Effect of forestry practices on the biological characteristics of soils (Case study: Beech Forest of Asalem)

In forest management, it is essential to maintain soil performance. Forest soils control and support many forest ecosystem services and tree growth. So, maintaining soil health is critical to sustainable forest management. Forest management practices, such as converting degraded forests into man-made forests, lead to a wide range of adverse effects on soil performance and microbial communities, including negative impacts on organic carbon, nitrogen, bacterial biomass, fungal biomass, microbial biomass carbon, and fungi-to-bacteria ratio. It is possible to achieve the appropriate method of forest management by considering the biological stability of the soil. Therefore, in this stduy, it has tried to gain a better understanding of the relationship between soil biological conditions and forest management methods and their application in sustainable forest and soil management by evaluating the effect of different forestry methods on soil biological characteristics.

To influence forest management practices on soil biological properties, three study areas with different management histories in the Asalem forest, Guilan province were selected and soil sampling using a random systematic method was collected. The selected plots included 1) control, 2) a plot with a history of project implementation in the medium term of maximum 20 years under selective management and 3) a plot with a history of long-term plan implementation, which was under the management of shelterwood method for more than 50 years. There may be effects of the implementation of past plans in the forest for many years. The number of 15 samples in each plot was collected from the nearest tree to the center of the intersection of the sides of the sampling network, from a depth of 0-30 cm, and transported to the soil laboratory at a temperature of 4°C in the winter of 2016. Sampling from all plots in the forest area was done only in the pure type of beech, so in this study, the effect of the type is constant. In this study, micro-scale habitat conditions considered to investigate microbial activities were homogeneous. In this research, three parcels with an area of ​​about 132 ha were selected. In each sample, the biological characteristics of the soil, including basic respiration, stimulated respiration, microbial carbon dioxide, and the population of microorganisms were measured, and indicators of microbial benefit and metabolic benefit were calculated. Some soil characteristics including soil organic carbon, electrical conductivity (EC) and pH were also measured. The normality of the data was checked using the Kolmogorov-Smirnov test and the homogeneity of variances was checked using the Levene's test. Due to the fact that the data had a normal distribution, one-way analysis of variance test was used for totla mean comparisons, Tukey test was used to compare the average indicators in the studied parts, and the relationship between chemical indicators the Spearman correlation test was also used for soil biology. In some cases, due to the impossibility of normalization and other assumptions, the non-parametric test has been used. Statistical analysis was done using SPSS version 22 software. Excel was used to draw graphs.

The results showed that there was no significant difference between the three components in terms of organic carbon, microbial quotient, electrical conductivity, and acidity. But baseline respiration, exhaled breath, microorganism population, metabolic rate, and carbon microbial degradation showed a significant difference in the three parts. The highest basal respiration rate (46.8 mg of carbon dioxide in one day in one gram of dry soil), substrate-induced respiration (42.77 mg of carbon-dioxide in one gram of dry soil in six hours) and microorganism population (1.09 x 108 in one gram of dry soil) and carbon microbial degradation (16.5 mg of carbon in one gram of dry soil) were obtained with a patchy management method and the lowest in the selective portion. The highest metabolic quotient (1.2 mg of oxidized carbon in basic respiration per kg of dry soil per day) in selective fraction and the lowest in solitary incremental part were calculated. The soil texture is sandy-loamy in most of the three plots and loamy-sandy in some areas. EC was in the range of 0.629-3.83 dS m-1 and soil acidity was also in the range of 5-6.5 in all three plots. There was no significant difference in soil organic carbon in three plots. Correlation analysis results of forest soil biological indicators show that soil microorganisms have a significant positive correlation at the level of 1% probability with microbial biomass. In addition to soil micro-organisms, microbial biomass carbon showed a significant positive correlation with basal respiration at the 1% probability level. Basal respiration also has a significant positive correlation at the probability level of 1% with the amount of substrate-induced respiration, soil microorganisms, and microbial biomass carbon, and besides that, the organic carbon has a significant positive correlation at the probability level of 1% with soil microorganisms, microbial biomass carbon, basal respiration, and substrate-induced respiration.

The control plot has a higher quality soil compared to the plot under shelterwood management due to the least human interference (although illegal harvests have been observed in the forest, but compared to the other two plots, human interference was minimal). According to the results, it can be acknowledged that the plot under shelterwood's management has better conditions in terms of soil biological characteristics. Knowledge of the effectiveness of the biological characteristics of the soil from the application of different methods of forest silviculture and human interventions, provides the possibility of choosing suitable methods with the habitat conditions. At the same time, it will be very beneficial to determine the intensity of breeding interventions in forest stands based on the prediction of its effects. The stability of the forest does not depend only on increasing the biological quality of the soil. Hence, it is recommended to implement silviculture operations in sheltered plots and to increase the mixture of forest stand and support species with fast decomposition of litter such as horbean in selective plots.