Cold tolerance of photosynthesis as a determinant of tree species regeneration patterns in an evergreen temperate forest

Niche partitioning of light among seedling species is a key mechanism supporting coexistence in forests. Species sort along light gradients through direct responses to light and through indirect responses mediated by other environmental factors. Canopy gaps in temperate evergreen rainforests experience sub-zero temperatures and thus gap-dependent species are vulnerable to cold photoinhibition from exposure to high light at low temperatures. We used a shadehouse experiment to test two hypotheses: (1) that gap-dependent species are resistant to cold photoinhibition; and (2) that gap-dependence observed in the field may be driven by the interaction between high light and low temperatures. Specifically, we predicted that some species restricted to shade in the field are excluded from gaps because of low resistance to cold photoinhibition. Gap dependence of angiosperm and conifer seedlings was estimated from expert opinion, and from experimental growth and survival responses to light treatments representing a forest understorey and forest gap. Additional seedlings were used to evaluate resistance to cold photoinhibition (sub-zero temperatures at dawn). Gap-dependent species were resistant to cold photoinhibition. Our second hypothesis was supported by Beilschmiedia tawa (Lauraceae), which had low resistance to photoinhibition, a strong positive growth response to the light treatments, and is restricted to shade in the field. Seedling regeneration niches in temperate rainforest are shaped in part by the interaction between light and low temperatures, and this interaction will be crucial for determining seedling responses to climate warming.     

Species dynamics and colonization patterns in an abandoned forest in an urban landscape

Species dynamics in an abandoned urban forest of Central Japan is described in this paper. The dominant species in the urban plantation were Cryptomeria japonica and Chamaecyparis obtusa. A variety of eight patches of the canopy was produced by previous forest management practices. Progressive and retrogressive species dynamics within these eight patches are investigated in this paper. The study elucidates the deterministic role of patchiness in the nature of species colonization and the maintenance of species diversity in an urban forest. Altogether 139 native and/or naturalized species, including 23 shrub and 35 tree species, were recorded in the study area of 3.2 ha. The performance of species varied according to their successional attributes indicating a selective canopy influence. Twenty percent of the tree species were shade-intolerant pioneers (e.g. Cornus spp., Rhus javanica var. roxburghii) re-established under selective tree-felling. Thirty percent were shade-tolerant climax species (e.g. Neolitsea sericea, Persea thunbergii) dominant in remnant closed patches. The remaining 50% belonged to various seral types with aggressive deciduous species (e.g. Aphananthe aspera, Celtis sinensis) in most of the patches. Some ruderal herbaceous species dominated heavily disturbed clear-felled patches. This study suggests that canopy modification influences the subsequent colonization pattern. Furthermore, heterogeneous patches contribute to greater species diversity and dynamics in isolated woodlands.     

Leaf ties as colonization sites for forest arthropods: an experimental study

Abstract.  1. Secondary colonization of leaf shelters constructed by caterpillars has been reported from a number of systems. Both the mechanism (larval or adult movement vs. oviposition) and the cues used by arthropods in locating leaf shelters, however, have received little attention.
2. Artificial leaf shelters (i.e. leaf ties or pairs of leaves clipped together to form sandwiches) were constructed on understorey white oak ( Quercus alba L.) trees and the abundance and species composition of arthropods colonizing and ovipositing on leaf pairs was examined in three treatments: occupied leaf ties (containing a leaf-tying caterpillar), unoccupied leaf ties, and non-tied control leaves.
3. The density of arthropods present in the occupied and unoccupied leaf ties after two weeks was seven and four times greater respectively, than non-tied controls. The guild composition of these early colonists differed among treatments, with the highest densities of leaf chewers, scavengers, and predators in occupied ties and the lowest densities in non-tied controls.
4. The densities of all arthropods ovipositing on leaf pairs in the occupied and unoccupied leaf tie treatments were four and three times greater than non-tied controls. Leaf-chewing insects (including leaf-tiers and non-tying inquiline species) and scavengers showed strong oviposition preferences for tied leaves. However, most species of leaf-tying caterpillars and the psocids (Psocoptera) did not distinguish between occupied and unoccupied ties, suggesting that these groups do not use occupancy-related cues in selecting oviposition sites.     

Spatio‐temporal colonization patterns of forest plant species in a mixed deciduous forest

Abstract. An integrated analysis of the colonization patterns of forest plant species was carried out in a 34‐ha, mixed deciduous forest in northern Belgium. First, we sought to describe the relationships between land use history and environmental conditions. Land use history and soil type were related and negative correlations between pH and secondary forest age were found. The density of the shrub layer increases with secondary forest age. Litter quantity and cover of Urtica dioica were mainly indirectly influenced by land use history. Litter starts accumulating at low pH values and high shrub density and Urtica dioica grows vigorously on nutrient enriched soils where much light can reach the ground. Next, the importance of these human‐altered environmental conditions for the colonization of forest plant species was assessed relative to the importance of dispersal limitation. Therefore, the distribution of 16 forest species was mapped and species‐specific spatio‐temporal isolation measures were calculated. The analysis revealed that the colonization patterns of the slowly colonizing species (i.e. ‘ancient forest plant species’) are best explained by a combination of spatio‐temporal isolation, soil type, pH and the (non‐)cover of Urtica dioica. By contrast, spatio‐temporal isolation was never a limiting factor for good colonizing forest species. Our results suggest that colonization of ‘ancient forest plant species’ is hampered by a combination of dispersal‐ and recruitment limitation and that the relative importance of both factors is species‐specific.     

Temperamental variation as a determinant of learning efficiency in cercopithecoid monkeys

Adult and juvenileM. mulatta andM. speciosa were given two tests of emotional responsivity and three learning tasks, in order of increasing difficulty, to evaluate possible group differences in the learning measures as a function of temperamental factors. Results provided evidence of reliable differences in affective behavior, and, while no differences were seen in the simple learning task, differences in learning of the more complex tasks by adults appeared to be negatively correlated with intensity of affect. By contrast, although juveniles also mastered the learning tasks, neither group showed comparable changes.Data for this study were collected, in part, while at the University of Cincinnati. Funds were furnished by the Graduate School to the Department of Psychology of that institution. Data collection was completed at the present institution.     

Trade-off between water transport efficiency and leaf life-span in a tropical dry forest

Drought-deciduous and evergreen species coexist in tropical dry forests. Drought-deciduous species must cope with greater seasonal leaf water-potential fluctuations than evergreen species and this may increase their susceptibility to drought-induced xylem embolism. The relationship between water transport efficiency and leaf life-span were determined for both groups. They differed in seasonal changes of both, wood water content (W _c) and wood specific gravity (G). During the dry season, the W _c in drought-deciduous species declined and the minimum value was recorded when leaf fall was complete. At this time, the volumetric fraction of gas (V _g) increased indicating air entry into xylem vessels. In contrast, W _c, G and V _g changed only slightly throughout the year for evergreen species. Maximum hydraulic conductivity of drought-deciduous species was 2–6 times that of the evergreen species. but was severely reduced at leaf fall. In the evergreen species, similar water conductivities were measured during wet and dry seasons. The trade-off between xylem water transport capacity and leaf lifespan found in species coexisting in this forest reveals the existence of contrasting but successful adaptations to this environment. Drought-deciduous species maximize production in the short term with higher water transport efficiency which leads to the seasonal occurrence of embolisms. Conversely, the behaviour of evergreen species with reduced maximum efficiency is conservative but safe in relation to xylem embolism.     

Seasonal patterns of ammonium and nitrate uptake in nine temperate forest ecosystems

Summary Seasonal patterns of net N mineralization and nitrification in the 0–10 cm mineral soil of 9 temperate forest sites were analyzed using approximately monthlyin situ soil incubations. Measured nitrification rates in incubated soils were found to be good estimates of nitrification in surrounding forest soils. Monthly net N mineralization rates and pools of ammonium-N in soil fluctuated during the growing season at all sites. Nitrate-N pools in soil were generally smaller than ammonium-N pools and monthly nitrification rates were less variable than net N mineralization rates. Nitrate supplied most of the N taken up annually by vegetation at 8 of the 9 sites. Furthermore, despite the large fluctuations in ammonium-N pools and monthly net N mineralization, nitrate was taken up at relatively uniform rates during the growing season at most sites.     

物种多样性地理格局的能量假说

物种多样性地理分布格局及其成因是生物地理学和宏观生态学研究的核心问题之一。为了解释物种多样性的分布格局, 人们提出了多种假说, 其中讨论最多的是能量假说。该假说认为, 物种多样性的变化受能量控制。根据能量的不同形式及其对物种多样性的影响机制, 能量假说包括以下几种形式: 生产力假说(productivity hypothesis)、水分—能量动态假说(water–energy dynamic hypothesis)、环境能量假说(ambient energy hypothesis)、寒冷忍耐假说(freezing tolerance hypothesis)以及生态学代谢假说(metabolic theory of ecology, MTE)。本文系统介绍了每种能量假说的含义、所使用的能量形式及表征变量, 以及对物种多样性的影响机制, 并对不同形式的能量假说进行了比较, 在此基础上, 分析了每种能量假说的优点和缺点以及各自面临的问题。     

Stream hydraulics as a major determinant of benthic invertebrate zonation patterns

SUMMARY. 1. Studies on the zonation of benthic fauna in fourteen streams situated in a variety of latitudes from Alaska to New Zealand have been evaluated.
2. We suggest that physical characteristics of flow ('stream hydraulics') are the most important environmental factor governing the zonation of stream benthos on a world-wide scale.
3. From the source to the mouth of a stream, zones of transition in stream hydraulics' occur, to which the general pattern of stream invertebrate assemblages can be related. In these zones benthic community stability and resilience must be different from those upstream and downstream of the hydraulic transition zones.     

Root growth as a function of ammonium and nitrate in the root zone

We examined the effect of soil NH₄⁺ and NO₃^? content upon the root systems of field-grown tomatoes, and the influence of constant, low concentrations of NH₄⁺ or NO₃^? upon root growth in solution culture. In two field experiments, few roots were present in soil zones with low extractable NH₄⁺ or NO₃^?; they increased to a maximum in zones having 2μg-N NO₃^? g^?1 soil and 6 μg-N NO₃⁼ g^?1 soil, but decreased in zones having higher NH₄⁺ or NO₃^? levels. Root branching was relatively insensitive to available mineral nitrogen. Plants maintained in solution culture at constant levels of NH₄⁺ or NO₃^?, had similar shoot biomass, but all root parameters – biomass, length, branching and area – were greater under NH4 nutrition than under NO₃^?. These results suggest that the size of root system depends on a functional equilibrium between roots and shoots (Brouwer 1967) and on the balance between soil NH₄⁺ and NO₃^?.     

Cellular transport of lysosomal enzymes: an alternative hypothesis.

Hickman & Neufeld [(1972) Biochem, Biophys. Res. Commun. 49, 992-999] have proposed that lysosomal enzymes reach the lysosomes by means of exocytosis and subsequent pinocytic reincorporation. The results leading to this conclusion are re-assessed and an alternative explanation is advanced that relates to the necessity for membrane recycling in endocytic cells.     

Microhabitat availability in Welsh moorland and forest streams as a determinant of macroinvertebrate distribution

SUMMARY. 1 Eighteen streams in mid-Wales were sampled for macro-invertebrates in both riffles and margins in April 1985–87. Stream macro-flora, substrata and marginal habitats were surveyed in May 1988.
2. TWINSPAN classification of the macroinvertebrate data indicated three major stream groups. One was distinguished by circumneutral pH and had a flora and fauna typical of such conditions. The other two groups consisted of acidic streams with moorland and conifer afforested catchments respectively. The forest streams were the more acidic but the two groups also differed significantly in the composition of their marginal habitats.
3 The acidic moorland streams had more vegetation ('soft' features) in the margins and supported several invertebrate taxa which were relative more abundant there than in the riffles. These taxa may be excluded from forest streams because the margins are 'hard' due to greater erosiveness and shading.
4. In view of the increasing cover by conifer afforestation in Britain, it is clearly necessary to elucidate all its effects on stream ecosystems, which include changes to the physical environment.     

Root environment acidity as a regulatory factor in ammonium assimilation by the bean plant

Previous experiments have revealed a much greater efficiency of ammonium utilization by bean plants (Phaseolus vulgaris L.) when the acidity of the ambient medium was maintained at near-neutral conditions with carbonates or hydroxides. The present investigation, in which ¹⁵N-labeled ammonium was used, permitted an assessment of the origin of nitrogen in tissue nitrogen pools with and without acidity control (CaCO₃ treated and untreated, respectively) in the root environment. Control of acidity resulted in greater ammonium uptake and greater incorporation into the amino fraction, amide, and ethanol-insoluble nitrogen by the root tissue. These differences were clearly evident by the fifth day after ammonium nitrogen had been applied.     

Spatial patterns of herbivory by gall-forming insects: a test of the soil fertility hypothesis in a Mexican tropical dry forest

It has been proposed that fertile soils reduce the incidence of gall-forming insect (GFI) species in plant communities. This is known as the soil fertility hypothesis. The main objective of this study was to analyze the spatial distribution of GFI species under different habitats in a tropical dry forest at the Chamela-Cuixmala Biosphere Reserve, Mexico. Eight habitats which differ in soil type, topography, nutrient availability and vegetation were chosen. We found that 38 GFI species specialize on their host plant species. GFI species richness was negatively correlated with phosphorous and nitrogen availability. Using phosphorous as an indicator of soil fertility, we found low frequency and density of GFI on fertile soils. Our study indicates that soil fertility is one of the factors that negatively affects the patterns of spatial distribution of species richness, incidence and abundance of GFI at the community level in two different ways: i) indirectly affecting GFI species richness in plants adapted to infertile soils and ii) directly affecting GFI responses to plant traits of hosts found in a fertility gradient.