Seed rain and advanced regeneration in a tropical rain forest

By comparing seed rain, seedling and sapling community structures we assessed the possible role played by vertebrate seed dispersal as a structuring factor in advanced regeneration of closed-canopied sites in the tropical rain forest of Los Tuxtlas, Mexico. Seed weight, initial morphology of seedlings and species abundance were also analyzed to determine if these traits influenced the probability of establishment in the shade.About half of the seed species falling in five closed forest sites (25×25 m) during one year came from fruiting trees growing within the sites (local seeds) and half from fruiting trees found outside the sites (immigrant seeds). Seeds of liana and upper-canopy species were over-represented among immigrant seeds compared with seeds of understory tree species. This probably reflects the activity of frugivorous arboreal mammals, bats, and birds. Species with immigrant seeds had both a lower abundance and a narrower spatial distribution than locally produced seeds. Therefore, immigrant seeds showed higher diversity values than locally produced seeds.Average seed size and the proportion of epigeous seedlings were similar in local and immigrant species. Under closed-canopied sites, factors affecting community organization seem to operate selectively, favoring the establishment of large-seeded, local abundant species in the advanced regeneration. However, the fact that some saplings of immigrant species were found in the plots suggest that a slow species infiltration may be occurring leading to a slow shift in the advanced regeneration species composition. We propose that the influence of seed dispersal on advanced regeneration structure depends on the disturbance history of the patches where seeds land.     

Flowering,fruiting and seed germination in Chilean rain forest myrtaceae: ecological and phylogenetic constraints

Phenological studies in plant communities have generally focused on taxonomically heterogeneous species assemblages, and have only occasionally examined the evolutionary and ecological constraints on the phenological patterns of species within a single family or a genus. Here, we determine relative importance of phylogenetic versus other constraints on the flowering and fruiting periods of 12 species and the germination ecology of 10 species of Myrtaceae sympatric to the temperate rainforest of Isla Grande de Chiloé (42 °Cs 30 S), in southern Chile.We found that, for most species in the family Myrtaceae, flowering was strongly aggregated in January and February. Although this pattern is consistent with the expectation of the 'facilitation' hypothesis (i.e., interspecific overlaps are maximized to attract pollinators), available evidence suggests that pollinators, mainly hymenopterans and dipterans, do not limit fruit production in these species of Myrtaceae in the temperate rainforest. In contrast to flowering, fruiting occurred all-year-round, showing greater segregation in time among the species. According to the their temporal patterns of fruit ripening, two functional groups were defined within the Myrtaceae: those that ripen their fruits immediately after flowering (species in the subtribe Myrtinae) and those in which green fruit develops slowly for several months before ripening (subtribe Myrciinae). Seed germination in the field occurred mainly between August and October. Lab assays showed that the species of Myrtaceae, subtribe Myrtinae, exhibited a long seed dormancy (>40 days), while the seeds of species in the subtribe Myrciinae often germinated within one week after harvesting. The analysis of the phenology of reproductive events in the species of Myrtaceae in this rainforest suggests that: (1) flowering periods patterns are constrained mainly by phylogenetic inertia at the family level, and (2) differences in fruiting patterns and dormancy periods are determined mainly by fruit and seed size, which in turn are associated primarily with phylogenetic closeness within the family, and secondarily with the activity of vertebrate seed dispersers.     

Ecology of seed germination of eight non-pioneer tree species from a tropical seasonal rain forest in southwest China

We compared various aspects of the seed biology of eight non-pioneer tree species from a tropical seasonal rain forest in Xishuangbanna, SW China, that differ in time of dispersal, size and fresh seed moisture content (MC). Seeds were tested for germination under laboratory conditions after dehydration to different moisture levels and under 3.5, 10 and 30% solar irradiances in neutral-shade houses. For six species, germination was also compared in forest understory (3.5% light) and center of a forest gap (32.5% light). Under continuous dehydration over activated silica gel, 100% of seeds of four species had lost the ability to germinate after 48 h, and those of all species except Castanopsis hystrix (decreased from >90 to 30% germination) had lost the ability to germinate after 120 h. Four species did not differ in final germination percentages at the three irradiances (i.e. uniform germination). However, final germination percentages of Horsfieldia pandurifolia and Litsea pierrei var. szemaois were significantly lower in 30% than in 10 or 3.5% light, and seeds of Antiaris toxicaria and C. hystrix germinated to higher percentages in 30 and 10% than in 3.5% light. Mean time to germination (MTG) of the eight species (forest and shade house data combined) ranged from 5–5 days for Pometia tomentosa to 72–207days for L. pierrei; MTG for four species was ≤21 days. There was no obvious relationship between relative desiccation resistance and either time of dispersal, MTG or uniformity of germination at the three light levels, or between seed size and MC or MTG. However, the relationship between seed MC at maturity (25–60% fresh mass basis) and MC at 50% loss of seed viability (12.4–42.5%) was significant. Seven of the species fit Garwood’s (Ecol Monogr 53:159–181, 1983) rapid-rainy germination syndrome and one, L. pierrei, either her delayed-rainy or intermediate-dry germination syndrome. However, fresh, non-dehydrated seeds of all eight species germinated in ≤30 days at constant 30°C in light.     

Soil seed bank composition and diversity in a managed temperate deciduous forest

Little is known about the influence of forest management on the interaction between seed bank and aboveground vegetation. We surveyed seed banks and vegetation in 10 forest stands under similar abiotic conditions but submitted either to a coppice-with-standards treatment (n=5) or to a selective-cutting system (n=5). We analyzed species composition and diversity, community ecological profile, and distribution of taxa among different life forms, strategy, morphology and functional type categories. A total of 2085 seedlings (8296 seedsm^–2) germinated-corresponding to 28 species, among which Juncus effusus was the most abundant. Fifty-seven percent of the species were also recorded in the aboveground vegetation, the dominant species being Rubus fruticosus agg., but only 28% of the aboveground species were present in the seed bank. Our results suggest that (1) vernal geophytes and shade-tolerant perennials, which group most true forest species, are not incorporated in the seed bank, (2) parent plants of most seeds were present either in the stand in an earlier dynamic stage or apart from the stand and long-distance dispersed, (3) as expected, early-successional species are well represented in the seed bank, (4) forestry vehicles seem to be a major means of dispersion for stress-tolerant species normally found in forest lanes and wheel tracks. We conclude that seed banks contain species that have a potentially negative impact on the true forest flora and, thus, forest management should minimize soil disturbance and retain remnants of old-coppice woods to conserve disturbance-sensitive true forest species.     

Seasonal rhythms of seed rain and seedling emergence in two tropical rain forests in southern Brazil

Seasonal tropical forests show rhythms in reproductive activities due to water stress during dry seasons. If both seed dispersal and seed germination occur in the best environmental conditions, mortality will be minimised and forest regeneration will occur. To evaluate whether non-seasonal forests also show rhythms, for 2 years we studied the seed rain and seedling emergence in two sandy coastal forests (flooded and unflooded) in southern Brazil. In each forest, one 100 x 30-m grid was marked and inside it 30 stations comprising two seed traps (0.5 x 0.5 m each) and one plot (2 x 2 m) were established for monthly monitoring of seed rain and a seedling emergence study, respectively. Despite differences in soil moisture and incident light on the understorey, flooded and unflooded forests had similar dispersal and germination patterns. Seed rain was seasonal and bimodal (peaks at the end of the wetter season and in the less wet season) and seedling emergence was seasonal and unimodal (peaking in the wetter season). Approximately 57% of the total species number had seedling emergence 4 or more months after dispersal. Therefore, both seed dormancy and the timing of seed dispersal drive the rhythm of seedling emergence in these forests. The peak in germination occurs in the wetter season, when soil fertility is higher and other phenological events also occur. The strong seasonality in these plant communities, even in this weakly seasonal climate, suggests that factors such as daylength, plant sensitivity to small changes in the environment (e.g. water and nutrient availability) or phylogenetic constraints cause seasonal rhythms in the plants.     

Conservation of temperate forest birds in Chile: implications from the study of an isolated forest relict

We characterize the bird assemblage of an isolated relict temperaterainforest (Santa Inés) in terms of its structure, composition anddynamics. The relict character and long-term isolation of this forest remnant,immersed in a matrix of semiarid scrub, provide a natural experiment to assessthe consequences of long-term isolation and forest area reduction for temperatebird species. Bird surveys were conducted in a forest fragment and thesurrounding scrub matrix between April 1999 (austral autumn) and October 2000(austral spring) on a seasonal basis. Within the forest fragment wedistinguished two microhabitat types: creeks and areas far from creeks (i.e.slopes). A total of 36 species were recorded in the study site, of which 21were inside the relict forest. Highest bird abundance and richness wererecorded during winter and spring, and these were always higher in creek plotsrather than slope plots. Comparisons between this assemblage and thosedistributed in the continuous temperate forest (located more than 900km southwards) indicate that this bird assemblage shares moresimilarities, with regard to bird species composition, to southern temperateforest localities and to other relict forests, than to nearer scrub habitats.However, there are eight species, endemic to temperate forests in southern SouthAmerica, missing from our system. In this regard, our analyses indicate thatthese eight endemic species should be of great conservation concern and willlikely be the ones that will go extinct first if the fragmentation of thetemperate forest continues.     

Ants on oaks: effects of forest structure on species composition

The ant fauna of oak forest canopies in Northern Bavaria was studied by canopy fogging on 45 trees in August 2000 and May 2001. The study focused on a comparison of several different forestry management practices resulting in several types of canopy cover. Forests surveyed were: (1) high forest (high canopy cover), (2) coppice with standards (low canopy cover), (3) forest pasture with mostly solitary trees (very low canopy cover) and (4) transitional forest from former coppice with standards to high forest (approaching high canopy cover). This comprised a full gradient of canopy coverage. On the 45 oak trees sampled, a total of 17 ant species were found. Species composition was dependent on the different forestry management practices. The total number of species and the number of species listed in the Red Data Books of both Germany and Bavaria were much higher in the forest pasture and the coppice with standards, as compared to the high forest. The transitional forest was at an intermediate level. The highest number of ant species was found in the forest pasture. This can be explained by the occurrence of species of open habitats and thermophilous species. In the coppice with standards, forest dwelling and arboricolous species dominated, whereas the high forest showed much lower frequencies of arboricolous species like Temnothorax corticalis, Dolichoderus quadripunctatus and Temnothorax affinis. A multivariate analysis revealed that canopy cover (measured as “shade”, in percentage intervals of canopy cover) was the best parameter for explaining species distribution and dataset variation, and to a lesser extent the amount of dead wood, canopy and trunk diameter. Thus ant fauna composition was mostly driven by structural differences associated to the different forestry management practices. Many ant species clearly preferred the more open and light forest stands of the coppice with standards as compared to the dense and shady high forest.     

Light-dependent changes in the relationship between seed mass and seedling traits: a meta-analysis for rain forest tree species

Seed mass is considered to be an important attribute for the establishment success of plant species being linked with their seed production, establishment, and survival. This meta-analysis shows that seed mass is also closely correlated to growth-related species attributes of the established phase of rain forest tree species, and that the strength of this relationship varies with light conditions. Seed mass is an especially good predictor of species traits under high-light conditions, when the species attain their full growth potential. At high irradiance (>20% of full light) seed mass is negatively correlated with RGR, NAR, LAR, SLA and LMF. At low irradiance (<5% of full light), seed mass is only negatively correlated with LAR and SLA. Correlations between seed mass and morphological traits are therefore strongest at low irradiance where light interception is important. Conversely, correlations between seed mass and a physiological trait are strongest at high irradiance, where maximisation of photosynthetic rates is important. The strength of the correlation between growth parameters and seed mass declines over time, and disappears after 1–4 years. Seed mass appears to be a good proxy for the shade tolerance of tropical tree species, especially at the younger stages of the life cycle.     

Pollen dispersal and representation in a neotropical rain forest

Results of 3 years of pollen trapping on Barro Colorado Island, Panama, are presented. Minimum pollen dispersal distances are estimated for the most abundant pollen taxa. Dispersal distances for some taxa appear to be as low as 5 m, while for other taxa at least 50% of the trapped pollen had travelled more than 40 m. No consistent pattern of spatial variation was reflected in the pollen rain, however, samples close to large canopy gaps had exceptional abundances of 'disturbance' taxa. A preliminary analysis of the representation of canopy components indicates that as much as 19% of pollen caught in the traps was derived from large tree species.     

Spatial variation of species diversity across scales in an old-growth temperate forest of China

Species richness and abundance are the two most important diversity variables. Species abundance is additive when aggregated across spatial scale, whereas species richness is non-additive. This study analyzes the effect of spatial scale and site on species abundance and richness in a 25-ha temperate forest plot in the Changbai Mountains, northeastern China. The result shows that species abundance and richness are not only dependent on spatial scales, but also dependent on site. Species abundance responds linearly to changes of spatial scale with no intersection in different sites of the study area. However, although species richness also increases with the increase of spatial scale, there are some intersections for the different sites, suggesting that a species-rich site does not always have a high value if the spatial scale is changed. In all, with respect to additive variables, it is relatively easy to extrapolate them from one spatial scale to another spatial scale, as they and the spatial scale usually form a linear relationship. In contrast, non-additive variables are difficult to extrapolate across spatial scales, because they often respond nonlinearly to spatial scale changes. In order to extrapolate these non-additive variables across spatial scales, it is necessary to estimate the relationships between them and spatial scales. As a result, extrapolation of information among spatial scales may be possible, but very difficult, especially for non-additive variables. Because the 25-ha Changbai plot is very small compared to the extent of the world temperate forests, and the vegetation is a relatively uniform type, more such studies in other ecosystems are needed before theories and generalization about scaling effects can be formulated.     

Seed germination ecology of Polymnia canadensis (Asteraceae), a monocarpic species of the North American Temperate Deciduous Forest

The seed germination of Polymnia canadensis was studied in relation to its wide variation in life history and its ecology as a mostly facultative biennial, a life cycle type that is rare in stable forest habitats in eastern North America. The seed dormancy and germination characteristics of P. canadensis were like some other herbaceous woodland species of diverse life cycle types. That is, its seeds have physiological dormancy, and they (1) germinated to higher percentages after cold stratification, (2) germinated better in light than in darkness and (3) formed a persistent soil seed bank. Since its seed dormancy and germination characteristics are not uncommon and are not particularly associated with any one life cycle type in woodlands, those properties do not contribute to the rarity of its life cycle type in deciduous forests. These properties are also found in many facultative biennials of open, disturbed habitats and in other Asteraceae of various life cycle types. In addition, the germination phenology of P. canadensis differed between mesic and dry field sites in central Kentucky. At the dry sites, most of the yearly germination occurred in fall, while at the mesic sites most germination occurred in the spring due to being inhibited during fall. A reciprocal seed transplant experiment conducted in two different years demonstrated that the cause of this difference was environmental and that there was no source x site interaction; i.e., no difference between sources in phenotypic plasticity for germination phenology. Absence of genetic effects was also shown by no consistent pattern in the few differences between seed sources in seed incubation laboratory experiments and in a germination phenology experiment in glasshouse flats. Exposure of seeds to a high ratio of far-red/red light prior to or during incubation did not inhibit germination. Neither did changes in leaf litter thickness qualitatively alter germination phenology in field quadrats or in glasshouse flats. Thus, germination in fall at mesic sites was inhibited by other unknown factor(s), perhaps interacting with the effects of closed tree canopy and/or thick leaf litter.     

Seed dispersal by red howling monkeys (Alouatta seniculus) in the tropical rain forest of French Guiana

A 2-year field study of the frugivorous diet of a howling monkey troop, in a tropical rain forest in French Guiana, shows that they disperse by endozoochory ≥95% of plant species from which they eat ripe fruit. Passage through the digestive tract of howlers does not significantly modify the germination success of most plant species samples. Their low digestion rate (X = 20 hr 40 min) is the ultimate cause of a bimodal defecation rhythm that results in the concentration of 60% of defecations being deposited under sleeping sites. The distance of seed dispersal can reach more than 550 m from parent trees,with a mean of 260 m. Although howling monkeys consume fruits differing in morphological characteristics, they are particularly able to disseminate seeds of species whose fruits have a hard and indehiscent external coat or large seeds or both. In French Guiana, they may be especially important dispersers of the Sapotaceae with fruits that simultaneously present both characteristics.     

Species number, species abundance and body length relationships of arboreal beetles in Bornean lowland rain forest trees

ABSTRACT.

• 1 The relationships between number of species, abundance per species, and body length are examined for 859 species of beetles in samples of arthropods collected from ten Bornean lowland forest trees by insecticide fogging. Similar relationships are examined for different feeding guilds of these beetles, and for those beetles from different species of trees.
• 2 The data are used to construct four interrelated graphs, namely species: abundance, species: body length, population abundance: body length and total number of individuals: body length distributions.
• 3 In contrast to a number of previous studies, no consistent linear relationship between population density and body length was found for the Bornean beetles and it is suggested that, as in birds, the added dispersal ability of flight reduces critical population densities necessary for persistence in small species. Previous relationships between body weight and population abundance may also be artefacts of the way in which data were gathered.
• 4 Despite large samples, we failed to locate the mode in plots of the number of species in each abundance category (species: abundance distribution).
• 5 Species: body length and total number of individuals: body length plots were similar to those found in previous studies, although using data for Coleoptera alone may have produced a steeper decline in the total number of individuals as body size increases than is apparent in samples of all arthropods.
• 6 We present the first three-dimensional graph relating numbers of species, body lengths and population abundances. The surface of this three-dimensional relationship is relatively simple.

     

Seed reserve composition in 19 tree species of a tropical deciduous forest in Mexico and its relationship to seed germination and seedling growth

Background and Aims

The size and composition of seed reserves may reflect the ecological strategy and evolutionary history of a species and also temporal variation in resource availability. The seed mass and composition of seed reserves of 19 co-existing tree species were studied, and we examined how they varied among species in relation to germination and seedling growth rates, as well as between two years with contrasting precipitation (652 and 384 mm).

Methods

Seeds were collected from a tropical deciduous forest in the northwest of Mexico (Chamela Biological Station). The seed dry mass, with and without the seed coat, and the concentrations of lipids, nitrogen and non-structural carbohydrates for the seed minus seed coat were determined. The anatomical localization of these reserves was examined using histochemical analysis. The germination capacity, rate and lag time were determined. The correlations among these variables, and their relationship to previously reported seedling relative growth rates, were evaluated with and without phylogenetic consideration.

Key Results

There were interannual differences in seed mass and reserve composition. Seed was significantly heavier after the drier year in five species. Nitrogen concentration was positively correlated with seed coat fraction, and was significantly higher after the drier year in 12 species. The rate and lag time of germination were negatively correlated with each other. These trait correlations were also supported for phylogenetic independent contrasts. Principal component analysis supported these correlations, and indicated a negative association of seedling relative growth rate with seed size, and a positive association of germination rate with nitrogen and lipid concentrations.

Conclusions

Nitrogen concentration tended to be higher after the drier year and, while interannual variations in seed size and reserve composition were not sufficient to affect interspecific correlations among seed and seedling traits, some of the reserves were related to germination variables and seedling relative growth rate.     

Seed dispersal patterns in a temperate forest during a mast event: performance of alternative dispersal kernels

Seed dispersal patterns were studied in a north-western Spain temperate forest community to assess the performances of alternative dispersal kernels during two years with ecologically contrasting scenarios; a non-mast year, and a mast year of the dominant canopy species, beech Fagus sylvatica. Dispersal kernels were fitted under a Bayesian modeling framework. Both simple and mixture kernels were considered for the five more abundant tree species (Corylus avellana, Crataegus monogyna, F. sylvatica, Ilex aquifolium and Taxus baccata). Mixture kernels provided a better fit for almost all species, and the log-normal performed best for T. baccata. No relationship between dispersal syndromes and the best dispersal kernel function emerged. However, we found temporal changes in the shape of the dispersal kernels that seemed to be related to variation in relative fruit production among species and the resulting changes in the responses of dispersal vectors. This reveals a potential role for disperser-mediated indirect effects in terms of introducing temporal variation in species spread. In this sense, our results highlight the need to consider single species seed dispersal as a community process. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Asymptotic height as a predictor of growth and allometric characteristics in malaysian rain forest trees

The growth and physiological characteristics of canopy trees are expected to differ systematically from those of understory trees on the basis of size-dependent aspects of biomechanics, resource availability, and life history. Although such differences have previously been noted, there has been relatively little effort to quantify these in terms of interspecific allometric relationships. Asymptotic maximal height (H_max) is advocated as a measure of the size of dicotyledonous woody plants for this purpose. Height diameter (H–D) relationships in 38 species within six genera of Malaysian rain forest trees are well described by an asymptotic model, and thus provide a basis for estimating H_max using static observational data. Three important aspects of tree growth strategies are shown to be predictable on the basis of these values: average tree growth rates are positively related to H_max, while wood density and the initial allometric slope of (species-specific) H–D relationships are negatively related to H_max. These patterns may be explained by an association of low light levels with slow growth and high density wood in understory species; the latter property may in turn allow for relatively high allometric slopes of H–D relationships in saplings of small-statured species. Analyses that control for phylogenetic differences provide evidence that such interspecific allometric patterns are the product of convergent evolution. These results are consistent with the idea that much ecological variation within species-rich taxa of southeast Asian rain forest trees is related to differentiation along a vertical axis of tree size.     

Determination of seed viability of eight wild Saudi Arabian species by germination and X-ray tests

Our purpose was to evaluate the usefulness of the germination vs. the X-ray test in determining the initial viability of seeds of eight wild species (Salvia spinosa, Salvia aegyptiaca, Ochradenus baccatus, Ochradenus arabicus, Suaeda aegyptiaca, Suaeda vermiculata, Prosopisfarcta and Panicumturgidum) from Saudi Arabia. Several days were required to determine viability of all eight species via germination tests, while immediate results on filled/viable seeds were obtained with the X-ray test. Seeds of all the species, except Sa.aegyptiaca, showed high viability in both the germination (98–70% at 25/15 °C, 93–66% at 35/25 °C) and X-ray (100–75%) test. Furthermore, there was general agreement between the germination (10% at 25/15 °C and 8% at 35/25 °C) and X-ray (5%) tests that seed viability of Sa.aegyptiaca was very low, and X-ray analysis revealed that this was due to poor embryo development. Seeds of P.farcta have physical dormancy, which was broken by scarification in concentrated sulfuric acid (10 min), and they exhibited high viability in both the germination (98% at 25/15 °C and 93% at 35/25 °C) and X-ray (98%) test. Most of the nongerminated seeds of the eight species except those of Sa.aegyptiaca were alive as judged by the tetrazolium test (TZ). Thus, for the eight species examined, the X-ray test was a good and rapid predictor of seed viability.