some nesting passerines (Poulin et al. 2002), and might also affect the availability
of nest-sites for some species. Consistent high water levels over many years have,
though, been implicated in the regress of reeds (Van der Putten 1997). The ideal
is to have a mixture of hydrological regimes. Regular monitoring of water levels
is important in informing hydrological management and interpreting its effects.
Water levels are best monitored using gaugeboards leveled to a benchmark. The
relationship between gaugeboard readings and water levels within the reedbed
can be determined by mapping water depths on a grid when water levels are at a
known, high gaugeboard level. These data can then be used to determine water
depths within the reedbed when water levels are lower.
Sparse, early-succesional reed can be encouraged by lowering the ground
surface to provide open water into which reed can spread or be planted. Excavation
can be difficult in reedbeds, though, and disposal of excavated material can be
problematic. However, if excavation is carried out sensitively, it can be used to
create a gradient from open water and early successional emergent vegetation, to
later successional swamp and fen. It is most frequently used along ditch edges
to maximize the length of sparse reed/open water interface, but has been used on
a larger scale to lower areas of tens of hectares to provide sparse, open reed for
breeding Bitterns in the United Kingdom (Smith et al. 2000) (Figure 14.7). The
Managing wetlands| 359Fig. 14.7Bitterns prefer feeding in sparse, early successional reedbed close to open
water. One method to set back reedbed succession is to lower the surface of the
reedbed relative to the water. Minsmere RSPB Reserve (RSPB Images)