Plant Community Structure, Fire Disturbance, and Recovery in ...

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26 Contributions to the Study of Biological Diversity Vol. 3 Figure 1.17. Location of the Roystonea oleracea community on the Waini Peninsula, within the approximate area of the elevated central zone of the peninsula that became known as APalm Hill.@ The initial excursion to the site was made on 8 April 2001 (Palm Sunday). location of the population strongly suggested that it was not likely planted by people. - The Riverine Mangrove Swamps The swamps that line the tidal Waini River are inundated twice daily with brackish river water, since there are no barriers to tides similar to the beach ridges isolating many Coastal Mangrove swamps. That allows comparatively unimpeded dispersal of mangrove propagules in this zone, which may be partly responsible for the dominance of Rhizophora racemosa G. Mey., which fringes the Waini River and extends inland on the soft, muddy substrate to the tidal limit. That species is very similar to R. mangle in vegetative appearance, having similar conspicuous prop and aerial roots and indistinguishable leaves and bark. It differs distinctively from R. mangle in having 30 to 60 flowers per inflorescence, as compared to 2 to 3 for Rhizophora mangle; in having buds with obtuse apices as opposed to buds with acute apices in Rhizophora mangle; and in having propagules with much longer hypocotyls extending from the viviparous fruits, up to 50 cm. in length as opposed to hypocotyls up to 20 cm in length in Rhizophora mangle (Gray 1981). Rhizophora racemosa trees tend to have more aerial roots extending from higher branches to the water’s surface. Those two Rhizophora species have been considered by some to form the hybrid Rhizophora x harrisonii Leechm., which has been ascribed to similar brackish riverine habitats and is supposedly intermediate between the two species in reproductive morphology (Gray 1981; Tomlinson 1986). In practice, it was difficult to distinguish that putative hybrid from R. racemosa, and some specialists consider it to be synonymous with R. racemosa (Duke et al. 2001). In several descriptions of riverine mangroves in the Guianas, R. racemosa has been unmentioned, with only the name R. mangle used, although that is almost certainly inaccurate. The Riverine Mangrove swamp understory was, in places, moderately dense with Rhizophora saplings and Acrostichum aureum ferns (Figure 1.18). The non-native mangrove palm Nypa fruticans Wurmb. was also common in the Riverine Mangrove swamp, sometimes Figure 1.18. Riverine Mangrove forest dominated by Rhizophora racemosa. Some Nypa fruticans palms were in the understory (center background) and some fronds of the mangrove fern Acrostichum are visible in the foreground. in dense patches along river margins and often as an occasional component of the understory. Upriver, around 59° 30' W, Nypa was no longer present. At that point Rhizophora trees were also infrequent along the river margin, although they were observed as far up the Waini River as its confluence with the Barama River, and were seen occasionally on the Baramanni River. Along some segments of the Waini River the roots of Rhizophora racemosa were found covered with the red alga Bostrichia and occasionally with barnacles. Farther up the river, where the water became less brackish, freshwater swamp tree species including Pterocarpus, Mora Benth., Machaerium Pers., Inga Mill., Euterpe and Pachira Aubl. were
increasingly common along the banks. Contributions to the Study of Biological Diversity Vol. 3 Burned Areas The manual delineation using the Landsat red band (3) included 27.4 km 2 of burned vegetation at Almond Beach and 28.8 km 2 of burned vegetation at the Kamwatta (Figure 1.19). The major result of the fires detected in band 3 was apparently bare soil, which reflected Figure 1.19. Manual delineation of burned areas using Landsat ETM + band 3, red. red portions of the spectrum and appeared as light areas of the image. Using Landsat band 4 (near infrared), the manual delineation included 26.5 km 2 of burned vegetation at Almond Beach and 22.6 km 2 of burned vegetation at the Kamwatta site (Figure 1.20). That band was useful for detecting vegetation (high reflectance) and open water (low reflectance). The burned area totals were calculated by a union of the red Figure 1.20. Manual delineation of burned areas using Landsat ETM + band 4, near infrared. 27 and near infrared band results. The intersection of the total burns with the plant communities classifications provided areas of each community that were impacted. Totals burned areas for each plant community type and locality are given in Table 1.1. It was estimated that 34.5 km 2 of the forests in the Almond Beach area were burned, and 30.5 km 2 of the forests in the Kamwatta area were burned, for a total of 64.6 km 2 of burned forest for the entire area of interest on the Waini Peninsula (Figure 1.21). Areas of burns detected with each of the two Landsat bands are listed by locality in Table 1.2. Figure 1.21. Combined areas of manual delineations of burns using the red and infrared bands from the December 3 1999 Landsat ETM + image. The total burned area was measured as 64.58 km 2 . Table 1.2. Manual burn delineation results by burn area and bands 3 (Red) and 4 (Near Infrared), for the Landsat ETM + image of 3 December 1999. Band / area IR Almond Beach IR Kamwatta RED Almond Beach RED Kamwatta km 2 26.4 21.9 27.4 28.7 The fires left large areas with few surviving mangrove trees to supply propagules for regeneration. After that large-scale disturbance, limitations on dispersal would likely retard recolonization by some species. Species that are wind or animal dispersed might be favored over those dependent on water dispersal. Additionally, variations of soil salinity levels
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130 Ipomoea violacea L. Merremia ci
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138 Guatteria flexilis R.E. Fr. Gua
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142 Diospyros tetrandra Hiern Elaeo
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144 Aniba hostmanniana (Nees) Mez A
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148 Rhizophora racemosa G. Mey. Con
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150 Turneraceae Turnera scabra Mill
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158 Asplundia glandulosa (Gleason)
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160 Bellucia grossularioides (L.) T
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162 Psychotria wessels-boeri Steyer
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164 Celastraceae Elaeodendron xyloc
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