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A long-term study of carex vesicaria and phalaris arundinacea population dynamics in permanent plots

Odland Arvid

Polish Journal of Ecology

2023

Vol. 71, nr 2-3

49--57

It is well known that the population structure of plants in permanent plots change from year to year. Species abundances probably shift with time due to both species biology and variation in environmental factors. The main purpose of the study has been to describe and analyse long-term variation in the abundance (coverage) of blister sedge Carex vesicaria and reed canary grass Phalaris arundinacea in relation to time and space after a permanent lowering of a lake water level and exposition of new areas for species colonization. The study area lies in outer edge of a freshwater fluvial delta in the northern part of the Myrkdalen lake (229 m a.s.l.) West Norway, which was exposed after a permanent 1.4 m lowering of the summer water level in 1987. A 40 m long transect with ten 0.5 m × 4 m plot was established on the lower parts of the exposed delta in 1987. Study plots were situated at mean heights between 13 and 92 cm above the new summer water level. Floristic composition of the plots was monitored and analysed from 1988 to 2020, a total of 19 times. The plants show major differences in establishment, growth, and long-time dynamics in the permanent plots. The coverage of C. vesicaria and P. arundinacea was highly variable over the study period. Variations in coverage were related to time using regression analyses. The trends were mostly best described by cubic functions. Both species showed relatively low coverages between 18 and 26 years after the lake water drawdown, but increased again over the last study periods. Maximum coverage of the species was in time gradually separated by elevation. C. vesicaria became dominant in plots less than ca. 50 cm above the mean summer water, and P. arundinacea reached higher coverage above that elevation. The study indicates that elevation, as a proxy for flooding duration, and not aboveground species competition was the main factor for this difference in distribution.

Vascular plant succession on an exposed fluvial delta plain after a permanent lake water level drawdown : a 33-year time course

Odland Arvid

Polish Journal of Ecology

2022

Vol. 70, nr 2-3

79--88

A permanent lake water level drawdown initiates a vegetation succession on exposed sediments. This study aims to quantify long-term vascular plant changes on the sediments in time (number of years after drawdown) and space (elevation above the new water level). Shortly after a 1.4 m permanent drawdown of Myrkdalen lake, W Norway, a 40 m long transect running from the original lowermost vegetation toward the new water level was established. Species cover percentages in the 2 m2 study plots were determined by visual estimates and data sampling was performed from 1988 until 2020; in total, 19 times. During the study period both mean richness and plant percentage cover varied significantly in relation to space and time. Carex vesicaria and Phalaris arundinacea increased gradually especially in the lower parts. The successional changes as quantified by a DCA ordination showed rapid changes during the first 15-20 years, but later the vegetation appeared to be more stabilized. Elevation explained the mean floristic variation in a linear fashion while a quadratic model better explained the variation in relation to time. Variation in summer and June water level explained a small part of the succession change during the study period.