Influence of soil properties and burial depth on Persian oak (Quercus brantii Lindl.) establishment in different microhabitats resulting from traditional forest practices

Abstract

In seasonally dry environments such as the Zagros woodlands (Iran), severe drought stress and lack of appropriate management practices can cause failure of oak afforestation or reforestation. We investigated the effect of soil properties and burial depth on Persian oak (Quercus brantii Lindl.) establishment in different microhabitats resulting from traditional forest practices. Four microhabitats that were based on forest structure were considered for oak acorn seeding: (1) inside old sprout clumps (ISPC); (2) under the canopy of tall trees (UCTT); (3) outside the canopy of tall trees and sprout clumps; and (4) near recent stumps or sprout clumps. Acorns were seeded at two depths (2 and 5 cm), and seedling survival and growth variables were recorded for 4 years, together with soil chemical and biological attributes. Stepwise discriminant analysis showed that a combination of total soil nitrogen, cation exchange capacity, available phosphorus and potassium, litter depth, microbial quotient, metabolic coefficient, substrate-induced respiration and earthworm abundance was the best variables to characterise the microhabitats. With the exception of pH, bulk density and soil texture, these variables were higher in UCTT and ISPC than in the other microhabitats. Seedling emergence and survival were greater at a seed depth of 5 cm than at 2 cm. Seedling height and shoot, root and leaf biomasses were higher in the UCTT microhabitat compared to the other microhabitats and correlated positively with soil nutrients contents and most of the soil biological variables but negatively with soil bulk density. This study emphasised the role of microhabitats in creating a “canopy effect” producing favourable physical, chemical and biological soil conditions. In particular, large oak trees form islands of fertility and therefore are of key importance for successful seedling establishment in forests subjected to intense human activities.