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1.
Martina Petrů 《Plant Ecology》2005,181(2):289-298
In 1998–2001, I studied disturbance effects on the population structure and dynamics of a grassland strict biennial Pedicularis sylvatica, and on the species demography (monthly dynamics of seedling recruitment in 1998 and within- and between-year survival in
1998–2000). In two Czech populations, I established three experimental disturbance regimes: (1) a gap treatment, that simulated
grazing by clipping vegetation and creating small gaps, (2) a mowing treatment, where I clipped the vegetation, and (3) a
no management treatment, where I left the vegetation untreated. The number of recruiting seedlings varied greatly by year,
and demographic structure of populations showed significant year-to-year oscillations in mean seedling numbers, from low (3
± 0.7 s.e. per 0.25 m2 plot) to high (103 ± 20). Inversely in the same years and plots, mean adult numbers in populations oscillated from high (12
± 2) to low (0.7 ± 0.3). Disturbance effects were only important for seedling recruitment in early census dates in all years.
In 1998, most seedlings recruited in April–May in gaps in both sites, but most died before winter. Within- and between-year
survival was not affected by disturbance regimes but fluctuated significantly among years. Between-year survival increased
with increasing size of the overwintering bud and was higher in disturbance treatments. Since the oscillations in population
structure did not significantly vary in response to experimental disturbances, population dynamics may be driven endogenously
rather than by disturbance events. The weak disturbance effects on species demography may also indicate population resilience
to changes in habitat quality. However, since disturbances promoted seedling recruitment, grazing or mowing regimes are strongly
recommended, as they create regeneration opportunities and maintain habitat quality, meeting the species long-term conservation
goals. 相似文献
2.
Julian M. Norghauer Christopher M. Free R. Matthew Landis James Grogan Jay R. Malcolm Sean C. Thomas 《Oikos》2016,125(1):137-148
The Janzen–Connell hypothesis proposes that specialized herbivores maintain high numbers of tree species in tropical forests by restricting adult recruitment so that host populations remain at low densities. We tested this prediction for the large timber tree species, Swietenia macrophylla, whose seeds and seedlings are preyed upon by small mammals and a host‐specific moth caterpillar Steniscadia poliophaea, respectively. At a primary forest site, experimental seed additions to gaps – canopy‐disturbed areas that enhance seedling growth into saplings – over three years revealed lower survival and seedling recruitment closer to conspecific trees and in higher basal area neighborhoods, as well as reduced subsequent seedling survival and height growth. When we included these Janzen–Connell effects in a spatially explicit individual‐based population model, the caterpillar's impact was critical to limiting Swietenia's adult tree density, with a > 10‐fold reduction estimated at 300 years. Our research demonstrates the crucial but oft‐ignored linkage between Janzen–Connell effects on offspring and population‐level consequences for a long‐lived, potentially dominant tree species. 相似文献
3.
Dominant understorey species influence forest dynamics by preventing tree regeneration at the seedling stage. We examined
factors driving the spatial distribution of the monocarpic species Isoglossa woodii, a dominant understorey herb in coastal dune forests, and the effect that its cover has on forest regeneration. We used line
transects to quantify the area of the forest understorey with I. woodii cover and with gaps in the cover. Paired experimental plots were established in semi-permanent understorey gaps with I. woodii naturally absent and in adjacent areas with I. woodii present to compare plant community composition, soil, and light availability between the two habitats. Isoglossa woodii was widespread, covering 65–95% of the understorey, while gaps covered the remaining 5–35% of the area. The spatial distribution
of this species was strongly related to tree canopy structure, with I.␣woodii excluded from sites with dense tree cover. Seedling establishment was inhibited by low light availability (<1% of PAR) beneath
I.␣woodii. When present, I. woodii reduced the density and species richness of tree seedlings. The tree seedling community beneath I. woodii represented a subset of the seedling community in gaps. Some species that were found in gaps did not occur beneath I. woodii at all. There were no significant differences between the sapling and canopy tree communities in areas with I. woodii gaps and cover. In the coastal dune forest system, seedling survival under I. woodii is dependent on a species’ shade tolerance, its ability to grow quickly during I. woodii dieback, and/or the capacity to regenerate by re-sprouting and multi-stemming. We propose a general conceptual model of forest
regeneration dynamics in which the abundant understorey species, I. woodii, limits local tree seedling establishment and survival but gaps in the understorey maintain tree species diversity on a landscape
scale. 相似文献
4.
Bruce M. Leaman 《Environmental Biology of Fishes》1991,30(1-2):253-271
Synopsis The characteristics of lightly and heavily exploited Pacific ocean perch,Sebastes alutus, stocks are evaluated relative to the predictions of life history theory. These long-lived species (50–100 year lifespan)
show limited phenotypic plasticity and have little buffering against the effects of reduced lifespan. Reduced stock abundance
has generated some compensatory increase in growth rate. Length at first maturity varies only slightly with increased growth
rate, although age at maturity may decrease by 1–4 years. Grooth increases yield larger (15–20%) size at age and increased
reproductive effort at younger ages, but lower size-specific fecundity for these faster-growing fish. This suggests an energy
allocation protocol favouring growth over reproduction in these long-lived animals. Rockfishes have late recruitment to fisheries
(ages 10–15), and the detection time for results of management actions is equally long. Their vulnerability to overfishing
means that indices of population changes, more representative of fishing effects than the catch rate index presently used,
are required. Reproductive value indices are shown to be extremely sensitive and continuous with population abundance changes.
Their incorporation into monitoring programs would permit more timely evaluation of management actions. Management policies
developed for shorter-lived species are shown to be inappropriate for rockfishes. The need for an improved match in the time
frame of the species' life history, and that of management strategies, is stressed. 相似文献
5.
6.
The dynamics of aseasonal lowland dipterocarp forest in Borneo is influenced by perturbation from droughts. These events might
be increasing in frequency and intensity in the future. This paper describes drought-affected dynamics between 1986 and 2001
in Sabah, Malaysia, and considers how it is possible, reliably and accurately, to measure both coarse- and fine-scale responses
of the forest. Some fundamental concerns about methodology and data analysis emerge. In two plots forming 8 ha, mortality,
recruitment, and stem growth rates of trees ≥10 cm gbh (girth at breast height) were measured in a ‘pre-drought’ period (1986–1996), and in a period (1996–2001) including the 1997–1998
ENSO-drought. For 2.56 ha of subplots, mortality and growth rates of small trees (10–<50 cm gbh) were found also for two sub-periods (1996–1999, 1999–2001). A total of c. 19 K trees were recorded. Mortality rate increased by 25% while both recruitment and relative growth rates increased by
12% for all trees at the coarse scale. For small trees, at the fine scale, mortality increased by 6% and 9% from pre-drought
to drought and on to ‘post-drought’ sub-periods. Relative growth rates correspondingly decreased by 38% and increased by 98%.
Tree size and topography interacted in a complex manner with between-plot differences. The forest appears to have been sustained
by off-setting elevated tree mortality by highly resilient stem growth. This last is seen as the key integrating tree variable
which links the external driver (drought causing water stress) and population dynamics recorded as mortality and recruitment.
Suitably sound measurements of stem girth, leading to valid growth rates, are needed to understand and model tree dynamic
responses to perturbations. The proportion of sound data, however, is in part determined by the drought itself.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
This paper contributes to the relatively sparse literature on the effects of insect herbivory on the population dynamics
of plants and is probably unique in that it reports the long-term effects of combinations of three insect herbivore species
on the population densities of a moderately long-lived tree species. The tree is Sesbania punicea, a leguminous perennial from South America that has been the target of a biological control programme in South Africa for
almost 20 years. Sixteen infestations of the weed have been monitored for periods of up to 10 years to determine changes in
the density of the mature, reproductive plants under the influence of different combinations of three biological control agents
(i.e. with one, two or three of the agent species present in the weed infestation). The three biological control agents, all
weevil species, include Trichapion lativentre, which primarily destroys the flower-buds, Rhyssomatus marginatus, which destroys the developing seeds, and Neodiplogrammus quadrivittatus, whose larvae bore into the trunk and stems of the plants. While T. lativentre occurs throughout the range of the weed in South Africa, the other two species are less mobile, more recent introductions
and are largely confined to the vicinity of selected release sites. There has been a significant decline in the density of
mature S. punicea in areas where two or more of the agents are established. The decline of the weed has been most evident where N. quadrivittatus is active and particularly so where both of the other two weevil species are also present.
Received: 2 April 1997 / Accepted: 30 November 1997 相似文献
8.
Fires shape fundamental properties of many forest ecosystems and climate change will increase their relevance in regions where
fires occur infrequently today. In ecosystems that are not adapted to fire, post-fire tree recruitment is often sparse, a
fact that might be attributed to a transient lack of mycorrhizae. Ectomycorrhizal (EcM) fungi play an important role for recruitment
by enhancing nutrient and water uptake of their hosts. The questions arise whether and for how long the EcM community is transformed
by fire. We investigated the resistance and resilience of EcM fungal communities on a chronosequence of 12 Pinus sylvestris stands in Valais (Switzerland) and Val d’Aosta (Italy) affected by fire between 1990 and 2006. Soil samples from burnt and
non-burnt forests were analyzed with respect to EcM fungi by means of a bioassay. The number of EcM species was significantly
lower in samples from recently (2–5 years) burnt sites than non-burnt forest, and increased with time since fire reaching
levels of adjacent forests after 15–18 years. Community composition changed after fire but did not converge to that of non-burnt
sites over the 18 year period. Only Rhizopogon roseolus and Cenococcum geophilum were abundant in both burnt sites and adjacent forest. Our data indicate fire resistance of some EcM fungal species as well
as rapid resilience in terms of species number, but not in species composition. As long as the function of different EcM species
for seedling establishment is unknown, the consequences of long-term shifts in EcM community composition for tree recruitment
remain unclear. 相似文献
9.
Akifumi Makita 《Ecological Research》1992,7(3):245-254
The survivorship of a monocarpic bamboo grass,Sasa kurilensis, during the early regeneration process was documented by a 10 year observation of the seedling population after mass flowering
in the Hakkoda Mountains, northern Japan. Three phases were recognized: the establishment, density-stable and thinning phases.
The mortality of the densely germinated seedlings (932.9m−2 in aBetula ermanii forest and 1222.3 m−2 in aSasa grassland) was high, up to 0.5 year−1, in the establishment phase (0–1 year after germination) and low in the density-stable phase (1–3 years after germination).
After reaching full density state, the seedling population showed a nearly constant mortality of 0.18 year−1 due to self-thinning (the thinning phase). The high C/F ratio presumably caused suppressed seedlings to die. Recovery of
theS. kurilensis population was estimated to requireca 20 years in the study plots, judging from the height growth and the decrease in culm density of the seedling population.
The illuminance on the ground was higher in the flowered population than in the unflowered one for 5 years after mass death.
The duration of high ground illuminance is an important factor affecting the dynamics of forests withSasa undergrowth, because tree seedlings need to establish under high ground illuminance for the successful regeneration of the
forests. 相似文献
10.
We conducted a census of the rare pine, Pinus torreyana ssp. torreyana, to determine (a) its population size and whether it is stable, growing, or declining; (b) the spatial variation in population
structure; (c) the spatial patterning of trees in different life stages; and (d) the environmental factors that are related
to seedling recruitment. Trees were classified into four stage classes: adult (>160 cm tall with cones); sub-adult (>160 cm
without cones); saplings (30–160 cm); and seedlings (<30 cm). Stem diameter was measured for adults and sub-adults, and height
for saplings and seedlings. Stands were defined by spatial clustering of the tree map. Univariate and bivariate point pattern
analyses were used to explore spatial patterns for adult and juvenile trees and identify potential stand development processes
such as density dependence, dispersal limitations, and patchy recruitment. Logistic regression was used to analyze seedling
establishment and survival in relation to environmental variables derived from digital maps. Earlier studies reported little
or no recruitment. We mapped 5,394 individuals, and tree size had “reverse J-shaped” distribution suggestive of a recruiting
population. However, population structure was variable among stands. The predominant spatial pattern detected for adult and
juvenile trees was clustering at lag distances <10 m. Bivariate pattern analysis did not suggest repulsion between adult and
juvenile size classes. Seedlings tended to be found close to adults and on certain soil types. This suggests that the clustered
patterns resulting from patchy recruitment of juveniles persist over time. 相似文献
11.
Both temporal and spatial scales are important in the evaluation of population dynamics, but the latter often receives less
attention in demographic analyses. We used a 5-year demographic data set for a long-lived geophyte, Calochortus lyallii, to investigate the pattern and components of spatial variation at two scales (population and microsite). We found that neither
the projected population structure nor asymptotic population growth rate (λ) varied greatly across either scale, although
the underlying contributors to the variation in λ, V(λ), did differ between scales. Life table response experiment analyses showed that V(λ) among populations came primarily from variation in seedling survival and progression of non-reproductive plants, whereas
V(λ) among microsites was primarily due to the variable fertility of large adults. Prolonged dormancy was important in reducing
V(λ) among quadrats at both the scales, partly countering fluctuations in other transitions such as recruitment. This result
represents some of the first evidence that underground “bulb banks” could function to offset the effects of a spatially heterogeneous
environment in a manner analogous to seed banks. Future work is needed to isolate the specific, sometimes idiosyncratic, life
history phenomena acting to modulate plant population dynamics in a spatial context. 相似文献
12.
Forest fragmentation can negatively affect plants if animal seed-dispersers become locally extinct in fragments. We conducted
a 2-year experiment to evaluate the importance of tree squirrels (Sciurus) as seed dispersers for Quercus, Carya, and Juglans, and to assess dispersal consequences in patches where fragmentation-sensitive eastern gray squirrels (Sciurus carolinensis) are absent. We accounted for fates of ∼15,700 seeds from five tree species in four exclosure treatments at 18 fragments
during a high (2003–2004) and low seed (2004–2005) year. Two treatments excluded Sciurus to mimic disperser loss. We sampled nut-tree seedling density at 259 sites across eight watersheds, half of which were too
fragmented to support S. carolinensis, but supported fragmentation-tolerant fox squirrels (Sciurus niger). Autumn-to-spring seed survival was low (∼1%) for all species during low seed production. During high seed production, survival
was higher for Juglans nigra (20%) and Carya ovata (16%) than for three Quercus species (∼4% for Quercus palustris and Quercus rubra in two exclosure types; ∼1% for Quercus alba in all treatments). Survival of J. nigra, C. ovata, and Q. rubra was ≥2.1–7.7 times higher for seeds in exclosures that Sciurus could access. Seed displacement distance was higher in the low seed than the seed-rich year, but the proportion of seeds
surviving to greater distances was higher in seed-rich years for all seed types except Q. rubra. This affirms the importance of masting to seed survival and dispersal, but also suggests an advantage to trees of producing
seed in non-mast years. Seedling densities were comparable in watersheds with and without S. carolinensis. These results demonstrate the importance of tree squirrels as dispersers of nut-bearing trees, but suggest that fragmentation
may not disrupt dispersal of certain species if losing S. carolinensis from disturbed landscapes is compensated for by fragmentation-tolerant fox squirrels (S. niger). 相似文献
13.
The temporal availability of propagules is a critical factor in sustaining pioneer riparian tree populations along snowmelt-driven
rivers because seedling establishment is strongly linked to seasonal hydrology. River regulation in semi-arid regions threatens
to decouple seed development and dispersal from the discharge regime to which they evolved. Using the lower Tuolumne River
as a model system, we quantified and modeled propagule availability for Populus fremontii (POFR), Salix gooddingii (SAGO), and Salix exigua (SAEX), the tree and shrub species that dominate near-channel riparian stands in the San Joaquin Basin, CA. A degree-day
model was fit to field data of seasonal seed density and local temperature from three sites in 2002–2004 to predict the onset
of the peak dispersal period. To evaluate historical synchrony of seed dispersal and seasonal river hydrology, we compared
peak spring runoff timing to modeled peak seed release periods for the last 75 years. The peak seed release period began on
May 15 for POFR (range April 23–June 10), May 30 for SAGO (range May 19–June 11) and May 31 for SAEX (range May 8–June 30).
Degree-day models for the onset of seed release reduced prediction error by 40–67% over day-of-year means; the models predicted
best the interannual, versus site-to-site, variation in timing. The historical analysis suggests that POFR seed release coincided
with peak runoff in almost all years, whereas SAGO and SAEX dispersal occurred during the spring flood recession. The degree-day
modeling approach reduce uncertainty in dispersal timing and shows potential for guiding flow releases on regulated rivers
to increase riparian tree recruitment at the lowest water cost. 相似文献
14.
Alfredo Cascante-Marín Victor Meza-Picado Armando Estrada-Chavarría 《Plant Ecology》2011,212(7):1101-1108
Tropical premontane forests between 700 and 1,400 m.a.s.l. represent a particular component of the gamma diversity of neotropical
ecosystems; however, the extent of information about their dynamics lags behind the more studied lowland rain forests. Data
from three 1-ha permanent plots in a premontane forest in Costa Rica collected during an 11-year period (1998–2009) suggested
a high tree turnover rate for this ecosystem (high mortality rate, λ = 2.4% and annual recruitment, μ = 2.6%). The floristic composition did not significantly change during the study period, but its high dynamism (2.4%) exceeded
that of several reported values from highly diverse neotropical lowland rain forests. The documented decrease in abundance
(8.6%) and basal area (14.3%) of trees ≥10 cm in DBH differs from the general trend of increase described for several lowland
tropical rain forests in recent decades. We detected a significant population reduction (>15% of individuals from 1998 to
2009) in several relatively abundant tree species, whereas the populations of the three most dominant species remained nearly
constant. The high tree turnover recorded for this premontane forest might not have affected tree diversity; but it might
be promoting recruitment and growth of some tree species that may eventually become over-dominant in this ecosystem. 相似文献
15.
Rodent seed predation and seedling recruitment in mesic grassland 总被引:11,自引:0,他引:11
Seedling recruitment of two grasses (Arrhenatherum elatius and Festuca rubra) and two herbs (Centaurea nigra and Rumex acetosa) was measured in areas with and without rodents to which seeds of each species were sown at three seed densities (1000, 10,000
and 50,000 seeds m−2) in two seasons (spring and autumn 1995). Seed removal was measured for 10-day periods and the fate of seedlings was followed
for 15 months after sowing. The proportion of seed removed ranged from 6 to 85% and increased with increasing seed density
for each species. Rodents had no effect on seedling emergence or survival in the spring sowing. In the autumn sowing, rodents
reduced seedling emergence of all four species sown at 1000 and 10,000 seeds m−2 but had no impact at 50,000 seeds m−2, presumably because of microsite limitation. We suggest the difference between spring and autumn arose because emergence
was seed limited in autumn but microsite limited in spring; microsite availability was higher in autumn because a summer drought
killed plants, reduced plant biomass and opened up the sward. Fifteen months after the autumn sowing, fewer A. elatius and C. nigra seedlings survived on plots exposed to rodents. This result reflected not only the reduced seedling emergence but also increased
seedling mortality (seedling herbivory) in sites exposed to rodents. In contrast, F. rubra and R.acteosa showed density-dependent seedling survival which compensated for initial differences in seedling emergence, so that no effect
of rodents remained after 15 months. The results suggest that rodent seed predation and seedling herbivory exert strong effects
on seedling recruitment of A.elatius and C. nigra when recruitment conditions are favourable (conditions that lead to high microsite availability) and may contribute to both
species being maintained at low densities in the grassland. The results also demonstrate that highly significant impacts of
rodent seed predation at the seedling emergence stage can disappear by the time of plant maturation.
Received: 2 March 1998 / Accepted: 28 September 1998 相似文献
16.
Zifa Deng Ziwang Deng Shuqing An Zhongsheng Wang Yuhong Liu Yan Ouyang Changfang Zhou Yinbiao Zhi Hongli Li 《Hydrobiologia》2009,630(1):287-297
To elucidate the seed–seedling conflict and the process of habitat choices during the expansion of S. alterniflora, densities of seeds and seedlings in three different habitats, foreland, Spartina meadow, and canopy gap patch, were measured. Statistical analyses of these measurements were performed to investigate the
interaction between seeds or seedlings and environmental factors. Also, the process of habitat choice during the expansion
of S. alterniflora was explored. The results show that, in the upper soil seed bank (0–5 cm), both the ratio of germinated seeds and the ratio
of survival seedlings to total seeds do not differ significantly among the three habitats. However, in the lower soil seed
bank (5–10 cm), these ratios differ significantly, suggesting the seed–seedling conflict of S. alterniflora generally occurs in the lower soil seed bank. The remarkable conflict occurs in the meadow habitat. Greenhouse experiments
indicate that the germination rate decreases significantly and the mortality of pre-emerged seedlings increases significantly
with increasing burial depth. The maximal burial depth of emerged seedlings varies with sediment types. Comparisons of burial
depth effects on seedling height, mesocotyl length, coleoptile length, and root length show that the major responses of S. alterniflora pre-emerged seedlings to the burial treatments are the elongation of coleoptiles and mesocotyls, which favor seedling survival
by enhancing aeration and accelerating emergence. These results suggest that burial treatment is a key selection factor, which
leads to the seed–seedling conflict in recruitment of S. alterniflora population, and directly affects the expansion rate and the area infected by S. alterniflora.
Handling editor: S. M. Thomaz
Ziwang Deng: co-first author. 相似文献
17.
Ectomycorrhizal (ECM) communities of mature trees and regenerating seedlings of a non-native tree species Pinus mugo grown in a harsh environment of the coastal region of the Curonian Spit National Park in Lithuania were assessed. We established
three study sites (S1, S2, and S3) that were separated from each other by 15 km. The ECM species richness was rather low in
particular for mature, 100-year-old trees: 12 ectomycorrhizal taxa were identified by molecular analysis from 11 distinguished
morphotypes. All 12 taxa were present on seedlings and on mature trees, with between 8–11 and 9–11 taxa present on seedlings
and mature trees, respectively. Cenococcum geophilum dominated all ECM communities, but the relative abundance of C. geophilum mycorrhizas was nearly two times higher on seedlings than on mature trees. Mycorrhizal associations formed by Wilcoxina sp., Lactarius rufus, and Russula paludosa were also abundant. Several fungal taxa were only occasionally detected, including Cortinarius sp., Cortinarius obtusus, Cortinarius croceus, and Meliniomyces sp. Shannon’s diversity indices for the ECM assemblages of P. mugo ranged from 0.98 to 1.09 for seedling and from 1.05 to 1.31 for mature trees. According to analysis of similarity, the mycorrhizal
communities were similar between the sites (R = 0.085; P = 0.06) and only slightly separated between seedlings and mature trees (R = 0.24; P < 0.0001). An incidental fruiting body survey that was conducted weakly reflected the below-ground assessment of the ECM
fungal community and once again showed that ECM and fruiting body studies commonly supply different partial accounts of the
true ECM fungal diversity. Our results show that P. mugo has moved into quite distinct habitats and is able to adapt a suite of ECM symbionts that sufficiently support growth and
development of this tree and allow for natural seedling regeneration. 相似文献
18.
In the Hawaiian Islands, native Heteropogon contortus (pili grass) is being replaced by alien grasses, one of which is Pennisetum setaceum (fountain grass). Both grasses depend on seeds for population growth. To help understand factors promoting the spread of the alien and decline of the native, we investigated the effects of physical disturbance, nutrient addition, and seed supplementation on seedling recruitment in experimental field plots. In the first year, our field site experienced an unusual drought, and seedling recruitment was greater for H. contortus than for P. setaceum under all treatments. Disturbance increased recruitment of H. contortus seedlings during some sampling periods. Recruitment was not significantly increased by seed additions for either species despite our finding of only 49 and 4 seeds m–2 in the seed bank for H. contortus and P. setaceum, respectively. In the first year, most P. setaceum seedlings died between monthly surveys. We resurveyed our field plots in a second, wetter year and found the pattern was reversed: recruitment of P. setaceum seedlings was greater than H. contortus seedlings in most treatments. Greenhouse comparisons of seedling survival under three drought regimes (water every 5,7 and 10 days) revealed that H. contortus seedlings tolerate drought better than P. setaceum seedlings. Seedling recruitment for these species in the leeward Hawaiian Islands appears to be primarily dependent on water availability, with the alien having the advantage in wetter years. Once seedlings of the long-lived alien become established, the alien seems capable of maintaining its dominance over H. contortus, even during periods of drought. 相似文献
19.
The dark taiga of Siberia is a boreal vegetation dominated by Picea obovata, Abies sibirica, and Pinus sibirica during the late succession. This paper investigates the population and age structure of 18 stands representing different stages after fire, wind throw, and insect damage. To our knowledge, this is the first time that the forest dynamics of the Siberian dark taiga is described quantitatively in terms of succession, and age after disturbance, stand density, and basal area. The basis for the curve–linear age/diameter relation of trees is being analyzed. (1) After a stand-replacing fire Betula dominates (4,000 trees) for about 70 years. Although tree density of Betula decreases rapidly, basal area (BA) reached >30 m2/ha after 40 years. (2) After fire, Abies, Picea, and Pinus establish at the same time as Betula, but grow slower, continue to gain height and eventually replace Betula. Abies has the highest seedling number (about 1,000 trees/ha) and the highest mortality. Picea establishes with 100–400 trees/ha, it has less mortality, but reached the highest age (>350 years, DBH 51 cm). Picea is the most important indicator for successional age after disturbance. Pinus sibirica is an accompanying species. The widely distributed “mixed boreal forest” is a stage about 120 years after fire reaching a BA of >40 m2/ha. (3) Wind throw and insect damage occur in old conifer stands. Betula does not establish. Abies initially dominates (2,000–6,000 trees/ha), but Picea becomes dominant after 150–200 years since Abies is shorter lived. (4) Without disturbance the forest develops into a pure coniferous canopy (BA 40–50 m2/ha) with a self-regenerating density of 1,000 coniferous canopy trees/ha. There is no collapse of old-growth stands. The dark taiga may serve as an example in which a limited set to tree species may gain dominance under certain disturbance conditions without ever getting monotypic. 相似文献
20.
Plasticity in fitness and fitness-related traits at ramet and genet levels in a tillering grass Panicum miliaceum under patchy soil nutrients 总被引:1,自引:0,他引:1
Seedling and root sprout recruitment after a volcanic deforestation was examined in a Prunus ssiori population. According to genotypes of five microsatellite (SSR) loci, 44 genets were identified among 188 ramets ≥ 5 cm DBH
in a 2.3-ha plot in 2000. The genets formed mutually exclusive patches. Because only one repeat change in an SSR locus distinguished
five genets from adjacent genets, there is a possibility that the five genets derived from somatic mutations as well as sexual
reproduction. Thus, at least 39 genets originated from seedlings, and at least 144 ramets derived from root sprouts. The seedlings
were recruited after the volcanic eruptions in 1739 and before 1972 because trees of 5 cm DBH were 28 years of age, estimated
from annual rings. As the largest ramet recruited from a root sprout was estimated to be 94 years old, root sprout recruitment
began between 1739 and 1906. Thus, the estimated minimum rates of recruitment from seedlings and root sprouts were 0.167 y–1 and 0.618-2.182 y–1, respectively. The clonal diversity of the P. ssiori population (Simpson's D = 0.92) was higher than that of other clonal plant populations. The inbreeding coefficient was significantly negative (Wright's
F
IS = −0.069). These results suggest that the frequent seedling recruitment in an outbreeding system maintains the clonal diversity
in the population.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献