Fine-scale topographic influence on the spatial distribution of tree species diameter in old-growth beech (Fagus orientalis Lipsky.) forests, northern Iran

Abstract

The Hyrcanian forest in northern Iran is threatened by human use and encroachment and has suffered degradation in some areas. The forest has been declared a World Heritage Site and management in the region is shifting from timber production to conservation. There is considerable interest in developing a greater understanding of these diverse forest communities to inform forest management and multiple use plans to maintain the diversity and resilience of these forests. The Hyrcanian forest is characterized by a complex topography of catenas ranging up mountain slopes. Topographic gradients greatly influence microhabitat conditions which in turn impact tree distribution. To date there has been limited research on the impacts of this diverse topography on the spatial distribution of tree species and tree diameters in Hyrcanian forests. Such information is necessary to better understand the regional traits of tree diameters in these natural mixed temperate forests before forest management occurs. We examined the influence of the area’s catena topography on the spatial pattern of tree species and on species stand structure in terms of tree diameter distribution. To quantify these dynamics, we conducted a complete enumeration inventory of all trees with dbh >12 cm within a 7.947 ha study area that included three C-shaped (concave) and three V-shaped (convex) catenas. Geostatistical variogram analysis and Clark and Evans aggregation index were utilized to study the spatial distribution of tree diameters. Beech, alder, hornbeam, linden and Persian maple exhibited clustered patterns, and sour cherry, ash, and oak exhibited random patterns. Geostatistical analysis clearly revealed the substantial influence of catena topography on the diameter distributions of alder and linden, more subtle influence on the diameter distributions of beech, and a possible influence on Persian maple, providing valuable insight into stand structure over neighborhood-based indices alone. Alder and linden both exhibited strong spatial structure in their diameter distributions (56% and 86%, respectively) where their diameter was strongly correlated with trees within 108 m and 83 m, respectively, sharing more similar diameters to each other than trees beyond that distance. Beech, maple, and hornbeam exhibited very weak if any spatial structure over short distances. These findings can be used to support the alignment of forest management practices in managed Hyrcanian forests with goals of protecting and maintaining biodiversity and sustainable forest ecosystems, and to inform geospatial modeling of species diameter distributions in areas where a complete stem-map is not feasible.

Tree dieback, woody plant diversity, and ecosystem driven by topography in semi-arid mountain forests: Implication for ecosystem management

“…4). These results support studies showing that the positions along the slope, by contrasting soil quality and microclimatic conditions, modify the shape and growth of plant species in mountain areas (Heydari et al, 2021;Rita et al, 2021;Fazlollahi Mohammadi et al, 2022). Rock cover would favor the establishment and distribution of stress-tolerant plants by creating protection conditions for them in arid areas (Petersa et al, 2008).…”

“…A series of different positions along a slope and successive surface roughness is called 'catena' (Wells et al, 2018;Fayyadh et al, 2021). A catena modulates the spatial biotic patterns by controlling their environments and their responses to the environment (Fazlollahi Mohammadi et al, 2022). Along slope, landscape heterogeneity can be driven by micro-scale variability in soil quality and moisture, which are partly controlled by elevation; the higher the altitude, the lower the temperature, the higher the humidity and, thinner the soil depth (see also López-Marcos et al 2020).…”