Regeneration Dynamics and Development of Seedlings in Sessile Oak Forests in Relation to the Light Availability and Competing Vegetation

Abstract

Natural regeneration of sessile oak forests is a complex process whose final outcome is influenced by numerous factors. The initial phase of development of sessile oak seedlings stands out as the most critical period in the process of natural regeneration of sessile oak forests. As the available light and competition from the accompanying woody species and ground vegetation are some of the main predictors of the success of sessile oak forest regeneration, this paper presents the results of studying the influence of these factors on the regeneration dynamics and development of sessile oak seedlings. The research was conducted in sessile oak forests in northeastern Serbia in the period from 2015 to 2020. At the end of the growing season each year, the following data were collected on 180 smaller sampling plots of 1 m2 in different conditions of canopy openness: the number, height, and root collar diameter of sessile oak seedlings. Also, the percent cover of competing woody species and ground vegetation was estimated on these sample plots. The obtained results indicated that the success of sessile oak forest regeneration largely depends on the initial number of sessile oak seedlings and silvicultural treatments during the rejuvenation period, which determine the microclimatic conditions in the stand and control the competing vegetation. They also indicate that with an increase in the available light, the impact of the competing vegetation on the dynamics of regeneration and development of sessile oak seedlings is less pronounced. Accordingly, as young sessile oak seedlings need a large amount of light for survival and development, it is necessary to increase the available amount of light intensively in a short period of time (six–eight years) by reducing canopy openness and thus providing optimal conditions in which sessile oak seedlings can gain an advantage over the competing vegetation.

Competition Between Sessile Oak Seedlings and Competing Vegetation Under a Shelterwood

“…This indicates a pronounced presence of the main competing species of woody vegetation and ground flora. Kanjevac et al (2021) also pointed out the pronounced presence of competing species in the regeneration layer of sessile oak forests in the area of northeastern Serbia. Also, a large number of authors point out competing vegetation as one of the key factors that threaten the success of the natural regeneration of sessile oak forests (Kohler et al 2020).…”

“…In addition to the fact that the blackberry can outgrow the sessile oak seedlings and thus significantly reduce the available amount of light, blackberry is also known to affect forest regeneration by forming dense thickets that overgrow and eventually press seedlings to the ground under heavy snow (Krstic et al 2017;Kohler et al 2020). Blackberry mostly occurs in places with greater canopy openness, i.e., the available amount of light, whereby it prefers deep and moist soils, rich in nutrients (Krstic et al 2017;Kanjevac et al 2021). The presence of blackberries is significantly dependent on the initial number of seedlings during the regeneration of sessile oak forests, which is why it is often considered that the initial number of seedlings per unit area is one of the key factors influencing the success of the regeneration of sessile oak forests (Kuehne et al 2020;Kanjevac et al 2021).…”

“…Blackberry mostly occurs in places with greater canopy openness, i.e., the available amount of light, whereby it prefers deep and moist soils, rich in nutrients (Krstic et al 2017;Kanjevac et al 2021). The presence of blackberries is significantly dependent on the initial number of seedlings during the regeneration of sessile oak forests, which is why it is often considered that the initial number of seedlings per unit area is one of the key factors influencing the success of the regeneration of sessile oak forests (Kuehne et al 2020;Kanjevac et al 2021). The average value of the root collar diameter of eight-year-old sessile oak seedlings in the studied stand is 8.0 mm, while the minimum value is 2.0 mm and the maximum is 24.0 mm (Table 2).…”

“…One of the key phases that largely determine the outcome of the natural regeneration of sessile oak forests is the phase of the initial development of the young seedlings when its survival is most endangered (Harmer et al 2005;Annighöfer et al 2015;Krstic et al 2017;Krstic et al 2018;Kanjevac 2020;Kanjevac et al 2021). By regulating the canopy of the stand, i.e., by the controlled addition of light in this phase, the development of the seedlings can be significantly influenced, which indirectly reflects on its qualitative characteristics (Govedar 2006).…”

“…In accordance with the above, a large number of authors point to the endangerment of sessile oak seedlings in relation to weed species such as Rubus spp. (Modrow et al 2020;Kanjevac et al 2021), or species that better tolerate shade, such as beech (Fagus sylvatica L.), hornbeam (Carpinus betulus L.), silver linden (Tilia tomentosa Moench. ), etc.…”