The decliningtrend in the natural forest areas has long raised a global concern, mainly dueto worry about potential poverty reduction as well as loss of basic commodities,e.g., food, material and energy source, andforest environmental services including water filtration, soil ablation control,and microclimate alignment (Trumbore Brando and Hartmann, 2015). Iran is categorized as a Low ForestCover Country (LFCC) covered with only 7.6% forest ecosystems (IUFRO, 2004).
Hyrcanian forests are one of the most antique andmomentous ecoregions in Iran and the last remains of natural deciduous forestsin the world. These forests are located at the northern slopes of the AlborzMountains, with expanding about 1.9 million ha in the southern Caspian Sea (IUFRO, 2004), but unfortunately, the majority of these forests has been deforestedbecause of human manipulation, urbanization, land-use changes and agriculturalpurposes (Kooch, et al. 2015). Giventhe high destruction rate of the world’s natural forests and population growthas well as the growing need for wood and other forest services, the importanceand necessity of forestation is highly obvious to regenerate the degraded areasand to provide supplies of community (Yousefi, et al. 2010;Rahimabady, et al.
2015). Restorationof degraded forest areas could be accompanied by alterations in the physicochemicaland biological properties of the soil, thus improving forest ecosystem services(Kooch, et al. 2017a,b). Reforestation success and soildevelopment are mainly associated to the selection of suitable tree species (Wo?and Pietrzykowski, 2015); for example, establishing broadleaf speciesseems to be more effective and to grow well on degraded sites in the tropics thanconifer ones (Parrotta,et al. 1997).
In temperate forests, oak (Quercus castaneifolia) is an important species withhigh economic value in Iran. It possessesthe capability to grow along an elevation gradient from flood-prone area tohigh topographical positions up to 1,000 m abovesea level (a.s.l.
) (Sabeti, 2009); that is, the tree can be foundfrom the plateau, together with other broad-leaved trees in particular with boxtree, to where it is mixed with common hornbeam. The upper distribution limitof this species depends on both climate and soil properties and geomorphology,and at higher altitudes it prefers warm and sunny slopes (Talebi, et al. 2005). The optimal rotation age (ORA) might facilitate the greatest level of soilquality. Lack of information is available concerning ORA for oak plantation,and also no research has been conducted to evaluate its long-term effects onlitter and topsoil in oak plantation in degraded natural forest lands. Over time,soil properties will be changed following forest aging, and in turn alters the soil C and N process (Zhang,et al. 2017).
Previous studies focused on changes in soil C and Ncycles following afforestation in temperate forest lands (Bárcena,et al. 2014; Nave, et al. 2013). Therefore, there is aneed to identify and describe bio-geochemical cycles at the regionalspatiotemporal scale, which is the scale at which landscape policies areimplemented.
Not only the quantity and quality of soil organicmatter (SOM) but also C and N inputs are the overriding controls on soilmicrobial biomass and activity (Kallenbach and Grandy,2011). Hence, distinct organic amendments can stimulate microbialbiomass through enhancing the labile organic matter on time frames from monthsto decades (Kallenbach and Grandy, 2011). However, studies reporting the seasonal changes inmicrobial properties of C and N are still lacking in the temperate treeplantation soils (Mori, et al.
2016). Owingto high sensitivity of the soil microbial community to natural andanthropogenic factors, soil microbial activities seem to be reliable indicatorsfor soil quality (Utobo and Tewari, 2015). Thus, the study was aimed toevaluate physicochemical-, biological-, and biochemical properties of soil and litterquality in three different stages of an oak plantation, to assess the influence of stand age on soil C and N microbialindices, to test the hypothesis that soil C and N microbial indices willincrease in the top soil layer following increasing stand age.