Individual study: Effects of prescribed burns and mowing on reed Phragmites australis yield and shoot density at Zuidelijk Flevoland polder, Flevoland, the Netherlands
Mook J.H. & van Der Toorn J. (1982) The influence of environmental factors and management on stands of Phragmites australis. II. Effects on yield and its relationships with shoot density. Journal of Applied Ecology, 19, 501-517
Common reed Phragmites australis was sown by air in extensive areas of two recent polders: IJsselmeer (Oostelijk) and Zuidelijk Flevoland. In Flevoland it was observed that 4-5 yr after the reed establishment a closed vegetation developed with a marked decrease in production, drier areas were also prone to invasion by weeds such as creeping thistle Cirsium arvense. The study summarised here investigated reed development (specifically yield and shoot density) in both wet and dry environments under winter burning or mowing management regimes.
The study was undertaken in an experimental field (500 x 1,100 m²) over a period of 5 years in the new polder of Zuid Flevoland from 1971 to 1976. This polder was drained in 1968 and reed sown over most of its area in May 1968. In 1971, the area where the experimental field was situated had an almost closed reed vegetation, except for small patches of hairy willow-herb Epilobium hirsutum.
The field was divided into 14 plots, some wet and some dry. In plots, three treatments were applied, i.e. burning in the spring, mowing and removal of shoots in the winter, and no disturbance (controls). The influence of the treatments were evaluated in terms of density and dimensions of the reed shoots. Sampling (1972-1976) was performed by repeated harvests during the growing season.
In the wet-burned treatment the only important damage to shoots early in the growing season (spring) was caused by late burning. Damage to just-emerging shoots in April or early May by burning (wet- and dry-burned plots) retarded leaf growth and shoots for 1-2 weeks, but relative growth rate and the maximal levels reached were not significantly lower than in the undamaged situation by the end of the year. Early frost (dry-burned and dry-mown plots) similarly damaged shoots. Heavy frost damage was restricted to the dry-burned and dry-mown treatments.
Heavy damage by late ground-frost (end of May, dry-burned plot) or by the stem-boring larvae of the moth Archanara geminipuncta (wet-undisturbed plot) lowered shoot biomass by around 25-35%. Heavy infestation by the rhizome boring larvae of another moth, Rhizedra lutosa (dry-undisturbed and dry-mown plots during later years) resulted in yield reduction of c. 45-60%.
Self-thinning of shoots was found in the treatments with high shoot densities as the results of damage due to burning or early frost. This resulted in a negative trend of yield in summer on shoot density.
Conclusions: This study shows that Phragmites development in the early growing season can be strongly influenced by injury inflicted by inappropriate management, e.g. spring burns. Management by burning or mowing should be undertaken prior to shoot emergence if the desired outcome is to avoid damaging that years shoot growth.
Note: The compilation and addition of this summary was funded by the Journal of Applied Ecology (BES). If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://links.jstor.org/sici?sici=0021-8901%28198208%2919%3A2%3C477%3ATIOEFA%3E2.0.CO%3B2-6