摘要:

Active sand dunes in Fremont County, Idaho, move northeastward at an approximate rate of 3 m/year. Sand deposits, continuous in some areas for several kilometers, extend to windward from the dunes in the form of long ridges, parallel to the wind direction. Five successional vegetation stages, distinct as to dominant species, appear on the deposits as belts transverse to the direction of dune movement. Elymus flavascens and Psoralea lanceolata dominate the pioneer stage, which lasts up to about 30 years. The second stage, dominated by Chrysothamnus nauseosus with an understory of the two pioneer species, lasts from 10 to 70 years. Purshia tridentata then replaces much of the C. nauseosus to form a third stage lasting for about 50 to 70 years. Dominant species in the fourth stage are Artemisia tridentata, P. tridentata, and in many areas Prunus virginiana var. demissa. Very little A. tridentata is found after 700 to 900 years of stabilization, and the final and most extensive stage on deep sand is dominated by dense P. tridentata with clumps of P. virginiana var. demissa. Vegetation on old, shallow deposits has characteristics of both that on deep sand and the Artemisia/bunchgrass type on the surrounding native soil. Fields that were plowed and abandoned in the early 1930's now support dense stands of Stipa comata. The presence of dense shrub stands on dunes now topographically sheltered by the wind, but not on migrating dunes, indicates that establishment of a species on sand depends on relative site stability rather than on soil nutrient buildup caused by previous vegetation. Deep sand holds moisture available to plants throughout the dry part of the growing season while the native soil does not, which probably accounts for the greater shrub density and vigor on sand.

ISSN:0012-9658    

DOI:10.2307/1934008

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

The effects of a 2—year drought on native grasses in South Texas were investigated on the Welder Wildlife Foundation Research Area during the summer of 1963. The percentage mortality on Victoria clay, Nueces fine sand, and Miguel find sandy loan was determined for seacoast bluestem (Andropogon scoparius Michx. var. littoralis (Nash) Hitch.), silver bluestem (Andropogon saccharoides Swartz var. longipaniculata Gould), filly panicum (Panicum filipes, Scribn.), buffalograss (Buchloe dactyloides (Nutt.) Engelm.), Pan American balsamscale (Elyonurus tripsacoides Humb. and Bonpl.), and brownseed paspalum (Paspalum plicatulum Michx.). Mortality ranged from an average low of 3407% for silver bluestem on Victoria clay to an average high of 76.8% for seacoast bluestem on Miguel fine sandy loam. Differences in percentage mortality between soils and between species on given soil types were highly significant. Mortality among individual clones ranged from 0% to 100%. In some instances a significant positive correlation existed between size of grass clones and percentage mortality. As diameter of clones increased, percentage mortality increased.

ISSN:0012-9658    

DOI:10.2307/1934009

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

A 2—year study of basal area change of six tree species was conducted with vernier growth bands in the northern conifer—hardwood sub—formation in north—central Wisconsin. Curves of basal area change per unit of stem circumference satisfactorily expressed differences in initiation of stem expansion, rate and duration of growth, and winter shrinkage for various species and crown classes. Seasonal growth for all species and crown classes was represented by a sigmoid curve beginning with a short period of slow basal area increase in early spring and ending with a longer period of declining growth rates leading to relative stability through late summer and fall. Winter shrinkage, most marked in basswood, began in early winter and often exceeded total summer growth by midwinter. Recovery was complete by early spring. Hemlock began rapid growth earlier and ceased growth later than any other species studied. Basswood began and ceased growth later than sugar maple, white and yellow birch, and trembling aspen. Timing of rapid growth initiation was somewhat affected by weather and tree condition. The decreasing order of vigor in competition of the major species was (1) sugar maple, (2) hemlock, and (3) yellow birch and basswood. Differences in amounts of cambial growth of species and crown classes were traceable to differences in both rate and duration of growth. Delay of rapid stem expansion in lower crown classes was much less marked than in lower crown classes of pure coniferous stands studied elsewhere, probably because of less canopy shading in spring. Differences in times of cessation of growth of crown classes were more marked, with the most suppressed trees ceasing growth earliest. Effects of particular stand conditions were most evident in growth of suppressed crown classes.

ISSN:0012-9658    

DOI:10.2307/1934010

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

Douglas—fir seedlings of the geographic varieties menziesii and glauca were grown from seed collection from southern Vancouver Island, B. C., and western Montana. Photosynthetic and respiratory rates were compared for a range of temperatures, light intensities, and under constant high—intensity illumination. Maximum apparent photosynthesis occurred near temperatures of 20 degrees—25 degrees C for 35— and 65—day—old seedlings. Seedlings from Vancouver Island had significantly higher rates of photosynthesis than seedlings from Montana at certain temperatures at both ages. Respiratory rates of 35—day—old seedlings from Vancouver Island were significantly higher at 20 degrees—35 degrees C than those from Montana, but at 65 days of age only at 15 degrees and 40 degrees C. Seedlings from Montana required more light to reach the compensation point at 20 degrees C, and photosynthesized less at light intensities of 200 to 1,000 ft—c than did Vancouver Islands seedlings. Saturation intensity for seedlings from both varieties was near 3,000 ft—c. After 11 hours of illumination at 10,000 ft—c, the photosynthetic rate of Vancouver Island seedlings had declined from the initial rate significantly more than had Montana seedlings. Observed differences in photosynthesis and respiration between young seedlings from these two regions often decrease as seedlings become slightly older. Comparison of two Vancouver Island and two Montana sources showed that differences between seedlings of the same geographic variety can be greater than between seedlings of the two varieties.

ISSN:0012-9658    

DOI:10.2307/1934011

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

Seedlings were grown from 17 seed samples collected throughout the natural range of Pinus sabiniana in California. Five collections came from soils derived from ultra—basic serpentinized rock. The seedlings were grown in a greenhouse in cans filled with two different soils. One series of 36 seedlings per sample grew in a fertile, loamy sand forest soil. This planting was replicated in a sterile, highly serpentinized soil gathered at one seed collection site. Significant differences in shoot and root growth were found between populations within each soil treatment. But the relative ranking of populations was similar in both cases. On both soils populations of non—serpentinite origin made the most vigorous growth. Seedlings from the serpentinite soil collection locality made relatively poor growth in the serpentinite soil. No adaptation to the serpentinite soil conditions by populations which came from serpentinite areas was suggested. All seedlings populations appeared to have a high tolerance for extreme serpentinite conditions. The correlation between mean seed size and mean seedling size was low (r = 0.24) in the fertile soil, but much higher (r = 0.68) in the serpentine soil.

ISSN:0012-9658    

DOI:10.2307/1934012

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

A 286—cm core of sediments was taken from the center of Potato Lake, Coconino Co., Arizona. Pollen, chemical, and physical analyses were made on the sediment. Pluvial conditions, evidenced by high PAP percentages, exist until approximately the 120—cm level of the core; at this level a major change in pollen types occurs with pine assuming dominance. A core section at 142—172 cm was dated at 14,000 plus or minus 300 BP. Post—pluvial climate, as reflected by the pollen diagram, was fairly stable. Loss on ignition at 550 degrees C of the sediment material implies that eutrophication of Potato Lake began at the close of the pluvial. Variations of iron, manganese, and calcium may be explained by lake succession from oligotrophic to eutrophic conditions

ISSN:0012-9658    

DOI:10.2307/1934013

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

The aquatic vegetation of Long Lake (T 144 N, R 36, 37 W) in northwestern Minnesota was surveyed by means of line transects run underwater with SCUBA apparatus. Eight stations were established about the lake and 12 transects were run from each station. The transects were run along depth contours at ½—m depth and 1—m intervals from 1 through 11 m depth. No vegetation was observed deeper than 11 m. Each transect was 20 m long, and the presence of plant species was recorded at intervals of ⅓ m. The data were recorded underwater by writing on a sheet of aluminum foil held in a mental clipboard. The aquatic vegetation was more abundant on the southwest—facing slope than on the northeast—facing slope of the lake bottom. This difference has been attributed to a difference in solar insolation. Some of the significant interspecies correlations which were observed appeared to be related to water depth and the texture of the substrate.

ISSN:0012-9658    

DOI:10.2307/1934014

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

The Hawaiian Islands are in the trade wind belt; they have about a 1—m tide. Along open coasts the effect of the tide on the zonation of inshore fishes is minor compared to that of the surge. Above sea level, pools depend primarily on wave splash for replenishment. The higher splash pools have few species of fishes, and those that occur there are ecologically well differentiated. On the exposed rocky benches just above sea level, there is usually abundant seaweed, but one herbivorous blenny is the only fish that lives there. For some 6 m or more just below sea level on open coasts horizontal water movement frequently scours the bottom, often with the abrasive action of sand added. The bottom here is of rock or sand. Most of the species of the area are herbivores which graze on such short algal stubble as exists on the rocks. Indeed, in both species and individuals, the maximum number of herbivorous fishes would seem to occur in this zone. In the quiet water offshore from, and just below the surge zone the best live coral formations in the Hawaiian waters grow. Here there is also a fishes below this point are scarce. Preliminary information suggests that the differentiation of the fish fauna at deeper levels is far more gradual, and that there is still a considerable number of species to at least half a mile in depth. Around the high Hawaiian Islands the waters protected by fringing reefs appear to have a mixed zonal fauna containing partly surge zone fishes, partly fishes that come in from quiet, deeper water, and partly forms restricted, so far as known, to such areas.

ISSN:0012-9658    

DOI:10.2307/1934015

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

Numbers, deaths and growth rates were observed for three years in a delimited population of Acmaea digitalis whose members had been individually marked. The zone of vertical distribution of the species is determined by the behavior of these snails. In the fall and winter they ascend in the intertidal, and descend a smaller distance in the spring. This leads to a differential distribution of size classes. The oldest and largest animals are found highest in the intertidal zone. That the vertical movements are adaptive is suggested by death rates which are highest in the upper portions in summer, but rise in the lowest zone in winter. Probability of survival improves with age. Growth rate was remarkably consistent during the period of observation. It was fastest in the fall and winter months. During the month of July, and in part of June and August growth ceased, at least as measured by a change in shell length. Crowding decreased growth slightly but significantly. Growth rates in different areas suggest that time available for feeding may be a significant variable. Experimental manipulation of density indicates that emigration rates are density—dependent. The mechanism of density regulation is postulated as operating even at low overall densities because of the behavior pattern of the species.

ISSN:0012-9658    

DOI:10.2307/1934016

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY

摘要:

Following the Sedan test of July 6, 1962, adult Cnemidophorus tigris, Crotaphytus wislizeni, and Uta stansburiana were exterminated to a distance of 4,000 ft from ground zero. Very few adult lizards of any species were observed within 6,000 ft of ground zero during August and November 1962, but the posttest observations in 1962 may have reflected seasonal inactivity. Sampling in June of 1963 indicated that the apparent absence of adults within 4,000 ft was real. No changes attributable to the test were detected at 8,500 to 9,000 ft. Eggs of the three species hatched following the tests in areas where adults did not survive. Young Uta stansburiana were numerous in August from 2,600 to 9,000 ft from ground zero. By October, the young lizards at 2,600 ft were gone, and mortality at 3,800 ft was extremely heavy. At 9,000 ft the apparent density of young Uta was only slightly reduced as compared to that in August. In June of 1963, adults of the three species were observed between 4,500 and 5,000 ft from ground zero, and Uta was apparently most abundant. It is possible that Cnemidophorus is more sensitive than Uta to the deleterious influences involved in this study. The immediate mortality within 4,000 ft is attributed to the gross physical effects of the detonation–dirt fall and blast–which destroyed all of the vegetation out to 2,000 ft and caused partial damage to 5,000 ft from ground zero. Delayed mortality–as that exhibited by juveniles which hatched after the test–is attributed to destruction of habitat. Neither the depletion of food resources nor the residual gamma radiation is likely to have been lethal. Absorbed tissue doses, as registered by three microdosimeters implanted in lizards before the test and recovered July 28 were probably significantly less than the free—air dose registered in the same area.

ISSN:0012-9658    

DOI:10.2307/1934017

出版商:Ecological Society of America    

年代:1965

数据来源: WILEY