Vulnerability analysis of the rare woodland fern Polystichum braunii (Dryopteridaceae) in Germany

by Robin Schwerbrock
Doctoral thesis
Date of Examination:2016-10-22
Date of issue:2017-10-18
Advisor:Prof. Dr. Christoph Leuschner
Referee:Prof. Dr. Christoph Leuschner
Referee:Prof. Dr. Markus Hauck
Persistent Address: http://dx.doi.org/10.53846/goediss-6535

 

 

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Abstract

English

Background: Various rare and endangered temperate ferns are being threatened by their recent population decline, but there is limited understanding of the causes behind it. Aims: This study attempted to identify the possible drivers of regional population decline and extinction in the globally distributed woodland fern Polystichum braunii. Methods: A comparison was undertaken of the climatic, edaphic and phytosociological characteristics of sites with increasing, decreasing or recently extinct populations in Germany. Results: A significantly higher frequency of episodes of low relative air humidity (<60 %) was found at sites with decreasing or extinct populations compared to habitats with population increases. Sites with decreasing or extinct populations were also characterised as having less summer precipitation (<500 mm year-1) and a shorter duration of snow cover (<110 days year-1) than sites with increasing populations. The latter had significantly higher moss cover (56 % of the forest floor), but less cover by a tree litter layer (23 %) compared to decreasing (36 % and 38 %) or recently extinct populations (22 % and 52 %). All increasing populations were located in intact Tilia - Acer ravine forests, while those suffering population decline were mostly located in Fagus-dominated forests. Conclusions: It was concluded that the probable causes of the recent decline in German P. braunii populations are reduced air humidity levels, decreasing snow duration or a shift from moss-covered to tree litter-covered forest floors due to climate warming or altered forest management.
Keywords: Polystichum braunii, air humidity, climate chamber experiment, climate change, foliar water uptake
 
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