Modelling Impact of Site and Terrain Morphological Characteristics on Biomass of Tree Species in Putorana Region

Regionally Compatible Individual Tree Growth Model under the Combined Influence of Environment and Competition

To explore the effects of competition, site, and climate on the growth of Chinese fir individual tree diameter at breast height (DBH) and tree height (H), a regionally compatible individual tree growth model under the combined influence of environment and competition was constructed. Using continuous forest inventory (CFI) sample plot data from Fujian Province between 1993 and 2018, we constructed an individual tree DBH model and an H model based on re-parameterization (RP), BP neural network (BP), and random forest (RF), which compared the accuracy of the different modeling methods. The results showed that the inclusion of competition and environmental factors could improve the prediction accuracy of the model. Among the site factors, slope position (PW) had the most significant effect, followed by elevation (HB) and slope aspect (PX). Among the climate factors, the highest contribution was made by degree-days above 18 °C (DD18), followed by mean annual precipitation (MAP) and Hargreaves reference evaporation (Eref). The comparison results of the three modeling methods show that the RF model has the best fitting effect. The R² of the individual DBH model based on RF is 0.849, RMSE is 1.691 cm, and MAE is 1.267 cm. The R² of the individual H model based on RF is 0.845, RMSE is 1.267 m, and MAE is 1.153 m. The model constructed in this study has the advantages of environmental sensitivity, statistical reliability, and prediction efficiency. The results can provide theoretical support for management decision-making and harvest prediction of mixed uneven-aged forest.

Interrelationships among mountain relief, surface organic layer, soil organic carbon, and its mineral association under subarctic forest tundra

Efforts to estimate the impact of climate change-induced forest expansion on soil carbon stocks in cold regions are hindered by the lack of soil organic carbon (SOC) concentration data. The presented study addressed the information gap by establishing SOC concentration and its variability in two catchments inside the vast, remote, and rugged Putorana Plateau. Additionally, it explored interrelationships among the terrain relief, vegetation cover, surface organic layer, SOC and its mineral association on the northernmost boundary of the forest-tundra biome traversing the northwestern part of the Central Siberian Tableland. Soil samples were taken from the active layer on the slope base, middle, and below the upper forest boundary. Subsequently, they were analyzed for SOC concentration by dry combustion. Multiple linear regression identified associations between slope angle and surface organic layer thickness and between SOC concentration and surface organic layer thickness, clay content, and dithionite-extracted Al. Clay content and surface organic layer thickness explained 68% of the overall SOC concentration variability. When used with data produced by remote sensing-based multipurpose large-scale mapping of selected biophysical factors, the acquired regression equations could aid the estimation of SOC across the rugged terrain of the Siberian Traps.

Declining Growth Response of Siberian Spruce to Climate Variability on the Taiga–Tundra Border in the Putorana Mountains (Northwest Siberia)

Global warming is most pronounced at high latitudes where temperatures increase twice as fast as the global average. Boreal forest growth is generally limited by low temperatures, so elevated temperature is supposed to enhance biomass production and carbon sequestration. A large amount of evidence has recently shown inconsistent responses of tree growth derived from annual tree rings to increasing temperature. We studied Siberian spruce growth in the remote and isolated Putorana Mts, Western Siberia in populations at its natural distribution limit. Tree ring cores were sampled along vertical transect in 100, 200 and 350 m a.s.l. as the aim was to identify the tree growth rate at different altitudes. Detailed sampling site descriptions served to identify possible factors controlling the growth rate in extremely heterogeneous environments. Monthly climate data for the period 1900–2020 were extracted from the gridded CRU database. Tree ring chronologies confirmed long-lasting limited growth, and despite high year-to-year ring width variability, synchronous growth at vertical study sites dominantly controlled by climate. The positive tree ring growth response to summer temperature was significant for most of the 20th century but dramatically changed in recent decades, when unusually warm summers were reported. There was no, or even a negative growth rate correlation with precipitation, which indicates a sufficient water supply at the study sites. Elevated temperature in this region with a continental climate might turn the study localities to water-limited areas with many negative consequences on tree growth and related ecosystem services.