. Specifically, the air temperature below the canopy of these forests is lower than in nearby grasslands or agricultural areas. For example, a study conducted in pedunculate oak forests in Belgium showed that the mean daily air temperature during the growing season was on average 1.5 °C lower than in the nearby grassland [37]. Similarly, measurements in pedunculate oak forests in France found average air temperatures 0.7 °C lower than at the forest edge [38].
In summer, the average difference in air temperatures between old stands and stands with the preparatory cut was 0.92 °C, old stands and stands with seed cut was 0.5 °C, and old stands and stands with the final cut was 0.53 °C.
According to Kovács et al. [39], microclimatic variables changed immediately after interventions in the forest stand and differed from the microclimatic situation in stands with dense canopy structures. In pedunculate oak stands in the Spačva area, microclimatic conditions also changed immediately after felling.
The microclimate is sensitive to changes in the structure of the forest stand caused by tree felling [15]. The microclimate of the forest changes even with selective felling [40], and especially with more intensive felling, especially when removing the entire stand, for example with a final cut. With a seed cut, we change the forest climate, or microclimate, compared to the old forest stand. The average air temperature was the highest in the stand with the preparatory cut, although there are small differences between the stands on an annual level. The results are influenced by the spatial distribution of trees, local climate, stand position, and extreme minimum temperatures.
Von Arx et al. [5] present research results on an increase in air temperature by <1 °C on average for the entire growing season. Similar results were obtained in research on the microclimate of oak forests by Kovács et al. [39]. According to our research results, on an annual basis, the stand in the final cut had an average air temperature lower by 0.44 °C compared to the old stand, which is probably the result of the influence of the local climate, the position of the stand within the forest complex, and the influence of wind. However, the stand in the final cut had an average soil temperature higher by 0.86 °C compared to the old stand, which is the result of the extremely open structure and greater exposure to solar radiation, which increases the soil temperature.
In forestry, microclimates are regulated to support tree regeneration [41] and reduce frost damage [42]. That is why pedunculate oak shelterwood is carried out gradually in several cuts, over several years, and even with subsequent cuts. In our study, there were no subsequent cuts, but three cuts were successively carried out, preparatory, seed, and final cut, but in a fairly short period of time.
According to the results of this study, as the cutting intensity increases, the amplitudes of air and soil temperatures are larger, with the minimum air and soil temperatures getting lower and the maximum ones higher. However, the summer minimum soil temperature increased in the old forest related to a final cut.
The soil cools and warms much more slowly so that the amplitudes and deviations of soil temperatures are smaller. Also, the autocorrelations are maintained much longer; that is, the soil temperature at a certain moment is much more and longer related to previous temperatures. Air and soil temperatures are highly correlated in all shelterwood phases (Figure S1).
In general, the soil under the canopy is warmer in winter and cooler in summer compared to areas where felling has occurred. According to Liechty [43], these phenomena can be detected to a depth of 80 to 100 cm, and temperature differences can reach 4 to 5 °C. In our study, the average summer soil temperature amplitude at a depth of 10 cm between the old forest stand and the stand with a final cut was 2.8 °C, and in winter it was 0.78 °C.
In this study, the different types of cutting (preparatory, seed, and final) significantly affect microclimatic elements such as air temperature and soil temperature. The results show that average air temperatures are higher in areas with a preparatory cut (11.81 °C); the absolute minimum temperature was recorded in areas with a final cut (−15.90 °C), while the absolute maximum was 40.20 °C also in the stand with a final cut. The openness of the canopy after felling increases exposure to sunlight and increases temperature fluctuations. Such results are in line with the literature suggesting that greater daily and seasonal temperature variations are recorded after more intensive felling [3,4,44].
According to the research of Kovács et al. [39], it can be concluded that the forest canopy performs its mitigation function more at the maximum values than at the minimum values of microclimatic variables. The same results were shown by our research of the maximum values of microclimatic elements in pedunculate oak stands in the Spačva area (Table 2). Our results show greater differences in minimum air temperatures between the old forest and the final cut stand compared to the research by Kovács et al. [39]. Also, our results show that the crowns of trees in the old forest stand somehow equally moderate the minimum and maximum air temperature values compared to the final cut stand.
Preparatory cuts changed only the conditions in the forest stand to a minor extent [39]. However, in our case, the microclimatic conditions, i.e., air temperature and soil temperature in the stand with preparatory cut, were significantly different from the values in the old stand. On an annual basis, the stand with the preparatory cut had the highest average air temperature, while the average soil temperature was the highest in the stand with the final cut.
Under the tree crowns, direct sunlight and wind speed were significantly reduced, which led to the mitigation of temperature variations. Extreme temperatures are often significantly mitigated in forests compared to open habitats, with lower maximum temperatures below the canopy and higher minimum temperatures [25,45]. According to the results of the study in Spačva, the highest absolute maximum and minimum air and soil temperatures were in a stand with a final cut in which old trees were removed.
Compared to complete-felling, older stands with a complete canopy had lower maximum and higher minimum temperatures [46,47]. These research results are in line with the results of our microclimate research in old stands and stands with final cutting.
According to Kovács et al. [39], in oak forests during complete-felling of trees, the most drastic increase in incoming light occurred, and consequently in the mean air and soil temperatures, as well as their variability, which was highest precisely in the area with complete-felling. We also obtained such results by researching the microclimate in a pedunculate oak stand with final cutting. According to the results of Muscolo et al. [48], the soil temperature was highest in areas with complete-felling in summer, then in stands with intensive thinning, moderate thinning, and finally in the control plot. We came to these results by investigating soil temperature, which increased on average with the intensity of shelterwood and the regeneration phase of forest stands.
Air temperature as well as heat in the forest stand are related to exposure to solar radiation. Since complete-cutting created the most open environment, the air temperature was highest in this treatment [39]. We also obtained similar results in the stand with final cutting, which had the largest amplitude of air temperature, i.e., the highest maximum and lowest minimum of air temperature. In a shelterwood system, the old stand is gradually removed with one or more fellings while the next generation of trees is established under the old trees [49] so that the shelterwood system retains some characteristics of the living conditions in the lower storey: cooler temperature, higher relative humidity, and less intense solar radiation compared to the open system [50]. This is partly confirmed by our research on air and soil temperatures in stands with shelterwood compared to the old forest stand. We can say that this method of oak forest regeneration is ecologically justified and in accordance with the ecological requirements of the species being rejuvenated. The macroclimate affects the microclimate, and thus the warming of the macroclimate affects the microclimate in forests [51]. However, it is not clear whether the magnitude of the temperature deviation between the macroclimate and forest microclimates will remain stable, increase, or decrease over time as the macroclimate warms. Therefore, it is necessary to establish climate monitoring of forest ecosystems, i.e., microclimate. Sudden and excessive opening of the crown structure in regeneration processes without appropriate planning can lead to unfavorable microclimatic conditions, such as high temperatures, that can negatively affect the regeneration. Therefore, gradual opening of the crown structure, gradual increase in the intensity of shelterwood cutting, and preservation of favorable microclimatic conditions are crucial for the regeneration of pedunculate oak forests and sustainable management of these forest ecosystems. Shelterwood phases should not be carried out successively year after year but gradually over a certain period of time in order to protect young plants from the harmful effects of meteorological conditions such as solar radiation, heat stress, or frost. It is important to point out that, while descriptively useful, the estimated SARIMA models are not suitable for predictions. The fit was good enough to detect patterns, but there was still some autocorrelation in the residuals, suggesting that a more complex model is needed. Some of this was perhaps due to measurement errors, or there is a possibility that we were unable to capture other variables that might affect the measurements. This was beyond the scope of our current research, but it is an interesting direction for future work.

5. Conclusions

The shelterwood phases significantly affect microclimate conditions within forest stands. As the intensity of cutting increased, so did the amplitude of air and soil temperatures. Increasing extreme temperatures in the context of climate change can threaten young plants and disrupt forest stand regeneration. This highlights the importance of microclimate in sustainable forest management practices. Changes in air and soil temperature clearly indicate variability between forest stands of different stages of regeneration. With the increase in cutting intensity, seasonal and annual amplitudes of air and soil temperatures increased.
Compared to air temperature data from weather stations, minimum air temperatures were higher in forest stands, while maximum temperatures were similar, with the exception of final cut stands. Also, average air temperatures were lower in forest stands.
Extremes in microclimatic conditions were recorded in the stands with final cut, which indicates a change in the forest climate, i.e., changed microclimatic conditions and a decrease in temperature stability after the removal of the crown. In the final cut stand, annual air temperature amplitudes were lowest in spring (38.5 °C) and highest in summer (41.8 °C), likely due to increased solar radiation and heat allowing greater heating of the air during summer months. Consequently, soil temperature amplitudes were lowest in winter (8.2 °C) because of snow cover, leaf litter, and organic matter. Soil temperature amplitudes were highest in spring (17.7 °C), possibly because of the delayed response of soil to seasonal warming and the absence of leaves at the beginning of the vegetation period, which allows more direct solar penetration into the soil during spring. In an old forest stand with a complete canopy, the crowns mitigate minimum and maximum air temperatures equally compared to a stand with a final cut without a canopy structure.
The highest daily and annual amplitudes of air and soil temperatures were in the stand with a final cut. Annual amplitudes of air temperatures in the stand with a final cut were lowest in spring (38.5 °C) and highest in summer (41.8 °C), while annual amplitudes of soil temperatures were lowest in winter (8.2 °C) and highest in spring (17.7 °C).
Air and soil temperatures are influenced not only by the cutting intensity and the distribution of trees in the stand after cutting but also by the local climate and the position of the researched stands within the forest complex. However, these influences are more pronounced with air temperatures.
The highest number of icy days, cold days, and hot days was in the stand with a final cut. SARIMA models are not an ideal fit for temperature differences because there are some unexplained residuals, but the models are suitable to prove that there is indeed a difference (not accidental). Large temperature amplitudes can threaten forest regeneration and ecosystem stability, so it will most likely be necessary to develop adaptive management strategies for these forests in the future. In the context of sustainable forest management, research results indicate that shelterwood should be planned and carried out with a time gap between phases in order to protect young plants from extreme temperatures and the harmful effects of meteorological conditions.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/su17115106/s1, Table S1: Synoptic temperature data from near weather stations; Figure S1: Air and soil temperature correlation.

Author Contributions

Conceptualization, D.U. and K.P.; methodology, D.U.; software, K.P.; validation, K.P., D.U. and A.T.; formal analysis, A.T.; investigation, K.P.; resources, K.P.; data curation, K.P., D.U., I.Š., A.T., I.T. and D.B.; writing—original draft preparation, K.P., D.U., I.Š., A.T., I.T. and D.B.; writing—review and editing, I.Š.; visualization, I.Š.; supervision, D.U. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

Krešimir Popić is employed by Croatian Forests Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Sustainability 17 05106 g001
Figure 1. Research area (OF—Old forest; PC—Preparatory cut; SC—Seed cut; FC—Final cut).
Figure 1. Research area (OF—Old forest; PC—Preparatory cut; SC—Seed cut; FC—Final cut).
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Figure 2. Daily air temperature amplitudes by season.
Figure 2. Daily air temperature amplitudes by season.
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Figure 3. Time series of air temperature differences.
Figure 3. Time series of air temperature differences.
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Figure 4. Daily soil temperature amplitudes by season.
Figure 4. Daily soil temperature amplitudes by season.
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Figure 5. Time series of soil temperature differences.
Figure 5. Time series of soil temperature differences.
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Table 1. Site description of analyzed forest stands.
Table 1. Site description of analyzed forest stands.
Old Forest (OF)Preparatory Cut (PC)Seed Cut (SC)Final Cut (FC)
Coordinates19.023; 45.02018.874; 44.94718.911; 45.06319.018; 45.012
Altitude (m)80–8182–8482–8479–81
Soil typeGleyLuvisolGleyGley
Age (years)1311321524
Average tree diameter (cm)5960611–5
Average tree height (m)3837350.6–0.7
Cut intensity (%)038.2643.6651.21
Density (N ha−1)35431625664,915
Basal Area (m2 ha−1)32.4331.3628.1926.87
Volume (m3 ha−1)525294459405
Pedunculate oak (%)64.814469.8156.83
Hornbeam (%)29.1233.1929.84
Narrow leaved-ash (%)4.213125.611.15
Table 2. Descriptive statistics of air and soil temperature.
Table 2. Descriptive statistics of air and soil temperature.
SeasonStageTemperature (°C)
Air Soil
MinMaxMeanSt. Dev.MinMaxMeanSt. Dev.
SpringOF3.2829.9715.035.674.818.611.413.21
PC−1.633.414.426.824.119.311.064.56
SC−3.431.714.077.094.818.312.023.27
FC−4.733.814.118.174.622.313.534.3
SummerOF5.5535.1620.685.7913.621.618.591.97
PC7.338.221.66.3314.422.419.651.87
SC5.936.421.186.4714.922.119.211.71
FC1.640.221.219.1514.725.821.392.88
FallOF−5.825.97.075.693.916.29.263.09
PC−4.627.57.45.694.8179.83.13
SC−7.228.36.946.084.316.79.553.45
FC−8.930.66.546.963178.593.75
WinterOF−11.7323.163.516.051.35.93.981.1
PC−9.623.13.835.841.59.14.511.43
SC−13.423.53.216.270.79.741.8
FC−15.9242.677.170.18.33.21.76
Growing seasonOF3.2935.1618.066.385.621.615.44.16
PC−1.638.218.047.54.122.416.294.93
SC−3.436.417.647.685.922.116.044.08
FC−5.940.217.619.25.325.817.855.01
AnnualOF−11.7335.1611.238.981.321.610.75.89
PC−9.638.211.539.241.522.410.966.29
SC−13.436.411.069.510.722.111.076.18
FC−15.940.210.8110.570.125.811.537.56
Location: OF—Old forest; PC—Preparatory cut; SC—Seed cut; FC—Final cut.
Table 3. Number of icy, cold, warm, and hot days by forest stands.
Table 3. Number of icy, cold, warm, and hot days by forest stands.
Old Forest (OF)Preparatory Cut (PC)Seed Cut (SC)Final Cut (FC)
Icy 20214
Cold10296122139
Warm47495849
Hot 29454269
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Popić, K.; Tafro, A.; Baričević, D.; Šapić, I.; Tikvić, I.; Ugarković, D. Microclimate of Pedunculate Oak (Quercus robur L.) Sustainable Managed Forest Stands—A Study of Air and Soil Temperatures in Shelterwood Cutting. Sustainability 2025, 17, 5106. https://doi.org/10.3390/su17115106

AMA Style

Popić K, Tafro A, Baričević D, Šapić I, Tikvić I, Ugarković D. Microclimate of Pedunculate Oak (Quercus robur L.) Sustainable Managed Forest Stands—A Study of Air and Soil Temperatures in Shelterwood Cutting. Sustainability. 2025; 17(11):5106. https://doi.org/10.3390/su17115106

Chicago/Turabian Style

Popić, Krešimir, Azra Tafro, Dario Baričević, Irena Šapić, Ivica Tikvić, and Damir Ugarković. 2025. "Microclimate of Pedunculate Oak (Quercus robur L.) Sustainable Managed Forest Stands—A Study of Air and Soil Temperatures in Shelterwood Cutting" Sustainability 17, no. 11: 5106. https://doi.org/10.3390/su17115106

APA Style

Popić, K., Tafro, A., Baričević, D., Šapić, I., Tikvić, I., & Ugarković, D. (2025). Microclimate of Pedunculate Oak (Quercus robur L.) Sustainable Managed Forest Stands—A Study of Air and Soil Temperatures in Shelterwood Cutting. Sustainability, 17(11), 5106. https://doi.org/10.3390/su17115106

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