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1.
Vulnerability to strong winds for major tree species in a northern Japanese mixed forest: analyses of historical data 总被引:2,自引:0,他引:2
This study examined historical census data to evaluate the vulnerability of major tall-tree species in northern Japan to strong
winds. Intensive data, which measured more than 20,000 damaged trees (defined as trees that were killed or lost their major
crown) in >500 ha of a natural mixed forest, were collected immediately after a severe typhoon in 1954. More than half of
the damaged trees had been uprooted, and the negative size-dependency was found for the proportion of uprooting throughout
species. Simple correlation analyses with respect to the averaged species-specific characteristics suggested that tree species
with a high crown-depth/height tended to uproot (against to stem breakage) in a size-class with diameter at breast height
30–50 cm. Although the census data had yielded no information about non-damaged trees, the estimation of pre-disturbed stand
(based on 63 1-ha plot data together with aerial photographs and GIS) revealed that the observed damage reached ca. 25% in
terms of basal area. The proportion of damaged trees seemed to be doubled among species (15–42% in basal area). A higher proportion
of uprooting, which indicates a large supply of tip-up mounds, and mixture of less vulnerable species, might contribute to
recovery process after a wind disturbance in this type of mixed forests. 相似文献
2.
Root Morphology and Anchorage of Six Native Tree Species from a Tropical Montane Forest and an Elfin Forest in Ecuador 总被引:1,自引:1,他引:0
Root architecture of tree species was investigated at two different altitudes in tropical forests in Ecuador. Increasing altitude
was accompanied by higher wind speeds and more shallow soils, while slope angles of both sites were comparable (20–50°). Three
tree species typical for the montane forest at 1900 m (Graffenrieda emarginata (Ruiz & Pav.) Triana (Melastomataceae), Clethra revoluta (Ruiz & Pav.) Spreng. (Clethraceae), Vismia tomentosa Ruiz & Pav. (Clusiaceae)) and for the elfin forest at 3000 m (Weinmannia loxensis Harling (Cunoniaceae), Clusia spec. (Clusiacaea) Styrax foveolaria Perkins (Styraceae)) were examined. At 1900 m, 92% of the trees grew upright, in comparison to 52% at 3000 m. At 3000 m,
48% of the trees were inclined, lying or even partly uprooted. At this altitude, all trees with tap roots or with shoots connected
by coarse rhizomes, 83% of the trees with stilt roots, and 50% of the trees in which stems or roots were supported by other
trees grew upright, suggesting that these characteristics were relevant for tree stability. Root system morphology differed
markedly between altitudes. In contrast to 1900 m, where 20% of structural roots originated in the deeper mineral soil, root
origin at 3000 m was restricted to the forest floor. The mean ratio of root cross sectional area to tree height decreased
significantly from 6.1 × 10−3 m2 m−1 at 1900 m to 3.2 × 10−3 m2 m−1 at 3000 m. The extent of root asymmetry increased significantly from 0.29 at 1900 m to 0.62 at 3000 m. This was accompanied
by a significantly lower number of dominant roots at 3000 m (2.3 compared to 3.8 at 1900 m). In conclusion, native tree species
growing in tropical montane and elfin forests show a variety of root traits that improve tree stability. Root system asymmetry
is less important for tree stability where anchorage is provided by a deep and solid root–soil plate. When deep rooting is
impeded, root traits improving the horizontal extension of the root–soil plate are more pronounced or occur more frequently.
Furthermore, mutual mechanical support of roots and stems of neighboring trees seems to be an appropriate mechanism to provide
anchorage in soils with low bulk density and in environments with high wind speeds. 相似文献
3.
Aims: Large hurricanes have profound impacts on temperate forests,but owing to their infrequent nature these effects have rarelybeen examined in detail. In 1996, Hurricane Fran significantlydamaged many long-term tree census plots in the Duke Foreston the North Carolina Piedmont, thereby providing an exceptionalopportunity to examine pre- and post-hurricane forest compositionaltrajectories. Our goal was to examine immediate, short-term(0–4 years) and longer term (5 year) hurricane-inducedstructural, spatial and compositional changes in the tree population(stem d.b.h > 1 cm) in the context of our detailed, long-termknowledge of the dynamics of these forests. Methods: We surveyed stem damage and tree mortality in 34 long-term permanentplots (ca. 70-year record; 404–1 012 m2) and 7 large mappedtree stands (ca. 20-year record; 5 250–65 000 m2) representingboth transition-phase, even-aged pine stands and uneven-agedupland hardwood forests. We employed three types of damage measuresto quantify stand-level damage severity: percentage of stemsdamaged, percentage of basal area lost and a stand-leveldamage index. Second-order spatial analysis (Ripley'sK-function) was used to investigate patterns in tree mortality. Important findings: Our study found hurricane effects on the structural attributesof Piedmont forests to be variable and patchy. Changes in treespecies composition, however, were modest. Uprooting was themajor damage type for the overstory trees [diameter at breastheight (d.b.h.) >10 cm] apparently due to the exposure ofthe crowns to high wind combined with heavy rainfall prior toand during the storm. Saplings, juvenile trees and small trees(1–10 cm d.b.h.) of the understory and midstory were mainlydamaged by being pinned or bent by their damaged large neighbors.Hurricane-induced tree mortality varied weakly among species,was positively correlated with pre-hurricane tree size and remainedup to 2-fold higher than pre-hurricane background mortality5 years after the hurricane. Spatial point pattern analysisrevealed a patchy distribution of tree mortality during thehurricane sampling interval. Hurricane Fran resulted in a dramaticincrease in average gap size from ca. 400 m2 pre-hurricane toca 1100 m2 after the hurricane, whereas maximum gap sizes reached18–34 times larger than the pre-hurricane levels. 相似文献
4.
Canopy gap formation strongly influences the diversity and dynamics of both tropical and temperate forests. It is often viewed as inherently beneficial for understory plants, primarily because growth and flowering are enhanced when light is no longer a limiting resource. It can also be detrimental, however, because plants can be damaged by falling crowns or branches. To elucidate the responses of the Amazonian understory herb Heliconia acuminata to damage sustained during gap formation, we transplanted both experimentally damaged and control plants to canopy gaps and the forest understory. We then measured their patterns of growth and biomass allocation 10 mo later. Despite losing approximately 50% of their leaf area, all damaged plants survived the duration of our experiment. Furthermore, damaged plants transplanted to gaps had relative growth rates that far exceeded those of undamaged plants in both gaps and the forest understory. There were also significant interactions between damage and destination habitat type on root to shoot ratios and leaf-area ratios. Our results suggest the ability of herbaceous plants to recover from damage, as well as patterns of post-damage biomass allocation, may be habitat-dependent in ways that have previously remained unexplored. 相似文献
5.
Shin-Ichi Yamamoto 《Ecological Research》1993,8(3):277-285
Gap characteristics and gap regeneration were studied in three mature stands belonging to different community types in a subalpine
coniferous forest on Mt Ontake, central Honshu, Japan. Gap disturbance regimes were remarkably similar among stands studied;
percentage gap area to surveyed area, gap density and mean gap size were 7.3–8.5%, 17.8–20.0 ha−1 and 40.8–42.5 m2, respectively. The gap size class distributions were also similar and showed a strong positive skewness with a few large
and many small gaps; gaps <40m2 were most frequent and gaps >200m2 were rare. Forty-five to 66% of gaps were due to the death of single canopy trees. Canopy trees more often died leaving standing
dead wood (40–5.7%) or broken trunks (43–49%). Shade tolerantAbies mariesii andAbies veitchii, frequently, andTsuga diversifolia, less frequently, regenerated in gaps, from advance regenerations recruited before gap formation.Picea jezoensis var.hondoensis may regenerate in gaps, from new individuals recruited after gap formation. The breakage of denseSasa coverage and the mineral soils exposed by the uprooted plants that form gaps might provide regeneration opportunities for
shade intolerantBetula. Of the important species limited to the ridge site,Chamaecyparis obtusa, frequently, andThuja standishii, infrequently, regenerated from plants alreadyin situ. Regeneration ofPinus parviflora was not seen. Based on the gap characteristics and gap regeneration behaviour of each species described, stand dynamics in
each stand are discussed. 相似文献
6.
台风是重要的森林干扰因子之一,会对森林生态系统的结构和功能产生较大的影响。2012年的台风"布拉万"对我国东北地区局部森林造成了严重的破坏。以受灾最重的吉林省汪清林业局的近天然落叶松云冷杉林为对象,采用方差分析和相关分析方法,研究林分结构和地形条件对林木株数损伤率的影响。结果表明:(1)林木损伤类型可分为折断、连根拔起、搭挂、压弯4种,其中连根拔起为最主要的损伤类型,占总损伤株数的52%,台风灾害造成的林木株数损伤率平均为14.09%。(2)径级大小对林木株数损伤率的影响显著。损伤主要发生于径级较小林分处,径级越大,其株数损伤率越小。(3)林木株数损伤率随林分密度的增加有减小的趋势,但在统计学上它们的关系不显著。(4)不同树种间的林木株数损伤率差异显著,落叶松、冷杉等针叶树种损伤株数最多。(5)林分的树种多样性指数与林木株数损伤率无显著的相关性。(6)海拔、坡度和坡位对林木株数损伤率的影响不显著,但坡向的影响显著,东北坡向林分的林木株数损伤率最大。研究结果可以为灾后森林恢复和减少风灾影响的森林培育措施提供依据。 相似文献
7.
We used canopy fogging to study the high (20–26 m), intermediate (13–19 m) and low (5–6 m) strata in three European beech
patches (Fagus sylvatica) in nine months (2005–2007) and estimate species richness and diversity of arboreal spiders. Eight species (10%) were previously
unseen in European beech trees, and one of these is likely a new species. Moreover, two species are on the Bavarian red list.
Our results revealed that the high stratum of the old-growth trees provided unique resources and possessed the greatest diversity
and evenness, whereas intermediate and low strata had high similarity in respect to diversity, dominance, species, and family
composition. Since the majority of beech forests consists of mature and young trees in Central Europe, and old-growth forests
are rarely preserved, we recommend young beech be used in a sampling protocol for rapid biodiversity assessment. However,
adding samples from the two higher strata to the lowest stratum (55 species), almost doubled the estimated species richness
(102 species). This suggests that the lower stratum alone does not represent a true image of the total canopy fauna inventory
in this, and likely other, beech stands. To complete this comprehensive inventory in European beeches, the Chao1 predicted
that additional sampling would be needed in the highest stratum, where there is a high probability to find previously undetected
species in a next survey. Our study clearly shows that neglecting the crowns of the largest, tallest trees risks underestimating
the overall spider diversity in Central European forests. 相似文献
8.
Diana Selyemová Peter Zach Danka Némethová Ján Kulfan Miroslav Úradník Milada Holecová Branislav Kršiak Katarína Vargová Tomáš Olšovský 《Biologia》2007,62(5):610-616
In two successive years we recorded a total of 3,636 individuals and 17 species of adult lady beetles (Coleoptera, Coccinellidae)
in the spruce forests of Pol’ana Mts (the West Carpathians) at altitudes ranging from 600 m to 1,300 m a.s.l. Four lady beetle
species were documented as predominating (dominance of abundance > 5%) over the study period. They were the following: Aphidecta obliterata (1,828 individuals and 50.3%), Coccinella septempunctata (634 individuals and 17.4%), Adalia conglomerata (594 individuals and 16.3%) and Anatis ocellata (279 individuals and 7.7%). The assemblages of lady beetles differed among the areas and also between the years. The season
revealed neglegible effect on distribution of lady beetles, whereas the effect of altitude was more pronounced. A. conglomerata preferred the areas at lower altitude (600–725 m) to those at middle (900–925 m) and/or upper altitude (1,250–1,300 m). In
contrast, A. obliterata and C. septempuctata were most abundant in the area at middle altitude. The altitudinal location of area partly explained the variability in abundance
of lady beetles. The first ordination axis constructed by means of correspondence analysis (CA) represented an altitudinal
gradient and accounted for 19.4% of the total variance of the species data. The great proportion of lady beetle species not
typically associated with spruce and/or other coniferous trees than spruce (70.6%, n = 17) may be explained by an ecotonal effect. 相似文献
9.
Skip J. Van Bloem Peter G. Murphy Ariel E. Lugo Rebecca Ostertag María Rivera Costa Ivelisse Ruiz Bernard Sandra Molina Coln Miguel Canals Mora 《Biotropica》2005,37(4):571-583
In 1998, we measured the effects of Hurricane Georges after it passed over long‐term research sites in Puerto Rican dry forest. Our primary objectives were to quantify hurricane effects on forest structure, to compare effects in a large tract of forest versus a series of nearby forest fragments, to evaluate short‐term response to hurricane disturbance in terms of mortality and sprouting, and to assess the ability of hurricanes to maintain forest structure. We sampled damage from 33 plots (1.3 ha) across a 3000‐ha tract of forest as well as in 19 fragments. For stems with 2.5‐cm minimum diameter, 1004 stems/ha (12.4%) suffered structural damage, while 69 percent of the undamaged stems were at least 50 percent defoliated. Basal area lost to structural damage equaled 4.0 m2/ha (22%) in south‐facing native forests. Structural damage and defoliation increased with stem diameter and were more common in certain dry forest species. South‐facing forests and those on ridgetops incurred more damage than north‐facing forests or those comprised primarily of introduced species. Stem mortality was only 2 percent of all stems after 9 mo. Structural damage did not necessarily result in stem mortality. Hurricane‐induced mortality was not associated with stem height or diameter, but was ten times greater than background mortality. Basal sprouting was proportional to the amount of structural damage incurred in a stand. Forest fragments experienced the same patterns of hurricane effects as the reference forest. The low, dense structure of Caribbean dry forest can be maintained by hurricane damage to larger stems and induction of basal sprouting to generate multistemmed trees. 相似文献
10.
Species composition, physiognomy, and plant diversity of the less known cloud forests in Yunnan were studied based on data
collected from 35 sample plots at seven sites. In floristic composition, the cloud forests are mainly comprised of Fagaceae,
Ericaceae, Vacciniaceae, Aceraceae, Magnoliaceae, Theaceae, Aquifoliaceae, Illiciaceae, Lauraceae, and Rosaceae. Physiognomically,
the forests are dominated by tree and shrub species. Lianas are rare in the forests. The plants with microphyllous or nanophyllous
leaves comprise 44.32–63.46% of the total species, and plants with an entire leaf margin account for more than 50% of the
tree and shrub species. There are few tree and shrub species with a drip tip leaf apex and papery leaves. Evergreen species
make up more than 75% of the total tree and shrub species. In a 2,500 m2 sampling area, the number of vascular species ranged between 57 and 110; Simpson’s diversity index ranged from 0.7719 to
0.9544, Shannon–Winner’s diversity index from 1.8251 to 3.2905, and Pielou’s evenness index from 0.5836 to 0.8982 for trees.
The cloud forests in Yunnan are physiognomically similar to the tropical cloud forests in America and Southeast Asia. They
very much resemble the mountain dwarf mossy forest in Hainan Island, southeastern China, and the Mountain ericaceous forests
in the Malay Peninsula. The cloud forests in Yunnan are considered to be developed, as are the tropical upper montane cloud
forests in Asia. 相似文献
11.
Liana species have a variety of habitat preferences. Although morphological traits connected to resource acquisition may vary
by habitat preference, few studies have investigated such associations in lianas. In previous work on temperate lianas, we
observed (1) free standing leafy shoots and (2) climbing shoots that clung to host plants; we examined relationships between
habitat preference and shoot production patterns in five liana species. Among the five species, two were more frequent at
the forest edges (forest-edge species), and two were more common within the forests (forest-interior species). The proportion
of climbing shoots in current-year shoot mass of young plants (3–8 m in height) was greater in the forest-edge species (45–60%)
than in the forest-interior species (6–30%). In consequence, there was a greater leaf mass ratio in the total current-year
shoots of forest-interior species. This, combined with a greater specific leaf area, endows forest-interior species with a
leaf area per unit shoot mass double that of forest-edge species. Forest-edge species had longer individual climbing shoots
whose length per unit stem mass was smaller than in forest-interior lianas. Extension efficiency, measured as the sum of the
climbing stem length per unit current-year shoot mass, was thus similar between forest-edge and interior species. In conclusion,
liana shoot production patterns were related to species habitat preferences. A trade-off between current potential productivity
(leaves) and the ability to search for hosts and/or well-lit environments (climbing stems) may underpin these relationships. 相似文献
12.
Choonsig Kim Kyung-Soo Jang Joon-Bum Kim Jae-Kyung Byun Choong-Hwa Lee Kwon-Seok Jeon 《Landscape and Ecological Engineering》2010,6(1):119-124
This study was conducted to evaluate and compare soil properties between pine stands either damaged or undamaged by pine wilt
disease in Jinju and Sacheon Cities, which are areas in Korea severely affected by the disease. Soil physical and chemical
properties were generally similar between damaged and undamaged pine stands. There was no significant difference in soil factors
related to soil nutrient fertility between damaged and undamaged pine stands, although the incidence of pine wilt disease
was affected by soil clay content, which was significantly (P < 0.05) higher in the damaged (24.8%) than in the undamaged (20.1%) pine stands. However, this relationship should be treated
with caution because small scale topographical variation may simply reflect the incidence of pine wilt disease. The results
suggest that incidence of pine wilt disease was not influenced by soil nutrient properties at a small stand scale. 相似文献
13.
Habitat associations with topography and canopy structure of tree species in a tropical montane forest on Mount Kinabalu,Borneo 总被引:1,自引:0,他引:1
Habitat associations with topography and canopy structure of 42 abundant tree species were studied in a 2.74-ha plot of tropical
montane forest on Mount Kinabalu, Borneo. Many of these species belong to the same higher taxa including eight families and
four genera. Analysis of intraspecific spatial distributions for stems ≥ 10 cm diameter revealed that 28 species (including
all six species of Fagaceae) showed aggregated distributions at the 100-m2 and/or 400-m2 scales, and that 20 species showed habitat associations with topography by torus-translation tests; 17 species showed both
characteristics. Species' associations with the local canopy structure were characterized by crown position index (CPI), which
was defined relative to neighbour trees. The CPI differed greatly among individual stems at 10–40 cm diameter, and 19 species
showed significantly different frequencies of crowns exposed vertically versus those shaded beneath the canopy. Mean growth
rates at 10–40 cm diameter and size distributions of species were not related to topographic associations, but were explained
by the associations with canopy structure; species with more exposed crowns grew faster and had less positively skewed distributions.
Diversity in habitat associations was manifest between two genera (Syzygium and Tristaniopsis) in the family Myrtaceae and among species in these genera, but was less evident in other families and two genera (Garcinia and Lithocarpus).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
We used a controlled experiment to investigate how disturbance scale (canopy gap area) and herbivory influence post-disturbance
plant community dynamics. Twenty canopy gaps were installed in a temperate hemlock-hardwood forest during the winter of 2002–2003:
seven small gaps (50–150 m2), seven medium gaps (151–250 m2), and six large gaps (251–450 m2). Within each gap, we established 4–12 sample plots (depending on gap size); 1–3 of which were enclosed with wire mesh white-tailed
deer (Odocoileus virginianus) exclosures in 2005. Gaps were revisited and intensively sampled in 2007. After five growing seasons, ground-layer plant
communities in non-exclosed plots were more similar compositionally than exclosure plots. Non-exclosed plots in small and
medium gaps were more similar to non-exclosed plots in large gaps than they were to exclosed plots in their respective gap
size class. Shade-tolerant forbs and trees were less common outside exclosures, while generalist species associated with higher
understory light levels and exotics were more prevalent outside exclosures. Our results suggest that even in forests with
relatively low deer densities (6.5–9.3 deer km−2), white-tailed deer herbivory may influence the developmental trajectory of post-disturbance plant communities and be a mechanism
for decreasing β-diversity along environmental gradients. 相似文献
15.
Introduced social wasps (Vespula vulgaris) reach high densities in some New Zealand beech forests, because honeydew provides an abundant high-energy food source. We
manipulated wasp density to estimate an “ecological damage threshold” for large, free-living Lepidoptera larvae. There will
be a continuum of ecological damage thresholds for wasp density depending on the prey species or habitat. Experimentally placed
small caterpillars had a significantly higher survival rate than large caterpillars, and the survival rate of both groups
decreased with increasing wasp density. Spring-occurring caterpillars have a probability of surviving of 0.90–0.95, assuming
wasps are the only source of mortality. However, at the peak of the wasp season we predict caterpillars would have virtually
no chance (probability of 10−78 to 10−40) of surviving to adults. Wasp abundance must be reduced by at least 88% to conserve the more vulnerable species of free-living
caterpillars at wasp densities similar to those observed in our study sites. This equates to a damage threshold of 2.7 wasps
per Malaise trap per day. It was exceeded for about 5 months of the year in non-poisoned sites. There are currently no biological
or chemical control techniques available in New Zealand that will reduce wasp abundance below this damage threshold throughout
the year. Our models show that most Lepidoptera with spring caterpillars will be able to persist, but species with caterpillars
occurring in the peak wasp season will be eliminated.
Received: 5 January 1998 / Accepted: 10 February 1999 相似文献
16.
Morphological and coenological differences between closely related speciesStellaria nemorum L. andS. montana
Pierrat are described.Stellaria montana is frequent in Slovenia and occurs mostly in the montane belt (altitude 600–1200 m). It has been recorded in thirty two forest
communities (associations or lower syntaxa). Although widely distributed in EuropeS. nemorum is more rare in Slovenia. It occurs mostly in upper-montane (altimontane) and subalpine belt (altitude 1200–1600 m) in ten
forest or shrubby communities. Both,S. nemorum andS. montana are valuable diagnostic species for certain associations. They characterize sites with fresh soil, rich in nitrogen. As an
example we present two syntaxa of beech forests of Slovenia, in which the species of theS. nemorum group have high constancy and cover value. 相似文献
17.
Aquatic insect communities were investigated from the Muonghoa Stream in the Sapa Highland (highest peak 3,143 m), a subtropical
mountain stream in northern Vietnam. Field investigations for quantitative (Surber net 50 cm × 50 cm, mesh size 0.2 mm, riffle
and pool/run) and qualitative (hand net, mesh size 1 mm) sampling were conducted at nine sites along the watercourse between
27 November and 2 December 2005. As a result, a total of 216 species (the majority of them undescribed) belonging to 139 genera,
61 families, and nine orders were recognized: 53 Ephemeroptera species (24.5%), nine Odonata species (4.2%), 15 Plecoptera
species (6.9%), seven Hemiptera species (3.2%), 35 Coleoptera species (16.2%), one Megaloptera species (0.5%), 29 Diptera
species (13.4%), 66 Trichoptera species (30.6%), and one Lepidoptera species (0.5%). Trichoptera, Ephemeroptera, and Coleoptera
represented the major aquatic insect groups with regard to taxonomic and individual richness, whereas Hemiptera and Odonata
were relatively less diverse and abundant than in studies of other tropical Southeast Asian streams. The dominance, richness,
and diversity indices (H′) fell within the following ranges [mean ± standard deviation (SD)]: 0.18–0.76 (0.42 ± 0.19), 4.13–9.19
(7.06 ± 1.45), and 1.61–3.22 (2.67 ± 0.55), respectively. Riffle habitats generally yielded numbers of aquatic insect species
and individuals approximately twice that sampled in pool/run habitats. Shredders were relatively larger in proportion within
the headwater reach, whereas scrapers and collector-gatherers were more abundant in the middle and lower stream reaches. This
functional feeding group composition is characteristic of temperate streams in East Asia. The results of detrended correspondence
analysis and Bray–Curtis cluster analysis indicated that aquatic insect compositions at the sampling sites were very reflective
of the reach characteristics, which evidence gradual changes with altitude and stream order along the stream watercourse.
This is the first comprehensive investigation of aquatic insects in highland Southeast Asian regions. 相似文献
18.
Species diversity, abundance, and vertical size structure of rattans in Borneo and Java 总被引:1,自引:0,他引:1
We studied rattan communities in four forest types in Borneo and Java to clarify the pattern of species diversity and vegetation
structure. Within six plots of 4.82 ha in total, we found 42 rattan species in six genera with 4,736 stems (≥20 cm long).
There was a significant positive correlation between rattans and trees in species diversity, decreasing in the order mixed
dipterocarp (for rattans: Shannon–Wiener diversity index, H′ = 2.87–3.34) > alluvial (1.96) > lower montane (1.43) > peat swamp forests (1.34). This pattern coincided with the diversity
of the regional flora. The density of rattan stems (ha–1) decreased in the order lower montane (5,997) > mixed dipterocarp (598–992) > alluvial (592) > peat swamp forests (162).
The maximum height of rattans would be determined by the canopy height, rather than by the maximum tree height. The rattan
stem volume ranged from 0.25 to 1.88 m3 ha−1 and was not correlated with the stem density. The cool montane climate seemed to decrease the maximum height of rattans,
and a few small rattans made denser colonies. Swampy environments apparently suppressed the survival of non-climbing rattans
strongly, but that of tall climbing rattans less so. 相似文献
19.
Effects of forest clearing and succession on the carbon and nitrogen content of soils in Puerto Rico and US Virgin Islands 总被引:8,自引:0,他引:8
Soil samples from mature and secondary forests and agricultural sites in three subtropical life zones of Puerto Rico and the
US Virgin Islands were collected to determine the effects of forest conversion to agriculture and succession on soil organic
carbon (C) and nitrogen (N) contents. Site characteristics that may affect soil C and N (slope, elevation, aspect, and texture)
were as uniform as possible. Carbon contents (to 50 cm depth or bedrock) of cultivated sites, as a percent of corresponding
mature forests, were lower in the wet (44%) and moist (31%) than in the dry (86%) life zones whereas N contents were relatively
high regardless of life zone (60–130% of the mature forests). Conversion of forests to pasture resulted in less soil C and
N loss than conversion to crops. The time for recovery of soil C and N during succession was approximately the same in all
three life zones, about 40–50 yr for C about 15–20 yr for N. However, the rate of recovery of soil C was faster in the wet
and moist life zone, whereas N appeared to recover faster in the dry life zone. Evidence for loss of soil C during cultivation
and gain during succession to soil depths of 50–100 cm is presented. 相似文献
20.
Victor O. Sadras 《Oecologia》1997,109(3):427-432
In indeterminate plant species, the rate of vegetative growth usually declines during the stage of active reproductive growth.
Fruit shedding, as induced by insect herbivores, could counteract this decline. Due to the relative increase in vegetative
growth, plants that have suffered reproductive damage could be better able to intercept light and acquire soil resources than
undamaged plants. If so, plants with damaged neighbours might grow less than their counterparts with smaller, undamaged neighbours.
This hypothesis was tested in high- and low-density cotton crops subjected to three treatments: (i) undamaged controls; (ii)
uniformly damaged, in which all plants were damaged; (iii) non-uniformly damaged, in which every second plant was damaged.
Damaged plants had their flowerbuds and young fruits manually removed at 85 days after sowing to simulate shedding as induced
by Helicoverpa spp. (Lepidoptera) and mirid bugs (Hemiptera). As expected, damaged plants had greater leaf area and more vegetative dry matter
than undamaged ones. This was most pronounced at high plant density. Neighbour status did not affect vegetative growth but
it had a substantial, asymmetric effect on the reproductive growth of target plants. Damaged targets recovered to the level
of undamaged controls in terms of total fruit number but had a large reduction in the mass of mature fruit due to the limited
time available for recovery. The effect of neighbour status, if any, on the production of mature fruit in damaged targets
was overridden by the limit imposed to recovery by the duration of the growing season. In contrast, neighbour status affected
the production of mature fruit of undamaged targets: undamaged targets with damaged neighbours had 34% (low density) and 56%
(high density) less mature fruit mass than their counterparts with undamaged neighbours. This was because (i) reproductive
allocation and (ii) the proportion of total fruit that reached maturity in target plants declined with increasing neighbour
interference. Most studies dealing with changes in competitive relationships among plants subjected to differential herbivory
have shown how undamaged plants may benefit from herbivores that feed on their neighbours. This study shows that differential
reproductive damage can cause the opposite effect, as undamaged plants may have a significant reduction in productivity due
to the influence of neighbours whose vegetative growth was stimulated by the loss of reproductive organs.
Received: 2 June 1996 / Accepted: 8 September 1996 相似文献