摘要:

The development of the vegetation and floras of the Krakatau Islands in the Sunda Straits, Indonesia, since their "sterilization" in 1883 is described. Key features of the post—1883 environment, such as pedogenesis, geomorphology (coastal change), human influence, and recent volcanic activity are detailed, and their possible influence on spatial and temporal patterns in both vegetation and flora is discussed. Field work conducted in 1979, 1983, and 1984 has enabled an assessment of the present state of vegetation development, aided by plot—based sampling and analysis of the arboreal component, employing numerical classification (by TWINSPAN) and ordination (by DCA). The coastal communities were established early and have remained little changed, although the distribution of the various components has changed according to the influence of a dynamic coastal geomorphology. Fifty years after forest closure, the forest of the interiors remain species—poor and composed of typical early—seral species. Rakata was dominated inland by Neonauclea calycina and Ficus pubinervis up to ≈550 m altitude, above which a mossy forest of Ficus spp. and Schefflera polybotrya scrub was recorded. The main inland forest types on Rakata Kecil and Sertung were of young, evenaged stands of Timonius compressicaulis (extensive) and older stands of Dysoxylum gaudichaudianum (often with a T. compressicaulis understory). The principal axes of variation within the data were found to be between extremes of the Rakata forest types, with Sertung and R. Kecil stands remaining undifferentiated until lower levels of the analyses. These patterns were ascribed to a mix of environmental variation (coastal and altitudinal factors), chance variations in colonization, and to volcanic action following the emergence of Anak Krakatau in 1927. Disturbance by volcanism (e.g., in 1930, 1934—1936, 1939, 1952—1953, 1961) has resulted in the deflection of vegetation succession on R. Kecil and Sertung into a different pathway from that followed on Rakata, which has remained unaffected by the activity. On Anak Krakatau, volcanic action has prevented successful colonization away from accreting coastal deposits, and has several times eliminated the entire flora. In addition, the major source of propagules for Anak Krakatau is from within the group, and for these several reasons the new island is shown to be a poor analogue for the early recovery phases of the other islands. Complete floral lists are given for each recorded survey for each island in the group, including data from surveys in 1979, 1982, and 1983. These data have been revised from previous publications on the basis of recent herbarium work and literature searches. The data are analyzed according to several different models: cumulative species totals, species totals for particular combinations of surveys, and totals calculated on the assumption of minimum turnover. The early beach spermatophyte assemblages of Rakata have undergone relatively few losses in comparison to the assemblages of the interior, while within the latter there has been a relatively high proportion of losses among the pioneering pteridophytes. The possession of major habitat types has been identified as critical in determining the shape of the overall colonization curve, through the passive sampling of different source pools. The diversity of the floras of the group as a whole and of Rakata and Anak Krakatau has continued to increase. The curves of species present on Sertung and R. Kecil have levelled and fallen respectively, as a result of the volcanic activity of Anak Krakatau. It is shown that the number of animal—transported species on the Krakatau group has continued to increase over the last 50 yr, and that this accounts for the majority of the increase in the size of the spermatophyte flora. The animal—transported species and the early sea—dispersed species appear to be species—stable groups. Later sea—dispersed species included ephemerals and species of temporary habitats, and have experienced a relatively high proportion of losses. Few beach species that have established on all of the three main islands have subsequently become extinct from the group. The number of pteridophytes on the islands has increased over the last 50 yr, mainly through the addition of forest species. A large proportion of plant species has been found only on Rakata, which samples an upland source pool not represented on the other islands. It is argued that the assumptions of "classical" island biogeography are inappropriate to these data and that the pattern in floral recolonization can best be understood as a successional process involving broad habitat and dispersal mechanism determinants. The implication of these findings is that community dynamics are highly significant in determining rates of immigration, colonization (i.e., successful immigration), and extinction, and that the probabilities of each vary among different groups of species and through time.

ISSN:0012-9615    

DOI:10.2307/2937282

出版商:Ecological Society of America    

年代:1989

数据来源: WILEY

摘要:

The pollen and plant—macrofossil records from four small lakes in the subalpine and alpine zone of the White Mountains, New Hampshire, give a 13 000—yr paleoenvironmental history. The White Mountains were deglaciated before 13 000 yr BP. Downwasting of the continental ice sheet was rapid. The summits projected above the ice as nunataks for only a brief period of time. Residual ice may have existed in Franconia Notch until 11 000 yr BP. From 13 000 to 11 750 yr BP a barren periglacial desert covered the highest altitudes in the White Mountains. Tundra vegetation occupied the lower slopes and valleys. The mean annual temperature was roughly 5°—10°C colder than today. Sparse tundra vegetation surrounded all four high—elevation sites from 11 750 to 10 300 yr ago and several taxa, particularly Artemisia and Caryophyllaceae, indicate disturbance. The summits were subjected to intense periglacial activity. The mean annual temperature was 4—6° lower than present. By 10 300 yr BP shrubs such as willow, juniper, and dwarf birch had invaded the tundra at Lake of the Clouds. Spruce woodland dominated the lower slopes and valleys. At 10 300 yr BP spruce populations arrived at high—elevation sites. Macrofossils of fir, birch, and shrubs also occur in sediments of this age. The temperature increased to or exceeded modern levels. Tree species did not reach the Franconia Notch sites until 9750 yr BP. At these sites the establishment of subalpine forests spanned a much shorter time period. Forest with poplar, spruce, and birch replaced the spruce woodlands of low elevations. Subalpine fir forests became well established by 9000 yr BP. Evidence from the alpine site shows that the fir trees were more abundant and treeline higher than today from 10 300 to 5000 yr BP. After 5000 yr BP, the pollen percentages of alpine indicators increased and the numbers of fir macrofossils dropped. Of the three sites in subalpine fir firest, only the lowest shows any evidence of a warmer interval in the early Holocene. Treeline is apparently a poor temperature indicator because wind and moisture are the major factors determining its position. Taxa of the Northern Hardwood Forest (e.g., white pine, hemlock, yellow birch, sugar maple, and beech) arrived at lower elevations by 6500 yr BP, but the zones of modern vegetation became established only after 2000 yr BP when spruce populations expanded at low elevations between 750 and 1200 m.

ISSN:0012-9615    

DOI:10.2307/2937283

出版商:Ecological Society of America    

年代:1989

数据来源: WILEY

摘要:

This study evaluated the ecological and taxonomic correlates of seed mass variation among 648 angiosperm species of the Indiana Dunes region (113 families, 507 genera in the original flora). The sample represented 50% of the species, 60% of the genera, and 67% of the families reported from the area. Species were chosen at random from the published flora. Each species was characterized by family membership, habitat, life history, phenological characters, and native vs. alien status, in order to determine the relationship among species between these variables and mean seed mass. Unique to this study are measurements of the effects of phenology and taxonomic family on seed mass. Each species occurred in ≥1 of 13 habitat types described in the Intiana Dunes flora. To determine the effect of apparent water and light availability on seed mass, each habitat was assigned to one of four categories representing combinations of inferred water and light availability. Life histories or life forms represented were: annuals, biennials, herbaceous vines, parasites, perennials, short—lived perennials, shrubs, small trees, trees, and woody vines. Two phenological variables were available for most species: the time at which flowering begins (early, middle, or late), and the duration of flowering (short:44% of the total variance in seed mass among species. The results of this study parallel previous comparative works that have demonstrated associations between seed mass and life form or habitat type. Seed mass does segregate among species occupying distinct habitats, but this relationship is due largely to associations among taxonomic family, life form, and habitat.

ISSN:0012-9615    

DOI:10.2307/2937284

出版商:Ecological Society of America    

年代:1989

数据来源: WILEY

摘要:

We monitored woody plant seed deposition, seedling emergence, and the survival and growth of seedlings (i.e., plants ≤0.5 m tall regardless of age) in an East Texas river floodplain forest from 1979 through 1984. In addition, we estimated the relative importance of flooding, drought, fungal attack, herbivory, proximity to a conspecific adult, and shade in causing seedling mortality. Tree species fell into two major groups on the basis of their demographic characteristics and responses to unfavorable conditions. The first group was composed of heavy—seeded species, of which water oak (Quercus nigra) was the primary example. They produced few seeds, but had high seedling survival. Seedlings of these species emerged late in the summer, thereby avoiding peak periods of flooding and damping—off mortality. Seedling survival was little affected by drought, herbivory, or proximity to a conspecific adult. The second group included most of the common tree species (e.g., ironwood, Carpinus caroliniana; sweetgum, Liquidambar styraciflua; red maple, Acer rubrum; American elm, Ulmus americana). They produced large crops of light seeds which dispersed throughout the study area. In these species, seedling survival was low for the 1st yr, but increased substantially thereafter. Flooding, drought, damping—off, proximity to a conspecific adult, and herbivory were important causes of 1st—yr seedling mortality. for these species was not constant over the growing season, but was concentrated in peaks associated with particular events (e.g., a drought in 1980, and flooding and damping—off in 1981 and 1982). Seedlings emerging earlier in the spring were usually better able to survive these periods of environmental stress. During the course of the study, extensive flooding in 1979 and during 1983—1984 resulted in increases in the proportion of water oak in the seedling layer, while periods of reduced flooding during 1980—1982 allowed several of the more prolific, lighter seeded species (especially ironwood, sweetgum, and deciduous holly, Ilex decidua) to increase in importance. The two spring—dispersing, light—seeded species, red maple and elm, emerged late in the spring and therefore increased in relative abundance during 1984 when early floods killed seedlings of earlier emerging, autumn—dispersing species. Thus, spatial and temporal variation in understory seedling composition in our study was due largely to (1) species differences in the ability to increase rapidly in numbers during favorable periods as compared to the ability to survive stressful periods, and (2) the interaction of emergence phenology with the occurrence of environmental stress. These results demonstrate that variation in flooding or other environmental stresses can alter seedling layer species composition and may thereby influence opportunities for canopy replacement, thus helping to maintain species diversity in southern floodplain forests.

ISSN:0012-9615    

DOI:10.2307/2937285

出版商:Ecological Society of America    

年代:1989

数据来源: WILEY

ISSN:0012-9615    

DOI:10.2307/2937286

出版商:Ecological Society of America    

年代:1989

数据来源: WILEY