Early growth and seasonal chemical composition of three indigenous multipurpose tree species (MPTS) in Abeokuta,Nigeria

A study was carried out to evaluate the growth parameters and nutritive qualities of Moringa oleifera, Millettia griffoniana and Pterocarpus santalinoides. The main objective of the study was to assess the potential of the MPTS in supplementing the feed of ruminant animals during the dry season when grasses are scarce and their quality generally fall short of animal requirements. Leaf samples were randomly collected from the trees for estimation of the proximate composition, neutral detergent fibre, acid detergent fibre and gas production using the in vitro technique. Samples were collected three times to represent seasonal variations as follows: November: Early Dry; February: Mid Dry and April: Late Dry seasons. Gas production was recorded at 3, 6, 9, 12, 15, 18, 21, 24, 48, 72 and 96 h of incubation. Mortality rate was less than 5%. M. oleifera recorded the best overall growth respectively followed by P. santalinoides and M. griffoniana. P. santalinoides and M. oleifera retained more leaves in the dry season than M. griffoniana. The dry matter (DM) and ether extract (EE) contents of the MPTS were significantly (P < 0.05) affected by seasons and plant species while there were significant (P < 0.05) species effects on the CP and ADF values. The gas production values and the fermentation parameters indicated the presence of potentially degradable nutrients in the MPTS, which underscores the importance of the tree species as sources of nutrient for ruminant animals during the dry season.     

雷州市九龙山风景区植物区系与植被

广东省雷州市九龙山风景区植物共记录有种子植物112科394属579种（包括变种）,其中裸子植物7科9属14种,被子植物105科385属565种;其中野生81科294属423种,栽培69科162属227种;植物区系表现了我国北热带植物区系资源的典型性,植物种类丰富,广布种较多;天然植被以湿地红树林群落、次生季雨林和灌丛为优势,人工植被以坡地尾叶桉和热带作物等为优势;是一个具有极大科研价值和保存价值的地区。建议加快红树林国家级湿地公园建设,加强其自然资源保护与生态旅游开发力度。     

Floristic diversity, regeneration status, and vegetation structure of woodlands in Metema Area, Amhara National Regional State, Northwestern Ethiopia

We studied woodland vegetation in broad-leaved deciduous woodlands of Metema in northwestern Amhara regional state, Ethiopia Our objective was to describe plant species composition, diversity, regeneration status, and population structure by a selective approach with asystematic sampling design. A total of 74 quadrats (each for 25 m × 25 m,spaced at intervals of 150 200 m) were sampled along established transect lines following the homogeneity of the vegetation. Vegetation data including cover-abundance, height, diameter at breast height (DBH), and numbers of seedlings and saplings of woody species were analyzed using Excel spreadsheet, Shannon Weiner diversity index, and PAST version 1.62. A total of 87 vascular plant species of 74 genera and 36 families were recorded. The dominant family was Fabaceae represented by 16(18.39 %) species of 13 genera. Shannon Weiner diversity and evenness were 3.67 and 0.82, respectively, which showed that the area was endowed with rich floral diversity evenly distributed. The vegetation structure, as quantified by cumulative diameter class frequency distribution,plotted as an interrupted inverted-J-shape pattern with a sharp decreasein the 2nd diameter class. This indicated poor vegetation structure. The diameter classes frequency distributions of selected species plotted infour general patterns i.e., interrupted Inverted-J-shape, J-shape,Bell-shape and Irregular-shape. In conclusion, although the area showedhigh floral diversity and evenness, woody species including Sterculea setigera, Boswellia papyrifera, and Pterocarpus lucens showed lowest recruitment of seedlings and saplings.     

Hopper (Homoptera: Auchenorrhyncha) diversity in shaded coffee systems of Turrialba, Costa Rica

Diversity of hopper species (suborder Auchenorryncha) in coffee (Coffea arabica) plantations with no shade (C) was compared with the diversity in plantations with shade of either poró (Erythrina poeppigiana) (CP) or poró plus laurel (Cordia alliodora) (CPL) in Turrialba, Costa Rica. Species-abundance and rarefaction curves were plotted for each system, and indices of diversity (Shannon-Wiener), dominance (Simpson), species evenness, and similarity (Jaccard) were calculated. The majority of hopper species and individuals belonged to the Cicadellidae family. A particular species dominated in each system: Graphocephala sp. (C), Fusigonalia lativittata (CP) and Hebralebra nicaraguensis (CPL). The richness and diversity of hopper species were highest in the CP system, followed by the CPL and C systems. Species similarity was closest between the CP and CPL systems, but varied considerably according to plant component and geographic location of each plot. Even though hoppers have not been reported as coffee pests in Mesoamerica, some of them cause serious problems elsewhere. This revised version was published online in June 2006 with corrections to the Cover Date.     

Genetic diversity and conservation of two threatened dipterocarps(Dipterocarpaceae) in southeast Vietnam

Two threatened dipterocarp species,Dipterocarpus costatus and Dipterocarpus alatus are well-known endangered species in lowland forests of southeastern Vietnam,primarily from habitat loss and over-exploitation of their wood.To develop conservation strategies for these species,we analyzed 242 samples using nine microsatellite markers to determine the genetic variability within and among five populations of D.alatus and three of D.costatus,representing the natural range of dipterocarps in Southeast Vietnam.Results indicated low levels of genetic variability within populations with an average gene diversity of 0.223 for D.alatus and 0.152 for D.costatus.Results of bottleneck tests indicated a reduction in population size of both species(P>0.05).Genetic differentiation among populations was high(FST=0.347 for D.costatus and 0.274 for D.alatus),indicating limited gene flow(Nm=0.662 for D.costatus and 0.47 for D.alatus)and isolated populations related to geographical distances.Analysis of molecular variance showed high genetic variation within populations(72.92%for D.alatus and 60.81%for D.costatus)compared to among populations.Bayesian analysis and UPGMA tree also indicated the two optimal genetic clusters related to geographical distances.These results will provide a platform for the conservation,management and restoration of these species.     

Effects of deforestation on microbial diversity in a Siberian larch(Larix sibirica) stand in Mongolia

For evaluating microbial community changes in a Siberian larch stand disturbed by forest fire or clearcutting,357 clones were randomly selected and sequenced using a culture-independent approach and 16S rRNA sequencing to characterize the bacterial composition and diversity from the different disturbed Siberian larch stands.Interestingly,the burned larch stand had an increase in the relative amounts of b-proteobacteria and Firmicutes and a decrease in Acidobacteria,while Gemmatimonadetes increased Verrucomicrobia decreased in the harvested larch stand.Microbial diversity and richness were higher in the undisturbed larch stand than the disturbed(burned or clear-cut)larch stands,and the influence of clear-cutting was more negative than that of the forest fire.This study indicates that evaluating the microbial diversity of undisturbed,burned,and clear-cutting Siberian larch stands provides information about the impact of forest disturbances on soil microbial communities,which may be helpful for understanding and evaluating soil health and devising reafforestation strategies for larch.     

Links between plant diversity, carbon stocks and environmental factors along a successional gradient in a subalpine coniferous forest in Southwest China

In all, 48 sites of subalpine coniferous forest that had undergone natural regeneration for 5-310 years were selected as study locations in the Southwest China. We compared species richness (S), plant diversity (Shannon-Wiener index, H′; Margalef index, R), and above- and below-ground ecosystem carbon (C) pools of six plant communities along a chronosequence of vegetation restoration, and we also examined evidence for a functional relationship between plant diversity and C storage. Our results showed that above-ground C increased significantly (over 52-fold), mainly due to the increase of C in aboveground living plants and surface litter. Soil organic carbon (SOC) content increased from the herb community type (dominated by Deyeuxia scabrescens, P1) to mixed forest type (dominated by Betula spp. and Abies faxoniana, P4), which constituted the main C pool of the system (63-89%), but decreased thereafter (communities P5-P6). The mean C stock in the whole ecosystem - trees, litter layer and mineral soil - ranged from 105 to 730 Mg C ha⁻¹ and was especially high in the spruce forest community type (dominated by Picea purpurea, P6). On the other hand, the relationships between C stocks (soil, aboveground) and mean annual temperature or altitude were generally weak (P > 0.05). Moreover, we did not detect a relationship between S and aboveground C storage, while we found a significant negative relationship between H′, R and aboveground C storage. In addition, our experiment demonstrated that total root biomass and litter C/N ratio were significant functional traits influencing SOC, while S, R, and H′ had little effect. Path analysis also revealed that litter C/N ratio predominantly regulated SOC through changes in the quantity of microorganisms and soil invertase enzyme activity.     

Influence of skidder traffic and canopy removal intensities on the ground flora in a clearcut-with-reserves northern hardwood stand in Minnesota,USA

We investigated the effects of skidder traffic intensity, soil disturbance intensity, and canopy removal intensity on the richness, diversity, composition, and cover of the entire ground flora (woody and herbaceous vegetation ≤2 m tall), various individual life forms, invasive/noxious species, and species with different requirements with respect to moisture, nutrients, heat, and light (synecological coordinates) in a mesic northern hardwood stand 6 years after a clearcut-with-reserves regeneration harvest removed 50–100% of the canopy. Skidder traffic was restricted to a network of trails and a global positioning system (GPS) tracked skidder movement to quantify the number of passes at pre-established sampling points along the anticipated soil disturbance gradient on and off skid trails. Soil disturbance intensity within the top 15 cm of soil was quantified by relativized resistance to penetration (RRP) compared to untrafficked plots; post-harvest increases in RRP ranged from 81 to 272%. Regression analysis and ordination revealed a pattern of increasing difference from pre-disturbance composition with increasing skidder traffic (i.e., forest floor disturbance), with increased RRP (i.e., soil compaction) and (less so) canopy removal intensity. The ground flora shifted from interior forest species such as Anemone quiquefolia, Aralia nudicaulis, Clintonia borealis, Maianthemum canadense, and Oryzopsis asperifolia to more ruderal, invasive/noxious, and disturbed-forest species such as Aster lateriflorus, Cirsium spp., Phleum pretense, Rubus idaeus, and Trifolium spp. The relative resistance of the initial ground flora to change (inverse of the distances between pre- and post-harvest samples in ordination space) was nonlinearly related to skidder traffic intensity and linearly related to RRP, indicating that the largest compositional changes occurred with the first few passes of the skidder. Mean plot scores for the synecological coordinates revealed that the post-harvest species were on average less demanding of water and nutrients; the opposite was true for light. Plots exposed to less skidder traffic and RRP had higher herb cover and higher nutrient scores; those with more skidder traffic and higher RRP levels had higher shrub cover and higher light scores. We conclude that protection of the ground flora from forest floor and soil disturbance requires careful planning of skid trail networks. Concentrating skidder traffic to a designated skid trail system can result in less area disturbed and spatially connected networks of larger, untrafficked remnant forest patches that may maintain species that are sensitive to forest floor and soil disturbance.     

Line thinning fosters the abundance and diversity of understory Hymenoptera (Insecta) in Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don) plantations

We investigated the effects of line thinning on the abundance of Hymenoptera in two Japanese cedar plantations in northern Hyogo Prefecture, central Japan, in order to evaluate the effectiveness of this silvicultural treatment for ecosystem management. Line thinning is a silvicultural treatment practiced in Japan, where linear stand sections are cut (25%–35% of the total number of trees) retaining one to two rows of trees. We used Malaise traps to capture Hymenoptera from the line-thinned stand (treatment plot, including thinned and retained sections) and the unthinned stand (control plot). Overall, the total number of Hymenoptera was greater in the treatment plot than in the control plot. The treatment plot hosted more functional groups and families of Hymenoptera than the control plot in both plantations. In the Kuchiotani plantation (high-elevation site), the overall abundance of Hymenoptera and of many Hymenopteran functional groups were positively correlated with both species richness and biomass of understory plants. In the Sugi plantation (low-elevation site), understory vegetation was less developed and there was no correlation with abundance of Hymenoptera. Our study indicates that line thinning is an effective silvicultural treatment for future management of overstocked Japanese cedar plantations because it can fulfill biodiversity objectives, but the effectiveness may depend on silvicultural and landscape factors.     

Plant diversity and phenological pattern in the montane wet temperate forests of the southern Western Ghats, India

Plants diversity and phenological pattern of the trees were monitored in a montane wet temperate forest (shola) in the     

Impact of Macrotermes termitaria as a source of heterogeneity on tree diversity and structure in a Sudanian savannah under controlled grazing and annual prescribed fire (Burkina Faso)

Macrotermes termitaria are conspicuous features of savannah ecosystems in the Sudanian and Sahelian zones of West Africa. The mounds, alive or abandoned, are a major source of heterogeneity in the landscape. The purpose of the present study was to assess the impact of termitaria on tree community in a state forest of the Sudanian regional centre (Tiogo forest, Burkina Faso), under controlled burning and grazing experiments. A comparative inventory was carried out in a split-plot experiment (16 subplots of 2500 m²): 8 subplots where fire regime and grazing were controlled and 8 subplots exposed to grazing and with annual prescribed fire since 1992. All tree individuals (≥1.5 m) were recorded, both on termitaria and outside and their basal area at stump level was measured. A total of 61 observed (or 65.7 ± 2.4 estimated) tree species were recorded on 28 Macrotermes subhyalinus mounds (54 observed species or 60.8 ± 3.3 estimated), the immediate surroundings (44 observed and 59.0 ± 0.0 estimated species) and the rest of subplots (56 observed and 63.6 ± 0.0 estimated). Specific density was higher on mounds in comparison with the surroundings (P < 0.05). Results showed that termitaria played a key role in maintaining higher species diversity as compared to their surroundings (P < 0.05). Differences in species diversity between termitaria and immediate surroundings appeared more pronounced in disturbed plots (submitted to both fire and grazing). Some species, such as Tamarindus indica, Boscia senegalensis, Cadaba farinosa, Capparis sepiaria and Maerua angolensis are found solely on termitaria. Besides, the density of trees was significantly higher on termitaria compared to the surrounding (P < 0.05), as well as total basal area per unit of 100 m² area (P < 0.05). We concluded that Macrotermes termitaria play an important role as a source of heterogeneity in this Sudanian savannah woodland ecosystem. This role is particularly important in ecosystems under stresses. Termitaria acted as refuge for tree vegetation. The density and dynamics of M. subhyalinus termitaria should, therefore, be taken into account in the global strategy of the forest resources management and conservation.     

Simultaneous reduction in incidence of Bemisia tabaci (Hemiptera: Aleyrodidae) and Sylepta derogata (Lepidoptera: Pyralidae) using velvetleaf,Abutilon theophrasti as a trap crop

Journal of Pest Science - Trap cropping is a useful tool in sustainable pest management. Trap crops usually target a single species or genus of insect pests. In this study, we assessed the...     

Genetic diversity of sea buckthorn (Hippophae rhamnoides) populations in northeastern and northwestern China as revealed by ISSR markers

As a N₂-fixing tree species, sea buckthorn (Hippophae rhamnoides) is well adapted to arid regions and is utilized for multiple purposes in China. Current knowledge of genetic variability of H. rhamnoides is limited in terms of rangewide distributions. Eleven natural populations of sea buckthorn in northeastern and northwestern China were analyzed to detect genetic variation among and within populations, by use of ISSR (inter-simple sequence repeats) markers. Using eight primers, 207 polymorphic loci were observed, ranging in size from 250 to 2500 bp. The coefficient of gene differentiation (Gst = 0.0679) showed that the total molecular variance of 11 populations was mainly existed within populations. The genetic variation within and among the 11 populations was 93.21 and 6.79%, respectively. No significant correlation between genetic and geographic distances of the populations was found using ISSR markers. Our study provides a population-level genetic profile for further investigation and conservation of genetic diversity of sea buckthorn.     

Variability and grouping of leaf traits in multi-species reforestation (Leyte,Philippines)

Conventional reforestation in the tropics often results in stands with low tree species and functional diversities. A different approach to reforestation, the so-called rainforestation, has been developed in the Philippines. It emphasizes mixed stands and the preferential use of native species supplemented by fruit trees. In such stands, we studied several functional leaf traits (stomatal conductance for water vapour, leaf morphology and chemistry) with the objectives (1) of assessing the species-specific variation of leaf traits and in particular that of maximal leaf stomatal conductance (g_smax), (2) of determining relationships between g_smax and other tree variables, and (3) of assessing whether leaf traits group the species studied. Sixteen broad-leaved species were studied, using five individual trees per species and ten fully expanded sunlit leaves per individual tree. Species-specific g_smax differed fivefold (165–772 mmol m⁻² s⁻¹). Among studied leaf traits, only the carbon isotope ratio δ¹³C exhibited a simple linear correlation with g_smax. A separate analysis for dipterocarp species indicated a strong negative relationship between g_smax and specific leaf area (SLA) (r² = 0.96, P < 0.001, n = 5). For all 16 species, a multiple linear regression with the combinations leaf size/tree height and leaf size/canopy projection area also resulted in significant relationships, which partly explained the variability in g_smax. A multivariate approach (principal component analysis) combining the leaf traits provided an explanation of 75% of the variability along the first two axes. All native dipterocarps species, a native Guttiferae and the durian tree (Durio zibethinus) were associated with more depleted δ¹³C, small leaves and a low leaf width to length ratio. Two exotic species frequently used for reforestation (Gmelina arborea and Swietenia macrophylla) and the native early successional Terminalia microcarpa were differentiated by their high SLA and high leaf nitrogen content per leaf area (N_area). Both species of Artocarpus (A. blancoi and A. odoratissima) were also differentiated and had large leaves with low SLA and low N_area. These associations of species with leaf traits as variables indicate that species have different leaf investment strategies, which may imply that there are differences in whole plant performance. We conclude that rainforestation creates substantial variation in leaf traits, which is based on the combination of species with different leaf trait groupings. This can be seen as an important step towards – partly – restoring the functional diversity which characterizes many natural tropical rainforests.     

Genetic variation in fruitfulness in a hinoki (Chamaecyparis obtusa Endl.) seed orchard and its impact on the maintenance of genetic diversity in seedlots

Genetic variation in seed/cone production among clones was studied in a hinoki (Chamaecyparis obtusa Endl.) seed orchard containing 25 plus-trees by analyzing the number of cones, the yield of cones and seeds of individual ramets for 5 successive years (1982 to 1986). There was significant variation among clones each year and parental contribution in the seed orchard. Specifically, in the years 1982, 1983, 1984, 1985, and 1986, 20% of the clones produced 37.2, 60.6, 36.0, 44.3, and 44.8% of the total cones, respectively. The size of the crop greatly influenced the parental balance in the resulting seed/cone crops. The product moment correlation coefficients and Spearman’s coefficients of rank correlation were small and insignificant between consecutive years, but large and highly significant between alternate years, suggesting the presence of carry-over effects in seed/cone production. The broad-sense heritability on a clone mean basis was 0.74 ± 0.15 for the number of cones, 0.72 ± 0.14 for the yield of cones, and 0.68 ± 0.13 for the yield of seeds. The corresponding heritabilities from analyses combined over all years were 0.24, 0.558, and 0.724, respectively. These results indicate that seed/cone production in hinoki is under strong genetic control. Several managerial measures are discussed that maintain the genetic diversity in seedlots used for reforestation, by reducing the variation in seed/cone production among clones and producing seed crops with equal contributions from all parents.     

Post-logging loss of genetic diversity in a mahogany (Swietenia macrophylla King,Meliaceae) population in Brazilian Amazonia

Big-leaf mahogany (Swietenia macrophylla King, Meliaceae) is the most valuable widely traded timber species from the Neotropics. Mahogany has been severely overexploited throughout its natural range, which stretches from southern Mexico through Central and South America as far south as the Bolivian Amazon. We investigated effects of selective logging on the genetic diversity of a mahogany population in eastern Amazonia. Using eight hypervariable microsatellite loci, we estimated the number of alleles per locus (A), mean expected and observed heterozygosity (H_e, H_o), the number of distinct multilocus genotypes (G_o), and the inbreeding coefficient (f) for pre- and post-logging cohorts (adults and seedlings) collected over identical spatial scales. We found a significant reduction in the number of alleles, observed heterozygosity, and distinct multilocus genotype number in the post- compared to the pre-logging cohort. The loss of genetic diversity is likely to have occurred due to a reduction in the effective population size as a consequence of logging, which leads to the loss of alleles and limits mating possibilities. The results raise concerns about the conservation genetics of logged mahogany populations where a high proportion of adults are removed from the system. We suggest initiatives to promote the maintenance of genetic diversity as an integral part of the production system, allowing genetically sustainable use of this valuable timber resource.     

斑背大尾莺汉口亚种(Locustella pryeri sinensis)遗传多样性及种群结构研究

采用线粒体控制区（807bp）序列分析对中国境内斑背大尾驾3个繁殖种群及1个越冬种群的遗传多样性及种群遗传结构,结果表明：斑背大尾莺的单倍型歧义度（Hd）为0.759&#177;0.056,核苷酸多样性较（π）为0.002。三个地理种群的FST值以及繁殖种群同越冬种群之间的ΦST值表明不同地理单元之间无显著遗传分化。对不同单倍型的聚类分析（UPGMA）结果以及网络图（Network picture）结果也支持不同种群之间无显著分化。分子变异分析 （AMOVA）显示斑背大尾莺汉口亚种不同地理种群间遗传差异不大,98.5%的差异源自种群内部,仅1.5%源自种群间。中性检验结果Fu’sFS值为负值,错配分布分析结果呈单峰,表明斑背大尾驾在我国的进化史经历了种群扩张。这一假设也得到Tajima’D检验和Fu’s检验结果的支持（D=-1.80,p=0.02;Fs=-22.11,p=0.001）,该扩张大约发生在28,700年前。     

不同干扰梯度下尼泊尔森林树种多样性和优势种的变化(英文)

中度干扰可以增强多样性,因此干扰常作为一种管理手段。因而,了解森林干扰的频度和强度以及对林分结构、优势度以及森林多样性等的作用是非常重要的。本研究在尼泊尔设立25个1 ha样地,调查了不同干扰程度对以婆罗双树为优势种的5个林地生物多样性和优势度的影响。共记录67个树种,其中41个树种在轻度干扰的森林,10个在重度干扰的森林。林地之间α多样性差异显著。α多样性随干扰梯度线性降低,而优势度则呈线性增加。婆罗双树相对基面积随干扰强度而增加,重度干扰林下该树种重要值是轻度干扰林下的2倍。α多样性随婆罗叔树相对基面积的增加而以3倍的比率降低。在任意一对干扰林中,树种组成相似性均很低(相似性指数57%),说明β多样性较高。结论:婆罗双树林多样性随干扰强度增加而降低,但是优势度增加。建议控制优势种(婆罗双树)种群,来提高多样性,实现多功能利用的森林管理目标。图5表6参32。     

Effect of livestock grazing and human uses on herbaceous species diversity in oriental beech （Fagus orientalis Lipsky） forests,Guilan, Masal,northern Iran

Plant diversity plays key ecological roles in forest ecosystems, including influencing succession, resilience and nutrient cycling. This study was conducted to investigate the effect of livestock grazing and human uses on herbaceous species diversity. We surveyed 50 ha of protected area and 50 ha of unprotected area to evaluate herbaceous species diversity in oriental beech （Fagus orientalis Lipsky） forests in northern Iran. We calculated and compared three indices each of diversity and evenness, and species richness between the two areas. Herbaceous cover was higher in the unprotected area while leaf litter depth and tree canopy cover were higher in the protected area. The diversity indices, H （Shan- non-Wiener index ）, N~ （McArthur index）, N2 （Hill＇s index）, EQ （Modified Nee index）, E,ar （Smith-Wilson index）, E5 （modified index of Hill） and R=S （species richness） and species richness R=S were greater in the protected area than in the unprotected area, suggesting that protection from grazing results in increased numbers of plants and species. The effect of land protection on plant diversity was more pronounced for evenness than for species richness and the positive correlation between diversity and evenness indices was higher than that between diversity and richness.     

Density-dependent effects of northern hardwood competition on selected environmental resources and young white spruce (Picea glauca) plantation growth, mineral nutrition, and stand structural development – a 5-year study

The effects of competition from red raspberry (Rubus idaeus L.) and northern hardwood tree species on white spruce (Picea glauca (Moench) Voss) seedlings were examined on a clearcut site of the boreal mixedwood forest of the Bas-Saint-Laurent region of Quebec, Canada. A controlled experiment involving a gradient of five vegetation densities on the basis of the leaf area index (LAI) was established in a completely randomized plot design with six replications. Each of the five levels of vegetation cover (including vegetation-free plots) were examined to evaluate how they affected environmental factors (quantity and quality of light reaching the spruce seedlings, and soil temperature), spruce growth (height, basal diameter, volume index, and above-ground biomass), spruce mortality, browsing damage, spruce foliar mineral nutrition, as well as the stand structural development, during the first 5 years after seedling planting.

Each spruce growth variable analyzed in this study, according to a RMANOVA procedure, followed a negative hyperbolic form of density dependence of competitive effects. Loss of growth in young white spruce plantations in competition with northern hardwoods is likely to occur with the first few competitors. In cases where higher levels of competing vegetation were maintained over time, loss of spruce growth was extremely severe, to an extent where the exponential growth character of the young trees has been lost. At the end of the fifth year, spruce growing with no interference were larger in mean total above-ground biomass by a factor of 9.7 than those growing with the highest level of vegetation cover. Spruce did not develop a strategy of shade avoidance by increasing tree height, on the contrary. Spruce mortality differed among treatments only in the fifth year, indicating that early evaluation of spruce survival is not a strong indicator of competitive effects, when compared to diameter growth. Spruce foliar N and Ca contents were significantly reduced by the first level of competing vegetation cover, while K increased with the density of the vegetation cover, and P and Mg were not affected. Nitrogen nutrition of young white spruce planted on recently disturbed sites is discussed in relation to the potential root discrimination of this species against soil nitrate, a reaction observed by Kronzucker et al. [Kronzucker, H.J., Siddiqi, M.Y., Glass, A.D.M., 1997. Conifer root discrimination against soil nitrate and the ecology of forest succession. Nature London 385, 59–61]. The effects of hardwood competition indicate a prevalence of competition for light over a competition for nutrients, as revealed by the substantial increase in the h/d ratio of white spruce. Two indicators, h/d ratio and the quantity of light received at the tree seedling level, are suggested as a basis for the management of hardwood competition in a white spruce plantation.

Analysis of the stand structural development indicates that spruce height distribution was affected only by moderate or dense cover of vegetation, while diameter distribution, when compared to competing vegetation-free plots, was affected by the lowest level of vegetation cover. This study shows that competition influenced the stand structural development in the same way as genetic and micro-site factors by aggravating the amplitude of size inequality. The impact of hardwood competition is discussed in view of reaching an equilibrium between optimal spruce plantation growth and benefits from further silvicultural treatments, and maintaining hardwood species known to improve long term site quality, within a white spruce plantation.