Range Of Size Classes Research Articles

Exploring the Variability of Tropical Savanna Tree Structural Allometry with Terrestrial Laser Scanning

Individual tree carbon stock estimates typically rely on allometric scaling relationships established between field-measured stem diameter (DBH) and destructively harvested biomass. The use of DBH-based allometric equations to estimate the carbon stored over larger areas therefore, assumes that tree architecture, including branching and crown structures, are consistent for a given DBH, and that minor variations cancel out at the plot scale. We aimed to explore the degree of structural variation present at the individual tree level across a range of size-classes. We used terrestrial laser scanning (TLS) to measure the 3D structure of each tree in a 1 ha savanna plot, with coincident field-inventory. We found that stem reconstructions from TLS captured both the spatial distribution pattern and the DBH of individual trees with high confidence when compared with manual measurements (R2 = 0.98, RMSE = 0.0102 m). Our exploration of the relationship between DBH, crown size and tree height revealed significant variability in savanna tree crown structure (measured as crown area). These findings question the reliability of DBH-based allometric equations for adequately representing diversity in tree architecture, and therefore carbon storage, in tropical savannas. However, adoption of TLS outside environmental research has been slow due to considerable capital cost and monitoring programs often continue to rely on sub-plot monitoring and traditional allometric equations. A central aspect of our study explores the utility of a lower-cost TLS system not generally used for vegetation surveys. We discuss the potential benefits of alternative TLS-based approaches, such as explicit modelling of tree structure or voxel-based analyses, to capture the diverse 3D structures of savanna trees. Our research highlights structural heterogeneity as a source of uncertainty in savanna tree carbon estimates and demonstrates the potential for greater inclusion of cost-effective TLS technology in national monitoring programs.

Species-Specific Characteristics Influence Contaminant Accumulation Trajectories and Signatures Across Ontogeny in Three Pelagic Shark Species.

Factors influencing organic contaminant accumulation in sharks, especially across ontogeny, are not well-known. Contaminant concentrations were measured in three species of sharks (Blue, Shortfin Mako, and Common Thresher) across a range of size classes (neonatal to adult) that vary in their ecological and physiological characteristics. Empirical data was compared to a theoretical framework that predicted the shape of lifetime accumulation curves. We found that a one-size-fits-all accumulation model was not appropriate as species-specific characteristics had a significant effect on contaminant accumulation trajectories. Maternal offloading likely has an important effect on determining neonatal shark contaminant starting points, and trophic ecology and physiology may interact to affect the shape of species' contaminant accumulation curves. Makos were found to have the highest accumulation potential and Blues the lowest, with Threshers being intermediate in accumulation potential. Changes in species' ecology and/or physiology were also reflected in contaminant signature changes over ontogeny. If contaminant concentrations are to be used as a proxy for risk, species-specific characteristics need to be taken into account when estimating contaminant exposure and its potential negative effects on shark health and human consumption safety.

Patterns of primary production in the Red Sea

This paper presents data on various parameters of primary production (chlorophyll concentration, carbon uptake, nitrogen uptake, phytoplankton groups) measured in 4 cruises in the Saudi Arabian waters of the Red Sea between 2012 and 2015. The results showed that while there was a tendency for an increase from north to south, the meridional distributions were distinguished by alternating high and low concentrations of chlorophyll, carbon uptake rates and cell densities of various phytoplankton groups, with the higher levels being associated with zonal currents and the lower values lying in between. These patterns of distributions lead us to conclude that the biological production in the Red Sea is influenced more by anticyclonic eddy, and less by meridional, circulations at any time of the year. Synthesizing the present results with earlier ones on the patterns of distributions of nutrients and the flow of Gulf of Aden Intermediate Water (GAIW), we also conclude that entrainment of GAIW in successive eddies is the cause for higher nutrients and biological production in the regions of eddy boundary currents. Data on size-fractionated carbon uptake and nitrogen uptake showed that the eddies in Red Sea favour the proliferation of producers across a range of size classes rather than one class. The amount of nutrients injected into the euphotic zone in the eddy boundary currents is probably not high enough to induce a definite shift in phytoplankton size classes, and the primary production still remains to a significant extent regenerated nutrient-driven.

Estimating Stem Diameter Distributions in a Management Context for a Tolerant Hardwood Forest Using ALS Height and Intensity Data

Two types of nonparametric modeling techniques and various metrics derived from airborne laser scanning (ALS) data were examined in terms of their utility for modeling stem diameter distributions in an uneven-aged tolerant hardwood forest in Ontario, Canada. Using an area-based approach (ABA), the frequency distribution of trees across 6 size classes was predicted using k-nearest neighbor (k-NN) imputation and Random Forest (RF) regression. Predictor variables derived from ALS height and intensity data were divided into 3 groups: height only, intensity only, and all metrics. Prediction results demonstrated that the first 2 groups of predictor variables exhibited similar predictive accuracy, whereas the synergy of both resulted in enhanced performance. The utility of intensity-based metrics was corroborated by an importance measure obtained from RF. The size class-specific stem density estimation approach based on RF was more accurate and flexible than the simultaneous estimation approach based on k-NN models. After the predicted diameter distributions were grouped into 9 structural groups, heterogeneous accuracy scores revealed the challenges for predicting select diameter distributions. Although successes were observed for certain size classes, there remains additional research (e.g., development of additional metrics or data types) to be done to accurately predict a complete range of size classes.

Defining the allometric relationship between size and individual fatty acid turnover in barramundi Lates calcarifer

An experiment was conducted with barramundi (Asian seabass; Lates calcarifer) to examine the allometric scaling effect of individual fatty acids. Six treatment size classes of fish were deprived of food for 21days (Treatment A, 10.5±0.13g; Treatment B, 19.2±0.11g; Treatment C, 28.3±0.05g; Treatment D, 122.4±0.10g; Treatment E, 217.6±0.36g; Treatment F, 443.7±1.48g; mean±SD) with each treatment comprising of fifteen fish, in triplicate. The assessment of somatic losses of whole-body energy and lipid were consistent with previous studies, validating the methodology to be extended to individual fatty acids. Live-weight (LW) exponent values were determined to be 0.817±0.010 for energy and 0.895±0.007 for lipid. There were significant differences among the fatty acids ranging from 0.687±0.005 for 20:5n-3 (eicosapentaenoic acid) and 0.954±0.008 for 18:1n-9 (oleic acid). The LW exponent values were applied to existing fatty acid intake and deposition data of barramundi fed with either 100% fish oil or 100% poultry oil. From this the maintenance requirement for each fatty acid was determined. The metabolic demands for maintenance and growth were then iteratively determined for fish over a range of size classes. Application of these exponent values to varying levels of fatty acid intake demonstrated that the biggest driver in the utilisation of fatty acids in this species is deposition demand and despite their reputed importance, the long-chain polyunsaturated fatty acids had nominal to no maintenance requirement.

Soil biota of different size classes change the impact of soil compaction on a plant community

Question Does a reduction in size class of soil biota aggravate the impacts of soil compaction on plant communities? Location Controlled mesocosm study with a European ruderal plant community exposed to soil compaction and soil biota communities of different size classes. Methods We evaluated the individual and combined effects of soil compaction and soil biota communities of different size classes (<2000, <212, <20 μm, natural control) on the structure and productivity of a ruderal plant community, and the establishment of a neophyte (Lupinus polyphyllus) in a full-factorial mesocosm study. Results Soil compaction reduced the productivity of the plant community, but the negative effect decreased in magnitude as the size class of the soil biota community was reduced. Consistently, shoot growth of the dominant grasses was most reduced by soil compaction when bigger soil biota were present; the shoot growth of forbs showed an opposite pattern. In contrast, legumes seem to profit from soil compaction independent of the size class of the soil biota community, and were detrimentally affected only in the natural control soil. Establishment of the neophyte L. polyphyllus was best under natural soil conditions and was not affected by soil compaction. Conclusions A reduction in soil biota size due to intensified management may change the impacts of soil compaction on plant communities. The results indicate that soil compaction has the most detrimental effect on primary productivity in soil communities where a range of size classes of soil biota is present and the functional complexity of the soil biota community is therefore high.

Implications of hypoxia tolerance for wetland refugia use in Lake Nabugabo, Uganda

AbstractAquatic hypoxia can affect predator‐prey interactions by altering the success rate of the predator and/or the vulnerability of prey. For example, in the Lake Victoria basin of East Africa, native prey exploit hypoxic wetlands as refugia from predation by introduced Nile perch (Lates niloticus). Here, it is predicted that species exploitation of wetlands depends on their hypoxia tolerance relative to the heterogeneity of wetland hypoxia. In this study, we compared the hypoxia tolerance of four fish taxa that differ in their use of hypoxic wetlands in Lake Nabugabo, Uganda: the cichlid Pseudocrenilabrus multicolor victoriae that inhabits the dense swamp interior; and three taxa that inhabit wetland ecotones including Nile tilapia (Oreochromis niloticus), L. niloticus and juvenile endemic haplochromine cichlids. We characterised hypoxia tolerance by exposing fish to progressive hypoxia and quantifying variation in aquatic surface respiration (ASR). The effect of body size on tolerance was explored in L. niloticus by quantifying ASR behaviour across a range of size classes. ASR behaviour was also compared between O. niloticus groups from wetland versus open‐water habitats to detect habitat‐associated intraspecific variation. The most tolerant taxon was the swamp specialist P. multicolor, indicated by its low ASR thresholds and small percentage of fish using ASR during the final sample interval. The other three taxa did not differ in ASR behaviour, and no differences were detected between O. niloticus groups. Body size effects were present for L. niloticus suggesting a lower tolerance to hypoxia in larger‐bodied individuals, thus limiting their ability to penetrate wetlands.

The Gulf of Manfredonia: a new neritic foraging area for loggerhead sea turtles in the Adriatic Sea

The Adriatic Sea is an important foraging area for the loggerhead sea turtle, Caretta caretta, but neritic habitats for this species along the Italian coast were identi- fied in the northern shallow area only. The Gulf of Manfredonia is a relatively wide shallow area in the south-west Adriatic and its features and preliminary information make it a potential foraging ground for turtles. In order to assess sea turtle occur - rence in the area, we monitored seven bottom trawlers based in the port of Manfredo- nia during the period Oct 2010 - Jul 2011 through a voluntary logbook programme, resulting in a total of 62 turtle captures during 617 fishing days. Since a turtle capture represents a rare event during such sampling, data were analysed by a zero-inflated Poisson (ZIP) model. Results indicate that: (i) the Gulf is a neritic foraging ground for loggerhead turtles which occur there with a relatively high density comparable to oth- er Mediterranean foraging grounds, (ii) it is frequented by a wide range of size classes, including small juveniles as well as adults, (iii) the highest occurrence is during the period Jun-Dec, (iv) over 1700 turtle captures occur in the Gulf annually. Preliminary findings about recaptured individuals suggest that part of the turtles are resident in the area. The peculiar features of the Gulf of Manfredonia and the collaboration of the fishing fleet, make it a valuable index site for studying current trends of sea turtle populations at sea as well as other aspects of sea turtle biology and conservation.

Returning biodiversity of rehabilitated forest on a coal mined site at Tanjung Enim, South Sumatra

Suhartoyo H, Munawar A, Wiryono. 2012. Returning biodiversity of rehabilitated forest on a coal mined site at Tanjung Enim, South Sumatra. Biodiversitas 13: 13-17. Restoring disturbed mined land is challenging since the outcomes of various rehabilitation procedures on mined sites in terms of vegetation structure, composition and ecological function are not presently understood, especially in the developing countries. This study examined the mechanism of biodiversity recruitment, especially on structural attributes of an undisturbed forest community and rehabilitated forests of different ages on sites disturbed by coal-mining operations at Tanjung Enim, South Sumatra. Un-mined forest was characterized by complex structural features including a dense stand of trees in a range of sizeclasses, an almost closed canopy, and a shrubby understorey. In contrast, young mined sites were characterized by a low density of woody stems, a relatively open canopy and herbaceous ground cover. Soil characteristics of rehabilitated site were progressing towards the reference site. The marked differences in structural complexity between unmined and mined sites suggest that it will take very long time for the mined sites to recover into their original conditions. So, more restoration intervention will be needed to speed the recoveryprocesses.&#x0D; Key words: restoration, mining, biodiversity, structural complexity.INTRODUCTIONRehabilitation of disturbed areas due to miningactivities is intended to assist the environment in returningto a stable and sustainable land use as soon as possible(Bell 1996; Parker 1997). The nature of the post-miningland use will depend on a number of factors including theecological potential of the mined environment and thewishes of the neighboring society. Currently, in Australia,many mining operations are using native plant species inrehabilitation programs leading to the establishment ofpastures and forests (Bell 1996, 2001; Gardner 2001),however in Indonesia, mining operators are mostly usingfast growing exotic species in their rehabilitation(Suhartoyo 2008), as in many other countries al around theworld (Martínez-Ruiz et al. 2007; Alday et al. 2010).As more mine operators need to establish their postmining plan

USING AN EXPERIMENTAL IN SITU FISHWAY TO PROVIDE KEY DESIGN CRITERIA FOR LATERAL FISH PASSAGE IN TROPICAL RIVERS: A CASE STUDY FROM THE MEKONG RIVER, CENTRAL LAO PDR

ABSTRACTFish passage through an experimental vertical‐slot fishway was assessed at a floodplain regulator on the Mekong River in Central Laos between April and July 2009. Experiments were conducted to investigate the influence of fishway floor slope (1v:15h or 1v:7.5h) on fish passage success with a view to developing a series of optimal design criteria for the construction of vertical‐slot fishways at other barriers to fish passage in the Lower Mekong Basin. A total of 14 661 fish from 73 species were captured during the experiments. Catches were dominated by riverine (white) (n = 51; 69% of total) and floodplain (black) species (n = 15; 20%) which represented 19 families in total. The work demonstrated that fish were actively attempting upstream passage from the Mekong River to an adjacent floodplain and displayed strong migratory behaviour during river level rises. Migratory activity was greatest during sharp rises in water level but reduced substantially when river level fell. Fish community composition varied greatly among the two fishway floor slopes and the control group. More fish species were collected from control samples, but the most fish and species were collected when the fishway was configured on a moderate hydraulic slope (1v:15h). A range of size classes were also collected from control and moderate‐slope groups, but steeper‐gradient catches were dominated by larger fish. This study demonstrated that vertical‐slot fishways could provide passage for a biodiverse fish community where fish move laterally onto floodplains. The construction of fishways which consider the local fish ecology and hydrology may therefore represent a valuable management tool to help restore important movement pathways for tropical freshwater fish. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Age-specific responses to climate identified in the growth of Quercus alba

The objective of this research was to determine whether the dendroclimatic responses of young Quercus alba (aged 29–126 years) differ from those of old Q. alba (149–312 years). We collected Q. alba increment cores across a range of size classes from Buffalo Mountain Natural Area Preserve, an oak-hickory forest in southcentral Virginia, USA. Tree cores were crossdated and raw ring widths were detrended to remove the influence of increasing circumference with age, microsite, and local stand dynamics. Standardized ring widths were averaged to develop two master chronologies from the 20 oldest and youngest trees. Ring-width indices were correlated with temperature, precipitation, and Palmer Drought Severity Index (PDSI). Annual tree-ring growth in old and young Q. alba was significantly correlated with precipitation from the previous growing season, but was not significantly correlated with temperature. Only the old trees showed a significant correlation between annual ring width and PDSI. These results may indicate that growth in old trees is more sensitive to drought than in young trees. If future climate change includes the predicted increase in mid-growing season droughts, tree-level responses are likely to be age-dependent with older trees experiencing relatively greater reductions in growth.

Investigational piscivory of some juvenile Australian freshwater fishes by the introduced Mozambique tilapia Oreochromis mossambicus

Experimental tanks were used to observe predatory effects in three different size classes of Mozambique tilapia Oreochromis mossambicus (one of the world's most widespread exotic species and generally regarded to be a herbivore or both herbivore and detritivore) when tested against 10 juvenile Australian freshwater fish species, and significant levels of predation against all were recorded. There was a general trend for larger O. mossambicus to kill more prey and this was also reflected in a separate series of experiments using juvenile barramundi Lates calcarifer over a range of size classes. Predatory effects by O. mossambicus broadly reflected the accepted models of predator-prey interactions, being that mortality (and survival) was closely related to relative body size and mouth gape limitation. Experimental evidence for piscivory in O. mossambicus was supported by field sampling that detected prey fish remains in 16% of all fish surveyed (n = 176). The recognition of active piscivory by O. mossambicus in laboratory and field situations is the first such evidence, and suggests a need to re-evaluate the nature of their effects in introduced environments.

Diversity and natural history of a Lithothamnion muelleri-Sargassum horridum community in the Gulf of California

We quantitatively assessed the relative contribution of the rhodolith form of Lithothamnion muelleri, a likely foundation species, to macroorganism diversity in a community also inhabited by the large fucalean Sargassum horridum at a site near Cabo Los Machos at the mouth of Bahía Concepción, Baja California Sur, Mexico. The composition and abundance of seaweeds, epibenthic invertebrates, and fish were estimated in March and October 2003, and invertebrates within rhodoliths (cryptofauna) in March 2003. Rhodoliths and Sargassum horridum had the highest cover of all organisms within the 0.5-km2, 2–8-m-deep cobble-sand site. A total of 29 species of seaweeds, 40 taxa of benthic invertebrates, and 33 species of fish were sampled in transects and quadrats. Macroalgal and fish diversity were similar between sampling times as a result of loss and replacement of taxa, but benthic invertebrate diversity declined without replacement from March to October. Rhodolith cover was similar at both sampling times. The cover and density of S. horridum were highly seasonal, and the non-rhodolith flora changed from abundant S. horridum (35% cover) in March to abundant red algal turf in October (22% cover). The sea urchin Arbacia incisa, tunicates, and polychaetes were the most abundant epibenthic invertebrates in March, but declined by October, the former to zero. Grunts (Haemulon maculicauda) and porgies (Calamus brachysomus) were the most abundant fish at both sampling times, but there were large temporal changes in some other species, especially schooling fishes. Rhodolith density in March was 24 ind m–2, with numerous individuals &gt;8 cm diameter. Fifteen rhodoliths from a range of size classes contained 114 cryptofaunal taxa with an average of 40 taxa/individual in the largest rhodoliths. These results show the importance of rhodolith habitat to diversity, the large temporal changes in some assemblages, and the exceptionally high diversity of this subtropical community.

Use of commercial vessels in survey augmentation: the size-frequency distribution

The trend towards use of commercial vessels to enhance survey data requires assessment of the advantages and limitations of various options for their use. One application is to augment information on size-frequency distributions obtained in multispecies trawl surveys where stratum boundaries and sampling density are not optimal for all species. Analysis focused on ten recreationally and commercially important species: bluefish, butterfish, Loligo squid, weakfish, summer flounder, winter flounder, silver hake (whiting), black sea bass, striped bass, and scup (porgy). The commercial vessel took 59 tows in the sampled domain south of Long Island, New York and the survey vessel 18. Black sea bass, Loligo squid, and summer flounder demonstrated an onshore-offshore gradient such that smaller fish were caught disproportionately inshore and larger fish offshore. Butterfish, silver hake, and weakfish were characterized by a southwest-northeast gradient such that larger fish were caught disproportionately northeast of the southwestern-most sector. All sizes of scup, striped bass, and bluefish were caught predominately inshore. Winter flounder were caught predominately offshore. The commercial vessel was characterized by an increased frequency of large catches for most species. Consequently, patchiness was assayed to be higher by the commercial vessel in nearly all cases. The size-frequency distribution obtained by the survey vessel for six of the ten species, bluefish, butterfish, Loligo squid, summer flounder, weakfish, and silver hake, could not be obtained by chance from the size-frequency distribution obtained by the commercial vessel. The difference in sample density did not significantly influence the size-frequency distribution. Of the six species characterized by significant differences in size-frequency distribution between boats, all but one was patchy at the population level and all had one or more size classes so characterized. Although the variance-to-mean ratio was typically higher for the commercial vessel, five of the six cases that were otherwise were among the species for which the size-frequency distribution differed between the two vessels. Thus, the origin of the significant differences observed between vessels would appear to lie in the spatial pattern of the species as it interacts with the tendency for one vessel to obtain large catches more frequently for some size classes. One consequence of differential distribution and catchability is that more large fish were present in the commercial vessel catches than in the survey vessel catches in cases where the two vessels obtained different size-frequency distributions. Application of commercial vessels to the evaluation of size frequency hinges on understanding how to interpret differences among boats, gear, and sampling design. Here we show that key ingredients to this understanding are the degree of nonlinearity in catchability across a range of size classes, the interaction of varying spatial arrangements among size classes and the sampling design, and the interaction of varying spatial arrangements with differential catchability.

A NEW MYXOZOAN FROM FERAL GOLDFISH (CARASSIUS AURATUS)

In February 2004, a mass die-off of common goldfish Carassius auratus L., presumptively caused by bacterial coldwater disease (Flavobacterium psychrophilum), occurred at Fern Ridge Reservoir, Oregon. A range of size classes was affected, but all mature fish were female and all fish were infected with a single myxozoan, Chloromyxum auratum n. sp. No histological changes were observed associated with the parasite. Infection was represented by mictosporic plasmodia and free-floating spores in the gall bladder. Parasite spores were nearly spherical, 13.6 microm long x 12.6 microm wide x 13.1 microm thick, and possessed 4 equal-sized polar capsules. Spores had a coglike appearance in apical view because of distinct ridges 2.1 microm high protruding from the valve cells. There were 6-9 extrasutural ridges per valve (15-20 ridges per spore), aligned along the longitudinal axis, with some branching, and convergence at both poles. Morphologically, spores identified most closely with Chloromyxum cristatum Léger, 1906; however, 18S rDNA sequence data indicated only 97.5% similarity over 2,076 bp with Chloromyxum cyprini, the only synonym of C. cristatum for which DNA data are available; additional sequence data may reveal the other synonyms to be distinct species. This is the first record of a species of Chloromyxum from goldfish.

Effects of spatial variability and colony size on the reproductive output and gonadal development cycle of the Mediterranean red coral (Corallium rubrum L.)

Red coral (Corallium rubrum, L. 1758) is an over-exploited Mediterranean gorgonian. The gonadal development cycle of this gorgonian is examined at the Costa Brava (NW Mediterranean) taking into account for the first time colony size, depth and spatial horizontal variability. This study compares the gonad development and fertility in two colony size classes (colonies 10-cm height, both at 40–45-m depth), and two populations at different depths (16–18-m depth, and 40–45-m depth, both consisting of 12 cm high colonies, in 2 cm intervals) was examined in the deep population, where large colonies were present. Furthermore, reproductive output was compared in 6 populations (distributed along more than 70-km coastline) one month before spawning (June). Red coral was found to be dioecious and gonochoric with a sex ratio of 1:1, which differs from other NW Mediterranean populations. On the other hand, fertility of different size classes indicates that small colonies of 2-cm height already produce gonads, which is in line with previous studies. Female and male polyp fertility and sperm sac size increase significantly with colony size [sperm sac diameter: 476±144 μm (mean±SD) and 305±150 μm in the >10-cm and 12 cm, thus the recommendation of this study is that a minimum height should be incorporated into fishing regulations. The six studied populations at the Costa Brava showed a comparable reproductive potential, which demonstrates little variability within the homogenous population structure and range of size classes (due to overharvesting) found at the Costa Brava. The study of reproductive output is an important tool for ecosystem management, and this work recommends basing specific exploitation laws for distinctive populations on colony size, which is found to have a larger effect on reproductive potential than mesoscale variability.

Surface activity of Corophium volutator: A role for parasites?

In soft-bottom intertidal habitats, the normally infaunal amphipod Corophium volutator is often found active on the sediment surface during low tide, exposed to desiccation and shorebird predation. Here we examine whether such risky behaviour is related to parasite infections. Surface-active and buried C. volutator were collected during a low tide period in the Danish Wadden Sea, and the infection patterns of the two groups were described in relation to sex and size. Surface-active males and females were more heavily infested by microphallid trematodes (four species) than buried specimens of the same sex and size class. Although the density of surfaced amphipods decreased as a function of exposure time, the mean parasite load of those that remained on the surface increased. A narrow size-specific parasite intensity threshold above which the amphipods were always surface active did not exist: heavily infected individuals were also found buried in the substrate. Although likely to be beneficial to the parasites, this suggests that the behavioural alteration is a side-effect of the infections rather than a consequence of direct parasitic manipulation. Besides the presumed mortality associated with the parasite-related surface activity in a range of size-classes, the intensity-size frequency distribution indicated that larger and hence heavily infected hosts are removed from the population. Together it demonstrates that microphallid trematodes impact the population dynamics of C. volutator.

Development of forest structure on cleared rainforest land in eastern Australia under different styles of reforestation

Rainforests in eastern Australia have been extensively cleared over the past two centuries. In recent decades, there have been increasing efforts to reforest some of these cleared lands, using a variety of methods, to meet a range of economic and environmental objectives. However, the extent to which the various styles of reforestation restore structure, composition and ecological function to cleared land is not presently understood. In this study, we develop and apply a method for quantifying the structural attributes of reforestation sites in tropical and subtropical Australia. The types of reforestation studied were plantation monocultures, mixed-species cabinet timber plots, diverse restoration plantings and unmanaged regrowth. Two age classes of reforestation were examined: ‘young’ (5–22 years), incorporating sites from all categories, and ‘old’ (30–70 years), in which only monoculture plantations and regrowth were represented. A total of 104 sites were surveyed including reference sites in intact rainforest and pasture. Intact rainforest was characterised by a suite of complex structural features including abundant special life forms (vines, epiphytes, hemi-epiphytes and strangler figs), a dense stand of trees in a range of size classes, a closed canopy, a shrubby understorey and a well-developed ground layer of leaf litter and woody debris. These features were lost on conversion to pasture. While all types of reforestation returned some elements of structural complexity to cleared land, young plantation monocultures, cabinet timber plots and young regrowth had a relatively simple structure. These sites typically had a low density of woody stems, a relatively open canopy and grassy ground cover, and lacked large trees, coarse woody debris and most special life forms. Restoration plantings and old regrowth were more complex, with a high density of woody stems, a relatively closed canopy and shrubby understorey. Old monoculture plantations in the tropics had acquired many of the structural attributes of intact forest, however this was not the case in the subtropics, where plantations were subject to more intensive management. The marked differences in structural complexity between sites suggest that the different types of reforestation practiced in eastern Australia are likely to vary considerably in their value as habitat for rainforest biota.

Regulation of water flux through tropical forest canopy trees: do universal rules apply?

Tropical moist forests are notable for their richness in tree species. The presence of such a diverse tree flora presents potential problems for scaling up estimates of water use from individual trees to entire stands and for drawing generalizations about physiological regulation of water use in tropical trees. We measured sapwood area or sap flow, or both, in 27 co-occurring canopy species in a Panamanian forest to determine the extent to which relationships between tree size, sapwood area and sap flow were species-specific, or whether they were constrained by universal functional relationships between tree size, conducting xylem area, and water use. For the 24 species in which active xylem area was estimated over a range of size classes, diameter at breast height (DBH) accounted for 98% of the variation in sapwood area and 67% of the variation in sapwood depth when data for all species were combined. The DBH alone also accounted for > or = 90% of the variation in both maximum and total daily sap flux density in the outermost 2 cm of sapwood for all species taken together. Maximum sap flux density measured near the base of the tree occurred at about 1,400 h in the largest trees and 1,130 h in the smallest trees studied, and DBH accounted for 93% of the variation in the time of day at which maximum sap flow occurred. The shared relationship between tree size and time of maximum sap flow at the base of the tree suggests that a common relationship between diurnal stem water storage capacity and tree size existed. These results are consistent with a recent hypothesis that allometric scaling of plant vascular systems, and therefore water use, is universal.

Experimental verification of a mathematical model for pelleted growth of Streptomyces coelicolor A3(2) in submerged batch culture

A published mathematical model for growth of pellets of filamentous microorganisms has been tested by comparison of model predictions with experimental data on growth of Streptomyces coelicolor in liquid batch culture. The original model considered the classification of pellets into a range of size classes. Growth resulted in movement of pellets to classes of increasing size, while shear forces produced mycelial fragments which entered the smallest size class, from which they grew to form further pellets. This model did not correctly describe changes in pellet size distributions during growth and was therefore modified in two ways. In the first, new pellets were assumed to be formed by the break-up, by shear forces, of existing pellets into two pellets of equal size, rather than removal of small hyphal fragments from the pellet surface. The second modification assumed that the outer shell of active mycelial biomass had a density less than 1 g cm-3 and that hyphal density within this shell decreased with distance from the pellet centre. The modified model generated predictions which agreed closely with experimental data on biomass concentration, pellet size distribution, pellet number and pellet radius during batch growth, thereby supporting the assumptions on which the model was based. The model did not accurately describe final biomass concentration, through lack of consideration of autolysis of mycelia at the centre of larger pellets in which growth was limited by diffusion of nutrients. Attempts to incorporate autolysis into the model improved prediction of biomass concentration but were not based on sound biological assumptions and increased the complexity of the model. Further experimental work is required for accurate description of the effects of autolysis on pellet growth.