Abstract
Abstract. A strong temperature increase in the Arctic is expected to lead to latitudinal treeline shift. This tundra–taiga turnover would cause a positive vegetation–climate feedback due to albedo decrease. However, reliable estimates of tree migration rates are currently lacking due to the complex processes involved in forest establishment, which depend strongly on seed dispersal. We aim to fill this gap using LAVESI, an individual-based and spatially explicit Larix vegetation simulator. LAVESI was designed to simulate plots within homogeneous forests. Here, we improve the implementation of the seed dispersal function via field-based investigations. We inferred the effective seed dispersal distances of a typical open-forest stand on the southern Taymyr Peninsula (northern central Siberia) from genetic parentage analysis using eight nuclear microsatellite markers. The parentage analysis gives effective seed dispersal distances (median ∼10 m) close to the seed parents. A comparison between simulated and observed effective seed dispersal distances reveals an overestimation of recruits close to the releasing tree and a shorter dispersal distance generally. We thus adapted our model and used the newly parameterised version to simulate south-to-north transects; a slow-moving treeline front was revealed. The colonisation of the tundra areas was assisted by occasional long-distance seed dispersal events beyond the treeline area. The treeline (∼1 tree ha−1) advanced by ∼1.6 m yr−1, whereas the forest line (∼100 trees ha−1) advanced by only ∼0.6 m yr−1. We conclude that the treeline in northern central Siberia currently lags behind the current strong warming and will continue to lag in the near future.
Highlights
Changing climate forces species worldwide to migrate (Arctic Climate Impact Assessment, 2004; IPCC, 2013)
We inferred the effective seed dispersal distance from a genetic parentage analysis based on nuclear microsatellites and second, we improved the dispersal process of the model according to the observed dispersal pattern
We found a genetically diverse tree population at a location within the treeline close to the tundra in Siberia
Summary
Changing climate forces species worldwide to migrate (Arctic Climate Impact Assessment, 2004; IPCC, 2013). Warming is pronounced in the Arctic, where the tundra–taiga ecotone demarks the transition from forest stands to treeless areas, which is expected to move northwards (Harsch et al, 2009; Holtmeier and Broll, 2005) Such tree range expansion is of major interest because the establishment of forest in the dwarf-shrub tundra would reduce the surface albedo and promote a positive feedback to global temperature (Bonan, 2008). Trees migrate via seed dispersal and face several ecological barriers (Svenning et al, 2014): first, viable seeds need to be produced; second, these need to be dispersed; and, third, seeds need to germinate and survive to grow to new individuals This process, called “effective seed dispersal” (Connell, 1971; Janzen, 1970), determines the speed and spatial pattern of a species’ response to climate change. Closely dispersed seeds and a long generation time re-
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