Individual study: Dormant season prescribed fire as a management tool for the control of coastal plain willow Salix caroliniana in a floodplain marsh, Lake Washington, Florida, USA
Lee M.A.B, Snyder K.L., Valentine-Darby P., Miller S.J. & Ponzio K.J. (2005) Dormant season prescribed fire as a management tool for the control of Salix caroliniana Michx. in a floodplain marsh. Wetlands Ecology and Management, 13, 479-487
Expansion of woody species into herbaceous wetlands is a serious concern in conservation and management of some wetland habitats. In south-east USA and elsewhere, this expansion is commonly attributed to a decline in wildfire frequency. However fire is not always effective in decreasing shrubs in wetlands in part because many woody species resprout after fire disturbance. We compared the responses of Salix caroliniana to three treatments: repeated dormant season fires (two fires over a three year period), a single dormant season fire, and no fire.
Study site: The study was conducted in floodplain marsh in the upper St. Johns River basin in east central Florida, southeast USA. The study site was located on the west side of Lake Washington, a run-of-the-river lake. The floodplain marsh surrounding the lake has experienced a large increase in the area dominated by willow in recent years.
Experimental design: The study area of 160 ha was divided into three sections of approximately equal size. Sections were randomly assigned to one of three treatments; no fire (site A), burned once (site B), burned twice (site C). Salix was sampled in each section in permanent 1 m wide belt transects. In each transect the number of willow stems was counted and the diameter at a height of 0.5 m was measured. Each transect was divided into 1 x 3 m quadrats and canopy cover (>1.5 m) was visually estimated by category (<5, 5-25, 26-50, 51-75 and >75%) in each quadrat.
Additionally, understory plant species composition and cover was measured in 1 m² quadrats placed 1 m apart along the transect. Cover was visually estimated using the same categories as that used for willow cover.
Pre-event sampling was done in September 1996 and the first prescribed fire was conducted in February 1997. Post-fire sampling was done in November 1997. Sampling was again conducted in November 1998, and the second prescribed fire conducted in March 1999. The final sampling event occurred in November 1999.
Unburned site (site A): Salix expanded over the course of the study. All metrics were significantly greater at the end of the study than at the beginning.
Burned sites (sites B and C): The first fire decreased stem basal area and cover in both burned sites, although it did not have an impact on stem density. This was because the fire destroyed the large stems and stimulated resprouting which resulted in many small stems. In the two years between fires, Salix increased in both sites. In site B, basal area and cover recovered to pre-fire levels and stem density increased. In site C, basal area and cover remained significantly lower than in the pre-fire sampling. There was no change in stem density. The second fire resulted in a further decline in cover in site C. But in site B over this period of time stem density and cover both increased.
At the end of the experiment: Site B (burned once) was not significantly different from site A, the unburned site, in willow stem density or canopy cover. Site C was significantly different from site A in both these measures. However in site C, stem density was not different before and after the fires.
Understory species: Frequently occurring species with high cover values included maidencane Pancium hemitomon, lanceleaf arrowhead Sagittaria lancifolia, dotted smartweed Polygonum punctatum and climbing hempvine Mikania scandens. Some species were common in one site but not in others. The frequency of occurrence of understory species varied in all three sites during the experiment, however, no patterns in variation could be discerned. Changes in frequency of occurrence and in cover were observed in the unburned as well as the two burned sites. None of the observed changes could be attributed to the fires.
Conclusions: Repeated dormant season fires were an effective strategy to manage Salix caroliniana encroachment in this floodplain marsh.
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