Effect of Invasive Rhododendron ponticum L. on Natural Regeneration and Structure of Fagus orientalis Lipsky Forests in the Black Sea Region

Abstract

Biological invasions threaten global biodiversity and forest ecosystems; therefore, it is necessary to use appropriate strategies for combating the spread of invasive species. Natural regeneration of eastern beech (Fagus orientalis Lipsky) is considerably limited by an aggressive invasive shrub, pontic rhododendron (Rhododendron ponticum L.), in the Black Sea Region of Turkey. Therefore, the future character of the region’s forests is uncertain. The aim of this research was to evaluate the structure of beech forests with different management regimes of rhododedron and to determine the interaction among tree layer, rhododendron cover, and natural regeneration in Düzce Province using the FieldMap technology. The following variants of forests were compared: without intervention (control) and three and six years after rhododendron clearance. The results showed that tree density ranged between 175–381 trees ha−1 and stand volume between 331–589 m3 ha−1. The horizontal structure of the tree layer was mostly random, and the spatial pattern of natural regeneration was aggregated. Recruit density and height in the beech stands were significantly differentiated due to the influence of presence or absence of invasive rhododendron. Rhododendron cover ranged between 81%–97%, and woody stems amounted to 72,178–86,884 ha−1 in unmanaged forests. Canopy in the overstory did not have a significant effect on the density of regeneration and rhododendron cover. Tree layer had a significant negative influence on natural regeneration within a 4 m radius on the plots without rhododendron. However, on the plots with dense rhododendron cover, tree layer had a positive influence on regeneration within a 1.5 m radius. Natural regeneration density was significantly higher when rhododendron was cleared than the plots without intervention. On the plots without woody clearance, there was an insufficient regeneration (113–619 recruits ha−1); however, they had higher mean height compared to the sites without rhododendron. After three and six years of rhododendron clearance, the numbers of recruits in natural regeneration were 63,981 ha−1 and 105,075 ha−1, respectively. In conclusion, invasive spread of rhododendron was a limiting factor of the prosperous regeneration and tree species diversity, and manual clearance of rhododendron is recommended in managed beech forests of the study region.

Effect of game browsing on natural regeneration of European beech (Fagus sylvatica L.) forests in the Krušné hory Mts. (Czech Republic and Germany)

“…The vertical structure was evaluated according to the Gini index (Gini 1921) and the spatial distribution according to the index of cluster size (David & Moore 1954). The equations of diversity indices are given in Vacek et al (2020c).…”

Managed vs. unmanaged Fagus orientalis Lipsky forests: Structure and diversity of natural regeneration in northern Iran

“…Increases in the density may be temporary (Schnitzer, Carson 2001) and may pass over time. For example, tree regeneration may be inhibited over time by disturbing plant layers or invasive species (Kern et al 2012;Vacek et al 2020). From our findings, it seems that man-made gaps have been created where advanced regeneration was present.…”

“…Numerous studies have emphasised the effect of the understory vegetation on the overall structure of the forest (Spies, Franklin 1991;Berger, Puettmann 2000;Sullivan et al 2001;Anderson, Meikle 2006;Dröβler 2006;Hinsley et al 2009;Nagel et al 2013;Feldmann et al 2018). Vacek et al (2020) showed that after three and six years of management (rhododendron clearance) in the Black Sea region Oriental beech forest (Fagus orientalis Lipsky) of Turkey, the number of natural regenerations increased from 63 981 ha -1 to 105 075 ha -1 .…”

Patterns of understory invasion in invasive timber stands of a tropical sky island

“…Their presence and influence may also facilitate the invasion of other non‐natives, especially in the understory (Kuebbing & Nuñez, 2015 ; O'Loughlin & Green, 2018 ). Such understory invasives can have cascading impacts by competing with natural forest regeneration (Dyderski et al, 2017 ; Vacek et al, 2020 ), impacting animal movements (Habel et al, 2016 ; Stewart et al, 2021 ), and enhancing edge effects (McDonald & Urban, 2006 ). Mapping such invasions at a landscape level becomes imperative to understand if particular overstory invasive species are associated with specific understory invasive species.…”