Increasing Size Classes Research Articles

Assessment of Tree Species Diversity, Family Composition and Diameter Size Class of Tree Species in Igbo-Olua Sacred Groove, Ondo State, Nigeria

This study was carried out to assess the tree species diversity, family composition and diameter size distribution of the tree species in Igbo-Olua sacred groove, Ondo state, Nigeria using appropriate standard techniques. A total of 34 tree species distributed in 23 families were recorded. Sterculiaceae family (66) had the highest number of individual stem per ha while Moraceae family had the highest number in terms of tree species per hectare (7). The distribution of the diameter structure is typical of the natural forest type with high number of tree species in the smaller size classes or interval (12.5) and the number of tree species decreases with increasing size class or interval. Diversity measures obtained included Shannon-Weiner index (3.09), Evenness (0.64) and Margalef index (6.36). Awakening the consciousness of people towards the protection of sacred groves has practical implications on their survival. Hence government and other allied institutions should gear efforts towards grove conservation.

Fluted giant clam (Tridacna squamosa) restocking experiment in an urban turbid reef environment

Abstract Giant clam populations in Singapore are endangered due to historical exploitation, habitat loss, and sediment pollution. Transplanting cultured giant clams onto reefs is a potential conservation strategy. This study examined the growth and survival of three initial size classes (50.0–60.0 mm, 60.1–70.0 mm, >70 mm) of cultured juvenile fluted giant clams, Tridacna squamosa, transplanted to three reef sites under two caging treatments (caged and uncaged). After 145 days, there was no significant difference in clam survival within the size classes and within caging treatments across reef sites, even though environmental conditions varied greatly between sites. However, there was a significant effect of initial size class on T. squamosa survival, with higher survival with increasing size class (50.0–60.0 mm: 11.1%; 60.1–70.0 mm: 34.1%; >70.0 mm: 46.9%). Clams in caged treatments had significantly lower survival (16.7%) than uncaged clams (43.1%), likely due to biofouling atop caged treatments reducing light availability. Growth rates in the caged treatment (2.2 ± SD 1.8 mm month−1) were also lower than those in the uncaged treatment (3.9 ± SD 2.2 mm month−1). By optimizing transplant procedures for Singapore's turbid reef conditions, T. squamosa restocking efforts could play an important role in boosting local population numbers to facilitate natural recovery.

Soil aggregate-associated heavy metals subjected to different types of land use in subtropical China

Heavy metal distribution in soils is strongly influenced by soil aggregate size. In this study, we collected surface soil samples from farmlands (FL), woodlands (WL), and bare lands (BL). Air-dried soils were sieved into four size fractions (>3, 1–3, 0.25–1, and <0.25 mm in diameter) to determine the concentrations of eight heavy metals (Cd, Cr, Cu, Ni, Pb, Zn, As, and Mn) in soil aggregates using wet digestion method. Our results found that the amount of macroaggregates (>0.25 mm) was significantly higher than that of microaggregates (<0.25 mm) in all soil samples. Moreover, the proportion of large macroaggregates (>3 mm) showed an order of FL > ML > BL, while the proportion of microaggregates (<0.25 mm) showed an order of FL < ML < BL. The soil Cd and Pb levels in woodlands were significantly higher than those in farmlands and bare lands. In addition, the concentrations of soil Cu and Zn were elevated in farmlands compared to woodlands and bare lands. For the aggregate-associated heavy metal, contents of most metal elements (except As) in soil aggregates slightly decreased with increasing size class in farmlands. Heavy metals were generally depleted in the larger aggregates but enriched in the smaller aggregates. Interestingly, soil organic matter content was positively related to soil Cd, Cr, Ni, and Pb concentrations, but negatively correlated with soil Cu and As levels. The findings suggest that land use changes can affect the concentrations of soil aggregate-associated heavy metals, and these effects vary among different metals.

English

In this study, we examined vegetation structure and regeneration status of woody plants in the Hallideghie wildlife reserve, Ethiopia. We collected data on abundance, height and diameter at breast height (DBH) of woody plant species with DBH &gt;2.5 cm within sixty-six 20 m &times; 20 m sample plots and counted number of individuals of seedlings (that is, individuals with height &lt;1.5 m) and saplings (height &gt;1.5 m and DBH &lt;2.5 cm) of each species within five 1 m &times; 1 m subplots nested within each main plot. To describe vegetation structure, we computed DBH and height size frequency distributions of individuals and species importance value indexes (IVI). Overall, we recorded 986 individuals of tree/shrub stems, belonging to 46 woody plant species. Both the number of species and individuals represented in each DBH size class and height size class showed decreasing trends with increasing size classes. However, different species showed varying patterns of DBH size structure. IVI of species varied from 0.3 to 69.1. The average density of seedlings, saplings and matured woody plants in the HWR were 1345, 899 and 374 individuals/ha, respectively. Balanites aegyptiaca and Acacia tortilis, species with high IVIs, were also among those species that exhibited poor regeneration status. &nbsp; Key words: DBH, importance values index (IVI), Prosopis juliflora, density, invasive species.

Developmental Trends of Black Spruce Fibre Attributes in Maturing Plantations

This study assessed the temporal developmental patterns of commercially relevant fibre attributes (tracheid length and diameters, wall thickness, specific surface area, wood density, microfibril angle, fibre coarseness, and modulus of elasticity) and their interrelationships within maturing black spruce (Picea mariana(Mill.) B.S.P.) plantations. A size-based stratified random sample procedure within 5 semimature plantations located in the Canadian Boreal Forest Region was used to select 50 trees from which radial cross-sectional xylem sequences at breast-height (1.3 m) were cut and analyzed. Statistically, the graphical and linear correlation analyses indicated that the attributes exhibited significant (p≤0.05) relationships among themselves and with morphological tree characteristics. Relative variation of each annually measured attribute declined with increasing size class (basal area quintile). The transitional shifts in temporal correlation patterns occurring at the time of approximate crown closure where suggestive of intrinsic differences in juvenile and mature wood formation processes. The temporal cumulative development patterns of all 8 of the annually measured attributes varied systematically with tree size and exhibited the most rapid rates of change before the trees reached a cambial age of 20 years. At approximately 50 years after establishment, plantation mean attribute values were not dissimilar from those reported for more mature natural-origin stands.

Evidence for ontogenetic feeding strategies in four calanoid copepods in the East Sea (Japan Sea) in summer, revealed by stable isotope analysis

Deciphering the ontogenetic feeding ecology of copepods is essential to understanding their role in the energy transfer of marine ecosystems. We used stable isotope analysis to examine the ontogenetic feeding strategies of the four coexisting calanoid copepods, Mesocalanus tenuicornis, Metridia pacifica, Calanus sinicus, and Neocalanus plumchrus, in the East Sea (Japan Sea) in summer. Moreover, we used the stable carbon and nitrogen isotope composition of small-sized plankton in three cell size fractions, pico- (< 2 μm), nano- (2–20 μm) and microplankton (20–200 μm), to identify the dietary preference at each developmental stage. The relative carbon masses of pico-, nano- and microplankton were 18, 38, and 44%, respectively, and their δ13C and δ15N values gradually increased with increasing size classes. The ontogenetic trophic position of four copepods were relatively low and ranged from 2.1 to 2.6, indicating that herbivores feed on small-sized phytoplankton, pico- and nanoplankton. Among copepodid stages, the δ13C and δ15N values of M. tenuicornis and C. sinicus differed significantly, while those of M. pacifica and N. plumchrus were not significantly different. In M. tenuicornis, the smallest species among the four copepods examined, the diet preference of CIV for picoplankton changed to nanoplankton in the adult stage. When M. pacifica developed from CIV to adult, the diet preference changed from pico- to microplankton. The proportion of microplankton in the diet of C. sinicus and N. plumchrus increased from CIV to female adult and from CIII to CV, respectively. During the developmental progress in copepodid stages, the smaller copepods significantly changed their dietary preference from pico- to microplankton, while the larger copepods consistently fed on microplankton. We suggest that smaller copepods have an advantage in survival at early copepodid stages compared with larger copepods in summer when microplankton biomass is relatively low.

Neighborhood diversity of large trees shows independent species patterns in a mixed dipterocarp forest in Sri Lanka.

Interactions among neighboring individuals influence plant performance and should create spatial patterns in local community structure. In order to assess the role of large trees in generating spatial patterns in local species richness, we used the individual species-area relationship (ISAR) to evaluate the species richness of trees of different size classes (and dead trees) in circular neighborhoods with varying radius around large trees of different focal species. To reveal signals of species interactions, we compared the ISAR function of the individuals of focal species with that of randomly selected nearby locations. We expected that large trees should strongly affect the community structure of smaller trees in their neighborhood, but that these effects should fade away with increasing size class. Unexpectedly, we found that only few focal species showed signals of species interactions with trees of the different size classes and that this was less likely for less abundant focal species. However, the few and relatively weak departures from independence were consistent with expectations of the effect of competition for space and the dispersal syndrome on spatial patterns. A noisy signal of competition for space found for large trees built up gradually with increasing life stage; it was not yet present for large saplings but detectable for intermediates. Additionally, focal species with animal-dispersed seeds showed higher species richness in their neighborhood than those with gravity- and gyration-dispersed seeds. Our analysis across the entire ontogeny from recruits to large trees supports the hypothesis that stochastic effects dilute deterministic species interactions in highly diverse communities. Stochastic dilution is a consequence of the stochastic geometry of biodiversity in species-rich communities where the identities of the nearest neighbors of a given plant are largely unpredictable. While the outcome of local species interactions is governed for each plant by deterministic fitness and niche differences, the large variability of competitors causes also a large variability in the outcomes of interactions and does not allow for strong directed responses at the species level. Collectively, our results highlight the critical effect of the stochastic geometry of biodiversity in structuring local spatial patterns of tropical forest diversity.

Spatial distribution pattern of the dominant species Gironniera subaequalis in tropical montane rainforest of Jianfengling, Hainan Island, China

Aims Dominant species play a major role in the formation of community. Our objectives were to detect and assess the spatial pattern of Gironniera subaequalis, which is a dominant species with the second largest importance value in the tropical montane rainforest of Jianfengling, and to explore the effects of environmental heterogeneity, density-dependent mortality and dispersal limitation on the formation of its current spatial pattern. Methods 10 022 individuals were categorized into six size classes and three life-history stages, i.e. young trees, middle-aged trees and adult trees, respectively. The spatial pattern of each age class was analyzed by pair-correlation function. The spatial associations between paris of life-history stages were analyzed by bivariate pair-correlation function and mark-connection function. The impacts of topographic factors on the distributions of young trees, middle-aged trees and adult trees were analyzed by Berman test. Important findings Results showed that the size classes I, II, III, and IV of G. subaequalis occurred in aggregated distributions. The aggregation intensities declined with increasing size classes. Size classes V and VI exhibited a uniform distribution at the smaller scales and a random distribution mainly at the larger scales. Young trees and middle-aged trees had a positive association; whereas young trees and adult trees had a negative association. Middle-aged trees and adult trees had a negative association at smaller scales and a weakly positive association at larger scales. The individuals of different life-history stages were separated from each other. There were no direct facilitative interactions between pairs of individuals. The tree topographic factors, slope degree, altitude and concave-convex, had significant impacts on the distribution of small trees; slope degree and concave-convex had significant impacts on the distribution of the middle-aged trees; whilst only slope degree had significant impacts on the adults trees. We inferred that the environmental heterogeneity and density-dependent mortality contributed to current spatial pattern of G. subaequalis, while the effects of dispersal limitation were not obvious.

Functional and phylogenetic assembly in a Chinese tropical tree community across size classes, spatial scales and habitats

Summary Increasingly, ecologists are using functional and phylogenetic approaches to quantify the relative importance of stochastic, abiotic filtering and biotic filtering processes shaping the pattern of species co‐occurrence. A remaining challenge in functional and phylogenetic analyses of tropical tree communities is to successfully integrate the functional and phylogenetic structure of tree communities across spatial and size scales and habitats in a single analysis. We analysed the functional and phylogenetic structure of tree assemblages in a 20‐ha tropical forest dynamics plot in south‐west China. Because the influence of biotic interactions may become more apparent as cohorts age, on local scales, and in resource‐rich environments, we perform our analyses across three size classes, six spatial scales and six distinct habitat types, using 10 plant functional traits and a molecular phylogeny for the &gt;400 tree taxa found in the plot. All traits, except leaf area and stem‐specific resistance, had significant, albeit weak phylogenetic signal. For canopy species, phylogenetic clustering in small and medium size classes turned to phylogenetic overdispersion in the largest size class and this change in dispersion with size was found in each habitat type and across all spatial scales. On fine spatial scales, functional dispersion changed from clustering to overdispersion with increasing size classes. However, on larger spatial scales assemblages were functionally clustered for all size classes and habitats. Phylogenetic and functional structure across spatial and size scales and habitats gave strong support for a deterministic model of species co‐occurrence rather than for a neutral model. The results also support the hypothesis that abiotic determinism is more important at larger scales, while biotic determinism is more important on smaller scales within habitats.

Tree growth-competition relationships in thinned Eucalyptus plantations vary with stand structure and site quality

Growth responses to thinning can vary with site quality and age, however, the direction of the response varies. An understanding of the mechanisms behind thinning responses could help forest managers optimise production as well as inform modellers and ecologists about the functioning of tree stands. Thinning was used to create a range of stand densities in eleven Eucalyptus plantation stands on seven sites in south-eastern Australia. Basal area periodic annual increment (PAI; cm2 year−1) of individual dominant and codominant trees was then related to competition, such that PAI = a + b ln(Competition). Competition was defined as the sum of the basal area of neighbouring trees within a radius of 6.5 m. The relative (%) and absolute (cm2 year−1) responses to competition were quantified using b, which was correlated with site quality and stand structure of unthinned stands. Stand structure was quantified using statistics or parameters that describe the diameter distribution for the given age, species and site, including skewness, the coefficient of variation and parameters of the Weibull probability distribution. Relative and absolute responses both increased with increasing site quality and in stands with more negatively skewed diameter distributions (higher proportion of larger trees) or lower coefficients of variation. Absolute thinning responses often increased with increasing size class, while relative thinning responses often decreased. Variables describing diameter distributions (size-class structure) were able to describe some of the variation in competition responses that site quality could not. This indicates why stands on similar site qualities but with different stand structures can have correspondingly different thinning responses. Stand structural variables may be more useful predictors of thinning responses in stands that experience large temporal changes in diameter distributions compared with site quality, which is a more static variable. Thus, knowledge about the development of diameter distributions might help to refine thinning regimes.

Fogo e dinâmica da comunidade lenhosa em cerrado sentido restrito, Barra do Garças, Mato Grosso

Estudos sobre a dinâmica e estrutura da vegetação lenhosa após incêndios naturais ocorridos no Parque Estadual da Serra Azul mostram que as queimadas afetam a sobrevivência e o crescimento das plantas sendo o impacto dependente da intensidade, frequência e duração dos incêndios. Dez parcelas (20 × 50 m) queimaram em 2002 e 2007 (Área 1) e outras 10 (Área 2) queimaram em 2002, 2005 e 2007. Em janeiro de 2009, a Área 1 apresentou menor mortalidade (2,0%) e maior recrutamento (3,7%) que a Área 2 (4,3% e 0,05% respectivamente). A mortalidade decresceu com o aumento das classes de diâmetro. O tamanho médio (altura e diâmetro) dos indivíduos decresceu na Área 2. O padrão de rebrotas após o fogo foi relacionado ao tamanho dos indivíduos. As rebrotas ocorreram na base dos indivíduos pertencentes às menores classes de tamanho e na copa daqueles pertencentes às maiores classes de tamanho. Os estimadores Jacknife e Chao 2 indicaram redução da riqueza na Área 2 submetida a maior freqüência de queimadas. A longevidade das árvores adultas e a persistência de indivíduos menores através das rebrotas podem determinar a manutenção da comunidade lenhosa no cerrado se os intervalos entre queimadas não forem inferiores a cinco anos.

Spatial distributions of species in an old-growth temperate forest, northeastern China

Studying spatial distributions of species can provide important insights into processes and mechanisms that maintain species richness. We used the relative neighborhood density Ω based on the average density of conspecific species in circular neighborhoods around each species to quantify spatial distributions of species with ≥10 individuals in a fully mapped 25 ha temperate plot at Changbaishan, northeastern China. Our results show that spatial aggregation is a dominant pattern of species in the Changbaishan temperate forests. However, the percentage of significantly aggregated species decreases with spatial scale, especially for rare species. Rare species are more aggregated than intermediate and common species. The aggregation intensity declines with increasing size class (diameter at breast height), i.e., species become more regularly spaced as species grow, which is consistent with the predictions of self-thinning and Janzen–Connell spacing effects. Species functional traits (canopy layer, seed dispersal ability, shade tolerant, etc) also havea significant effect on the spatial distributions of species. Our results partially conform to the prediction that better dispersal reduces aggregation. Consequently, dispersal limitation, self-thinning, Janzen–Connell spacing effects, and habitat heterogeneity may primarily contribute to spatial distributions of species in the temperate forests.

Optimised effluent treatment by stabilised trout faeces

The efficiency of mechanical effluent treatment depends on the ratio of particle bound waste load to total waste load and on the size distribution of the suspended solids. We tested an innovative approach to increase mechanical treatment efficiency by adding small amounts of indigestible binders to trout feed. The hypothesis was that the addition of binders would enhance faecal stability and improve shear resistance. This should slow the breakdown of faeces by water turbulences resulting in larger particles. These are easier to remove by filtration and should be more resistant to leaching than small particles, so more soluble waste remains particle-bound and removable. In two separate trials, portion size trout were fed diets containing indigestible binders, while control groups received the same basal diet without binder. The fish were reared in 500 L circular tanks. The effect of each binder on the stability (viscosity and elastic resistance) of dissected faeces was measured by a rheometer. Both stability parameters increased significantly by the addition of the binders. Addition of Guar gum increased the viscosity of the faeces best by 183% and 140% in Trial 1 and Trial 2 respectively, while Alginate increased elastic resistance best by 173% and 125%. The digestibility of the diets was not affected. The dissected faeces were exposed to controlled turbulence in the laboratory. The particle size distributions of the suspensions were measured using a laser-based technique applying the ‘time-of-transition’ theory. The Guar gum and Alginate treatments led to significantly larger particles compared to the control. Based on these data the beneficial effect of the Guar gum binder on post-filtration suspended solid load (100 μm gauze) was calculated to be 40.2% and 18.2% for Trials 1 and 2 respectively. In a leaching experiment, faecal particles were suspended in distilled water and allowed to leach for 1 h. The solids were fractionated by sieving and their relative phosphorus and nitrogen content was determined. The relative phosphorus and nitrogen content of the particles increased significantly with increasing size class. In a second experiment, larger particles of the Guar gum treatment yielded significantly higher total amounts of phosphorus and more dry matter remained solid-bound compared to the control. The present study demonstrates promising potential for binders as tools in significantly reducing the effluent load of fish farms without affecting feed efficiency.

Inhibitory Effects of Feeding with Carrots or (−)-Falcarinol on Development of Azoxymethane-Induced Preneoplastic Lesions in the Rat Colon

The effects of intake of dietary amounts of carrot or corresponding amounts of (-)-(3R)-falcarinol from carrots on development of azoxymethane (AOM)-induced colon preneoplastic lesions were examined in male BDIX rats. Three groups of eight AOM-treated rats were fed the standard rat feed Altromin supplemented with either 10% (w/w) freeze-dried carrots with a natural content of 35 mug falcarinol/g, 10% maize starch to which was added 35 mug falcarinol/g purified from carrots, or 10% maize starch (control). After 18 weeks, the animals were euthanized and the colon was examined for tumors and aberrant crypt foci (ACF), which were classified into four size classes. Although the number of small ACF was unaffected by the feeding treatments, the numbers of lesions as a function of increasing size class decreased significantly in the rats that received one of the two experimental treatments, as compared with the control treatment. This indicates that the dietary treatments with carrot and falcarinol delayed or retarded the development of large ACF and tumors. The present study provides a new perspective on the known epidemiological associations between high intake of carrots and reduced incidence of cancers.

Attenuated tree species diversity in human-impacted tropical evergreen forest sites at Kolli hills, Eastern Ghats, India.

Tree diversity (≥30 cm gbh) in undisturbed and human-impacted tropical evergreen forest sites was investigated in the Kolli hills, Eastern Ghats, India. Four 2-ha contiguous permanent plots were erected, one each in Perumakkai shola (site PS), Vengodai shola (VS), Kuzhivalavu shola (KS) and Mottukkadu shola (MS) at 1000, 1050, 1200 and 1250 m elevation, with increasing human disturbance, to evaluate the difference in tree species composition, stand structure and dynamics. This paper discusses the results of the first survey. A total of 3825 individuals and 78 species from 61 genera and 36 families were enumerated in the 8 ha area. Among the four 2-ha sites, species richness was greatest (58) in the undisturbed site PS and lowest (39) in the highly disturbed site MS. Shannon, Simpson, Hill diversity and evenness indexes revealed a progressive reduction in diversity with increasing disturbance. The asymptote species-area curves imply adequate site sampling. Tree density (1151 to 651 trees ha−2) and basal area (106 to 46.6 m2 ha−2) decreased from undisturbed to disturbed site, due to selective felling. Single species, Memecylon umbellatum dominated sites MS (39%) and VS (26%), while Nothopegia heyneana, Memecylon umbellatum and Diospyros ovalifolia were dominant in PS, and Meliosma simplicifolia, Myristica dactyloides and Phoebe wightii in KS. Based on species abundance, we classify the study area as Memecylon–Phoebe–Beilschmiedia association with Neolitsea and Myristica as codominants. Tree population structure revealed a step-wise decline in girth frequencies with increasing size class in undisturbed site PS, whereas tree density fell sharp (>50%) in medium girth class in the disturbed site MS. Population of the dominant species varied widely. The diversity values of this inventory are compared with similar studies in India and other tropical forests. Evidently, the reduction in species richness (by 52%), basal area (56%) and tree density (58%) in disturbed sites, with 57.6% of species rarity of this tropical evergreen forest, in secluded patches (‘sholas’) of Kolli hills, underlines conservation need to prevent species loss.

Behaviour of price transmissions in vertically coordinated markets: The case of frozen black tiger shrimp (Penaeus monodon)*

This study analyses the behaviour of the price transmission process for the leading cultured shrimp species, black tiger shrimp (Penaeus monodon), in both forward and backward directions between Thai and Indonesian shrimp packer markets and the Japan Tokyo wholesale market. The bivariate cointegration approach using the Engle‐Granger two‐stage estimation procedure is applied in this study. The results show that Tokyo wholesale prices appear to have stronger backward influences on the formation of overseas contract prices used by Japanese shrimp importers in the Thai and Indonesian shrimp packer markets. In addition, there is a tendency for the speed of price transmissions in the long term to increase with increasing size class (from 26 to 30–21–25 and 16–20 counts per pound) of black tiger shrimp, regardless of estimation specification in the direction of price transmissions and the shrimp country of origin.

A method for estimating the flocculation time of monodispersed sediment suspensions

A new method is presented for determining the flocculation time of monodispersed sediment suspensions. Flocculation time is the critical time at which abrupt changes in the particle size spectrum of an aggregative suspension occurs. This method predicts flocculation times to within 6% of values predicted by a geometric sectional aggregation model (Batterham, R.J., Hall, J.S. and Barton, G., 1981. In: Proceedings, 3rd International Symposium on Agglomeration, Nürnberg, Federal Republic of Germany, pp. A136–A150) but uses only a fraction of the computational effort. Flocculation times estimated in this way are superior to estimates of flocculation time scale made using half-life because particle geometry and differential settling encounter are taken into account. The proposed model is based on typical size distributions calculated using the Batterham et al. model. These size distributions have approximately equal mass in geometrically increasing size classes, i.e. they are Junge-dispersed. By assuming that the suspension remains Junge-dispersed throughout its evolution, the system of differential equations required to describe the suspension reduces to a single differential equation. Flocculation times are calculated for three values of maximum floc size ( d max={10,1,0.1 mm}), a maximum settling velocity of w s=1 mm s -1, and a variety of initial conditions. For a given set of inputs, flocculation times calculated in this way are linearly related to those calculated using the Batterham et al. model, but the slope of the relationship varies with fractal dimension. Multiple linear regression equations are developed to directly relate the two. The effect of including sinking losses into the Batterham et al. model is also investigated. If the sinking loss time scale is much longer than the flocculation time, then the suspension becomes flocculated at roughly the same time it would have had there been no sinking losses, and the new method can be used. Conversely, if the sinking time scale is less than or equal to the flocculation time, then the new method cannot be used.

Signal and noise in length frequency analysis

Length frequency analysis is an important tool for the estimation of the age structure of a population. This is particularly important in decapods since they do not have permanent calcified structures where age can be read directly. Length distributions generally possess some amount of noise, due to variability phenomena inherent to the sampling procedure, in particular when samples are small and/or many age groups are present. This is expressed by peaks that do not represent true peaks in the population, resulting in the masking of the signal one wishes to identify, i.e. the mean length-at-age of the different age groups. Some data transformation techniques applied to the raw data have been used to improve the estimation of mean length-at-age. These transformations aim at the reduction of the noise resulting from sampling limitations. They include increasing the length class width or applying running averages to the length distributions. In this study both procedures were evaluated in terms of parameter recovery using simulated samples with known age structure. The samples were generated taking into consideration the biology and fishery of the Norway lobster from the South coast of Portugal. Class widths of 1 to 5 mm and running averages of three and five classes (1 mm) were tested. In general, better results were obtained with moving averages than by increasing size class width. Both techniques resulted in the reduction of some noise. Grouping data into wider classes also resulted in the loss of a considerable amount of information. Overall, moving averages produced the best results.

Diameter and height distributions in a gallery forest tree community and some of its main species in central Brazil over a six-year period (1985-1991)

(Diameter and height distributions in a gallery forest tree community and some of its main species in central Brazil over a six-year period (1985-1991)). The diameter and height structure were studied over six years in approximately 64 ha of the Gama gallery forest in Brasilia, DF. Trees from 10 cm dbh were measured every three years from 1985 in 151 (10 x 20 m) permanent plots. Natural regeneration (individuals under 10 cm dbh) was measured in subplots within the 200 m2 plots. Most individuals and species were under 45 cm diameter and 20 m high while the maximum diameter for individual species ranged from 30 to 95 cm. The diameter structure was typical of a mixed tropical forest with the number of individuals decreasing with increasing size classes and showing little change over the six years. The most abundant species occupy different positions in the canopy and have different size structures.

Diversity, structure and dynamics of a gallery forest in central Brazil

The structure and dynamics of approximately 64 ha of undisturbed gallery forest were studied over six years. Trees from 31 cm gbh (c. 10 cm dbh) were measured every three years from 1985. They were in 151 (10×20 m) permanent plots in the Gama forest in the Federal District of Brazil. Natural regeneration (individuals under 31 cm gbh) was measured in subplots (of 2×2 m, 5×5 m and 10×10 m) within the 200 m2 plots. The total tree flora (gbh≥31 cm) consisted of 93 species, 81 genera and 44 families in 1985. The Leguminosae, Myrtaceae and Rubiaceae were the families richest in number of species. Most individuals and species were under 45 cm diameter and 20 m high while the maximum diameter per species ranged from 30 to 95 cm. The density structure of trees and natural regeneration was similar, in which the densities of c. 80% of the species represented less than 1% of the total density. The periodic mean annual diameter increment for trees from 10 cm dbh, was c. 0.25 cm/year. Variability was high with coefficients of variation c. 100% or more. The Gama community may maintain tree diversity and structure in undisturbed conditions. Regeneration of c. 80% of the species was found in the establishing phase (poles); the diameter structure was typical of native forests with the number of individuals decreasing with increasing size classes and showing little change over the six years; recruitment compensated for the mortality of most of the abundant species. The soils in Gama gallery forest were dystrophic with high aluminium content. Multivariate analysis suggested the stream, natural gaps and edges as the main causes of floristic differentiation at the community level.