BIODIVERSITAS ISSN: 1412-033X Volume 14, Number 1, April 2013 E-ISSN: 2085-4722 Pages: 25-30 DOI: 10.13057/biodiv/d140104 Variability of soil physical indicators imposed by beech and hornbeam individual trees in a local scale YAHYA KOOCH 1,♥ , SEYED MOHSEN HOSSEINI 1 , SEYED MOHAMMAD HOJJATI 2 , ASGHAR FALLAH 2 1 Department of Forestry, Faculty of Natural Resources & Marine Sciences, Tarbiat Modares University, 46417-76489, Noor, Mazandaran, Iran. Tel: +98-122-6253101 (-3), Fax: +98-122-6253499,  email: yahya.kooch@modares.ac.ir 2 Department of Forestry, University of Natural Resources and Agriculture Sciences of Sari, Mazandaran, Iran. Manuscript received: 25 March 2013. Revision accepted: 26 April 2013. ABSTRACT Kooch Y, SM Hosseini, Hojjati SM, Fallah A. 2013. Variability of soil physical indicators imposed by beech and hornbeam individual trees in a local scale. Biodiversitas 14: 25-30. The objective of our study was to determine if soil physical indicators could be related to the influence of the individual trees in stands of mixed species growing on steep slopes in the Hyrcanian forests of Iran. Research was conducted in a forest dominated by beech (Fagus orientalis Lipsky) and hornbeam (Carpinus betulus L.) interspread with the other deciduous tree species. Due to, twenty hectare areas of Experimental Forest Station of Tarbiat Modares University was considered in northern Iran. The positions of trees with diameter at breast height more than 45cm were recorded by Geographical Position System (GPS). Three single-trees (trees with canopy cover separated from other trees and covered distinguished space) considered for soil sampling from every tree species and diameter class as three replications. All of soil samples were excavated in north aspect and at the nearest point to tree collar for more precision. Soil samples were taken at 0-15, 15-30 and 30-45cm depths using auger soil sampler with 81cm 2 cross section. The result of this research showed that bulk density was significantly greater under beech than under hornbeam. This character tends to be less in 0-15cm depth than in 15-30cm and 30-45cm depths. Variable amounts of this character were found among diameter classes of beech and hornbeam also. Silt and clay were significantly greater under hornbeam than under beech. Moisture was significantly higher under beech than under hornbeam, whereas soil depths and diameter classes did not show any significant difference. Current research has shown that the influence of individual trees with different diameter classes can be detected in forest floors and upper minerals soil layers even under mixed stands in steepy sloping landscapes. This subject should be considered in natural forests management. Key words: Bulk density, Hyrcanian forest, moisture, old trees, soil texture INTRODUCTION Tree-soil interactions and their influence on tree fitness and forest community dynamics are complex. Many current theories on spatial heterogeneity and species diversity of forest communities are based on the premise that species interaction is controlled by competition for resources such as light, water, nutrients (Binkley and Menyailo 2005). Although these resources are largely constrained by the physical environment, the influence of canopy trees on resources can be of significant importance in forest ecosystem dynamics. This biotic control over resources has received little attention until recently in understanding forest ecosystem dynamics. Several authors have demonstrated the existence of a close interaction between plant and soil (Lovett et al. 2002; Compton et al. 2003; Templer et al. 2005). The evidence above suggests that tree-soil feedbacks need to be incorporated into the concept of species diversity and spatial heterogeneity in forest ecosystems in order to gain more insight in long-term forest dynamics. The soil under the influence of a forest develops properties that vary spatially with relation to the location of the trees. This variation in soil properties is frequently reflected in the distribution of the various species of the ground flora. The amelioration or degradation of the forest soil takes place with each tree as a center of influence (Kooch et al. 2011). Individual species are an important control on soil properties such as structure, water availability, and biota, as well as nutrient cycling. Tree species may influence soil nutrient cycling directly, via nutrient uptake (Turner et al. 1993), litter inputs (Prescott 2002), and induced leaching losses (Compton et al. 2003; Templer et al. 2005), and indirectly, via alteration of microclimate and disturbance regime (Chapin et al. 2002), precipitation chemistry and floral and faunal activities (Smolander and Kitunen 2002). Studies of trees grown in monocultures effectively isolate species effects on soils, but may not adequately capture species effects in mixed stands (Rothe and Binkley 2001). Despite continued research into tree species effects on soil nutrient cycles, the generality of these effects remains unknown (Binkley and Menyailo 2005). For example, leaf litter decomposition experiments have shown that mixtures of litter of different species can exhibit additive, neutral, and antagonistic effects on overall decomposition that are not easily predicted from the characteristics of the individual litters alone (Gartner and Cardon 2004). More generally, experimental studies of