Restrictions on natural regeneration of storm-felled spruce sites by silver birch ( Betula pendula Roth) through limitat
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ORIGINAL PAPER
Restrictions on natural regeneration of storm‑felled spruce sites by silver birch (Betula pendula Roth) through limitations in fructification and seed dispersal Katharina Tiebel1 · Franka Huth1 · Nico Frischbier2 · Sven Wagner1 Received: 11 August 2019 / Revised: 4 March 2020 / Accepted: 3 April 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Particularly after disturbance events, the early successional colonist Betula pendula Roth is experiencing renewed silvicultural interest with respect to the natural regeneration of large disturbed forest areas. In a case study, we therefore studied the seed dispersal of B. pendula from two adjacent spruce stands to large storm-felled sites at high altitudes in the Thuringian Forest (Germany) over a 2-year period. We applied inverse modelling to describe the distance-dependent seed distribution using a negative exponential kernel and seed production function of birch seed trees. Maximum seed numbers of 2015 n m−2 (non-mast year) and 9557 n m−2 (medium year) occurred within 40‒50 m distance to a seed tree. The predicted seed production rate of a birch seed tree with a reference dbh of 20 cm was approximately 350,000 n tree−1 (non-mast year) and 1,500,000 n tree−1 (medium year). Regardless of the seed crop, the dispersal distances were similar in both years. The isotropic model showed mean dispersal distances of 86 and 97 m (uphill) and 367 and 380 m (downhill) for the 2 years of seed sampling. No directionality in seed dispersal was found. The findings showed birch seed dispersal to be strongly influenced by site inclination, seed tree position (valley, slope or plateau) and distance to the storm-felled site. Furthermore, the seed shadow is influenced by the number of seed sources. Therefore, risk-adapted forest management should include the ‘spatial optimization’ of birch seed trees, ideally creating a network of small seed tree groups scattered more or less regularly within pure conifer forests. Keywords Silver birch · Seed rain · Pioneer trees · Disturbances · Forest restoration · Inverse modelling
Introduction
Communicated by Christian Ammer. * Katharina Tiebel [email protected] Franka Huth [email protected]‑dresden.de Nico Frischbier [email protected] Sven Wagner [email protected]‑dresden.de 1
Chair of Silviculture, Institute of Silviculture and Forest Protection, TU Dresden, Pienner Str. 8, 01737 Tharandt, Germany
Forestry Research and Competence Center, ThüringenForst, Jägerstraße 1, 99867 Gotha, Germany
2
As an anemochorously dispersed pioneer tree species with a wide natural range throughout Eurasia, silver birch (Betula pendula Roth) has a high ecological value within temperate and boreal forest ecosystems (Atkinson 1992; Hynynen et al. 2010). Silver birches enhance soil nutrition and soil stability, provide watershed protection, act as structural elements with a long-term stabilizing effect, and provide habitats and food for many organisms (see Patterson 1993; Humphrey et al. 1998; Ferri
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