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1.
Teak is the most important timber species in northern Thailand, and as such, large areas of teak forest have been disturbed or become highly degraded. Teak plantations have been established on this highly degraded land, where the rate of natural recovery is relatively slow. At the study site, five mixed or pure teak plantation types have been established to ameliorate limiting soil properties in order that long-term productivity is maintained. Observations within these plantations in northern Thailand have suggested that native species become established naturally under the shade of a “nurse” plantation, one that shades out early successional species. The objective of this study was to investigate the influence of the number of species in nurse plantations on the diversity and number of seedlings representative of mature native forests that become established within the plantations. Five types of plantations were investigated: (1) Tectona grandis L.f. (T); (2) T.grandis and Tamarindus indica L. (TT); (3) T.grandis and Gmelina arborea Roxb. (TG); (4) T.grandis, T. indica and G. arborea (TTG); (5) T.grandis, T.indica and Anacardium occidentale L. (TTA). These plantations were established primarily for the production of T.grandis (teak), with the other species introduced as economic trees. The plantations were surrounded by native stands of species representative of late successional and mature teak forests. In each of the plantations studies measurements were made on species density, species diversity, and evenness of plants regenerating in the understorey. Results showed that plantations consisting of several species in the overstorey had a higher diversity of native forest species in the understorey than the single-species plantation. Mixed plantation types were also found to reduce the density of the grass Imperata cylindrica (L.) P. Beauv. Consideration of the establishment of woody species found that TG and TTA had high densities of trees and shrubs. This suggested that if the goal of management was to regenerate forest with a high diversity of tree species similar to that found in native mature forests, multiple-species plantations, especially TG and TTA, would be more effective nurse communities than the single-species plantation in providing an environment into which seeds of native species could disperse and germinate. In addition, several climax species, such as Xylia xylocarpa (Roxb.) Taub. var. kerrii (Craib & Hutch) I.C. Nielsen, Pterocarpus macrocarpus Kurz, Largerstroemia sp., Afzelia xylocarpa (Kurz) Craib, Lannea coromandelica (Houtt) Merr., Spondias pinnata (L.f.) Kurz, Garuya pinnata Roxb., Terminalia mucronata Craib & Hutchison, Diospyoros mollis Griff., Irvingia malayana Oliv. ex Benn., Milletia leucantha Kurz, Dalbergia oliviri Gamble ex Prain, Chukrasia tabularis A. Juss and Schleichera oleosa (Lour.) Oken, were found in the early stages of succession, thus indicating that some may be suitable for planting in future restoration processes in order to accelerate natural succession and provide economic returns to managers.  相似文献   

2.
The pine processionary moth, Thaumetopoea pityocampa (Den. & Schiff.) is one of the most destructive pine pests in the Mediterranean countries. The first objective of this study was to analyse the spatial distribution of this insect on the tree on Pinus pinaster Ait., in northeast Portugal. The second objective was to develop two sampling plans: a sampling plan with fixed levels of precision for estimating T. pityocampa populations and a sequential sampling plan to classify the pest. Population estimates were made by registering the number of insect egg batches on 90 trees distributed over 3 stands during a 3-year study (1997–2000). Taylor's power law and Iwao regression were used to analyse the spatial distribution of the pest. Taylor's power law fitted the data better (r2 = 0.775) than Iwao's regression model (r2 = 0.704). The aggregation indices (b and β) were both significantly greater than one, indicating the aggregation of T. pityocampa egg batches. Optimal sample sizes for fixed precision levels of 0.10, 0.15 and 0.25 were estimated with Taylor's regression coefficients. Required sample sizes increased dramatically with increased levels of precision. The two sampling plans presented should be a tool for research on population dynamics and pest management decision.  相似文献   

3.
In Costa Rica, most reforestation trials with native species were established in the tropical humid regions. In the dry tropics, research on the performance of native species in forest plantations is incipient and trials comparing pure and mixed designs are limited. This paper presents the results of two experimental plantations with native trees in pure and mixed plots in the dry tropics of Costa Rica. The growth and productivity of 13 native species in pure and mixed plantations was compared with Tectona grandis (L.f.) Lam., an exotic species broadly used in the region. In a plantation of relatively slower growing species, measurements taken at 68 months of age resulted in Samanea saman (Jacq.) Merril. and Dalbergia retusa Hemsl. demonstrating the best growth, followed by Astronium graveolens Jacq. and Swietenia macrophylla King. Measurements in a plantation of relatively faster growing species, at 68 months of age, showed that growth of Schizolobium parahyba (Vell.) Blake was greatest in the pure and mixed plots, followed by Terminalia oblonga (Ruiz & Pav.) Steud., Anarcadium excelsum (Bert. & Balb. ex Kunth) Skeels and Pseudosamanea guachapele (Kunth) Harms. The native species grew better in the mixed plots. The pure plots of T. grandis (L.f.) Lam. were the most productive, compared to all species and the mixture of species. Plantations of T. grandis (L.f.) Lam. seem to be well adapted to the region and are certainly a commercially interesting alternative. Nevertheless, mixed plantations with native species would contribute more to sustainable management, because while single-species plantations do not provide a great range of goods and services when compared to the natural forest, mixed plantations are likely to increase this range of benefits.  相似文献   

4.
Carapa guianensis Aublet. is a tropical tree with strong multiple-use characteristics, and is valued for both the high quality oil extracted from its seeds and as a timber resource. This study compares the population structure of this economically important rainforest tree in two contrasting forest types: occasionally inundated and terra firme forests. Main study objectives were (a) to assess the density, spatial distribution, and size class structure of C. guianensis in these two forest types and (b) to use patterns of abundance, distribution and demographic structure to help infer key demographic stages or ecological variables that merit special focus for management. Four 400 m × 400 m plots, two in each forest type, were established to determine distribution and density patterns of C. guianensis ≥10 cm diameter at breast height (dbh) at the landscape level, and 32 10 m × 10 m subplots were randomly nested within each of the larger plots to measure individuals <10 cm dbh. Larger individuals (≥10 cm dbh) were found at higher densities in occasionally inundated forest than in terra firme forest: 25.7 trees ha−1 and 14.6 trees ha−1, respectively. Mean density of C. guianensis individuals <10 cm dbh was also higher in occasionally inundated forests, but variation of regeneration density among the subplots was high. Spatial distribution methods revealed a tendency toward clumping in both forest types, and both had similar size class structures, suggesting that both environments are suitable for C. guianensis. This new finding illustrates the potential for C. guianensis management in terra firme forests. High densities and clumped distributions in both forest types are also indices favorable for sustainable species management. Finally, several ecological variables (tree density and reproductive potential) were sufficiently different between terra firme and occasionally inundated forests to recommend stratification by forest type when conducting further studies on key ecological and management variables of C. guianensis.  相似文献   

5.
For sustainable forest management, it is important to know the response of timber species to the change in environment caused by logging. We performed a 2-year study on germination, survival and growth of four timber species, Cedrela odorata, Swietenia macrophylla, Hymenaea courbaril, and Cariniana micrantha, and one non-commercial species Tachigali vasquezii. We sowed seeds of these species in five microenvironments: log landing, gap-crown and gap-trunk, skidder trail and understory, in a tropical lowland moist rain forest in northern Bolivia. We related seed and seedling performance to light availability, soil compaction, and plant competition. Germination did not differ significantly between microenvironments but survival of germinated seeds for most species was significantly higher (P < 0.05) in the log landing (46–100%) than in the understory (0–7%). After 2 years, the tallest plants were always found in the log landing (119–190 cm) and the smallest in the understory (12–26 cm) caused by a higher relative height growth rate (RHGR) in the log landing (0.003–0.004 cm cm−1 per day) compared to the understory (0.000–0.001 cm cm−1 per day). During the first year RHGR was positively related to canopy openness for all species and negatively to the number of overtopping competitors for three species. During the second year also water infiltration explained observed variation to RHGR. These results show that abandoned log landings and logging gaps are suitable environments for the regeneration of timber species studied. This finding suggests that the removal of competitors in log landings and logging gaps combined with leaving seed trees near these microenvironments or sowing seeds, will improve regeneration of timber species in tropical forests.  相似文献   

6.
The influence of above-ground insect herbivory and other agents of damage to seedlings was studied in a field experiment. Nine different tree species were planted in each of five randomised blocks. The species were: Alnus glutinosa (L.) Gaertner, Betula pendula Roth., Fagus sylvatica L., Fraxinus excelsior L., Larix eurolepis Henry, Picea abies (L.) Karst., Prunus avium L., Quercus robur L. and Tilia cordata Mill. The seedlings were monitored through the 2000–2002 growing seasons. Pine weevils (Hylobius abietis L.) fed significantly more on Norway spruce seedlings than on all other tree species. The following rough preference order was obtained: Norway sprucelarch>birch, beech, oak>cherry>alder, ash, lime. Thus, during the conversion of single-species coniferous plantations to mixed-species broadleaved stands, the use of costly insecticides against pine weevil is not required. Short-snouted weevils (e.g. Strophosoma melanogrammum Forst. and Otiorhynchus scaber L.) and other insects caused leaf and needle area loss primarily during the first growing season.  相似文献   

7.
After an absence of approximately 70 years, gray wolves (Canis lupus) were re-introduced into Yellowstone National Park in the mid-1990s. We studied the potential influence of wolf/ungulate interactions upon willow (Salix spp.) growth in the valleys of the Gallatin and Lamar Rivers, as well as Slough and Soda Butte Creeks, in the northern Yellowstone ecosystem. When we compared willow heights from photographs taken prior to 1998 (willows <2 m tall) with those taken in 2004, we found an increase in willow height for 22 of 42 sites within the study area. Based on comparisons of the chronosequence photos, since wolf introduction none of the 16 upland riparian sites showed an increase in willow height, while 22 of 26 of the valley-bottom riparian sites had willow height increases. In 2004, willow height exhibited a strong inverse relationship with the percentage of browsed stems (r = −0.81, p < 0.01, n = 42). Results of regressions for valley-bottom sites indicated that view distance, impediment distance, and the number of bison (Bison bison) flops were inversely related to willow height (p ≤ 0.02). Increased willow heights were not significantly (p = 0.18) related to patterns of moisture availability. Willow height increases documented in this study appear to have been at least partially due to behaviorally mediated trophic cascades involving wolves and ungulates, via a mechanism of predation risk. While willow release (i.e., increased height growth) within the study area is in a very early stage, results suggest potentially important indirect effects of a top carnivore in a terrestrial food chain that may aid in the restoration of riparian species and the preservation of biodiversity.  相似文献   

8.
This study is a continuation of earlier work on apical dominance inTriplochiton scleroxylon K. Schum., aimed at the development of an early clonal selection test for branching habit and yield in tree improvement programmes. Decapitated plants of five to seven clones were treated with either: (i) two photon flux densities (photosynthetically active radiation at full or 10% sunlight, approximately 2000 and 200 μmol quanta m−2s−1 measured at midday on a clear day); (ii) two temperatures (ambient 30°C or 40°C in a polythene tent); (iii) two humidities (ambient=40–70% relative humidity at 30°C or with humidification=95–100% relative humidity at 28°C). Bud activity, shoot length and numbers of leaves produced following decapitation were all increased by high photon flux density and high humidity. In contrast to similar studies under glasshouse conditions in Britain, dominance was not re-established following the initial period of sprouting. The sprouting phase was similar in Nigeria and Britain. Clonal differences in bud activity were similar under different treatments, although there were minor changes in ranking. Increasing the air temperatures from 30 to 40°C resulted in leaf areas of 165 cm2 and 23 cm2, respectively. Normal polarity of lateral shoot production following decapitation was completely inverted by high temperature.  相似文献   

9.
I examined contrasts in response to moderate-intensity fire between two pine species (Pinus leiophylla Schiede and Deppe and P. engelmannii Carr.) and four oak species (Quercus hypoleucoides Camus., Q. arizonica Sarg., Q. emoryi Torr., and Q. rugosa Nee.) in Madrean forests in southeastern Arizona. Stem survival of pines after fire was greater than for oaks, but oaks sprouted more successfully after top-kill than did the only sprouting pine species, P. leiophylla. As a result, post-fire decline and subsequent recovery in oak populations was more marked than for the pines, and the ratio of oaks to pines decreased as a result of fire but increased during recovery. In typical forest stands, most individuals established from 1860 to 1920 at the interface between a period of high fire frequency and the onset of fire exclusion. Ages of Q. hypoleucoides were more clustered than for the pines, suggesting post-fire sprouting rather than long-term top-survival of fire. The results point to contrasts in mechanisms of persistence in this fire-prone ecosystem: fire resistance in the pines versus post-fire sprouting in the oaks. As a result, fire regime controls the balance between the two groups, with moderate-intensity fire favoring the pines and periods of low fire frequency – due to natural causes or anthropogenic fire exclusion – favoring the oaks. The species and community response patterns found in this study may apply generally to other pine-oak communities.  相似文献   

10.
The establishment and early growth of 12 species within the genera Eucalyptus, Casuarina, Melaleuca and Tipuana was tested on a saline site in southeast Queensland. Electrical conductivity (EC) in the top 50 cm of soil was measured using an electromagnetic induction method and calibrated against the EC of 1:5 soil:water suspensions. The site was then stratified into five salinity classes: 0.75–1.0, 1.0–1.25, 1.25–1.5, 1.5–1.75 and over 1.75 dSm−1. Relationships were developed for predicting the survival and height production of 18-month-old trees. These regressions explained 15–88% of the variation in survival and 2–66% of the variation in height production. Tree species were grouped by determining the EC level where height production declined by 25% relative to that at 0.75 ds m−1. Casuarina glauca, Melaleuca bracteata, Eucalyptus moluccana, Eucalyptus camaldulensis, Eucalyptus tericornis and Eucalyptus raveretiana were all highly salt tolerant (25% reductions over 1.5 dS m−1). Casuarina cunninghamiana, Eucalyptus grandis, Eucalyptus melliodora and Eucalyptus robusta exhibited moderate salt tolerance (25% reductions between 1.0 and 1.5 dS m−1). The responses to increased salinity of Tipuana tipu and Eucalyptus intermedia (25% reductions at less than 1.0 dS m−1) suggest that these species are not suitable for revegetating similar saline sites.  相似文献   

11.
In a sacred grove climax forest (protected by the local Khasi tribe for religious reasons) at Cherrapunji in north-eastern India (mean annual rainfall, 10 372 mm), litter dynamics and related fine root dynamics were studied. Litterfall and its decomposition were very pronounced during the monsoon season, unlike in other rain forests in the region. High levels of nitrogen (2.13–3.58%) phosphorus (0.62–0.91%) and potassium (1.45–1.98%) in the leaf litter of four dominant tree species—Englehardtia spicata Bl., Echinocarpus dasycarpus Benth, Sysygium cuminii (L.) Skeels and Drimycarpus racemosus Hk.f.—suggest that these species help in conserving nutrient elements, thus ensuring their rapid recycling. Different species have different nutrient release patterns which are related to litter quality and seasonal environmental factors.

The highly developed fine root system (14 000 kg ha−1) of which about 48% is located in the 0–10 cm soil depth, is important for nutrient storage and rapid recycling of nutrients. With a productivity of 3200 kg ha−1 per year, the fine root component of the climax sacred grove ecosystem has a key role to play in tight nutrient cycling. It is concluded that these results are important in understanding the fragility of rainforest ecosystems and their management.  相似文献   


12.
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   

13.
For 3 years following a severe, November 1992 tornado, abundance and growth of tree regeneration in intact forest-floor and windthrow-pit microsites were studied in three mixed pine and hardwood stands in the Georgia Piedmont, USA. The research had two objectives: (1) determine if performance of tree regeneration differed between microsite types and between pre- and post-tornado cohorts on intact forest-floor microsites, and (2) determine if variation in light and soil water availability from the disturbance affected performance of eight species artificially seeded into intact forest-floor microsites. Near each of the 42 sample points (12–20 per site) spaced on 15 m grids, species and height of tree seedlings were recorded within a 1 m radius plot of intact forest floor and the nearest windthrow pit. Intact forest-floor microsites were dominated by two late-successional species, Acer rubrum (3.5 pre-tornado stems per m2 and 1.8 post-tornado stems per m2) and Ostrya virginiana (2.6 post-tornado stems per m2), while windthrow pits were dominated by an early successional species, Liriodendron tulipifera (1.7 stems per m2). Although seedling survival did not vary significantly among species or microsite types, first-year height of seedlings in intact forest-floor microsites (24 cm) was significantly greater than those in windthrow-pit microsites (19 cm). Second-year height growth of new seedlings of Cornus florida in intact forest-floor microsites (52 cm) significantly exceeded that of many other combinations of species and microsite type. Species artificially-seeded into intact forest-floor microsites in 1994 and 1995 varied considerably in emergence (<1–24%), survival (<1–16%), and height (5–15 cm), and those with the heaviest seed survived best. From 1994 to 1995, average gap fraction, an index of light availability, decreased 17% from 0.23 to 0.19. Soil water content in 1995 under gap fractions of greater than 0.3 (21%) averaged significantly less than under gap fractions of either 0.1–0.3 (24%) or less than 0.1 (26%). Significant positive correlations were detected for relationships of emergence and survival of several species to soil water content. Overall rankings of seedling performance between microsites (intact forest floor>windthrow pits), between cohorts (pre-tornado>post-tornado origin), and among species (mid- to late->early-successional species) indicate that advanced regeneration and new seedlings of A. rubrum, O. virginiana, and C. florida will be long-term dominants of the understory because of their high abundance, initial growth responses, and shade tolerance.  相似文献   

14.
The profitability of growing a naturally emerged birch (Betula pendula Roth or Betula pubescens Ehrh.) overstory in a young Norway spruce (Picea abies (L.) Karst.) plantation was examined with empirical stand structure, growth and yield, logging cost, and logging damage models. In the projected alternatives, an overstory of either birch species was thinned to 200–1000 stems per ha at the age of 15 years and retained for another 15 years. Development of the remaining spruce stand was simulated up to rotation age (70–85 years). Alternative treatments included removing the overstory completely at 15 years, and managing a pure spruce stand that was kept free of birch throughout.

Growing a birch overstory of 200–1000 stems per ha up to age 30 years resulted in a 61–93 m3 ha−1 or 9.1–16.8% yield loss for the spruce stand due to growth retardation, and a mortality of 382–498 out of 1900 stems per ha through logging damage. This was compensated for or exceeded by the additional yield of the birch (54–173 m3 ha−1) except for the lowest stocking (200–400 stems per ha) alternatives with B. pubescens. Treatment regimes with a birch overstory were clearly the most profitable alternatives, yielding up to 151% (B. pendula) and 113% (B. pubescens) of the net present value of the pure spruce alternative, at 4% interest rate. Removing the birch overstory already at 15 years was the least profitable alternative with 79 and 83% net present values, respectively. The most profitable treatment with current technology, price, and cost structure appears to be to grow 500–800 birch per ha up to about age 40 years for B. pendula and 45–50 years for B. pubescens.  相似文献   


15.
The competition–density (C–D) effect for Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) and Masson pine (Pinus massoniana Lamb.) stands was analyzed using the reciprocal equation of the C–D effect, i.e. 1/w=Aρ+B, where w and ρ, respectively, represent mean stem volume and stand density. The C–D curve, which is given by the reciprocal equation on logarithmic coordinates, shifted upward with the progress of time. The coefficients A and B included in the reciprocal equation were calculated at each growth stage. The biological time τ defined as the integral of λ(t), the coefficient of growth in the general logistic growth curve, with respect to physical time t, tended to increase to an asymptote with increasing t. With increasing τ, the coefficient A, the reciprocal of which means the asymptote of yield (=wρ), increased abruptly up to a maximum value and then tended to decrease gradually to a constant level. On the other hand, the coefficient B, the reciprocal of which means the asymptote of mean stem volume, decreased exponentially and tended to close to zero with increasing τ. The λ(t) decreased with increasing stand age, whereas the final yield Y(t) defined as W(t) ρ, where W(t) is the asymptote of w in the general logistic growth curve, tended to increase gradually with increasing stand age.  相似文献   

16.
Research reported here has evaluated interactions of factors limiting the biological potential of slash pine (Pinus elliottii var. elliottii Engelm.) and loblolly pine (P. Taeda L.). Water and nutrients were manipulated by irrigation, weed control, and intensive fertilization. Genetic factors were incorporated as (1) improved loblolly seedlings from a commercial clonal seed orchard and (2) slash seedlings from four fast-growing, open-pollinated seed-orchard clones. Three replications of a 2 × 2 × 2 factorial experiment were established on a Typic Haplaquod soil in northern Florida using four cultural treatments: no treatment (F0H0); weed control (F0H1); fertilizer (F1F0); and combination of weed control and fertilizer (F1H1) for each species. During the first year there were large, sustained responses to all cultural practices. Loblolly and slash pine showed similar growth responses and had a lengthened growing season (60–100 days). Slash pine growth was superior to that of loblolly. Growth responses observed during the first year continued. After 4 years, irrigation had no measurable effect on tree growth. Both pine species responded equally to F1H0 and F0H1, but slash retained a slight edge. Extra nutrients]available via fertilizer, reduced competition, or additional rooting space, increased slash-pine volume index from an average of 2.0 m3 ha−1 (F0H0) to 11.90 and 13.59 m3 ha−1 (F0H1 and F1H0, respectively). The F1H1 treatment produced the largest slash-pine response, diameter at breast height (Dbh) averaged 9.84 cm, height reached 5.02 m, and volume index rose to about 22.94 m3 ha−1. With teh F1H1 treatment, average loblolly-pine height and volume exceeded that of the average slash pine. At age 4, the growth response due to increased nutrient supply was 13–29 times that of the best genetic response within F0H0 trees of the four slash-pine progenies. The best-growing slash-pine family (6–56) exceeded loblolly-pine growth under all four treatments and approximated the vigor shown by slash pine in the southern hemisphere.  相似文献   

17.
In 1989, the first recorded outbreak of hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) occurred in New Brunswick, Canada. Data were collected from ten plots established in an area infested from 1992–1994, to assess impacts of hemlock looper. Ocular and branch sample assessments of current defoliation and ocular assessments of total defoliation (all age classes of foliage) were conducted for balsam fir (Abies balsamea [L.] Mill.), white spruce (Picea glauca [Moench] Voss), and black spruce (Picea mariana (Mill.) B.S.P.). Stand response was assessed and related to cumulative defoliation. Ocular assessments were found to accurately estimate defoliation, which was significantly related to tree mortality. Ninety-two percent of balsam fir trees that had cumulative defoliation >90% died. Mortality of balsam fir was significantly (p < 0.05) related to tree size, in both lightly and severely defoliated plots; trees with DBH <11 cm sustained 22–48% higher mortality than larger trees. Mortality of balsam fir, in terms of both percent stems/ha and m3/ha merchantable volume, increased exponentially in relation to three estimates of cumulative (summed) plot mean defoliation. The strongest relationships (r2 = 0.75–0.79) were between mortality and the ocular defoliation assessment for 1990–1993 foliage. Tree mortality caused by the looper outbreak ranged from 4–14% stems/ha in lightly defoliated and from 32–100% in severely defoliated plots; merchantable volume killed was 3–14 m3/ha and 51–119 m3/ha, respectively. Relationships between mortality and defoliation were similar when defoliation was assessed for 1987–1993 and 1990–1993 foliage age classes.  相似文献   

18.
Three instrumented sites were established in 1985 along a 160-km transect from coastal evergreen rainforest on lowlands near Cairns, through rainforest on the Atherton Tableland, to semideciduous vine forest southwest of Mount Garnet. Mean annual rainfall graded from 2800 mm at coastal site (1), through 1400 mm on Atherton Tableland (2), to 760 mm at inland site (3). Each site was equipped with scaffold towers to provide regular access to upper and middle canopy.

Two shade-intolerant rainforest tree species which occurred at all three sites were used to compare tree growth and water relations; these were Acacia aulacocarpa (brown salwood) which was evergreen, and Melia azederach var. australasica (white cedar) which was leafless during onset of drought. Drought responses from coastal to inland sites were qualitatively different between Acacia and Melia. While Acacia foliage endured persistent low-moisture status, the deciduous habit of Melia provided a means of drought-avoidance.

Mean minimum leaf water-potential for deciduous Melia varied from −1.7 MPa to −2.3 MPa across all sites and seasons. By contrast, evergreen Acacia experienced increasing seasonal drought stress from coast to inland, reducing dry-season water-potentials from −2.1 Mpa to −6.4 Mpa, respectively.

Annual patterns of growth in stem cross-sectional area also varied according to species and site. For Acacia, current annual increment ( ) was 54.1 and 56.9 cm2 year−1 for coastal and tableland sites respectively. Acacia at the inland site was only 3.1 cm2 year−1.

Present results are relevant to species selection criteria in the tropics, where establishment of rainforest species can be limited by seasonal drought.  相似文献   


19.
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   

20.
Many forest plantations in the humid neo-tropics are established on degraded soils in abandoned pasture land and, with some exceptions, the species planted have not grown successfully. Studies of adaptability and growth under these conditions are scarce, particularly for native species. In this paper we present data on growth and tree form at 3 years of age for 11 species planted in abandoned pastures. The research plantation was established at La Selva Biological Station, in the Atlantic lowlands of Costa Rica (10° 26′N, 83° 59′W). Survival, diameter at breast height (DBH), total height, basal area, volume index and tree form were used to evaluate the species performance. After 3 years, Vochysia guatemalensis displayed a survival significantly higher (98%) than that of the other species. The lowest survival was 75% for Pinus tecunumanii. There were significant differences in growth measures among species. Acacia mangium exhibited significantly higher growth rates than the other species. Although this species grew rapidly, it did not develop straight single stems. About 14% of trees of A. mangium had bifurcation below DBH and more than 50% showed multiple axes or branches as large in diameter as the principal axis. The native species with the highest growth rate was Vochysia guatemalensis (DBH 12.7 cm, total height 7.5 m, volume index 55 m3 ha−1 at 3 years of age). Vochysia ferruginea exhibited a slightly lower growth rate. Both Vochysia species were ranked highly with regard to tree form, with more than 80% straight single stemmed trees. The lowest growth rates were exhibited by Pentaclethra macroloba, Pithecellobium macradenium and Virola koschnyi; however, the latter two species formed straight single terms. Pentaclethra macroloba and Inga edulis failed to form straight single stems. In general, the growth rates of the species studied were high in comparison with results reported from other tree plantations in the tropics. In spite of this, it is not prudent to draw final conclusions on the basis of these 3 year measurements.  相似文献   

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