Dissimilar responses of larch stands in northern Siberia to increasing temperatures—a field and simulation based study

Abstract

Arctic and alpine treelines worldwide differ in their reactions to climate change. A northward advance of or densification within the treeline ecotone will likely influence climate-vegetation feedback mechanisms. In our study, which was conducted in the Taimyr Depression in the North Siberian Lowlands, w present a combined field- and model-based approach helping us to better understand the population processes involved in the responses of the whole treeline ecotone, spanning from closed forest to single-tree tundra, to climate warming. Using information on stand structure, tree age, and seed quality and quantity from seven sites, we investigate effects of intra-specific competition and seed availability on the specific impact of recent climate warming on larch stands. Field data show that tree density is highest in the forest-tundra, and average tree size decreases from closed forest to single-tree tundra. Age-structure analyses indicate that the trees in the closed forest and forest-tundra have been present for at least ~240 yr. At all sites except the most southerly ones, past establishment is positively correlated with regional temperature increase. In the single-tree tundra, however, a change in growth form from krummholz to erect trees, beginning ~130 yr ago, rather than establishment date has been recorded. Seed mass decreases from south to north, while seed quantity increases. Simulations with LAVESI (Larix Vegetation Simulator) further suggest that relative density changes strongly in response to a warming signal in the forest-tundra while intra-specific competition limits densification in the closed forest and seed limitation hinders densification in the single-tree tundra. We find striking differences in strength and timing of responses to recent climate warming. While forest-tundra stands recently densified, recruitment is almost non-existent at the southern and northern end of the ecotone due to autecological processes. Palaeo-treelines may therefore be inappropriate to infer past temperature changes at a fine scale. Moreover, a lagged treeline response to past warming will, via feedback mechanisms, influence climate change in the future.

Treeline Research—From the Roots of the Past to Present Time. A Review

“…In addition, historical displacement of treeline by humans and a delay of treeline response to climate change also play a major role in the respect. Hence, at finer scales, treeline position is often out-of-phase with climate (e.g., [1,[161][162][163][164][165][166][167][168][169][170][171][172][173][174][175][176]). Global overviews, necessarily disregarding the local differences, may easily overemphasize coarse drivers such as temperature [167,177,178].…”

Dispersal distances and migration rates at the arctic treeline in Siberia – a genetic and simulation-based study

“…To project future species ranges, the potential migration rate under global warming is estimated via simulation studies (Kaplan and New, 2006;Roberts and Hamann, 2016;Snell and Cowling, 2015). However, these simulations depend strongly on the dispersal configuration of the model (Bhagwat and Willis, 2008;McLachlan et al, 2005;Stewart et al, 2010;Willis and Van Andel, 2004). Most empirical attempts to estimate historical migration rates are based on records of fossil pollen and macrofossils in sediment cores as indicators of species presence (MacDonald et al, 2008;Pisaric et al, 2001), but the interpretation is compromised because of a lack of knowledge of glacial refugia, particularly small "cryptic" refugia that can be easily overlooked in the fossil record (e.g.…”

Pollen-based quantitative land-cover reconstruction for northern Asia covering the last 40 ka cal BP

“…Additionally, some field studies and dynamic vegetation models infer a rapid response of the treeline to warming in northern Siberia (e.g. Moiseev, 2002;Soja et al, 2007;Kirdyanov et al, 2012), but combined modeland field-based investigations of larch stands in north-central Siberia reveal only a densification of tree stands, not an areal expansion (Kruse et al, 2016;Wieczorek et al, 2017).…”