Growth,biomass allocation and plant nitrogen concentration in Chilean temperate rainforest tree seedlings: effects of nutrient availability

Seedlings of nine southern Chilean trees were grown at three nutrient supply rates, to examine the roles of growth rate, biomass distribution and nutrient use traits in determining species natural distributions on resource gradients. Relative growth rate (RGR) showed no overall relationship with species site requirements, although RGR of fertile-site species tended to be more responsive to nutrient supply. In the low-nutrient treatment, infertility-tolerant Fitzroya cupressoides showed a higher RGR rank than a fertility-demanding species (Laurelia philippiana) which outgrew it substantially at the highest supply rate. This reversal of RGR ranks was associated with divergent nutrient use responses: at high nutrient supply both spp. had similar plant nitrogen concentrations (PNC), whereas at the low supply rate Fitzroya’s production of biomass per unit of assimilated N was twice that of Laurelia’s. However, this pattern does not appear to serve as a general explanation of the respective distributions of the study species, as RGR ranks of most species were unaltered by nutrient supply. At low nutrient availability, no clear differences in shoot:root ratio (SRR) were apparent between poor-site and fertile-site species. However, at high nutrient availability, SRR was markedly higher in the latter, resulting from differences in biomass allocation to stems (not leaves). Leaf area ratios (LAR) were higher in fertile-site species than in those tolerant of low fertility, because of differences in specific leaf area rather than leaf weight ratio. Very high LAR at high nutrient supply was characteristic of most shade-tolerant angiosperms, but not of shade-tolerant conifers. Although PNC showed no overall differences between poor- and fertile-site species, sensitivity of PNC to external supply rate was greatest in two infertility-tolerant conifers. In contrast, the angiosperm Weinmannia trichosperma, although tolerant of low fertility, responded to increased nutrient supply with greatly increased RGR and little change in PNC. Results show little trait convergence between conifers and angiosperms in adaptation both to shade and to infertile soils; i.e. fitness of different taxa in a given environment may hinge on different trait combinations. Received: 12 September 1995 /Accepted: 14 June 1996     

Age structure and regeneration of old growthCryptomeria japonica forests on Yakushima Island

The regeneration process ofCryptomeria japonica forests was studied from surveys of age and initial growth of the coniferous stumps in plots of 2.66 ha in total on Yakushima Island, south Japan. The conifers germinated during particular regeneration periods each of which was shorter than 100 years. The periods repeated themselves several times in each plot, and conifers of each period formed patches. Both tree cutting and natural gap formation of the canopies initiated the regenerations. The saplings that were thought to have germinated before the initiation of the regeneration grew slowly. After the initiation, the saplings that germinated earlier grew more quickly. For the three codominant conifers:Cryptomeria japonica, Tsuga sieboldii, andAbies firma, the shade tolerance was inversely correlated with maximum age. Even the most shade-tolerantA. firma was a gap-dependent species in regeneration periods, and there were no species differences in the colonizing times during the regeneration period. Shade-intolerant long-lived species and shade-tolerant short-lived species coexisted as climax species, not as alternate species in the sere of succession.     

Regeneration dynamics and life history differences in southern Chilean Nothofagus forests: a synthesis

Large, infrequent natural disturbances have been proposed as a key component in determining the distribution and abundance of Nothofagus in southern Andean temperate forests. In this study, a comparison of influences of small-to-intermediate-sized natural disturbances and effects of selective logging on the establishment and growth of Nothofagus forests in south-central Chile are synthesized with the results of other forest studies to develop general hypotheses on the regeneration dynamics of southern Chilean Nothofagus alpina forests. A synthesis is given for regeneration pattern in the abundance of 18 temperate rain forests in the Andean Range, Chile. The study aimed to determine the role of life history differences in promoting coexistence of the five main tree species (N. alpina, N. dombeyi, N. pumilio, N. macrocarpa and Laurelia philippiana) in N. alpina-dominated forests. Age data reported for N. alpina, a shade mid-tolerant emergent tree in the temperate rain forests of southern Chile, indicate maximum lifespans > 650 years, figures unprecedented for N. alpina. In low elevation stands, N. alpina coexists with broad-leaved evergreen tree species, such as L. philippiana, L. sempervirens, Persea lingue, and in these stands an intermittent establishment of Nothofagus occurred and appeared to be most dependent on small-to-intermediate disturbances. In high-elevation stands, in contrast, Nothofagus establishment was less dependent on disturbance, regeneration being much more continuous even in the absence of canopy openings. The forests studied provide another example of the general pattern of increasing dependence of Nothofagus on disturbance towards the more productive end of the environmental gradients. As a long-lived pioneer and despite its dependence on disturbance in lowland sites, N. alpina has been subject to selection for complementary growth, adult survivorship, and mid-tolerance to shade. Thus, interspecific differences in juvenile and adult life history characteristics of N. alpina and its competitors may be sufficient to maintain its persistence in the landscape. In conclusion, this study of population structures and replacement patterns provides a comprehensive picture on our understanding of regeneration dynamics and trait differentiation in southern temperate forests by recognizing both the influences of environmental gradients (i.e., altitude) on competing species and the disturbance regimes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Removal of Encroaching Conifers to Regenerate Degraded Aspen Stands in the Sierra Nevada

Aspen is considered a keystone species, and aspen communities are critical for maintaining biodiversity in western landscapes. Inventories of aspen stand health across the Eagle Lake Ranger District (ELRD), Lassen National Forest, California, U.S.A., indicate that 77% of stands are in decline and at risk of loss as defined by almost complete loss of mature aspen with little or no regeneration. This decline is due to competition from conifers establishing within aspen stands as a result of modification of natural fire regimes coupled with excessive browsing by livestock. Restoration treatments were implemented in four aspen stands in 1999 using mechanical equipment to remove competing conifers to enhance the growth environment for aspen. Recruitment and establishment of aspen stems were measured in treated stands (removal of competing conifers) and non‐treated stands (control) immediately prior to treatment and 2 and 4 years post‐treatment. There was a significant increase in total aspen stem density and in two of three aspen regeneration size classes for treated stands compared to controls. Pre‐treatment total aspen density was positively associated with total aspen density and density in all size classes of aspen (p < 0.001). The results demonstrate that mechanical removal of conifers is an effective treatment for restoring aspen.     

Seed size and shade-tolerance: a comparative analysis of North American temperate trees

Large seed size is a trait associated with plant species of mature, closed habitats, and is thought to supply an ample nutrient reserve necessary for seedling establishment. While this relationship has been shown for annuals and short-lived perennials, it is poorly documented for trees. A comparative method was used to determine whether North American temperate tree species which typically establish in shady conditions have larger seeds than those requiring more open conditions. Both angiosperms (hardwoods) and gymnosperms (conifers) were involved in the study. A significant relationship was found between large seed mass and shade-tolerance for angiosperms, but not for gymnosperms. These contrasting results seem to relate to unique evolutionary opportunities or constraints in different taxa. The absence of a relationship for gymnosperms is discussed in terms of character traits which might prevent seed size selection in response to shade. The finding for angiosperms underlines the importance of the regeneration niche in promoting coexistence among temperate hardwood species through seed size differentiation. Received: 18 March 1997 / Accepted: 26 November 1997     

A long‐term record of Nothofagus dominance in the southern Andes,Chile

Abstract The general model of regeneration dynamics in Nothofagus forests of southern South America could have value in community ecology if predictive relationships between disturbance history, functional traits and site attributes could be identified. Examined here is the proposal that on favourable sites shade‐intolerant Nothofagus are likely not to survive in competition with shade‐tolerant, broad‐leaved evergreen taxa of temperate rain forests, and persistence, thus, is dependent on periodic coarse‐scale disturbance. Comparison of stand dynamics of three old‐growth Nothofagus forests at different elevations in the southern Andes, Chile where deciduous Nothofagus alpina dominates the upper canopy, and examination of the life history trade‐offs of this variation were made. Stem density of all stems ≥5.0 cm d.b.h. was 233–303 stems per hectare, and basal area was 123.9–171.0 m²ha^?1. Maximum lifespan of N. alpina was found to be greater than ca 640 years, exceeding all previously reported ages for this species in the region. Forests had a stable canopy composition for this long‐term, but some appeared to lack effective regeneration of N. alpina in recent years. Regeneration of N. alpina was generally greater in disturbed stands and higher elevation than in undisturbed stands and at lower elevation. Recruitment emerged to be strongly affected by competitive over‐ and understorey associates. There was a gradient of increasing dependence of N. alpina on disturbance towards the more productive end of the environment gradients, and hence less dependence of N. alpina on disturbance for its regeneration towards higher elevation. The study confirms that changes in forest composition may be explained by processes occurring in accordance with the predictions of the existing model of Nothofagus regeneration dynamics, providing stronger evidence specifically directed at mid‐tolerant N. alpina, and by factoring out regeneration dynamics on favourable sites. Thus, for N. alpina, trait differences probably contribute to the competitive advantage over its associates in productive habitats, and may be linked to small‐to‐intermediate‐sized disturbances which inevitably occur as older trees die, enabling N. alpina to persist in forests and therefore maintain species coexistence for the long‐term.     

A latitudinal gradient in tree growth response to climate warming in the Siberian taiga

We investigated the climate response of three Siberian taiga species, Larix cajanderi, Picea obovata, and Pinus sylvestris, across a latitudinal gradient in central Siberia. We hypothesized that warming is more frequently associated with increased growth for evergreen conifers (P. obovata and P. sylvestris) than for L. cajanderi, and for northern than for southern sites; we also hypothesized that increased growth is associated with a positive trend in normalized difference vegetation index (NDVI). In mixed stands, growth of L. cajanderi and P. obovata increased over time, but the larger growth increases in P. obovata may presage a shift in competitive balance between these species. Climate response varied among and within populations of all species, and positive responses to temperature prevailed at northern sites, where trees grew faster in years with warm early summers. Negative responses to warming declined along the south to north latitudinal gradient. We observed considerable variability in climate response within populations which even exceeded that among species or sites. Tree response to climate was correlated with NDVI trends, indicating that patterns of tree‐growth response to climate were indicative of a coherent landscape‐scale response to warming. Our findings suggest that increased productivity with warming is likely only in the northern reaches of the Siberian taiga. An increased prevalence of evergreen conifers in areas currently dominated by deciduous Larix species also seems likely.     

Regeneration and coexistence of two Abies species dominating subalpine forests in central Japan

Summary The mechanism of coexistence of the dominant firs Abies veitchii and A. mariesii is described in relation to regeneration patterns for climax subalpine forests of the northern Yatsugatake Mountains, central Honshu, Japan. Two mature stand types, pure conifer stands of Abies spp., and mixed stands of Abies spp. and hardwoods (mainly the birch Betula ermanii), are distinguished. Pure stands are likely to show simultaneous decay, followed by evenaged regeneration of stand-floor seedlings (<20 cm tall), Rapidly growing A. veitchii dominates over A. mariesii in this type of regeneration, which is occasionally invaded by light-demanding Betula. In constrast, mixed stands degenerate rather slowly, followed by the regeneration of Abies from the bank of suppressed saplings (>20 cm tall), which persist only in mixed stands. The more shade-tolerant A. mariesii is supeior in this type of regeneration, while Betula does not succeed, and mixed stands change to pure stands with time. The fact that two patterns of Abies regeneration occur in a certain ratio in the forest is what enables the two Abies species to coexist. A simple dynamical system model supports this conclusion.     

Development patterns in young conifer-hardwood forests of interior Alaska

Abstract. The age structure and growth patterns of 53 young conifer-hardwood stands on upland, south-facing sites of interior Alaska were analyzed to determine the length of time for stand establishment after disturbance, the composition of early-successional stands compared to existing stands, and the potential for late-successional stands dominated by conifers. Mixed stands of Picea glauca, Populus tremuloides and Betula papyrifera represented five plant community types and developed as single cohorts after stand-replacement fires. In the Populus tremuloides/Arctostaphylos uva-ursi and Populus tremuloides/Shepherdia canadensis community types, hardwoods established rapidly and Picea glauca established slowly. In contrast, stands in the Betula papyrifera-Populus tremuloides/Viburnum edule, Betula papyrifera-Populus tremuloides/Alnus crispa, and Picea glauca-Betula papyrifera/Hylocomium splendens community types generally developed as a result of rapid, concurrent establishment of conifers and hardwoods. These single-cohort, mixed species development patterns are not consistent with continual establishment of conifers and are likely the result of unique life-history traits and frequent stand-replacement fires.     

Relationships of leaf dark respiration with light environment and tissue nitrogen content in juveniles of 11 cold-temperate tree species

It has been argued that plants adapted to low light should have lower carbon losses via dark respiration (Rd) than those not so adapted, and similarly, all species would be expected to down-regulate Rd in deep shade, because the associated advantages of high metabolic potential cannot be realized in such habitats. In order to test these hypotheses, and to explore the determinants of intraspecific variation in respiration rates, we measured Rd, leaf mass per unit area (LMA), and nitrogen content of mature foliage in juveniles of 11 cold-temperate tree species (angiosperms and conifers), growing in diverse light environments in forest understories in northern Minnesota. Among the seven angiosperm species, respiration on mass, area, and nitrogen bases showed significant negative overall relationships with shade tolerance level. Mass-based respiration rates (Rd _mass) of angiosperms as a group showed a significant positive overall relationship with an index of light availability (percentage canopy openness, %CO). Rd _mass of most conifers also showed evidence of acclimation of Rd _mass to light availability. LMA of all species also increased with increasing %CO, but this response was generally much stronger in angiosperms than in conifers. As a result, the response of area-based respiration (Rd _area) to %CO was dominated by ΔRd _mass for conifers, and by ΔLMA for most angiosperms, i.e., functional types differed in the components of acclimation of Rd _area to light availability. Among the seven angiosperm species, the relationships of leaf N on a mass basis (N _mass) with %CO were modulated by shade tolerance: negative slopes in shade-tolerant species may be related to the steep increases in LMA of these taxa along gradients of increasing light intensity, and associated dilution of N-rich, metabolically active tissue by increasing investment in leaf structural components. Although N _mass was therefore an unreliable predictor of variation in Rd _mass along light gradients, respiration per unit leaf N (Rd/N) was significantly positively correlated with %CO for most species. This probably reflects variation in the proportion of leaf N allocated to protein and/or the influence of leaf carbohydrate status on Rd. Species shade tolerance differences were not significantly correlated with the magnitude of either ΔRd _mass or ΔRd _area, indicating that variation in acclimation potential of Rd is much less important than inherent differences in this trait. Acclimation of Rd _mass to light availability appears to be a generalized feature of juvenile trees, and the important ecological trade-off is likely between high metabolic capacity in high light and low respiratory losses in low light. Received: 15 April 1999 / Accepted: 24 October 1999     

Persistent soil seed banks in old-growth Hyrcanian Box tree (Buxus hyrcana) stands in northern Iran

Little is known about the soil seed bank and the influence of plant communities on the interaction between the seed bank and aboveground vegetation in the Hyrcanian temperate deciduous forest. We surveyed species composition and diversity of the persistent soil seed bank and the aboveground vegetation in six community types in old-growth Hyrcanian Box tree (Buxus hyrcana) stands in northern Iran. Fifty-two species with an average of 3,808 seeds/spores m⁻² germinated; forbs accounted for 64% of the seed bank flora. Thirty-four species in the aboveground vegetation were not presented in the seed bank, 32 species in the seed bank were not found in the vegetation, and 20 species were in both. The dominant tree species were Diospyros lotus and Alnus subcordata with an average of 17 and 4.6 seeds m⁻², respectively. Our results suggest that (1) vernal geophytes and shade-tolerant perennials are not incorporated in the seed bank, (2) early successional species are well represented in the seed bank, (3) plant community type has significant impacts on seed bank densities, and seed bank richness and diversity were significantly related to presence/absence of Box tree in the aboveground vegetation. The persistent seed bank contained species that potentially have a negative impact on the regeneration of forests, thus forest managers should retain old-growth Hyrcanian Box tree stands to conserve disturbance-sensitive indicator forest species.     

Nesting habitat of Warbling Vireos across an elevational gradient in the southern Sierra Nevada

ABSTRACT.   Populations of Warbling Vireos ( Vireo gilvus ) are declining in California, apparently due to low reproductive success. From 1989–2002, I studied the nest-site selection and reproductive success of Warbling Vireos across an elevational gradient in the southern Sierra Nevada. Warbling Vireos regularly nested in upland coniferous forests with few or no deciduous trees, and tree species used by nesting vireos included five species of conifers and four species of deciduous trees. Overall, hardwoods were used more than expected based on their availability, but 69% of all nests were in conifers. Hardwood trees were found only in low and mid-elevation ponderosa pine ( Pinus ponderosa ) and mixed-conifer sites. In low-elevation ponderosa pine habitat, 87% of nests were in hardwoods, with 67% in California black oaks ( Quercus kelloggii ), a species that typically occupies upland sites. In mixed-conifer sites where reproductive success was high, 65% of nests were in incense cedar ( Calocedrus decurrens ) and California black oak was the next most commonly used species. Because fire suppression has likely increased numbers of shade-tolerant tree species like incense cedar, shade-intolerant species like black oaks may have been more important as a nest substrate for vireos in the past. Only conifers were used as nesting substrates at higher elevations. Nest success was greater for Warbling Vireos that nested in tall trees in areas with high basal area. My results suggest that Warbling Vireos in the Sierra Nevada would benefit from management activities that encourage retention and recruitment of California black oaks at lower elevations, and development of stands with large trees, dense foliage, and semi-open canopy throughout their elevation range.     

Differential effects of emergent Nothofagus dombeyi on growth and basal area of canopy species in an old‐growth temperate rainforest

Question: Does overyielding of tree species mixtures in vertically stratified forests depend on complementary light use? Location: Andes of south‐central Chile. Methods: Basal area data were obtained from 80 circular plots distributed regularly throughout old‐growth stands with an emergent Nothofagus dombeyi tier over a canopy composed mainly of Laureliopsis philippiana and Saxegothaea conspicua. Radial growth was measured from cores obtained from trees at the centre of each plot. The effects of competition on growth were evaluated through a competition index (CI) based on distances to and diameters of the two nearest neighbours. Results: Overall, basal area of the canopy species was only weakly affected by the number of N. dombeyi per plot, and with basal area of N. dombeyi. However, the two main canopy species responded differently: whereas basal area of S. conspicua was negatively correlated with that of N. dombeyi, that of L. philippiana showed no response. Radial growth of S. conspicua was negatively correlated with CI calculated from canopy trees and more weakly so from emergent N. dombeyi. In contrast, radial growth of L. philippiana was not affected by competition with either canopy or emergent neighbours. Conclusions: Results indicate that emergent N. dombeyi tend to depress growth and basal area of S. conspicua, but not of the more shade‐tolerant L. philippiana. This supports the proposal that enhancement of wood production in stratified mixtures will be greatest when component species have strongly contrasting light use traits.     

Tree regeneration and future dynamics of the laurel forest on Tenerife,Canary Islands

Abstract. We studied two sites in the laurel forest of Tenerife to predict future changes in canopy composition. We used two projection methods: Horn's ‘Markovian Projection’, which utilizes information on juveniles in the vicinity of canopy trees, and a 'Stand Projection’, which ignores such information. We performed these projections both including and excluding a-sexual regeneration. Although all of our projections predict a change in species composition, inclusion of a-sexual reproduction decreased the magnitude of successional change. The persistence of Prunus lusitanica and Ilex canariensis appears to be highly dependent on a-sexual regeneration. Both the Markov- and stand projections predict a slight convergence in species composition between the two sites when only sexual regeneration is considered, and also a higher dominance of the shade-tolerant species Laurus azorica. When a-sexual regeneration is also considered, some divergence is shown, with less projected change in the stand projection than in the Markov projection. In spite of some differences between the models, general patterns such as an increase of shade-tolerant species (Laurus azorica and Prunus lusitanica) and a decrease of shade-intolerant species (Erica arborea, Erica scoparia and Myrica faya) are consistent.     

The tortoise and the hare: ecology of angiosperm dominance and gymnosperm persistence

Gymnosperms, and conifers in particular, are sometimes very productive trees yet angiosperms dominate most temperate and tropical vegetation. Current explanations for angiosperm success emphasize the advantages of insect pollination and seed dispersal by animals for the colonization of isolated habitats. Differences between gymnosperm and angiosperm reproductive and vegetative growth rates have been largely ignored. Gymnosperms are all woody, perennial and usually have long reproductive cycles. Their leaves are not as fully vascularized as those of angiosperms and are more stereotyped in shape and size. Gymnosperm tracheids are generally more resistant to solute flow than angiosperm vessels. A consequence of the less efficient transport system is that maximum growth rates of gymnosperms are lower than maximum growth rates of angiosperms in well lit, well watered habitats. Gymnosperm seedlings may be particularly uncompetitive since their growth depends on a single cohort of relatively inefficient leaves. Later, some gymnosperms attain a higher productivity than co-occurring angiosperm trees by accumulating several cohorts of leaves with a higher total leaf area. These functional constraints on gymnosperm growth rates suggest that gymnosperms will be restricted to areas where growth of angiosperm competitors is reduced, for example, by cold or nutrient shortages. Biogeographic evidence supports this prediction since conifers are largely confined to high latitudes and elevations or nutrient-poor soils. Experimental studies show that competition in the regeneration niche (between conifer seedlings and angiosperm herbs and shrubs) is common and significantly affects conifer growth and survival, Fast-growing angiosperms, especially herbs and shrubs, may also change the frequency of disturbance regimes thereby excluding slower-growing gymnosperms. Shade-tolerant and early successional conifers share similar characteristics of slow initial growth and low plasticity to a change in resources. Shade-tolerant gymnosperms would be expected to occur only where forest openings are small or otherwise unsuitable for rapid filling by fast-growing angiosperm trees, lianas or shrubs. The limited evidence available suggests that shade-tolerant conifers are confined to forests with small gap sizes where large disturbances are very rare. The regeneration hypothesis for gymnosperm exclusion by angiosperms is consistent with several aspects of the fossil record such as the early disappearance of gymnosperms from early successional environments where competition with angiosperms would have been most severe. However there are unresolved difficulties in interpreting process from paleoecological pattern which prevent the testing of alternative hypotheses.     

Increase in nonnative understorey vegetation cover after nonnative conifer removal and passive restoration

Nonnative conifers are widespread in the southern hemisphere, where their use as plantation species has led to adverse ecosystem impacts sometimes intensified by invasion. Mechanical removal is a common strategy used to reduce or eliminate the negative impacts of nonnative conifers, and encourage native regeneration. However, a variety of factors may preclude active ecological restoration following removal. As a result, passive restoration – unassisted natural vegetation regeneration – is common following conifer removal. We asked, ‘what is the response of understorey cover to removal of nonnative conifer stands followed by passive restoration?' We sampled understorey cover in three site types: two‐ to ten‐year‐old clearcuts, native forest and current plantations. We then grouped understorey species by origin (native/nonnative) and growth form, and compared proportion and per cent cover of these groups as well as of bare ground and litter between the three site types. For clearcuts, we also analysed the effect of time since clearcut on the studied variables. We found that clearcuts had a significantly higher average proportion of nonnative understorey vegetation cover than native forest sites, where nonnative vegetation was nearly absent. The understorey of clearcut sites also averaged more overall vegetation cover and more nonnative vegetation cover (in particular nonnative shrubs and herbaceous species) than either plantation or native forest sites. Notably, 99% of nonnative shrub cover in clearcuts was the invasive nonnative species Scotch broom (Cytisus scoparius). After ten years of passive recovery since clearcutting, the proportion of understorey vegetation cover that is native has not increased and remains far below the proportion observed in native forest sites. Reduced natural regeneration capacity of the native ecosystem, presence of invasive species in the surrounding landscape and land‐use legacies from plantation forestry may inhibit native vegetation recovery and benefit opportunistic invasives, limiting the effectiveness of passive restoration in this context. Abstract in Spanish is available with online material.     

Seed size,establishment sites and species coexistence in a Chilean rain forest

Abstract. Seedling densities on the forest floor and on elevated microsites (logs and stumps) were compared for eight woody species in a temperate rain forest in southern Chile. Degree of association with elevated microsites varied significantly between species, showed no systematic relationship with reported shade tolerance, but was significantly negatively correlated with seed mass. Large-seeded Podocarpus nubigena established preferentially on undisturbed forest floor sites, whereas seedlings of small-seeded species such as Nothofagus nitida and Laurelia philippiana were found mainly on fallen logs and stumps. The abundance of large seedlings and saplings of N. nitida on logs/stumps, and the growth forms of canopy trees, confirm that recruitment of this species occurs mainly on decaying wood. The relationship between seed size and microsite preferences may be caused by effects of seed size on (1) ability to establish in forest floor litter and (2) retention of seeds on logs. Seedling occupancy of logs and stumps varied with state of decay. Few seedlings of any species were present on logs in the early stages of decay. N. nitida established earlier than the other species, attaining maximum abundance on wood in the middle decay classes. Species richness and overall seedling abundance were highest on wood in advanced stages of decay. Seed size differences are suggested as a determinant of differential utilization of forest floor heterogeneity, and hence of plant species coexistence.     

Conifer regeneration failure in New Zealand: dynamics of montane Libocedrus bidwillii stands

Size and age structure analysis were used to reconstruct the population dynamics of six apparently old and stable stands dominated by the conifers Libocedrus bidwillii and/or Dacrydium biforme in Camp Creek, Westland, New Zealand. All stands contained relatively even-aged groups of Libocedrus that had probably originated after either mass movement or windthrow. The age distributions of stands reflected the effects of disturbances 200–400 yr ago.There was no evidence to support synchronous failure of regeneration of Libocedrus and Dacrydium biforme. Between 1600 and 1800 A.D., the period of the postulated conifer regeneration gap, over 70% of trees of these species had established. A lack of Libocedrus regeneration over the last 200 yr reflects a lack of disturbance over that time. Because of the dominating influence of disturbances and other factors it may be inappropriate to use tree population structures alone to substantiate or refute claims of recent climate change.     

Dynamics of forests with Araucariaceae in the western Pacific

Abstract. Several species of Araucaria and Agathis (Araucariaceae) occur as canopy emergents in rain forests of the western pacific region, often representing major components of total stand biomass. New data from permanent forest plots (and other published work) for three species (Araucaria hunsteinii from New Guinea, A. laubenfelsii from New Caledonia, and Agathis australis from New Zealand) are used to test the validity of the temporal stand replacement model proposed by Ogden (1985) and Ogden & Stewart (1995) to explain the structural and compositional properties of New Zealand rain forests containing the conifer Agathis australis. Here we propose the model as a general one which explains the stand dynamics of rain forests with Araucariaceae across a range of sites and species in the western Pacific. Forest stands representing putative stages in the model were examined for changes through time in species recruitment, growth and survivorship, and stand richness, density and basal area. Support for the model was found on the basis of: 1. Evidence for a phase of massive conifer recruitment following landscape-scale disturbances (e.g. by fire at the Huapai site, New Zealand for Agathis australis); 2. Increasing species richness of angiosperm trees in the pole stage of forest stand development (i.e. as the initial cohort of conifers reach tree size; >10 cm DBH); 3. A high turnover rate for angiosperms (<100 yr), and low turnover for conifers (≥ 100 yr) in the pole stage, but similar turnover rates for both components (50–100 yr) as forests enter the mature to senescent phase for the initial conifer cohort; 4. Very low rates of recruitment for conifers within mature stands, and projected forest compositions which show increasing dominance by angiosperm tree species; 5. A low probability of conifer recruitment in large canopy gaps created by conifer tree falls during the initial cohort senescent phase, which could produce a second generation low density stand in the absence of landscape scale disturbance; 6. Evidence that each of the three species examined required open canopy conditions (canopy openness > 10 %) for successful recruitment. The evidence presented here supports the temporal stand replacement model, but more long-term supporting data are needed, especially for the phase immediately following landscape level disturbance.     

Gap formation, microsite variation and the conifer seedling occurrence in a subalpine old-growth forest, central Japan

To evaluate the effects of canopy gaps and forest floor microsites (soil, fallen logs, root-mounds, buttresses and stumps) on regeneration of subalpine forests, the gap regeneration and seedling occurrence of conifers (Abies mariesii, Abies veitchii, Picea jezoensis var. hondoensis and Tsuga diversifolia) were studied in two stands of a subalpine old-growth forest, central Japan. The percentage of gap area to total surveyed area was 11.2–11.3% in the stands. Gap regeneration was not common for P. jezoensis var. hondoensis and T. diversifolia. In contrast, gap regeneration by advanced regeneration was relatively common for Abies. Seedling occurrence of P. jezoensis var. hondoensis and T. diversifolia was restricted on elevated surfaces such as stumps and root-mounds, while Abies seedlings could occur on soil as well as on elevated surfaces. Rotten stumps were the most favorable microsites for conifer seedling occurrence, which covered small area in the forest floor. Although canopy gaps were not always favorable for seedling occurrence, all conifer seedlings were larger under canopy gaps than under closed canopy. Canopy gaps and forest floor microsites clearly affected seedling occurrence and growth of conifers. This suggests that regeneration of conifers is related to the difference of growth advantage under canopy gaps and favorable microsites for seedling occurrence.