Tree Competition and Species Coexistence in a Sub-boreal Forest, Northern Japan

The growth and mortality patterns and the mode of competitionof six tree species forming a sub-boreal climax forest in Hokkaido,northern Japan, were investigated based on the diffusion modelat the level of the individual tree 2 m height in a 2·3-hastudy site. Picea jezoensis, Picea glehnii, Betula ermanii andAbies sachalinensis were dominant species, occupying approx.94% of the total basal area. Sorbus commixta and Acer ukurunduensewere subordinate species occupying approx. 6% of the total basalarea. A model for individual growth was developed, consideringboth intra- and inter-specific competition and the degree ofcompetitive asymmetry. Asymmetry was found in intraspecificcompetition of Sorbus commixta and Acer ukurunduense. Piceajezoensis, Betula ermanii and Abies sachalinensis showed symmetricintraspecific competition. There was little interspecific competitionamongst Picea jezoensis, Picea glehnii and Betula ermanii. Abiessachalinensis competed symmetrically with Picea jezoensis (onlyvery weakly, P < 0·1) and Betula ermanii (P < 0·01).Picea glehnii gave no indication of inter- or intra-specificcompetition. The growth of the four dominant species was neveraffected by the two subordinate species; the growth of the twosubordinate species was governed by the abundances of the fourdominant species, the sum of which almost amounted to standcrowdedness (i.e. symmetric competitive effect and one-sidedcompetitive direction). On the scale of 2·3 ha of thesub-boreal forest, symmetric competition prevailed over one-sidedor asymmetric competition although statistical evidence forany competitive effects was rather weak. This was probably dueto the relatively low tree density and stand crowdedness ofthis climax forest. Little competition between the dominantspecies suggested by relatively low proportions of r²-valuesattributable to competitive effects indicates weak organizationamongst the component species (i.e. species were more or lessindependent of each other) at the level of the individual tree 2 m height on the 2·3-ha scale.Copyright 1995, 1999Academic Press Climax forest, diffusion model, individual growth, one-sided competition, size structure, symmetric competition     

Calcium Additions and Microbial Nitrogen Cycle Processes in a Northern Hardwood Forest

Evaluating, and possibly ameliorating, the effects of base cation depletion in forest soils caused by acid deposition is an important topic in the northeastern United States. We added 850 kg Ca ha⁻¹ as wollastonite (CaSiO₃) to an 11.8-ha watershed at the Hubbard Brook Experimental Forest (HBEF), a northern hardwood forest in New Hampshire, USA, in fall 1999 to replace calcium (Ca) leached from the ecosystem by acid deposition over the past 6 decades. Soil microbial biomass carbon (C) and nitrogen (N) concentrations, gross and potential net N mineralization and nitrification rates, soil solution and stream chemistry, soil:atmosphere trace gas (CO₂, N₂O, CH₄) fluxes, and foliar N concentrations have been monitored in the treated watershed and in reference areas at the HBEF before and since the Ca addition. We expected that rates of microbial C and N cycle processes would increase in response to the treatment. By 2000, soil pH was increased by a full unit in the Oie soil horizon, and by 2002 it was increased by nearly 0.5 units in the Oa soil horizon. However, there were declines in the N content of the microbial biomass, potential net and gross N mineralization rates, and soil inorganic N pools in the Oie horizon of the treated watershed. Stream, soil solution, and foliar concentrations of N showed no response to treatment. The lack of stimulation of N cycling by Ca addition suggests that microbes may not be stimulated by increased pH and Ca levels in the naturally acidic soils at the HBEF, or that other factors (for example, phosphorus, or Ca binding of labile organic matter) may constrain the capacity of microbes to respond to increased pH in the treated watershed. Possible fates for the approximately 10 kg N ha⁻¹ decline in microbial and soil inorganic pools include components of the plant community that we did not measure (for example, seedlings, understory shrubs), increased fluxes of N₂ and/or N storage in soil organic matter. These results raise questions about the factors regulating microbial biomass and activity in northern hardwood forests that should be considered in the context of proposals to mitigate the depletion of nutrient cations in soil.     

Climate Variation and Soil Carbon and Nitrogen Cycling Processes in a Northern Hardwood Forest

We exploited the natural climate gradient in the northern hardwood forest at the Hubbard Brook Experimental Forest (HBEF) to evaluate the effects of climate variation similar to what is predicted to occur with global warming over the next 50–100 years for northeastern North America on soil carbon (C) and nitrogen (N) cycle processes. Our objectives were to (1) characterize differences in soil temperature, moisture and frost associated with elevation at the HBEF and (2) evaluate variation in total soil (TSR) and microbial respiration, N mineralization, nitrification, denitrification, nitrous oxide (N₂O) flux, and methane (CH₄) uptake along this gradient. Low elevation sites were consistently warmer (1.5–2.5°C) and drier than high elevation sites. Despite higher temperatures, low elevation plots had less snow and more soil frost than high elevation plots. Net N mineralization and nitrification were slower in warmer, low elevation plots, in both summer and winter. In summer, this pattern was driven by lower soil moisture in warmer soils and in winter the pattern was linked to less snow and more soil freezing in warmer soils. These data suggest that N cycling and supply to plants in northern hardwood ecosystems will be reduced in a warmer climate due to changes in both winter and summer conditions. TSR was consistently faster in the warmer, low elevation plots. N cycling processes appeared to be more sensitive to variation in soil moisture induced by climate variation, whereas C cycling processes appeared to be more strongly influenced by temperature.     

Flowering Phenology of Understory Herbaceous Species in a Cool Temperate Deciduous Forest in Ogawa Forest Reserve, Central Japan

Received 12 October 1999/ Accepted in revised form 26 September 2000     

Species Coexistence and Periodicity in Host-Host-Pathogen Models

Models for the transmission of an infectious disease in one and two host populations with and without self-regulation are analyzed. Many unusual behaviors such as multiple positive equilibria and periodic solutions occur in previous models that use the mass-action (density-dependent) incidence. In contrast, the models formulated using the frequency-dependent (standard) incidence have the behavior of a classic endemic model, since below the threshold, the disease dies out, and above the threshold, the disease persists and the infectious fractions approach an endemic equilibrium. The results given here reinforce previous examples in which there are major differences in behavior between models using mass-action and frequency-dependent incidences.     

大别山北坡落叶阔叶林的物种多样性

应用Simpson生态优势度指数（C）,Shannon—Wiener多样性指数（H）和均匀度（E）等指标,对落叶阔叶林的4个组合类型的物种多样性进行了分析。结果表明;乔木层树种的多样性指数H变化在1.4709-3.8875之间,以T_3（3.8875）最高,依次为T_4、T_2、T_1（1.4709）最低;均匀度E为T_3＞T_4＞T_1＞T_2,而生态优势度C与H的变化相反。表现出物种多样性不只受到海拔高度、生境条件的影响,人为活动、群落的稳定性等因素也有重要作用。相反,灌木层和草本层的物种多样性受人为活动的影响相对较小,表现出常规的变化,即随海拔升高,H和E值降低,C值则升高。格局检验的结果表明：栓皮栎种群为集群分布,短柄枹群呈随机分布。而化香种则呈现在化香林中的集群分布,在短柄枹林中又为随机分布的特点。     

Crown Architecture and Species Coexistence in Plant Communities

The relationships between crown architecture and species coexistencewere studied using the diffusion model and the canopy photosynthesismodel for multi-species plant communities. The present paperdeals with two species having different crown shapes [conic-canopyplant (CCP) and spheroidal-canopy plant (SCP)], for variousinitial mean sizes at the establishment stage and physiologicalparameter values (photosynthetic rate, etc.). Recruitment processeswere not incorporated into the model, and thus simulations weremade for the effects on the pattern of species coexistence ofeither sapling competition starting from different sapling banksor competition in single-cohort stands with little continualestablishment of species until a stand-replacement disturbance.The following predictions were derived: (1) SCPs can establishlater/slowly in the lower canopy layer even if they are overtoppedby a CCP which established first/rapidly; (2) if SCPs establishedfirst/rapidly and occupy the upper canopy layer, a CCP can rarelyestablish later/slowly in the lower canopy layer; (3) smallest-sizedCCPs can persist well in the lowermost canopy layer overtoppedby a SCP, suggesting a waiting strategy of CCP's saplings inthe understorey of a crowded stand; (4) even if CCPs establishedfirst/rapidly and occupy the upper canopy layer, an SCP canestablish later/slowly in the lower canopy layer. Therefore,the species diversity of SCPs which established first/rapidlyand occupy the upper canopy layer limits the number of CCP specieswhich can establish later/slowly. In contrast, the species diversityof CCPs which established first/rapidly and occupy the uppercanopy layer does not affect the number of SCP species whichcan establish later/slowly. The combination of initial sizesof a CCP and an SCP at the establishment stage (i.e. establishmenttiming) affects the segregation of vertical positions in thecanopy between the two species with different crown shape, andnot only species-specific physiological traits but also crownarchitecture greatly affects the coexistence pattern betweenspecies with different crown architectures. The theoreticalpredictions obtained here can explain coexistence patterns foundin single-cohort conifer-hardwood boreal and sub-boreal forests,pointing to the significance of crown architecture for speciescoexistence. Diffusion equation model; canopy photosynthesis model; conifer-hardwood boreal/sub-boreal forest; sapling establishment; vertical foliage profile     

Root Strength and Root Area Ratio of Forest Species in Lombardy (Northern Italy)

Forest vegetation is known to increase hillslope stability by reinforcing soil shear resistance and by influencing hydrologic conditions of soil. Although the importance of plant root systems for hillslope stability has received considerable attention in recent years, the quantification of such an effect needs more investigation. In this paper, we present a synthesis of the data gathered in the last 5 years for some species in different locations of the Alps and Prealps of Lombardy (Northern Italy) with the aim to increase our knowledge on root tensile strength and on Root Area Ratio distribution within the soil. Concerning root tensile strength we developed tensile strength–diameter relationships for eight species: green alder (Alnus viridis(Chaix) D.C.), beech (Fagus sylvatica L.), red willow (Salix purpurea L.), goat willow (Salix caprea L.), hazel (Corylus avellana L.), European ash (Fraxinus excelsior L.), Norway spruce (Picea abies (L.) Karst.) and European larch (Larix decidua Mill.). Results show a great variability among the different species and also for the same species. In general, however, root strength (in terms of tension) tends to decrease with diameter according to a power law, as observed by other Authors. Comparing the power law fitting curves for the considered species, it can be observed that they fall in a relatively narrow band, with the exception of hazel, which appears the most resistant. Concerning the evaluation of root distribution within the soil we estimated the Root Area Ratio (the ratio between the area occupied by roots in a unit area of soil) according to its depth for five species (beech, Norway spruce, European larch, mixed hazel and ash) in three locations of Lombardy. Results show that there is a great variability of root density for the same species well as for different points at the same locality. The general behaviour of root density, in any case, is to decrease with depth according to a gamma function for all the studied species. The results presented in this paper contribute to expanding the knowledge on root resistance behaviour and on root density distribution within the soil. The studied location have allowed the implementation of soil–root reinforcement models and the evaluation of the vegetation contribution to soil stability.     

Spatial Complementarity and the Coexistence of Species

Coexistence of apparently similar species remains an enduring paradox in ecology. Spatial structure has been predicted to enable coexistence even when population-level models predict competitive exclusion if it causes each species to limit its own population more than that of its competitor. Nevertheless, existing hypotheses conflict with regard to whether clustering favours or precludes coexistence. The spatial segregation hypothesis predicts that in clustered populations the frequency of intra-specific interactions will be increased, causing each species to be self-limiting. Alternatively, individuals of the same species might compete over greater distances, known as heteromyopia, breaking down clusters and opening space for a second species to invade. In this study we create an individual-based model in homogeneous two-dimensional space for two putative sessile species differing only in their demographic rates and the range and strength of their competitive interactions. We fully characterise the parameter space within which coexistence occurs beyond population-level predictions, thereby revealing a region of coexistence generated by a previously-unrecognised process which we term the triadic mechanism. Here coexistence occurs due to the ability of a second generation of offspring of the rarer species to escape competition from their ancestors. We diagnose the conditions under which each of three spatial coexistence mechanisms operates and their characteristic spatial signatures. Deriving insights from a novel metric — ecological pressure — we demonstrate that coexistence is not solely determined by features of the numerically-dominant species. This results in a common framework for predicting, given any pair of species and knowledge of the relevant parameters, whether they will coexist, the mechanism by which they will do so, and the resultant spatial pattern of the community. Spatial coexistence arises from complementary combinations of traits in each species rather than solely through self-limitation.     

Energetic Constraints on Species Coexistence in Birds

The association between species richness and ecosystem energy availability is one of the major geographic trends in biodiversity. It is often explained in terms of energetic constraints, such that coexistence among competing species is limited in low productivity environments. However, it has proven challenging to reject alternative views, including the null hypothesis that species richness has simply had more time to accumulate in productive regions, and thus the role of energetic constraints in limiting coexistence remains largely unknown. We use the phylogenetic relationships and geographic ranges of sister species (pairs of lineages who are each other’s closest extant relatives) to examine the association between energy availability and coexistence across an entire vertebrate class (Aves). We show that the incidence of coexistence among sister species increases with overall species richness and is elevated in more productive ecosystems, even when accounting for differences in the evolutionary time available for coexistence to occur. Our results indicate that energy availability promotes species coexistence in closely related lineages, providing a key step toward a more mechanistic understanding of the productivity–richness relationship underlying global gradients in biodiversity.     

Savanna–Forest Coexistence Across a Fire Gradient

Ecosystems - Tropical forests and savannas can co-occur in a range of macro-environmental conditions. In these conditions, disturbances and resource availability are thought to control savanna and...     

Competition and Coexistence Among Four Estuarine Species of Fundulus

Four sympatric species of Fundulus (F. heteroclitus, F. majalis,F. diaphanus, and F. luciae) are distributed along tidal heightand salinity gradients such that F. heteroclitus co-occurs witheach species, while the remaining species rarely occur together.Feeding habitats of all the species are similar, and food hasbeen shown to limit population size of F. heteroclitus. Thispaper examines whether competition is an important structuringforce within this guild by addressing two questions: 1) is thespatial separation exhibited by three of the species due tophysiological barriers or due to competitive exlusion? and 2)when F. heteroclitus occurs with other Fundulus species doescompetition for resources take place? Laboratory studies indicate that all four species are tolerantof a wide range of environmental conditions; available evidencesuggests that physiological barriers are an unlikely explanationfor spatial segregation among some members of this guild. Competitiveexclusion seems a likely alternate explanation, but is supportedonly by studies of diet overlap. Similarly, only inference fromdiet overlap is available to answer the second question. A fieldexperiment is presented here in which F. heteroclitus and F.majalis were placed in enclosures separately and together. Competitionbetween these species appears to be important, and similar fieldexperiments are recommended to investigate competitive interactionsamong other species pairs within the genus     

Soil Nematode Diversity: Species Coexistence and Ecosystem Function

Soil nematode species diversity is often high, both at ecosystem and single soil-core scales. First, how can so many species coexist? There is evidence of niche partitioning, notably of physical space, but vast interspecific overlaps and trait plasticity seem equally common. It appears that coexistence of species with similar resource needs is made possible by small-scale disturbance and predation, which likely reduce local population sizes and interspecific competition. Regional processes such as dispersal, large-scale disturbance, and aggregation, which govern ecosystem level diversity, may also affect local species interactions and soil-core scale diversity. Second, what is the significance of having so many species, with so few trophic functions, for ecosystem processes? Focusing on bacterivore diversity, it is clear that species contributions to decomposition, likely to differ as a function of individual biologies, are concealed by the trophic group approach. However, considerable functional redundancy probably exists, which may explain why decomposition processes are maintained in highly disturbed soils despite the extinction of many species. Thus, soil nematode diversity is important for the long-term stability of soil functioning, and merits protection and further study.     

Coexistence of Competing Parasitoid Species on a Host with a Variable Life Cycle

Several special cases of a general model in which two parasitoid species attack different developmental stages of a single host species are presented. The inclusion of different mathematical forms of a maturation weighting function allows us to investigate the effect of several aspects of variation in immature stage durations on the outcome of competitition between the parasitoids. The two parasitoid species cannot coexist if the host developmental stages are fixed in duration. The outcome of competition depends in part on the relative duration of the two stages attacked by the parasitoid species. However, coexistence is possible if there is sufficient variation in the time that different host individuals remain in each stage. Distributed host developmental delays promote coexistence because they cause the host population to be composed of a mixture of host types with different relative egg versus larval stage durations. Each host type is thus largely available to only one of the parasitoid species.     

Paludification and Forest Retreat in Northern Oceanic Environments

Examination of temperature variations over the past centuryfor Europe and the Arctic from northern Norway to Siberia suggeststhat variations in the North Atlantic Oscillation are associatedwith an increase in oceanicity in certain maritime regions.A southward depression of the treeline in favour of wet heaths,bogs and wetland tundra communities is also observed in northernoceanic environments. The physiological basis for this changein ecological succession from forest to bog is discussed inrelation to the long-term effects of flooding on tree survival.The heightened values currently detected in the North AtlanticOscillation Index, together with rising winter temperatures,and increased rainfall in many areas in northern Europe, presentsan increasing risk of paludification with adverse consequencesfor forest regeneration, particularly in areas with oceanicclimates. Climatic warming in oceanic areas may increase thearea covered by bogs and, contrary to general expectations,lead to a retreat rather than an advance in the northern limitof the boreal forest. High water-table levels are not automaticallydetrimental to forest survival as can be seen in swamp, bottomlandand mangrove forests. Consequently, the inhibitory effects offlooding on tree survival and regeneration in northern regionsshould not be uncritically accepted as merely due to high waterlevels. Evidence is discussed which suggests that physiologicaland ecological factors may interact to inhibit forest regenerationin habitats where there is a risk of prolonged winter-floodingcombined with warmer winters and cool moist summers.     

Element Fluxes and Landscape Position in a Northern Hardwood Forest Watershed Ecosystem

Chemical changes along headwater streams at the Hubbard Brook Experimental Forest in New Hampshire suggest that important differences exist in biogeochemical cycles along an altitudinal gradient within small watershed ecosystems. Using data collected during the period 1982–92, we have constructed element budgets [Ca, Mg, K, Na, Si, Al, dissolved organic carbon (DOC), S, and N] for three subcatchments within watershed 6, a forested watershed last logged around 1917–20. The biogeochemistry of the high-elevation spruce-fir–white birch subcatchment was dominated by processes involving naturally occuring organic compounds. Stream water and soil solutions in this zone had elevated concentrations of organic acidity, DOC, and organically bound monomeric aluminum (Al_o), relative to lower-elevation sites. The middle-elevation subcatchment, dominated by hardwood vegetation, had the greatest net production of inorganic-monomeric aluminum (Al_i), and exhibited net immobilization of DOC and Al_o. The low-elevation subcatchment, also characterized by deciduous vegetation, had the highest rates of net production of base cations (Ca²⁺, Mg²⁺, K⁺, Na⁺) among the subcatchments. Living biomass of trees declined slightly in the spruce-fir–white birch subcatchment during the study period, remained constant in the middle-elevation zone, and increased by 5% in the low-elevation subcatchment. Coupling the corresponding changes in biomass nutrient pools with the geochemical patterns, we observed up to 15-fold differences in the net production of Ca, Mg, K, Na, and Si in soils of the three subcatchments within this 13.2-ha watershed. Release of Ca, Na, and dissolved Si in the highest-elevation subcatchment could be explained by the congruent dissolution of 185 mol ha⁻¹ y⁻¹ of plagioclase feldspar. The rate of plagioclase weathering, based on the net output of Na, increased downslope to 189 and 435 mol ha⁻¹ y⁻¹ in the middle-elevation and low-elevation subcatchments, respectively. However, the dissolution of feldspar in the hardwood subcatchments could account for only 26%–37% of the observed net Ca output. The loss of Ca from soil exchange sites and organic matter is the most likely source of the unexplained net export. Furthermore, this depletion appears to be occurring most rapidly in the lower half of watershed 6. The small watersheds at the Hubbard Brook Experimental Forest occupy a soil catena in which soil depth and soil-water contact time increase downslope. By influencing hydrologic flowpaths and acid neutralization processes, these factors exert an important influence on biogeochemical fluxes within small watersheds, but their influence on forest vigor is less clear. Our results illustrate the sensitivity of watershed-level studies to spatial scale. However, it appears that much of the variation in element fluxes occurs in the first 10–20 ha of drainage area. Received 13 August 1998; accepted 7 September 1999.     

Species Composition and Structure of Ichthyoplankton of the Northern Part of the Sea of Japan in Summer of 2017

Journal of Ichthyology - The ichthyoplankton of the upper epipelagic zone (0–50 m) was studied in the northern part of the Sea of ​​Japan in July–August 2017. Eggs of seven...