Effects of winter burning and structural marsh management on vegetation and winter bird abundance in the Gulf Coast Chenier Plain, USA

Published source details Gabrey S.W., Afton A.D. & Wilson B.C. (1999) Effects of winter burning and structural marsh management on vegetation and winter bird abundance in the Gulf Coast Chenier Plain, USA. Wetlands, 19, 594-603.
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This study is summarised as evidence for the following.

	Action	Category
	Use prescribed fire to control problematic plants: brackish/salt marshes Action Link
	Actively manage water level: brackish/salt marshes Action Link

Use prescribed fire to control problematic plants: brackish/salt marshes

A replicated, randomized, paired, controlled study in 1995–1997 in 14 brackish and salt marshes in Louisiana, USA (Gabrey et al. 1999) reported that prescribed winter burning had no significant effect on plant species richness, vegetation structure and overall vegetation cover in the following winter, but increased cover of the two dominant plant species and reduced cover of dead vegetation. Unless specified, statistical significance was not assessed. After one year, a total of 5–8 plant species were recorded across burned plots (vs 6–7 species across unburned plots). Burned and unburned plots created statistically similar visual obstruction (data reported as an index combining plant height and horizontal cover) and had statistically similar overall vegetation cover (burned: 72%; unburned: 76%). However, burned plots had greater live cover of the two dominant plant species (saltmeadow cordgrass Spartina patens: 28–59%; saltgrass Distichlis spicata: 2–11%) and less cover of standing dead vegetation (35–61%) than unburned plots (saltmeadow cordgrass: 19–23%; saltgrass: 1–5%; dead: 75–76%). Vegetation was also surveyed 1–2 months after burning. At this point, all metrics apart from species richness were lower in burned than unburned plots (see original paper for data). Methods: The experiment was carried out in 14 coastal marshes of varying salinity and tidal influence. In winter 1995/1996, when 5 cm of water covered the marshes, one random half of each marsh was burned. In January–February 1996 and 1997, vegetation was surveyed at 40 points in each half of each marsh. This study was based on the same experimental set-up as (3).

(Summarised by: Nigel Taylor)
Actively manage water level: brackish/salt marshes

A replicated, site comparison study in 1996–1998 of 14 coastal brackish and salt marshes in Louisiana, USA (Gabrey et al. 1999) reported that active management of water levels within impoundments had mixed effects on winter vegetation cover, structure and species richness, depending on the year and whether marshes had been recently burned. In two of two years, impounded marshes had statistically similar overall vegetation cover (62–72%) to open marshes (56–78%). In one of two years, vegetation in impounded marshes created less visual obstruction than vegetation in open marshes (data reported as an index combining height and horizontal cover; other year no significant difference). Compared to open marshes, impounded marshes had similar or lower saltgrass Distichlis spicata cover (impounded: 0–2%; open: <1–11%), similar or higher cover of standing dead vegetation (impounded: 5–76%; open: 3–75%), and similar or higher plant species richness (impounded: 6–8 species/marsh; open: 4–6 species/marsh). Impounded marshes typically had higher saltmeadow cordgrass Spartina patens cover (three of four comparisons, for which impounded: 1–23%; open: <1–19%). Statistical significance of these cover results was not assessed. Methods: In January–February 1996 and 1997, vegetation was surveyed at 80 points in each of 14 brackish or saline marshes. Eight marshes had been impounded since the late 1950s, meaning water levels could be controlled (e.g. maintained relatively high in winter). Water levels were not controlled in the other six marshes (i.e. open to natural tidal influence). In each marsh, 40 points had been burned earlier in winter 1995/1996 and 40 had not. This study included the marshes studied in (6).

(Summarised by: Nigel Taylor)