Líffræðifélag Íslands - biologia.is
Líffræðiráðstefnan 2019

Erindi/veggspjald / Talk/poster E47

Spatial and temporal patterns of early population establishment and growth of downy birch (Betula pubescens Ehr.) on a glacial outwash plain

Höfundar / Authors: Guðrún Óskarsdóttir (1), Hulda Margrét Birkisdóttir (1), Þóra Ellen Þórhallsdóttir (1) & Kristín Svavarsdóttir (2)

Starfsvettvangur / Affiliations: 1. University of Iceland, 2. The Soil Conservation Service of Iceland

Kynnir / Presenter: Guðrún Óskarsdóttir

Downy birch (Betula pubescens) first colonized the central upper part of the 1000 km² outwash plain Skeiðarársandur around 1990 and has since expanded to cover 35 km², all land at early stages of primary succession. In 2008, a detailed survey of birch density, plant size and fecundity was carried out at four sites (4,500 m² in total) that differed in the time of initial birch colonization. We repeated this at the same sites in 2018, allowing us to distinguish decadal patterns of population development from early establishment and variation reflecting environmental heterogeneity. Our results show that even though Skeiðarársandur appears homogeneous to the human eye, there are significant spatial differences in birch growth and reproduction patterns. Even among the two highest density sites, which are only 500 m apart, growth and recruitment varied markedly. At site 3, birch density increased by 15% from 2008-2018 (0.13 – 0.15 plants per m²) but over 100-fold at site 4 (0.08 – 9.49 plants per m²). Excluding new saplings, mean annual growth increment at site 3 was 3.8 cm compared to 6.7 at site 4. At site 4, the tallest tree was 2.63 m but at all other sites, trees were <2 m tall. Density of reproductive plants in 2018 was also highest at site 4 (560 plants per ha), each one bearing up to 1,100 female catkins. The four sub-populations appear to follow different trajectories influenced by both environmental heterogeneity and time since colonization.