Inter-Annual Change of Forest Stand Canopy Characteristics in a Highland Landscape with Gradually Transforming Forest Stands

Dependent upon the relatively severe ecological conditions of the forest stands at the highland landscapes, they sometimes experience transformations. Forest stand tree species, which are a bit more tolerant to these conditions, gain advantage over the others, and hence often tend to intrude into the nearby stands, transforming them and influencing their canopy characteristics. At a highland landscape of Western Black Sea Region in Turkey, a sessile oak stand, which had remained young and pure along the 20 years (1986–2006), has then been invaded by the Bornmüllerian fir seeds from the surrounding stands and consequently been transformed into young-mature mixed stand throughout the subsequent 15 years (2006–2021). Therefore, then intruded Bornmüllerian firs have primarily and gradually altered the physiological characteristics of the canopies within this mixed stand. The aim of this study is to monitor and analyse the inter-annual physiological changes of these tree canopies using some canopy parameters following the occurrence of the species mixture. The stand canopy physiological characteristics were monitored and analysed by hemispherical photographs and associated parameters obtained from them. These canopy parameters; Leaf Area Index (LAI), Light Transmission (LT), Gap Fraction (GF), Canopy Openness (CO), were acquired for the Junes of the years, 2015, 2018 and 2021. The mean LAI had increased almost 0.50 m² m^–2 within the stand along the eight years period (2007–2015). However, it could only increase 0.20 m² m^–2 along the subsequent six years monitoring period. On the other hand, the percentage values of the other canopy parameters had accordingly decreased. This situation indicated that the first occurrence of the Bornmüllerian fir canopies together with the canopies of the sessile oaks along those eight years period had led to the sudden rise of the mean LAI. Nevertheless, the gradual and slight increment of the mean LAI along the subsequent six years monitoring period, has been attributed to the normal physiological development of the tree species; Bornmülerian firs in particular. In fact, due to the case with the study parcel, the highland landscape has potentially been experiencing gradual increment in the percentage of eco-physiologically more tolerant Bornmüllerian firs and conversely gradual decline in the percentage of eco-physiologically sensitive sessile oaks, whose sustainability within highland landscape should be supported with the ecological and comprehensive management proposals.