Tree Phenology in Adjacent Amazonian Flooded and Unflooded Forests1

Most phenological studies to date have taken place in upland forest above the maximum flood level of nearby streams and rivers. In this paper, we examine the phenological patterns of tree assemblages in a large Amazonian forest landscape, including both upland (terra firme) and seasonally flooded (várzea and igapó) forest. The abundance of vegetative and reproductive phenophases was very seasonal in all forests types. Both types of flooded forest were more deciduous than terra firme, shedding most of their leaves during the inundation period. Pulses of new leaves occurred mainly during the dry season in terra firme, whereas those in the two floodplain forests were largely restricted to the end of the inundation period. Flowering was concentrated in the dry season in all forest types and was strongly correlated with the decrease in rainfall. The two floodplain forests concentrated their fruiting peaks during the inundation period, whereas trees in terra firme tended to bear fruits at the onset of the wet season. The results suggest that the phenological patterns of all forest types are largely predictable and that the regular and prolonged seasonal flood pulse is a major determinant of phenological patterns in várzea and igapó, whereas rainfall and solar irradiance appear to be important in terra firme. The three forest types provide a mosaic of food resources that has important implications for the conservation and maintenance of wide‐ranging frugivore populations in Amazonian forests.     

Seasonal Patterns of Flowering and Fruiting in a Dry Tropical Forest in Jamaica1

Tropical dry forests occupy more area and are more endangered than rainforests, yet their regeneration ecology has received less study and is consequently poorly understood. We recorded the flowering and fruiting phenology of a tropical dry forest in Jamaica over a period of 26 mo within ten 15 × 15‐m plots. Community‐wide recruitment reached a maximum in the wet season, whereas no recruitment occurred during the dry season. We observed a unimodal peak in rainfall and fruit production, and the periodicity and intensity of seed production were significantly correlated with rainfall seasonality (the optimal time for germination). Flowering at the community and system levels lagged behind a significant increase and subsequent decrease in rainfall by 7 and 3 mo, respectively, indicating that the dominant factor controlling flowering periodicity is the passage of the major (4‐mo long) rainy season and changes in soil moisture conditions. Fruiting lagged behind flowering by 2 mo and a significant increase in fruiting occurred 2 mo prior to a significant increase in rainfall. At the population level, a correspondence analysis identified a major dichotomy in the patterns of flowering and fruiting between species and indicated two broad species groups based on their time of peak fruiting and the number of times they were in fruit. These were either individuals which were usually in peak fruit 1–2 mo prior to the start of the major rainy season or those that were in fruit more or less continuously throughout the year with no peak fruiting time. This study supports the view that seasonal variation in rainfall and hence soil water availability constitutes both the proximate and the ultimate cause of flowering periodicity in tropical dry forests.     

Seed Dispersal Spectrum of Woody Species in South Ecuadorian Dry Forests: Environmental Correlates and the Effect of Considering Species Abundance

This study examines the seed dispersal spectrum of the tropical dry forests of Southern Ecuador, in an effort to contribute to the knowledge of the complex dynamics of tropical dry forests. Seed dispersal spectrum was described for a total number of 160 species. Relationships of dispersal syndromes with plant growth form and climatic seasonality were explored. For a subset of 97 species, we determined whether dispersal spectrum changes when species abundance, in addition to species number, is taken into account. The same subset was used to relate dispersal syndromes with the environmental conditions. Zoochorous species dominated in the studied community. When considering the individual abundance of each species, however, anemochory was the prevalent dispersal syndrome. We found a significant difference in the frequency of dispersal syndromes among plant growth forms, with epizoochory only occurring in shrub species. The dispersal spectrum was dependent on climatic seasonality. The largest proportion of anemochorous species fructified during the dry season, while zoochorous diaspores dominated during the rainy season. A fourth‐corner analysis indicated that the seed dispersal spectrum of Southern Ecuador dry forests is controlled by environmental conditions such as annual precipitation, annual temperature range or topography. Our results suggest that spatio‐temporal changes in the environmental conditions may affect important ecological processes for dispersal. Thus, the predominance of one syndrome or another may depend on the spatial variation of environmental conditions. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Research Priorities for Neotropical Dry Forests1

Our understanding of the human and biophysical dimensions of tropical dry forest change and its cumulative effects is still in the early stages of academic discovery. The papers in this special section on Neotropical dry forests cover a wide range of sites and problems ranging from the use of multispectral and hyperspectral remote sensing platforms to the impact of hurricanes on tropical dry forest regeneration. Here, we present to the scientific community the results of a workshop on which research priorities for tropical dry forests were discussed. This discussion focuses on the need to develop linkages between remote sensing, ecological, and social science research. The incorporation of social sciences into ecological research could contribute dramatically to our understandings of tropical dry forests by providing important contextual information to ecologists, and by helping to develop an important science–policy–public nexus on which environmental management can succeed.     

The Impact of Annual and Seasonal Rainfall Patterns on Growth and Phenology of Emergent Tree Species in Southeastern Amazonia,Brazil

Understanding tree growth in response to rainfall distribution is critical to predicting forest and species population responses to climate change. We investigated inter‐annual and seasonal variation in stem diameter by three emergent tree species in a seasonally dry tropical forest in southeast Pará, Brazil. Annual diameter growth rates by Swietenia macrophylla demonstrated strong positive correlation with annual rainfall totals during 1997–2009; Hymenaea courbaril growth rates demonstrated weak positive correlation, whereas Parkia pendula exhibited weak negative correlation. For both Swietenia and Hymenaea, annual diameter growth rates correlated positively and significantly with rainfall totals during the first 6 mo of the growing year (July to December). Vernier dendrometer bands monitored at 4‐wk intervals during 3–5 yr confirmed strong seasonal effects on stem diameter expansion. Individuals of all three species expanded in unison during wet season months and were static or even contracted during dry season months. Stems of the deciduous Swietenia contracted as crowns were shed during the early dry season, expanded slightly as new crowns were flushed, and then contracted further during 3–5 wk flowering periods in the late dry season by newly mature crowns. The three species’ physiographic distribution patterns at the study site may partially underlie observed differences in annual and seasonal growth. With most global circulation models predicting conditions becoming gradually drier in southeast Amazonia over the coming decades, species such as Swietenia that perform best on the ‘wet end’ of current conditions may experience reduced growth rates. However, population viability will not necessarily be threatened if life history and ecophysiological responses to changing conditions are compensatory.     

Disparity in Onset Timing and Frequency of Flowering and Fruiting Events in Two Bornean Peat‐Swamp Forests

The timing and frequency of flowering and fruiting events are key tropical forest characteristics that have substantial influence on fauna. Although our understanding of geographic variation in habitat‐wide timing and frequency of flowering and fruiting is advancing, corresponding information for individual tree species is limited. Thus, we compared climate and reproductive phenology of 16 tree species over 70 mo at two Bornean tropical peat‐swamp forest sites. We found significant inter‐site correlations in rainfall and temperature, and only small absolute temperature differences. In both sites, most species exhibited within‐site synchrony in flowering and fruiting onset. Broad‐scale flowering and fruiting onset frequency classifications showed high congruence between sites. Significant correlations in flowering and fruiting onset timing between sites were found for only 19 and 17 percent of the species, respectively. This remained the case when applying 1‐ and 2‐month lag periods for both sites, with neither site consistently lagging behind. Significant differences in the exact frequency of new flowering and fruiting events were detected for 44 and 58 percent of species, respectively, and no significant relationships between the onset timing synchrony and exact frequency of new reproductive events were found for either flowers or fruit. We conclude that inter‐site climatic and ecological similarities do not necessarily lead to high inter‐site synchrony in either onset timing or exact frequency of tree reproductive events. Potential reasons for this are discussed, as are the implications for understanding tropical forest ecology and improving forest restoration project seed collections.     

Deforestation Trends of Tropical Dry Forests in Central Brazil

Tropical dry forests are the most threatened forest type in the world yet a paucity of research about them stymies development of appropriate conservation actions. The Paranã River Basin has the most significant dry forest formations in the Cerrado biome of central Brazil and is threatened by intense land conversion to pastures and agriculture. We examined changes in Paranã River Basin deforestation rates and fragmentation across three time intervals that covered 31 yr using Landsat imagery. Our results indicated a 66.3 percent decrease in forest extent between 1977 and 2008, with an annual rate of forest cover change of 3.5 percent. Landscape metrics further indicated severe forest loss and fragmentation, resulting in an increase in the number of fragments and reduction in patch sizes. Forest fragments in flatlands have virtually disappeared and the only significant forest remnants are mostly found over limestone outcrops in the eastern part of the basin. If current patterns persist, we project that these forests will likely disappear within 25 yr. These patterns may be reversed with creation of protected areas and involvement of local people to preserve small fragments that can be managed for restoration.     

Effects of Season and Successional Stage on Leaf Area Index and Spectral Vegetation Indices in Three Mesoamerican Tropical Dry Forests1

We compared plant area index (PAI) and canopy openness for different successional stages in three tropical dry forest sites: Chamela, Mexico; Santa Rosa, Costa Rica; and Palo Verde, Costa Rica, in the wet and dry seasons. We also compared leaf area index (LAI) for the Costa Rican sites during the wet and dry seasons. In addition, we examined differences in canopy structure to ascertain the most influential factors on PAI/LAI. Subsequently, we explored relationships between spectral vegetation indices derived from Landsat 7 ETM+ satellite imagery and PAI/LAI to create maps of PAI/LAI for the wet season for the three sites. Specific forest structure characteristics with the greatest influence on PAI/LAI varied among the sites and were linked to climatic differences. The differences in PAI/LAI and canopy openness among the sites were explained by both the past land‐use history and forest management practices. For all sites, the best‐fit regression model between the spectral vegetation indices and PAI/LAI was a Lorentzian Cumulative Function. Overall, this study aimed to further research linkages between PAI/LAI and remotely sensed data while exploring unique challenges posed by this ecosystem.     

Litter Nutrient Dynamics During Succession in Dry Tropical Forests of the Yucatan: Regional and Seasonal Effects

Land-use change in the tropics is creating secondary forest at an unprecedented rate. In the tropical Americas, mature dry tropical forest is rapidly being converted to secondary forest during the fallow period of shifting cultivation. We investigated litter phosphorus (P) and nitrogen (N) dynamics in forests recovering from shifting cultivation of maize (corn) in three regions of the Southern Yucatan Peninsula, Mexico. Our goal was to understand how nutrient and water availability affect forest recovery following conversion of mature forest to agricultural land. To investigate such changes at a regional scale, newly fallen litter was collected monthly along a seasonal, a successional, and a precipitation gradient. Reflecting possible P limitation, litter P concentration declined with forest age, while litter N concentration did not differ between age classes. Average litter P concentration from the southern, wettest region was 0.87 mg/g, almost twice the litter P concentration in the drier central and northern regions (0.44 and 0.45 mg/g, respectively). Average N concentrations of litter from the three regions ranged from 1.1% to 1.2%, with no regional differences. However, minima in both P and N concentration from all regions were pronouncedly timed with peak litterfall, suggesting nutrient retranslocation during periods of water stress. Additionally, successional differences in litter P were clearest during wetter months. P nutrient-use efficiency was lowest in the southern region and highest in the central and northern study regions. N nutrient-use efficiency was up to 40 times lower than P nutrient-use efficiency and showed no regional differences. Overall, our results suggest that litter nutrient dynamics in secondary dry tropical forests of the Southern Yucatan are strongly influenced by water and nutrient availability, especially P, as well as land-use history.     

Seedling Establishment of a Canopy Tree Species in Malaysian Tropical Rain Forests

Abstract Unlike many other canopy tree species in tropical rain forests, Dryobalanops aromatica (Dipterocar-paceae, local name: Kapur) establishes monospecific dominant (monodominant) forests in Peninsular Malaysia. In natural conditions, monodominance of Kapur does not necessarily mean low species diversity of the Kapur forests. While the emergent canopy layer is occupied by Kapur, many other plant species, which are common to lowland dipterocarp primary forests in the same region, are found in lower canopy layer and understory.
To understand the ecological implications of the monodominance of Kapur, we monitored post dispersal survival and seedling establishment in a pure stand of Kapur in a plantation in Kepong, near Kuala Lumpur. Immediately after seed fall, seeds and cotyledon-stage seedlings suffered high predation by vertebrates such as rodents. The predation pressure was higher in a more general fruiting year (1991) than in a sporadic fruiting year (1992). In contrast to the high mortality of seeds and newly emerged seedlings, seedlings surviving to the six-leaf stage showed low mortality, which allowed the establishment of a sapling bank.
The occurrence of saplings of Kapur with a wide range of size classes in natural forests indicates that this species is more shade tolerant than other dipterocarp species such as the Shorea group and that it could well respond to enhanced light conditions caused by canopy opening. These characteristics may partly contribute to maintaining monodominance of Kapur.     

Mating Systems of Three Tropical Dry Forest Tree Species1

Polymorphic allozyme loci were used to estimate outcrossing rates for three tree species from a disturbed dry forest in southern Costa Rica. Estimates of the multilocus outcrossing rates of Cedrela odorata and Jacaranda copaia were 0.969 and 0.982, respectively, and suggest that these species may be self-incompatible. The subcanopy tree Stemmadenia donnell-smithii also demonstrated little self-fertilization based on an estimated outcrossing rate of 0.896. Significant heterogeneity in pollen allele frequencies among maternal trees was detected for at least two enzyme loci for each species. A test of correlated mating between progeny of S. donnell-smithii revealed that all seeds within a fruit were singly sired. In addition, the low estimates of biparental inbreeding and significant differences in pollen and ovule allele frequencies for this species suggest that gene flow into the sampled forest fragment may occur. The implications of deforestation on the mating systems of these tropical tree taxa are discussed.     

Seedling Traits Determine Drought Tolerance of Tropical Tree Species

Water availability is the most important factor determining tree species distribution in the tropics, but the underlying mechanisms are still not clear. In this study, we compared functional traits of 38 tropical tree species from dry and moist forest, and quantified their ability to survive drought in a dry‐down experiment in which wilting and survival were monitored. We evaluated how seedling traits affect drought survival, and how drought survival determines species distribution along the rainfall gradient. Dry forest species tended to have compound leaves, high stem dry matter content (stem dry mass/fresh mass), and low leaf area ratio, suggesting that reduction of transpiration and avoidance of xylem cavitation are important for their success. Three functional groups were identified based on the seedling traits: (1) drought avoiders with a deciduous leaf habitat and taproots; (2) drought resisters with tough tissues (i.e., a high dry matter content); and (3) light‐demanding moist forest species with a large belowground foraging capacity. Dry forest species had a longer drought survival time (62 d) than moist forest species (25 d). Deciduousness explained 69 percent of interspecific variation in drought survival. Among evergreen species, stem density explained 20 percent of the drought survival. Drought survival was not related to species distribution along the rainfall gradient, because it was mainly determined by deciduousness, and species with deciduous seedlings are found in both dry and moist forests. Among evergreen species, drought survival explained 28 percent of the variation in species position along the rainfall gradient. This suggests that, apart from drought tolerance, other factors such as history, dispersal limitation, shade tolerance, and fire shape species distribution patterns along the rainfall gradient.     

Phenology of a northern hardwood forest canopy

While commonplace in other parts of the world, long‐term and ongoing observations of the phenology of native tree species are rare in North America. We use 14 years of field survey data from the Hubbard Brook Experimental Forest to fit simple models of canopy phenology for three northern hardwood species, sugar maple (Acer saccharum), American beech (Fagus grandifolia), and yellow birch (Betula alleghaniensis). These models are then run with historical meteorological data to investigate potential climate change effects on phenology. Development and senescence are quantified using an index that ranges from 0 (dormant, no leaves) to 4 (full, green canopy). Sugar maple is the first species to leaf out in the spring, whereas American beech is the last species to drop its leaves in the fall. Across an elevational range from 250 to 825 m ASL, the onset of spring is delayed by 2.7±0.4 days for every 100 m increase in elevation, which is in reasonable agreement with Hopkin's law. More than 90% of the variation in spring canopy development, and just slightly less than 90% of the variation in autumn canopy senescence, is accounted for by a logistic model based on accumulated degree‐days. However, degree‐day based models fit to Hubbard Brook data appear to overestimate the rate at which spring development occurs at the more southerly Harvard Forest. Autumn senescence at the Harvard Forest can be predicted with reasonable accuracy in sugar maple but not American beech. Retrospective modeling using five decades (1957–2004) of Hubbard Brook daily mean temperature data suggests significant trends (P≤0.05) towards an earlier spring (e.g. sugar maple, rate of change=0.18 days earlier/yr), consistent with other studies documenting measurable climate change effects on the onset of spring in both North America and Europe. Our results also suggest that green canopy duration has increased by about 10 days (e.g. sugar maple, rate of change=0.21 days longer/yr) over the period of study.     

Phenology and Pollination Ecology of Three Brazilian Fig Species (Moraceae)

The phenology and pollination ecology of three native fig species were studied in southeastern Brazil. Populations displayed continual syconia production, with one species showing intra-tree flowering asynchrony. Pollination of the fig flowers was necessary for the development of the syconia; lack of pollination induced abortion of syconia. All three species follow the general pattern of pollination known for figs, but the behavior of the pollinator wasps, Pegoscapus spp., differed in some aspects from those of other neotropical and paleotropical fig wasps, mainly with respect to pollen loading and unloading during pollination. The longevity of Pegoscapus wasps outside the syconium was about two days.     

Tree fruiting phenology in Kalinzu Forest, Uganda

The spatial and temporal variations in species composition and abundance of trees that fruited in mechanically logged, intensively pit‐sawn and essentially undisturbed forest areas in Kalinzu Forest (0°17′S, 0°30′S and 30°00′, 30°07′E) were assessed. The duration and frequency of fruiting episodes of selected pioneer, understorey and canopy tree species were also determined. These phenology aspects were monitored for 18 months (between February 1997 and July 1998) in 99 plots, each 20 m × 20 m in size. Eighty species consisting of 1489 trees fruited during the study. Most of the species were recorded in the undisturbed forest area and least in the mechanically logged areas. Monthly number of individuals and species that fruited in each forest condition were significantly related to monthly rainfall. Two pioneer species (Musanga leo‐errerae and Trema orientalis), one sub‐canopy (Funtumia africana) and canopy (Parinari excelsa) species had extended fruiting phases (>5 months). Two understorey species (Oxyancius speciosus and Tabernaemontana spp.) had an extended phase while the third (Teclea nobilis) had a short (≤5 months) fruiting phase. Of the selected species, only Strombosia scheffleri (a sub‐canopy species) and P. excelsa had more than one fruiting episode.     

Regional‐Scale Variation in Litter Production and Seasonality in Tropical Dry Forests of Southern Mexico1

Highly seasonal rainfall creates a pulse of litterfall in the southern Yucatan peninsula region, with cascading effects on the timing of essential nutrient fluxes, microbial dynamics, and vegetation growth. I investigated whether forest age or a regional environmental gradient related to rainfall has a greater effect on patterns of litterfall in this increasingly human‐dominated landscape. Litterfall was sampled in 10–13 stands in each of three locations spanning a rainfall gradient of ca 900–1400 mm/yr. Litter was collected monthly from November 1998 through January 2000 in mature forests and in secondary forests aged 2–25 yr. Despite a substantial precipitation gradient, age was the only significant predictor of annual litter mass. Two‐ to five‐yr‐old forests produced significantly less litter than 12–25‐yr‐old secondary forests (4.6 vs. 6.2 Mg/ha/yr), but the difference between older secondary forests and mature forests (9 percent) was not significant. Litter production increased with rainfall, but not significantly so. The pattern of litterfall was similar across locations and age classes, with a peak during late March or early April. However, litterfall seasonality was most pronounced in the old secondary and mature forests. Litterfall was more evenly distributed throughout the year in forests under 10 yr old. Seasonality of litterfall was also less pronounced at the wettest site, with less disparity between peak litterfall and off‐peak months. Seasonality was not related to soil texture. Forest age and rainfall are important drivers of litterfall dynamics; however, both litter mass and degree of seasonality depended more strongly on forest age. Thus, the impact of land‐use change on litter nutrient cycling is as great, if not greater, than the constraint imposed by the major natural environmental factor affecting tropical dry forests.