Forest and steppe communities in the Altai region of Central Asia are highly vulnerable to climate change and anthropogenic pressure. Knowledge about vegetation and fire responses to past climate and land use changes may contribute to refine the understanding of future ecosystem dynamics. Specifically, increasing drought under global warming scenarios and growing anthropogenic pressure may cause collapses of moisture demanding plant communities, such as forests. We present a unique paleoecological record from the high-alpine Tsambagarav glacier in the Mongolian Altai. The ice core provides novel vegetation information at the landscape scale covering the past 5500 years with an exceptional temporal resolution which we compare to an existing palynological record from Belukha glacier in the densely forested Russian Altai. We infer vegetation composition and structure with pollen and spores, fire activity with microscopic charcoal, and atmospheric pollution due to fossil fuel combustion with spheroidal carbonaceous particles (SCPs).
Results/Conclusions
Our palynological record identifies several late-Holocene boreal forest expansions, collapses, and subsequent recoveries. Maximum forest expansions occurred at 3100–2800 BC, 2400–2100 BC (substantial Abies sibirica), and 2000–1800 BC. After 1800 BC mixed Pinus sibirica-Larix sibirica and Betula communities definitively declined. Fires reached a maximum at 1600 BC, 200 years after the definite forest collapse possibly in response to moisture declines that released tree diebacks, resulting in dead biomass accumulation, and thus fire fuel. The record suggests a decoupling of vegetation and fire from climate after 1700 AD when first signs of industrial pollution became apparent. Given that diebacks of boreal forest communities were associated to drying, not warming, moisture availability was more important for past vegetation dynamics. Our results contribute to assess ecosystem responses under global change. Comparing the Mongolian to the Russian Altai with similar species composition underscores the vulnerability of Central Asian steppe and forest conmunities to predicted future moisture declines. Specifically, extant forest stands in the Russian Altai may react similarly to those in the Mongolian Altai ca. 3800 years ago, when Pinus sibirica, Larix sibirica, Abies sibirica, and Betula pendula collapsed rapidly in response to reduced moisture availability. Even more exposed to climate change might be the relict Mongolian Altai forest communities that are growing at their hygric limits.