Mean Leaf Longevity Research Articles

Leaf Longevity in a Timberline Tree Species Juniperus saltuaria in the Sergymla Mountains, Southeastern Tibet

Leaf longevity is an important adaptive strategy that allows plants to maximize photosynthetic carbon gain. Due to the difficulty of identifying overwintering bud scars and distinguishing the age sequence of twigs, leaf longevity is rarely studied in Cupressaceae species, which further limits our understanding of the leaf economic spectrum (LES) for these populations. Here, we investigated the leaf longevity, as well as mass-based leaf nitrogen concentration (Nmass), of Juniperus saltuaria at different canopy heights for both subalpine and alpine timberline forests in the Sergymla Mountains, southeastern Tibet. We found that the mean leaf longevity was 4.2±1.2 years, and overall it did not differ significantly between different elevations. Along the vertical profiles of juniper canopies, the leaf longevity did not reflect a linear trend. With increasing leaf longevity, Nmass showed declining trends. We further analyzed the relationship between leaf longevity and the corresponding length of green twigs, and found that the length of green twigs could only explain 1%–3% of the variation in leaf longevity, indicating that the length of green twigs is a poor predictor for the variation in leaf longevity. In summary, for the J. saltuaria species in timberline or nearby subalpine forests, the effects of elevation and canopy depths on leaf longevity are minor, and the leaf trait analysis is in accordance with the prediction of LES.

Key-factors and key-stages that determine the leaf longevity of an evergreen broad-leaved tree, Neolitsea sericea (Lauraceae) at different growing sites in southern Japan

Chronological distribution pattern of leaves is an important factor to determine plant productivity in relation to photosynthesis. Therefore, intensive studies of leaf longevity are essential in plant ecology. Leaf longevity of Neolitsea sericea (Lauraceae) was surveyed from 1972 to 1995. Mean leaf longevity varied from 5.6 to 53.8 months among different year classes of leaf emergence. To detect factors and stages determining the leaf longevity, we adopted the method of key-factor/key-stage analysis. We categorized N. sericea trees into four groups; short and tall trees in an evergreen broad-leaved forest, short trees along the forest edge, and short trees in a Moso bamboo forest, where N. sericea grows as an understory plant. This categorization enabled us to realize how the factors and stages differently influenced leaf longevity at different sites. Four groups of factors (growing site, cecidomyiid gall induction, stem boring by a cerambycid, typhoon) and eight stages (every 6 month after leaf emergence until a leaf age of 48 months) were distinguished in the analysis. Effects of annual precipitation and annual mean temperature were evaluated separately. In a bamboo forest, cerambycid negatively affected leaf survival in the first year. In an evergreen broad-leaved forest, cerambycid and typhoon affected leaf survival of short and tall trees but cerambycid damage was compensated in later stages. Short trees along the forest edge suffered severe leaf fall from typhoon but were positively affected by annual precipitation. This study gives suggestions for better understanding of chronological distribution patterns of leaves.

Stand structure, phenology and litterfall dynamics of a subtropical mangrove Bruguiera gymnorrhiza

We evaluated the phenology and litterfall dynamics of the mangrove Bruguieragymnorrhiza (L.) Lamk along the Okukubi River, Okinawa Island, Japan. Over 3 years, this species showed the highest litterfall of leaves and stipules in summer and the lowest litterfall in winter. From Kendall’s coefficient of concordance, the monthly changes in leaf, stipule, and branch were strongly and significantly concordant among years. Leaf and stipule litterfall could be governed by monthly maximum wind speed, monthly day length, and monthly mean air temperature. Branch litterfall depended on monthly maximum wind speed and monthly rainfall, and increased exponentially with increasing monthly maximum wind speed. Mean total litterfall was 11.8 Mg ha−1 yr−1, with the largest component being leaf litterfall (65.8 %). Annual leaf litterfall per plot was almost constant regardless of the tree density of the plot. Mean leaf longevity was 18 months. Flower and mature propagule litterfall might be influenced by monthly mean air temperature, monthly day length and monthly mean air temperature. The average development periods from flower buds to flowers and flower buds to mature propagules were 1 and 8 months, respectively. Except for leaf and branch, all vegetative and reproductive organ litterfall had clear annual cycles. B.gymnorrhiza showed a positive correlation between leaf production and reproductive organ production.

A model of seasonal foliage dynamics of the subtropical mangrove species Rhizophora stylosa Griff. growing at the northern limit of its distribution

Progress of forest production in response to the environment requires a quantitative understanding of leaf area development. Therefore, it is necessary to investigate the dynamics of seasonal crown foliage in order to understand the productivity of mangroves, which play an important role in the subtropical and tropical coastlines of the world. Crown foliage dynamics of the mangrove Rhizophora stylosa were studies to reveal patterns of leaf recruitment, survival and seasonal leaf area growth. Flushing of leaves occurred throughout the year, but both flushing and leaf area growth pattern of leaves varied with season. Maximum flushing occurred in summer, but leaf areas did not differ significantly with season. The half-expansion period is longer, and the intrinsic rate of increase was lower in winter. Summer flushed leaves grew faster at their initial stage and reached their maximum area over a shorter period of time. The difference in temperature and air vapor pressure deficit (VPD) between summer and winter contributed to the present dynamics of foliage patterns. The mean leaf longevity was estimated to be 13.1 month. The crown foliage area was almost stable throughout the year. Homeostatic control of the crown foliage area may be accompanied by the existence of ecophysiological mechanisms in R. stylosa. Integrating crown foliage dynamics into forest models represents an important step towards incorporating physiological mechanisms into the models for predicting growth responses to environmental changes and for understanding the complex responses of tree growth and litter production.

Ontogenetic transition in leaf traits: a new cost associated with the increase in leaf longevity

Aims Recent work has identified a worldwide ‘economics’ spectrum of correlated leaf traits that mainly reflects the compromises between maximizing leaf longevity and short-term productivity. However, during the early stages of tree growth different species tend to exhibit a common strategy, because competition for soil water and nutrients forces the maximization of short-term productivity owing to the need for rapid growth during the most vulnerable part of the tree’s life cycle. Accordingly, our aim here was to compare the variations that occur during ontogeny in the different leaf traits (morphology and leaf chemical composition) of several coexisting Mediterranean woody species differing in their leaf life spans and to test our hypothesis that tree species with a long leaf life span should exhibit larger shifts in leaf characteristics along ontogeny. Methods Six Mediterranean tree species differing in leaf life span, selected from three plots located in central-western Spain, were studied during three growth stages: seedlings, juveniles and mature trees. Leaf life span, leaf morphology (leaf area, dry weight, thickness and mass per unit area) and chemical composition (N and fibre concentrations) were measured in all six species. The magnitude of the ontogenetic changes in the different traits was estimated and related to the mean leaf longevity of the different species. Important Findings Along ontogeny, strong changes were observed in all variables analysed. The early growth stages showed lower leaf thickness, leaf thickness and mass per unit area and N, cellulose and hemicellulose concentrations than mature trees, but a higher lignin content. However, these changes were especially marked in species with a longer leaf life span at maturity. Interspecific differences in leaf life span, leaf morphology and chemical composition were stronger at the mature stage than at the seedling stage. We conclude that greater plasticity and more intense strategy shifts along ontogeny are necessarily associated with long leaf life span. Our results thus provide a new aspect that should be incorporated into the analysis of the costs and benefits associated with the different strategies related to leaf persistence displayed by the different species. Accordingly, the intensity of the alterations in leaf traits among different growth stages should be added to the suite of traits that change along the leaf economics spectrum.

Vegetative and reproductive phenological traits of Rhizophora mucronata Lamk. and Sonneratia alba Sm.

Mangrove phenology is important in understanding the past, present and future response of mangrove species to impacts of climate change. Our study is the first long term direct observation of the phenology of Rhizophora mucronata and Sonneratia alba in Kenya. Objective of the study was to determine, interpret and document the timing of the various phenoevents and phenophases, and to establish relationships between phenology and the climatic variables. Phenological traits were investigated in six monospecific mangrove stands in Gazi Bay, south of Mombasa, for 2 years. Leaf emergence, leaf fall, flower bud, flower and fruit initiation data were recorded every fortnight in 54 shoots of 9 trees at each site. Continuous leaf emergence and loss characterized by multimodal peaks was observed for the two species. Leaf emergence and leaf fall peaked in the wet months and was reduced in the dry months. There was a relationship between the leaf emergence and drop with the reproductive phenology in the two species. Mean leaf longevity for R. mucronata and S. alba was 12.8±1.2 and 4.9±0.5 months respectively. The reproductive cycle took approximately 16–20 months in R. mucronata and 4–5 months in S. alba. Bud initiation in R. mucronata was seasonal and occurred in October and September. Buds were observed for 8–11 months developing slowly on the shoots. Shifts were observed in the timing of flower initiation, and the flowering period lasted in total for 4–5 months. The time period from flower appearance to the developmental start of immature propagules lasted about 1 month at reforested sites and up to 5 months in stands of natural vegetation. In R. mucronata initiation of immature propagules was not seasonal and varied among the sites. Fruiting in S. alba was short and seasonal without overlap, and shifts were observed in the timing of flowering, flowering and fruiting peaks. Abscission of reproductive parts started in July and in June, respectively, in the years 2005 and 2006. Fruiting was observed starting in August in both years, and fruiting peak was reached in October in 2005 and one month earlier in 2006. In R. mucronata vegetative and reproductive phenophases significantly correlated with climatic variables, whereas in S. alba only leaf emergence and leaf fall correlated with temperature. The flowering plasticity in the reproductive phenology of the two species indicates possible sensitivity to certain climatic and environmental triggers. Our results also indicate that R. mucronata trees have a distinctly higher investment in the reproductive cycle than S. alba.

Leaf turnover and herbivory in the tall tussock grass Festuca orthophylla in the Andean Altiplano

Tall grass tussocks dominate the Andean highlands above 3,800 m a.s.l., with often no other life form contributing significantly to standing crop biomass and productivity, thus, representing the dominant source of fodder for camelid grazing. To assess the productivity of these semi-arid tropical rangelands (350 mm of annual rainfall confined to a 4–5 months rainy season) is challenging, given the ‘evergreen’ nature of leaves and the unknown periodicity of leaf growth. The aim of this study was to explore the seasonal course of new foliage formation, foliage duration, and the response of leaf elongation and emergence to simulated llama grazing (clipping). The repeated census of Festuca orthophylla leaves in the Sajama National Park at 4,250 m elevation (Bolivia) provided clear evidence that leaf production is not confined to the rainy season, but also occurs during the dry season. Our data revealed a mean leaf longevity of 141 days for peripheral control tillers (unclipped) and 169 days for central control tillers. Leaves grow slower and reach shorter length during the dry season compared to the rainy season, and peripheral tillers are always shorter but more vigorous than central tillers (shorter intervals between the emergence of two leaves). There was no stimulation of leaf growth in tillers that were clipped (no overcompensation). Overall, this study suggests ca. two-fold replacement of foliage per year. We explain the continued growth in the dry season by, on average, six times greater soil area occupied by roots than by the leaf canopy, and thus, much greater water availability per tussock than meteorological data would suggest. Wide spacing of tussocks and a large root-sphere mitigate the impact of periodic drought on tissue formation, providing year-round forage for llamas.

Vegetative and reproductive phenology of the mangrove Bruguiera gymnorrhiza (L.) Lam. on Okinawa Island, Japan

Vegetative and reproductive phenology of the subtropical mangrove Bruguieragymnorrhiza was investigated at Manko Wetland, Okinawa Island, Japan. Phenology was assessed using litterfall data over 4 years. Leaf and stipule litterfall occurred throughout the year, with distinct seasonal patterns. Kendall’s coefficient of concordance, W, revealed that the monthly changes in leaf and stipule litterfall were strongly and significantly concordant among years. Leaf litterfall was linked to monthly day length and maximum wind speed, and stipule litterfall was linked to monthly mean air temperature, monthly rainfall, and maximum wind speed. Branch litterfall showed no clear monthly pattern, but tended to vary with monthly maximum wind speed. Mean leaf longevity was 19 months. Mean total litterfall was 10.1 Mg ha−1 year−1, with the largest component being vegetative organs (58 %). Flower and propagule litterfall were highest in autumn and summer, respectively, and lowest in winter. The W values revealed that, of the reproductive organs, only flower litterfall had a significant monthly trend. Flower litterfall was correlated with monthly mean air temperature and relative humidity. The average development periods from flower buds to flowers and from flowers to mature propagules were approximately 1 and 8 months, respectively. It took 9 months to produce mature propagules from flower buds. Except for branches, all vegetative and reproductive components of litterfall had clear annual cycles.

Leaf phenological traits and leaf longevity of three mangrove species (Rhizophoraceae) on Okinawa Island, Japan

Data on leaf phenological traits and longevity of mangroves are important for improved understanding of the adaptation strategies, growth, and productivity of these trees. We studied leaf phenological traits and longevity of Rhizophora stylosa, Bruguiera gymnorrhiza, and Kandelia obovata monthly from April 2008 to March 2009. Both tree sampling (direct observation) and litterfall (indirect observation) were used. All leaves and branches of each sample tree were numbered and marked with tags at the beginning of the experiment. Peaks of leaf recruitment and death occurred in July and June, respectively, for B. gymnorrhiza and K. obovata but both occurred in July for R. stylosa. Leaf recruitment for all the species was lowest in January; leaf death was minimum in December for R. stylosa and B. gymnorrhiza, and in January for K. obovata. Leaf recruitment for the three species was significantly correlated with monthly mean air temperature and monthly hours of sunshine. K. obovata and R. stylosa leaf death was correlated with monthly mean air temperature, monthly hours of sunshine, monthly mean air vapor pressure deficit, and monthly rainfall; B. gymnorrhiza leaf death was not correlated with any environmental factors. Specific leaf area for R. stylosa (45.4 ± 1.0 cm2 g−1) and K. obovata (48.6 ± 0.8 cm2 g−1) was not significantly different, but means for these two species were significantly different from that for B. gymnorrhiza (71.0 ± 2.8 cm2 g−1). Mean leaf longevity was 13.9 months for R. stylosa, 17.2 months for B. gymnorrhiza, and 12.1 months for K. obovata. Different measured variables between B. gymnorrhiza and the other two species may have been because of the growth strategy and shade tolerance of B. gymnorrhiza. Mean leaf longevity increased with increasing mean annual air temperature.

Litterfall dynamics in an overcrowded mangrove Kandelia obovata (S., L.) Yong stand over five years

Abstract Organic matter fluxes into marginal wetland areas require to be quantified given their support for the detrital components. Following their study for 5 years in a mangrove ( Kandelia obovata ) stand near the northernmost limit of the species’ distribution in East Asia, leaf and stipule litterfalls exhibited a clear monthly pattern, with maximum values in July and minimum values in February. In this region, mangroves experience a distinct seasonal climate characterised by low temperatures and frequent typhoons. Propagule litterfall was largest in April and May, whereas no propagule litterfall occurred in summer. Kendall’s coefficient of concordance revealed that the monthly trends of litterfall did not significantly differ among years (branch, p p −2 yr −1 , of which leaf litterfall constituted 49.3–67.9%. Higher annual total litterfall was caused by high production of branch litterfall during typhoons. Stipule litterfall (an indicator of new-leaf flush) decreased with increasing levels of flower/fruit and propagule litterfalls and mean annual leaf litterfall per tree decreased with increasing tree density among plots. Annual leaf litterfall per plot was almost constant regardless of tree density and mean leaf longevity was estimated to be 12.04 ± 0.04 month.

Ash and Mineral Contents in Leaves of Woody Species: Analysis by Near‐Infrared Reflectance Spectroscopy

Near‐infrared reflectance spectroscopy (NIRS) was evaluated for its effectiveness to determine ash and mineral concentrations [potassium (K), magnesium (Mg), copper (Cu), iron (Fe), and zinc (Zn)], in a total of 182 leaf samples of 17 woody species located in the central‐western region of the Iberian Peninsula. Chemical analysis revealed great variability in all leaf mineral elements. This variability was mainly related to differences in leaf habit (deciduous versus evergreen) and to differences in mean leaf longevity and among leaf age classes within evergreen species. A set of samples including all 17 species and leaf age classes was used to develop the calibration equations using multiple linear regression (MLR) and partial‐least squares regression (PLSR). The set of samples that did not enter in the calibration was used for external validation. In general, the most satisfactory results were obtained using PLSR and derivative transformations. Despite the strong heterogeneity of the samples included in the study, the results showed that NIRS can be employed as an effective tool, alternative to the more time‐consuming standard methods. The best predictive model was obtained for ash content. Models with acceptable accuracy were obtained in the prediction of K and Mg contents. However, their applicability for the determination of trace elements was more limited.

Prerelease Assessment of Impact on Biomass Production of an Invasive Weed,Lygodium microphyllum(Lygodiaceae: Pteridophyta), by a Potential Biological Control Agent,Floracarus perrepae(Acariformes: Eriophyidae)

Abstract A prerelease assessment of impact by a potential biological control agent, Floracarus perrepae Knihinicki and Boczek, on the invasive weed, Lygodium microphyllum (Cav.) R. Br., was conducted in a 2-yr field study in their native range—Australia. Thirty-two pairs of test plants were planted in a field plot with two levels of shade, with one plant in each pair treated biweekly with the miticide abamectin. The mite caused a significant reduction in biomass of above ground stems and leaves and below ground roots and rhizomes. The mean leaf longevity was significantly longer for the treated versus the mite infested untreated plants. Populations of native predator mites were low throughout the study; however, the mite pathogen Hirsutella thompsonii Fisher was common in the second year of the study, but neither reduced the impact of F. perrepae. Based on its potential to cause significant damage to L. microphyllum under field conditions in the native range and extremely narrow field host range, F. perre...

Leaf demography and leaf traits of temperate-deciduous and tropical evergreen-broadleaved trees in a Mexican montane cloud forest

Leaf demography of four deciduous and five evergreen broadleaved tree species was studied in two replicate tropical montane cloud forest fragments (1250-1400 m elevation) in Veracruz, Mexico. The objectives were to investigate leaf life spans, expansion rates, survivorship curves, specific leaf area (SLA) and nitrogen concentration in tree species of contrasting leaf habits and phytogeographical affinities growing naturally in the same forest type. Tagged leaves were located in the mid forest canopy and were reached with a six-m ladder. A total of 2688 leaves from 78 trees were monitored from bud burst to death. Mean leaf longevity was 8.25 mo for deciduous tree species and 15.0 mo for evergreens. Mean leaf longevity was highly variable among evergreen species which included both the longest (Magnolia, 36.4 mo) and the shortest (Hedyosmum, 6.4 mo) values. Patterns of leaf emergence were similar for eight species with a pronounced peak at the beginning of the calendar year. The only exception was Hedyosmum with a multiple flush pattern. More than 50% leaf expansion occurred in less than a month for three deciduous species (Carpinus, Liquidambar, Quercus) and two evergreens (Oreopanax and Magnolia), but required more than a month for Clethra (deciduous) and Cinnamomum, Hedyosmum and Turpinia (evergreen). Leaf survivorship curves were similar between the two study sites, but they differed between deciduous and evergreen species. There was no significant difference between leaf habit groups in SLA, leaf area, or nitrogen concentration, however, SLA was inversely correlated with leaf longevity. Arranging the studied taxa from primitive to advanced reaveled that species in more primitive groups have the longest life-spans (Magnolia, Cinnamomum) and more advanced taxa have the shortest life spans (Carpinus, Quercus). Phylogenetic relationships between species should be taken into account when studying leaf traits.

Decline of photosynthetic capacity with leaf age in relation to leaf longevities for five tropical canopy tree species

The effect of leaf aging on photosynthetic capacities was examined for upper canopy leaves of five tropical tree species in a seasonally dry forest in Panama. These species varied in mean leaf longevity between 174 and 315 d, and in maximum leaf life span between 304 and 679 d. The light-saturated CO2 exchange rates of leaves produced during the primary annual leaf flush measured at 7-8 mo of age were 33-65% of the rates measured at 1-2 mo of age for species with leaf life span of < 1 yr. The negative regression slopes of photosynthetic capacity against leaf age were steeper for species with shorter maximum leaf longevity. In all species, regression slopes were less steep than the slopes predicted by assuming a linear decline toward the maximum leaf age (20-80% of the predicted decline rate). Maximum oxygen evolution rates and leaf nitrogen content declined faster with age for species with shorter leaf life spans. Statistical significance of regression slopes of oxygen evolution rates against leaf age was strongest on a leaf mass basis (r = 0.49-0.87), followed by leaf nitrogen basis (r = 0.48-0.77), and weakest on a leaf area basis (r = 0.35-0.70).

Leaf longevity in evergreen shrubs: variation within and among European species.

Leaf longevities were determined for 16 species of evergreen shurbs (Ericaceae and Empetraceae) at different habitats at three latitudes (c. 47°, 55-58° and 68°N) in central and north Europe to determine whether any general trends exist in variation in leaf longevity within and among species. Among these species and sites, mean leaf longevity varied between 1.4 and 3.8 seasons, which is similar to the values reported for other evergreen shrubs, but shorter than for many evergreen conifers. Consistent differences in leaf longevity were found when comparing latitudes (ignoring altitude and habitat type): longevities were longer at 68°N than at the two lower latitudes. No consistent trends were found among species within altitudes.

Leaf life spans in wild perennial herbaceous plants: a survey and attempts at a functional interpretation.

Leaf longevity in 29 herbaceous plant species of Central Europe was studied by inspecting tagged leaves at weekly intervals. About half of the species are elements of the lowland meadow flora, the other half comprises a representative sample of species from the highest sites where vascular plants grow in the Alps. Shaded and water-stressed sites were avoided. Overall mean leaf longevity did not differ significantly between sites and amounted to 71±5 days at low and 68±4 days at high altitude. Leaf life spans ranged (with no clear altitudinal trend) from 41 to 95 days. Low-altitude forbs and grasses produced several leaf cohorts during their growth period, while most alpine species produced only one. Correlations were found between leaf duration and percent nitrogen content and carbon-cost/carbon-gain ratios, but not with leaf dry mass per unit leaf area and photosynthetic capacity alone. As leaf life spans increase, more C tends to be invested per unit CO2 uptake and less N is invested per unit invested C. Thus, mass relationships rather than area relationships seem to be linked to leaf life span in these species, suggesting that leaf duration is associated with properties other than the efficiency of light utilization (e.g. mechanical strength, herbivory or pathogen resistance). It seems that the explanations of leaf duration that have been developed for evergreen/deciduous plants and for plants along steep light gradients do not apply to the variable life spans in leaves of perennial herbaceous plants of open habitats.

Leaf respiration in Piper species native to a Mexican rainforest

We measured leaf respiration with a Clark‐type oxygen‐electrode in 6 species of the genus Piper (Piperaceae) growing naturally in wet evergreen rainforest, in microsites characterized by a broad range of light availabilities. Species normally found in large gaps and clearings (Piper auritum and P. umbellatum) had approximately twice the dark respiration per unit of leaf area or dry mass as species found predominantly in shaded understory sites (P. aequale, P. lapathifolium and P. amalago). within a species, dark respiration was lower in the individuals growing in low‐light sites than in the individuals growing in high‐light sites. Over all species, leaf respiration was positively correlated with the average daily photosynthetically active photon flux density (PFD) at each site, and negatively correlated with mean leaf longevity. Respiration was insensitive to leaf age in a shade species. (P. lapathifolium) and in a generalist (P. hispidum) but decreased with increasing leaf age in a gap specialist (P. aurtium).In experiments on greenhouse‐grown plants, we titrated respiration with potassium cyanide (KCN) and/or salicylhydroxamic acid (SHAM) to determine the cytochrome and alternative pathway components to respiration in 4 Piper species. All 4 species, representing gap, generalist and shade species, exhibited alternative pathway respiration. Engagement of the cytochrome pathway (ϱcyt) varied from 0.69 in P. auritum to 1.04 in P. lapathifolium and engagement of the alternative pathway (ϱalt varied from 0.41 to 1.02. Although the shade species had lower respiration rates than the gap species, the capacities for cytochrome and alternative pathway respiration made up similar or greater fractions of total respiration in shade species.

LONGEVITY AND PRODUCTIVITY OF LEAVES OF A CULTIVATED ANNUAL, GLYCINEMAX MERRILL

SummaryTo understand the structure and dynamics of the leaf population composing a canopy, a life table analysis using rates of leaf emergence, mortality and dry matter production was applied to the foliage of soybean plants grown at three densities and sown at three times.The mean leaf longevity differed greatly depending on the time of sowing, but in the early sown plants little difference was found among the leaves of lower and middle layers of the canopy in spite of the wide difference in the irradiance of the layers.The rate of net photosynthesis of upper leaves in full daylight tended to decline gradually owing to senescence in leaves older than 20 d. That of lower‐layer leaves, in very dark conditions, decreased very rapidly owing to both shading and senescence. Analyses of the survivorship curves and the time trends of net photosynthetic rates showed that lower leaves in densely planted populations survived for quite a long time after they had lost the ability to produce additional dry matter.The rate of canopy net photosynthesis tended to follow a saturation curve with the increase in the leaf area index of whole canopy. There was no optimum leaf area index that maximized canopy photosynthetic rate.

Observations on the Floral and Vegetative Phenologies of North-Eastern Australian Mangroves

The mangrove forests of north-eastern Australia are both species-rich and well developed but there is very little information available on their vegetative growth or flowering and fruiting behaviour. This account attempts to rectify this situation by presenting the results of at least 4 years of field studies and observations. Previous reports recorded no less than 35 mangrove species occumng along the north-eastern coast and observations of the flowering and fruiting status of all these species were made. The results are supported by some litter fall studies and overall they reflect the diversity of mangrove species by displaying a range of peak activity months. However, there are some common trends and most species flower mainly during the dry hot summer (September-December) prior to the rainy season when they drop their propaguies during the morniks of peak rainfall (around February). Detailed studies of litter fall were camed out in Missionary Bay, Hinchinbrook Island (18° 16̸2S.,146° 13̸2E.), and care was taken to record components of floral development and vegetative growth. The results for five species (Rhizophora apiculata, R. stylosa, R. × lamarckii, Bruguiera gymnorhiza and Ceriops tagal var. tagal) include estimates of mean leaf longevity and also suggest that the floral and vegetative cycles are coordinated.