Experimental management of Mediterranean temporary pools for conservation of the rare quillwort Isoetes setacea

Summary

Study 1

Mediterranean temporary pools are species-rich, containing many rare and endangered species. Land use changes, however, have resulted in invasion of pools by shrub and tree species. In this study, shrubs were experimentally removed from a temporary pool to determine the effect on a rare Mediterranean quillwort, Isoetes setacea. (See Case 351 for the additional effects of leaf litter removal or addition on I.setacea growth).

Study site & experimental design: One pool harboring quillwort Isoetes setacea was selected at Roque-Haute Natural Reserve in the province of Languedoc-Roussillon, southern France. The pool (surface area = 352 m²) was invaded mainly by elm Ulmus trees, and was shaded by shrubs from the surrounding arid shrubland. I.setacea was present but scattered in the pool. The pool was divided into two halves: a control zone (176 m²) and a cleared zone (160 m²). The cleared zone was cut in November 2000 using a chainsaw and a brush cutter. All cut material was removed but the leaf-litter was left.

The frequency of I.setacea was measured in May 2000 (pre-clearance) and May 2001 (post-clearance), in quadrats at 2 m intervals along eight permanent parallel transects, totaling 35 quadrats in the control zone and 42 quadrats in the cleared zone. The quadrats (0.3 x 0.3 m) were divided into nine squares (0.1 x 0.1 m) and the presence/absence of I.setacea was recorded in each, giving a frequency from 0 to 9.

In May 2000, I.setacea was located in 36 of the 77 quadrats, of which 13 were in the control zone and 23 in the zone that was to be cleared. The frequency of I.setacea was not significantly different between the two zones prior to the management work. After clearing, the frequency of I.setacea increased significantly in the cleared zone (May 2001, median 6.5) compared to the pre-clearance frequency (May 2000, median 2.5). Furthermore, there was a significantly higher frequency in the cleared zone than in the control zone (median = 0) in May 2001. Finally, in the control zone there was no significant difference in the frequency of I.setacea between May 2000 and May 2001.

Conclusions: Results from the Roque-Haute Natural Reserve suggest that scrub clearance is an effective management tool for increasing the density of I.setacea in Mediterranean temporal pools. Over what duration the benefits of scrub removal are on I.setacea populations is unknown, and presumably will vary from locality to locality.

 

Study 2

Mediterranean temporary pools are species-rich, containing many rare and endangered species. Land use changes, however, have resulted in invasion of pools by shrubs and trees. In this study, leaf litter was removed or added from plots in a temporary pool to determine the effect on a rare Mediterranean quillwort, Isoetes setacea. This management was combined with the experimental clearance of scrub from the pool (see Case 350).

Study site & experimental design: One pool harboring quillwort Isoetes setacea was selected at Roque-Haute Natural Reserve (situated in the province of Languedoc-Roussillon) for leaf-litter removal or addition. The pool (surface area = 352 m²) was invaded mainly by elm Ulmus trees, and was shaded by shrubs from the surrounding dry shrubland. I.setacea was present but scattered in the pool. The pool was divided into two halves: a control zone (176 m²) and a zone to be cleared of scrub and trees (160 m). In May 2000, the frequency of I.setacea and the thickness of the litter was measured in 16 continuous quadrats (0.3 x 0.3 m) placed within each of 20 plots (1.2 x 1.2 m); the plots were equally divided between the control zone and the zone to be cleared. Each quadrat was divided into nine squares (0.1 x 0.1 m) and the presence/absence of I.setacea was recorded in each, giving a frequency from 0 to 9. Litter depth was measured with a ruler pushed vertically down through the litter until the underlying sediment was reached.

In November 2000, the scrub was cleared using a chainsaw and a brush cutter. Also, within each of the two zones, five randomly chosen plots had their leaf litter removed and the litter was added to the remaining five plots, doubling litter thickness. In May 2001, the frequency of I.setacea and the thickness of the litter was re-measured for each of the continuous quadrats.

Litter thickness was an average of 18.8 mm (± 8.1 Standard Deviation) in the cleared and 40.5 mm (± 15.9) in the control zone in May 2000. After litter addition, thickness was 63.1 mm (± 1.9). The frequency of I.setacea was significantly higher after litter removal in the cleared zone, with numbers (estimated from original figure)as follows:

In plots with litter removed, quillwort frequency increased by an average of 15. In plots with litter added, the frequency fell by four but this was not a significant decrease.

A similar pattern was seen in the control plots with numbers (estimated from original figure) as follows:

Litter removal resulted in an increase in frequency of three and litter addition a decrease in frequency of 1.5, these changes in frequencies, were however, not significant.

Conclusions: At Roque-Haute Natural Reserve, removal of accumulated vegetation litter combined with scrub clearance had a strong positive effect on the growth of I.setacea.



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