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1.
Productivity of temperate broad-leaved forest stands differing in tree species diversity 总被引：1，自引：0，他引：1
2.
《Forest Ecology and Management》1997,95(2):161-171
We studied forest structure and composition along a chronosequence of secondary forest succession in Northwest Argentina's montane forests (‘Yungas’) at 27°S, between 700 and 900 m. Early herbaceous stages, forested stages of 11, 25, 45, and 50 years after abandonment, and old-growth forests were surveyed. Secondary forests included stands that originated in abandoned herbaceous crops and in abandoned fruit orchards. Basal area and species composition differed between 50-year-old secondary forests and old-growth forests. In contrast, tree density and species diversity were similar in the 50-year-old and in the old-growth forests. The previous use (herbaceous crops or fruit orchards) was an important influence on secondary forest composition. Whereas stands originating in herbaceous fields were dominated by wind-dispersed native species such as Heliocarpus popayanensis, Tecoma stans, Parapiptadenia excelsa, and Tipuana tipu, fruit-orchard-originated stands were dominated by animal-dispersed species. Among the animal-dispersed species, the exotic tree Morus alba was the most abundant, and its abundance in secondary forests seems to slow the succession toward old-growth forest composition. Overall, after accounting for differences attributable to pre-abandonment conditions, secondary forest succession showed a trend toward compositional convergence, with the rate of succession apparently regulated by the demography of long-lived pioneer species. 相似文献
3.
The aim of our study was to characterize the structure and regeneration dynamics of dominant tree species along altitudinal gradient in dry valley slopes of the Bhutan Himalaya. In the typical dry valley slopes of west-central Bhutan, we analyzed forest stratification, tree crown projection, and population structure from lower dry valley bottom (1520 m a.s.l.) to upper humid ridge top (3370 m a.s.l.) across five major forest types: i.e. (1) dry pine forest with Pinus roxburghii as a dominant species; (2) mixed broad-leaved forest with Quercus lanata (evergreen), Quercus griffithii, (deciduous), and Rhododendron arboreum (evergreen) as major canopy species; (3) evergreen broad-leaved forest dominated by Quercus semecarpifolia, Quercus glauca and Quercus oxyodon; (4) cool conifer forest dominated by Abies densa and Tsuga dumosa; (5) cold conifer forest with A. densa and Juniperus recurva as dominants. In general, regeneration pattern of major dominant species shifted from inverse-J (lower altitudes), to sporadic (mid-altitudes), and to uni-modal type (upper altitudes) corresponding to three regeneration trends: (1) invasive at the lower, warm, dry forest under relatively strong human disturbances; (2) stable/balanced at the mid-altitude, in a relatively stable, mature moist evergreen broad-leaved forest with gap regeneration; and (3) poor/low regeneration at the upper, cool, humid conifer forest with a continuously cattle-grazed understory. Overall, regeneration patterns were balanced in all forest types, however care should be taken to prevent excessive exploitation of dry pine forest of lower valley bottom, and to control cattle grazing at higher altitudes. Our findings can be incorporated into management plans for sustainable management and conservation of mountain forests. 相似文献
4.
Subtropical forests in the Ryukyu Islands have been degraded by silvicultural practices, and thus their structural attributes
are being shifted to other states dominated by a few tree species. This study clarified the mechanisms of the change, and
examined the effect of clear logging on the resilience of a subtropical forest. Sprouting regeneration and typhoon disturbance
were introduced into an individual-based model, SEIB-DGVM, for describing stand development and succession. The regeneration
dynamics from young secondary to old-growth stands were reproduced fairly well with the model. Sprouting recruitment produced
high stem density at the beginning of stand development, which caused a self-thinning trajectory following the −3/2 power
law. In the late development stage after 70 years, tree species diversity fluctuated because of the regenerative response
of sprouting species and the facilitatory effect of typhoon disturbance on the coexistence of subordinate species. The death
of canopy trees because of typhoon disturbances reduced the dominance of Castanopsis sieboldii, and depressed its dominance in the understory. Consequently, the understory species could establish by virtue of fallen
canopy trees, and tree species diversity increased at the stand level. Clear logging experiments in the model revealed that
species diversity deteriorated, especially in the stand dominated by sprouting species. Resilience of subtropical forests
was determined by initial species composition before clear logging. Our simulation results suggest that repeated logging drives
subtropical forests with high species diversity to a stand monopolized by C. sieboldii. 相似文献
5.
To improve the silvicultural targets for ecologically sustainable forestry, we quantified functionally important structural features for the first time in a representative set of old-growth forests in hemiboreal Europe. Altogether, 23 old-growth stands of four site-type groups were compared with mature commercial stands nearby in the Estonian state forests that hold the Forest Stewardship Council (FSC) certificate of sustainable forestry. These two treatments did not differ significantly in terms of tree-species diversity, volumes of woody debris of <20 cm diameter (including fine woody debris) and its decay-stage composition. However, mature stands had many more early-successional trees and lacked late-successional deciduous species; they also had a higher overall density and volume of live trees, due to abundant individuals of 10–39 cm diameter at breast height. Old-growth stands had at least twice as many live trees ≥40 cm, standing dead trees ≥30 cm and lying wood ≥20 cm in diameter, any freshly fallen debris, and regeneration. For lying wood ≥20 cm in diameter, the treatment effect depended on site type: both treatments of Vaccinium-type dry boreal forests were remarkably deadwood-poor (indicating historical management of the old-growth stands), while mature eutrophic stands of Aegopodium-type were most impoverished relative to old-growth levels. We conclude that many functional characteristics of old growth were present in the FSC-certified, mostly naturally regenerated, commercial stands. The main problem is the lack of very large trees, particularly of late-successional deciduous species, which should be addressed by their well-planned retention in cut areas and reconsideration of salvage logging strategies. A dense regeneration in old-growth stands also indicated the potential of selection cuttings. The study highlighted the need for region- and site-type specific numerical targets for sustainable forest management, which in the hemiboreal region should address the characteristic occurrence of late-successional deciduous trees on fertile soils and higher natural deadwood volumes than in typical boreal forests. For certification, the issues of structural impoverishment revealed both the inadequacy of some silvicultural practices and some indicators set by the national FSC-standard in Estonia. 相似文献
6.
7.
The coastal forest of Gabon abounds in monospecific secondary Aucoumea klaineana stands derived from natural regeneration after shifting cultivation. This paper aims to describe the changes in the structure and dynamics of these stands with age. It then assesses the impact of selective thinning in the upper storey on both structural and dynamic parameters.
The experiment consisted of 34 Permanent Plots in stands from establishment to more mature stages (ca. 50 years old). Thirteen plots (17–45 years old) were thinned. More than 80% of the removal came from supernumerary dominant A. klaineana.
A. klaineana represented 60% of the total density in stands ca. 15 years old but >90% of the dominant trees in older stands. The changes with age in the floristic composition of the unthinned stands showed three successional stages during which pioneer species associated with A. klaineana (from establishment to ca. 15 years) were progressively replaced by mature forest species.
Basal area increased and density decreased with age before reaching stable values at ca. 40–45 years. Mortality was very high in young stands but decreased in the older ones. Mortality generally affected small diameter individuals in the dominated storey. Diameter and basal area increments showed that the stand growth resulted from the growth of dominant A. klaineana. Diameter increments of A. klaineana were elevated during the first years of colonisation (1.9 cm/year) and were still ca. 0.7 cm/year for 50-year-old dominant trees.
Thinning did not increase the mortality of the dominant population. It favoured the individual growth of A. klaineana. The gain was substantial for dominated trees and small dominant trees (from 60 to 100%) but was lower for large dominant trees (ca. 25–30%). Therefore, stimulation of individual growth did not compensate for the loss of basal area at the stand level. 相似文献
8.
In the last decades, a large body of literature has grown to evaluate the impact of forest management on epiphytic lichens in boreal coniferous forests. However, information is still lacking on coniferous forests of the Alps. This study compares lichen diversity between spruce forest stands of four successional stages: (1) young, (2) intermediate, (3) mature forests managed for timber production with a rotation cycle of 120–180 years, and (4) old-growth protected forests. The emphasis was placed on the occurrence of nationally rare and calicioid species (lichens and fungi traditionally referred to as Caliciales, known to be indicative of forest age and continuity). For each forest successional stage, four plots were selected. In each plot, 7 spruce individuals were surveyed for epiphytic lichens according to a standardised sampling method. Species richness increased from young to mature stands, while no difference was detected between mature and old-growth stands. This pattern was also confirmed for rare and calicioid species which are, however, more frequent in old-growth stands. Differences in species composition were also found between the different forest successional stages. Mature and old-growth plots slightly overlap, indicating that to some extent comparable lichen assemblages could be found in these stands. A nested pattern of species assemblages was found, old-growth stands hosting most of the species which were also found in stands belonging to the previous forest successional stages. Our results support the hypothesis that the management regime applied to spruce forests of the Italian Alps renders mature stands managed for timber production somewhat similar to old-growth stands as lichen habitat. However, we found a higher complexity in old-growth forests, and many species of conservation concern clearly preferred old-growth stands. In this perspective, a further prolongation of the normal cycle it is likely to be a most favourable conservation-oriented management to be recommended at least within protected areas and Natura 2000 sites, where conservation purposes should receive a high priority. 相似文献
9.
We studied the species composition and stand structure of secondary pine forests affected by pine wilt disease, caused by epidemic attacks of the nematode Bursaphelenchus xylophilus, in western Japan. Based on the species composition, the vegetation was divided into four types: (1) Cladonia rangiferina, (2) Wikstroemia sikokiana, (3) Quercus glauca, and (4) Gleichenia japonica. The sequence of types from (1) to (3) represents a successional series in accordance with topographical position. The relative basal areas of Rhododendron reticulatum and Juniperus rigida in the C. rangiferina and W. sikokiana types were larger than in the Q. glauca type. The relative basal areas of Q. serrata, Clethra barbinervis, and Eurya japonica in the C. rangiferina and W. sikokiana types were less than in the Q. glauca type. The mortality of light-demanding trees was higher in the Q. glauca type than in the C. rangiferina and W. sikokiana types. In stands that were severely affected by pine wilt disease, light was reduced and soil became moist after rapid growth of Q. serrata and other species which are not affected by the disease. The numbers of species and components of evergreen broad-leaved natural forests were decreased, because pine forests in the study area had been cut frequently and the land had degraded. Pine wilt disease has shifted the dominance of pine forests from Pinus densiflora to deciduous oaks such as Q. serrata and physical conditions seemed to provide a safe site for shade-tolerant plant species, which are components of evergreen broad-leaved forests. Moreover, the seed dispersal of evergreen oaks appears to be an important factor in the succession to evergreen broad-leaved forest in degraded areas. 相似文献
10.
J. Christopher Haney 《Forest Ecology and Management》1999,120(1-3):203-217
Populations of forest birds were studied during two years of an outbreak of the elm spanworm Ennomus subsignarius (Hbn.) in a silviculturally unmanaged, old-growth conifer–northern hardwood forest on the Appalachian Plateau, PA. Canopy defoliation of hardwoods (mostly American beech Fagus grandifolia and red maple Acer rubrum) increased by at least 50% during the local peak of the outbreak (1993); territorial densities of birds were the highest (15% greater) during the regional peak of the outbreak (1994). Compared to a nearby but uninfested forest of similar age and composition, total bird abundance was as much as 22–33% higher at sites with extensive spanworm defoliation. In addition to canopy gleaners, several other foraging guilds exhibited one or more significant numerical responses to outbreak location or intensity, including bark foraging, understory gleaning, ground foraging, and pursuing species. Like other irruptions of forest Lepidoptera, populations of arboreal canopy-gleaning Parulinae (the warblers D. magnolia, D. fusca) were especially prone to fluctuate during this geometrid irruption. 相似文献
11.
Elisa Carrari Evy Ampoorter Andrea Coppi 《Scandinavian Journal of Forest Research》2016,31(5):484-494
One of the prominent compositional features of thermophilous deciduous forests of southern Europe is their richness in secondary woody species (AWS). To date, no studies have focused on the diversity and contribution to the ecosystem functions and socio-economic benefits provided by these species. Here, we first characterized species richness and diversity for three main functional groups of AWS, sporadic trees, shrubs and vines, in 53 representative stands of central Italy. Secondly, we explored variations in AWS diversity and composition along a four-level gradient of species richness of dominant trees under comparable site conditions. The 40 AWS taxa recorded showed a remarkable taxonomic singularity at both the genus and the family rank. Dominant tree species richness had no significant effect on AWS species richness and composition, while Shannon diversity of AWS, especially shrubs, was associated with cover of the dominant trees. Each AWS possessed, on average, ca. five ability traits over a total of 13 considered that contributed to important ecosystem functions or expected socio-economic benefits such as wood and food production, conservation of genetic resources (wild crop relatives) and ornamentals. This highlights the key role of AWS, and in particular of sporadic trees, for enhancing multifunctionality of thermophilous deciduous forests. 相似文献
12.
Our study focused on the functional aspects of plant species and vegetation at the transition from larch (Larix decidua Mill.) forest to mountain pine (Pinus mugo Turra) stands on the alpine treeline ecotone. With increasing elevation, living conditions grow harsher, which is reflected in the plant species and functional trait composition of plant communities. At four different localities in the Slovenian Alps, relevés along an altitudinal gradient and according to vegetation type were made (European larch forests, larch trees-mountain pine shrubs, mountain pine shrubs), using standard Central European phytocoenological method. In the upper mountain pine belt, few differential species were found, since most species represented in mountain pine stands also occurred in the lower two vegetation belts, while there were many differential species in the lower forest belt. Species with considerable competitive ability and moderate stress tolerance dominated the upper treeline ecotone, whereas ruderality is poorly expressed. The importance of stress tolerance in plant strategies increased slightly in the mountain pine belt. Changes in the representation of some functional traits attributes were detected by vegetation belts, but complete species turnover did not occur. Changes in dominant life form involved greater cover of chamaephytes and nanophanerophytes in the upper mountain pine belt. Species with evergreen leaves dominated mountain pine stands and deciduous forest stands. The share of species with scleromorphic leaves increased in the direction of the mountain pine belt while the share of species with mesomorphic and hygromorphic leaves declined. Mountain pine stands create good conditions for the regeneration of tree species and colonisation by ecologically more demanding forest species while species of alpine grasslands withdraw on open areas. Since today’s treeline is lowered due to past human activity, an upward shift is expected. Also, considering the great importance of competition strategy, current conditions in mountain pine stands are favourable for future forest succession. 相似文献
13.
The post disturbance natural succession of the Mediterranean maquis, which turns open and species-rich landscapes into dense, closed stands of sclerophyllous woody vegetation is a principal threat to plant and animal diversity. Therefore, in the absence of traditional agricultural disturbance, active management regimes that include cutting and grazing are proposed to preserve biodiversity. The Mediterranean woody vegetation in Israel is strongly dominated by one species - the evergreen sclerophyllous Quercus calliprinos (Kermes oak). We hypothesized that under cutting and grazing, the evergreen Q. calliprinos has a relative regrowth advantage over other competing tree species. Here we examined the effect of grazing and the effect of tree structural traits on the regrowth after clear cutting of all trees in our study plots at Mt. Meron LTER site, Israel. All trees were removed from five blocks of 2000 m2 and each block was divided into two plots, five of which were exposed to grazing livestock while five were wire-fenced and ungrazed. The regrowth rate of Q. calliprinos under grazing was higher than that of all other tree species suggesting that in the long-term, under such a conservation management regime, the dominance of the evergreen sclerophyllous Q. calliprinos over the deciduous tree species will increase and consequently will decrease plant and animal diversity. Therefore, we conclude that to protect landscape and species diversity in Mediterranean ecosystems dominated by evergreen oaks, when cutting and grazing are applied, special care must be paid to trees that are more negatively affected by such treatment. 相似文献
14.
Ladivania Medeiros do Nascimento Everardo Valadares de Sá Barretto Sampaio Maria Jesus Nogueira Rodal Ana Carolina Borges Lins-e-Silva 《Journal of Forest Research》2014,19(6):501-513
Changes in physiognomy, species composition and structure, and dispersal mechanisms of canopy and subcanopy plant assemblages were investigated along a chronosequence of three ages: 12, 20, and 50+ years old (=old-growth), three replications in each, in an Atlantic Forest landscape in Northeastern Brazil. Our objective was to investigate whether there is floristic and structural convergence along secondary succession. There were significant differences between secondary and old-growth forests in density and basal area only for the subcanopy. Differences in density between forest ages were noted when the assemblage was analyzed per diameter and height classes. Richness of canopy species of both secondary ages differed from those of old-growth forests. Some dominant species in the canopy of secondary forests showed a significant decrease in density with increasing age, which indicates an ongoing process of floristic changes. The low level of shared species between secondary and old-growth forests supports the idea that species composition is one of the last components to recover during successional process. Zoochory was the most important dispersal guild in species percentage and number, irrespective of stand age. Although regenerating areas can take alternative pathways, our results indicate that secondary Atlantic Forest sites have a high potential for natural regeneration. This recovery is recorded as a physiognomic convergence of the canopy layer in as little as 12 years, and progressive introductions of later successional species into the plant assemblage that lead to convergence in terms of the diversity and richness of the subcanopy and of dispersal guilds just 20 years after abandonment. 相似文献
15.
King DA 《Tree physiology》1991,9(3):369-381
Relationships between tree height and crown dimensions and trunk diameter were determined for shade-tolerant species of old-growth forests of western Oregon. The study included both understory and overstory species, deciduous and evergreen angiosperms and evergreen conifers. A comparison of adult understory species with sapling overstory species of similar height showed greater crown width and trunk diameter in the former, whether the comparison is made among conifers or deciduous trees. Conifer saplings had wider crowns than deciduous saplings, but the crown widths of the two groups converged with increase in tree height. Conifer saplings had thicker trunks than deciduous saplings of similar crown width, possibly because of selection for resistance to stem bending under snow loads. The results suggest that understory species have morphologies that increase light interception and persistence in the understory, whereas overstory species allocate their biomass for efficient height growth, thereby attaining the high-light environment of the canopy. The greater crown widths and the additional strength requirements imposed by snow loads on conifer saplings result in less height growth per biomass increment in conifer saplings than in deciduous saplings. However, the convergence in crown width of the two groups at heights greater than 20 m, and the proportionately smaller effect of snow loads on large trees, may result in older conifers equalling or surpassing deciduous trees in biomass allocation to height growth. 相似文献
16.
Interactions between forest canopy characteristics and plants in the forest understory are important determinants of forest community structure and dynamics. In the highlands of southwestern, China the dwarf bamboo Bashania fangiana Yi is an understory dominant beneath a mixed canopy of the evergreen Abies faxoniana (Rheder & Wilson) and the deciduous Betula utilis (D. Don). The goal of this study was to better understand the role of bamboo dominance, canopy characteristics, and periodic bamboo dieback on forest development. To achieve this goal, we measured tree seedling, tree saplings, and trees, forest canopy characteristics, and bamboo cover in permanent forest (n = 4) and gap plots (n = 31) in a mixed A. faxoniana and B. utilis forest in Sichuan, China. Dwarf bamboos died off in 1983 in the gap plots, and in three of the four forest plots. Forest development was assessed for the period 1984–1996. The seedling bank in forest and gap plots increased after bamboo die-off. A. faxoniana seedlings increased more than B. utilis in forest plots; the opposite pattern characterized gap plots. The proportion of seedlings on raised micro-sites on the forest floor also changed and new seedling were more abundant on the forest floor. By 1996, bamboo seedling cover and biomass had recovered to ca. 45% or their pre-flowering values. Rates of bamboo seedling recovery were faster beneath canopy gaps and deciduous trees than beneath forest or evergreen trees. Tree mortality exceeded recruitment in plots with dense bamboo; the opposite pattern was found in the plot with little bamboo. The mortality rate for B. utilis trees (2.4% year−1) was higher than that for A. faxoniana (0.8% year−1) and forests with dense bamboos became more open over the census period. Tree mortality was size-dependent and intermediate sized trees had the lowest rates of mortality. Stand basal area increased mainly due to greater basal area gain than loss for A. faxoniana. Interactions between tree species life history, canopy type, and bamboo life-cycles create heterogeneous conditions that influence tree and bamboo regeneration and contribute to the coexistence of A. faxoniana and B. utilis in old-growth forests in southwestern China. 相似文献
17.
Thomas P. Sullivan Druscilla S. Sullivan Pontus M.F. Lindgren Douglas B. Ransome 《Forest Ecology and Management》2007,240(1-3):32-41
Pre-commercial thinning (PCT) is a silvicultural practice that can provide diverse understory and overstory vegetation conditions. We tested the hypothesis that relative habitat use by snowshoe hare (Lepus americanus), mule deer (Odocoileus hemionus), and moose (Alces alces) would increase in response to enhanced abundance of herbs and shrubs, and species diversity and structural diversity of conifers, in heavily thinned (≤1000 stems/ha) stands, at 12–15 years post-thinning. Replicate study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada. Each study area had three young pine stands thinned to densities of 500 stems/ha (low), 1000 stems/ha (medium), and 2000 stems/ha (high), with an unthinned young pine and old-growth pine stand for comparison.
Relative habitat use, based on counts of fecal pellets and pellet-groups, was similar among the five treatment stands for hares (P = 0.24), deer (P = 0.23), and moose (P = 0.16). However, low-density stands (500 stems/ha) had ca. 3–20 times as many deer pellet-groups, and ca. 2–4 times as many moose pellet-groups, than other stands. Low-density stands had significantly greater canopy openness, volume of shrubs <2 m, and horizontal hiding cover <1.6 m than other treatments. Relative habitat use by deer and moose was positively related to understory characteristics such as enhanced abundance of forage and security cover. These results support our hypothesis that deer and moose responded positively to enhanced volume of herbs and shrubs as well as to species diversity and structural diversity of conifers and overall vegetation in heavily thinned (≤1000 stems/ha) stands at 12–15 years post-thinning. Our results suggest that ungulate management would be enhanced if greater emphasis was placed on forage enhancement throughout the year, which differs from current management recommendations which tend to focus on winter range and snow-interception cover. 相似文献
18.
Jarosław Skłodowski Paula Bajor Michał Trynkos 《European Journal of Forest Research》2018,137(5):745-757
The released excess anthropogenic nitrogen and carbon produces habitat enrichment, as exemplified by the modification of one-storied pine stands by introducing deciduous species into the understory or second story. In this study, we discuss the validity of pine stand modification by pitfall-trapping epigeic carabid beetles. Two hypotheses were formulated: (1) proportion of late-successional species is higher in assemblages inhabiting pine stands with understory or a second story than in one-storied pine stands; (2) plant litter composition affects carabid beetle assemblages more than other environmental variables. Additionally, characteristic carabid species of the respective pine stand types were identified. GLMM analysis revealed a higher proportion of late-successional species in pine stands with understory or a second story than in one-storied ones. NMDS separated those pine stand types. RDA analysis indicated that pine litter and humus had the strongest effect on carabid beetle assemblage structure in one-storied stands, being drier and thicker in this stand type than in the others. Indicator value analysis identified two characteristic non-forest species in one-storied stands The study revealed that the introduction of understory and particularly a second story into pine stands increased carabid beetle diversity and the proportion of late-successional species, confirming the validity of pine stand modification. 相似文献
19.
20.
We compared the understory communities (herbs, shrubs, and tree seedlings and saplings) of old-growth and second-growth eastern hemlock forests (Tsuga canadensis) in western Massachusetts, USA. Second-growth hemlock forests originated following clear-cut logging in the late 1800s and were 108–136 years old at the time of sampling. Old-growth hemlock forests contained total ground cover of herbaceous and shrub species that was approximately 4 times greater than in second-growth forests (4.02 ± 0.41%/m2 versus 1.06 ± 0.47%/m2) and supported greater overall species richness and diversity. In addition, seedling and sapling densities were greater in old-growth stands compared to second-growth stands and the composition of these layers was positively correlated with overstory species composition (Mantel tests, r > 0.26, P < 0.05) highlighting the strong positive neighborhood effects in these systems. Ordination of study site understory species composition identified a strong gradient in community composition from second-growth to old-growth stands. Vector overlays of environmental and forest structural variables indicated that these gradients were related to differences in overstory tree density, nitrogen availability, and coarse woody debris characteristics among hemlock stands. These relationships suggest that differences in resource availability (e.g., light, moisture, and nutrients) and microhabitat heterogeneity between old-growth and second-growth stands were likely driving these compositional patterns. Interestingly, several common forest understory plants, including Aralia nudicaulis, Dryopteris intermedia, and Viburnum alnifolium, were significant indicator species for old-growth hemlock stands, highlighting the lasting legacy of past land use on the reestablishment and growth of these common species within second-growth areas. The return of old-growth understory conditions to these second-growth areas will largely be dependent on disturbance and self-thinning mediated changes in overstory structure, resource availability, and microhabitat heterogeneity. 相似文献