Study

Accelerating the restoration of vegetation in a southern California salt marsh

  • Published source details O’Brien E.L., & Zedler J.B. (2006) Accelerating the restoration of vegetation in a southern California salt marsh. Wetlands Ecology and Management, 14, 269-286.

Actions

This study is summarised as evidence for the following.

Action Category

Facilitate tidal exchange before/after planting non-woody plants: brackish/saline wetlands

Action Link
Marsh and Swamp Conservation

Disturb soil/sediment surface before planting non-woody plants: brackish/saline wetlands

Action Link
Marsh and Swamp Conservation

Facilitate tidal exchange before/after planting non-woody plants: brackish/saline wetlands

Action Link
Marsh and Swamp Conservation

Add below-ground organic matter before/after planting non-woody plants: brackish/saline wetlands

Action Link
Marsh and Swamp Conservation

Add below-ground organic matter before/after planting non-woody plants: brackish/saline wetlands

Action Link
Marsh and Swamp Conservation

Directly plant non-woody plants: brackish/saline wetlands

Action Link
Marsh and Swamp Conservation
  1. Facilitate tidal exchange before/after planting non-woody plants: brackish/saline wetlands

    A replicated, controlled study in 1999–2002 in an estuary in California, USA (O’Brien & Zedler 2006) found that excavating tidal creeks before planting salt marsh plants typically had no significant effect on their survival or size. Over the first year after initial planting, dead plants were replaced by new plants of a similar age. The number of replacements needed per plot, and for four of five species, was statistically similar in catchments with or without a tidal creek (data not reported). Over the second year of the study, plot-level survival was statistically similar under both treatments (creek: 3.3; no creek: 2.9 survivors/plot). The survival rate was similar under each treatment for three of five planted species (creek: 24–80%; no creek: 37–70%) but higher in catchments with a creek for the other two species (creek: 63–93%; no creek: 48–74%). Across both years, surviving plants were a similar size (combination of height and lateral extent) in catchments with and without tidal creeks. This was true for both plot- and species-level comparisons (data not reported). Methods: In winter 1999/2000, an area of estuarine sediment was reprofiled to intertidal elevations. A tidal creek was dug in three of six catchments within the site. In December 2000, 90 greenhouse-reared salt marsh plants were planted in each catchment (five plants, each a different species, in each of eighteen 2.24-m2 plots/catchment). Some plots had also been tilled and/or amended with kelp compost. Colonizing vegetation was removed until October 2001. Until December 2001, dead planted vegetation was replaced. Replacements were counted. In August 2002, final survival, height and lateral spread of planted vegetation were recorded.

    (Summarised by: Nigel Taylor)

  2. Disturb soil/sediment surface before planting non-woody plants: brackish/saline wetlands

    A replicated, randomized, paired, controlled study in 2000–2002 in an estuary in California, USA (O’Brien & Zedler 2006) found that tilling plots before planting salt marsh plants typically had no significant effect on their survival or size. Over the first year after initial planting, dead plants were replaced by stock plants of a similar age. The number of replacements needed was statistically similar in tilled plots (9.1 replacements/plot) and undisturbed plots (9.7 replacements/plot). Over the second year of the study, the treatments supported a similar average number of surviving plants (tilled: 2.9; undisturbed: 2.8 survivors/plot) and a similar survival rate under each treatment for five of five planted species (tilled: 31–72%; undisturbed: 19–86%). Across both years, surviving plants were typically a similar size in tilled and undisturbed plots (data reported as an index combining height and lateral extent). This was true in four of four comparisons of the average size of plants per plot, and 9 of 10 comparisons of the average size of individual species. Methods: In January 2000, seventy-two 2.24-m2 plots were established (in 6 sets of 12) on intertidal sediment excavated earlier that winter. Half of the plots (six random plots/set) were rototilled to 30 cm depth. The other plots were left undisturbed. In December 2000, five greenhouse-reared plants (each a different species) were planted into each plot. Colonizing vegetation was removed until October 2001. Dead planted vegetation was replaced until December 2001 to maintain 36 plants/species/soil treatment. Survival, height and lateral spread of planted vegetation were recorded in August 2002.

    (Summarised by: Nigel Taylor)

  3. Facilitate tidal exchange before/after planting non-woody plants: brackish/saline wetlands

    A replicated, controlled study in 1999–2002 in an estuary in California, USA (O’Brien & Zedler 2006) found that excavating tidal creeks before planting California cordgrass Spartina foliosa did not significantly affect cordgrass density or height. After three growing seasons, the density of California cordgrass stems was statistically similar in catchments with or without a tidal creek. The same was true for the average height of those stems. No data were reported. Methods: In winter 1999/2000, twelve 15 x 30 m plots were established during the excavation of a salt marsh. Six plots were within the catchments of three excavated tidal creeks. The other six plots were in three catchments without tidal creeks. Kelp compost was also added to half of the plots. In February 2000, plugs of California cordgrass (range 50–100 cm tall) were dug from a nearby marsh and planted (2 m apart) in the plots. In August 2002, cordgrass stems were counted and measured in four 0.25-m2 quadrats/plot (each with ≥15 stems).

    (Summarised by: Nigel Taylor)

  4. Add below-ground organic matter before/after planting non-woody plants: brackish/saline wetlands

    A replicated, paired, controlled study in 1999–2002 in an estuary in California, USA (O’Brien & Zedler 2006) found that mixing kelp compost into the sediment before planting California cordgrass Spartina foliosa increased its density and height. After three growing seasons, plots amended with kelp compost contained a higher density of California cordgrass (237 stems/m2) than unamended plots (126 stems/m2). The average height of California cordgrass was also greater in amended plots (48 cm) than unamended plots (37 cm). Methods: In winter 1999/2000, six pairs of 15 x 30 m plots were established during the excavation of a salt marsh. Kelp compost (an industrial waste product) was mixed into the top 30 cm of sediment in one plot/pair (2:1 sediment:compost ratio). No compost was added to the other six plots. In February 2000, plugs of California cordgrass (range 50–100 cm tall) were dug from a nearby marsh and planted (2 m apart) in the plots. In August 2002, cordgrass stems were counted and measured in four 0.25-m2 quadrats/plot (each with ≥15 stems). This study used the same marsh as (3), but a different experimental set-up.

    (Summarised by: Nigel Taylor)

  5. Add below-ground organic matter before/after planting non-woody plants: brackish/saline wetlands

    A replicated, randomized, paired, controlled study in 2000–2002 in an estuary in California, USA (O’Brien & Zedler 2006) found that tilling kelp compost into plots before planting salt marsh plants increased their overall survival and size, but did not always have significant effects on the survival or size individual species. Over the first year after initial planting, dead plants were replaced by stock plants of a similar age. Fewer replacements were needed in composted plots (8 replacements/plot) than in uncomposted plots (tilled: 9.1; undisturbed: 9.7). Over the second year of the study, composted plots supported a higher number of surviving plants on average (3.5 survivors/plot) than uncomposted plots (tilled: 2.9; undisturbed: 2.8). However, the survival rate of individual species was similar under each treatment in 9 of 10 comparisons (for which composted: 42–92%; tilled: 31–72%; undisturbed: 19–86%). Across both years, surviving plants were typically larger in composted than uncomposted plots (data reported as an index combining height and lateral extent). This was true in four of four comparisons of the average size of plants per plot, and 16 of 20 comparisons of the average size of each species. Methods: In January 2000, one hundred and eight 2.24-m2 plots were established (in 6 sets of 18) on intertidal sediment excavated earlier that winter. Thirty-six plots (six random plots/set) received each soil treatment: tilling 40 L of kelp compost into the top 30 cm of soil, tilling only, or no disturbance (no compost or tilling). In December 2000, five greenhouse-reared plants (each a different species) were planted into each plot. Colonizing vegetation was removed until October 2001. Dead planted vegetation was replaced until December 2001 to maintain 36 plants/species/soil treatment. Survival, height and lateral spread of planted vegetation were recorded in August 2002. This study used the same marsh as (2), but a different experimental set-up.

    (Summarised by: Nigel Taylor)

  6. Directly plant non-woody plants: brackish/saline wetlands

    A replicated study in 2000–2002 in an estuary in California, USA (O’Brien & Zedler 2006) reported 31–83% survival of five planted salt marsh species over the second year after planting began, and that the average size of survivors increased. In December 2001, the study site contained 108 plants of each of five species (one plant/species in 108 plots). In August 2002, 33–90 plants/species were still alive, with an average of 2.7–3.5 surviving plants/plot. Initial planting occurred in December 2000, but dead plants were replaced until December 2001 to maintain the total of 108 plants/species (129–290 replacements/species). Between October 2001 and August 2002, the average size of surviving plants increased in 15 of 15 comparisons (statistical significant not assessed; data reported as an index combining height and lateral extent). Survival rates and plant size were typically increased by adding kelp compost to plots (see Action: Add below-ground organic matter before/after planting) but not significantly affected by the spacing of planting or excavation of tidal creeks (see original paper and Action: Facilitate tidal exchange before/after planting). Methods: In December 2000, one-year-old, greenhouse-reared herbs/succulents were planted into intertidal sediment excavated the previous winter. The species were saltwort Batis maritima, alkali heath Frankenia salina, salt marsh daisy Jaumea carnosa, California sea lavender Limonium californicum and estuary seablite Suaeda esteroa. Half of the plots were in the catchment of excavated tidal creeks. Kelp compost was tilled into some plots, some plots were tilled, and some were left undisturbed. Colonizing vegetation was removed until October 2001. This study included some of the plots used in (17).

    (Summarised by: Nigel Taylor)

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