Advantages of rough wetland designs

Posted on June 1, 2016

In natural wetlands, the unevenness of the ground creates variation in environmental factors such as soil moisture and temperature, and this variability is a positive influence on the range of plant species that are able to colonise the area. As they become established, plants such as sedges and rushes slowly create tussocks, which further increase surface variability. Restoration ecologists at the University of Wisconsin, U.S.A. wondered if artificially-produced substrate variation could help to buffer wetland plantings against climatic fluctuations. In field experiments they created artificial mounds that mimicked the tussocks (10-40 cm in height) that are typically formed by the sedge Carex stricta in natural meadows. Experimental treatments included small (8-cm), medium (16-cm) and large (32-cm) soil mounds, medium mounds of woodchips and soil, 16-cm deep pots filled with peat, shallow depressions in the ground (10 cm-deep, with 15-cm sides), and control areas of flat ground. The experimental plots were planted with plugs of nursery-grown sedge and watered regularly. Soil moisture was monitored using a probe and plant growth was assessed by measuring the maximum leaf length in each plug. Analysis revealed that most (62-77%) of the variation in soil moisture was explained by a plug’s relative elevation, moisture levels being about 1.6 times higher in flat ground than in large mounds. In a wet year, sedge growth was fast in soil mounds but slow in soil depressions, while planting plugs in moisture-retaining peat allowed them to survive and sustain growth even in a dry year. Given that irrigation isn’t usually feasible in restoration sites, creating mounds and digging holes are viable ways of widening the available range of microsites, moderating stressful conditions and increasing the chances of plant survival.

Reference: Doherty, J.M. & Zedler, J.B. 2015. Increasing substrate heterogeneity as a bet-hedging strategy for restoring wetland vegetation. Restoration Ecology 23(1), 15–25.