Relationships between aboveground and belowground biomass stock - a case study from mountain area temperate forests in the northern Carpathians

The content of organic carbon in forest is partitioned between organic carbon accumulated in aboveground biomass (AGB) and belowground biomass (BGB) and is impacted by various natural and human factors. Growing interest in estimates of global biomass (and organic carbon) pools require research on a local scale in the context of potential environmental factors affecting their spatial distribution. Therefore, our aim of the research was to both derive and evaluate the relationship between aboveground biomass consisting mainly of European beech (Fagus sylvatica L.), spruce (Picea abies L. Karst) and fir (Abies alba Mill.) and BGB with particular emphasis on fine root biomass (FRB) as the most dynamic part of the root system and soil organic matter stock (SOM). Data were collected at 32 national forest inventory plots in mountainous temperate forests with different history of forest management located across the Carpathian range in Poland. All study plots were characterized with very similar soil properties (Cambisols). Moreover, numerous environmental factors affecting biomass distribution were taken under consideration. The largest aboveground biomass occurred in beech-dominated stands (~40 Mg ha-1 to over ~ 440 Mg ha-1). In the sampled depth layer (0-40 cm) the highest SOM stock was identified in soils under beech-dominated stands (median ~158 Mg ha-1). FRB was the highest under fir-dominated stands (median ~3.7 Mg ha-1). The amount of SOM and FRB differed also in the analyzed soil depth layers (10 cm interval up to 40 cm) reaching mostly the highest values at soil depths of 0-10 cm. The highest amount of biomass (both aboveground and the belowground) has been identified in beech-dominated forests. We examined relationships between AGB, FRB, and SOM, but were not able to identify clear significant correlations based only on vegetation parameters. Derived results illustrate the complexity of identifying significant relationships between aboveground and belowground biomass stocks. Employing the same models may be an erroneous strategy for different study sites because of local environmental factors that strongly determine aboveground and belowground biomass stock. Accordingly, creating biomass and carbon models at larger scales in northern Carpathians based on forest aboveground data may cause an over- or underestimation due to the significant impact of both abiotic and biotic factors. This research study was funded by the Polish National Science Centre (RS4FOR Project: Forest change detection and monitoring using passive and active remote sensing data (No. 2015/19/B/ST10/02127) and via Project No. UJ/IGiGP/K/DSC/004779.