The dynamics of old-growth Pseudotsuga forests in the western Cascade Range,Oregon, USA

Size and age structure, spatial analysis, and disturbance history were used to analyse the population structures and regeneration patterns of 8 conifer stands in the central western Cascade Range, Oregon, USA. Variation in forest structure reflected the effects of frequent (20–50 yr) low-intensity fires and treefalls, infrequent (100–200 yr) localised, intense fires, and extensive fires that resulted in stand replacement (every ca 400 yr?).The amount of canopy removed and the size of openings formed by fires and treefalls were important determinants of subsequent forest establishment. Single or several species stands of Pseudotsuga and/or Abies procera, or mixed species stands of Pseudotsuga, Abies procera, Tsuga heterophylla and Abies amabilis established in openings where intense fires had removed most of the canopy trees over several ha. Multi-tiered and multi-aged stands, often containing 400–500 yr-old Pseudotsuga and variously-sized more or less even-aged patches of younger shade tolerant Tsuga heterophylla and/or Abies amabilis, occurred where lower-intensity fires did not kill all overstorey trees or where treefalls occurred after the initial fire.Current regeneration processes are influenced by overstorey composition, the availability and size of canopy openings, and the availability of substrates suitable for regeneration. Tsuga heterophylla and Abies amabilis established under Pseudotsuga menziesii and Abies procera canopies and in small canopy openings (<400 m²) created by windfalls, but rarely under Tsuga. Down logs and stumps were favoured establishment sites for Tsuga.The disturbance regime of fires of low-to moderate-intensity, windfalls, and occasional fires that result in extensive stand replacement contrasts with the pattern of infrequent, catastrophic disturbances proposed for other areas of the Pacific Northwest. Although fires at stand establishment commonly determine much of the composition, structure, and subsequent stand development, canopy replacement by shade tolerant species occurs as the different life histories of the species are expressed in response to various disturbances differing in intensity and frequency. Such a non-equilibrium view of vegetation change is consistent with many other fire-dominated forests of the western United States.     

Aluminum,Fe, Ca,Mg, K,Mn, Cu,Zn and P in above- and belowground biomass. I.Abies amabilis andTsuga mertensiana

In a mature mixed subalpine stand ofTsuga mertensiana andAbies amabilis, significantly higher Al levels were found in foliage, branch and root tissues ofT. mertensiana.Tsuga mertensiana had significant increases in Al, Ca and Mn levels with increasing foliage age. In current foliage,T. mertensiana had lower levels of Ca, similar levels of Mg and P, and higher levels of Mn thanA. amabilis. Both tree species had Cu and Fe present at higher levels in branch than foliage tissues. Fine roots had the highest concentrations of Al, Fe and Cu but the lowest Ca and Mn concentrations of all tissues analyzed. In the roots of both species, phloem tissues always had significantly higher Al levels than xylem. Fine roots (< 1 and 1–2 mm) ofT. mertensiana had higher Al levels than were found inA. amabilis. Roots greater than 2 mm in diameter exhibited no significant differences in Al levels in phloem or xylem tissue betweenA. amabilis andT. mertensiana. The two species show a clear difference in their ability to accumulate specific elements from the soil.     

Growth releases of three shade‐tolerant species following canopy gap formation in old‐growth forests

Questions: Do the number, duration and magnitude of growth releases following formation of natural, fine‐scale canopy gaps differ among shade‐tolerant Thuja plicata, Tsuga heterophylla and Abies amabilis? What is the relative importance of tree‐level and gap‐level variables in predicting the magnitude and duration of releases? What does this tell us about mechanisms of tree species coexistence in such old‐growth forests? Location: Coastal British Columbia, Canada. Methods: We estimated the timing of formation of 20 gaps using dendroecological techniques and extracted increment cores from all three species growing around or within gaps. Using a species‐ and ecosystem‐specific release‐detection method, we determined the number of trees experiencing a release following gap formation. We quantified the duration and magnitude of individual releases and estimated the influence of tree‐level and gap‐level variables on these release attributes. Results: Eighty‐seven per cent (304 of 348) of all trees experienced a release following gap formation. T. heterophylla and A. amabilis experienced higher magnitude and longer duration releases than T. plicata. The effect of diameter on the duration of releases varied among species, with T. heterophylla and A. amabilis experiencing decreasing, and T. plicata experiencing increasing, duration of releases with increasing diameter. The effect of growth rate prior to a release on the magnitude of releases varied among trees of different diameters, with the slowest growing and smallest individuals of all species experiencing the most intensive releases. Conclusions: Our results provide detailed information on the number, duration and magnitude of growth releases of the above three species following gap formation. Differences in response to canopy gaps suggest differences in how these species ascend to the canopy strata. T. plicata may be less dependent on gaps to reach the canopy. Differing strategies for ascending to the canopy strata may be important in facilitating coexistence of these three species in old‐growth forests of coastal British Columbia.     

From canopy to seed: Loss of snow drives directional changes in forest composition

Climate change is altering the conditions for tree recruitment, growth, and survival, and impacting forest community composition. Across southeast Alaska, USA, and British Columbia, Canada, Callitropsis nootkatensis (Alaska yellow‐cedar) is experiencing extensive climate change‐induced canopy mortality due to fine‐root death during soil freezing events following warmer winters and the loss of insulating snowpack. Here, we examine the effects of ongoing, climate‐driven canopy mortality on forest community composition and identify potential shifts in stand trajectories due to the loss of a single canopy species. We sampled canopy and regenerating forest communities across the extent of C. nootkatensis decline in southeast Alaska to quantify the effects of climate, community, and stand‐level drivers on C. nootkatensis canopy mortality and regeneration as well as postdecline regenerating community composition. Across the plot network, C. nootkatensis exhibited significantly higher mortality than co‐occurring conifers across all size classes and locations. Regenerating community composition was highly variable but closely related to the severity of C. nootkatensis mortality. Callitropsis nootkatensis canopy mortality was correlated with winter temperatures and precipitation as well as local soil drainage, with regenerating community composition and C. nootkatensis regeneration abundances best explained by available seed source. In areas of high C. nootkatensis mortality, C. nootkatensis regeneration was low and replaced by Tsuga. Our study suggests that climate‐induced forest mortality is driving alternate successional pathways in forests where C. nootkatensis was once a major component. These pathways are likely to lead to long‐term shifts in forest community composition and stand dynamics. Our analysis fills a critical knowledge gap on forest ecosystem response and rearrangement following the climate‐driven decline of a single species, providing new insight into stand dynamics in a changing climate. As tree species across the globe are increasingly stressed by climate change‐induced alteration of suitable habitat, identifying the autecological factors contributing to successful regeneration, or lack thereof, will provide key insight into forest resilience and persistence on the landscape.     

Vesicular endophytes in roots of the Pinaceae

Vesicles and hyphae typical of vesicular-arbuscular mycorrhizae (VAM) were common in seedlings of Pseudotsuga menziesii, Abies lasiocarpa and Tsuga mertensiana growing in openings where herbaceous hosts of these fungi were common. Seedlings of A. lasiocarpa, Tsuga heterophylla, and T. mertensiana growing under closed forest canopies also had vesicles but at a much lower incidence than seedlings in the openings. The Pinaceae are generally assumed to be ectomycorrhizal, but Glomus-type colonizations occurred on the same seedlings as the ectomycorrhizae. The ecological significance of abundant VAM-type endophytes in otherwise ectomycorrhizal hosts deserves comprehensive study.     

Loss of oak dominance in dry-mesic deciduous forests predicted by gap capture methods

Gap capture methods predict future forest canopy species composition from the tallest trees growing in canopy gaps rather than from random samples of shaded understory trees. We used gap capture methods and a simulation approach to forecast canopy composition in three old oak forests (Quercus spp.) on dry-mesic sites in southern Wisconsin, USA. In the simulation, a gap sapling is considered successful if it exceeds a threshold height of 13–17 m (height of maximum crown width of canopy trees) before its crown center can be overtopped by lateral crown growth of mature trees. The composition of both the tallest gap trees and simulated gap captures suggests that 68–90% of the next generation of canopy trees in the stands will consist of non-Quercus species, particularly Ulmus rubra, Carya ovata and Prunus serotina. Quercus species will probably remain as a lesser stand component, with Quercus alba and Quercus rubra predicted to comprise about 19% of successful gap trees across the three stands. Several methods of predicting future canopy composition gave similar results, probably because no gap opportunist species were present in these stands and there was an even distribution of species among height strata in gaps. Gap trees of competing species already average 11–13 m tall, and mean expected time for these trees to reach full canopy height is only 19 years. For these reasons, we suggest that dominance will shift from oaks to other species, even though late successional species (e.g., Acer and Tilia) are not presently common in the understories of these stands.     

The spatial pattern and canopy-understory association of trees in a cool temperate,mixed forest in western Japan

The spatial distribution pattern of trees and the association between canopy and understory individuals were examined with reference to the distribution of tree crowns in a cool temperate, mixed forest in Ohdaigahara, western Japan. Line transect and contact sampling methods were used to examine the pattern over various spatial scales. These methods are useful to detect patterns over a large study area. The dominance ofChamaecyparis obtusa on steep slopes forming large patches suggested that the distribution of this species is a consequence of landslides. UnderstoryFagus crenata showed a clumped distribution, and the relative coverage of this species was larger in canopy gaps than under a closed canopy. Understory individuals ofAbies homolepis showed a positive association with canopy trees ofF. crenata but a negative association with conspecific canopy individuals. These patterns suggested thatF. crenata regenerates in canopy gaps and is replaced byA. homolepis. The dynamics of these two species are consistent with the process of gap dynamics. The effects of both small- and large-scale disturbance must be evaluated to understand the mechanisms of patch formation and the coexistence of forest tree species.     

The influence of canopy cover on understorey development in forests of the western Cascade Range,Oregon, USA

Natural disturbances, especially fire and treefalls, influence tree canopy composition in the Pseudotsuga menziesii forests of the western Cascade Range, Oregon. The composition of tree, shrub, and herb assemblages in the understorey of stands with different canopy types, such as maturing Pseudotsuga, Tsuga heterophylla, or mixed species stands, also differs.Differences in both canopy type and the prevalence of canopy openings correlated with different degrees of understorey development in stands of similar ages. This suggests that understorey assemblages also reflect disturbance history. Before understorey assemblages can be used to relate community samples to community or habitat types, the extent to which their composition reflects long term influences of stand history vs. differences in site potential must be determined.     

Landscape- vs Gap-level Controls on the Abundance of a Fire-sensitive,Late-successional Tree Species

Tsuga heterophylla (western hemlock), a fire-sensitive, late-successional tree species, is an important component of old-growth forests in the Pacific Northwest, USA. In the Oregon Coast Range, however, T. heterophylla occurs at low densities in or is completely absent from many conifer stands. We used a cellular automata-based simulation model to explore the influences of the fire regime and gap disturbances on T. heterophylla dynamics at a landscape scale. The abundance of T. heterophylla in the simulated landscape was particularly sensitive to variation in fire return interval and fire severity. T. heterophylla was less sensitive to canopy gap return interval, probability of recruitment in canopy gaps, and the probability of rare long-distance dispersal events. Relatively short periods of high fire frequency caused a rapid and persistent decline in the amount of T. heterophylla in the landscape. Based on the simulation results, we propose two new hypotheses. The first is that landscape-level constraints imposed by the frequency, severity, and pattern of wildfires will limit the potential for gap-level processes to affect T. heterophylla regeneration patterns at the landscape scale. The second, related hypothesis is that legacies of cumulative fire effects will have a strong influence on the subsequent development of late-successional forest structure. Received 29 August 2000; accepted 18 October 2001.     

THE RELATIONSHIP AND ORIGIN OF TSUGA HETEROPHYLLA AND TSUGA MERTENSIANA BASED ON PHYTOCHEMICAL AND MORPHOLOGICAL INTERPRETATIONS

Morphological intermediacy between Tsuga heterophylla and Tsuga mertensiana has stimulated controversy concerning the relationship between these two hemlock species and has led to wide acceptance of hybridization as a causative factor of intermediate forms in areas of distributional overlap. In this study, comparative’ chemical analyses were used to test the theory of hybrid derivation of intermediates. Chromatographic analyses were further applied to the phylogenetic ranking of several North American and Asian species of Tsuga and to the examination of the hypothesis that Tsuga mertensiana is a derivative of intergeneric hybridization involving Tsuga heterophylla and Picea sitchensis. Chromatographic data derived from extensive sampling in the western Cascades of Washington led me to conclude that hybridization of Tsuga heterophylla and T. mertensiana is a possible but rare phenomenon and is not necessarily indicated by morphological intermediacy. Phylogenetically both of these species are typical representatives of Tsuga and are distinct from species of Picea. There is, however, some support for the derivation of Tsuga mertensiana by intergeneric hybridization.     

SEEDLING ESTABLISHMENT IN FORESTS AFFECTED BY TEPHRA FROM MOUNT ST. HELENS

Seedling density on permanent plots at five sites was monitored for the first four summers following the deposition of 4.5 to 15 cm of tephra from the 1980 eruption of Mount St. Helens. Because the old-growth forests at the sites were not destroyed by the volcanic eruption, the plots were under a normal tree canopy. Almost no seedlings established in 1980. By 1983 tree seedling density exceeded 35 m^−-2 at all sites. Tsuga heterophylla seedlings were most common, with Abies amabilis seedlings next in abundance. A dense layer of small trees may develop on the tephra and long-term forest dynamics could be affected. There was no successful invasion by species not already present in the stands. Seedlings of some forest herbs, especially Tiarella trifoliata, were common, but many other common forest species produced none. It is still problematical if or when these species will return to areas of the forest from which they were extirpated.     

Dendrochronological analysis of the canopy history of two Ohio old-growth forests

This study examined the temporal patterns of establishment, suppression, and release of major tree species in two old-growth Ohio forest remnants as a means to determine the past disturbance history of these forests. Increment cores were taken from a total of 154 trees from two well-drained, upland plots and two poorly-drained, bottomland plots in each of the two forested areas. Acer saccharum and Fagus grandifolia exhibited multiple episodes of suppression and release prior to becoming canopy trees, and could tolerate suppressions as long as 84 years. In contrast, Quercus macrocarpa, Q. muehlenbergii, Prunus serotina, and Acer saccharinum rerely exhibited any tolerance to suppression and appeared to have entered the canopy after single disturbances had opened large areas of canopy. There was clear synchrony in the temporal pattern of establishment and final release from suppression among trees from bottomland plots scattered throughout the stands, indicating that relatively large disturbances were important in these poorly-drained areas. In contrast, there was little synchrony among trees from well-drained upland plots, except in a single instance where selective cutting of Quercus trees opened the canopy. Thus, the canopy of upland site was likely subjected only to small disturbances resulting from the death of one or a few trees. At the whole of forest level, there was evidence of episodic recruitment of canopy trees in both forests. Establishment of Fraxinus spp. and Quercus spp. were particularly episodic, and few Fraxinus or Quercus trees alive today established during the last century. These data suggest that large disturbances have affected canopy dynamics of both upland and bottomland areas prior to 1900 and in bottomland forests through this century. In contrast, disturbances in upland areas during this century have been restricted to small, treefall-generated canopy gaps.     

Patterns of tree replacement: canopy effects on understory pattern in hemlock-northern hardwood forests

The effect of canopy trees on understory seedling and sapling distribution is examined in near-climax hemlock-northern hardwood forests in order to predict tree replacement patterns and assess compositional stability. Canopy trees and saplings were mapped in 65 0.1-ha plots in 16 tracts of old-growth forests dominated by Tsuga canadensis, Acer saccharum, Fagus grandifolia, Tilia americana, and Betula lutea in the northeastern United States. Seedlings were tallied in sub-plots. Canopy influence on individual saplings and sub-plots was calculated, using several indices for canopy species individually and in total. For each species sapling and seedling distributions were compared to those distributions expected if saplings were located independently of canopy influence. Non-random distributions indicated that sapling and seedling establishment or mortality were related to the species of nearby canopy trees. Hemlock canopy trees discriminate against beech and maple saplings while sugar maple canopy favors beech saplings relative to other species. Basswood canopy discourages growth of saplings of other species, but produces basal sprouts. Yellow birch saplings were rarely seen beneath intact canopy. Since trees in these forests are usually replaced by suppressed seedlings or saplings, canopy-understory interactions should influence replacement probabilities and, ultimately, stand composition. I suggest that hemlock and basswood tend to be self-replacing, maple and beech tend to replace each other, and birch survives as a fugitive by occupying occasional suitable gaps. This suggests that these species may co-exist within stands for long periods with little likelihood of successional elimination of any species. There is some suggestion of geographical variation in these patterns.     

Gap-scale disturbance processes in secondary hardwood stands on the Cumberland Plateau,Tennessee, USA

Disturbance regimes in many temperate, old growth forests are characterized by gap-scale events. However, prior to a complex stage of development, canopy gaps may still serve as mechanisms for canopy tree replacement and stand structural changes associated with older forests. We investigated 40 canopy gaps in secondary hardwood stands on the Cumberland Plateau in Tennessee to analyze gap-scale disturbance processes in developing forests. Gap origin, age, land fraction, size, shape, orientation, and gap maker characteristics were documented to investigate gap formation mechanisms and physical gap attributes. We also quantified density and diversity within gaps, gap closure, and gap-phase replacement to examine the influence of localized disturbances on forest development. The majority of canopy gaps were single-treefall events caused by uprooted or snapped stems. The fraction of the forest in canopy gaps was within the range reported from old growth remnants throughout the region. However, gap size was smaller in the developing stands, indicating that secondary forests contain a higher density of smaller gaps. The majority of canopy gaps were projected to close by lateral crown expansion rather than height growth of subcanopy individuals. However, canopy gaps still provided a means for understory trees to recruit to larger size classes. This process may allow overtopped trees to reach intermediate positions, and eventually the canopy, after future disturbance events. Over half of the trees located in true gaps with intermediate crown classifications were Acer saccharum, A. rubrum, or Liriodendron tulipifera. Because the gaps were relatively small and close by lateral branch growth of perimeter trees, the most shade-tolerant A. saccharum has the greatest probability of becoming dominant in the canopy under the current disturbance regime. Half of the gap maker trees removed from the canopy were Quercus; however, Acer species are the most probable replacement trees. These data indicate that canopy gaps are important drivers of forest change prior to a complex stage of development. Even in relatively young forests, gaps provide the mechanisms for stands to develop a complex structure, and may be used to explain patterns of shifting species composition in secondary forests of eastern North America.     

辽西低山丘陵区不同年龄荆条冠层截留降雨模拟实验研究

为揭示辽西低山丘陵区不同年龄荆条冠层降雨截留的变化规律,采用人工模拟降雨动态监测荆条冠层降雨截留情况,并建立了经验模型。结果表明：荆条冠层未截留量与降雨量呈线性显著正相关,且随年龄增加,未截留量的增加速率减小;250 min时未截留率趋向稳定为1年生91.87% > 2年生89.75% > 3年生85.08% > 4年生79.00%,未截留率与降雨量显著正相关;荆条截留量随着降雨量的增加而增加,在250 min时4年生为（5.25±0.49）mm > 3年生（3.73±0.65）mm > 2年生（2.60±0.23）mm > 1年生（1.93±0.55）mm,且1、2年生荆条截留量趋向稳定;250 min后冠层截留率逐渐变小并趋向稳定值,4年生21.00% > 3年生14.92% > 2年生10.25% > 1年生8.13%;荆条附加截留量4年生为（0.27±0.03）mm > 3年生（0.17±0.04）mm > 2年生（0.14±0.01）mm > 1年生（0.09±0.02）mm。揭示了不同年龄荆条冠层截留降雨的基本规律,验证了附加截留量,为进一步研究荆条的生态水文效应提供了科学的理论依据,对水土保持树种优选和辽西地区水土流失治理具有一定的指导意义。     

The mountain forests of british columbia and the american northwest: Floristic patterns and syntaxonomy

An overview of the montane and subalpine forests ofAbies lasiocarpa, Picea engelmannii, Abies amabilis andTsuga mertensiana of northwestern North America is provided based on 541 relevés of forest vegetation from coastal and inland British Columbia, Washington and northwestern Montana. A new classification is proposed based on an examination of the floristic patterns across these communities. Owing to their broadscale floristic similarities, coastal subalpineAbies amabilis-Tsuga mertensiana forests and inland forests ofAbies lasiocarpa, Picea engelmannii, P. glauca, Thuja plicata andTsuga heterophylla are combined into a single order,Thujetalia plicatae. The floristic patterns within this order in turn support the recognition of four alliances. These are (1)Tsugion mertensianae, including coastal and inland subalpine forests ofTsuga mertensiana, Abies amabilis, A. lasiocarpa andPicea engelmannii, with deep winter snowpacks and an often luxuriously developed shrub layer; (2)Abieti-Tsugion heterophyllae all. nov., including mesic inland montaneThuja plicata-Tsuga heterophylla andAbies lasiocarpa-Picea engelmannii forests and related southern borealAbies lasiocarpa-Picea glauca communities; (3)Gymnocarpio-Abietion lasiocarpae, including moist coastal and inland forests dominated by a fern-rich understory andOplopanax horridus; and (4)Lysichito-Chamaecyparidion nootkatensis, which includes wet coastal subalpine forests withLysichiton americanum. A total of five new associations are described, bringing the number of recognized associations within the order to twenty-five. An extensive synonymy and crosswalk to other classification systems is provided.     

On the life history ofTurnerella mertensiana (Rhodophyta,Gigartinales)

Turnerella (Gigartinales) withT. mertensiana known from northern Japan was studied to determine its life history. Carpospores cultured from foliose female plants gave rise on germination to crustose plants containing tetrasporangia, as noted previously inT. pennyi from the Atlantic. The crusts were slow to develop and required 3–5 years to achieve reproductive maturity. Tetraspores liberated in culturedT. mertensiana gave rise on germination eventually to thalli similar to gametophyticT. mertensiana. Thus this species may be said to adhere to the pattern of life history in which a large, foliose gametophyte alternates with a small crustose tetrasporophyte. The erect filaments of the small sporophytes branch laterally and tetrasporangial mother cells are found there, exemplifying an unusual method for crustose species to produce tetrasporangia.     

Diameter Growth of Juvenile Trees after Gap Formation in a Bolivian Rain Forest: Responses are Strongly Species‐specific and Size‐dependent

We evaluated growth responses to gap formation for juvenile individuals of three canopy rain forest species: Peltogyne cf. heterophylla, Clarisia racemosa and Cedrelinga catenaeformis. Gaps were formed during selective logging operations 7 yr before sampling in a Bolivian rain forest. We collected wood samples for tree‐ring analyses at different distances to the stump (<10, 10–40 and >40 m) and from trees with different diameters (5–30 cm diameter at breast height [dbh]). Tree‐rings width was measured in at least two radii and converted to average diameter growth. Changes in 7‐yr median diameter growth before and after selective logging were analyzed. Diameter growth rates significantly increased by 0.7–0.8 mm/yr after gap formation for P. heterophylla and C. catenaeformis, but not for C. racemosa. We applied a multiple regression analysis to explain variation in growth responses of P. heterophylla and C. catenaeformis by distance to logging gap and tree size. For P. heterophylla we found that growth increase occurring close to logging gaps was strongest for large juvenile trees (20–25 cm dbh) and almost absent in small juveniles. For C. catenaeformis, variation in growth responses was not related to tree size or distance to gaps. Our results show that growth responses to gap formation strongly differ across species and tree sizes. This finding calls for caution in the interpretation of growth releases in tree‐ring series, as gap formation does not necessarily invoke growth responses and if such growth responses occur, their strength is species‐ and size specific.     

Comparative studies on acorn and seedling dynamics of fourQuercus species in an evergreen broad-leaved forest

The dynamics and regeneration probabilities ofQuercus acuta, Q. gilva, Q. salicina, andQ. sessilifolia were studied in a 0.48 ha plot in an old-growth evergreen broad-leaved forest, Kagoshima prefecture, southwestern Japan. The canopy was well closed and had only one small gap. Seventeen tree species occurred in the canopy. The fourQuercus species ranked second to fifth in basal area. Excluding the trees originated from sprouts,Q. acuta and Q. gilva lacked trees at the subcanopy layer, andQ. salicina andQ. sessilifolia had some trees at the same layer. For eachQuercus species, the amount of fallen acorns fluctuated from year to year. The number of current year seedlings was positively correlated with the number of fallen acorns in the previous year. A disproportion between the spatial distribution of fallen acorns and that of established seedlings has been shown. The establishment of seedlings was frequently observed where no acorns had fallen in the previous year. Saplings of four species survived for several years and formed sapling banks under the closed canopy. During the three years of the study, the mortality ofQ. salicina andQ. sessilifolia saplings was lower than that ofQ. acuta andQ. gilva. However, the differences in the average annual height growth of saplings between four species were not significant, and the most of them did not grow much. These results suggest that the saplings of the fourQuercus, especiallyQ. gilva andQ. acuta, have no chance to recruit to the canopy or subcanopy layer within a closed stand, and that some changes in the environment caused by gap formation are required for their recruitment.     

Stand development and regeneration during a 33-year period in a seral Picea glehnii forest, northern Japan

Stand development and regeneration were studied during a 33-year period (1965-1998) in a 1-ha plot in a seral Picea glehnii forest in northern Japan. P. glehnii was mono-dominant in the upper canopy layer, but its understory trees were rarely found in 1965. Other species were scarcely observed in 1965. Many recruited saplings of Abies sachalinensis which had grown to > 5 cm diameter at breast height (DBH) by 1998 had become dominant in the understory layer. Mortality of P. glehnii canopy trees was low. Therefore, the stand basal area increased during the census period due to the growth of surviving canopy trees. Stand development brought about intense competition among trees by increasing local crowding for each tree, and promoted dominance of larger trees and suppression of smaller trees. Although growth rates of understory trees of the two conifers decreased with the increase in local crowding, the growth rate of A. sachalinensis was consistently higher than that of P. glehnii at all extents of local crowding. The recruitment rate (growing to 5 cm DBH) of the two conifers was less affected by local crowding. However, the number of recruits of P. glehnii was only about a quarter of that of A. sachalinensis during the census period because the regeneration of P. glehnii was largely restricted to fallen logs and within 1 m of the base of any live tree > 20 cm DBH. Therefore, our long-term study suggests that A. sachalinensis will dominate over P. glehnii in the seral forest because of higher recruitment and growth rates of the former than the latter in the understory.An erratum to this article can be found at