2012 SOUTHEASTERN NATURALIST 11(2):331–336 Growth of Serenoa repens Planted in a Former Agricultural Site Tammy E. Foster1,2, * and Paul A. Schmalzer1 Abstract - Serenoa repens (Saw Palmetto) is an important plant in many Florida habitats; not only does it provide food and shelter for numerous species, but it is also a highly flammable species that is fuel for fire in many of Florida’s fire-maintained ecosystems. With loss of natural area due to development and agriculture, restoration of highly degraded lands may become an increasing focus of land managers. Published literature indicates that Saw Palmetto is a slow-growing species, with stems growing only a few centimeters per year. However, these growth rates are for Saw Palmetto growing in natural systems. A 16-year planting study done at the Kennedy Space Center/Merritt Island National Wildlife Refuge shows that Saw Palmettos in a former citrus grove can have highly variable growth rates, often exceeding that in native habitats. Stem length varied from 0–166 cm and crown width ranged from 13–510 cm for Saw Palmettos planted 16 years earlier as 1-gallon-sized nursery stock. Individuals growing in dense Bahiagrass had much slower growth (stem length, height, and crown width) than individuals grown without Bahiagrass. Introduction Serenoa repens (W. Bartram) Small (Saw Palmetto) is an important component of many Florida habitats, and its inclusion in habitat restoration efforts may be necessary for success. However, the benefits of including Saw Palmetto in restoration projects may be overlooked because of its reputation as a slow-growing species. Understanding how Saw Palmetto grows when planted as part of a restoration project is important because of the large number of animal species that use Saw Palmetto and the importance of Saw Palmetto as fuel for wildland fire. Over 100 bird, 27 mammal, 25 amphibian, and 61 reptile species utilize Saw Palmetto for food or shelter (Maehr and Layne 1996), and a large number of insects have been found to visit Saw Palmetto (Carrington et al. 2003, Maehr and Layne 1996). Saw Palmettos’ highly flammable nature makes it an integral part of Florida’s fire-maintained landscape. Behm et al. (2004) found that Saw Palmetto contained the highest fine, coarse, and total fuel biomass as well as the greatest accumulated debris and total energy content of ten common Florida understory species, indicating it was one of the most flammable species in the study. Saw Palmetto is rarely killed by fire and the leafy crown rapidly recovers (Abrahamson 1984, Schmalzer 2003, Schmalzer and Hinkle 1992, Tanner et al. 1999). Saw Palmetto is considered a slow-growing, dwarf palm. The growth habit of Saw Palmetto is unusual for a palm: stems grow horizontally along the ground 1Innovative Health Applications, Mailcode IHA-300, Kennedy Space Center, fl32899. 2Department of Integrative Biology, University of South Florida, Tampa, fl33620. *Corresponding author - tammy.foster-1@nasa.gov. 332 Southeastern Naturalist Vol. 11, No. 2 with leaves (fronds) developing from the stem apex at, or close to, ground level, and the stems may branch so that there can be multiple growing points on a single plant. Growth of palmetto stems is minimal in natural settings, increasing in length only centimeters a year. Hilmon (1968) found that Saw Palmetto stem elongation averaged less than 3 cm/yr. Stem growth ranged from 0.6 cm/yr in scrubby flatwoods to 2.2 cm/yr in flatwoods on the Lake Wales Ridge in Florida (Abrahamson 1995). Tanner et al. (1999), reported Saw Palmetto stem growth ranged from 0.10 cm/yr in Georgia to 0.25 cm/yr in Florida. Abrahamson and Abrahamson (2009) found that after 19 years, seedlings of Saw Palmetto on the Lake Wales Ridge had gains in height growth of less than 0.5 cm/yr and in crown width of less than 0.3 cm/yr. Florida’s natural and semi-natural lands have decreased an estimated 13.3% (1.32 million ha) from the mid- to late 1980s to 2003 as the state’s human population increased from approximately 12.9 million to 17.4 million, and tourism reached an estimated 80 million visitors in 2004 (Kautz et al. 2007). One ecosystem that has been highly affected by development is Florida scrub (Myers 1990). With the large loss of natural area in Florida due to urbanization, attention is being directed to habitat restoration. Creation of habitat or restoration of highly degraded habitat may require planting of native species. Concern about the slow growth of palmetto in natural settings may dissuade managers from including Saw Palmetto in restoration efforts. However, a 16-year scrub restoration study conducted at Kennedy Space Center/Merritt Island National Wildlife Refuge (KSC/MINWR) provides long-term data on Saw Palmetto growth when planted on a disturbed site and shows the potential for more rapid growth. Methods In 1992, a scrub restoration project was initiated on an abandoned citrus grove on the northern part of KSC/MINWR (Schmalzer et al. 1994). To date, this is the only large-scale planting site on KSC/MINWR. This grove occurred on well-drained soils (Astatula and Paola series) associated with scrub and scrubby flatwoods in the region and is adjacent to extant scrub vegetation (Schmalzer et al. 2002). Some soil chemistry parameters differed between the grove and intact scrub, with the scrub having higher organic matter, available iron, exchangeable aluminum, and ammonium nitrogen and the grove having higher pH, nitrate-nitrogen, available copper, and available zinc (see Schmalzer et al. 2002 for a more detailed description of the site). The grove was abandoned after a freeze in 1987, and the trees were cleared and burned in 1988. In 1992, the grove was prepared for planting by removal of Sabal palmetto (Walter) Lodd. ex Schult. & Schult. f. (Cabbage Palm), mowing, and two applications of glyphosate herbicide. Seedlings of scrub oaks (Quercus chapmanni Sarg. [Chapman Oak], Q. geminata Small [Sand Live Oak], and Q. myrtifolia Willd. [Myrtle Oak]) were planted in 1992. In July and August 1993, additional scrub oaks were planted along with several other scrub species including five hundred 2012 T.E. Foster and P.A. Schmalzer 333 1-gallon–pot-sized Saw Palmettos. All plant material was grown by a native nursery (The Natives, Lakeland, FL). Although data on the planted material are not available, the standard 1-gallon-pot Saw Palmetto from this nursery would usually be about 3 years old from seed. The plants would have received a slowrelease fertilizer when potted to 1 gallon (Nancy Bissett, The Natives Lakeland, FL, pers. comm.). There was no further treatment to the site after planting. Thirty-four Saw Palmettos were selected randomly for annual monitoring. Height and survival data were collected annually through 2009. Ten 15-m long line-intercept transects were established in the planting site to follow changes in community composition over time. Results After planting, there was no mortality until 1995 when 4 plants died, and an additional 9 plants died by the 1996 sampling. Plant mortality was most likely the result of Sus scrofa L. (Feral Pig) rooting on the developing stems (Schmalzer et al. 2002). No mortality occurred among monitored Saw Palmettos since 1996. In 2009, 16 years after planting, we measured crown width, crown height, stem number, and length of the longest stem on the 21 surviving marked Saw Palmettos because field observations indicated large differences in size among planted palmettos. Crown width was measured along the longest axis between leaves crossing through the origin of the plant, leaves could be on different horizontal stems (Fig. 1). Crown height was the distance from the ground to the top of the tallest leaf (Fig. 1). Stem length was measured from the beginning of the stem (the point of origin of the plant) to the apical meristem. Our objective was to examine the variability in growth of Saw Palmettos planted in this scrub restoration project. In 2009 height ranged almost tenfold; whereas, the ranges for crown width, stem number, and stem length far exceeded a tenfold difference (Table 1). As Saw Palmetto height increased, so did crown width and stem length (Fig. 2). Height, Figure 1. Photos of Saw Palmetto in the restoration site displaying variable size of Saw Palmetto. Left: individual growing without Bahiagrass; height 260 cm, width 493 cm, 11 stems with the longest stem 137 cm. Right: individual growing in dense Bahiagrass; height 57 cm, width 62 cm, and 1 stem. 334 Southeastern Naturalist Vol. 11, No. 2 therefore, may serve as a good indicator of overall plant size. Height of Saw Palmetto continued to increase over the entire course of the study (Fig. 3). Initially, height was similar between all planted Saw Palmettos (x̅ = 19.5 cm, sd = 5.7 cm, n = 34) but diverged as time since planting increased (Table 1). Variability of the stem length was high (Table 1); several of the planted Saw Palmettos far exceeded the mean length, with one palmetto having a stem of 166 cm; however, three plants had stems that had not grown in 16 years. Two distinct groups of Saw Palmetto (Figs. 1 and 3) are separated by a sand road in the former citrus grove. The area north and south of the sand road are similar in physical properties; they are at similar elevation, and soil characteristics do not differ. Most individuals south of the sand road have grown in the presence of Paspalum notatum Flugge (Bahiagrass), whereas north of the sand Table 1. Variability of Saw Palmetto parameters sampled in December 2009 (n = 21). Saw Palmettos were planted in 1993 as 1-gallon-size plants in an abandoned citrus grove. Range Mean (sd) Height 32–285 cm 157.0 cm (67.5) Crown width 13–510 cm 268.0 cm (147.6) Stem # 1–16 7.0 (3.6) Stem length 0–166 cm 50.8 cm (45.5) Figure 2. Crown width and stem length as a function of height for the surviving Saw Palmettos in 2009 (n = 21). Regressions were forced to fit to the origin. Crown width: R2 = 0.974, P < 0.001; rhizome length: R2 = 0.857, P < 0.001. 2012 T.E. Foster and P.A. Schmalzer 335 road plants grew with minimal exotic grass cover. Percent composition data from the line transects show that although the Bahiagrass cover was minimal directly after herbicide treatment, Bahiagrass cover was approximately 50.0% in the section south of the sand road within three years after planting, while no Bahiagrass was found on vegetation transects north of the sand road at that time. The height of plants south of the sand road was significantly lower (ANCOVA: P < 0.001, F1,17 = 63.6) than the height of plants north of the sand road (Fig. 3); crown width, stem number, and stem length were also significantly lower for individuals south of the sand road. Presence of Bahiagrass resulted in slower growth of Saw Palmetto most likely due to competition. Discussion These results suggest that Saw Palmetto should not be excluded from restoration efforts based on low growth rates observed in natural settings. We found that Saw Palmetto growth in a restoration site can be rapid under certain conditions, often exceeding published values. These results indicate the need for understanding how Saw Palmetto growth varies in restoration sites compared to intact habitats and the effect of competition on Saw Palmetto growth in these sites. Restoration efforts may regain some ecosystem functions, particularly the maintenance of the fire regime, if Saw Palmetto restoration is successful. Figure 3. Height growth of Saw Palmettos north (n = 14) and south (n = 7) of the sand road (ANCOVA: P < 0.001). The site has burned several times, and short-duration decreases in plant height (e.g., 80 months) were due to recent burn activity. 336 Southeastern Naturalist Vol. 11, No. 2 Literature Cited Abrahamson, W.G. 1984. Species responses to fire on the Florida Lake Wales Ridge. Amer. J. Bot. 71:35–43. Abrahamson, W.G. 1995. Habitat distribution and competitive neighborhoods of two Florida palmettos. 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Saw-palmetto: An ecologically and economically important native palm. Circular WEC-109, University of Florida Cooperative Extension Service Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL.