The declining trend in the natural forest areas has longraised a global concern, mainly due to worry about economical poverty reductionas well as loss of forest environmental services including water filtration,soil erosion control, and microclimate modification (Trumbore Brando and Hartmann, 2015). Iran is categorized as a Low Forest Cover Country (LFCC)covered with only 7.6% forest ecosystems (IUFRO, 2004).
Hyrcanian forests areone of the most antique and momentous ecoregions in Iran and the last remainsof natural deciduous forests in the world. These forests are located at thenorthern slopes of the Alborz Mountains, with expanding about 1.9 million ha inthe southern Caspian Sea (IUFRO,2004), but unfortunately, the majority of these forests has beendeforested because of human manipulation, urbanization, land-use changes andagricultural purposes (Kooch, etal. 2015). Given the high destruction rate ofthe world’s natural forests and population growth as well as the growing needfor wood and other forest services, the importance and necessity of forestationis highly obvious to regenerate the degraded areas and to provide supplies ofcommunity (Yousefi, et al.2010; Rahimabady, et al. 2015).
Restorationof degraded forest areas could be accompanied by alterations in thephysicochemical and biological properties of the soil, thus improving forestecosystem services (Kooch,et al. 2017a, b). Reforestationsuccess and soil development are mainly associated to the selection of suitabletree species (Wo? and Pietrzykowski,2015); for example, establishingbroadleaf species seems to be more effective and to grow well on degraded sitesin the tropics than conifer ones (Parrotta, et al.
1997). In temperateforests, oak(Quercus castaneifolia) is an important species with higheconomic value in Iran. It possesses the capability to grow along an elevationgradient from flood-prone area to high topographical positions up to 1,000 m above sea level (a.s.
l.) (Sabeti, 2009); that is, the tree canbe found from the plateau, together with other broad-leaved trees in particularwith box tree, to where it is mixed with common hornbeam. The upperdistribution limit of this species depends on both climate and soil propertiesand geomorphology, and at higher altitudes it prefers warm and sunny slopes (Talebi, et al. 2005). The optimal rotation age (ORA) mightfacilitate the greatest level of soil quality.
Lack of information is availableconcerning ORA for oak plantation, and also no research has been conducted toevaluate its long-term effects on litter and topsoil in oak plantation indegraded natural forest lands. Over time, soil properties will be changed following forest aging,and in turn alters thesoil C and N processes (Zhang, etal. 2017). Previous studiesfocused on changes in soil C and N cycles following afforestation in temperateforest lands (Bárcena, et al.
2014; Nave, et al. 2013).Not only the quantity and quality of soil organic matter (SOM)but also C and N inputs are the overriding controls on soil microbial biomassand activity (Kallenbach and Grandy, 2011).Hence, distinct organic amendments can stimulate microbial biomass throughenhancing the labile organic matter on time frames from months to decades (Kallenbach and Grandy, 2011).
However,studies reporting the seasonal changes in microbial properties of C and N arestill lacking in the temperate tree plantation soils (Mori, et al. 2016). Owing to high sensitivity of the soilmicrobial community to natural and anthropogenic factors, soil microbialactivities seem to be reliable indicators for soil quality (Utobo and Tewari, 2015), and it isnecessary to identify and describe bio-geochemical cycles at a regionalspatiotemporal scale. Thus, the study was aimed to evaluate physicochemical,biological, and biochemical properties of soil and litter quality in three oakplantations with different ages, to assess theinfluence of stand age on soil Cand N microbial indices, to test the hypothesis that soil C and N microbialindices will increase in the top soil layer following increasing stand age.