Baseline Alligator Nesting Data in Arthur R. Marshall Loxahatchee National Wildlife Refuge to Inform Monitoring

Monitoring key ecological attributes helps land managers understand the current state of the resource and decide if management action is necessary. Baseline data on spatial and temporal variability of attributes to be monitored is important for development of successful monitoring programs. In this study, I collected data from 2000 to 2004 on American alligator Alligator mississippiensis nesting in the Arthur R. Marshall Loxahatchee National Wildlife Refuge to determine feasibility of conducting alligator nest surveys and collect baseline data on alligator nesting status and variability. I used nest data to provide examples of potential monitoring strategies for tracking trends over time or understanding the effects of different hydrologic conditions on alligator nesting. Conducting ground surveys with airboats in Arthur R. Marshall Loxahatchee National Wildlife Refuge proved to be an effective method of finding alligator nests. Number of nests per 1.6 km × 1.6 km (256-ha) plot ranged from 1 to 12, and by year from 28 to 53. Overall, average number of nests per hour ranged from 1.8 ± 0.26 (SE) in 2000 to a low of 0.84 ± 0.08 in 2004. Using data from this study for the six plots sampled each year, and assuming no change in variability, power analysis shows that 10 y of sampling would allow for detection of an annual 10% change in number of nests per hour, with power and level of certainty set equal at 90% (β and α both 0.10). Additionally, 15 y of data would allow for a detection of a 5% change per year. Thirty-seven plots per area would be necessary to assess a 40% difference in number of alligator nests per hour in areas with different hydrologic conditions with power and level of certainty at 90%. Land managers can use these data and analyses, along with examples of monitoring strategies, to guide development of more specific monitoring protocols that address restoration objectives and management actions throughout the Florida Everglades.

Repeated Herbicide Application for Control of Old World Climbing Fern (Lygodium microphyllum) and the Effects on Nontarget Vegetation on Everglade Tree Islands

The effects of annual, aerial and ground, herbicide treatments with glyphosate and metsulfuron were evaluated for control of Old World climbing fern (OWCF) and effects on native plants on tree islands in Arthur R. Marshall Loxahatchee National Wildlife Refuge during 2006 to 2009. Initial aerial herbicide treatments reduced OWCF cover by greater than 98% on metsulfuron-treated islands and greater than 88% on glyphosate-treated islands, but there was a concomitant decrease in native ground cover with both herbicides. Follow-up ground treatments, during years two and three of the study, were effective at maintaining low levels of OWCF. OWCF cover at the end of the study was 1 to 2% of pretreatment cover on metsulfuron-treated islands and 8 to 10% on glyphosate-treated islands. At the end of the study (3 yr after treatment), species richness was dominated by ruderal native species not typically found on tree islands. The survival rate of tree and shrubs was 65 to 93% on islands treated with metsulfuron and 6 to 20% on islands treated with glyphosate. Minimum effects were recorded for canopy cover on tree islands treated with metsulfuron compared with glyphosate. These data indicate that the aerial application of metsulfuron can be used for control of OWCF on tree islands. Follow-up ground treatments will be required for OWCF regrowth and new sporelings and should be conducted within 1 yr of the aerial application.

Recruitment and Growth of Old World Climbing Fern in Hurricane-Caused Canopy Gaps

Following 2 y of severe hurricanes in 2004 and 2005, we examined the role of canopy gaps in promoting recruitment and growth of the exotic fern, Old World climbing fern Lygodium microphyllum (hereafter Lygodium), on tree islands of the Arthur R. Marshall Loxahatchee National Wildlife Refuge, Florida. We selected 12 sample tree islands, on which we placed three 1-m2 plots in a hurricane-caused canopy gap and three plots in an adjacent closed canopy area. Spore traps were placed in canopy gaps and closed canopy areas to quantify the number of spores reaching the forest floor on each island. In addition, in each plot occurrence and growth of Lygodium was measured across four height classes (recruitment class, understory, midstory, and canopy). We predicted that recruitment and growth of Lygodium would be higher in canopy gaps than in closed canopy areas. After 3 y of biannual monitoring, a significantly greater number of spores were foundin canopy gaps (4,804 spores·m2·d) than in closed canopy areas (4,288 spores·m2·d). Furthermore, we observed significantly greater recruitment and growth in canopy gaps compared with closed canopy areas in the recruitment class only. Presence of recruitment-class Lygodium in canopy gaps increased from four to five treatment areas and decreased from 1 to 0 treatment areas in closed canopy areas. These results suggest differences in recruitment and growth of Lygodium between canopy gaps and closed canopy areas on tree islands after severe hurricanes. However, despite the large number of spores in both canopy gaps and closed canopy areas, recruitment and growth were much lower than expected, with only two treatment areas having an average percent cover greater than 10% in any height class. If conducted within several years after a hurricane, focused monitoring efforts on hurricane-impacted tree islands may allow managers to detect and treat new infestations before they are able to overrun tree islands.