Responses of native and invasive plant species to selective logging in an Acacia koa‐Metrosideros polymorpha forest in Hawai'i

Questions: Is the introduced timber species Fraxinus uhdei invasive in Hawai'i? Has logging disturbance facilitated the spread of Fraxinus and other alien species? Location: Windward Mauna Kea, island of Hawai'i. Methods: We surveyed 29 plots which were established before selective logging of the native tree Acacia koa in 1971 to determine if Fraxinus spread beyond the borders of an existing plantation and if other alien species increased. We created gaps in the canopy of the Fraxinus plantation and measured seed rain and regeneration, and we sampled foliar and soil nutrients inside and around the plantation. Results: Basal area of Fraxinus increased from 0.7 m².ha^‐1in 1971 to 10.8 m².ha^‐1 in 2000. Fraxinus was not found in plots that were located more than 500 m from those where it occurred in 1971 except along a road. Basal area of Acacia koa decreased after logging but subsequently recovered. Occurrence of the alien vine Passiflora tarminiana and alien grass Ehrharta stipoides decreased. Seedling regeneration of Fraxinus was prolific in gaps but did not occur under the canopy. Basal area of Fraxinus did not correlate with soil nutrient concentrations. Conclusions: Fraxinus was able to regenerate following logging more rapidly than native tree species. Basal area growth of Fraxinus was great enough to offset a decline in native trees and cause an increase in forest productivity. If the Fraxinus plantation is harvested, managers should plan ways of favoring regeneration of the native Acacia which is more valuable both for timber and for conservation.     

Species diversity of Chinese beech forests in relation to warmth and climatic disturbances

The trends in the occurrence of climatic disturbances in the ChineseFagus range are described, and the relationship between woody species diversity and climatic factors in eight old-growth Chinese beech forests is characterized. In the ChineseFagus range that lies in the humid mountains of southern China, wind storms and heavy rain frequency increase towards the eastern coast. Thunderstorm frequency increases southwards. Snowfall frequency increases northwards. Glaze storm frequency peaks in the center near Lake Dongtian, but much higher in the east than in the west. Hailstorm frequency also peaks in the center. The forests sampled in this study are widely separated. Their canopies consist of either deciduous broad-leaved trees or a mixture of evergreen and deciduous broad-leaved trees. Their species diversity increases towards warmer sites and towards the east. The importance of the evergreen trees in relation to warmth and minimum temperature increases southwards. Our analysis suggests that wind storms and heavy rains enhance the species diversity of Chinese beech forests. Cold disturbances such as glaze and snow diminish the diversity and canopy dominance of evergreen broad-leaved trees but favor deciduous broad-leaved trees, especially beech. The annual precipitation received by the forests in this study varies from 1400–2550 mm. This is not correlated with diversity, however, probably because all of these forests grow in humid conditions with sufficient water being supplied by precipitation throughout the year.     

Codominance of <Emphasis Type="Italic">Acer saccharum</Emphasis> and <Emphasis Type="Italic">Fagus grandifolia</Emphasis>: the role of <Emphasis Type="Italic">Fagus</Emphasis> root sprouts along a slope gradient in an old-growth forest

We studied how the unusual capacity of mature Fagus grandifolia to form clumps of clonal stems from root sprouts can contribute to its frequent codominance with Acer saccharum in southern Quebec, Canada. In an old-growth forest, the degree of dominance by the two species shifted along topographic gradients spanning a few hundreds of meters, with Fagus more frequent on lower slopes and Acer on upper slopes. The frequency distribution of Fagus stem diameter had an inverse J distribution at all slope positions, which is indicative of continuous recruitment. Acer stem diameter also had an inverse J pattern, except at lower slope positions where size structure was discontinuous. For stems <2 m tall, Fagus regenerated mainly by sprouts at the upper and mid-slopes, while regeneration from seed was more pronounced on the lower slope. This change of regeneration mode affected the spatial pattern of Fagus stems. Understory trees of Fagus were positively correlated with conspecific canopy trees on upper and mid-slopes, but not on lower slopes where Fagus regenerated mainly by seedlings. Understory trees of Acer were positively correlated with conspecific canopy trees only on the mid-slope. There were many Fagus seedlings around Acer canopy trees at the lower slope, suggesting the potential replacement of Acer canopy trees by Fagus. This study suggests that the regeneration traits of the two species changed with slope position and that Fagus patches originating from root sprouts can contribute to the maintenance of Acer–Fagus codominance at the scale of local landscapes.     

Forest gap formation and closure along an altitudinal gradient in Tongariro National Park,New Zealand

24 treefall gaps accumulated over a 10 year period along an altitudinal transectcovering 4.6ha on Mt. Hauhungatahi, Tongariro National Park, New Zealand were described quantitatively in terms of the area of damage (‘expanded gap’), the canopy opening (‘Tight-gap’) and the size of the root mound. Tree mortality and branch loss following cyclone Bola, 1988, were recorded. In each gap saplings were ranked by species according to their vigour. Pre-gap and post-gap vertical and horizontal branch growth rates were calculated. Effects in the subalpine forest (> 1050 m) were compared with those in the montane zone. Tree mortality was highly episodic, associated with major storms, and patchy. Falling canopy trees destroyed, on average, 1.3 additional trees (> 10 cm diameter at 1 m). About half the trees were uprooted and the remainder broken off. Uprooted angiosperm (canopy) trees frequently resprouted from their bases, gymnosperms rarely. Expanded gap area averaged 56 m² in the sub-alpine forest and 88 m² in the montane zone. Median expanded gap areas were about twice those of light gaps. Gap size frequency distribution was highly skewed. The largest gap was formed by a single Dacrydium cupressinum which destroyed six other trees creating a gap of ca. 0.03 ha. Expanded gaps, light gaps, and root mounds comprised 4.5, 2.8 and 0.1 % of the forest area in the sub-alpine zone, and 3.8, 2.5 and 0.06 % in the montane forest. These values represent 10 years of accumulation, and imply light gap ‘return times’ of 360 years for the sub-alpine and 400 years for the montane forest. These periods are in agreement with the known longevities of the canopy and emergent trees. Vertical shoot growth rate was about twice that in the horizontal plane, and both increased following gap formation. The relative increase was greatest in the subalpine forest. Using the measured growth rates it is estimated that gaps of median dimensions are filled by lateral extension growth in 31–44 yr. Saplings require longer to reach the mean canopy height and consequently require large (multiple tree) gaps or sequential gap events.     

Spatial patterns of tree seedling establishment and their relationship to environmental variables in a cold-temperate deciduous forest of eastern North America

Patterns of seedling recruitment may have persistent effects on population and community processes. Assuming seed availability is not limiting, the environmental sieve (i.e., the suite of factors influencing seed germination and seedling emergence and survival) determines how many seedlings establish and, most importantly, where they do so. In this study, we identify the spatial structure of some resources and abiotic conditions known to be significant for tree seedling emergence and survival and determine how these environmental factors influence the establishment of Fagus grandifolia, Acer saccharum, Fraxinus americana, and Ostrya virginiana in a deciduous forest of southern Québec (Canada). We expect an increase from Fagus, through Acer and Fraxinus, to Ostrya in the control of environmental variables on seedling emergence and survival, because of differences in the seed size of these species. Density of newly-emerged seedlings of all four species showed positive spatial autocorrelation at distances of up to ca. 10 m. Environmental variables were also structured at the same spatial scale, except for soil moisture. Acer seedling emergence pattern was positively correlated to photosynthetic photon flux density (PPFD), and the pattern of Fraxinus to soil N and moisture. Seedling survival was not spatially autocorrelated for any of the four species, although it was positively density-dependent in Acer and Fagus. In only Ostrya was seedling survival correlated (positively) to one of the environmental variables studied, i.e., PPFD. Overall, environmental variables were spatially less heterogeneous than seedling emergence and survival. Either seed availability was not saturating or factors not considered here, such as competition and predation (the intensity of which often varies with resources and/or abiotic conditions), modified the influence that the physical environment had on patterns of seedling establishment. Our prediction of a greater environmental control on seedling emergence and survival in small-seed species was not totally confirmed.     

A relict population of Fagus grandifolia var. mexicana at the Acatlan Volcano, Mexico: structure, litterfall, phenology and dendroecology

Aim Fagus grandifolia var. mexicana (Martinez) Little has an extraordinarily restricted distribution in the Mexican montane cloud forests. Isolated Fagus (beech) populations have been recorded in less than 10 small areas (2–40 ha) in the eastern Sierra Madre at altitudes from 1400 to 2000 m. The objectives were to determine tree and seedling age, forest structure, phenology, litterfall patterns and the relationship between mast and climatic variables. Location We report on three Fagus stands at the Acatlan Volcano, Veracruz, Mexico. Methods Changes in forest cover were determined using aerial photographs. Within each stand, basal area, density and tree species composition were determined in a 0.1‐ha band transect. Additionally, litterfall production was quantified and phenophases were recorded monthly over a 3‐year period, and 60 tree cores were collected to determine age distribution and tree‐ring growth. Results The forest was atypical in several respects. Fagus was the only dominant tree species in the crater stand, although in the rim and at the top of the volcano it was codominant with other tree species. Juveniles occurred only on the rim, but there was a seedling bank in the crater. Although forest cover in the area increased between 1968 and 1993, the Fagus stands did not change in size. Leaf production peaked in March and April, and leaf fall occurred from October through February. Litterfall production was the highest in November. During mast years, flowering started in February and between mast events there were no flowers or fruits. Minimum temperatures were highly correlated with Fagus litterfall and leaf fall. Seedlings ranged in age from 2 to 18 years and were 13–60 cm tall. Tree cores ranged from 76 to 120 years, but trees were older than the core samples. Main conclusions Although beech is considered a gap regeneration species that reaches the canopy after alternating periods of release and suppression, the trees in the crater were released when less than 1.5 m tall and have suffered few periods of suppression since. The results indicate that the crater stand was established after a severe disturbance destroyed the existing forest. We conclude that the relict beech population should be able to maintain itself, if not severely disturbed by humans or by climatic changes related to global warming.     

Implications of 19th century landscape patterns for the recovery of Fagus crenata forests

Questions: What is the effect of the 19th century (pre‐industrialization) landscape pattern on the recovery of climax forests in cool‐temperate mountain areas dominated by Fagus crenata (Japanese beech)? Location: Secondary forests on Mt. Daisen, western Japan. Methods: Vegetation patterns before and after industrialization were obtained from maps drawn in 1898 and 1979. Tree measurements were made in 12 plots in 1997. Correlation between current Fagus crenata dominance and forest edge in the 19th century was analysed using an S‐shaped regression curve. Fagus juvenile density was counted in the plots, and distances from each plot to the five nearest mother trees were measured to determine the dispersal kernel. Results: Secondary grassland covered a substantial area in 1898, whereas forest covered most of the area in 1997. Fagus was dominant in places in the interior forest 100 years ago, and mature Fagus trees were absent in secondary forests that had been grasslands in 1898. The expected number of juveniles decreased to one individual per 100 m² at 43.5 m from the mother tree. Conclusions: The pre‐industrialization landscape greatly affected recovery of Fagus forest. Forests found on the 1898 vegetation map might have acted as refugia for Fagus. The limited dispersal ability of Fagus suggests that it would take many generations (several hundred years) for Fagus forests to recover at the centre of what had been grasslands in the 19th century.     

Stand structure and regeneration in a Kamchatka mixed boreal forest

Abstract. A 1‐ha plot was established in a Betula platyphylla‐Picea ajanensis mixed boreal forest in the central Kamchatka peninsula in Russia to investigate stand structure and regeneration. This forest was relatively sparse; total density and stand basal area were 1071/ha and 25.8 m²/ha, respectively, for trees > 2.0 cm in trunk diameter at breast height (DBH). 25% of Betula regenerated by sprouting, and its frequency distribution of DBH had a reverse J‐shaped pattern. In contrast, Picea had a bimodal distribution. The growth rates of both species were high, reaching 20 m in ca. 120 yr. The two species had clumped distributions, especially for saplings. Betula saplings were not distributed in canopy gaps. Small Picea saplings were distributed irrespective of the presence/absence of gaps, while larger saplings aggregated in gaps. At the examined spatial scales (6.25–400 m²) the spatial distribution of Betula saplings was positively correlated with living Betula canopy trees and negatively with dead Picea canopy trees. This suggests that Betula saplings regenerated under the crowns of Betula canopy trees and did not invade the gaps created by Picea canopy trees. The spatial distribution of Picea saplings was negatively correlated with living and dead Betula canopy trees and positively with dead Picea canopy trees. Most small Picea seedlings were distributed under the crowns of Picea trees but not under the crowns of Betula trees or in gaps. This suggests that Picea seedlings establish under the crowns of Picea canopy trees and can grow to large sizes after the death of overhead Picea canopy trees. Evidence of competitive exclusion between the two species was not found. At a 20 m × 20 m scale both skewness and the coefficient of variation of DBH frequency distribution of Picea decreased with an increase in total basal area of Picea while those of Betula were unchanged irrespective of the increase in total basal area of Betula. This indicates that the size structure of Picea is more variable with stand development than that of Betula on a small scale. This study suggests that Betula regenerates continuously by sprouting and Picea regenerates discontinuously after gap formation and that the species do not exclude each other.     

油樟幼苗对马尾松林窗面积的光合响应特征

为了解马尾松人工林窗对伴生树种的影响,为马尾松人工纯林的团块状混交提供科学依据,研究了10 m×10 m(T1)、15 m×15 m(T2)、20 m×20 m(T3)、25 m×25 m(T4)、30 m×30 m(T5)、35 m×35 m(T6)和40 m×40 m(T7)马尾松人工林窗中油樟(Cinnamomum longepaniculatum)幼苗叶片形态和光合生理特征的变化,探讨马尾松林窗斑块对混生树种生长的影响。结果表明:1)林窗面积低于20 m×20 m时,油樟幼苗叶片最大净光合速率显著低于旷地对照;2)叶片比叶重随着林窗面积的增大显著升高;林窗内油樟幼苗叶氮含量在小林窗中(10 m×10 m)显著低于旷地对照,但在大林窗中(如20 m×20 m)显著高于对照;林窗内幼苗叶磷含量则与旷地无显著性差异;3)叶氮在光合组分中的总分配系数随着林窗面积的增加而增大,其中叶氮在羧化组分中的分配系数升高尤为明显,而捕光组分的分配系数在林窗面积10 m×10 m—20 m×20 m范围内随林窗面积的增加而显著降低。可见,当马尾松林窗面积低于20 m×20 m时,林窗环境会显著影响油樟幼苗的光合能力,油樟幼苗可以通过调节比叶面积、叶氮含量以及叶氮在光合组分中的分配等形态、生理适应特征来适应林窗环境的变化。     

The remnant mangroves of Sei Kecil,Simpang Hilir,West Kalimantan,Indonesia

Phytosociological analysis of the remnant mangrove forest was carried out in Sei Kecil, Telok Melano, West Kalimantan, to describe the forest composition and structure, and to assess the regeneration strategy of the important mangrove species. Six transect plots of 20 × 60 m, 20 × 80 m and 20 × 90 m, with a total area of one hectare were established perpendicular to the coast line.A total of 20 species of trees and saplings, two species of herbs and one species of nypa palm was recorded. Three community types were recognized namely Rhizophora apiculata, Excoecaria agallocha-Rhizophora apiculata and Excoecaria agallocha reflecting the zonation in this forest.The number of trees, saplings and seedlings were 510, 1220 and 11 085 per ha respectively. Rhizophora apiculata was most successful in regeneration with 6231 seedlings per ha (56.2%) and followed by Bruguiera parviflora with 3810 seedlings per ha (34.4%). Seedlings of the first species were mostly growing under gaps while the second species occurred mostly around the mother trees.     

Growth Ecology of Carapa nicaraguensis Aublet. (Meliaceae): Implications for Natural Forest Management1

The probability of achieving a sustainable tropical logging operation is increased if the growth of surviving trees is maximized after logging. This research examined the growth ecology of seedlings and trees of the Neotropical timber species, Carapa nicaraguensis (Meliaceae). Shadehouse experiments, field plantings, and growth rate analyses tested the hypothesis that Carapa seedlings and trees experience higher growth rates in high light levels (recently formed logging gaps or logged forest plots) than in low light levels (old logging gaps or undisturbed forest plots). Consistently poor seedling growth rates under low light conditions suggest that seedlings establishing in newly formed gaps will be more successful than those establishing in building-phase gaps. Thus, the first year after logging is a critical time for gap recolonization by Carapa, and seed casting into gaps after logging is recommended. Growth of Carapa trees was significantly faster in logged forest than in undisturbed forest, and was positively associated with light availability. The results provide evidence that harvest models can be both diameter- and illumination-based. Crown illumination was not significantly higher in logged forest than in undisturbed forest, indicating that the illumination scale for this study was not sensitive enough to detect increases in light availability brought about by selective logging. Potential silvicul-tural methods (particularly poison-girdling) that maintain adequate forest light levels in Carapa swamps without significantly altering long-term tree diversity or allowing invasion of secondary species should be explored.     

Spatial distribution of Eurya japonica in an old-growth evergreen broad-leaved forest,SW Japan

Abstract. The spatial distribution of Eurya japonica, an evergreen understorey species, was studied on a 4-ha permanent plot in an old-growth, temperate, evergreen broad-leaved forest in southwestern Japan. The pattern of spatial dispersion varied with size class, the environmental heterogeneity produced by tree-fall gaps and microtopography and the scale of observation. Seedlings (0.05 to < 0.5 m high) had the most clumped distributions, followed by saplings (0.5 to 1.3 m high) and adults (> 1.3 m). Individuals were more clumped at the smallest grid size, 1.56m × 1.56 m, and became less clumped as grid size increased for all size classes. On grids of less than 6.25 m × 6.25 m, no spatial correlations were found between seedlings and larger size classes; positive spatial correlations were found between saplings and adults at this scale. Abundant seedlings appeared in tree-fall gaps formed by uprooted trees, but seedlings were frequent on ridge tops and upper slopes. Saplings and adults also occurred on upper slopes, but their spatial distribution had little relation to current tree-fall gaps. The spatial distribution of E. japonica individuals was largely attributed to the distribution of tree-fall gaps and the differential responses to microtopographic variation by individuals at different size classes.     

Confirmation of clonal reproduction of Fagus crenata Blume from Sado Island,Niigata Prefecture

While clonal growth is important in the East Asian Fagus subgenus Engleriana and the North American Fagus grandifolia (subgenus Fagus), for other subgenus Fagus species the vast majority of regeneration involves sexual reproduction with clonal growth only rarely observed. Here we aim to confirm using nuclear microsatellite markers whether clonal growth occurs in the Japanese endemic species Fagus crenata (subgenus Fagus) by investigating the origin of multi-stemmed clumps found within a high-elevation dwarf beech forest on Sado Island, Niigata Prefecture. We found that all stems collected from three separate clumps belonged to the same clump-specific multi-locus genotypes. The maximum size of clones was 3–4 m in diameter, comparable in size to those seen in the predominantly asexually regenerating Japanese species Fagus japonica (subgenus Engleriana). The species capacity for clonal growth is likely to underlie its ability to persist at high-elevation exposed sites at the limits of its ecological range.     

Determinants of woody species richness in Scot pine and beech forests: climate, forest patch size and forest structure

We analysed patterns of woody species richness in Pinus sylvestris and Fagus sylvatica forests in Catalonia (NE Spain) from forestry inventory databank in relation to climate and landscape structure. Both types of forests are found within the same climatic range, although they have been managed following somewhat different goals. Overall, woody species richness significantly increased when conditions get closer to the Mediterranean ones, with milder temperatures. Differences between the two types of forests arose when comparing the relationship between richness and forest patch size. Woody species richness increased in pine forests with patch size, while the opposite trend was observed in beech forests. This pattern is explained by the different behaviour of structural canopy properties, since leaf area index and canopy cover showed a steeper increase with increasing forest patch size in Fagus forests than in Pinus ones. Accordingly, richness decreased with canopy cover in Fagus plots, but not in Pinus ones. We suggest that these differences would be related to management history, which may have enhanced the preservation of beech stands in larger forest landscape units.     

The regeneration process in a mixed forest in central Hokkaido,Japan

The regeneration process in a mixed forest was investigated in Nopporo National Forest, Hokkaido. The analysis of age structure in an 80 m×80 m plot revealed that almost all of the species regenerated intermittently. In eleven gaps observed in the plot, the regeneration of a boreal conifer (Abies sachalinensis) was seldom observed. Temperate hardwoods, even climax species (Acer mono, Quercus mongolica var. grosseserrata, Tilia japonica), regenerated vigorously in the gaps. The age structure in ten additional plots scattered all over the forest showed that Abies tended to regenerate synchronously. From previous records, regeneration of Abies could be ascribed to catastrophic storms causing serious windfalls. On the other hand, regeneration of the temperate hardwoods was not synchronous but independent in different places within the forest. They could regenerate not only after those catastrophic storms but also after less severe disturbances which caused the death and fall of one or several trees. It is concluded that the coexistence of boreal coniferous species and temperate deciduous broad-leaved species in mixed forests may be maintained not only by the difference in habitat but also by the balance between the less frequent large disturbances, and the more frequent smaller ones.     

Gap structure,disturbance and regeneration in a primeval Picea abies forest

We investigated patterns of disturbance and recovery in Fiby urskog, a primeval spruce (Picea abies) forest, situated south of the border between the Boreo-nemoral and Boreal regions in East-central Sweden. The main types of disturbances are storm damage, fungal infection and insect attacks. The response of the different tree species varied and the mode of tree-fall depended on the different combinations of disturbance agents. The DBH distributions of gap creators and gap-border trees were almost the same. There was a high age diversity (100–240 yr) among the fallen trees. We concluded that all canopy trees (DBH > 20 cm) had the same probability of being felled by storms, irrespective of their age and DBH. According to an estimate along transect lines, gaps made up 31% of the spruce forest area. Individual gap sizes ranged from 9 m² to 360 m², but 83% of the gaps were < 150 m². The varied age structure of logs in individual gaps indicated that gap enlargements were common. 96 tree-falls were observed on four days with an hourly mean wind speed > 12.0 m/s; all trees fell in the direction of the wind. However, when we consult the 30-yrrecord(l 959–1989)ofthemeanhourly wind speed >12.0 m/s, it is clear that the pattern of storm-directions does not match the pattern of orientation of fallen logs. The present disturbance regime and the predominance of small gaps were more favourable for the regeneration oí Picea abies than of light-demanding tree species. In one large, 2900 m² gap, not crossed by the transects, all the major tree species had established within 7 yr, suggesting that classical succession in the sense of complete species replacement or ‘relay floristics’ didnot occur. Our observations seem rather to fit the ‘initial floristic’ model. Estimates of turnover time ranged from 170 to 228 yr, depending on the method used.     

Influence of management on the species composition of epiphytic cryptogams in Danish Fagus forests

Abstract. The purpose of this study is to evaluate and to quantify the influence of management on the epiphytic species composition in Danish Fagus sylvatica forests. Trunks were chosen at random within selected blocks in both managed and unmanaged Fagus stands.117 trunks in 43 sample plots in three forests were investigated. Cover was estimated for 72 lichens, 29 bryophytes and two fungi on vertical trunks 0.3 ‐2 m above ground. 18 explanatory variables were recorded and arranged in three groups: eight management‐related variables, six micro‐climatic‐ and soil variables, and four geographical‐ and geological variables. Canonical Correspondence Analysis was used to test and to quantify the explaining power of the three groups of variables applying the variation partitioning approach. Detrended Correspondence Analysis was used to evaluate whether important gradients were ignored. It was concluded that the traditional ‘shelterwood uniform system’ used in Fagus forests has a marked influence on the epiphytic species composition. Thus, management‐related variables explained more than one third of the total variation explained, which equals 10.9% of the total variation. Microclimatic and soil variables explained 9.0%, and geographical and geological variables explained 6.0%. The following three recommendations are suggested to reduce the significant influence of management on the epiphytic species composition. First, it should be attempted to ensure a continuous occurrence of some big trees per ha to be left for natural death and decomposition. Second, regular thinning is necessary, especially in the first part of rotation. Third, a multi‐layered forest, where wind and desiccation effects are minimized, is recommended.     

Stem growth and canopy dynamics in a world-wide range of Fagus forests

Abstract. Forests dominated by Fagus (beech) occur widely in the Northern Hemisphere. Tree species dominant together with beech vary in tolerance of understorey conditions. They are deciduous broad-leaved, evergreen broad-leaved or evergreen coniferous. The frequency and intensity of events that reduce the forest canopy cover are important determinants of the ratio of beech to other species in the canopy. For trees in the understorey and the canopy, stem diameter growth rate is determined by light regime and growing space which in turn are determined by canopy cover. We evaluated increase in stem diameter growth rate as an indicator of sudden reductions in canopy cover and canopy dynamics. We used tree-ring chronologies and calculated an index of growth rate increase (GI) to compare the canopy dynamics of 11 natural beech forests. Per site, the annual average value of GI poorly reflected the effects of dry or cool summers, and it clearly reflected events like tornados and hurricanes that removed substantial canopy cover. Among groups of sites average values of GI were significantly different. In the sites with a lower level of average GI, the establishment of the more shade tolerant tree and shrub species in the understorey was favoured, and subcanopy layers became more dense. On the other hand, higher levels of average GI allowed for more light demanding tree species to reach the canopy.     

Analysis of seedling banks of a climax beech forest: ecological importance of seedling sprouts

Most of the common and dominant tree species in gaps of a climax Japanese beech (Fagus crenata) forest have large seedling banks on the forest floor. These seedlings were classified into “true seedlings” and “seedling sprouts”, each of which was further classified into two and three subtypes, respectively. Each species had a characteristic seedling form spectrum. The seedling bank of beech was composed almost solely of true seedlings, whereas, seedling sprouts predominated in the seedling banks of lower tree species such as Prunus grayana Maxim. and some species of Acer. The age structures suggested that seedling sprouts had longer life spans and had been recruited more constantly than true seedlings. The habit of sprouting and creeping seemed to enable seedlings of these species to persist for long periods, thus increasing their chance for eventual success in canopy gaps.     

Mechanical Resistance of Different Tree Species to Rockfall in the French Alps

In order to determine the mechanical resistance of several forest tree species to rockfall, an inventory of the type of damage sustained in an active rockfall corridor was carried out in the French Alps. The diameter, spatial position and type of damage incurred were measured in 423 trees. Only 5% of trees had sustained damage above a height of 1.3 m and in damaged trees, 66% of broken or uprooted trees were conifers. Larger trees were more likely to be wounded or dead than smaller trees, although the size of the wounds was relatively smaller in larger trees. The species with the least proportion of damage through stem breakage, uprooting or wounding was European beech (Fagus sylvatica L.). Winching tests were carried out on two conifer species, Norway spruce (Picea abies L.) and Silver fir (Abies alba Mill.), as well as European beech, in order to verify the hypothesis that beech was highly resistant to rockfall and that conifers were more susceptible to uprooting or stem breakage. Nineteen trees were winched downhill and the force necessary to cause failure was measured. The energy (E _fail) required to break or uproot a tree was then calculated. Most Silver fir trees failed in the stem and Norway spruce usually failed through uprooting. European beech was either uprooted or broke in the stem and was twice as resistant to failure as Silver fir, and three times more resistant than Norway spruce. E _fail was strongly related to stem diameter in European beech only, and was significantly higher in this species compared to Norway spruce. Results suggest that European beech would be a better species to plant with regards to protection against rockfall. Nevertheless, all types of different abiotic stresses on any particular alpine site should be considered by the forest manager, as planting only broadleaf species may compromise the protecting capacity of the forest e.g. in the case of snow avalanches.