Relationships between site index and ecological variables of trembling poplar forests (Populus tremula L.) in Türkiye.

This study was carried out to identify relationships between site index (dominant height at a reference age) and ecological variables of trembling poplar forests in Türkiye. Samples were collected from 78 plots differing in elevation, aspect, inclination, slope position, and site class. Physiographic factors of the sample plots were recorded, soil samples were collected from different predefined layers from soil pits, and bedrock samples were collected for identification. From three trees at the stand top height, the tree closest to the arithmetic mean height was felled, and its height and age were determined. Physical and chemical characteristics of the soil samples were analysed. Relationships of the soil properties, physiographic factors, and climate with site index were assessed with correlation, stepwise regression, and regression tree methods. Significant relationships were found between site index at 30 years and elevation from the physiographic factors; the maximum temperature and the number of snowy days of the coldest month from the climate characteristics; fine earth, silt, and pH from the percentage values of soil properties at different depths; and fine earth, silt, and clay from the soil characteristics aggregated on pedon level. The height growth of trembling poplar was 11.8% according to stepwise regression analysis and 18% according to the regression tree method. The models obtained in the current study might help evaluate the potential of sites regarding the growth of trembling poplar.

Natural radionuclide activities in forest soil horizons of Mount IDA/Kazdagi, Turkey.

Natural radioactivity distribution of (40)K, (238)U, and (232)Th isotopes in forest soils was investigated by using gamma-ray spectrometry. An extensive radioecological study was carried out between 2010 and 2013 in Mount IDA/Kazdagi, located in Edremit region in Turkey. A total of 341 soil samples were collected from the surface and organic horizons (OL, OF+OH, and A) in 118 soil profiles. The distributions of natural radioactivity levels in these horizons and corresponding absorbed dose rates from outdoors terrestrial gamma radiation throughout the region were mapped in detail. Mean (40)K activity values over the combined horizons varied between 43 and 1,008 Bq kg(-1); whereas, mean (226)Ra and (232)Th concentrations over the combined horizons ranged between 5-152 and 6-275 Bq kg(-1), respectively. Our data indicate that the radioactivity values of the study sites were within the universal normal range. The significant variation among the (232)Th, (226)Ra, and (40)K activities and gamma dose rate might be due to the geological variation in the study sites.

Estimation of vertical migration velocity of (137)Cs in the Mount IDA/Kazdagi, Turkey.

This paper presents the results obtained from a radioecological study carried out in the forest sites of Mount IDA (Kazdagi)/Edremit, Turkey. For 118 soil profiles, the depth distribution of (137)Cs activity was established by fitting the experimental points to an exponential, a gaussian or a log-normal function. The relaxation lengths were in the range of 1.09-16.7 cm with a mean of 5.73 cm, showing a slow transport and a strong retention capacity of (137)Cs even after the 26-y period of Chernobyl accident. From the data for the vertical distribution of (137)Cs in soil profiles, the mean annual migration velocity of (137)Cs was in the range of 0.11-0.62 cm year(-1) with a mean of 0.30 cm year(-1). Statistically significant correlations between the thickness of the humus layer and the mean annual velocity of (137)Cs were found for both coniferous and mixed forest sites. The mean annual velocity of (137)Cs in the forests sites with Pinus nigra var pallasiana was significantly higher than sites with Pinus brutia. External dose-rates from the (137)Cs in forest soils were estimated using a conversion factor used in many studies and comprised with the external dose-rates determined according to the vertical distribution of (137)Cs within the soil depth profiles. It is clearly seen that both levels and spatial distribution patterns of the external dose-rates from (137)Cs were influenced considerably with the vertical migration rate and the vertical distribution of (137)Cs.

Persistence of 137Cs in the litter layers of forest soil horizons of Mount IDA/Kazdagi, Turkey.

In 2010-2012, an extensive study was performed in forest sites of Mount IDA (Kazdagi)/Edremit 26 years after the Chernobyl accident. The (137)Cs activity concentrations were determined by gamma-ray spectrometry in the forest soil layers (OL, OF + OH and A horizons) separately. Based on 341 surface soil samples and 118 soil profiles, activity concentrations of (137)Cs in OL horizons varied between 0.25 ± 0.14 and 70 ± 1 Bq kg(-1), while the ranges of (137)Cs activity concentrations in OF + OH and A horizons were 13 ± 1-555 ± 3 Bq kg(-1) and 2 ± 1-253 ± 2 Bq kg(-1), respectively. Cesium-137 deposition in the study area was estimated to be in the range of 1-39 kBq m(-2) and a linear relationship between the deposition of (137)Cs and the altitude was observed. The distributions of (137)Cs activities in OL, OF + OH and A horizons throughout the region were mapped in detail. The highest (137)Cs activities were found in OF + OH horizons, with markedly lower (137)Cs activity in mineral horizons of soil profiles. It is observed that (137)Cs content of humus layer increases with the thickness of the humus layer for coniferous forest sites. The (137)Cs activity concentrations were higher than the recommended screening limits (150 Bq kg(-1)) at some of the investigated areas. The current activity concentration of top soil layers indicates that over many years since the initial deposition, (137)Cs activity is keeping still high in the organic horizons.