Management Project Summary: Fire effects on 3 subtropical invasive plants in Florida and the Caribbean—common bamboo, Natal grass, and white leadtree
TABLE OF CONTENTS
This report summarizes information on 3 nonnative species occurring in southern Florida and the Caribbean. Information was provided by members of the Caribbean Fire Invasives Learning Network at a meeting in December 2009, in San Juan, Puerto Rico, and in subsequent correspondence . This report is designed to share on-the-ground, local expertise of managers who have worked with invasive species in specific field locations. Information from managers is supplemented by some knowledge from scientific publications, but a comprehensive search of the literature was not conducted for this report. Readers should therefore be aware of the limited scope of knowledge given here, apply it with caution, monitor treatment results, and use an adaptive approach to management.
If you have additional knowledge on the species covered here, whether consistent with these reports or disagreeing with them, please share it in an email to firstname.lastname@example.org, with "invasive information for FEIS" in the subject line.
Common names are used throughout this summary. For a complete list of the common and scientific names of species discussed and for links to FEIS species reviews, see the Appendix.
Authorship and citation for this Management Project Summary:
Caribbean Fire Invasives Learning Network. 2011. Management Project Summary: Fire effects on 3 subtropical invasive plants in Florida and the Caribbean—Natal grass, common bamboo, and white leadtree. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ .
More information on these species is available from:
Information on the distribution of common bamboo is insufficient for determining the specific plant community types that may be invaded and describing their historical fire regimes.Response of common bamboo to fire:
Common bamboo resprouting after fire. Some clumps were burned and later were mechanically removed by excavators. Photo by Robert De Matas.
|Table 1. Frequency (%) of seeded Natal grass 6 months after planting and 4.5 years after planting |
|Proximity to unpaved road*||Roadside||Interior|
|Road and roadside soil type:
|~Sand amended with clay||50-100||0-25||70-100||0|
|~Sand amended with crushed limestone and clay||0-50||0-33||50-100||0|
|*Roadside measurements were taken within 3 feet (1 m) of road edge; interior measurements were taken at least 30 feet (10 m) from edge of same road, where soils were not ammended.|
Natal grass does not persist on soils that retain moisture and is inhibited by flooding (as little as 1 month of inundation). It is also inhibited by shade and cold, although seeds can germinate after freezing .
In the Bahamas, Natal grass occurs in farm areas and where farms have been abandoned. It is especially prevalent on limestone substrates, particularly in areas that have been fertilized for agriculture. Natal grass also occurs on sand dunes in the Bahamas. It is not considered invasive in natural areas of the Bahamas .
Impacts of Natal grass:
Natal grass establishes and regenerates most successfully on sites that have been mechanically disturbed, including road edges and firelines, but it can also spread from edges into the interior of undisturbed areas. It can thrive in drained sites, mowed firebreaks, fire-created openings , and mined areas . It can form a monoculture in disturbed areas, reducing native species, particularly graminoids. In Florida pine rocklands, the species richness of native graminoids was negatively associated with density of Natal grass (P<0.001), while richness of trees, shrubs, and vines was not significantly associated Natal grass density . On phosphate-mined uplands in Florida, first-year survival of planted Beyrich threeawn and lopsided indiangrass was greater where Natal grass had been removed .
Biology and ecology of Natal grass:
Natal grass is a short-lived grass (“annual to facultative perennial” ) that reproduces from small, wind-dispersed seeds. It does not have rhizomes . In Florida, it can reproduce year-round; 3 or 4 seed crops may be produced in a single season . Experiments showed that germination of Natal grass seed improved with storage, possibly indicating an afterripening mechanism. Fresh seed showed 55% germination, seed stored for 15 weeks showed 80% germination, and seed collected from the duff layer showed 95% germination. Germination occurred at temperatures between 70 and 90 °F (20-35 °C), with optimum germination at 90 °F (30 °C). Seedlings emerged from seeds buried 1 inch (2 cm) deep, though most seedlings emerged from seeds buried 0.2 inch (0.5 cm) deep or less. Natal grass required “fairly moist conditions” to germinate, suggesting that most germination is likely to occur during rainy periods . Natal grass can grow rapidly, maturing from seedling to seed-bearing adult in 8 weeks .
Fuel and fire regime information for
Fuel properties of Natal grass are similar to those of many native grasses, including wiregrasses. In the understory of pine rocklands, Natal grass co-occurs with native grasses and does not affect fuel loading or spatial arrangement. However, in dry areas and scrub habitats that historically supported discontinuous grass cover mixed with shrubs, Natal grass creates continuous fine surface fuels unlike those in natural stands. The dried grasses accumulate over winter, creating greater fuel loads in spring .
Natal grass burns readily, especially in winter and spring. Thick patches of dry Natal grass may provide a flashy fuel bed that burns "hot" and spreads fire rapidly. In the Bahamas, however, Natal grass is not considered a particularly flammable fuel .
Table 2 describes presettlement fire regime characteristics of some plant communities in central and southern Florida where Natal grass occurs:
|Table 2. Fire regime information on some vegetation communities where Natal grass occurs. This information is taken from the LANDFIRE Rapid Assessment Vegetation Models , which were developed by local experts using available literature, local data, and/or expert opinion. This table summarizes fire regime characteristics for each plant community listed. The PDF file linked from each plant community name describes the model and synthesizes the knowledge available on vegetation composition, structure, and dynamics in that community. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Surface or low||9%||20|
|Pond cypress savanna||Replacement||17%||120|
|Surface or low||57%||35|
|Surface or low||99%||3||1||5|
|Sand pine scrub||Replacement||90%||45||10||100|
Replacement: Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed: Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low: Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [4,5].
Response of Natal grass to fire:
Natal grass is tolerant of fire. It spreads into burned areas from wind-dispersed seed and establishes readily in openings created by fire. In pine rocklands, Natal grass populations increased after severe summer fires, possibly because these fires prevented regeneration of native species, including saw-palmetto. In pine rocklands and sand pine scrub, organic matter accumulates in the soil after many years without fire. Fires in these communities tend to be severe when the organic soil layers burn. Areas where woody debris has accumulated or been piled can also burn severely, increasing the potential for invasion by Natal grass .
Control of Natal grass:
Any treatment to control Natal grass requires repeated followup, at approximately 6- to 8-week intervals, since seeds germinate readily and new plants rapidly produce seed . Hand-pulling can be effective for controlling Natal grass. Most other control techniques in natural areas are likely to cause substantial collateral damage to some native species. Here are examples from field managers :
Distribution and site
requirements of white leadtree:
White leadtree is invasive in many subtropical and tropical areas, including Puerto Rico, Dominican Republic, and Florida. It has been widely promoted for tropical forage production and reforestation, although managers in Puerto Rico report that it is not a good forage plant. White leadtree populations can spread easily. The species is difficult to eradicate once established. White leadtree became invasive in southwestern Tobago as a result of the removal of mangroves and subsequent back-filling of the area by land developers.
White leadtree can tolerate a wide range of rainfall (from 20 to 140 inches/year (500 – 3,500 mm)) and can withstand dry seasons 6 to 8 months long. However, it is not frost hardy and grows poorly in relatively cool tropical highland sites. White leadtree also grows poorly on acid soils with high aluminum saturation.Impacts of white leadtree:
Biology and ecology of white leadtree:
White leadtree is a perennial shrub or tree that reaches up to 20 feet (6 m) tall. It produces flowers year-round, often in “massive” quantities. It is able to sprout after being cut.
White leadtree grows better in light than shade. Because of this property, it thrives in openings caused by hurricanes, fire, and land clearing.
Fuel and fire regime information for white
White leadtree itself does not seem to increase fuel loads or change the spatial distribution of fuels in the tree canopy. However, grass can grow under white leadtrees, whereas it does not grow well under native forest cover. Dense grass under the white leadtree canopy may increase the quantity and continuity of fine surface fuels; these changes have potential to increase fire spread and continuity.
Information on the distribution of white leadtree is insufficient for determining the specific plant community types that may be invaded and describing their historical fire regimes.
Response of white leadtree to fire:
Managers have observed white leadtree sprouting after top-kill by fire.
Control of white leadtree:
In Florida, managers have controlled white leadtree by burning it, then applying herbicide. Attempts to kill it with fire alone or herbicide alone have failed.
|Common name||Scientific name|
|Beyrich threeawn||Aristida beyrichiana|
|common bamboo||Bambusa vulgaris|
|creeping bluestem||Schizachyrium scoparium var. stoloniferum|
|Natal grass||Melinis repens (Rhynchelytrum repens)*|
|okra (ochro)||Abelmoschus esculentus|
|white leadtree||Leucaena leucocephala|
|*Names in parentheses are from the sources cited.|
1. Bradley, Keith; Gann, George D. 1999. The status of exotic plants in the preserves of southern Florida. In: Jones, David T.; Gamble, Brandon W., eds. Florida's garden of good and evil: Proceedings of the 1998 joint symposium of the Florida Exotic Pest Plant Council and the Florida Native Plant Society; 1998 June 3-7; Palm Beach Gardens, FL. West Palm Beach, FL: South Florida Water Management District: 36-41. 
2. Florida and Caribbean Fire and Invasives Learning Network. 2011. Workshop: Information gathering on invasive species. Notes from the 2nd meeting of the Florida and Caribbean Fire and Invasive Learning Network; 2009 December 8-10; Isla Verde, Carolina, Puerto Rico. Alamonte Springs, FL: The Nature Conservancy, Florida Chapter. [Smith, Jane Kapler, compiler]. Unpublished report on file with: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. 8 p. 
3. Gordon, Doria R.; Greenberg, Cathryn H.; Crownover, Stanley H.; Slapcinsky, Jodi L. 2005. Effects of unpaved road soil on persistence of three non-native grass species. Natural Areas Journal. 25(3): 257-262. 
4. Hann, Wendel; Havlina, Doug; Shlisky, Ayn; [and others]. 2010. Interagency fire regime condition class (FRCC) guidebook, [Online]. Version 3.0. In: (Frames Fire Research And Management Exchange System). National Interagency Fuels, Fire & Vegetation Technology Transfer (NIFTT) (Producer). Available: http://www.fire.org/niftt/released/FRCC_Guidebook_2010_final.pdf. 
5. LANDFIRE Rapid Assessment. 2005. Reference condition modeling manual (Version 2.1), [Online]. In: LANDFIRE. Cooperative Agreement 04-CA-11132543-189. Boulder, CO: The Nature Conservancy; U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior (Producers). 72 p. Available: http://www.landfire.gov/downloadfile.php?file=RA_Modeling_Manual_v2_1.pdf [2007, May 24]. 
6. LANDFIRE Rapid Assessment. 2007. Rapid assessment reference condition models, [Online]. In: LANDFIRE. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Lab; U.S. Geological Survey; The Nature Conservancy (Producers). Available: http://www.landfire.gov/models_EW.php [2008, April 18] 
7. MacDonald, Greg; Stokes, Courtney. 2009. Biology and management of natalgrass (Melinis repens) in Florida. Final Report. Gainesville, FL: University of Florida, Department of Agronomy. Unpublished report on file at: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Forestry Sciences Laboratory, Missoula, MT. 4 p. 
8. Possley, Jennifer; Maschinski, Joyce. 2006. Competitive effects of the invasive grass Rhynchelytrum repens (Willd.) C. E. Hubb. on pine rockland vegetation. Natural Areas Journal. 26(4): 391-395. 
9. Richardson, Steven G.; Bissett, Nancy; Knott, Cathy; Himel, Kate. 2003. Weed control and upland native plant establishment on phosphate mined lands in Florida. In: Cannizzaro, Patrick J., ed. Proceedings of the 30th annual conference on ecosystems restoration and creation; 2003 October; Plant City, FL. Tampa, FL: Hillsborough Community College: 126-138. 
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