The it is mixed with common hornbeam. The upper

The declining
trend in the natural forest areas has long raised a global concern, mainly due
to worry about potential poverty reduction as well as loss of basic commodities,
e.g., food, material and energy source,  and
forest environmental services including water filtration, soil ablation control,
and microclimate alignment (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 are one of the most antique and
momentous ecoregions in Iran and the last remains of natural deciduous forests
in the world. These forests are located at the northern slopes of the Alborz
Mountains, with expanding about 1.9 million ha in the southern Caspian Sea (IUFRO, 2004), but unfortunately, the majority of these forests has been deforested
because of human manipulation, urbanization, land-use changes and agricultural
purposes (Kooch, et al. 2015). Given
the high destruction rate of the world’s natural forests and population growth
as well as the growing need for wood and other forest services, the importance
and necessity of forestation is highly obvious to regenerate the degraded areas
and to provide supplies of community (Yousefi, et al. 2010;
Rahimabady, et al. 2015).

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       Restoration
of degraded forest areas could be accompanied by alterations in the physicochemical
and biological properties of the soil, thus improving forest ecosystem services
(Kooch, et al. 2017a,
b). Reforestation success and soil
development are mainly associated to the selection of suitable tree species (Wo?
and Pietrzykowski, 2015); for example, establishing broadleaf species
seems to be more effective and to grow well on degraded sites in the tropics than
conifer ones (Parrotta,
et al. 1997).  

       In temperate forests, oak (Quercus castaneifolia) is an important species with
high economic value in Iran. It  possesses
the capability to grow along an elevation gradient 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 can be found
from the plateau, together with other broad-leaved trees in particular with box
tree, to where it is mixed with common hornbeam. The upper distribution limit
of 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 soil
quality. Lack of information is available concerning ORA for oak plantation,
and also no research has been conducted to evaluate its long-term effects on
litter 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 N
cycles following afforestation in temperate forest lands (Bárcena,
et al. 2014; Nave, et al. 2013). Therefore, there is a
need to identify and describe bio-geochemical cycles at the regional
spatiotemporal scale, which is the scale at which landscape policies are
implemented. Not only the quantity and quality of soil organic
matter (SOM) but also C and N inputs are the overriding controls on soil
microbial biomass and activity (Kallenbach and Grandy,
2011). Hence, distinct organic amendments can stimulate microbial
biomass through enhancing 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 are still lacking in the temperate tree
plantation soils (Mori, et al. 2016).

        Owing
to high sensitivity of the soil microbial community to natural and
anthropogenic factors, soil microbial activities seem to be reliable indicators
for soil quality (Utobo and Tewari, 2015). Thus, the study was aimed to
evaluate physicochemical-, biological-, and biochemical properties of soil and litter
quality in three different stages of an oak plantation, to assess the influence of stand age on soil C and N microbial
indices, to test the hypothesis that soil C and N microbial indices will
increase in the top soil layer following increasing stand age.