Community composition of reserves and sites
A total of 36 taxa from 11 genera was found in the 23 225 individuals recorded in the sampled areas (Table 1), with most taxa present in all sampled areas. Taxa not recorded in the sampled area of a given reserve size class (Table 1) did not appear to be present in the unsampled portions of that reserve size class (A. Scariot, personal observation). Of the 36 taxa, 11 occurred in only some reserve sizes, but there was no tendency for the smaller forest fragments to be missing taxa relative to the larger reserves. Of these 11 taxa, only three, Astrocaryum acaule, Bactris killipii and Bactris oligocarpa, did not occur in 1-ha forest fragments. Five taxa, Attalea maripa, Bactris balanophora, Bactris sp2., Geonoma maxima var. chelidonura and Geonoma sp., were absent from 10-ha forest fragments, while seven taxa, Astrocaryum acaule, Attalea maripa, Bactris maraja var. maraja, Bactris oligocarpa, Geonoma sp., Geonoma stricta var. stricta and Lepidocaryum tenue, were not present in the 100-ha forest fragments. Five taxa, Astrocaryum acaule, Bactris maraja var. maraja, Bactris sp2, Bactris oligocarpa and Lepidocaryum tenue, did not occur in the continuous forest but they were represented by only 206 individuals (0.009% of the total number sampled) and occurred mainly in 1-ha (172 individuals) and 10-ha (33) forest fragments, being almost absent from the 100-ha (one) forest fragments. The natural history of these taxa is poorly known and without information on their life spans it is difficult to know if any of these taxa had had enough time to establish and reproduce in the fragments since isolation. Astrocaryum acaule and Bactris maraja var. maraja are secondary taxa that can occur in naturally disturbed patches of continuous forest (Henderson 1995), as also seems to be the case for Bactris sp2. Immature individuals were found for all three (one juvenile of Astrocaryum acaule, four seedlings of Bactris sp2 and two seedlings and seven juveniles of Bactris maraja var. maraja). Bactris oligocarpa, although being characteristic of lowland rain forest (Henderson 1995), was not found in the continuous forest and had all its four individuals (two adults and two seedlings across the three sites) in the 10-ha forest fragments. Either this taxon was in the fragments before isolation or it had had enough time to establish and reach maturity since isolation. Lepidocaryum tenue is the only invasive taxon, and all individuals (188 across all life stages) were restricted to the 1- and 10-ha fragments in Dimona.
Table 1. List of palm taxa (n = 36) occurring in plateaux in different reserve sizes and sites studied in central Amazonia. Presence of taxa are shown separately for reserve sizes and for sites. Taxa not occurring in continuous forests are either secondary (*), invasive (**) or of unclear status (***)
|Taxa||1 ha||10 ha||100 ha||Continuous forest||Esteio||Dimona||Porto Alegre|
|Astrocaryum acaule*|| ||x|| || || || ||x|
|Attalea maripa||x|| || ||x||x||x|| |
|Bactris acanthocarpa var. acanthocarpa||x||x||x||x||x||x||x|
|Bactris acanthocarpa var. intermedia||x||x||x||x||x||x||x|
|Bactris balanophora||x|| ||x||x|| ||x|| |
|Bactris hirta var. hirta||x||x||x||x||x||x||x|
|Bactris hirta var. pulchra||x||x||x||x||x||x||x|
|Bactris killipii|| ||x||x||x||x||x||x|
|Bactris maraja var. maraja*||x||x|| || ||x||x|| |
|Bactris oligocarpa***|| ||x|| || ||x||x||x|
|Bactris sp2*||x|| ||x|| || ||x||x|
|Bactris tomentosa var. tomentosa||x||x||x||x||x||x||x|
|Euterpe precatoria var. precatoria||x||x||x||x||x||x||x|
|Geonoma maxima var. chelidonura||x|| ||x||x||x||x||x|
|Geonoma maxima var. maxima||x||x||x||x||x||x||x|
|Geonoma maxima var. spixiana||x||x||x||x||x||x||x|
|Geonoma sp.||x|| || ||x||x|| ||x|
|Geonoma stricta var. stricta||x||x|| ||x||x||x|| |
|Lepidocaryum tenue**||x||x|| || || ||x|| |
|Oenocarpus bataua var. bataua||x||x||x||x||x||x||x|
Relatively few taxa (eight) were not found in all three sites (Table 1), and three were restricted to a single site. Bactris balanophora (five individuals) and Lepidocaryum tenue (188) were found only at Dimona, and Astrocaryum acaule (one individual) was found only at Porto Alegre. Although few taxa were restricted to a single site, none of the three sites included all of the 36 taxa observed in this study (Table 1).
Six palm taxa had subterranean trunks, 29 had aerial trunks and only one (Desmoncus phoenicocarpus) was a liana. There was no association between the number of taxa of each major habit (i.e. aerial or subterranean trunk) and reserve size (chi-square, d.f. = 3, P = 0.87) or site (chi-square, d.f. = 2, P = 0.89). Although most taxa had aerial trunks, only five (Attalea maripa, Euterpe precatoria var. precatoria, Oenocarpus bacaba, Oenocarpus bataua var. bataua and Socratea exorrhiza) were large arborescent taxa (up to 20 m tall). Six taxa were midstorey palms, reaching no more than 12–15 m tall: Astrocaryum gynacanthum, Bactris balanophora, Bactris constanciae, Iriartella setigera, Oenocarpus minor and Syagrus inajai. All other 25 taxa were confined to the understorey, which therefore dominated the composition of the community.
Most of the taxa–area curves reached an asymptote after sampling seven plots, indicating that data from 10 plots per reserve were enough to include all palm taxa (data not shown). Also, no taxon was found in the unsampled area of a reserve or site that had not been recorded in the sampled plots. Curves of the log abundance–taxa sequence were quite similar among sites and reserve sizes (Scariot 1996). The anovas performed on each life stage (in which the dependent variable is the slope of the cumulative taxa count regressed on the logarithm of the sampled area) revealed no significant differences among reserve sizes and among sites in terms of the slope of the curve (for seedlings, juveniles, adults and the total sampled, all values of F were between 0.008 and 2.6; P = 0.17–0.99). In all sites and reserves, the curves followed the log-normal taxa–abundance distribution that is characteristic of speciose communities (Preston 1962; May 1975), with very few highly abundant taxa and with most taxa occurring at low densities.