•A long term growth study across an elevation gradient.•MDF structure is potentially linked to landform stability.•MDF tree family dominance increases with time.•Canopy trees showed greater site ...overlap than understory.
Little work has examined the spatial and temporal changes of a tropical rain forest for long time periods. Here, we present an analysis of long-term plot data from a Sri Lankan Mixed-Dipterocarp forest (MDF). The plots were established in 1978 at three different elevations (low - 335m, medium - 560 m, and high - 915 m). At each site we measured all trees ≥ 10 cm DBH in 16 or 18 plots. The total area sampled amounted to 12.5 ha. We recorded 166 tree species, with each site comprising between 95 and 121 species. Stem densities and basal areas were different among sites, and declined over the period from 642.8 stems ha−1 and 41.8 m2 ha−1 for the 1978 census, to 496.2 stems ha−1 and 35.2 m2 ha−1 for the 2018 census. The lowest elevation exhibited the highest recruitment, mortality and turnover among sites but patterns changed and became less marked over time. Forest wide tree recruitment was about 1% y−1, while mortality was twice as much averaging about 2% y−1. Four families made up between 44% (1978 census) and 54% (2018 census) of the trees sampled. Two families – Clusiaceae, Dipterocarpaceae contributed up to 33.4% and 37.3% respectively, depending upon site and year of census. The five most common species represent between 31 and 54% of the basal area and between 25 and 66% of the stem density depending upon site. Percentage dominance by the most common species increased over the 40-year time period. Though many trees showed some degree of spatial differentiation, canopy trees showed greater site overlap in their distribution than understory and sub-canopy species. Our results provide an improved picture of variations in MDF structure and composition across the ever-wet realms of equatorial south and southeast Asia. We suggest that dominance in dipterocarps and the degree of closed canopy structure, as measured by basal area, is influenced by time, elevation, the degree of topographic variability within elevation, and topographic interactions with variabilities in climate (drought and windstorms). We propose higher standing basal areas and super dominance of dipterocarps in MDF are linked to site, succession, and landform stability. Dipterocarps increase in dominance with succession (time), with topography (ridges greater than valleys) and with elevation (lowland < hill < lower montane).
Mangroves are highly adapted to extreme environmental conditions that occur at the interface of salt and fresh water. Adaptations to the saline environment during germination are a key to mangrove ...survival, and thereby, its distribution. The main objective of this research was to study the effect of salinity on seed germination of selected mangrove species and the application of a hydrotime model to explain the relationship between water potential of the medium and rate of seed germination. Germination of seeds was examined at 15, 25 and 35°C in light/dark over a NaCl gradient. Germination time courses were prepared, and germination data were used to investigate whether these species behave according to the principles of the hydrotime model. The model was fitted for the germination of Acanthus ilicifolius seeds at 25°C. Final germination percentage was significantly influenced by species, osmotic potential and their interaction at 25°C. Moreover, temperature had a clear effect on seed germination (Sonneratia caseolaris and Pemphis acidula) which interacted with osmotic potential. Only A. ilicifolius seeds behaved according to the hydrotime principles and thus its threshold water potential was –1.8 MPa. Optimum germination rates for seeds of the other species occurred at osmotic potentials other than 0 MPa. The descending order of salinity tolerance of the tested species was Aegiceras corniculatum > Sonneratia caseolaris > Acanthus ilicifolius > Pemphis acidula > Allophylus cobbe, suggesting that the viviparous species (A. corniculatum) is highly salt tolerant compared with the non-viviparous species. The results revealed that seeds of the study species exhibited facultative halophytic behaviour in which they can germinate over a broad range of saline environments. Use of a hydrotime model for mangroves was limited as germination of their seeds did not meet model criteria.
► Native tree species can be used to accelerate succession on degraded grasslands. ► We examined the mechanisms limiting tree seedling growth and survival. ► Root competition exerted by grass ...inhibited seedling performance. ►
Symplocos cochinchinensis and
Macaranga indica can be used to accelerate succession.
The density of colonising tree seedlings is often very low in degraded human-induced tropical grasslands. To investigate the mechanisms that constrain seedling establishment in grasslands on former tea plantations in Sri Lanka we planted seedlings of the native tree species
Dimocarpus longan Lour.,
Macaranga indica Wight,
Symplocos cochinchinensis (Lour.) S. Moore and
Syzygium spathulatum Thw. and examined effects of vertebrate herbivory, and above- and below-ground competition exerted by the grass sward on seedling growth and survival over 28 months. Seedlings of the same species were also planted in remnant patches of lower montane rain forest to determine the effects of habitat on seedling growth and survival. Less than 40% of seedlings survived to 28 months post-transplantation. The highest survival was recorded for
Symplocos cochinchinensis in both grassland and forest, while Macaranga indica seedlings had the highest relative growth rate of height (RGRh) in both habitats. Root competition reduced survival of
Macaranga indica and the RGR
h of
Macaranga indica,
Symplocos cochinchinensis and
Syzygium spathulatum in the grassland, while above-ground competition and exclusion of vertebrate herbivores had no effects on seedling establishment. These results suggest that
Symplocos cochinchinensis would be suitable for re-establishing forest cover on degraded grasslands, although
Macaranga indica would be more likely to catalyse succession because it possesses animal-dispersed fruit. Measures that overcome or restrict the effects of root competition from grasses would enhance tree seedling growth and survival more than manipulation of the light environment or protection from vertebrate herbivores.
The Western Ghats of India and Sri Lanka biodiversity hotspot is often regarded as one unit because of shared biogeographical history. However, recent studies suggest that certain faunal components, ...particularly in the wet zones are distinct. This article looks at the existing information on species richness and endemicity of taxa in both regions. Data are available on some taxa but not on others, and many taxa have not received equal attention in both regions. The natural ecosystems of this hotspot are under threat and urgent conservation action is needed, especially in augmenting the protected area network. There is also the need for increasing the level of scientific collaboration in biodiversity studies between the two countries.
Long‐term surveys of entire communities of species are needed to measure fluctuations in natural populations and elucidate the mechanisms driving population dynamics and community assembly. We ...analysed changes in abundance of over 4000 tree species in 12 forests across the world over periods of 6–28 years. Abundance fluctuations in all forests are large and consistent with population dynamics models in which temporal environmental variance plays a central role. At some sites we identify clear environmental drivers, such as fire and drought, that could underlie these patterns, but at other sites there is a need for further research to identify drivers. In addition, cross‐site comparisons showed that abundance fluctuations were smaller at species‐rich sites, consistent with the idea that stable environmental conditions promote higher diversity. Much community ecology theory emphasises demographic variance and niche stabilisation; we encourage the development of theory in which temporal environmental variance plays a central role.
The future trajectory of global forests is closely intertwined with tree demography, and a major fundamental goal in ecology is to understand the key mechanisms governing spatio‐temporal patterns in ...tree population dynamics. While previous research has made substantial progress in identifying the mechanisms individually, their relative importance among forests remains unclear mainly due to practical limitations. One approach to overcome these limitations is to group mechanisms according to their shared effects on the variability of tree vital rates and quantify patterns therein. We developed a conceptual and statistical framework (variance partitioning of Bayesian multilevel models) that attributes the variability in tree growth, mortality, and recruitment to variation in species, space, and time, and their interactions – categories we refer to as organising principles (OPs). We applied the framework to data from 21 forest plots covering more than 2.9 million trees of approximately 6500 species. We found that differences among species, the species OP, proved a major source of variability in tree vital rates, explaining 28–33% of demographic variance alone, and 14–17% in interaction with space, totalling 40–43%. Our results support the hypothesis that the range of vital rates is similar across global forests. However, the average variability among species declined with species richness, indicating that diverse forests featured smaller interspecific differences in vital rates. Moreover, decomposing the variance in vital rates into the proposed OPs showed the importance of unexplained variability, which includes individual variation, in tree demography. A focus on how demographic variance is organized in forests can facilitate the construction of more targeted models with clearer expectations of which covariates might drive a vital rate. This study therefore highlights the most promising avenues for future research, both in terms of understanding the relative contributions of groups of mechanisms to forest demography and diversity, and for improving projections of forest ecosystems.
1. In the moist tropics, studies have demonstrated poor seedling establishment of latesuccessional trees on lands cleared of forest. Our study examined the potential for establishing ...late-successional tree species that dominate the canopy of rainforest by planting within and adjacent to experimental openings that were created within a Pinus caribaea plantation. 2. We tested five canopy tree species (Dipterocarpus zeylanicus, Mesua ferrea, Shorea disticha, S. megistophylla and S. trapezifolia) of tropical forest in south-western Sri Lanka. Seedlings were monitored for 2 years within treatments that removed either three rows or one row of Pinus canopy, a canopy edge treatment and a control that left the canopy intact. 3. The greatest growth and dry mass for all species were in the canopy removal treatments. In particular, S. trapezifolia and S. disticha exhibited the greatest height growth in these treatments. In the three-row canopy removal treatment, M. ferrea had a significantly lower dry mass than the other species. 4. Differences were shown in the number and area of leaves among species. Shorea trapezifolia and, to a lesser degree, S. disticha increased area by increasing leaf production. Dipterocarpus zeylanicus and, to a lesser degree, M. ferrea increased area by increasing the size of individual leaves. 5. Guidelines based on results from this study recommend that species grow best when seedlings are planted within openings created by the removal of three rows of Pinus canopy. Where planting without canopy removal is required, S. disticha or S. megistophylla should be selected because of greater shade and drought tolerance. 6. This experiment demonstrated that Pinus can be used as a nurse for facilitating the establishment of site-sensitive tropical forest tree species that are late-successional. In particular, results have application for similar mixed dipterocarp forest types in southeast Asia.
Data on the reproductive biology of the Annonaceae are rather fragmentary, particularly for paleotropical species. The pollination ecology and breeding system of the Sri Lankan endemic Xylopia ...championii (Annonaceae) are described in detail. The pollination ecology was investigated using a diverse range of approaches, including (1) observations of flower-level and population-level phenology, (2) assessments of floral visitors and effective pollinators, (3) monitoring of floral temperature in situ using a digital data logger, and (4) analysis of scent chemistry using solid-phase microextraction sampling and gas chromatography-mass spectrometry identification of volatiles. The breeding system was evaluated using pollen/ovule ratios and field-based controlled-pollination experiments. Intrafloral dichogamy (protogyny) occurs over a 2-d period, with a reproductively inactive phase between the pistillate and staminate phases, although there is no evidence of interfloral dichogamy. The inner petals close to form a pollination chamber during the reproductively active phases. The flowers are pollinated by a species of Endaeus weevil (Coleoptera: Curculionidae). Floral chamber temperatures are elevated to 8°C above ambient levels. The floral scent contains a combination of volatiles that have previously been observed in fruits and other flowers and that possibly mimic insect pheromones. Xylopia championii has an essentially xenogamous breeding system, promoted by protogyny. Although X. championii possesses numerous clear adaptations for cantharophily, there is no evidence for a species-specific interaction. The beetles are attracted to the flowers by strong scents; rewards offered to the beetles include heat energy and protection from predators. Low levels of fruit set in natural conditions suggest that pollinator availability may be a limiting factor.
Advances in forest carbon mapping have the potential to greatly reduce uncertainties in the global carbon budget and to facilitate effective emissions mitigation strategies such as REDD+ (Reducing ...Emissions from Deforestation and Forest Degradation). Though broad-scale mapping is based primarily on remote sensing data, the accuracy of resulting forest carbon stock estimates depends critically on the quality of field measurements and calibration procedures. The mismatch in spatial scales between field inventory plots and larger pixels of current and planned remote sensing products for forest biomass mapping is of particular concern, as it has the potential to introduce errors, especially if forest biomass shows strong local spatial variation. Here, we used 30 large (8-50 ha) globally distributed permanent forest plots to quantify the spatial variability in aboveground biomass density (AGBD in Mg ha-1) at spatial scales ranging from 5 to 250 m (0.025-6.25 ha), and to evaluate the implications of this variability for calibrating remote sensing products using simulated remote sensing footprints. We found that local spatial variability in AGBD is large for standard plot sizes, averaging 46.3% for replicate 0.1 ha subplots within a single large plot, and 16.6% for 1 ha subplots. AGBD showed weak spatial autocorrelation at distances of 20-400 m, with autocorrelation higher in sites with higher topographic variability and statistically significant in half of the sites. We further show that when field calibration plots are smaller than the remote sensing pixels, the high local spatial variability in AGBD leads to a substantial "dilution" bias in calibration parameters, a bias that cannot be removed with standard statistical methods. Our results suggest that topography should be explicitly accounted for in future sampling strategies and that much care must be taken in designing calibration schemes if remote sensing of forest carbon is to achieve its promise.
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