Factors promoting larch dominance in central Siberia: fire versus growth performance and implications for carbon dynamics at the boundary of evergreen and deciduous conifers

[摘要] The relative role of fire and of climate in determining canopy speciescomposition and aboveground carbon stocks were investigated. Measurementswere made along a transect extending from the dark taiga zone of centralSiberia, where Picea and Abies dominate the canopy, into the Larix zone of eastern Siberia.We test the hypotheses that the change in canopy species composition isbased (1) on climate-driven performance only, (2) on fire only, or (3) onfire-performance interactions. We show that the evergreen conifers Picea obovata andAbies sibirica are the natural late-successional species both in central and easternSiberia, provided there has been no fire for an extended period of time.There are no changes in performance of the observed species along thetransect. Fire appears to be the main factor explaining the dominance ofLarix and of soil carbon. Of lesser influence were longitude as a proxy forclimate, local hydrology and active-layer thickness. We can only partiallyexplain fire return frequency, which is not only related to climate and landcover, but also to human behavior.

Stand-replacing fires decreased from 300 to 50 yrs between the YeniseiRidge and the upper Tunguska. Repeated non-stand-replacing surface fireseliminated the regeneration of Abies and Picea. With every 100 yrs since the lastfire, the percentage of Larix decreased by 20%.

Biomass of stems of single trees did not show signs of age-related decline.Relative diameter increment was 0.41 ± 0.20% at breastheight and stem volume increased linearly over time with a rate of about0.36 t C ha⁻¹ yr⁻¹ independent of age class and species. Standbiomass reached about 130 t C ha⁻¹(equivalent to about 520 m³ ha⁻¹). Individual trees of Larix were older than 600 yrs. The maximum ageand biomass seemed to be limited by fungal rot of heart wood. 60% of oldLarix and Picea and 30% of Pinus sibirica trees were affected by stem rot. Implications for thefuture role of fire and of plant diseases are discussed.

[学科分类] 地球化学与岩石