Cross-scale determinants of palm species distribution

Abstract

We investigate palm species distribution, richness and abundance along the Mokoti, a seasonally-dry river of southeastern Amazon and compare it to the patterns observed at a large scale, comprising the entire Brazilian territory. A total of 694 palms belonging to 10 species were sampled at the Mokoti River basin. Although the species showed diverse distribution patterns, we found that local palm abundance, richness and tree basal area were significantly higher from the hills to the bottomlands of the study region, revealing a positive association of these measures with moisture. The analyses at the larger spatial scale also showed a strong influence of vapor pressure (a measure of moisture content of the air, in turn modulated by temperature) and seasonality in temperature: the richest regions were those where temperature and humidity were simultaneously high, and which also presented a lower degree of seasonality in temperature. These results indicate that the distribution of palms seems to be strongly associated with climatic variables, supporting the idea that, by 'putting all the eggs in one basket' (a consequence of survival depending on the preservation of a single irreplaceable bud), palms have become vulnerable to extreme environmental conditions. Hence, their distribution is concentrated in those tropical and sub-tropical regions with constant conditions of (mild to high) temperature and moisture all year round. KEY-WORDSAmazon, diversity, moisture, palms, tropical forests. Determinantes meta-espaciais da distribuição de palmeiras RESUMO Investigamos a distribuição, riqueza e abundância de espécies de palmeiras ao longo do Rio

Palm community transitions along a topographic gradient from floodplain to terra firme in the eastern Amazon

“…Indeed, the difference in altitude measured by Scariot et al (1989) in the Tocantins valley was also substantially shorter than the difference that we found in the 51 st BIS forest. The palm E. oleracea was rare in the study by Kahn (1987), and was not found in the other studied site southward in the Xingu basin (Salm et al 2007), where it is replaced by Euterpe precatoria.…”

“…Attalea phalerata, the next species in our rank of association was not documented in any of the three other nearest study sites (Kahn 1987;Scariot et al 1989;Salm et al 2007), despite its wide distribution in the southern limits of the Amazon (Henderson et al 1995). It is very abundant in the Pantanal-Matogrossense, the world's largest floodplain, where it occurs in both alluvial and periodically flooded soils, and islands of woody vegetation a few meters above the floodable areas (Henderson et al 1995).…”

“…Unfortunately, descriptions of palm communities are extremely patchy in the Amazon (Balslev et al 2010) in relation to species ranges. For that reason, the results of this study may only be compared to one other palm community study made on the Xingu river basin 500 km south (Salm et al 2007), and to two other studies that are geographically closest: one is 300 km to the east (Kahn 1987) and the other is 350 km southeast (Scariot et al 1989). Both are in the Tocantins River basin.…”

“…The palms were identified in the field with the assistance of the guide "Flora Brasileira -Arecaceae (Palmeiras)", and its nomenclature were used accordingly (Lorenzi et al 2010). Due to the morphological diversity of palms, arbitrary criteria were used to assign individuals of different species to an adult class, following methodology applied by Salm et al (2007). First, among those species that develop a subterranean stem (a stem that emerges to the surface at its approximated adult size diameter, like Attalea maripa or Astrocaryum aculeatum), the individual palms with an external and visible stem or with signs of present or past reproductive activity were considered adults.…”

“…Since then, few other studies also described such phenomena across Amazonian sites: in streams near Manaus (Kahn and Castro 1985), in the Tocantins River valley (Kahn 1987;Scariot et al 1989) in upper Urucu river (Peres 1994), and in the middle Xingu (Salm et al 2007).…”