Regeneration in experimental gaps of subalpine <Emphasis Type="Italic">Picea abies</Emphasis> forest in the Slovenian Alps

In 1998, we analysed regeneration success in four 20 year old medium-sized (600–800 m²) and four small experimental gaps (100–200 m²) in subalpine Norway spruce forest in Triglav National Park, Slovenia. We assessed the influence of site (depressions, slopes), gap size, and position within gap (centre, gap south, and north edge) on regeneration success and interactions between regeneration density, height, height increment, direct and diffuse light, ground vegetation, soil depth, thickness of humus horizons, presence of woody debris, and microrelief. Seedling density was higher in depressions, where more seedlings developed in central positions of gaps in both gap sizes, and in microsites with deeper soils, less competition from ground vegetation and convex microsites. On slopes, a higher seedling density was found in small gaps, and at the northern edge of gaps regardless of gap size. Here, seedling density was negatively influenced by diffuse radiation and positively by soil depth. The results suggest that regeneration should be initiated from medium to large gaps in depressions and small gaps on slopes. Development of established seedlings was enhanced by higher radiation levels on both sites, therefore favourable extension of the gaps would be lateral to northwards.     

Tree regeneration responses to microsite characteristics following a severe tornado in the Georgia Piedmont, USA

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

Response of Quercus robur L. seedlings to north-south asymmetry of light within gaps in floodplain forests of Slovenia

To examine Quercus robur establishment and growth in low to intermediate light levels, we analysed regeneration in different microsites created by light asymmetry within gaps in two main floodplain forest regions of Slovenia: Dolinsko and Krakovo. Four years after a mast year in 1995, we installed systematic grids of 1×1 m plots in 11 gaps (0.03–0.40 ha) on wet and dry site variants. In 256 plots, seedling species, cover, density, height, height increment, browsing damage, tree architecture, understory vegetation species and cover, and direct and diffuse light were measured. The average seedling density in all gaps was 15/m², but the highest densities were found in gap positions with low diffuse light levels (10–20%). Competing understory vegetation was more abundant in positions with high diffuse light. In gaps on dry site variants a combination of low diffuse and high direct light was favourable for regeneration. The results indicated that Q. robur can successfully establish in gaps. Here, both light components were sources of within gap resource heterogeneity, therefore knowledge of light asymmetry can improve regeneration success.     

林隙微生境及更新研究进展

系统评述了国内外关于林隙干扰及更新的最新研究进展.林隙是一种经常发生的小规模干扰,是森林群落时空格局变化的驱动力.不同的林隙干扰状况导致了林隙内光照的差异,进一步造成林隙内温度、湿度、土壤理化性质的变化,形成了微生境的时空异质性.林隙干扰通过改变微生境而对幼苗的出土、存活、定居和生长产生重要影响.林隙内种子库的物种丰富度变化很大,是幼苗分布格局的重要影响因子.更新幼苗的存活率和生长量受林隙大小及幼苗在林隙中位置的影响.指出了这一领域今后的研究方向.     

The influence of storm-induced microsites to tree regeneration patterns in boreal and hemiboreal forest

We reviewed studies dealing with regeneration under variable conditions in boreal and hemiboreal forests as affected by different microsite types by tree species functional groups. Generally, the importance of storm-induced microsites for regeneration dynamics in boreal forests depends on several factors: (1) distribution and type of microsites (generated by storm characteristics and stand conditions); (2) viable seed supply (stand history, species dispersal traits and status of surviving trees) and their species’ life history strategy; (3) climatic and site conditions (pre-storm conditions and storm-induced changes); and (4) delayed storm effects, such as retarded falling of trees, favoured vegetation growth, etc. Studies acknowledging the significance of microsites were mostly related to intermediate or severe events, causing sufficient changes in resource levels and growth conditions, and influencing extrinsic factors such as frost heaving, erosion and browsing. Also, the dispersal traits of available tree species, including sprouting and response of surviving trees, such as canopy expansion, should be considered in evaluating microsite importance in individual cases. In intermediate to severe windstorm events, pioneer species are generally profiting most from the additional offer in microsites, requiring bare mineral soil and elevated locations for their establishment and growth. Under gap dynamics, shade-tolerant species benefit from dead wood and elevated locations as these offer safe sites in stands with abundant understorey vegetation.     

Effects of gaps on regeneration of woody plants: a meta-analysis

Forest gaps, openings in the canopy caused by death of one or more trees, have a profound effect on forest regeneration and drive the forest growth cycle. It is therefore necessary to understand the effects of forest gaps on regeneration for modern forest management. In order to provide a quantitative assessment of the effects of forest gaps on regen-eration of woody plants, we conducted this review of gap effects on woody plant regeneration on the basis of 527 observations from 42 indi-vidual papers, and reported the results of these data in a meta-analysis. Overall, densities of regenerated woody plants were significantly greater （359%） in forest gaps than on the closed-canopy forest floor. The regen-eration density in gaps of plantation forests was significantly greater （P＆lt;0.05） than that of natural forest because the regeneration in gaps of plan-tation forests was improved by both gap effects and experimental meas-ures. Similarly, in comparison to natural gaps, regeneration was better enhanced in artificial gaps. Regeneration density exhibited a significantly positive correlation with gap size, but a negative correlation with gap age because the gap size decreased with increasing gap age. Shade tolerance of woody plants affected regeneration density in gaps and understory. Average regeneration density of shade-tolerant species exhibited a sig-nificantly positive response to gaps but densities remained lower in total than those of intermediate and shade-intolerant species. Gap effects on regeneration decreased in response to increasing temperature and pre-cipitation because of the limiting effects of lower temperature and moisture on woody plant regeneration. In summary, forest gaps enhance woody plant regeneration, and the effects of gaps varied by forest type, gap characteristics, environmental factors and plant traits. The results of this meta-analysis are useful for better understanding the effects and roles of gaps on forest regeneration and forest management.     

Contributions of root and stump sprouts to natural regeneration of a logged tropical dry forest in Bolivia

A major impediment to the sustainable management of tropical dry forests in Bolivia is the scarcity of natural regeneration of commercial timber tree species. Where regeneration is present, true seedlings of many species are outnumbered by vegetative sprouts from roots, broken stems, and the stumps of felled trees. This study evaluates the importance of resprouts promoted by logging operations for the regeneration of commercially important canopy tree species. The objectives of the study were: (1) to characterize stump and root sprouting behaviors of canopy tree species harvested for timber; (2) to quantify the effect of logging on relative abundances and growth rates of stump sprouts, root sprouts, and true seedlings; (3) to relate the species-specific probabilities of stump sprouting to stump diameter and stump height; and (4) to explore how sprouting varies with the ecological requirements of canopy tree species. The study was carried out 1–5 years after logging of a privately owned land in a Bolivian tropical dry forest. Twenty-seven of the 31 species monitored resprouted at least occasionally, among which Centrolobium microchaete (Leguminosae-Fabaceae) and Zeyheria tuberculosa (Bignoniaceae) were the most frequent stump sprouters, and Acosmium cardenasii (Leguminosae-Fabaceae) and C. microchaete were the most frequent root sprouters. In all species the number of sprouts declined with increasing stump diameter and stump height. The probability of stump resprouting differed among species but did not vary consistently with stump diameter, except in Z. tuberculosa in which it declined. Approximately 45% of juveniles <2 m tall of canopy tree species originated from root or stem sprouts. Light-demanding species tended to regenerate more from seeds and root sprouts than from stumps. Seedling densities were higher in microsites opened by logging, while root and stem sprouts were equally common across microsites. Given their abundance and the fact that root and stem sprouts at least initially grew faster than true seedlings, we conclude that vegetative regeneration in this tropical dry forest is an important mode of post-logging regeneration especially for species that regenerate poorly from seed. Resprout management should be considered as a potentially effective strategy for the procurement of regeneration following logging, especially for species that do not readily recruit from seed.     

The effects of gap size and age on natural regeneration of Picea mongolica in the semi-arid region of Northern China

The aim of this work was to study the effects of gap size and age on natural regeneration of endangered tree species Picea mongolica W. D. Xu, which is only found in the semi-arid region of Northern China. For this purpose, six random transect belts of varying size were established in Baiyinaobao Natural Reserve. The number, height and age of P. mongolica saplings were inventoried. Results show that the total number of saplings per hectare and corresponding number and relative share of saplings in height class I (0.1–0.99 m) decreased along with increasing gap size, opposite to height class III (6–9 m). In height class II (1–5.99 m) the number of saplings per hectare and their relative share increased first slightly and then decreased with the increase of gap size. The number of saplings and their relative share in each height class changed similarly with the increase in the distance to the edge of the mature stand (p < 0.05). Gap age also significantly affect the number of saplings per hectare or their height distribution except in height class II. The distance to the mature stand edge played a very important role in the success of natural regeneration for species P. mongolica.     

Effects of ground preparation and microenvironment on germination and natural regeneration of Juniperus procera and Afrocarpus gracilior in Ethiopia

The seedling establishment of Juniperus procera Hochst. ex Endl. and Afrocarpus gracilior (Pilger) C. N. Page was assessed in the Afromontane forests of Ethiopia. Percent light transmission, litter depth and percentage cover of vegetation were assessed for seedling microsites in five sites with different levels and history of disturbance. The response of natural and artificial regeneration to burning, mechanical scarification (removal of all logging waste and ground vegetation) and cultivation following clear felling and timber extraction was assessed 19 months after treatment.There was no evidence that regeneration was correlated with light intensity. Despite the presence of a viable seed bank in the undisturbed forest floor, removal of the overstorey vegetation by clear felling did not encourage natural regeneration of J. procera. This suggests that light may not be the main factor limiting regeneration of J. procera.Natural regeneration of J. procera can withstand exposure and is compatible with management by ‘clear cutting with seeding from adjacent stands’ together with ground treatment, particularly controlled burning which exposes the minearl soil and releases nutrients. In contrast, both clear felling and surface disturbance will discourage the natural (or artificial) regeneration of A. gracilior suggesting that J. procera is a pioneer species which is more exposure-tolerant, whilst A. gracilior is more shade-tolerant and exposure-intolerant.     

Species diversity,regeneration and dominance as influenced by canopy gaps and their characteristics in tropical evergreen forests of Western Ghats,India

Canopy gaps play a significant role in maintaining structure and composition of tropical forests. This study was carried out in tropical evergreen forests of central Western Ghats in India to understand the influence of canopy gap size and the relationship of gap regime attributes to diversity measures and regeneration. The average gap size in the study area was found to be 396 m2 and around half of gaps were 4–8 years old. Gaps created by natural single tree fall were smaller in size but significantly higher in number. Diversity and regeneration of woody species were compared with canopy gaps and intact vegetation. Species richness and diversity was higher in gaps than in intact vegetation. Macaranga peltata, a shade intolerant species dominated gaps while intact vegetation was dominated by shade tolerant Kingiodendron pinnatum.Gap size significantly influenced species diversity and regeneration. Gap area and age were significantly and negatively correlated with diversity measures but positively correlated with regeneration. Among all the attributes of gaps, regeneration was significantly positively correlated with light intensity. Gaps maintained species diversity and favored regeneration of woody species. In addition to gap size and age, other gap ecological attributes also affected species diversity and regeneration.     

Gap partitioning among temperate tree species across a regional soil gradient in windstorm-disturbed forests

Canopy closure and soil characteristics are commonly used to explain regeneration distribution at local and regional scales, although very few studies take both factors into account. The combination of environmental variables defined at broad and local scales is necessary to provide regeneration distribution models with a small resolution (tree scale) that are valid on a large spatial scale (regional scale). Our aim was to quantify how gap partitioning among tree species at the seedling stage varies across large soil and stand type gradients. Regeneration inventories performed 5 years after gap creation were used to analyse the combined effects of soil type, stand type, and position within canopy gaps on the regeneration development of eight western European broadleaved species: Acer campestre, Acer pseudoplatanus, Betulapendula, Carpinusbetulus, Fagussylvatica, Fraxinusexcelsior, Quercus sp., and Salixcaprea. A clear pattern of gap partitioning among the eight species was observed. All species had higher density at the gap edge except birch and willow showing the highest presence in gap centres. For all species, the probability of presence of tall seedlings (height > 0.5 m) increased from gap edge to gap centre. Small seedlings presented the opposite trend except birch and willow. Soil pH influenced probability of presence for each species, but did not affect the pattern of gap partitioning among species. Both local (location within the gap) and regional (soil pH and stand type) scale factors affect recruitment distribution and are thus necessary to predict seedling distribution. The models developed may be used to determine the optimal gap size in order to obtain a given species composition according to soil and stand type conditions.     

Small mammal responses to forest management for oak regeneration in southern Indiana

We used a 5-decade chronosequence of harvest openings to characterize population and community-level responses of small mammals to forest management targeting oak regeneration in southern Indiana. Live-trapping at 42 different sites allowed modeling of occupancy and relative abundance using environmental covariates while incorporating imperfect detection. Species richness was higher in smaller openings on southwest-facing aspects. Similarity between species richness of different age classes decreased with increasing site age. Eastern chipmunk (Tamias striatus) relative abundance was greater in early seral stages, i.e., at young sites with low basal areas. Relative abundance of white-footed mice (Peromyscus leucopus) exhibited different responses to coarse woody debris on sites versus microsites. Pine voles (Microtus pinetorum) and short-tailed shrews (Blarina brevicauda) were more likely to occupy older sites. We observed a greater relative abundance of short-tailed shrews at sites with steep and northeast-facing slopes. Northeast-facing slopes also resulted in higher short-tailed shrew occupancy rates. Incorporating detection probability enabled us to derive more accurate estimates of relative abundance and, when coupled with a Bayesian framework, permitted the estimation of occupancy for uncommon species. Our estimated responses can be used by forest managers to determine the potential impacts of even-aged and uneven-aged oak management on small mammals, and the statistical methodology we used can be applied even more broadly to improve understanding of wildlife responses to forest management.     

雪灾干扰下林窗对木荷幼苗更新的影响

林窗干扰是维持森林生态系统的重要驱动力之一,对种子萌发、幼苗等自然更新过程、森林物种组成和动态、森林生物多样性的维持具有重要作用。本研究以2008年雪灾干扰后的浙江江郎山木荷林为研究对象,对木荷林窗大小结构、幼苗更新、生长等进行调查研究,结果表明:扩展林窗以50 100 m2的林窗个数最多(占总数的45.45%),各等级林窗中以50 100 m2的林窗占总面积比例最大(占总面积的30.31%)。林窗中木荷幼苗的平均高度和地径较对照林分分别高1.44 cm和0.61 mm,幼树在林窗中的平均高度和地径则比对照林分中分别高45.37 cm和5.00 mm且差异显著;林窗大小对木荷幼苗、幼树的高度和地径生长影响显著,中林窗中幼苗的高度和地径均高于小林窗和大林窗中的幼苗且差异均显著(F=4.893,P=0.007;F=5.203,P=0.004;n=357);幼树的地径在不同大小林窗中差异显著(F=3.569,P=0.037;n=43)。林窗幼苗的更新密度随着林窗面积的增大而增大,在林窗面积达到76 m2时,更新密度达到最大值,而后随着林窗面积的增大下降;中林窗和小林窗中更新苗木以低矮植株(1级、2级)为主,面积100 m2大林窗中,木荷幼苗生长较快。与他人研究的森林天然林窗相比,雪灾干扰后改变了林窗的大小分布结构和面积,50 100 m2的林窗比例较大,一定程度上更利于幼苗更新,具有相对较大的林窗幼苗更新密度;不论林窗大小,林窗内的更新幼苗都比林内多,郁闭度较大的林内或大面积的空地上都不利于更新幼苗的生长。因此,从受灾木荷林窗大小结构、幼苗更新、生长等来看,中林窗是幼苗适宜更新的面积,为木荷灾后恢复与重建提供了科学依据。     

林隙影响天然林更新研究进展

林隙干扰是森林循环中经常发生的小规模干扰,林隙的存在为天然林幼苗更新提供了有利的微环境。文中综述了林隙大小、林隙年龄和林隙边缘木在天然林更新过程中所起的作用,以及林隙更新理论在林业生产中实际应用情况,指出林隙更新理论在森林经营上的应用是未来林隙研究中的重要方面。     

Survival and competitiveness of Quercus rubra regeneration associated with planting stocktype and harvest opening intensity

Successful regeneration of northern red oak (Quercus rubra L.) on productive sites is problematic in eastern North American forests. Natural and artificial regeneration often cannot compete with fast-growing, shade intolerant species such as yellow-poplar (Liriodendron tulipifera L.). This study examines 5-year survival, growth, and competitive ability of planted northern red oak seedlings in various group selection harvest sizes in south-central Indiana, USA. Seedling stocktypes consisted of high (BHD; 75 seedlings m^?2) and low (BLD; 21 seedlings m^?2) nursery-bed-density bareroot seedlings, and small (CS; 11.4 L) and large (CL; 18.9 L) container seedlings. Group selection openings included large (0.400 ha), medium (0.100 ha), and small (0.024 ha) circular gaps in four stands. Larger stocktypes and gap sizes improved seedling height, diameter, and growth; ANOVA indicated only gap size was significant for seedling survival. Logistic regression showed survival was positively correlated to diameter at year 1, and aspect, gap size, and stocktype were significant predictors of survival. Our data indicated no differences in density of natural regeneration among gap sizes, although trends suggest greater numbers of bigger competitors in larger gaps sizes. Yellow-poplar regeneration was the tallest competitor of more than 50% of all northern red oak seedlings. Competitive status of seedlings after 5 years differed only by stocktype, with large container stock in a better competitive position than bareroot stock. However, less than 20% of seedlings in all stocktypes in each gap treatment were considered competitive (i.e., ≥80% of the height of tallest competitor) against their tallest competitor. The use of larger planting stock may offer greater opportunities for successfully regenerating northern red oak seedlings on productive sites but likely would have to be accompanied by treatments to reduce woody competition.     

Enrichment planting of Picea glauca in boreal mixedwoods: can localized site preparation enhance early seedling survival and growth?

Conserving forest biodiversity has become a significant global concern. A change in forest composition, compared to pre-industrial values, is an important biodiversity issue. In this regard, there is a significant decrease in Picea glauca densities at the landscape level in boreal mixedwoods of northeastern Canada, compared to pre-industrial abundance. Enrichment planting is considered a promising silvicultural approach for improving P. glauca stocking and re-establishing its natural co-dominance with Abies balsamea. However, optimal enrichment scenarios must be identified, notably regarding site preparation treatments that can enhance planted seedling survival and growth while protecting Abies advance regeneration. We established a field trial in Quebec (Canada), laid out as a complete block split-plot design. Picea glauca and P. mariana seedlings (main plot) were planted according to 3 “microsite” treatments (subplot): (1) planting in the humus layer; (2) planting in the mineral soil, with minimal humus disturbance; and (3) planting in a microsite mechanically-prepared using modified brushsaws. After 3 growing seasons, P. mariana seedlings were taller than P. glauca seedlings, but had smaller ground-level diameters. Seedlings planted in the mineral soil had overcome the initial height difference they had with seedlings planted in the humus and mechanically-prepared microsites, with no interaction with species. Ground-level diameter was similar for seedlings planted in the humus and mechanically-prepared microsites, but smaller for seedlings planted in the mineral soil. Water potentials, available light, and foliar nutrient concentrations were not influenced by treatments or species; survival was >90 %. Our results indicate that P. glauca can be established through enrichment planting in boreal mixedwoods. Localized site preparation is not required to limit initial plantation stress in this ecosystem.     

Influence of forest structure and environmental variables on recruit survival and performance of two Mediterranean tree species (<Emphasis Type="Italic">Quercus faginea</Emphasis> L. and <Emphasis Type="Italic">Q. suber</Emphasis> Lam.)

We investigated the regeneration requirements of the two dominant tree species in a mixed-oak forest of SW Portugal: Quercus suber (cork oak, evergreen) and Q. faginea (Portuguese oak, winter-deciduous). We hypothesized that (1) recruits of different oak species are differentially influenced by soil and overstory variables and (2) different factors explain the recruitment occurrence and performance of the same species. We sampled the recruits’ height and diameter, and several environmental and forest structure variables of their microsites. Both recruitment occurrence and performance were modeled using generalized linear models. Our final models predicted the probability of occurrence of recruits of Q. faginea and Q. suber with 74 and 82% of accuracy, respectively, and explained about 50% of the variance of their recruitment performance. The recruits of Q. faginea tended to occur in microsites with higher canopy height, canopy density and litter cover, and closer to both conspecific and heterospecific adults, while the opposite was true for recruits of Q. suber. The performance of recruits of Q. suber was favored by the higher litter cover (a good surrogate for N and P availability), but negatively affected by the higher litter depth. We concluded the following: (1) there were significantly different regeneration niches for each species (Q. faginea and Q. suber); (2) the factors explaining the recruitment occurrence differed from those explaining the recruitment performance; (3) the overstory plays a complex and important role in the regeneration process; (4) different variables apparently related with the same environmental factor (e.g. litter cover and litter depth) could affect recruits in an opposite way; (5) sensitive trade-offs must be considered for delineating management actions, since they could favor the regeneration of Q. suber, but, at the same time, negatively affect the regeneration of Q. faginea.