Sheep grazing in young oak Quercus spp. and ash Fraxinus excelsior plantations: vegetation control, seasonality and tree damage

An experiment was carried out where sheep were grazed in temporary fenced paddocks at a stocking rate of 178 LSU ha⁻¹ in a 5-year old broadleaf plantation of oak (Quercus spp.) and ash (Fraxinus excelsior) (1.5 m spacing) on fertile, former lowland pasture in Northern Ireland. The grazing regime was rotational and intensive, with two grazing periods of 5 days in February and October 2001. Results showed that a significant proportion of the rank herbage height was removed within the first 24 h of livestock introduction. Herbage biomass was reduced by approximately half after 5 days. Sward height in grazed plots remained significantly lower than control plots for over 6 months after cessation of grazing, whilst biomass remained significantly lower for over 4 months after cessation of grazing. No significant tree damage to either oak or ash was measured during the February grazing trial, however significant damage to the lateral branches of both oak and ash was observed in the October grazing trial. Leader damage did not occur on trees greater than 152 cm. Ash was more commonly browsed than oak. Annual height increment of both tree species was unaffected by grazing, but annual stem diameter increment was significantly reduced in both oak and ash in February grazed plots. Oak trees in both February and October grazed plots were found to have a significantly smaller annual increase in canopy diameter than those in control plots. Results are discussed with regard to practical implementation of controlled grazing in young broadleaf forestry plantations on fertile, lowland soils.     

Pits and rocky microsites in a subalpine forest stand facilitate regeneration of spruce saplings by suppressing dwarf bamboo growth inside a deer-proof fence

We determined patterns of microsite suppression in dwarf bamboo Sasa nipponica when grazing deer were absent. This bamboo species is able to outcompete Hondo spruce (Picea jezoensis var. hondoensis) saplings under many environmental circumstances. We set up two 10 × 100 m plots inside a deer-proof fence within a subalpine forest on Mt. Ohdaigahara, central Japan, and two similarly sized plots outside the fence. Within the plots, we surveyed microsites where spruce saplings grew. We measured height and shoot elongation of all spruce saplings, and culm height and cover ratios of dwarf bamboo growing around each spruce sapling. Spruce sapling density and average height were higher inside the deer-proof fence than outside, as were bamboo height and cover. Thus, there was a negative effect of deer browsing on vegetation parameters outside the fence and a suppression of the negative effect of bamboo on spruce sapling growth inside the fence. Spruce sapling height was higher in tree-fall pits than in other microsites inside the fence, whereas both dwarf bamboo height and cover were lower in pits and rocky sites than elsewhere. In soil and collar microsites, spruce sapling shoot growth was lower and bamboo height and cover were higher than in pits and rocky sites. Inside the fence, dwarf bamboo cover was high, but pits and rocks suppressed its growth, allowing spruce saplings to flourish. To restore heavily damaged spruce forests with advanced saplings, it will be necessary to construct deer-proof fences and create and maintain microsites with pits and rocks.     

Light-related competitive effects of overstory trees on the understory conifer saplings in a subalpine forest

To clarify the mechanism by which overstory trees shade understory saplings, we investigated the relationships among light conditions of the saplings (measured as indirect site factor; ISF and direct site factor; DSF), the calculated competition effects of overstory trees on the saplings (W), and relative height growth rate of the saplings (RHGR). We calculated several W values in order to find a W value which can express the light conditions as appropriately as possible, and the results indicated that W explained only 21.9%–24.7% of the total variance of light conditions in the cases where W gave the best fit. In this study, W was calculated based on the basal areas of overstory trees. However, it is known that canopy structure also affects the light regimes in the forest understory, and this might yield the possible errors even within W representing the shading effects most adequately. Therefore, although W significantly represents the shading effect from overstory trees, a great proportion of the variance remained without being explained by W. RHGR was negatively correlated with W, and the W value which had the most adequate explanation of the shading effect also showed the best negative correlation with RHGR. This provides the evidence that the competitive effect of overstory trees on sapling growth is mediated by the shading effect, indicating that competition for light clearly exists within this forest. Such competition for light may closely relate to the well-known phenomenon of gap regeneration in subalpine forests in central Japan.     

Establishment patterns of woody species in low intensity-grazed pastures after the cessation of intensive agricultural use

Low intensity grazing with large herbivores is increasingly used to steer the development of mosaic landscapes (including wood-pastures) and woodland expansion on former agricultural land. We studied the establishment and early growth pattern of woody species in grasslands (formerly used for high intensity summer cattle grazing) in which a low intensity-grazing regime was set up between 4 and 11 years ago. We tested whether the developing vegetation patches, consisting of tall herbs and scrub, influenced this pattern. Further, we investigated if increased susceptibility to trampling disturbance by large herbivores on wet soils in floodplains influenced sapling establishment.Formerly intensively used grasslands were studied at six sites, four in floodplains and two in interfluvial zones on nutrient rich, heavy soils. In total, we sampled 141 plots with grassland, tall herb or scrub vegetation and recorded individuals of established tree and shrub species, their height, diameter, browsing damage and distance to potential seed sources. In the floodplains, we recorded soil disturbance by large herbivores (hoofprints) in wet and moist soils.Sapling frequencies, with Fraxinus excelsior as the most common species (>50% of all individuals), were two to three times higher in tall herb and scrub patches compared to grassland. Only the spiny Crataegus monogyna established in higher frequencies in grassland plots. In floodplains, we found two to three times more established woody saplings in wet tall herb plots, compared to moist and wet grassland plots and moist tall herb plots.Browsing reduced sapling height in grassland and tall herb patches. Only in scrub patches did average height (±2.5 m) reach above the browse line. We found 30–70% less browsing damage to saplings in scrub compared to damage in grassland and tall herb plots. In particular, damage to the apical shoot was strongly reduced.Our findings show that tree establishment occurs in spatial association with non-grassland patches that offer protection against browsing. Fast growing spiny shrubs like Rubus sp. offer protection for palatable saplings, allowing establishment and growing out beyond the browse line. Alternatively, increased establishment occurs in wet tall herb patches, where soil disturbance by moderate trampling favours germination and, subsequently, saplings are protected at least temporarily against browsing by unpalatable tall herbs.     

Influence of canopy structure on the survival and growth of underplanted seedlings

This study explores the indirect relationship between forest structural measures and initial seedling survival and growth along a structural gradient between 64% to 92% canopy closure. The gradient was created by applying various levels of midstory removal to fifty 0.05 ha areas located within a mixed-hardwood riparian forest corridor. Twelve yellow-poplar (Liriodendron tulipifera L.) and cherrybark oak (Quercus pagoda Raf.) containerized seedling pairs were underplanted within each area. Canopy closure was estimated using hemispherical photography; height-to-canopy and basal area were recorded at each seedling pair. Survival, basal diameter, and height were monitored through two growing seasons. Species-specific mortality and height growth models were developed for one and two growing seasons following underplanting. The interaction of height-to-canopy and basal area along with canopy closure were found to be the most strongly related to mortality. Height to the forest canopy and initial seedling size explained the most variance in height increment. Although the height increment models possess limited predictive power (R² range from 0.22 to 0.36), both mortality and growth analyses emphasize the importance of quantifying vertical canopy structure, along with the more commonly considered horizontal measures of forest structure (basal area and stem density), when evaluating seedling development beneath a forest canopy.     

Cattle grazing and pine survival and growth in subterranean clover pasture

When combining pines and cattle on tame pasture, grazing is often delayed for several years until trees are large enough to resist injury. As an alternative approach to delayed or deferred grazing during the early years, this study in central Louisiana, USA, examined the effects of cattle grazing in subterranean clover (Trifolium subterraneum L.) pastures on slash (Pinus elliottii Engelm.) and loblolly pine (P. taeda L.) seeding survival and growth during the first 3 years of tree establishment. Pines were planted at about 1200 trees/ha in 3 rows on 0.4-ha subclover units with 1.3 m spacing within rows. Three grazing treatments included: (1) ungrazed pines, (2) limited grazing with a single-wire electric fence above the planted pines, and (3) grazed pines. Thirty Brahman crossbred cows with calves and a bull grazed the tame pasture on a controlled grazing, rotational basis from December through May each year, during the subterranean clover growing season. Pine trampling injury during the year was 8% on the grazed seedlings while essentially none occured under limited grazing. During the first 2 growing seasons, survival and height of the pines were significantly less on the grazed seedlings than on either the limited grazing or ungrazed seedlings. Pine heights from the limited grazing and ungrazed treatments were not different during the 3-year study; loblolly pine heights from the limited grazing treatment continued to be taller than the grazed treatment through the third year while the slash pine heights were similar for all treatments by the third year. Seedling mortality became more acute as severity of grazing injury increased; the greatest mortality occured when the terminal bud and needles were both browsed off.     

Removing aboveground vegetation facilitates survival but slows height growth of spruce saplings in a fenced, degraded sub-alpine forest in central Japan

The effects of removing aboveground vegetation on survival and growth of Hondo spruce (Picea jezoensis var. hondoensis) saplings were examined in a dense dwarf bamboo (Sasa nipponica) field inside a deer-proof fence built in a degraded sub-alpine forest on Mt Ohdaigahara, central Japan. All bamboo culms were removed within a radius of 1 m from each sapling in a plot of 0.6 ha (removal plot), whereas no culms were removed in two control plots of 0.1 ha. We measured the height, crown depth, and main shoot elongation over 1 year for all spruce saplings, culm height and cover ratios of dwarf bamboo growing around each spruce sapling, and the light levels above each sapling. Removal of dwarf bamboo regulated the culm height and bamboo coverage until the following summer such that light conditions improved. The mortality of saplings smaller than the average culm height was lower in the removal plot (0.89%) than in a control plot (5.9%). After bamboo removal, sapling height growth was reduced with increasing bamboo cover in the previous year. Complete removal of the aboveground portions of covering bamboo improved sapling survival while regulating elongation growth, possibly because of the sudden increase in light intensity. Thus, controlling the extent of dwarf bamboo removal might be necessary to facilitate the growth of spruce saplings to restore the forest.     

Regeneration of commercial tree species in a logged forest in the Selva Maya, Mexico

One of the main threats to the sustainability of community forestry in the Selva Maya is insufficient regeneration of commercial tree species. We evaluated the regeneration status of 22 commercial tree species in a managed semideciduous tropical rain forest in Southern Mexico. The study was carried out in six harvesting areas along a 16-year chronosequence. In each area, 10 transects (1000 m²) were established and all trees >50 cm height and <10 cm diameter were recorded. We evaluated the relationships between seedling and sapling abundance, and canopy cover and disturbance condition (closed forest, canopy gap, log landing, skid road, primary road and secondary road). The area occupied by closed forest canopy increased with age of harvesting area (65–91% of sampled area), while the area occupied by canopy gaps decreased (22–9%). Log landings occupied less than 1% of the sampled area. The predominant canopy cover was 75–80% in all harvesting areas, even in the most recently harvested areas. The highest densities of seedlings and saplings, of both shade tolerant and intolerant species, were found in log landing and skid trails, followed by secondary roads. Even Simarouba glauca, a shade tolerant species, displayed higher densities in sites with ≤65% of canopy cover. Our results support previous findings and indicate that the levels of disturbance caused by existing harvesting procedures may be inadequate to promote sufficient regeneration of not only light demanding desirable species but also for some of the evaluated shade tolerant species of commercial interest. Seedling and sapling densities exhibited by Swietenia macrophylla, for example, are insufficient to support current harvesting rates. The application of a spatial mixed system with patch-cuts of different sizes, a consequence of group felling, could be applied to provide the necessary conditions for the regeneration of the main commercial species.     

Oak/Douglas-fir/sheep: A three-crop silvopastoral system

A small scale agroforestry study which was begun in 1952 was revisited in 1985 to evaluate the long-term influence of site preparation and grazing on tree growth and survival in a Douglas-fir (Pseudotsuga menziesii)-white oak (Quercus garryana)-sheep silvopastoral system. In 1952–1953, two-year-old Douglas-fir seedlings were planted at the rate of 2500 trees/ha under three levels of site preparation: (1) no treatment, (2) oak thinned by 50%, and (3) oak clearcut. From 1954 to 1960, yearling ewes grazed one-half of each of the three thinning treatments for 3–4 weeks each spring. The conifers have been undisturbed since grazing was discontinued in 1960. Survival of planted conifers averaged 64% in 1985 and did not vary among either site preparation or grazing treatments. From 1964 to 1985, trees on the thinned and clearcut plantations grew an average of 1060 and 990 cm in height, respectively, compared to 900 cm on the unthinned plantation. Diameter at breast height (dbh) averaged 3.8 and 5.6 cm greater on thinned or clearcut plantations, respectively, than on the unthinned control by 1985 (p < 0.05). Conifers on grazed plantations had increased height and dbh growth during the first 12 years of plantation life, averaging 63 cm taller (p < 0.10) and 0.7 cm greater in dbh (p < 0.05) than the ungrazed plots by 1964. By 1985 the difference in height (122 cm) and dbh (1.0 cm) between grazed and ungrazed plantations was not statistically significant. These data suggest that although site preparation can positively influence conifer growth, total clearfelling is no better than thinning oaks. Furthermore, proper grazing can increase height and dbh growth of the conifers during and immediately after the grazing years.     

Oak/Douglas-fir/sheep: A three-crop silvopastoral system

A small scale agroforestry study which was begun in 1952 was revisited in 1985 to evaluate the long-term influence of site preparation and grazing on tree growth and survival in a Douglas-fir (Pseudotsuga menziesii)-white oak (Quercus garryana)-sheep silvopastoral system. In 1952–1953, two-year-old Douglas-fir seedlings were planted at the rate of 2500 trees/ha under three levels of site preparation: (1) no treatment, (2) oak thinned by 50%, and (3) oak clearcut. From 1954 to 1960, yearling ewes grazed one-half of each of the three thinning treatments for 3–4 weeks each spring. The conifers have been undisturbed since grazing was discontinued in 1960. Survival of planted conifers averaged 64% in 1985 and did not vary among either site preparation or grazing treatments. From 1964 to 1985, trees on the thinned and clearcut plantations grew an average of 1060 and 990 cm in height, respectively, compared to 900 cm on the unthinned plantation. Diameter at breast height (dbh) averaged 3.8 and 5.6 cm greater on thinned or clearcut plantations, respectively, than on the unthinned control by 1985 (p < 0.05). Conifers on grazed plantations had increased height and dbh growth during the first 12 years of plantation life, averaging 63 cm taller (p < 0.10) and 0.7 cm greater in dbh (p < 0.05) than the ungrazed plots by 1964. By 1985 the difference in height (122 cm) and dbh (1.0 cm) between grazed and ungrazed plantations was not statistically significant. These data suggest that although site preparation can positively influence conifer growth, total clearfelling is no better than thinning oaks. Furthermore, proper grazing can increase height and dbh growth of the conifers during and immediately after the grazing years.     

The effects of selective logging on stand structure and the regeneration of subboreal forests in Hokkaido, northern Japan

We investigated the effects of selective logging on stand structure and regeneration in selectively logged subboreal forests in Taisetsuzan National Park in Hokkaido in northern Japan. The basal area decreased and the size structure of trees altered in the stands studied due to repeated, intense selective logging, in which larger trees were cut down as a priority. Sapling density in the stands was much lower than that in primary forests. In the simple and multiple regression analyses that were used to estimate the effects of selective logging on sapling density, sapling density had a significant positive correlation with tree density and had little correlation with the density of logged stumps or the height ofSasa (dwarf bamboo) growing on the forest floor. These results suggest that the establishment sites around canopy trees influenced the establishment of saplings, rather than the gaps caused by selective logging. However, both the coefficient of determination and the standardized partial regression coefficient of multiple regression analysis were higher for the stand with a dense cover ofSasa than for the stand with a sparse cover ofSasa. Thus, the success of regenerating forests with selective logging depends on both the site of advanced regeneration and the light conditions that regulate growth.     

Coupling of vegetation layers and environmental influences in a mature, second-growth Central Hardwood forest landscape

Forest communities across the landscape of the Central Hardwood Forest Region are experiencing a transition from dominance by oak (Quercus) and hickory (Carya) to maple (Acer) driven largely by a prolonged period of fire suppression. In many cases, this shift in community composition, structure, and function is considered undesirable as oak-hickory forests are valued for timber, wildlife habitat, and natural heritage. Considerable management and restoration efforts target the restoration of oak-hickory forest communities, yet treatments have yielded varying degrees of success. In some cases, difficulties in meeting targets may be due to ecological thresholds created by complex vegetation-environment interactions that maintain the maple-dominated community state. We examined direct and indirect interactions among vegetation layers and environmental gradients for the mature, second-growth forest communities of the Ironton Unit of the Wayne National Forest (WNF) in southeastern Ohio. Using a stratified random approach, we identified 72 study communities with trees at least 70 years old and without evidence of recent disturbance. Within these communities, we sampled all overstory vegetation on two-four 500 m² plots and recorded saplings and ground-flora species in nested sub-plots. At each plot, we also collected soil samples for physical and chemical analyses and recorded physiographic variables. Our first objective was to describe the Ironton forest landscape, where communities were likely transitioning from oak to maple. To identify such patterns, we used ordination analyses that relate species occurrence to implied environmental gradients. Our second objective was to use the relationships to develop a structural equation model (SEM) to quantify the strength of pathways among the canopy, sapling, and ground-flora vegetation layers and environmental factors (e.g., soil chemistry and physiographic position). Our results indicate that the forest landscape of the Ironton Unit of the WNF is at a transition point with communities dominated by either oak or maple, and a sapling layer dominated by maple. Maple may be most likely to replace oak and hickory in the canopies of communities at mid- and lower-slope positions with intermediate soil moisture. This transition will likely have cascading effects throughout the sapling and ground-flora layers, which SEM demonstrates are directly influenced by the canopy. We believe the simultaneous consideration of direct and indirect interactions shaping vegetation structure and composition using techniques such as SEM will advance understanding of the current transition from an oak-hickory to a maple-dominated forest landscape. This information will contribute to the continued improvement of appropriate forest management and ecosystem restoration techniques for the Central Hardwood Forest Region, including those designed to shift the dominance of forest communities from maple to oak.     

Canopy cover effects on cellulose decomposition in oak and pine stands

Cellulose mass loss was measured for four levels of canopy cover,i.e., clearcut, 25%, 75%, and uncut, in northern red oak (Quercus rubra) and red pine (Pinus resinosa) stands in northern Lower Michigan, USA. Cellulose mass loss was more rapid in the clearcut and 25% canopy cover treatments than in the 75% canopy cover and uncut treatments. After 4 month incubation of cellulose filter papers, mass loss rates averaged 75.2% in the clearcut, 56.3% in the 25% canopy cover, 46.9% in the 75% canopy cover, and 45.7% in the uncut stands. For the clearcut and the 25% canopy cover treatments, cellulose mass loss in the mineral soil layer was significantly higher than in the forest floor after 2 and 4 months of incubation, while cellulose mass loss of the uncut treatment was significantly lower in the soil layer than in the forest floor after 4 months of incubation. Cellulose mass loss was not significantly different between the oak and the pine stands (p > 0.05), but cellulose mass loss rates in other canopy cover treatments except for the clearcut were generally higher in red oak stands than in red pine stands. These results suggest that canopy manipulation increases cellulose decomposition and may stimulate nutrient cycling process in canopy removal stands. This study was supported in part by USDA Forest Service and Michigan Technological University.     

Regeneration niches of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis> [L.] Karst.) saplings in small canopy gaps in mixed mountain forests of the Bavarian Limestone Alps

Natural regeneration measurements are the main silvicultural objective in overaged protective forests of the Bavarian Limestone Alps. While manifold problems with these stands, especially the impact of browsing, are widely recognised, the regeneration niches of Norway spruce (Picea abies [L.] Karst.) are insufficiently known. The purpose of this study was to determine favourable combinations of site factors for the development of spruce in small, unfenced canopy gaps, located on Aposerido-Fagetum caricetosum albae forest sites. We recorded the occurrence of spruce saplings (as dependent variable) and of six site factors (as independent variables) on 480 0.5 m²-subplots. In addition, we estimated the coverage of six acid adapted plant species to determine correlations with the humus depth. A binary logistic regression analysis was used to predict the probability of the occurrence of a spruce sapling in dependency of the different site factors. Supported by other studies, we assumed that the supply of solar radiation was adequate for the sufficient regeneration of spruce within the canopy gaps. Other site factors significantly determined the regeneration niches of spruce saplings. More spruce saplings were found near hindrances and on rough surfaces than would be expected from a random occurrence of saplings. These microsite types may have characteristics, especially protection against snow gliding that promotes spruce establishment. A calculated “hindrance index”, which accounted for the number, and the distance of surrounding hindrances might be a good specific value to describe the influence of hindrances on steep slopes. The sapling establishment decreased on thin humus layers. Our assumption for the sites was that thick organic layers might represent a good seedbed for spruce. Decayed dead wood was scarce, but was exceedingly favoured by spruce saplings. Results obtained suggest that the natural regeneration establishment of spruce on steep slopes can be successfully influenced by site factors which inhibit the influence of snow gliding. According to a “positive microsite” concept, we recommend for artificial regeneration measurements with spruce, microsites close to hindrances (e.g. stumps, downed trees) and Vaccinium myrtillus as a predictor for thick, acid humus layers.     

Impact of targeted sheep grazing on herbage and holm oak saplings in a silvopastoral wildfire prevention system in south-eastern Spain

Several wildfire prevention programs in southern Europe are currently using livestock grazing for the maintenance of fuelbreaks. This silvopastoral management is valued for being sustainable and effective in reducing fuel loads, but few studies have analyzed other impacts linked to fuelbreak grazing. This paper reports on an experiment performed within the wildfire prevention program in Andalusia (southern Spain) with the aim of clarifying and quantifying the effect of fuelbreak grazing on herbage biomass, ground cover, herbage species composition, and growth of holm oak saplings. The study site, located in a semiarid Mediterranean environment, was grazed by a shepherded sheep flock from February to June in three consecutive years at a similar stocking rate. Livestock consumed between 33 and 68 % of herbage production in the different years, and the greatest fuel reduction (remaining dry matter of 200?kg?ha^?1) was registered in Year 2, when rainfall and herbage production was lowest. Ground cover was significantly affected by grazing: on average, the percentage of bare soil increased three-fold, while herbage cover was reduced by a quarter. The botanical composition of herbage varied remarkably between years, but very little between Grazed and Non-Grazed areas within each year. Non-browsed holm oak saplings became progressively larger than browsed ones, differences only reaching clear statistical significance at the end of the three experimental years. At this time, the volume of browsed saplings was 47–56 % smaller than that of non-browsed holm oaks, even though the former had also grown significantly in the course of the experiment.     

Demographic and height growth response of native broad-leaved deciduous tree saplings to overhead canopy release in a coastal Pinus thunbergii forest in Hokkaido, northern Japan

Prevention efforts to combat pine wilt disease must be instituted to avoid destruction of coastal forests in Hokkaido, northern Japan. We examine an alternative method involving the conversion of Pinus thunbergii forests to native broadleaf species through advancing their growth, but we have little knowledge about the response of advanced growth to overhead canopy release. To demonstrate the demographic and height growth response of advanced growth to the light change in a coastal Pinus thunbergii forest, canopy trees were removed and the sapling populations were monitored for 6?years. Inhibition in height growth caused by light increase was observed in Cerasus sargentii and Kalopanax septemlobus saplings. Especially in Kalopanax septemlobus, a remarkable decline was observed in the saplings growing in the darker positions which experienced light change. Therefore, large light changes should be carefully avoided for this species especially in the darker positions. In contrast, relative height growth rates of Quercus crispula and, especially, Quercus dentata increased with increasing light, and saplings tended to die in the darker positions. No dead trees of Sorbus commixta were observed during the study period. The saplings also showed good height growth even when under closed canopy. This species seems to be adaptive to a dark environment. Since Quercus dentata and Kalopanax septemlobus are the major components of the natural coastal forests in Hokkaido, gradual canopy release is available to foster advanced growth in coastal Pinus thunbergii forest, in accordance with the concept of density control in coastal forests.     

Effects of surface and light conditions of fallen logs on the emergence and survival of coniferous seedlings and saplings

We surveyed the germination number (N _cs) of 2-year and a 1-year survival of Abies sachalinensis and Picea jezoensis seedlings and saplings on 29 fallen logs from 2004 to 2005 in a natural coniferous forest in Hokkaido, northern Japan, in relation to the surface and light conditions of fallen logs. Moss height (H _moss), log hardness (Hardness), and the area of fallen log (Area) were measured as the surface conditions by each 1-m block from bottom to top of all fallen logs. The relative photosynthetic photon flux density (rPPFD) 10 cm above the tallest seedling in each block was measured as the light condition. In addition, the height of the tallest seedling or sapling in each block (H _max), the difference between a height of each seedling and sapling and the H _max (Shading), and a height of seedlings and saplings in 2004 (H _ini) were considered. N _cs of A. sachalinensis was affected by Hardness and Area, whereas N _cs of P. jezoensis was affected by H _moss, Hardness, Area, H _max, and rPPFD. The survival of seedlings (height < 5 cm) and saplings (5 cm ≤ height < 50 cm) were affected by H _ini, rPPFD, and shading for both species. However, the survival of P. jezoensis saplings was more sensitive to decrease in rPPFD and increase of shading than that of A. sachalinensis. Therefore, seedling emergence was influenced by surface conditions, whereas survival was affected by light conditions. Furthermore, P. jezoensis emergence and survival were more sensitive to surface and light conditions than that of A. sachalinensis.     

Oak (<Emphasis Type="Italic">Quercus robur</Emphasis> L.) regeneration as a response to natural dynamics of stands in European hemiboreal zone

The oak (Quercus robur L.) regeneration intensity was assessed in the core area of the Białowieża National Park (BNP) in Poland with respect to the selected ecological factors. The emphasis was placed on the response of oak regeneration to disturbances, including the large-scale dieback of spruce stands. Defining their effect could help predicting the role of oak in naturally developing lowland forest ecosystems in the European hemiboreal zone. The results of the study challenge the opinion that the ‘lime-oak-hornbeam forest’ is a ‘climax’ community, confirming a very poor regeneration represented by only two saplings taller than 0.5 m per hectare. By contrast, in spruce-dominated communities, from 49 to 848 taller saplings per hectare were found. The occurrence of saplings was associated with discontinuous canopy of late seral stage of stands, as well as with large gaps. Most of the best quality grown-up oak saplings developed in the immediate neighbourhood of spruce logs. The results of the research indicate that ‘lime-oak-hornbeam forest’ (Tilio-Carpinetum) should be rather perceived as a transient community, evolved from relict, culturally modified, oak woodlands. Because spruce had become a dominating species only after abandoning in mid-1800s the historical regime of anthropogenic disturbances (involving frequent forest fires), the observed phenomena related to the disintegration of spruce stands had probably no precedent over the last 500 years. To confirm whether the massive decline of spruce stands will finally result in the successful establishment of the new canopy oak generation, both in Białowieża and other forests of hemiboreal zone, further research is needed.     

Characteristics of the Light Response in Seedlings and Saplings of Two Mid-Successional Species,Ash and Kalopanax,During the Early Stage of Regeneration in a Mature Forest

Abstract

Growth characteristics of ash (Fraxinus mandshuricavar. japonicd)and kalopanax (Kalopanax pictus), two mid-succcs-sional species, were monitored in relation to seasonal light in a deciduous broadleaf forest. During the growing, relative light intensity of the gap was 4 to 6 times higher than that under the closed canopy. Seedlings could be found on the mixed hardwood forest floor where relative light intensity was around greater than 7% of full sunlight. When saplings gap openings which had relative light intensities above 20%, they quickly developed lateral branches and increased their foliage volume. The light-photosynthesis curve of seedlings of both species showed a curve typical of the “shade leaf” type even though they grew under sunlight. In contrast, saplings of both species showed the “sun leaf” type of light-photosynthesis curve. This seedling to sapling shift from shade to sun adaptation was also found in other foliage characteristics. This study shows that species can efficiently adjust their leaf and branch characteristics to changing light environments from shade to openings in a forest.