Feasibility of implementing thinning in even-aged <Emphasis Type="Italic">Larix olgensis</Emphasis> plantations to develop uneven-aged larch–broadleaved mixed forests

Thinning experiments were conducted in larch (Larix olgensis) plantations to assess the feasibility of converting even-aged plantation stands to uneven-aged forests with more complex stand structures. Stands established in 1965 and 1960 were thinned in 2004 (Regime A, for determining the effect of recent thinning on emergence of seedlings) and 1994 (Regime B, for examining the effects of the past thinning on establishments of recruitments), respectively, at two intensities each. Natural regeneration, together with litter depth, canopy openness and vegetation cover, was surveyed in the thinned plots. Results indicated that larch seedlings started to emerge in May, reached a peak in June, decreased from June through September, and then disappeared in October. No larch seedlings exceeded 1 year old in the thinned plots because of the low levels of light and dense litter and vegetation cover. However, there were many naturally regenerated seedlings (5–50 cm in height) and saplings (50–500 cm in height) of broadleaved tree species such as Acer spp., Fraxinus spp., Cornus controversa, Quercus mongolica, and even the climax tree species, Pinus koraiensis, in the thinned plots. The mean density of regenerated seedlings reached 6.7 and 4.5 stems m⁻² in Regimes A and B, respectively, whilst the mean density of regenerated saplings reached 4,595 stems ha⁻¹ in Regime B. These results suggest that it is impractical to turn even-aged larch plantations to uneven-aged larch forests, but it may be feasible to develop uneven-aged larch-broadleaved forests from even-aged larch plantations through thinning.     

Interacting effects of canopy gap, understory vegetation and leaf litter on tree seedling recruitment and composition in tropical secondary forests

We experimentally investigated interacting effects of canopy gaps, understory vegetation and leaf litter on recruitment and mortality of tree seedlings at the community level in a 20-year-old lowland forest in Costa Rica, and tested several predictions based on results of previous studies. We predicted that experimental canopy gaps would greatly enhance tree seedling recruitment, and that leaf litter removal would further enhance recruitment of small-seeded, shade-intolerant seedlings in gaps. We created a large (320–540 m²) gap in the center of 5 out of 10 40 m × 40 m experimental plots, and applied the following treatments bimonthly over a 14-month-period in a factorial, split–split plot design: clipping of understory vegetation (cut, uncut), and leaf litter manipulations (removal, addition, control). As expected, experimental gaps dramatically increased tree seedling recruitment, but gap effects varied among litter treatments. Litter addition reduced recruitment in gaps, but enhanced recruitment under intact canopy. Species composition of recruits also differed markedly between gap treatments: several small-seeded pioneer and long-lived pioneer species recruited almost exclusively in gaps. In contrast, a few medium-to-large-seeded shade-tolerant species recruited predominantly under intact canopy. Leaf litter represents a major barrier for seedling emergence and establishment of small-seeded, shade-intolerant species, but enhances emergence and establishment of large-seeded, shade-tolerant species, possibly through increased humidity and reduced detection by predators. Periodic clipping of the understory vegetation marginally reduced tree seedling mortality, but only in experimental gaps, where understory vegetation cover was greatly enhanced compared to intact canopy conditions. Successful regeneration of commercially valuable long-lived pioneer trees that dominate the forest canopy may require clear-cutting, as well as weeding and site preparation (litter removal) treatments in felling clearings. Management systems that mimic natural canopy gaps (reduced-impact selective logging) could favor the regeneration of shade-tolerant tree species, potentially accelerating convergence to old-growth forest composition. In contrast, systems that produce large canopy openings (clear-cutting) may re-initiate succession, potentially leading to less diverse but perhaps more easily managed “natural plantations” of long-lived pioneer tree 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.     

Influence of slope position, stand type and rhododendron (Rhododendron ponticum) on litter decomposition rates of Oriental beech (Fagus orientalis Lipsky.) and spruce [Picea orientalis (L.) Link]

Oriental beech (Fagus orientalis Lipsky.) and Oriental spruce [Picea orientalis (L.) Link] are the two most common tree species in northeast Turkey. Their distribution, stand type and understorey species are known to be influenced by topographical landforms. However, little information is available as to how these changes affect litter decomposition rates of these two species. Here, we investigated the effects of slope positions (top 1,800 m, middle 1,500 m and bottom 1,200 m), stand type (pure and mixed stands) and purple-flowered rhododendron (Rhododendron ponticum) on litter decomposition rates of Oriental beech and spruce for 4 years using the litterbag technique in the field. Among these three factors, stand type had the strongest influence on litter decomposition (P < 0.001, F = 58.8), followed by rhododendron (P < 0.001, F = 46.8) and slope position (P < 0.05, F = 11.6). Litter decomposition was highest under mixed beech/spruce forest, followed by pure beech and spruce forest. Beech and spruce litter decomposed much faster in mixed bags (beech–spruce) than they did separately under each stand type. Purple-flowered rhododendron significantly reduced litter decomposition of Oriental beech and spruce. Beech and spruce litter decomposed much slower at top slope position than at either bottom or middle position. Differential litter decomposition of Oriental beech and spruce was mainly due to adverse conditions in spruce forest and the presence of rhododendron on the ground which was associated with lower soil pH. Higher elevations (top slope position) slowed down litter decomposition by changing environmental conditions, most probably by decreasing temperature as also other factors are different (pH, precipitation) and no detailed investigations were made to differentiate these factors. The adverse conditions for litter decomposition in spruce forest can be effectively counteracted by admixture of beech to spruce monoculture and by using the clear-cutting method for controlling rhododendron.     

Establishment and early growth of introduced indigenous tree species in typical plantations and shrubland in South China

Unsuccessful colonization by indigenous tree species into established plantations has retarded the succession of artificial plantations to more natural, secondary forests in South China. To understand how to improve colonization by seedlings of indigenous species, we determined how performance of indigenous seedlings is affected by seedling species (the shade-intolerant Castanopsis chinensis, the moderately shade-intolerant Michelia chapensis, and the shade-tolerant Psychotria rubra), the site into which the seedlings were transplanted (a mixed-legume plantation, a eucalyptus plantation, a mixed-native plantation, a mixed-conifer plantation, and a shrubland), and site preparation (removal or retention of understory vegetation and litter). Seedling survival and growth were generally increased by removal of understory vegetation and litter. C. chinensis and M. chapensis grew better in the mixed-legume and mixed-conifer plantations, while P. rubra grew better in mixed-native and mixed-conifer plantations. Responses of the transplanted seedlings to environmental factors were species specific. The effects of light on seedling survival and growth were correlated with the shade tolerance of the species. Soil moisture was important; it was positively correlated with survival but negatively correlated with growth of C. chinensis seedlings. Growth of C. chinensis and M. chapensis was positively correlated with soil potassium, while growth of P. rubra was positively correlated with soil organic matter but negatively correlated with soil hydrolyzed nitrogen. These findings suggest that we should select suitable native species under the different plantations before improvement of plantations. Light and soil moisture are most important environmental factors for the selection of species specific. Site preparation and fertilizer are needed during the improvement of those plantations.     

Effect of stand density and humus removal on regeneration of Pinus densiflora seedlings in a mixed conifer and broad-leaved forest

We studied the impact of stand density and forest floor humus removal on regeneration of Pinus densiflora in a mixed conifer and broad-leaved forest on the Daimonji-Yama Mountain,Kyoto,Japan.Three levels of stand density were set,i.e.,a clear-cut site,a heavily thinned site and a lightly thinned site.In each density treatment,comparisons were carried out between humus removal (A 0 -free)and humus intact(A 0 -intact)subplots.We counted the emergence of sown pine seeds and measured survival and growth of pine seedlings over the next four years.In addition,light conditions and the recovery of understory were monitored.Results show that thinning intensity and humus removal promoted the establishment and growth of seedlings.One exception,however,was that seedling growth was minimal in the heavily thinned A 0 -intact subplots.This was due to a strong response of understory vegetation growth on the treatment combination,which hindered the pine seedling growth.Furthermore,we found that the canopy openness measured at 1.3-m height remained at least 35%for the heavily thinned site in 2008.The results suggest that the removal of the A 0 layer after heavy thinning is the most effective and labor-saving operation for P.densiflora regeneration.     

Effects site conditions on industrial fiber plantations of Lar/x olgensis

Plot sampling was conducted in the second cultivation areas ofLarix olgensis in Heilongjiang Province, China. By analyzing plot investigation data, wood properties, and kraft pulps of 840 plots and 248 sample trees in industrial plantations of L. olgensis on different sites, we examined the growth process of L. olgensis industrial plantation with suitable structure, the wood fiber feature, chemical composition, physical performance and pulp characteristics. It is suggested that site conditions have major effects on plantation growth, fiber contains, fiber length, rate between fiber length and fiber width, pulping rate and pulp physics intensity. The best site for L. olgensis industrial plantation growth is site class Ⅰ and site class Ⅱ, which are on lower locations. Site condition has an obvious influence on the wood characteristics. Within the range of site conditions and stand densities studied, the worse the site condition, the less the fiber contains, the shorter the fiber length, and the more the 1% NaOH extraction. This kind of relationship becomes more obvious as stand age increases. However, the influence of site condition on pulping rate and pulp physics intensity is not obvious. The result provides theoretical base for cultivation of industrial fiber plantation of L. olgensis.     

Thinning and chipping small-diameter ponderosa pine changes understory plant communities on the Colorado Front Range

Novel fire mitigation treatments that chip harvested biomass on site are increasingly prescribed to reduce the density of small-diameter trees, yet the ecological effects of these treatments are unknown. Our objective was to investigate the impacts of mechanical thinning and whole tree chipping on Pinus ponderosa (ponderosa pine) regeneration and understory plant communities to guide applications of these new fuel disposal methods. We sampled in three treatments: (1) unthinned forests (control), (2) thinned forests with harvested biomass removed (thin-only), and (3) thinned forests with harvested biomass chipped and broadcast on site (thin + chip). Plots were located in a ponderosa pine forest of Colorado and vegetation was sampled three to five growing seasons following treatment. Forest litter depth, augmented with chipped biomass, had a negative relationship with cover of understory plant species. In situ chipping often produces a mosaic of chipped patches tens of meters in size, creating a range of woodchip depths including areas lacking woodchip cover within thinned and chipped forest stands. Thin-only and thin + chip treatments had similar overall abundance and species richness of understory plants at the stand scale, but at smaller spatial scales, areas within thin + chip treatments that were free of woodchip cover had an increased abundance of understory vegetation compared to all other areas sampled. Relative cover of non-native plant species was significantly higher in the thin-only treatments compared to control and thin + chip areas. Thin + chip treated forests also had a significantly different understory plant community composition compared to control or thin-only treatments, including an increased richness of rhizomatous plant species. We suggest that thinning followed by either chipping or removing the harvested biomass could alter understory plant species composition in ponderosa pine forests of Colorado. When considering post-treatment responses, managers should be particularly aware of both the depth and the distribution of chipped biomass that is left in forested landscapes.     

Factors influencing establishment by direct seeding of indigenous tree species in typical plantations and shrubland in South China

Seed limitation of desired indigenous species has constrained the succession of established plantations from an early successional stage, to more natural forests in South China. Because of its low cost and time-saving advantages, direct seeding has been considered a useful method in forest regeneration. To improve our understanding of whether and how direct seeding can lead to the establishment of indigenous tree species, we carried out an experiment in four typical plantations (eucalyptus, mixed-native, mixed-legume, mixed-conifer) and a shrubland in South China. We also tested the effect of understory vegetation and litter removal on seedling establishment and growth. Seeds of three indigenous tree species (Castanopsis chinensis, Cryptocarya chinensis, and Psychotria rubra) were sown with understory vegetation and litter either retained or removed. Seedling emergence, survival, and growth were recorded for 21 months. We found that conditions that favored seedling emergence often differed from those that favored seedling survival. While the removal of understory vegetation and litter did not influence the final seedling establishments for all the three introduced species, growth of Psychotria rubra was influenced at several sites. Seed mass was positively correlated with seedling emergence and subsequent growth. The large-seeded Castanopsis chinensis showed higher emergence and growth than the intermediate-seeded Cryptocarya chinensis or the small-seeded Psychotria rubra. Seedlings of Castanopsis chinensis grew better in plant communities with high understory light penetration and high soil exchangeable potassium. Growth of P. rubra seedlings decreased significantly with soil hydrolyzed nitrogen. In conclusion, direct seeding can be useful for the establishment of indigenous tree species into plantations and shrubland. Optimizing early seedling establishment and growth will require the selection of suitable native species for improving seedling establishment in different plantations. Additionally, understory vegetation and litter and fertilizer should be properly managed to enhance the establishment of certain indigenous tree species.     

Relating the survival and growth of planted longleaf pine seedlings to microsite conditions altered by site preparation treatments

Pine plantations in the southeastern United States are often created using site preparation treatments to alleviate site conditions that may limit survival or growth of planted seedlings. However, little is understood about how site preparations affect longleaf pine (Pinus palustris P. Miller) seedlings planted on wet sites. In a 2-year study (2004 and 2005) on poorly drained, sandy soils of Onslow County, North Carolina, we examined the effects of common site preparation treatments on microsite conditions and quantified relationships between microsite conditions and longleaf pine seedling survival and growth. Treatments used in the study included site preparations designed to control competing vegetation (chopping and herbicide) combined with those that alter soil conditions (mounding and bedding). During both years, mounding and bedding treatments reduced the amount of moisture within the top 6 cm of soil and increased soil temperatures when compared to flat planting (p < 0.001). Soil moisture was inversely related to seedling mortality in 2004 (r² = 0.405) and inversely related to root collar diameter in 2005 (r² = 0.334), while light was positively related to root collar diameter in 2005 (r² = 0.262). Light availability at the seedling level was highest on treatments that effectively reduced surrounding vegetation. Herbicides were more effective than chopping at controlling vegetation in 2004 (p < 0.001) and 2005 (p = 0.036). Controlling competing vegetation, especially shrubs, was critical for increasing early longleaf pine seedling growth.     

Development of oak and beech seedlings planted under varying shelterwood densities and with different site preparation methods in southern Sweden

Effects of site preparation, shelterwood density and planting depth on the survival and growth of planted beech and oak seedlings were studied. Experiments were performed in one oak and one beech stand in southern Sweden. Two areas with different densities of shelterwood and one clearcut were established in each stand. Growth, damage and survival of the planted seedlings were observed for three years. Soil water potential was recorded weekly and radiation and soil temperatures were recorded continuously during the growing seasons.Neither site preparation methods nor planting depth affected oak seedling growth, when planting was carried out on fresh clearcuts or in shelterwoods, while growth of beech seedlings was positively affected by mounding. Growth of oak seedlings was inhibited by the shelterwood treatments. In beech seedlings, growth was lowest in dense shelterwood, while there was no difference in growth between seedlings on the clearcut area and in the shelterwood of low density. Differences in growth may be explained by differences in radiation and soil water potential.When planting was carried out on a one-year-old clearcut, site preparation improved the subsequent growth of oak and beech seedlings.     

Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis> L.) regeneration and growth of understory trees under single-tree selection silviculture in Finland

This study presents empirical data on regeneration and growth of understory trees and constructs simple models for predicting these characteristics at various stand structure and post-thinning standing volume levels. The field experiment was established on a grass/herb mineral soil site in central Finland. Regeneration and understory tree growth data were collected from 24 Norway spruce (Picea abies L.)-dominated mixed substands. Seedlings with heights from 5 to 130 cm were measured in 1996 and 2007. In addition, the annual height growth of Norway spruce seedlings was measured in 2007. The spatial pattern of the substands varied from clustered to regular with a decreasing standing volume. Stand complexity was uniform across the range of standing volume. In the 2007 survey, the amount of Norway spruce regeneration increased from approximately 400 to 5,000 seedlings ha⁻¹ when the post-thinning standing volume level was reduced from 230 to 90 m³ ha⁻¹, respectively. Nearly no seedlings were found when the standing volume was over 300 m³ ha⁻¹. The annual diameter increment in Norway spruce understory (dbh < 5 cm) trees decreased, on the average, from 2.3 to 0.3 mm with an increase in the standing volume level from 90 to 340 m³ ha⁻¹, respectively; their height growth showed also a decreasing trend when the standing volume increased. The results indicated that a post-thinning standing volume lower than 150 m³ ha⁻¹ with a regular overstory spatial structure provides a suitable environment for regeneration and growth of Norway spruce understory trees in the studied forest type.     

Long-term response of planted conifers, natural regeneration, and vegetation to harvesting, scalping, and weeding on a boreal mixedwood site

This study reports 14th-year response of a boreal mixedwood stand to different harvest intensities (uncut, 50% partial cut with and without removal of residuals after 3 years, and clearcut), spot site preparation treatments (none and scalped), and chemical weeding frequencies (none, single, and multiple) in northeastern Ontario. The response variables include the survival and growth of planted white spruce (Picea glauca [Moench] Voss) and jack pine (Pinus banksiana Lamb.), height and density of natural regeneration and shrubs, and cover of shrubs and non-woody vegetation. Harvesting and weeding generally improved survival and growth of planted trees, although white spruce survival did not significantly differ among the three weeding frequencies. Harvesting tended to increase heights of hardwood (mostly trembling aspen (Populus tremuloides Michx.)) and conifer (largely balsam fir (Abies balsamea (L.) Mill.).) natural regeneration, cover and density of shrubs, and cover of herbs, lichens, and ferns. Chemical weeding reduced height, density and cover of shrubs, height and density of hardwood regeneration, and fern cover, but increased moss and lichen cover. Spot scalping did not significantly affect planted seedling, natural regeneration, or the vegetation.Maximum survival and growth of planted white spruce and jack pine were achieved using a combination of clearcutting and multiple weeding. However, partial cutting followed by a single weeding produced acceptable survival and reasonable growth of planted trees, particularly for white spruce. Partial canopy removal alone substantially reduced the amount of hardwood regeneration, relative to clearcutting, but did not adequately suppress understory shrubs. Significant improvement in seedling growth following multiple weedings was evident primarily in the complete canopy removal treatments: 50% partial cut with removal of residuals after 3 years and clearcut. While the effects of harvesting and weeding on planted crop trees found in the 5th-year assessments generally persisted at year 14, survival decreased, likely due to light competition from developing hardwood and shrubs.     

Effects of site preparation on soil properties and on morphology of Pinus sylvestris and Picea abies seedlings sown at different dates

The aims of the study are to find out the effects of site preparation on soil properties and on the morphology of three-year-old Pinus sylvestris L. and Picea abies (L.) Karst. seedlings sown at different dates along a slope with variation in soil texture, water, and fertility. Based on the hypothesis that soil texture affects soil water content, water retention capacity, and nutrient content, we studied site preparation of varying intensities: exposed C horizon, mounds (broken O/E/B horizons piled over undisturbed ground), and exposed E/B horizon. Though the growing time difference between sowings was about one month, after three growing seasons, spring-sown seedlings were larger than summer-sown seedlings. P. sylvestris seedlings were largest with mounds and smallest with exposed C horizon, but site preparation did not affect the morphology of P. abies seedlings.     

Effects of overstorey retention on ash regeneration and bramble growth during conversion of a pine plantation to native broadleaved woodland

Conversion of monoculture plantations to mixed stands with greater diversity is an important aim of sustainable forest management, and in Britain, this is concentrated on the restoration of native broadleaved woodland on ancient woodland sites that were planted with conifers. Current British guidelines for this restoration have rarely been examined, and this study is the first to test their value for natural regeneration. The survival and growth of naturally regenerating ash (Fraxinus excelsior L.) seedlings was observed in thinned, selectively felled and clearfelled plots within a c. 40-year-old stand of Corsican pine (Pinus nigra Arnold ssp. laricio Maire). After felling in 2001, the ground flora in all treatments became dominated by bramble (Rubus fruticosus L. agg.) and its cover 5 years after felling was 75–95?% at a height of 0.9–1.2?m. During the study, seedling numbers declined 80–90?%. Although bramble had some adverse effects, seedling survival was unaffected by felling treatment. Seedling growth varied between treatments with those in the clearfell being tallest. Mean height of seedlings was always less than that of bramble, but by 2006 65?% of quadrats in the clearfelled plots had well-established individuals taller than the bramble compared with 35?% in the thinned plots. Models that described the relationships between seedling growth, basal area and bramble were complex, but results clearly indicate that maintaining canopy cover during restoration is probably an ineffective method of suppressing bramble on sites where it grows well. Results do not support the current British advice on conversion, but this may reflect the characteristics of pine canopies and the maintenance of canopy cover during conversion may be appropriate in stands of species, which cast more shade.     

Organic amendment and inorganic fertilization affect soil properties and quality of Larix olgensis bareroot stock

Bareroot Changbai larch (Larix olgensis Henry.) seedlings were reared with inorganic fertilizer (nitrogen (N):phosphorus (P) = 1:1, W/W) applied at a rate of 100 (F100) or 200 kg N ha⁻¹ (F200) with (+) or without (−) chicken manure as a soil amendment (O) in north-eastern China. An unfertilized control treatment was included. Inorganic and organic fertilizer treatments tended to increase soil ammonium, nitrate, available P, total P, organic carbon content and electrical conductivity, and biomass and N concentration in seedlings. Organic amendment improved first order lateral root number, tap root length, fine root morphology (length, surface area, volume) in seedlings, while the F100 treatment increased N accumulation in needles and stems compared to the F200 treatment, on average. Most fertilizer treatments tended to increase P content in combined stems and roots, but F200 − O and F100 + O treatments diluted P in needles. Organic amendment combined with inorganic fertilizer at a rate of 100 kg N and P ha⁻¹ is recommended to improve seedling growth and N reserves in woody tissues.     

Seedling emergence in uneven-aged Norway spruce stands in Finland

The emergence of Norway spruce seedlings on different types of germination sites in uneven-aged Norway spruce dominated stands four years after selection harvesting was studied. The data were collected from 20 stands in southern Finland. In each stand, ground cover was measured from a set of 64 one square metre subplots on a permanent experimental plot of 1600?m². Correlation analysis, direct comparison of subplots with and without seedlings and mixed-effects models were used to estimate the influence of ground and tree cover on seedling occurrence. Grass cover, dwarf shrub cover, cover of certain moss species and close vicinity of trees decreased the occurrence probability and number of seedlings, while greater stand and local basal area around the subplots increased the seedling number. The cover of vegetation free surfaces, usually considered as good germination sites, was rather low. Variation in seedling emergence between plots was high. We concluded that spruce regeneration was slightly more abundant in stands with greater overall stand density and local density within a stand in postharvest conditions.     

Understory plant diversity and biomass in hybrid poplar riparian buffer strips in pastures

Understory plant biomass, species richness and canopy openness were measured in six-year old hybrid poplar riparian buffer strips, in the understory of two unrelated clones (MxB-915311 and DxN-3570), planted along headwater streams at three pasture sites of southern Quebec. Canopy openness was an important factor affecting understory biomass in hybrid poplar buffers, with lower understory biomass observed on sites and under the clone with lower canopy openness. Although tree size was an important factor affecting canopy openness, relationships between total stem volume and canopy openness, for each clone, also support the hypothesis of a clonal effect on canopy openness. Understory biomass and canopy openness as low as 3.6 g m⁻² and 7.6% in 1 m² microplots were measured under clone MxB-915311 at the most productive site. This reduction of understory plant growth could compromise important buffer functions for water quality protection (runoff control, sediment trapping and surface soil stabilisation), particularly were concentrated runoff flow paths enter the buffer. On the other hand, tree buffers that maintain relatively low canopy openness could be interesting to promote native and wetland plant diversity. Significant positive relationships between canopy openness and introduced species richness (R ² = 0.46, p < 0.001) and cover (R ² = 0.51, p < 0.001) were obtained, while no significant relationship was observed between canopy openness and native (wetland) species richness and cover. These results suggest that planting riparian buffer strips of fast-growing trees can rapidly lead to the exclusion of shade-intolerant introduced species, typical colonisers of disturbed habitats such as riparian areas of pastures, while having no significant effect on native (wetland) diversity. Forest canopy created by the poplars was probably an important physical barrier controlling introduced plant richness and abundance in agricultural riparian corridors. A strong linear relationship (R ² = 0.73) between mean total species richness and mean introduced species richness was also observed, supporting the hypothesis that the richest communities are the most invaded by introduced species, possibly because of higher canopy openness, as seen at the least productive site (low poplar growth). Finally, results of this study highlight the need for a better understanding of relationships between tree growth, canopy openness, understory biomass and plant diversity in narrow strips of planted trees. This would be useful in designing multifunctional riparian buffer systems in agricultural landscapes.     

Response of a rising 2-year-old natural Piedmont upland stand to fertilization

Hardwood stands in the southern U.S. are often regenerated naturally following clearcutting, with little or no silvicultural intervention in the early stages of stand development. Fertilizer was applied to a young naturally regenerating stand in order to evaluate the effectiveness of nutrient addition as a silvicultural tool in recently clearcut stands and to better understand the ecological relationships between site fertility and stand development. The study was installed on a rising 2-year-old naturally regenerated mixed pine-hardwood stand in the Hill Demonstration Forest in the Piedmont region (Durham County) of North Carolina. Fertilizer treatments were control, N, N + P, and N + P + K (at 200 kg N per ha, 50 kg P per ha and 100 kg K per ha). On a whole stand basis, increased growth rates were observed for trees on N + P and N + P + K plots. Fertilizer treatments did not affect total stand density, but the density of loblolly pine significantly decreased in N + P plots compared to the Control. The density of stems of stump origin also increased in plots receiving N + P. Density of sweetgum (Liquidambar styraciflua) significantly increased and hickory (Carya spp.) density decreased with the application of N + P. Dominant hardwood species with the exception of yellow-poplar (Liriodendron tulipifera) responded with an increase in height to only N + P fertilizer treatments. Yellow-poplar increased in groundline diameter, height and mean tree volume index with the application of N + P. Loblolly pine (Pinus taeda) responded to N + P + K fertilizer treatment with an increase in height, diameter and volume index over the Control. There was no growth response among treatments for the 16 largest trees per species per plot, with the exception of red oak (Quercus rubra) which responded with an increase in height in N + P plots. Projected growth responses were modeled on a whole stand level and indicate that the use of N + P fertilizer may be an effective silvicultural instrument to increase growth, accelerate stand development, and shorten rotation length.