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ŠUMARSKI LIST 5-6/2019 str. 32     <-- 32 -->        PDF

Although the growing conditions were uniform in the experiment, the variances of the first growth flush (H1) of one-flush and multi-flush growth seedlings differed significantly (p = 0.0110, Table 3).
The one-flush growth seedlings finished their growth in the growing season when the primary axis was established while the multi-flush growth plants obtained their first growing phase. The differences in the means are pointing out towards the specific reaction of these two collectives of seedlings and that the multi-flush growth in Hungarian oak one-year-old seedlings was an induced trait in the way that was observed in pedunculate oak (Bobinac 1994). The variances of the total height of the seedlings, the number of leaves and the total leaf area are significantly different between the one-flush growth and multi-flush growth seedlings. This is pointing out to the different reaction of the seedlings to the same growing conditions. The higher total height, a larger number of leaves and the total leaf area of seedlings with multi-flush growth are the result of the induced apical activity, i.e. its prolonged activity in the growing season, compared to the one-flush growth seedlings.
The knowledge of the norm of reaction of Hungarian oak seedlings to different light conditions, i.e. different environmental conditions can give the information about the evolutionary biology and ontogenetic adaptation. This can provide the answers of the fundamental importance for the silviculture of these forests.
Multi-flush growth is typical for pedunculate oak and can be related to the optimum growing conditions (Le Hir et al., 2005). According to Spiess et al. (2012), the long term drought stress affect the multi-flush growth in pedunculate oak plants and the activation of growth flushes can be prolonged for the period after the drought stress. Sever et al. (2018) observed a five-flush growth in two-year-old pedunculate oak both in plants from the drought stress treatment (conducted in the first half of the growing season) and in optimum growth conditions, with the plants from the drought stress treatment prolonging their flushing for the post-drought period. This is pointing out to the adaptability of pedunculate oak to different growing conditions during the growing season. According to Roy et al. (1986), the occurrence of multi-flush growth is the result of the adaptation to higher levels of photosynthetically active radiation. Therefore, the multi-flush growth of the pedunculate oak young crop is an important indicator of the success of the natural regeneration in the pedunculate oak forests (Bobinac 2011). The multi-flush growth was used in the projection of the fungicide protection of young crop in the process of natural regeneration of pedunculate oak (Pap et al. 2012), and was recommended for defining the effects of the fungicide protection application (Pap et al. 2013).
Different oak species are expressing different adaptive abilities depending on the light conditions. For instance, multi-flush growth was recorded in full light and xerothermic conditions while in the conditions of the stand closure only plants with one-flush growth type were recorded (Bobinac 1997; 2001; Bobinac and Vilotić 1998). According to Bobinac (1997), one-flush growth type, two-flush growth type in full light conditions and one-flush growth type in stand closure conditions all make one homogenous statistical group regarding the mean total height, statistically differing only from three-flush growth type from full light conditions. However, when root collar diameter and the number of leaves are observed, there are significant differences between all the growth types, so the multiple flushing plants have higher values of root collar diameter and number of leaves. This indicates that even when there are no significant differences between the groups in terms of total height, the number of flushes is a good indicator of the general vigour of one-year-old Turkey oak seedlings. Similar conclusions were drawn for two-year-old Turkey oak seedlings, as well (Bobinac 2001).
According to Bercea (2013), in the group cuts conditions, during the first growing season, the second flush occurred only in 0.3% of the total number of seedlings analyzed; the plants finished their height growth until 30 May in the growing season with the average height of 11 cm (min 3, max 18 cm) with 3–5 leaves, and the second flushing was rare in Turkey oak seedlings as well. According to Bobinac (2002), the one-year-old young crop of Turkey oak, formed in the stand closure light conditions reacts slowly to improved light conditions. This characteristic of Turkey oak can be used in controlling its competitive ability when successful regeneration of other oak species that are growing with Turkey oak is needed.
In pedunculate oak one-year-old seedlings, multi-flush growth was observed as a mass phenomenon in different site and light conditions and the seedlings had up to five flushes of growth (Bobinac 2011; Pap et al. 2013). The strategy of heliophilous oak species in shade conditions is related to fast height growth in the first year in order to grow out of the shade zone (Grime, 1981). The heliophytes are developing in the multiple stress conditions and generally their life-form is characterized with short stems and internodiums (Stevanović and Janković, 2001). According to Bobinac (2011), that kind of growth is expressed in pedunculate and Turkey oak young crop in favourable light conditions created after seeding fellings in the stage of forming the primary axis (the first growth flush) that precedes the multiple flushing. The same conclusion, that the primary axis is shorter in plants with multiple flushing, compared to one-flush growth plants are confirmed in this Hungarian oak study in the field experiment. Also, the multi-flush growth is present on mass scale in the