Increasing substrate heterogeneity as a bet-hedging strategy for restoring wetland vegetation

Published source details Doherty J.M. & Zedler J.B. (2015) Increasing substrate heterogeneity as a bet-hedging strategy for restoring wetland vegetation. Restoration Ecology, 23, 15-25.
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This study is summarised as evidence for the following.

	Action	Category
	Create mounds or hollows before planting non-woody plants: freshwater wetlands Action Link
	Plant non-woody plants into moisture-retaining peat pots: freshwater wetlands Action Link
	Create mounds or hollows before planting non-woody plants: freshwater wetlands Action Link
	Add below-ground organic matter before/after planting non-woody plants: freshwater wetlands Action Link
	Directly plant non-woody plants: freshwater wetlands Action Link

Create mounds or hollows before planting non-woody plants: freshwater wetlands

A replicated, randomized, paired, controlled study in 2012–2013 in a freshwater wetland in Wisconsin, USA (Doherty & Zedler 2015) found that creating mounds before planting tussock sedge Carex stricta did not improve survival rates, and typically had no significant effect on sedge growth, biomass or cover. After two growing seasons, survival rates were lower for sedges planted in mounds than on flat ground in seven of eight comparisons (for which mounds: 27–93%; flat: 100%). There was typically no significant difference between treatments in sedge growth rate (11 of 16 comparisons; see original paper for data). In three of the other five growth rate comparisons, all in the second growing season after planting, sedges grew faster in mounds (0.021–0.028 mm/mm/day) than on flat ground (0.013 mm/mm/day). In most cases, there was also no significant difference between treatments for final above-ground sedge biomass (four of four comparisons, for which mounds: 5–34 g/plant; flat: 7–39 g/plant) and final sedge cover (three of four comparisons, for which mounds: 11–46%; flat: 38–62%). Methods: In spring 2012, thirty 1-m² plots were established, in six sets of five, in a wetland undergoing restoration. Soil mounds were built in 24 of the plots (five random plots/set). Mounds were either 8 cm tall, 16 cm tall, 16 cm tall with 50% woodchip, or 32 cm tall. The other six plots were left as flat ground. Five nursery-reared tussock sedges were planted into each plot (one plant/mound in plots with mounds) then regularly watered and weeded. Survival and above-ground biomass of planted sedges, and total tussock sedge cover, were surveyed in June–August 2013. Biomass was dried before weighing. Growth rates were calculated from leaf lengths measured in 2012 and 2013. This study used the same site as (2), but a different experimental set-up.

(Summarised by: Nigel Taylor)
Plant non-woody plants into moisture-retaining peat pots: freshwater wetlands

A replicated, randomized, paired, controlled study in 2012–2013 in a freshwater wetland in Wisconsin, USA (Doherty & Zedler 2015) found that planting tussock sedge Carex stricta into peat pots had no clear or significant effect on sedge survival, biomass or cover after two growing seasons, but did increase sedge growth rate in drier plots during the first growing season. After two growing seasons, sedges planted into peat pots or bare soil had similar survival rates (peat pots: 87–100%; bare soil: 100%; statistical significance not assessed). The above-ground biomass of surviving sedges was statistically similar under both treatments (peat pots: 6–34 g/plant; bare soil: 4–39 g/plant). The same was true for sedge cover (peat pots: 47–70%; bare soil: 38–62%). The growth rate of planted sedges was statistically similar in three of four comparisons (peat pots: 0.011–0.014 mm/mm/day; bare soil: 0.013–0.014 mm/mm/day). In the other comparison – in drier plots and in the first, drought-affected growing season – the growth rate was greater for sedges planted into peat pots (0.011 mm/mm/day) than sedges planted into bare soil (−0.003 mm/mm/day). Methods: In spring 2012, six pairs of 1-m² plots were established in a wetland undergoing restoration. Five nursery-reared tussock sedges were planted into each plot, then regularly watered and weeded. In half of the plots (one random plot/pair), the sedges were planted into peat pots sunk into the soil. Survival and above-ground biomass of planted sedges, and total tussock sedge cover, were surveyed in June–August 2013. Biomass was dried before weighing. Growth rates were calculated from leaf lengths measured in 2012 and 2013.

(Summarised by: Nigel Taylor)
Create mounds or hollows before planting non-woody plants: freshwater wetlands

A replicated, randomized, paired, controlled study in 2013 in a freshwater wetland in Wisconsin, USA (Doherty & Zedler 2015) found that creating mounds or hollows before planting tussock sedge Carex stricta typically had no significant effect on sedge growth, biomass or cover, and reported that creating hollows reduced survival rates. After one growing season, sedges planted in hollows had a lower survival rate (63%) than sedges planted on flat ground (≥90%; data for mounds not reported; statistical significance not assessed). The treatments had no significant effect, compared to planting in flat ground, on sedge growth rate (mounds: 0.026–0.028 mm/mm/day; hollows: 0.032–0.035 mm/mm/day; flat: 0.027–0.035 mm/mm/day), final above-ground sedge biomass (g/plant; data not reported), or final sedge cover (six of six comparisons, for which mounds: 11–38%; hollows: 3–11%; flat: 15%). Methods: In spring 2013, twenty-four 1-m² plots were established, in six sets of four, in a wetland undergoing restoration. Soil mounds (8 cm tall or 16 cm tall) were built in 12 of the plots (two random plots/set). Square hollows (10 cm deep; 15 cm across) were dug in six of the plots (one random plot/set). The final six plots were left as flat ground. Five nursery-reared tussock sedges were planted into each plot (one plant/mound or hollow where relevant). Survival and above-ground biomass of planted sedges, and total tussock sedge cover, were surveyed in June–August 2013. Biomass was dried before weighing. Growth rates were calculated from leaf lengths measured in 2013. This study used the same site as (1), but a different experimental set-up.

(Summarised by: Nigel Taylor)
Add below-ground organic matter before/after planting non-woody plants: freshwater wetlands

A replicated, randomized, paired, controlled study in 2012–2013 in a freshwater wetland in Wisconsin, USA (Doherty & Zedler 2015) reported that adding woodchips to soil before planting tussock sedge Carex stricta had mixed effects on sedge survival depending on soil moisture levels, but did not increase sedge growth, biomass or cover under either moisture level. Unless specified, statistical significance was not assessed. After two growing seasons and in a drier area, 67% of sedges survived when planted into mounds with woodchips vs only 27% in mounds without. However, in a wetter area, only 60% of sedges survived when planted into mounds with woodchips vs 93% in mounds without. In both areas, mounds with and without woodchips supported a statistically similar sedge growth rate (see original paper for data) and final above-ground biomass of surviving sedges (with: 2–15 g/plant; without: 2–8 g/ plant). Final sedge cover was lower in plots where sedges were planted into mounds with woodchips (11–18%) than mounds without (38%). Methods: In spring 2012, six pairs of 1-m² plots were established in a wetland undergoing restoration. Five 16-cm-tall mounds were built in each plot. In half of the plots (one random plot/pair), the mounds were built with a mix of 50% woodchip and 50% soil. In the other plots, the mounds were built with soil only. Nursery-reared tussock sedge was planted into each mound (one plant/mound), then regularly watered and weeded. Survival and above-ground biomass of planted sedges, and total tussock sedge cover, were surveyed in June–August 2013. Biomass was dried before weighing. Growth rates were calculated from leaf lengths measured in 2012 and 2013.

(Summarised by: Nigel Taylor)
Directly plant non-woody plants: freshwater wetlands

A replicated study in 2012–2013 in a freshwater wetland in Wisconsin, USA (Doherty & Zedler 2015) reported 27–100% survival of planted tussock sedge Carex stricta over 1–2 growing seasons, and that survivors grew. Survival rates depended on how wet plots were, and how sedges were planted. Survival was lowest for sedges planted into 16-cm-tall soil mounds in a drier area (27% after two growing seasons) and highest into 8-cm-tall mounds, peat pots or flat ground in a wetter area (100% after two growing seasons). Surviving plants grew, on average – although not in all cases during the first growing season (2012), when there was a drought (see original paper for data). After 1–2 growing seasons, planted plots contained 3–70% tussock sedge cover. As for survival, variation was related to plot wetness and planting method. Methods: Across spring 2012 and 2013, a total of 300 nursery-reared tussock sedges were planted into 60 plots in a wetland undergoing restoration (five sedges/plot). An invasive shrub that had colonized the site was cut down in January each year. Half of the plots were in a wetter area and half in a drier area. The sedges were planted into mounds, hollows or peat pots in 48 of the plots, and into flat ground in the other 12 plots. Sedges planted in 2012 were regularly watered and weeded. Survival and cover were surveyed in June–August 2013. Growth rates were calculated from leaf lengths measured in 2012 and 2013.

(Summarised by: Nigel Taylor)