缙云山常绿阔叶林不同演替阶段植物生活型谱比较研究

采用Raunkiner生活型分类系统,对缙云山常绿阔叶林不同演替阶段植物的生活型进行统计,编制了生活型谱,并与其他亚热带地区常绿阔叶林相比较。结果表明,缙云山植被属典型的中亚热带常绿阔叶林植被,高位芽植物占绝对优势,达80％以上,其中小高位芽植物最多,中高位芽与矮高位芽植物次之,藤本植物较丰富。缙云山不同演替阶段的植物的生活型谱不同。随着进展演替阶段的逐渐更替,高位芽植物的比例呈递增趋势,地面芽植物、地下芽植物成分有所减少。高位芽的常绿树种会逐渐代替针叶树种。     

Coexistence mechanisms of evergreen,deciduous and coniferous trees in a mid-montane mixed forest on Mt. Emei,Sichuan, China

Structure and regeneration of a mid-montane (2200 m a.s.l.)mixed forest codominated by evergreen (Lithocarpuscleistocarpus), deciduous (Acer flabellatum)andconiferous (Tsuga chinensis, Abies fabri, andTaxus chinensis) trees were analyzed in a 40m× 60 m plot on Mt. Emei, Sichuan, China. Plant communitystructure and composition varied depending on topographic micro-habitat withinthe plot. Four topographic communities (topo-communities) were distinguishedwith dominant species corresponding to topography: (1)Abies – valley bank, (2) Acer– lower steep slope, (3) Lithocarpus – uppergentle slope, and (4) Tsuga – ridge. The coexistencemechanisms of the evergreen, deciduous, and coniferous trees were determined byidentifying the regeneration process characteristic of each dominant species,asrepresented by their seedling dispersion patterns and seedling establishmentalong the topographic gradients. The saplings and seedlings of the dominantswere distributed differently according to the topography:Lithocarpus under the canopy of parent trees and in gapsofthe upper gentle slope and ridge, Acer mainly in bothwell-lit and shady sites on the lower steep slope and on fallen logs,Abies on the valley bank but only in well-lit sites,Tsuga on the ridge, Taxus mostly onrock and well-lit sites on the slopes. Distribution of surviving saplings andseedlings was also related to the species of nearby canopy trees. We suggestthat Lithocarpus, Tsuga and Acer tendto be self-replacing in their own topographic habitats, andAbies survives as a fugitive by occupying occasionalsuitable gaps. The variation in soil conditions, particularly nutrients, withtopography affected seedling establishment and the growth of trees. Thesuccessional change of quantitative species composition, as predicted by theMarkovian model, shows the mixed forest to be in a sustained climax stage.     

Facilitation by nurse shrubs of resprouting behavior in a post-fire shrubland in northern Patagonia,Argentina

Abstract. The nurse-plant syndrome is a widely recognized example of positive (facilitative) influences of plant species on the establishment and growth of other species. Most studies of the nurse-plant syndrome have been on species that reproduce mainly from seed rather than vegetatively. In this study, we experimentally compared the influences of two species of nurse shrubs, Schinus patagonicus and Berberis buxifolia, on the survival and growth of vegetatively reproducing herbaceous and woody plants in a post-fire shrubland in northern Patagonia, Argentina. The vegetation beneath shrubs was removed by clipping and, in a paired-sample design, one half of the canopy of each shrub was removed. We determined species richness, counted number of resprouts, and measured photon flux density and soil moisture beneath cut and uncut halves of each shrubs. Abundances of resprouts were several times greater beneath the uncut vs. the cut shrubs, as was the mean number of species. Thus, shrubs have a strong facilitating influence as measured by resprout densities and the number of species. Numbers of resprouts and of species were twice as high beneath Schinus as beneath Berberis, implying important differences in the facilitative effects of the two shrubs species. Microsites beneath Schinus were characterized by lower and more heterogeneous light levels but by greater soil moisture. Even though the reproductive mode in this post-fire shrubland is overwhelmingly vegetative, facilitation by nurse shrubs is important and differentially effective for different species of nurse shrubs.     

Effects of overstory and understory vegetation on the understory light environment in mixed boreal forests

Abstract. The percentage of above-canopy Photosynthetic Photon Flux Density (%PPFD) was measured at 0, 50 and 100 cm above the forest floor and above the main understory vegetation in stands of (1) pure Betula papyrifera (White birch), (2) pure Populus tremuloides (Trembling aspen), (3) mixed broad-leaf-conifer, (4) shade-tolerant conifer and (5) pure Pinus banksiana (Jack pine) occurring on both clay and till soil types. %PPFD was measured instantaneously under overcast sky conditions (nine locations within each of 29 stands) and continuously for a full day under clear sky conditions (five locations within each of eight stands). The percentage cover of the understory layer was estimated at the same locations as light measurements. Mean %PPFD varied from 2% at the forest floor under Populus forests to 15% above the understory vegetation cover under Betula forests. Percent PPFD above the understory vegetation cover was significantly higher under shade intolerant tree species such as Populus, Betula and Pinus than under shade tolerant conifers. No significant differences were found in %PPFD above the understory vegetation cover under similar tree species between clay and till soil types. The coefficient of variation in %PPFD measured in the nine locations within each stand was significantly lower under deciduous dominated forests (mean of 19%) than under coniferous dominated forests (mean of 40%). %PPFD measured at the forest floor was positively correlated with %PPFD measured above the understory vegetation and negatively correlated with cumulative total percent cover of the understory vegetation (R² = 0.852). The proportion of sunflecks above 250 and 500 mmol m^–2 s^–1 was much lower and %PPFD in shade much higher under Populus and Betula forests than under the other forests. Differences in the mean, variability and nature of the light environment found among forest and soil types are discussed in relation to their possible influences on tree succession.     

Vegetation succession among and within structural layers following wildfire in managed forests

Question: How does vegetation develop during the initial period following severe wildfire in managed forests? Location: Southwestern Oregon, USA. Methods: In severely burned plantations, dynamics of (1) shrub, herbaceous, and cryptogam richness; (2) cover; (3) topographic, overstory, and site influences were characterized on two contrasting aspects 2 to 4 years following fire. Analysis of variance was used to examine change in structural layer richness and cover over time. Non‐metric multidimensional scaling, multi‐response permutation procedure, and indicator species analysis were used to evaluate changes in community composition over time. Results: Vegetation established rapidly following wildfire in burned plantations, following an initial floristics model of succession among structural layers. Succession within structural layers followed a combination of initial and relay floristic models. Succession occurred simultaneously within and among structural layers following wildfire, but at different rates and with different drivers. Stochastic (fire severity and site history) and deterministic (species life history traits, topography, and pre‐disturbance plant community) factors determined starting points of succession. Multiple successional trajectories were evident in early succession. Conclusions: Mixed conifer forests are resilient to interacting effects of natural and human‐caused disturbances. Predicting the development of vegetation communities following disturbances requires an understanding of the various successional components, such as succession among and within structural layers, and the fire regime. Succession among and within structural layers can follow different successional models and trajectories, occurs at different rates, and is affected by multiple interacting factors.     

Effects of microsite light availability on the survival and growth of oak seedlings within a grassland

Effects of microsite light availability on the growth and survival of transplantedQuercus serrata Thunb. seedlings in aMiscanthus sinensis Anderss. grass canopy were investigated by a “plant's eye view” approach. Diffuse site factors, i.e., the fractional transmissions of diffuse photosynthetic photon flux density, were estimated at 15 cm aboveground in 108 microsites where the seedlings grew. Microsite diffuse site factors were significantly different between surviving and dead seedlings during the experiment period from April to October (F_[1,14]=10.9, P<0.01). Relative growth rate of dry weight for individual seedlings positively depended on the diffuse site factors (r²=0.482, P<0.001 in May; r²=0.312, P<0.001 in October). Only 16 seedlings produced their second stem flush within the grass canopy. The ratio of height to dry weight of the second stem flush was significantly higher for the seedlings grew in shady microsites than for those in less shady microsites (r²=0,471, P<0.01 in May). This study suggests that the microsite heterogeneity of light availability is one of the important factors affecting the establishment of tree seedlings in patchy grasslands.     

Limits to convergence of vegetation during early primary succession

Questions: Primary succession, measured by changes in species composition, is slow, usually forcing a chronose‐quence approach. A unique data set is used to explore spatial and temporal changes in vegetation structure after a 1980 volcanic eruption. On the basis of data from a transect of 20 permanent plots with an altitudinal range of 250 m sampled through 2005, two questions are asked: Do changes along the transect recapitulate succession? Do plots converge to similar composition over time? Location: A ridge between 1218 and 1468 m on Mount St. Helens, Washington, USA. Methods: Repeat sampling of plots for species cover along a 1‐km transect. Floristic changes were characterized by techniques including DCA, clustering and similarity. Results: Species richness and cover increased with time at rates that decreased with increasing elevation. The establishment of Lupinus lepidus accelerated the rate of succession and may control its trajectory. Diversity (H) at first increased with richness, then declined as dominance hierarchies developed. Primary succession was characterized by overlapping phases of species assembly (richness), vegetation maturation (diversity peaks, cover expands) and inhibition (diversity declines). Each plot passed through several community classes, but by 2005, only four classes persisted. Succession trajectories (measured by DCA) became shorter with elevation. Similarity between groups of plots defined by their classification in 2005 did not increase with time. Similarity within plot groups converged slightly at the lower elevations. Despite similarities between temporal and spatial trends in composition, trajectories of higher plots do not recapitulate those of lower plots, apparently because Lupinus was not an early colonist. Any vegetation convergence has been limited to plots that are in close proximity.     

Climate and pH as determinants of vegetation succession in Central European man‐made habitats

Questions: (1) What are the most important abiotic environmental variables influencing succession in central European man‐made habitats? (2) How do these variables interact with one another and with variation in community properties? Location: Central, western and southern parts of the Czech Republic. Habitats included old fields, urban sites, spoil heaps after coal mining, sites at water reservoirs, extracted sand pit and peatland and reclaimed sites in areas deforested by air pollution. Methods: We investigated vegetation patterns on 15 succes‐sional seres, sampled by the same methods. Time of succession over which the data were available ranged from 12 to 76 years. The cover of vascular plant species (in %) was estimated in 5 m × 5 m plots. The relationships between vegetation characteristics (species composition, total cover, cover of woody species, species number and rate of dominant species turnover) and 13 abiotic site factors, including climatic and soil variables, were tested using CCA ordination and regression models. Results: Substratum pH, the only substratum characteristic, and climate were the environmental variables significantly affecting the vegetation patterns in the course of succession. The rate of succession, measured as the turnover of dominant species, was significantly more rapid in lowland than in mountain climates. On alkaline soils, species numbers in succession increased towards warmer climates. However, acid soils prevented any increase in species numbers, regardless of the climate. Surprisingly, forms of nitrogen and contents of C, P and cations did not exhibit any significant effect on the vegetation characteristics studied. Conclusions: Our approach, to compare a number of seres, can contribute not only to our understanding of succession, but also to help restoration projects to predict vegetation change because the crucial environmental variables, as identified by this study, are easy to measure.     

The influence of white seabream (Diplodus sargus) production on macrobenthic colonization patterns

The present work evaluates the influence of fish production on macrobenthic colonization over large areas (approximately 700 m²), where the colonizing populations are not nearby the disturbed area. Sampling was undertaken within newly created aquaculture earthen ponds under two contrasting conditions: white seabream (Diplodus sargus) production and no production (control). Macrobenthic and geochemical samples were collected 7, 23, 54, 93 and 180 days after filling the earthen ponds with seawater pumped from a water reservoir for the first time. The water reservoir was also sampled, and is used as a reference for the colonizing populations. Macrobenthic colonization rate in the ponds was low, probably due to the isolation of the disturbed habitat, to the large size of the defaunated area, and possibly to geochemical constraints. Initial colonization was by insect larvae (mainly chironomids), the bivalves Cerastoderma spp., the polychaetes Pseudopolydora paucibranchiata and Hydrodoides elegans, and nemerteneans. The number of species was similar in control and production ponds, even though under production higher total abundance values were observed. Although well represented in the water reservoir, the amphipod Microdeutopus gryllotalpa was only observed within the new ponds after 6 months. Preliminary results suggest that macrobenthic colonization patterns were influenced by fish production, as assemblages were significantly different among ponds. Higher food availability due to fish production may explain the results obtained, but ecological reasons, such as predation, may also contribute for shaping the macrobenthic communities.