Stephen H. Bullock

Phenology of canopy trees of a tropical deciduous forest in México.

Our study focuses on a site of very low rainfall but exceptionally high diversity of woody plants, and describes events at the ecosystem, community, and population levels. We attempt to lead to some understanding of functions and consequences; to evaluate the generality of community patterns proposed from strudied at other sites; and, to make specific hypotheses and background available to other disciplines

Floristic diversity and structure of upland and arroyo forests of coastal Jalisco

The species richness at Chamela, Jalisco (average annual rainfall 748 mm, with a 4-month wet season), exceeded that of other Neotropical dry forests with more than twice its annual rainfall. Transect samples totaling 0.3 ha included 176 species and 1352 plants -2.5 cm DBH. The mean number of species per 100-m2 transect was 22.7. Upland and arroyo sites were similar in species number, but the latter included greater percentages of species of vines (11% vs 21%) and trees 10 cm DBH (24% vs 31%). The only species that were both common and ubiquitous were Trichilia trifolia, Caesalpinia eriostachys, and Cordia alliodora. Upland sites were typified by species of Croton, Lonchocarpus, and Cordia, and arroyo sites were typified by Thouinidium decandrum and a variety of vines. Families with the most species were Leguminosae, Euphorbiaceae, Rubiaceae, and Bignoniaceae. Total basal area averaged 0.24 m2/100 m2 in uplands but 0.52 m2/100 m2 in arroyos; most of the difference was due to trees -30 cm DBH. In all sites, over 50 percent of the stems were < 5 cm DBH, but vines and large trees were more abundant in arroyos. Stem densities averaged about 45/100 m2 in both sites.

Breeding systems in the flora of a tropical deciduous forest in Mexico

Floral sexuality was characterized for most of the flora (708 species) of a forest reserve at Chamela, Jalisco, and compatibility was determined for a sample of hermaphroditic species. Nine types of floral sexuality were found; the frequency of these types was related to life form and systematics. Monostylous hermaphroditism was typical of epiphytes (96%) and herbs (82%) but less so among vines (68%), shrubs (62%), and trees (54%). Dioecy increased across these groups (4%, 1%, 10%, 14%, and 24%, respectively). Monoecy was concentrated in Euphorbiaceae and Cucurbitaceae; Boraginaceae and Rubiaceae predominated among the few distylous species. Contrasting vegetation types had similar frequencies of sexuality types. Compatibility tests showed reduced fruiting from selfcompared to cross-pollination in 94 percent of 33 species from 14 families, and 76 percent were considered self-incompatible. Intraspecific variation was not salient, but in some cases congeners were notably divergent.

Climate of Chamela, Jalisco, and trends in the south coastal region of Mexico

SummaryThe warm, seasonally dry climate of Mexicos south coast is represented by data from the biological station at Chamela, Jalisco, and is compared with 26 other localities. The mean annual temperature was 24.9 °C; monthly mean maximums were equitable (29.1° to 32.0°) but minimums showed significant seasonal changes (14.8° to 22.9°). Local winds were strongest in the late dry season. Most cyclonic features moved parallel to the coast. Hurricanes made landfall much more frequently along some parts of the coast than others. The average annual precipitation was 748 mm, with a coefficient of variation of 16% for eight years. Rainfall was measurable on an average of 53 days per year, but the seven heaviest rains contributed over 50%.of the total; 80% of the total fell between 2 July and 4 November. Occasionally, there was substantial rain in December or January. For unsheltered lowland localities, rainfall increased with elevation, as did length of the wet season. Longer-term records (40 and more years) from four localities showed significant oscillations in precipitation that were correlated between sites.ZusammenfassungDas warme, jahreszeitlich trockene Klima der mexikanischen Küste wird anhand der Daten der biologischen Station Chamela (Jalisco) untersucht und mit 26 anderen Stationen verglichen. Das Jahresmittel der Temperatur betrug 24,9 °C, die mittleren Monatsmaxima schwankten geringfügig zwischen 29,1 und 32,0 °C, die mittleren Monatsminima dagegen stark zwischen 14,8 und 22,9 °C. Die lokalen Windsysteme entwickelten sich am besten am Ende der Trockenzeit. Die meisten Zyklonen zogen entlang der Küste, tropische Wirbelstürme drangen bevorzugt an bestimmten Küstenstreifen ins Landesinnere vor. Die Jahressumme des Niederschlags betrug 748 mm, mit einer 16%-Schwankung in acht Jahren. Meßbarer Niederschlag fiel an 53 Tagen im Jahr, mehr als 50% des Gesamtniederschlags stammte jedoch von den 7 stärksten Ereignissen. 80% der Jahressumme wurden zwischen 2. Juli und 4. November gemessen. Gelegentlich trat starker Niederschlag im Dezember oder Januar auf. Für nicht abgeschirmte Gebiete erhöhte sich der Gesamtniederschlag und die Dauer der Regenzeit mit der Seehöhe. Längere Zeitreihen (mindestens 40 Jahre) in vier Regionen zeigten bedeutende Schwankungen des Niederschlags, wobei die Stationen miteinander korreliert waren.

Demography of an undergrowth palm in littoral Cameroon.

This study of Podococcus barteri in Cameroon, equatorial West Africa, shows that the longevity of this small palm is in the range of 63-74 years. Seasonality is more pronounced in flowering than in leaf production. Adults produce one leaf per year, each lasting about five years in the crown. Proliferation by stolons begins many years before flowering. The leafy stolons may grow two-eight or more years before establishing the ramets. Inflorescence development, flowering, and seed maturation take about 1.4 years. Only 0.08 percent of the ovules become mature seeds. A stage projection matrix gives the annual population growth rate as 1.2 percent. The growth index X is more sensitive to changes in mortality of juveniles and young adults than of seeds-seedlings, mature-old adults, or stolons. Mortality at several stages of sexual reproduction and the size advantage of ramets account for the greater importance of cloning to population dynamics, although the relative energetics have not been assessed. IN LOWLAND WET FORESTS, the occasional disruption of the deep-shade and sunfleck environment by falling trees results in luxuriant growth of many species. Tree-fall gaps have been considered the main organizing feature of population and community dynamics (Aubreville 1938, Jones 1956, Whitmore 1975, Hartshorn 1978). The pattern of spatial and size distributions of many species reflects the focus of their establishment and/or maturation in gaps, but other species do not conform (e.g., Richards and Williamson 1975). The comparatively sparse plant cover of the long-enduring, abysmal gloom of the floor of mature forest has been largely ignored even in vegetation studies, and the growth and reproductive behavior of this flora is virtually unknown despite its accessibility. Palms are a particularly abundant part of this lower stratum, and convenient to study as their geometric simplicity much facilitates observation and analysis of their behavior. Even for relatively longlived species, demographic projections can be made from short-term observations (Hnatiuk 1977, Van Valen 1975 based largely on Bannister 1970). In contrast to the diversity of small palms in Malayan and American forests (Whitmore 1973, Moore 1973a), there are only two species in mature forest undergrowth in Africa. Podococcus barteri is occasionally common in the littoral region of Cameroon, growing in clusters often of 10-4 or 10-3 ha, with stem densities up to seven per m2. The habit, distribution, growth, and reproduction of Podococcus will be described here, with the purpose of assessing seasonality, the time scales relevant to individual life history, the stability of the population (of plant modules, not genets), and its sensitivity to disturbance of existing growth, reproduction, and mortality schedules. Demographic treatment of long-lived woody plants lags far behind that of herbs (Harper 1977), and is of particular interest for Podococcus as a species of the mature phase of lowland forest, and one which both clones and produces seed.

Comparative Experimental Study of Seed Dispersal on Animals

Studies of the plants Achyranthes aspera, Bidens sp. and Petiveria alliacea establish examples of seed attachment and detachment on dispersal surfaces that occur continuously during movement of a dispersal agent. In uniform one—species stands, dynamic saturation points for the dispersal surfaces were demonstrated. A parameter termed the retention rate (R) was determined for each species in various habitats, and was used to calculate mean distances of dispersal. Within and around established populations of Achyranthes, for example, the mean dispersal distance ranged from 2.4km, showing that settlement is selective and depends on the structure of existing vegetation. This relationship is also affected by the vertical distribution of seeds on the disperser. See full-text article at JSTOR

Episodic Flowering and Sexual Dimorphism in Guarea Rhopalocarpa in a Costa Rican Rain Forest

Two years of intensive phenological observations of Guarea rhopalocarpa showed that a population of this dioecious species flowered and fruited several times per year, in discrete episodes at irregular intervals. The percentage of participating trees differed between episodes by a factor of 3, but the total numbers of male and female inflorescences and fruit differed more among episodes (38x, 11 x, and 77x, respectively). The patterns of relative fecundity among episodes were different between sexes. Nearly all males flowered at least twice per year, while nearly all females flowered at least once; the tendencies to additional flowerings were similar. Males flowered more abundantly than females and often showed oscillations in fecundity between episodes. In females, fruiting in one episode clearly diminished the probability of fruiting in the next. Fruit-set was not linearly related to flowering effort. Fecundity in both sexes was poorly explained by trunk size. The sex ratio among adults was not significantly different from unity, and the sexes were similar in trunk size distribution and growth rates. The phenological patterns, fecundity, and dimorphism are consid- ered in relation to pollination, energetics, and sexual selection.

Population structure and reproduction in the neotropical dioecious tree Compsoneura sprucei

SummaryIn rain forest study plots, the sexes of Compsoneura sprucei (Myristicaceae) were radomly distributed and similar in vegetative dimensions. The sex ratio among adults was estimated as 1.25 male: female. The population showed two flowering episodes per year, of unequal intensity. Sexual dimorphisms in order of increasing difference included the frequency of flowering, the number of flowers per inflorescence and the number of inflorescences per tree. Most females matured only 0–10 seeds per tree per flowering episode. Tree size was a better indicator of fecundity in males than females. Reproduction in both sexes was dominated by a very few prolific trees.

Wind Pollination of Neotropical Dioecious Trees

Anemophily may be frequent in neotropical dioecious trees, of diverse taxonomic affinity, as shown here for 19 species in 13 families at one locality, on the basis of floral morphology and pollen presentation. Flower-visiting bees often are not pollinators but commensal or parasitic. The perceived scarcity of anemophily in tropical trees is brought into question by a reconsideration of the evidence regarding pollen type, nectar, weather, insect visitors, and tree density

Carbon Isotope Ratios of Plants of a Tropical Dry Forest in Mexico

Carbon isotope ratios were measured on leaves of the dominant species within a tropical dry forest in Mexico, which was characterized as being strongly drought deciduous. A variety of succulent epiphytes from diverse microsites had carbon isotope ratios indicating obligate crassulacean acid metabolism. All woody species examined had isotope ratios indicative of the C3 photosynthetic pathway, although there was a wide range of isotopic values. Two of the woody species that retained leaves during the dry season showed a large variation in carbon isotope ratios (up to 6 %o) that was dependent on microsite location. Key-words: Epiphytes, isotope ratios, crassulacean acid metabolism, water-use-efficiency, succulents