And Dynamics of Vegetation Islands

The nurse plant syndrome is effective when plant species shelter seedlings, young and/or adult individuals of other species through their ontogeny (Dias and Scarano 2007). In the restingas nurse plants are pioneers on the bare sand, and they comprise some small palms (e.g. Allagoptera arenaria; Fig. 8.2A) and bromeliads (e.g. Aechmea nudicaulis; Fig. 8.2B) but most importantly the shrubs of Clusia species, especially C. hilariana which is the dominant plant in the restingas of Rio de Janeiro (Sampaio et al. 2005). Therefore, restingas have also been called Clusia scrubs (Ule 1901). Characteristically nurse plants of the restingas are often terrestrial forms

Fig. 8.2A, B Establishment of new vegetation islands by nurse plants? A Allagoptera arenaria, the wind drawing circles on the sand by moving the leaves around (dry restinga of Massambaba, see Fig. 8.1). B Aechmea nudicaulis (foreground centre), Allagoptera arenaria (foreground left), dune forest (background) (intermediate restinga of Jurubatiba Park, see Fig. 8.1)

Fig. 8.2A, B Establishment of new vegetation islands by nurse plants? A Allagoptera arenaria, the wind drawing circles on the sand by moving the leaves around (dry restinga of Massambaba, see Fig. 8.1). B Aechmea nudicaulis (foreground centre), Allagoptera arenaria (foreground left), dune forest (background) (intermediate restinga of Jurubatiba Park, see Fig. 8.1)

of typical epiphytes of the neighbouring Atlantic rain forest possibly pre-adapted to stress related to missing or limited supplies of water and nutrients from a pe-dosphere (Scarano 2002). Many of them perform crassulacean acid metabolism (CAM), which is a biochemical adaptation of photosynthesis to stress due to high insolation and partially problematic supply of water (Sect. 5.2.2.2), i.e. bromeli-ads and Clusias including C. hilariana (Reinert et al. 1997; Scarano 2002; Lüttge 2007a,b).

Underneath the canopy of C. hilariana a higher species richness was found than under any other woody species (Zaluar 1997; Sampaio et al. 2005; Dias et al. 2005, 2007). The higher density and richness under scrubs of C. hilariana is mainly due to effects on seed dispersers and activation of dispersal (Dias et al. 2007). Aechmea nudicaulis does not germinate and grow seedlings on the open sand, among other reasons probably due to the high temperatures reached on the bare sand. It only germinates within vegetation islands. Via directional growth of rhizomes and ramets, however, it then acquires space and selects its own habitats (Fig. 8.2B; Sampaio et al. 2004, 2005; Dias et al. 2005). Conversely, however, it is not only C. hilar-iana scrub that nurses A. nudicaulis. The Clusia may germinate inside the tanks of the bromeliad and is nursed itself (Dias and Scarano 2007). These reciprocal interactions between different nurse plants generating vegetation islands underline the non-linear dynamics of the spatiotemporal patchiness (see also Sects. 3.3.1, 3.3.3 and 8.2.2) of the restinga ecosystem.

8.1.3 Ecophysiology of Photosynthesis of Restinga Plants

The performance of the special mode of photosynthesis CAM is quite frequent among the plants of the restingas with many species of bromeliads, orchids, cacti and Clusia. Comparative ecophysiological studies have been performed of various shrubs which are much determining the physiognomy of the restingas (Figs. 8.1A, 8.2B) such as the Clusiaceae Rheedia brasiliensis, Calophyllum brasiliense, Clusia hilariana and Clusia fluminensis, the Myrsinaceae Myrsine parviflora and the Fabaceae Andira legalis (Duarte et al. 2005; GeBler et al. 2005; Scarano et al. 2005b). Restingas where these plants were investigated show a moisture gradient dependent on annual rainfall, the ground water table and the degree of ground-water salinity. Table 8.1 summarizes some relations of maximum apparent rates of photosynthesis (ETRmax) deduced from measurements of instant light response curves (Sect. 4.1.7) to such moisture gradients, where intrinsic photosynthetic capacity given by ETRmax increases in three of the species shown at the drier sites and shows a decrease or no response in a fourth species (A. legalis).

Table 8.1 Maximum apparent rates of photosynthetic electron transport ETRmax (|imolm-2s-1) obtained from light curve measurements of four restinga shrubs along a moisture gradient. Within vertical columns different letters at the numbers indicate statistically significant differences. (Data from Duarte et al. 2005; GeBler et al. 2005; Scarano et al. 2005b)

Table 8.1 Maximum apparent rates of photosynthetic electron transport ETRmax (|imolm-2s-1) obtained from light curve measurements of four restinga shrubs along a moisture gradient. Within vertical columns different letters at the numbers indicate statistically significant differences. (Data from Duarte et al. 2005; GeBler et al. 2005; Scarano et al. 2005b)

Vegetation type

Myrsine parviflora

Rheedia brasiliensis

Clusia fluminensis

Andira legalis

Swamp forest at an intermediate restinga

63a

136a

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