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Are mangroves in the tropical Atlantic ripe for invasion? Exotic mangrove trees in the forests of South Florida

Methods

Abstract
Introduction
>Methods
Results
Discussion
Acknowledgments
References
Tables and Figures
Surveys at The Kampong, site of B. gymnorrhiza introduction

Between May 2008 and May 2009, we made approximately monthly visits to The Kampong (ca. 25.7147°N, 80.2495°W) in order to assess stand structure and flowering phenology in the mangrove stand where B. gymnorrhiza had been planted in 1940. All stems of B. gymnorrhiza (trees, saplings) were tagged with unique numbers and mapped (Smith 2004; Ward et al. 2006). However, because of the large area, native Florida mangroves (A. germinans, Laguncularia racemosa and R. mangle) were mapped only around the area of the densest B. gymnorrhiza stand. The resultant plot was 21 x 21 m in size (441 m2). A central position in the stand was determined and marked. The distance and bearing to all mangrove stems over 1.5 m in height was measured from that position. Stems were identified and measured for diameter at breast height (dbh, at ~ 1.5 m). Seedlings of B. gymnorrhiza (i.e. those individuals < 1.5 m) were also mapped. However, because of their high densities, native mangrove seedlings were not mapped. Random plots were established (n = 6) and seedlings of all species were counted within a 1 m radius of the plot's center (plot area = 3.14 m2). On May 13, June 16, August 1 and October 16, 2008, we assessed flowering/ fruiting status of subsamples of the tagged B. gymnorrhiza individuals.

In August 2008, we arbitrarily sampled 33 individuals from the B. gymnorrhiza population at The Kampong in order to determine the level of genetic diversity of the population. We collected two unexpanded young leaves still enclosed in the stipule from a terminal branch of each tree. These leaves were preserved in silica gel and stored at 4°C prior to DNA extraction.

Surveys of non-native mangroves at Fairchild Tropical Botanic Garden

We queried the plant records database at FTBG (ca. 25.6770°N, 80.2730°W) to determine the identity and planting dates of non-native mangrove tree species. We then conducted surveys to locate these individuals and determine if they had reproduced. Lumnitzera racemosa had spread; the area supporting individuals of this species was found to be quite extensive. We used Garmin GPS 60 units and ESRI ArcMap 9.3 to map the extent of the invasion. Twelve plots were sampled in the wetlands swale in and north of FTBG and extending into Matheson Hammock, a property managed by the Miami-Dade County Parks Department. The plots varied in size depending on densities of Lumnitzera racemosa encountered and ranged from 20 to 30 m2. All stems were identified to species and their dbh at ~ 1.4 m measured. The densest stands of Lumnitzera racemosa occurred in relatively narrow bands along shorelines or adjacent to mosquito control ditches; this precluded stem mapping. Because of the extent of the spread of this species and the proximity to other mangrove stands, an immediate eradication effort was begun.

Forest structure data analyses

The dbh data were used to construct size-frequency diagrams for all native and non-native mangrove species in the study. At both sites the data are on an areal basis (# ha-1). Differences in density of mangrove seedlings among mangrove species from The Kampong were analyzed as a simple one factor ANOVA.

Molecular genetic analysis of B. gymnorrhiza from The Kampong

Genomic DNA was extracted using a FastPrep FP120 tissue disrupter (Thermo Electron Corporation) and FastDNA spin kit (QBIOgene). Ten microsatellite regions previously designed for B. gymnorrhiza (Islam et al. 2006) were amplified via the polymerase chain reaction. PCR reactions were carried out in 25 µl volumes with ~ 50 ng genomic DNA, 2 mM MgCl2, each dNTP at 10 mM, 19 Promega GoTaq flexi buffer B, 0.75 units Promega Taq, and 1 µmole of each primer. PCR conditions included an initial denaturation step at 95°C for 5 min, and 36 cycles at 95°C for 30 s, 55°C for 45 s, and 72°C for 1 min. Microsatellite PCR products analyzed on an ABI Prism 3130 Genetic Analyzer using POP4 polymer, and fragment sizes were analyzed with GeneScan 3.7 or GeneMapper4 software (Applied Biosystems).

The data were analyzed using the programs GENALEX6 (Peakall and Smouse 2006) and GENEPOP 3.4 (Raymond and Rousset 1995) to test for Hardy-Weinberg equilibrium, to calculate observed and expected heterozygosities, and to characterize allele patterns.


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