Holdridge Life Zone System Research Articles

Seed Size as a Correlate of Temporal and Spatial Patterns of Seed Fall in a Neotropical Forest

Seed fall in a Brazilian subtropical lower montane, moist forest was measured over a year using 120 traps that had a total collecting surface of 174 M2. Twenty-two thousand seeds from 227 plant species were collected. Wind-dispersed species released seeds mainly during the late dry season and early wet season. Among nonwind-dispersed species, large-seeded species matured seeds primarily during the wet season. Small-seeded species were much less seasonal. This difference in seasonality may stem from a correlation between seed size and mode of animal dispersal. Arrival probability per collection period, approximated as the percentage of traps hit by free seeds of each species, was regressed against several independent variables. For nonwind-dispersed species, the logarithm of seed area best predicted arrival probability of free seeds, being inversely related to it. Existence of this inverse relationship has often been supposed but only now demonstrated. THE REPRODUCTIVE BIOLOGY of any seed-plant population is believed to reflect evolutionary compromise among various conflicting aspects of reproduction (Harper et al. 1970, Stebbins 1971). Of these, seed size is fundamental because it apparently influences many other aspects of reproduction. This paper examines relationships in a tropical forest between seed size and two other reproductive parameters: the temporal and spatial extent of seed fall. Numerous workers have assumed that small seeds are more widely dispersed than large ones (e.g., Harper et al. 1970), yet substantial data to test this idea have been lacking. Because of the great temporal and spatial spans over which seed dispersal occurs, the dispersal process at the community level is likely to remain intractable to direct study. Instead of attempting to measure dispersal, I measured arrival probabilities of free seeds at fixed locations. Arrival probability is clearly a crucial component of dispersibility. Seed size has also been hypothesized to influence the temporal pattern of seed fall in tropical forests. Smythe (1970) reported fruiting of largeseeded species in a Panamanian forest to be synchronous, whereas small-seeded species were less seasonal in fruiting time. I sought to determine whether such temporal patterns occur in another neotropical forest. STUDY SITE AND METHODS The study was conducted in a virgin evergreen forest at 800-900 m elevation in Reserva Biologica Nova Lombardia, Municipio de Santa Tereza, Espirito Santo, Brazil, at latitude 19? 53' S. The site is surrounded by several square kilometers of old-growth forest, although some agricultural clearings exist less than 2 km away. Jackson (1978) provides climatic data for the site. Reserva Nova Lombardia experiences a moderate temperature differential between winter (June-August) and summer (December-February) and a long but not severe dry season (April-September). In the Holdridge Life Zone System (Holdridge 1967) the vegetation is classified as Subtropical Lower Montane Moist Forest. As measured by frequency along line transects, the commonest trees are Manilkara elata (Sapotaceae), Lucumza laurifolia (Sapotaceae), Campomazesia warmingiana (Myrtaceae), Guarea petiolulata (Meliaceae), Emimotuni zitens (Icacinaceae), Didymnopanax longipetiolatuxm (Araliaceae), Nectandra puberula (Lauraceae), Psidiuni macrospermnuni (Myrtaceae), Ocotea declinata (Lauraceae), Andira stipulacea (Leguminosae), Clusia grandiflora (Guttiferae), Terminalia ijanuariensis (Combretaceae), Leandra alpestris (Melastomaceae), Sideroxylon gardnerianum (Sapotaceae), Cybianzthus cunieifolius (Myrsinaceae), Ocotea nmacropoda (Lauraceae), Copaifera langsdorffi (Leguminosae), and Ficus doliaria (Guttiferae) (A. Ruschi, pers. comm.). Falling seeds and fruits were sampled with 120 horizontally placed rectangles of green, plastic window screen. Each corner of a screen was secured with plastic cord to a vertical bamboo stake at one meter above the ground. Screens measured 1.4x1.2 m when flat (area 1.68 Mi2), but trap sag reduced the average collecting surface per trap to 1.44 m2?. The mesh in the screen was 1.2 mm square. The seed traps were set in two straight lines approximately 200 m apart. Sixty traps comprised each transect, with 6 m between adjacent traps. One transect began at midslope on a hill (836 m elevaBIOTROPICA 13(2): 121-13

Seasonality of Flowering and Leaf-Fall in a Brazilian Subtropical Lower Montane Moist Forest

In a lower montane moist forest of southeastern Brazil, leaf-fall was maximal (1.8-2.9 g/m2/day) during the period of greatest precipitation and high temperatures. Through most of the dry season leaf-fall was low (0.4-0.9 g/m2/day) although an increase occurred in the late dry season (1.1-1.4 g/m2/day). Number of species in flower per 10-day period was maximal (30-50) at the end of the dry season and the beginning of the wet season. Flowering was minimal during the middle and late wet season (8-22) and was moderate during the early and middle dry season (14-30). The seasonality of flowering is similar to the community-wide pattern typical of tropical forests, but the occurrence of the leaf-fall maximum during the wet season is unusual. It is suggested that, where benign climates permit, overlap of leaf generations not only provides continuous photosynthetic income but may allow energetic savings in the transfer of material from old to new leaves by obviating storage costs. To AID IN THE UNDERSTANDING of seasonality patterns in tropical plant communities that is emerging (Janzen 1967, Croat 1969, Foster 1973, Burger 1974, Frankie et al. 1974), this report provides data on flowering and leaf-fall from Reserva Biologica Nova Lombardia, Municipio de Santa Tereza, Espirito Santo, Brazil (fig. 1). Reserva Nova Loimbardia lies at latitude 19? 53' S and ranges in elevation from 700-1000 m. The altitude within the actual study area varies between 810-890 m. The following climatic data for Reserva Nova Lombardia were extracted from Ruschi (1950): mean annual biotemperature 170 C; mean annual total precipitation -1566 mm; mean annual evaporation -455 mm. From the temperature and precipitation data the vegetation is classified in the Holdridge Life Zone System (Holdridge 1967) as Subtropical Lower Montane Moist Forest. The mean annual biotemperature is exactly at the division between the Lower Montane and Premontane altitudinal belts, but because light frosts occasionally occur at the study area, and during the winter the temperature sometimes approximates 3-5? C for up to 48 hours, Lower Montane is the more appropriate characterization. Observations indicate that the vegetation is near the Moist-Wet transition rather than being typical Moist Forest. Temperatures are markedly lower during the dry season; thus moisture stress on the plants is less than in a more equatorial location with equivalent rainfall. Second, considerable cloudiness and fog are generated over Reserva Nova Lombardia as the southeast trade winds coming off the Atlantic Ocean strike the mountains a few score kilometers inland. Epiphytes, especially brormeliads, are abundant, much more so than in lowland Moist Forest of my acquaintance in Central America.