Transplanted seed bank response to drawdown time in a created wetland in east Texas

  • Published source details McKnight S.K. (1992) Transplanted seed bank response to drawdown time in a created wetland in east Texas. Wetlands, 12, 79-90.


This study is summarised as evidence for the following.

Action Category

Actively manage water level before/after planting non-woody plants: freshwater wetlands

Action Link
Marsh and Swamp Conservation

Transplant or replace wetland soil: freshwater marshes

Action Link
Marsh and Swamp Conservation
  1. Actively manage water level before/after planting non-woody plants: freshwater wetlands

    A study in 1990 in a created freshwater marsh in Texas, USA (McKnight 1992) found that the length of flooding and drawdown on shelves amended with wetland soil affected the abundance, richness and composition of submerged and emergent vegetation. The longer plots were flooded, the more submerged vegetation biomass they contained (five months flooding: 191; three months: 46; one month: 0 g/m2). In contrast, for emergent vegetation that matured after drawdown, plots flooded for longer contained less above-ground biomass (five months: 99; three months: 134; one month: 769 g/m2), fewer stems (five months: 1,126; three months: 340; one month: 1,851 stems/m2), fewer species (five months: 17; three months: 17; one month: 29 species/0.25 m2) and fewer species that “prefer wet or semi-wet soils” (five months: 10; three months: 8; one month: 13 species/0.25 m2). The duration of flooding also affected the biomass of individual plant species (see original paper for data). Methods: The study used a created marsh containing three shelves of differing height. In late February 1990, wetland soil was added to all shelves and then they were flooded. The water level was then drawn down in stages, exposing one shelf after one month, one after three months and one after five months. Vegetation was surveyed from 11–20 plots/shelf (each 0.25 m2). Submerged vegetation was collected immediately before drawdown. Emergent vegetation was collected once “mature”. Vegetation was dried before weighing.

    (Summarised by: Nigel Taylor)

  2. Transplant or replace wetland soil: freshwater marshes

    A replicated, randomized, paired, controlled, site comparison study in 1989–1990 in a created freshwater marsh in Texas, USA (McKnight 1992) reported that plots amended with soil from a donor marsh contained more plant species, more wetland-characteristic plant species and typically more plant biomass than unamended plots. Unless specified, statistical significance was not assessed. Mature vegetation in amended plots contained 17–28 plant species/0.25 m2 (vs unamended: 6–14) and 8–13 plant species/0.25 m2 that “prefer wet or semi-wet soils” (vs unamended: 1–3). In three of four comparisons, amended plots contained significantly more above-ground vegetation biomass (for which amended: 99–769 g/m2; unamended: 5–83 g/m2; other comparison no significant difference). Only 12 of the 20 plant taxa present in the donor site were present in amended plots, but they comprised 96% of the biomass in amended plots (see original paper for data on biomass of individual plant species). Methods: In February 1990, one hundred and twenty 0.25-m2 plots were established in a created marsh (formerly grassland), in four blocks of 30 according to moisture level. In eighty plots (20 plots/block), the top 6–7 cm of soil were removed and replaced with soil from the top 10–15 cm of a nearby donor marsh. The donor soil had been stockpiled over winter. The other 40 plots (10 plots/block) were left undisturbed. Later in 1990, when emergent vegetation was “mature”, it was cut from each plot then identified, dried and weighed. Vegetation in the donor marsh was surveyed along transects perpendicular to the shoreline in October 1989.

    (Summarised by: Nigel Taylor)

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