Palaeoecological analysis of an isolated stand of Nothofagus cunninghamii (Hook.) Oerst. in eastern Tasmania

Abstract Pollen analysis of the sediments of a small bog, supporting a stand of cool temperate rainforest in southeastern Tasmania, was undertaken in order to examine the history of the stand dominant, Nothofagus cunninghamii, presently growing outside its predicted climatic range. The pollen record covers at least the last 9000 years and reveals changes in the bog and in the surrounding vegetation, although pollen percentages of N. cunninghamii are sufficiently high to indicate that the species could have had a local presence throughout the recorded period. It is likely that this N. cunninghamii stand is relictual, surviving not only Holocene climates, but also the cool dry conditions of the last glacial period. This ability to survive changing and sometimes very unfavourable climates leads to the conclusion that great caution must be exercised in using present climates alone to predict the potential distribution of N. cunninghamii.     

Plasticity in seedling morphology,biomass allocation and physiology among ten temperate tree species in response to shade is related to shade tolerance and not leaf habit

• Mechanisms of shade tolerance in tree seedlings, and thus growth in shade, may differ by leaf habit and vary with ontogeny following seed germination. To examine early responses of seedlings to shade in relation to morphological, physiological and biomass allocation traits, we compared seedlings of 10 temperate species, varying in their leaf habit (broadleaved versus needle‐leaved) and observed tolerance to shade, when growing in two contrasting light treatments – open (about 20% of full sunlight) and shade (about 5% of full sunlight).
• We analyzed biomass allocation and its response to shade using allometric relationships. We also measured leaf gas exchange rates and leaf N in the two light treatments.
• Compared to the open treatment, shading significantly increased traits typically associated with high relative growth rate (RGR) – leaf area ratio (LAR), specific leaf area (SLA), and allocation of biomass into leaves, and reduced seedling mass and allocation to roots, and net assimilation rate (NAR). Interestingly, RGR was not affected by light treatment, likely because of morphological and physiological adjustments in shaded plants that offset reductions of in situ net assimilation of carbon in shade. Leaf area‐based rates of light‐saturated leaf gas exchange differed among species groups, but not between light treatments, as leaf N concentration increased in concert with increased SLA in shade.
• We found little evidence to support the hypothesis of a increased plasticity of broadleaved species compared to needle‐leaved conifers in response to shade. However, an expectation of higher plasticity in shade‐intolerant species than in shade‐tolerant ones, and in leaf and plant morphology than in biomass allocation was supported across species of contrasting leaf habit.

     

The ecology of Araucaria species in New Guinea. III. Population dynamics of sample stands

Life table data for A. cunninghamii and A. hunsteinii from a total of four sites near Bulolo, Papua New Guinea are presented. Sample populations are analysed using the Leslie matrix method. Values of λ, the ‘finite rate of natural increase’, vary between sites and species in the predicted manner. The value of λ calculated for the A. cunninghamii population is close to, and slightly above 1.0, while the three values calculated for A. hunsteinii show wide variation, with values both above and below 1.0. It is argued that A. hunsteinii is a gap regenerating species and cannot regenerate beneath a closed canopy. Evidence presented here and elsewhere indicates that A. cunninghamii is more shade tolerant and therefore, theoretically, better adapted to stable forest situations.     

Dynamics of Nothofagus-dominated rainforest on mainland Australia and lowland Tasmania

Cool temperate rainforest in Australia is commonly dominated by Nothofagus species. In Victoria and Tasmania, Nothofagus cunninghamii dominates old rainforest on optimal sites and is able to regenerate continuously. Size structure analysis of the major lowland tree species in this forest suggest that no major changes in species composition or dominance are occurring. This contrasts with the status of Nothofagus in lowland rainforest in New Zealand and rainforest below about 1000 m a.s.l. in south-central Chile. N. cunninghamii is a relatively light-demanding species, and is maintaining its dominance by seedling regeneration in canopy gaps created by the death of old individuals. The dynamics of the cool temperate rainforest in northern New South Wales are more complex. These forests are dominated by Nothofagus moorei, and size structure analysis indicates that persistence of this species within the rainforest is dependent on vegetative regeneration. On some sites this rainforest is being actively invaded by warm temperate and sub-tropical elements from lower altitudes. In these areas N. moorei in unable to regenerate beneath the canopy.Nomenclature follows Curtis (1963, 1967), Curtis & Morris (1975) and Williams (1982).We thank Mr. A. Floyd of the N.S.W. National Parks and Wildlife Service for his assistance in identifying species from the N.S.W. rainforests, and Mr. J. Hickey of the Tasmanian Forestry Commission for suggesting study sites in north-west Tasmania. Thanks are also due to the N.S.W. National Parks and Wildlife Service for allowing us access to National Parks for the purpose of this study. J. R. is supported by a Commonwealth Forestry Post-graduate Research Award.     

Altering Light Availability to Restore Invaded Forest: The Predictive Role of Plant Traits

Many studies have demonstrated that reduced light availability, which can be manipulated at local scales by planting or seeding canopy species, can curtail the growth of invasive species and promote the growth of native species. Species differences in functional traits, such as light use and stress tolerance, may be used to determine how native and invasive species will respond to these resource manipulations. We altered light availability in a mesic Hawaiian forest understory and found that low light levels reduced the biomass and growth of two invasive grasses (Pennisetum clandestinum and Ehrharta stipoides) relative to two native shrubs (Pipturus albidus and Coprosma rhynchocarpa) and two native canopy species (Metrosideros polymorpha and Acacia koa). Native species generally displayed traits associated with shade tolerance (high quantum yield, chlorophyll content, and leaf mass per area), whereas the two invasive grasses displayed traits associated with shade intolerance (high photosynthetic rate and growth rate). Several key traits pertaining to light acquisition and shade tolerance (quantum yield, chlorophyll content, and leaf mass per area) predicted seedling survival in low‐light treatments. Our data suggest that differences in light use among native and invasive species can help to determine the utility of resource manipulation as a restoration tool and, more specifically, to predict which native species will be optimal for restoration efforts that manipulate light availability.     

Shade tolerance and herbivory are associated with RGR of tree species via different functional traits

• Relative growth rate (RGR) plays an important role in plant adaptation to the light environment through the growth potential/survival trade‐off. RGR is a complex trait with physiological and biomass allocation components. It has been argued that herbivory may influence the evolution of plant strategies to cope with the light environment, but little is known about the relation between susceptibility to herbivores and growth‐related functional traits.
• Here, we examined in 11 evergreen tree species from a temperate rainforest the association between growth‐related functional traits and (i) species’ shade‐tolerance, and (ii) herbivory rate in the field. We aimed at elucidating the differential linkage of shade and herbivory with RGR via growth‐related functional traits.
• We found that RGR was associated negatively with shade‐tolerance and positively with herbivory rate. However, herbivory rate and shade‐tolerance were not significantly related. RGR was determined mainly by photosynthetic rate (A_max) and specific leaf area (SLA). Results suggest that shade tolerance and herbivore resistance do not covary with the same functional traits. Whereas shade‐tolerance was strongly related to A_max and to a lesser extent to leaf mass ratio (LMR) and dark respiration (R_d), herbivory rate was closely related to allocation traits (SLA and LMR) and slightly associated with protein content.
• The effects of low light on RGR would be mediated by A_max, while the effects of herbivory on RGR would be mediated by SLA. Our findings suggest that shade and herbivores may differentially contribute to shape RGR of tree species through their effects on different resource‐uptake functional traits.

     

不同光照条件下喜阴植物谢君魔芋对稳态和动态光源的响应特征

谢君魔芋(Amorphophallus xiei)是起源于云南西南地区热带雨林的典型喜阴植物,近年来得到了广泛种植和推广,在种植过程中,谢君魔芋需要采用遮荫栽培模式。为了揭示谢君魔芋对光照强度的适应策略,该研究探讨了生长在不同光照强度下(透光率为50%、29%、17%、7%)谢君魔芋叶片的光合作用特征、光合诱导特征、光合色素含量以及叶片氮素(N)含量和N分配。结果表明:随着生长环境光照强度的降低,单位叶面积和单位叶质量最大净光合速率、光合色素含量、最大羧化速率、最大电子传递速率及比叶面积均增大,而暗呼吸和光补偿点均减小。在光合诱导过程中,生长在透光率为17%光环境中的谢君魔芋完成50%光合诱导所需的时间最短,约为81.4 s;在光诱导进行10 min时,诱导状态最高,为87.3%。完成50%和90%光合诱导所需的时间与低光下初始气孔导度呈负相关关系。随着生长光照强度降低,叶片中的N分配到羧化组分和生物能转化组分中的比例先增大后减小,在透光率为17%的光环境下具有最大值;而叶片中的N分配到捕光色素组分中的比例随着生长环境光照强度降低而增加。该研究结果表明,喜阴植物谢君魔芋通过加强对低光和动态光源的利用能力及有效的N资源分配策略来适应低光照环境。     

Structural and physiological responses of two invasive weeds, <Emphasis Type="Italic">Mikania micrantha</Emphasis> and <Emphasis Type="Italic">Chromolaena odorata</Emphasis>, to contrasting light and soil water conditions

To better understand the requirement of light and soil water conditions in the invasion sites of two invasive weeds, Mikania micrantha and Chromolaena odorata, we investigated their structural and physiological traits in response to nine combined treatments of light [full, medium and low irradiance (LI)] and soil water (full, medium and low field water content) conditions in three glasshouses. Under the same light conditions, most variables for both species did not vary significantly among different water treatments. Irrespective of water treatment, both species showed significant decreases in maximum light saturated photosynthetic rate (P _max), photosynthetic nitrogen-use efficiency, and relative growth rate under LI relative to full irradiance; specific leaf area, however, increased significantly from full to LI though leaf area decreased significantly, indicating that limited light availability under extreme shade was the critical factor restricting the growth of both species. Our results also indicated that M. micrantha performed best under a high light and full soil water combination, while C. odorata was more efficient in growth under a high light and medium soil water combination.     

Photosynthetic responses to light in seedlings of selected Amazonian and Australian rainforest tree species

Summary Seedlings of the Caesalpinoids Hymenaea courbaril, H. parvifolia and Copaifera venezuelana, emergent trees of Amazonian rainforest canopies, and of the Araucarian conifers Agathis microstachya and A. robusta, important elements in tropical Australian rainforests, were grown at 6% (shade) and 100% full sunlight (sun) in glasshouses. All species produced more leaves in full sunlight than in shade and leaves of sun plants contained more nitrogen and less chlorophyll per unit leaf area, and had a higher specific leaf weight than leaves of shade plants. The photosynthetic response curves as a function of photon flux density for leaves of shade-grown seedlings showed lower compensation points, higher quantum yields and lower respiration rates per unit leaf area than those of sun-grown seedlings. However, except for A. robusta, photosynthetic acclimation between sun and shade was not observed; the light saturated rates of assimilation were not significantly different. Intercellular CO₂ partial pressure was similar in leaves of sun and shade-grown plants, and assimilation was limited more by intrinsic mesophyll factors than by stomata. Comparison of assimilation as a function of intercellular CO₂ partial pressure in sun- and shade-grown Agathis spp. showed a higher initial slope in leaves of sun plants, which was correlated with higher leaf nitrogen content. Assimilation was reduced at high transpiration rates and substantial photoinhibition was observed when seedlings were transferred from shade to sun. However, after transfer, newly formed leaves in A. robusta showed the same light responses as leaves of sun-grown seedlings. These observations on the limited potential for acclimation to high light in leaves of seedlings of rainforest trees are discussed in relation to regeneration following formation of gaps in the canopy.     

Microsatellites for use in Nothofagus cunninghamii (Nothofagaceae) and related species

Nothofagus cunninghamii (myrtle) has a widespread distribution through the temperate rainforest of southeastern Australia with some disjunct populations existing in putative glacial refugia. Polymorphic nuclear markers are required to resolve the biogeographical history of the species and will also be useful for conservation and forestry applications in this and other species of Nothofagus. Fourteen polymorphic microsatellite loci were isolated from N. cunninghamii, with four to 10 alleles amplified in 15 individuals tested. Transferability to other species of Nothofagus was successful, with six loci transferring to all eight other species tested.     

Light requirements of Australian tropical vs. cool-temperate rainforest tree species show different relationships with seedling growth and functional traits

Background and Aims

A trade-off between shade tolerance and growth in high light is thought to underlie the temporal dynamics of humid forests. On the other hand, it has been suggested that tree species sorting on temperature gradients involves a trade-off between growth rate and cold resistance. Little is known about how these two major trade-offs interact.

Methods

Seedlings of Australian tropical and cool-temperate rainforest trees were grown in glasshouse environments to compare growth versus shade-tolerance trade-offs in these two assemblages. Biomass distribution, photosynthetic capacity and vessel diameters were measured in order to examine the functional correlates of species differences in light requirements and growth rate. Species light requirements were assessed by field estimation of the light compensation point for stem growth.

Results

Light-demanding and shade-tolerant tropical species differed markedly in relative growth rates (RGR), but this trend was less evident among temperate species. This pattern was paralleled by biomass distribution data: specific leaf area (SLA) and leaf area ratio (LAR) of tropical species were significantly positively correlated with compensation points, but not those of cool-temperate species. The relatively slow growth and small SLA and LAR of Tasmanian light-demanders were associated with narrow vessels and low potential sapwood conductivity.

Conclusions

The conservative xylem traits, small LAR and modest RGR of Tasmanian light-demanders are consistent with selection for resistance to freeze–thaw embolism, at the expense of growth rate. Whereas competition for light favours rapid growth in light-demanding trees native to environments with warm, frost-free growing seasons, frost resistance may be an equally important determinant of the fitness of light-demanders in cool-temperate rainforest, as seedlings establishing in large openings are exposed to sub-zero temperatures that can occur throughout most of the year.     

观赏灌木小枝和叶性状在林下庇荫环境中的权衡关系

小枝与叶片间的关系能够很好地反映植物对环境的适应策略。目前,从枝叶间权衡关系的角度研究树木对庇荫环境适应性的报道尚少,其中主要包括"生长-生长"权衡和"生长-生存"权衡两种假说。因此,为了探讨灌木在庇荫环境中,是否会在小枝和叶性状间采取权衡策略,来提高光照资源的利用能力或增强生存和防御能力,在城市绿地的林隙和林冠下两种光环境中,选择了没有人工修枝、整形等经营措施的金银木(Lonicera maackii)、小花溲疏(Deutzia parviflora)和连翘(Forsythia suspensa)等11种、79株观赏灌木作为研究对象,采集其当年生小枝,观测并计算了每棵灌木所处环境的有效光合辐射(PAR)相对累积光量和红光/远红光(R/FR),以及灌木的小枝干重(TDW)、单位小枝叶干重(LDW)、出叶强度(LN/TDW)、叶面积支持效率(LA/TDW)、比枝长(TL/TDW)和单叶面积(ILA) 6个性状。对数据进行标准化和数据转换后,运用Pearson相关检验分析光环境指标和灌木枝叶性状间的相关性;采用标准化主轴估计法进行异速生长方程的参数估计;使用多元回归分析不同光强下各性状的相互关系。结果表明:(1) PAR相对累积光量和R/FR与TDW和LDW呈极显著(P0.01或P0.001)正相关,与TL/TDW、LA/TDW、LN/TDW呈极显著(P0.001)负相关,与ILA相关性不显著(P 0.05)。整体上,R/FR与各灌木性状的相关性大于PAR相对累积光量;(2) TDW和LDW存在极显著(P0.001)的异速生长正相关关系。随着光强的减小,灌木当年生小枝和叶片的生物量都趋于减小,但是表现出相对偏向于叶片生物量的投资偏好;(3) LA/TDW和TL/TDW存在极显著(P0.001)的等速生长正相关关系。但随着光强的减小,比枝长随叶面积支持效率增加而增加的速率却减小,说明灌木在庇荫条件下,更倾向于采取忍耐型的光资源利用策略;(4) ILA和LN/TDW呈极显著(P0.001)异速生长负相关关系。随着光强的减小,灌木趋向于表现出单位小枝上着生大量小叶的现象。所以总体上,庇荫环境下的观赏灌木存在投资偏好和权衡,倾向于通过枝叶生长提高光截获能力来适应弱光环境,与"生长-生长"的权衡假说相符,但整体上,观赏灌木的耐阴性较差,故不建议种植在庇荫环境中。     

不同光照梯度的遮荫处理对绒毛番龙眼幼苗生长的影响

在不同光照梯度,即100%自然全光照(natural sunlight,NS)、37.3%NS、15.5%NS、4.2%NS、1.6%NS和0.6%NS的人工遮荫条件下,研究了西双版纳季节雨林冠层树种绒毛番龙眼(Pometia tomentosa)幼苗的早期生长和定居后的生长特点。结果表明,光照是影响幼苗生长的重要环境因子。生长早期的幼苗基径和复叶数随遮荫程度的增加而降低;主根长、根冠比、总干重和单株叶面积均以37.3%NS处理最大;比叶面积随遮荫程度的增加而增大,而相对生长率则降低;幼苗株高在0.6%NS下增长最快,表明种子中贮藏的营养物质对幼苗的早期生长可能具有重要作用。37.3%NS处理对定居后绒毛番龙眼幼苗的生长最有利,幼苗的株高、基径、复叶数、叶轴长、复叶最多小叶数、单株叶面积、相对生长率和净同化率均在37.3%NS处理下获得最大增长;幼苗总干重随光照强度的减弱而降低;比叶面积在15.5%NS处理时最大。幼苗比叶面积和根冠比在生长过程中的波动可能是光照和土壤水分共同作用的结果。     

Herbivory on Temperate Rainforest Seedlings in Sun and Shade: Resistance,Tolerance and Habitat Distribution

Differential herbivory and/or differential plant resistance or tolerance in sun and shade environments may influence plant distribution along the light gradient. Embothrium coccineum is one of the few light-demanding tree species in the temperate rainforest of southern South America, and seedlings are frequently attacked by insects and snails. Herbivory may contribute to the exclusion of E. coccineum from the shade if 1) herbivory pressure is greater in the shade, which in turn can result from shade plants being less resistant or from habitat preferences of herbivores, and/or 2) consequences of damage are more detrimental in the shade, i.e., shade plants are less tolerant. We tested this in a field study with naturally established seedlings in treefall gaps (sun) and forest understory (shade) in a temperate rainforest of southern Chile. Seedlings growing in the sun sustained nearly 40% more herbivore damage and displayed half of the specific leaf area than those growing in the shade. A palatability test showed that a generalist snail consumed ten times more leaf area when fed on shade leaves compared to sun leaves, i.e., plant resistance was greater in sun-grown seedlings. Herbivore abundance (total biomass) was two-fold greater in treefall gaps compared to the forest understory. Undamaged seedlings survived better and showed a slightly higher growth rate in the sun. Whereas simulated herbivory in the shade decreased seedling survival and growth by 34% and 19%, respectively, damaged and undamaged seedlings showed similar survival and growth in the sun. Leaf tissue lost to herbivores in the shade appears to be too expensive to replace under the limiting light conditions of forest understory. Following evaluations of herbivore abundance and plant resistance and tolerance in contrasting light environments, we have shown how herbivory on a light-demanding tree species may contribute to its exclusion from shade sites. Thus, in the shaded forest understory, where the seedlings of some tree species are close to their physiological tolerance limit, herbivory could play an important role in plant establishment.     

Growth responses of tropical deciduous tree seedlings to contrasting light conditions

Summary The growth responses of seedlings of Amphipterygium adstringens, Caesalpinia eriostachys, and C. platyloba, species associated with undisturbed parts of the tropical deciduous forest in México, and Apoplanesia paniculata and Heliocarpus pallidus, two gap-requiring pioneer species, were determined under contrasting light conditions in a growth chamber experiment. The high (400 mol m^–2 s^–1) and low (80 mol m^–2 s^–1) light treatments correspond to the light available in a medium size gap and underneath the vegetation canopy in the deciduous forest during the rainy season, respectively. Following four destructive harvests the biomass production, relative growth rate, root/shoot ratio, specific leaf area, net assimilation rate, leaf area ratio and light dependency were determined for all species. In the high light treatment all species achieved higher relative growth rates and net assimilation rates than when growing at low light intensity. However, the two pioneer species showed the highest light dependency and were the species more affected by the low light treatment in biomass production. The two Caesalpinia species showed similar growth responses, but C. platyloba was the most shade tolerant species. Plastic adjustments in terms of the specific leaf area were more evident in the two pioneer species.     

A 1700-year Athrotaxis selaginoides tree-ring width chronology from southeastern Australia

Few Southern Hemisphere tree-ring chronologies exceed 1000 years in length. We present a ca. 1700 years of indexed values for the long-lived conifer Athrotaxis selaginoides at Cradle Mt in southeastern Australia and compare it with the only other published millennial-plus length tree-ring chronology for Australia: the nearby Mt Read Lagarostrobos franklinii. We use simple correlation function and pointer year analyses to compare the climate responses of the two species (temperature, precipitation and growing degree days). Both chronologies show accelerated growth at their modern ends, but this growth acceleration is not synchronous, beginning approximately a quarter of a century earlier at the Cradle Mt site. This discrepancy may highlight the relevance of chronology composition and/or physiological differences in the species. Although the seasonality of the climatic responses of the two species is similar, that of A. selaginoides is generally weaker than that of L. franklinii. Somewhat paradoxically, the only pointer years in common between the chronologies are 1898 and 1908 CE. The periods from 600 to 900 CE and ∼1200–1450 CE are conspicuous for their absence of positive pointer years while no negative pointer years occur for either site from ∼1200–1350 CE. It is possible that differing patterns of pointer years can be partially explained by a peak in establishment from ∼1150–1850 CE at the Mt Read L. franklinii site compared to continuous establishment at Cradle Mt. Although statistically significant and time-stable climate responses for the A. selaginoides chronology are too weak to base a single-chronology climate reconstruction on, the long chronology will likely make an important contribution to future multi-proxy temperature reconstructions for southeastern Australia.     

Scaling sun and shade photosynthetic acclimation of Alocasia macrorrhiza to whole-plant performance – II. Simulation of carbon balance and growth at different photon flux densities

A whole-plant carbon balance model incorporating a light acclimation response was developed for Alocasia macrorrhiza based on empirical data and the current understanding of light acclimation in this species. The model was used to predict the relative growth rate (RGR) for plants that acclimated to photon flux density (PFD) by changing their leaf type, and for plants that produced only sun or shade leaves regardless of PFD. The predicted RGR was substantially higher for plants with shade leaves than for those with sun leaves at low PFD. However, the predicted RGR was not higher, and in fact was slightly lower, for plants with sun leaves than for those with shade leaves at high PFD. The decreased leaf area ratios (LARs) of the plants with sun leaves counteracted their higher photosynthetic capacities per unit leaf area (A_max). The model was manipulated by changing parameters to examine the sensitivity of RGR to variation in single factors. Overall, RGR was most sensitive to LAR and showed relatively little sensitivity to variation in A_max or maintenance respiration. Similarly, RGR was relatively insensitive to increases in leaf life-span beyond those observed. Respiration affected RGR only at low PFD, whereas A_max was moderately important only at high PFD.     

Survival and growth of seedlings of 12 Chilean rainforest trees in two light environments: Gas exchange and biomass distribution correlates

Abstract Mortality, growth, gas exchange and biomass distribution were measured in the seedlings of 12 Chilean temperate rainforest angiosperm trees in two contrasting artificial light environments (150 and 12 μmoles m^?2 s^?1), in order to explore life history diversity in this forest type, and examine the physiological and/or morphological traits associated with interspecific variation in seedling performance. Gas exchange traits were measured only in the high‐light treatment (150 μmoles m^?2 s^?1), owing to the very small size of leaves in the low‐light treatment. Relative growth rates (RGR) in high light were strongly correlated with photosynthetic capacity (P< 0.0001). Mortality rates in low light had a strong positive correlation with light compensation point (P = 0.007) and photosynthetic capacity (P = 0.004). Furthermore, high‐light RGR was strongly positively correlated with low‐light mortality (P = 0.001). Biomass distribution traits showed little relationship with mortality or growth within either light level, except for a marginally significant positive correlation (P = 0.04) between leaf area ratio and mortality in low light. In view of the large interspecific differences in final size, the weak relationships between biomass distribution parameters and plant performance could be partially attributable to ontogenetic drift in these traits. Among taxa with high mortality rates in low light, short‐lived species (e.g. Aristotelia chilensis) had lower light compensation points, had greater phenotypic plasticity and grew much faster in both light environments than did longer‐lived species (Nothofagus dombeyi, Weinmannia trichosperma, Eucryphia cordifolia). Results support the view that survival of first‐year seedlings in low light is not enhanced by morphological traits that maximize growth potential (e.g. high leaf area ratio), and that leaf‐level gas exchange traits have an important role as determinants of interspecific variation in seedling performance. However, the limited range of interspecific variation observed in light compensation points indicates that other traits apart from those that we measured (e.g. carbon storage) must also be involved in seedling shade tolerance differences. The weak relationship between longevity and shade tolerance level among our 12 species suggests that it may not be feasible to ordinate life histories of Chilean temperate rainforest trees on a single axis of trait variation.     

The ecology of Araucaria species in New Guinea. II. Pattern in the distribution of young and mature individuals and light requirements of seedlings.

Conventional pattern analysis and segregation analysis were used to investigate the hypothesis that young and mature individuals of Araucaria hunsteinii were not usually found growing in close association whilst the distribution of young and mature individuals of A. cunninghamii was essentially random. It was considered that this pattern reflected a difference in regeneration strategy between the two species, A. hunsteinii being a gap regenerator and A. cunninghamii a shade-tolerant species. A seedling growth-experiment using three different shade treatments and four temperature treatments tested this hypothesis further. Results show that A. hunsteinii is more dependent on high light intensity than A. cunninghamii for the production of biomass. A. cunninghamii produces more biomass than A. hunsteinii under all treatment conditions.     

Responses to light changes in tropical deciduous woody seedlings with contrasting growth rates

We evaluated the responses in growth, biomass allocation, photosynthesis and stomatal conductance, to changes in light in woody seedlings from the tropical deciduous forest in Mexico, which shows a highly seasonal rain pattern. We studied ten species, which differed by 30-fold in relative growth rate (RGR). We analyzed plant growth in two contrasting light levels during 52 days and two transfers: from high to low (HL) and from low to high (LH) light intensity, and the respective controls in high (HH) and low (LL) light for another 52 days. The photosynthetic capacity (A _max) and stomatal conductance were measured at the day of the transfer between light conditions and at the end of the experiment. Species with high RGR showed the largest changes in RGR in response to contrasting light conditions (HH/LL ratio), and species with low RGR showed low responses. The fast-growing species were the most plastic, followed by species with intermediate growth rates, with the slow-growing species being the least plastic. Fast-growing species achieved higher maximum photosynthetic capacities (A _max) and stomatal conductance and higher response to light than slow-growing species. Species with high RGR showed a low RGR HH/LH ratio, suggesting a large response of L plants when transfered to H. The RGR of the species were associated with species specific leaf area and with the response in the leaf area, net assimilation rate and leaf weight ratio, suggesting the importance of the leaf area produced and the leaf characteristics rather than root:shoot ratio in determining RGR. Considering that seed germination is expected at the beginning of the rainy period, seedlings of most of the species will experience high-light conditions during its early growth. There are large annual variations in the time required for canopy closure (35–75 days). The influence of these variations may have different effect on the species studied. Species with intermediate growth rate and intermediate response to light changes were less affected by light reduction than fast-growing species. The intermediate-RGR species Caesalpiniaeriostachys is the most abundant and widely distributed species, perhaps this could be in part due to its ability to acclimate to both light increases and decreases. The fast-growing species studied here can be found in open sites in the forest and in areas cleared for pasture growth. These fast-growing species eventually reach the canopy, although this may require several canopy openings during their lives, which implies juvenile shade tolerance. In the tropical deciduous forest juvenile pioneer trees also benefit from the temporary high light available caused by the dry period during the rainy season. The slow-growing species Celaenodendronmexicanum forms small patches of monospecific forest; the adult trees are not completely deciduous, and they retain their old leaves for a long time period before shedding. Thus seedlings of this species may receive lower levels of light, in agreement with its shade tolerance and its lower response to light increases. Received: 14 April 1997 / Accepted: 29 July 1997