Sapling Abundance Research Articles

Landscape and Local Factors Affecting Northern White Cedar (Thuja Occidentalis) Recruitment in The Chequamegon-Nicolet National Forest, Wisconsin (U.S.A.)

ABSTRACT Northern white cedar (Thuja occidentalis L.) stands throughout the upper Midwestern United States have failed to recruit individuals to the canopy consistently for several decades. To examine local and landscape factors that influence cedar regeneration we recorded the abundance of cedar seedlings and saplings in 24 lowland cedar stands in the Chequamegon-Nicolet National Forest, Wisconsin, during summer 2001. Cedar seedlings (height <22 cm) were common (median = 1800 ha−1), but the largest size class (height ≥100 cm) was extremely rare (∼1 ha−1) and heavily browsed. We used information-theoretic model averaging of linear mixed-effects models to identify local and landscape variables important for predicting the density of seedlings and saplings. The density of newly germinated seedlings was higher along transects farther from roads and with more mature cedar. Large seedling and small sapling densities were higher along transects with open canopies located in landscapes with a higher ratio of d...

Effect of stand density on oak regeneration in flood plain forests in Lower Silesia, Poland

Summary The paper describes the structure, growth and vitality of natural oak regeneration in relation to stand density. To gain a better understanding of regeneration strategies, the investigation was carried out in oak forest fl ood plains in Poland, which were fl ooded in the summer of 1997. To study the stand structure and regeneration, 108 circular plots were established in stands managed using the shelterwood system. In addition, fi ve gaps were chosen in a stand managed using the group cutting system (Legnica forest district). The results of the study showed that oak regenerated spontaneously in all stands. The abundance and vitality of oak seedlings and saplings were very high. The number of oak seedlings and saplings signifi cantly depended on stand density. The greatest maximum height was found in gaps (146.0 cm) and in a stand with open canopy (88.9 cm) in Wo l ow. In Wo l ow and Mi e kinia, the shortest oaks grew in the worst light conditions. To regenerate naturally, oak stands in preparatory cutting should be reduced in the number of trees per hectare to ~ 150 and decreased in basal area to ~ 26 m 2 ha 1 . The group cutting system can be used in oak stands growing on fl ood plain sites, but there is the danger of ground vegetation development in openings.

Rainforest fragmentation and the demography of the economically important palm Oenocarpus bacaba in central Amazonia

We summarize a long-term study of the effects of edge creation on establishment of the economically important arboreal palm Oenocarpus bacaba in an experimentally fragmented landscape in central Amazonia. Recruitment and mortality of large individuals (≥10 cm diameter-at-breast-height) were recorded within 21 1-ha plots in fragmented and intact forests for periods of up to 22 years. In addition, 12 small (0.7 × 14 m) sub-plots within each 1-ha plot were used to enumerate the abundance of seedlings and saplings (5–400 cm tall). On average, the recruitment of large trees was over two times faster near forest edges, leading to a sharp (90%) increase in the mean population density of large individuals near forest edges, whereas the density of larger trees remained constant in the forest interior. Overall seedling and sapling density was significantly lower in edge than interior plots, but edge plots had a much higher proportion of larger (>100 cm tall) saplings. Our findings demonstrate that forest edges can have complex effects on tree demography and that one must consider all tree life stages in order to effectively assess their effects on plant populations.

Treefall gaps of certified, conventionally managed and natural forests as regeneration sites for Neotropical timber trees in northern Honduras

Forest certification programmes promote sustainable management of the world's forests. Certification can be given to a forest management system that fulfils certain environmental, social and economic criteria. The ecological criteria for certified forestry include limiting harvest intensity and minimizing the mechanical damage of logging. Based on these requirements, we hypothesized that in comparison to conventionally managed forests, the logging gaps of certified forests would (1) host more established saplings of timber trees, due to a higher abundance of seed trees left in the forest, and (2) provide more favourable environments for the establishment and growth of timber seedlings, due to the control of negative logging impacts. We tested these hypotheses, using regeneration data on 10 shade-tolerant Neotropical timber species in a total of 46 treefall gaps in certified, conventionally managed and natural broad-leaved forests in northern Honduras. We analysed 12 environmental gap characteristics as determinants of sapling abundance, using a statistical approach that emphasizes their sensitivity to the forest management system as well as their ecological role. We found that gaps in certified forests were characterized by lower levels of logging-related disturbance than gaps in conventionally managed forests. The differences were however relatively small, since loggings are done at low intensity and without heavy machinery in the area. Despite the more favourable gap environment, regeneration success was poorer in certified forests than in conventionally logged forests. As expected, highest regeneration was found in natural forests. The good regeneration success in conventionally logged forests was largely due to the high abundance of a single species, Mortoniodendron vestitum. To explain the remaining differences in regeneration between management types, we suggest that loggings in certified forests have been more intensive in the past, leading to a scarcity of timber seed trees. We further propose two alternative explanations related to treefall gap frequency: (a) low logging intensity after certification may have led to low frequency of treefall gaps, limiting the recruitment of timber species; or (b) intensive loggings currently maintain an environment with too much disturbance for the success of timber regeneration.

Tree regeneration and microclimate in a liana and bamboo-dominated semideciduous Atlantic Forest

We assessed the effect of native bamboo and lianas on microclimate, tree regeneration and forest structure in a semi-deciduous Atlantic Forest subjected to selective timber extraction during the last century. We hypothetized that bamboo and liana cutting would increase incoming solar radiation in the understory promoting establishment and survival of pioneer and light-requiring canopy tree species. A manipulative experiment consisting of bamboo and liana cutting was performed in a native forest stand in northeastern Argentina. In three permanent 1-ha plots bamboo and lianas were cut and allowed to decompose in situ, while other three plots were used as a control treatment. We measured solar radiation reaching the understory, soil water availability and air temperature in both bamboo and liana cutting and control plots. Tree sapling abundance and richness, stand basal area, bamboo density, and cover of lianas, herbs, shrubs, fallen trees and branches were also determined. We performed multivariate analyses to relate tree sapling abundance and richness with biotic and abiotic factors. Bamboo and liana cutting increased by 100% the solar radiation reaching the understory. The fraction of solar radiation transmitted at 0.7 m height above ground in control and treated plots was 0.1 and 0.2, respectively. Minimum soil matric potentials after a severe dry spell were less than −2 MPa. Soil water availability was higher under closed-canopy in the treated plots because liana transpiration was prevented by cutting. Although bamboo and liana cutting increased incoming solar radiation, tree seedling and sapling abundance of pioneer and light-demanding species was not improved by the treatment. Instead, an increased abundance of herbaceous plants was observed in gaps and open canopy areas (i.e., sites with amounts of herb cover greater than 75% represented the 11 and 2% of the total number of sites in treated and control plots, respectively). Sapling survival and growth rates, on the other hand, appeared to be promoted by bamboo and liana cutting. Bamboo inhibited tree sapling abundance and richness in gaps, whereas tree basal area had a positive effect. In the semideciduous Atlantic Forest, native bamboos modify gap phase regeneration, and may affect canopy cover and forest composition in the long term. Post-logging management techniques are needed for sustainable timber production in these forest stands.

Testing the utility of Nothofagus pumilio for dating a snow avalanche in Tierra del Fuego, Argentina

In the subalpine forest zone, snow avalanches are potentially stand-devastating disturbances. Historical data regarding past avalanches in Argentina are scarce, but sufficiently old trees can show signs of past avalanche episodes that can be accurately dated using dendrochronological methods. Tree-ring analysis has not yet been used for dating avalanches in Tierra del Fuego, even though these disturbances are important to the dynamics of these southern forests. In this study, we evaluated the quality of Nothofagus pumilio for dating the avalanche that took place in the Martial Valley in 1976. Tree-ring data, complemented with vegetation analysis, was used to study the avalanche path. The dendrochronological study consisted of the analysis of wood samples taken from living trees located on the boundary between the undisturbed forest and the avalanche path. The vegetation analysis compared the forest structure within the avalanche path with the unaffected nearby forest. Wood scars and the abrupt increase in tree growth confirmed the occurrence of an avalanche event in 1976 in the Martial Valley of Tierra del Fuego, Argentina. The vegetation structure within the avalanche path was considerably different than that of the undisturbed forest. We found an important relationship between sapling abundance within the avalanche path and their distance from the undisturbed forest and their altitudinal position. The dendrochronological dating obtained in this research confirmed that the techniques and methodology used for N. pumilio in this study can be successfully applied for dating other avalanches that lack historical information.

Density‐related effects of deer browsing on the regeneration dynamics of boreal forests

SummaryThe density of large herbivores is a major driver of forest ecosystem structure and function in conjunction with episodic disturbances, especially in forests with a regeneration strategy based on shade‐tolerant seedlings capable of re‐establishing canopy dominance (advance regeneration). Yet, uncertainty about the relationships between forest regeneration, herbivore density and other disturbances makes it difficult to set population goals. Using an innovative controlled browsing experiment, we investigated the relationships between the regeneration dynamics of balsam firAbies balsamea, the density of white‐tailed deerOdocoileus virginianusand timber harvesting.We hypothesize that advance tree regeneration either: (i) recovers approximately linearly as deer density is reduced; (ii) recovers exponentially; or (iii) does not recover because factors other than browsing control advance regeneration. We tested these alternatives through manipulation of deer densities (0, 7·5, 15 deer km−2andin situlocal densities) and forest cover (clearcut and uncut forest).Balsam fir seedling mortality decreased exponentially with decreasing deer density in clearcut and approximately linearly in uncut forest. Independently of deer density, the recruitment of seedlings in clearcut dropped from 56 ± 5% to 7 ± 1% within 3 years.Seedling growth increased exponentially with decreasing deer density in clearcut whereas no height growth was observed in uncut forest.Overall, the abundance of fir saplings recovered exponentially in clearcut but remained low and independent of deer density in uncut forest. The abundance of sprucePiceaspp. saplings was unrelated to deer density and increased with time.Synthesis and applications. Forest disturbance from selective browsing at high deer densities over an extended period of time leads to recruitment failure following a canopy disturbance such as a clearcut. Indirect competitive advantage given to species resistant to browsing can shift forest composition. Nonlinear relationships between fir regeneration and deer densities imply that the level of culling required to reach herbivore densities compatible with natural regeneration of native forest is larger than expected if tree regeneration was proportional to deer density. In the boreal forest of Anticosti Island, local densities &lt; 15 deer km−2achieved within 3 years following clearcut are compatible with the maintenance of native forest.

Tree seedling and sapling density and deer browsing incidence on recently logged and mature non-industrial private forestlands in Virginia, USA

We compared the density and species composition of seedlings and saplings as well as the evidence of browsing by white-tailed deer ( Odocoileus virginianus) on recently logged and mature non-industrial private forestland (NIPF) stands in south-central Virginia. Nine stands had been harvested within the past 2 years and the nine mature forest stands had not been harvested within the past 30–40 years. Seedling (trees <0.5 m tall) density was similar on recently logged and mature stands. Sapling (≥0.5 m tall, but <10 cm diameter at breast height) density was more than two times greater on recently logged stands than mature stands, although this difference was not statistically significant. There was no significant correlation between stand basal area and seedling or sapling density. Some evidence of browsing by deer was observed for almost all tree species recorded. For logged sites, 0.9% of all seedlings had evidence of browsing compared to 3.4% of seedlings in mature stands. There was significantly more evidence of browsing on saplings in mature forest stands (22.9%) compared to recently logged stands (6.1%) and browsing evidence significantly increased with increasing basal area. Evidence of high browsing pressure and low sapling density on mature forest stands may indicate a problem with advance regeneration on NIPF stands in this part of Virginia. Logged stands had a significantly higher abundance of seedlings and saplings of yellow-poplar ( Liriodendron tulipifera), the most valuable timber species in the study area and one that did not show much evidence of browsing by deer. Logging, however, appeared to promote the colonization of the nonnative invasive species ailanthus ( Ailanthus altissima).

Plant dispersal strategies and the colonization of Araucaria forest patches in a grassland-forest mosaic

Questions: In a natural grassland-forest mosaic: What is the influence of phylogeny and diaspore traits related to disperser attraction (DAT) on (1) seed size/number trade-off (SSNT) in woody species colonizing forest patches; (2) on the frequency of the species? 3. What is the influence of forest patch area on mean seed size and number. 4. Do phylogeny and DAT expressed at the species level affect this relationship? Location: Campos grassland and Araucaria forest in Sao Francisco de Paula, RS, Brazil, at ca. 29°28' S; 50°13' W. Methods: Forest patches of different sizes in a grassland site recovering for ten years since human disturbances were surveyed by the relative abundance of vertebrate-dispersed woody saplings. We described colonizer species according to taxonomic phylogenetic relationships and diaspore type, size and color. We analyzed with a variation partitioning method their influence on SSNT and on species frequency in the patches. At the community level we regressed mean seed size and number on forest patch area and evaluated how these relation ships were affected by phylogeny and DAT at the species level. Results: 1. Phylogeny and DAT mostly explained seed size and seed number per diaspore variation. 2. By controlling phylogeny and DAT influence the frequency of species in forest patches was positively associated with their seed number in the diaspores, and negatively associated with their seed size. 3. Mean seed size and seed number at the community level were positively associated with patch area. 4. When phylogeny and DAT influences on seed size were removed this relationship was stronger for seed size and weaker for seed number. Conclusions: 1. Energy allocation to dispersal in detriment of offspring survival increased the successful establishment of colonizer species in forest patches, despite phylogenetic relationships and DAT variation in their diaspores. 2. Although patch area exerted a selective pressure on seed size, habitat preferences of dispersers may also influence patch colonization.

Aspen demographics in relation to spatial context and ungulate browsing: Implications for conservation and forest management

Aspen has a high conservation value and has been targeted as a priority species in sustainable forest management. However, sustained and intense browsing pressure by ungulates has raised concerns about the recruitment of aspen to mature growth stages. Here we investigate the influence of ungulate browsing on the demographic structure of European aspen populations in two managed boreal forest areas in Sweden with contrasting amounts of aspen and high densities of ungulates. The contrast in size distribution of ramets in the two areas was striking. The aspen-poor environment contained a much lower density of small-sized ramets than the aspen-rich environment. Ramet abundance was strongly associated with the abundance of ramets in the smaller size classes in both areas, reflecting demographic inertia in these populations. Ungulate use was most strongly associated with abundance of medium-sized aspen saplings growing in forest interiors. Otherwise, use of ungulates was only weakly correlated with aspen population parameters. The strong demographic momentum exhibited by these populations suggests that aspen conservation and management should pay more attention to additional factors than browsing to promote ramet establishment. Large variation in abundance of ramets in the smallest size-class shows that some aspen stands have a disproportionate effect on aspen recruitment, particularly in areas where aspen is less abundant. Identifying aspen stands with a large capacity for self regeneration may be the key to meet aspen conservation goals.

Indirect Effects of Forest Management on Riparian Zone Characteristics in the Adirondack Uplands of New York

Abstract Riparian zones are transitional areas between streams and adjacent terrestrial habitats, and they typically have vegetation communities distinct from both. To identify possible effects of forest management within a watershed on riparian plant community structure and riparian zone width,understory vegetation was sampled in three managed and three unmanaged (Forest Preserve) watersheds (250ߝ550 ha) in the Adirondack Park, New York, at three lateral distances (2, 7, and 12 m) from the stream (n = 6). Abundance of herbs was greater at Preserve sites, althoughrichness was not affected by land use. Abundance and richness both decreased with distance from the stream within each land use type, and this decrease was less steep at Forest Preserve sites. Abundance of saplings was greater under management, and saplings did not respond to distance fromthe channel. Binary discriminant analysis demonstrated differences in herb community composition between land uses, although this difference decreased with increasing proximity to the channel. Although none of the riparian areas in this study have been directly logged, this study shows thatindirect effects of management in a watershed (e.g., increased light and evapotranspiration) can alter the riparian herbaceous community, increase the density of saplings, and narrow the riparian zone of small upland streams. North. J. Appl. For. 23(4):273–279.

Interference to Hardwood Regeneration in Northeastern North America: Ecological Characteristics of American Beech, Striped Maple, and Hobblebush

Abstract Several woody species may inhibit regeneration of desirable northern hardwoods. This includes a dense understory of American beech (Fagus grandifolia Ehrh.) that commonly occurs in stands infected with beech bark disease. Root injuries during logging and by natural causes alsopromote new suckers that, along with some stump sprouts, often maintain or increase the abundance of beech saplings. Additionally, browsing deer primarily bypass beech in favor of more palatable species. Where any of these factors has resulted in a dense understory of small beech, overstorycutting will promote its development, increase ground-level shading, and lead to a site conversion to beech. Similarly, striped maple (Acer pensylvanicum L.) often interferes with hardwood regeneration after overstory cutting. This species persists in heavy shade, grows rapidly afterrelease, and produces abundant seed. When dense, striped maple may interfere with the regeneration of other species. Hobblebush (Viburnum alnifolium Marsh.), a shrub, reproduces by rhizomes to form thickets when damaged during overstory cutting. Heavy shade by these thickets may preventregeneration of trees. This review summarizes characteristics of these three species with respect to their interference with desirable hardwoods in northeastern North America. It highlights the limited information about striped maple and hobblebush, and the abundance of sources that deal withAmerican beech.

Influence of between-year variation in the density of Rhus trichocarpa fruits on the removal of fruit by birds

The fruiting phenology and fruit removal patterns of Rhus trichocarpa Miq. (Anacardiaceae) were investigated in a warm-temperate secondary forest in Japan. Mature fruits of this species are dispersed by birds. Effects of fruit display size and canopy openness on fruit removal were investigated in years with different fruit densities (i.e., masting and non-masting years). Moreover, effects of increased canopy openness during winter on fruit removal were also investigated. Seasonal patterns of fruit removal were quite different between masting and non- masting years. In the non-mast year, fruits were removed by birds soon after maturation in the summer. In contrast, in the mast year, fruits were removed gradually by birds from summer to winter. Moreover, the rate of fruit removal was greater for trees with a larger display size in the non-mast year, whereas that was greater for trees with greater canopy openness in the mast year. Canopy openness increased in winter, and fruit removal in winter was enhanced in trees with a more open canopy only in the non-mast year. These observations strongly suggest that avian dispersers became satiated in the mast year, whereas fruit removal was enhanced in the non-mast year. In the mast year, although many fruits were not dispersed until winter, they were neither depredated nor rotten, and the long period of fruit removal by birds may have enhanced fruit dispersal. The large abundance of seedlings and saplings of this species in Japanese secondary forests suggests that this fruiting strategy is beneficial.

Long‐term dynamics of the long‐lived conifer Libocedrus bidwillii after a volcanic eruption 2000 years ago

Abstract. Question: Following a volcanic eruption of ca. 232 AD, known as the Taupo eruption, the emergent conifer Libocedrus bidwillii expanded on Mt. Hauhungatahi, upwards above the current tree‐line, and downwards into the mixed montane forest. We ask: (1) if current age‐structures at different altitudes support the patterns predicted by the temporal stand replacement model, with cohort senescence and progressively depleting recruitment at ca. 600 year intervals (average cohort age) since the eruption: and (2) if the case history of the population sheds light on the persistence of mixed conifer‐hardwood forests in general.Location: Mt. Hauhungatahi, Tongariro National Park, New Zealand.Methods: The species composition and structure of seven stands covering the altitudinal range of Libocedrus bidwillii, were quantified. Libocedrus trees were cored, and regression equations used to predict ages. Cohorts were identified.Results: Libocedrus densities and basal areas, and the abundance of seedlings and saplings, peaked at different altitudes. At the species’lower limits there has been no recruitment for ca. 550 years, and the angiosperm Weinmannia racemosa has gained dominance. In the tree line and sub‐alpine forest stands, a low level of continuous regeneration has been boosted by periodic cohort recruitment following exogenous disturbances.Conclusions: In the montane zone, the Libocedrus age structure, and its replacement by Weinmannia, are consistent with a model of depleting cohorts separated by ca. 600 years since the Taupo eruption. At higher altitudes more frequent disturbances and reduced competition have allowed Libocedrus persistence. Comparison with other studies suggests long‐term relationships between gymnosperms and angiosperms are mediated by the scale and frequency of disturbance.

Mortality and stand renewal patterns following the last spruce budworm outbreak in mixed forests of western Quebec

We studied mortality caused by the last spruce budworm ( Choristoneura fumiferana Clem.) outbreak (1972–1984) and the subsequent regeneration processes in the mixed conifer–hardwood forest zone of the Témiscamingue region, western Québec. Three kinds of late successional stands, undisturbed by human activities and representative of forest conditions on different sites, were studied using permanent plots, dendrochronology, and field data. The tree species affected directly by the spruce budworm, balsam fir ( Abies balsamea L.), white spruce ( Picea glauca Moench.), and black spruce ( Picea mariana Mill.) suffered high overall mortality rates during the 1972–1996 period covered by the permanent plot measurements (97.6, 63.5, and 59.6%, respectively). The mortality of balsam fir and white spruce were positively correlated with pre-outbreak balsam fir basal area in the plots, as was the mortality of a non-host species, white birch ( Betula papyrifera Marsh.). Mortality of host and non-host species following the outbreak might have been due in part to modified environmental conditions following canopy disruption, particularly on imperfectly drained sites that were dominated by balsam fir before the outbreak. This is also supported by the fact that radial increments of surviving white spruce trees remained significantly lower after the outbreak in balsam fir-dominated stands compared with other stand types. The outbreak has also favoured the emergence of an abundant sapling layer mostly dominated by balsam fir. Due to important fluctuations in the shape of canopy gaps over the years, the correlations between sapling abundance and actual canopy openings are low for all sapling species. In the present-day mixed species stands, density and species composition of the sapling layer seem to depend more on the presence of suitable micro-sites than canopy openings. These results suggest that the last outbreak gave rise to a gradient of stand regeneration patterns, depending on species composition before the outbreak and host and non-host mortality following it, ranging from overall stand mortality and replacement in balsam fir-dominated stands, dual-cohort structures in mixed boreal stands where mortality was partial, and quasi-gap dynamics in mixed hardwood stands dominated by yellow birch ( Betula alleghaniensis Britton).

The effects of environment and life stage on Quercus abundance in the eastern deciduous forest, USA: are sapling densities most responsive to environmental gradients?

Most studies that describe tree species distributions across environmental gradients focus only on the abundance of adults. This approach may overlook the response of younger life stages (i.e., seedlings and saplings) and thus may fail to identify the life stage that is most sensitive to a particular environmental gradient (i.e., site characteristics that vary across landscapes such as elevation or aspect). Alternatively, seedling and sapling abundance may be unrelated to environmental gradients and may be entirely dependent on adult abundance. In order to effectively manage eastern hardwood forests to promote species compositions that maximize economic or ecological value, we need to understand the relative roles of site characteristics and adult abundance on all life stages. To address this need, we examined the relationships between five site characteristics (aspect, slope position, site index, stand age and elevation) and the abundance of seedlings, saplings and adults of three species of oak ( Quercus rubra, Quercus alba, and Quercus prinus). We assessed these relationships by censusing seedlings, saplings, and adults in large plots (500 m 2) and quantifying local site characteristics in 21 forest stands in the Monongahela National Forest in North Central West Virginia. Adult white oak densities peaked on southwestern slopes ( R 2 = 0.24); adult chestnut oak densities peaked on ridge tops ( R 2 = 0.58); and adult northern red oak densities were not correlated with any site characteristics ( R 2 = 0.00). Densities of white oak and chestnut oak saplings were highly correlated with a combination of site characteristics and seedling densities ( R 2 = 0.75, 0.81, respectively), and northern red oak densities were highly correlated with site characteristics solely ( R 2 = 0.70). For seedlings, white oak and chestnut oak densities were correlated only with adult abundance ( R 2 = 0.53, 0.56, respectively), and northern red oak densities were correlated solely with site characteristics ( R 2 = 0.45). These data suggest that in the absence of disturbance, site characteristics have the strongest effects on abundance patterns of these oaks during the sapling stage. For each of the three species, seedling, sapling and adult densities were correlated with a different subset of factors meaning that different biotic and abiotic conditions promoted peak densities for each life stage. Such a pattern indicates that important “demographic conflicts” exist (sensu [Battaglia, L.L., Fore, S.A., Sharitz, R.R., 2000. Seedling emergence, survival and size in relation to light and water availability in two bottomland hardwood species. J. Ecol. 88, 1041–1050]).

The herb and dwarf shrubs colonization of decaying logs in subalpine forest in the Polish Tatra Mountains

This is a study of the colonization pattern of herbs and dwarf shrubs on rotten logs in subalpine spruce forests (Plagiothecio Piceetum) in the Tatra Mountains. On four study plots (total area 1.43 ha.) all dead logs were measured and the decomposition stage was estimated using the 8-degree scale. For each log the cover of all vascular species, bryophytes and lichens was determined according to the methods of classical phytosociology. Constancy and an index of coverage were calculated for all vascular species growing on logs. The total volume of logs was relatively high (93 m3 ha−1) and constituted 22% of the volume of living trees. Logs and stumps covered 411 m2 ha−1. These values are similar to those known from natural spruce forest from Carpathians and Scandinavia. The 8 stages of decomposition were equally represented, which indicates a constant supply of dead wood to the forest floor over time. The colonization of dead wood starts with lichens, followed by bryophytes and finally herbs and tree saplings. The first vascular plant colonists of dead logs appear at decay stage nr. 3 at least 20 years after tree death. The most suitable condition for most of the herb species corresponds to decay stage nr. 6 ca. 50 years after tree death. The herb cover is distinctively dominated by Vaccinium myrtillus. Simultaneously with herb species, tree seedlings colonize the logs. Constancy and abundance of Norway spruce saplings increases with advanced decomposition. It seems that the herb cover of logs does not hinder the regeneration of spruce.

Understorey light profiles in temperate deciduous forests: recovery process following selection cutting

1 We investigated recovery following small-scale disturbance, i.e. selection cutting, by determining how understorey light profiles vary over time in temperate deciduous forests in Quebec (Canada). 2 We measured light availability (% PPFD, photosynthetic photon flux density) 0.2, 1, 2 and 5 m above the forest floor, as well as the density of saplings < 5 m in height, in seven Acer saccharum-Betula alleghaniensis-Fagus grandifolia stands that had been subjected to selection cutting 1-13 years before the study, and in adjacent uncut plots. 3 In the most recent cut (1 year old), mean % PPFD was 3. 5 to 5 times higher (depending on height) than in the uncut plot. Light availability rapidly decreased over time following selection cutting, especially near the forest floor. By about 13 years after cutting, light availability was similar to levels observed in the uncut plots. 4 Light profiles were used to assess the temporal pattern of recovery of the understorey after selection cutting, and four recovery phases could be identified. Uncut stands were characterized by profiles with low light near the forest floor and with a rather slow increase in light with increasing height, and recent cuts (1-4 years old) were characterized by J-shaped light profiles with relatively high % PPFD at all heights. Intermediate-age cuts (7-8 years old) were characterized by reverse J-shaped profiles that had a high % PPFD (13-46%) at 5 m, and very dark conditions (< 2%) near the forest floor, and were associated with high abundance of saplings. The relative frequency of the various profiles found in older cuts (11-13 years old) was generally similar to that observed in the uncut stands, except that the reverse J-shaped profiles were slightly more frequent. 5 As the microsuccession that follows canopy disturbance is very much influenced by local understorey structure and composition, forestry practices should consider such microscale forest characteristics in their harvest planning to regenerate the desired tree species.

Multiple Effects of Introduced Mammalian Herbivores in a Temperate Forest

Introduced mammalian herbivores can significantly affect ecosystems. Here, I review evidence on effects of introduced mammalian herbivores in the temperate forest of the southern Andes. Available data suggest that introduced herbivores decrease the abundance of seedlings and saplings of dominant tree species in some forest types, which could impair forest regeneration. They also affect understory species composition. The mechanisms of the effects of introduced herbivores are complex, and include direct effects of browsing or trampling and more complex interactions such as indirect effects through other species. Some native mammalian and avian predators may benefit from increased food availability resulting from high densities of some introduced mammalian herbivores. In turn, enhanced populations of predators may have resulted in increased predation on native prey. Competition for resources and disease transmission have also been proposed as possible negative effects of introduced herbivores on native herbivores, but little evidence supports this claim. Little is known about effects on invertebrates.

Regional Variation in Recruitment of Hemlock Seedlings and Saplings in the Upper Great Lakes, USA

Mature eastern hemlock–northern hardwood forest cover decreased drastically in the upper Midwest following European settlement and has yet to rebound substantially. Previous studies show that stands retaining substantial hemlock canopy coverage have low hemlock seedling and sapling densities. Results from various geographically restricted studies suggest several possible mechanisms that could cause low seedling or sapling density. We examined the relative importance of these proposed mechanisms in the Southern Superior Uplands Section of the Laurentian Forest Province. We surveyed 294-m2 plots in 100 hemlock stands in northern Wisconsin and western upper Michigan to assess how these proposed mechanisms affect the number of hemlock seedlings and saplings in four sequential size classes. Seedling and sapling abundance increases with greater light availability and differs significantly among geographically distinct ecological units (ecological subsections). In contrast, the abundance of medium and large saplings (30–99 and 100–300 cm tall) appears unrelated to light and geographic factors but declines as deer browsing increases, diminishing recruitment of larger saplings. The abundance of seedlings and saplings in each size class also depends strongly on the number of seedlings or saplings in the next smaller size class at the same site, reflecting demographic inertia. Path analysis integrates and separates these effects, explaining 24% of the regional variation in seedling abundance, 63% of small sapling abundance, and ∼80% of medium and large sapling abundance. Light and ecological subsection directly affect the number of seedlings and small saplings, whereas deer browsing directly affects the number of medium saplings. Demographic inertia remains important for all larger size classes. These results imply that restoring hemlock populations requires both appropriate microsites for seedling establishment and sanctuary from excessive browse for successful recruitment.