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1.
? In mixed-species forest stands, large losses in tree species diversity often occur during the regeneration phase. In a former coppice-with-standards, we investigated whether the limiting stage in the recruitment process of advance regeneration is the immediate seedling response to canopy release. Experimental canopy gaps were opened and the survival and growth of advance seedlings (Fagus sylvatica, Acer pseudoplatanus, Acer campestre, Acer platanoides) growing in the gaps or under closed canopy were monitored for three years. ? All species responded positively and rapidly to canopy release. Survival was not affected by gap opening. Diameter increment after gap opening was similar across species, and height increment was greater for Acer platanoides and for Acer pseudoplatanus. Post-release diameter and height growth were mainly determined by pre-release seedling size. Competition from neighbouring seedlings did not affect growth in the three years following canopy opening. ? In the recruitment process of F. sylvatica and Acer sp. advance regeneration, the recovery from canopy release did not appear as a limiting step that would filter against some species. Pre-release size was the main factor accounting for post-release growth and is probably a major determinant of long-term seedling dominance. 相似文献
2.
? Seedling density and the regeneration mechanisms of five tree species, Anogeissus leiocarpa, Combretum aculeatum, Combretum micranthum, Combretum nigricans, and Pteleopsis suberosa were investigated in relation to latitudinal gradient across the Sahelo-Sudanian zone of West Africa. ? Data were collected on 461 quadrats (2 m × 5 m) laid out every 30 m on transect lines through Combretaceae communities at four latitudinal positions. Regeneration mechanisms were determined by excavating the below ground root system and assessing basal and aerial sprouts. ? The results showed a significant species × latitudinal position effect on the total density of seedling populations, and the density of single- and multi-stemmed individuals (p < 0.001). C. aculeatum and C. micranthum were abundant in the North-Sahelian sector, C. nigricans and P. suberosa in the Sudanian sector and A. leiocarpa across a wide range from the South-Sahelian to South-Sudanian sectors. In general, 58% of the seedlings were regenerated asexually (as coppice, water sprout, layer, and root sucker) while 42% were sexual recruits (as true seedling and seedling sprouts). The proportion of vegetatively propagated seedlings increased with increasing latitude for all species except C. micranthum, for which a clear decreasing trend was observed. The relative importance of the different regeneration mechanisms varied among species: seedling sprouts were important for A. leiocarpa, C. aculeatum and C. nigricans, coppice for C. micranthum and sucker for P. suberosa ? The significant interaction observed between species and latitudinal position highlights the importance of accurate species-site matching to ensure successful restoration of degraded areas in the Sahelo-Sudanian zone. Inter-species differences in regeneration mechanism could be related to their biology and ecological adaptation to the site-specific biotic and abiotic factors. 相似文献
3.
? The natural regeneration of shade-tolerant tree species is characterized by large spatial heterogeneity and temporal variability. The mechanisms producing those patterns are still poorly understood and the knowledge of long-term fluctuations in regeneration processes is very limited. ? We used data from long-term study plots in an old-growth stand dominated by European beech and silver fir to address three questions: (1) Is a tendency towards clumping in seedlings associated with a particular spatial scale? (2) Are the spatial patterns in seedlings constant over time? (3) Is the distribution of seedlings related to light intensity? ? Over the study period the seedling density varied from 2.5 to 6 ind./m2. Stronger fluctuations occurred at a fine scale. Seedlings were clumped at distances ranging from a few centimeters to a few meters. The distribution of places with high seedling densities was relatively constant over time, especially in beech. Positive but weak rank correlations were found between light intensity and densities of beech and fir seedlings. ? Despite large fluctuations in seedlings densities, caused by mast-seeding, a permanent seedling bank was maintained. Very pronounced clumping of tree seedlings found in this study was only partially explained by differences in light intensity. 相似文献
4.
? Fine-scale spatial and temporal establishment patterns of direct-seeded oaks on abandoned agricultural land have been little studied despite their potential importance for long-term stand structure. ? Here we periodically monitored seedling emergence and early growth of bur oak (Quercus macrocarpa Michx.) and red oak (Q. rubra L.) on an abandoned pasture, and tested the effects of herbaceous competition, rodents, and soil physicochemical properties. ? Herbaceous competition slightly decreased diameter growth, but rodents had little impact on establishment. Red oak seedlings emerged earlier than bur oak and in a greater proportion (92% vs. 56%). Seedling emergence and early growth of both species showed significant spatial structures that were partly explained by variation in soil physicochemical properties. Bur oak was more responsive to microenvironmental heterogeneity than red oak, yet much of the variation in emergence and growth of both species remained unexplained. ? This suggests that other factors, such as acorn size or genetic variability, may exert equal or greater control than microenvironmental heterogeneity over seedling emergence and early growth of these two oak species on abandoned pastureland. 相似文献
5.
? Fall fertilization may increase plant nutrient reserves, yet associated impacts on seedling cold hardiness are relatively unexplored. ? Bareroot red pine (Pinus resinosa Ait.) seedlings in north-central Minnesota, USA were fall fertilized at the end of the first growing season with ammonium nitrate (NH4NO3) at 0, 11, 22, 44, or 89 kg N ha?1. Seedling morphology and cold hardiness [assessed by freeze induced electrolyte leakage (FIEL)] were evaluated six weeks after fertilization and following the second growing season. ? Seedling height and number of needle primordia increased with fertilizer rate for both sampling years. Seedlings fertilized with 44 and 89 kg N ha?1 attained target height (15 cm) after the second growing season. Shoot and root N concentration increased after the first growing season in fall fertilized seedlings compared to controls. Fall fertilized seedlings had lower FIEL (i.e., increased cold hardiness) compared to controls when tested at ?40 °C after the first growing season, but no significant differences in FIEL of control and fertilized seedlings were observed after the second growing season. ? Results suggest that fall fertilization of red pine seedlings can help render desired target height in the nursery, while maintaining or increasing cold hardiness levels. 相似文献
6.
? In forests, the substitution of broadleaf species by conifers can reduce biodiversity because coniferous forests generally provide less diverse vascular understories than broadleaf forests. However, in some cases, former pine plantations might be useful for restoring native forests. We compared plant species composition on the plot scale in natural beech and mixed oak forests with that in plantations of Pinus radiata. Links between plant diversity and landscape parameters (patch size, fractal dimension and distance to the nearest patch of the same type) were investigated. ? The objective of this study was to evaluate the use of pine plantations for restoring native diversity in a zone where native forests are very fragmented. ? Similar to oak forests, plant diversity in pine plantations was high, mainly due to the presence of generalist species. Some species characteristic of oak forests also appeared in pine plantations, suggesting the onset of natural forest regeneration. ? These results suggest that pine plantations could be used to promote natural regeneration of original oak forests. Moreover, residual native stands should be conserved as important sources of native species and their seeds. 相似文献
7.
? To assess the sustainability of plantation forest management we compare two types of biodiversity indicators. We used the species richness of saproxylic beetles as a case study to test the “species” and “environmental” indicator approaches. We compared single species abundance or occurrence and deadwood volume or diversity as predictor variables. ? Beetles were sampled with flight interception traps in 40 Maritime pine plantation stands. The volume and diversity of deadwood was estimated with line intersect and plot sampling in the same stands. Predictive models of species richness were built with simple linear or Partial Least Square regressions. ? Deadwood variables appeared to be good predictors of saproxylic beetle richness at the stand-scale with at least 75% of variance explained. Deadwood diversity variables consistently provided better predictive models than volume variables. The best environmental indicator was the diversity of deadwood elements larger than 15 cm in diameter. ? By contrast, the use of “species variables” appeared to be less relevant. To reach the quality of prediction obtained with “environmental variables”, the abundance or occurrence of 6 to 7 species — some of which are difficult to identify — had to be used to build the indicator. 相似文献
8.
? Mixed coniferous, subalpine forest communities in the Rocky Mountains are historically dense and have experienced infrequent, high-severity fire. However, many of these high-elevation stands are thinned for a number of perceived benefits. ? We explored the effects of forest stand density on ecosystem properties in subalpine forests in Colorado, USA, 17–18 y after forests were managed for timber. ? Forest structure significantly altered the composition and chemical signature of plant communities. Previously managed stands contained lower density of overstory trees and higher ground cover compared to paired reference stands. Foliar phenolic concentration of several species was negatively related to basal area of overstory trees. Furthermore, reductions in stand density increased total foliar phenolic:nitrogen ratios in some species, suggesting that gap formation may drive long-term changes in litter quality. Despite significant changes in forest structure, reductions in stand density did not leave a strong legacy in surface soil properties, likely due to the integrity of soil organic matter reserves. ? Changes in forest structure associated with past management has left a long-term impact on plant communities but has only subtly altered soil nutrient cycling, possibly due to trade offs between litter decomposability and microclimate associated with reductions in canopy cover. 相似文献
9.
? The short-term effect of organic residue management on the growth and nutrition of Pinus pinaster Ait. seedlings, and on nutrient leaching and chemical properties of an acid soil was assessed through a lysimeter experiment. Treatments included absence, placement on the soil surface, and incorporation into the soil (with and without legume cover cropping) of organic residues (forest floor litter or forest floor litter plus harvest residues). ? Residues placed on the soil surface enhanced seedling growth. Organic residues reduced nutrient losses (NO 3 ? , Ca and Mg) and resulted in nutrient accumulation in the soil. Harvest residues positively affected K seedling nutrition status and enhanced K soil accumulation. ? Legume cover cropping reduced soil nutrient losses (N, Ca, Mg and K) during the early stage of seedling growth; it also improved seedling nutrition status (N and P), but without any effect on growth. ? Harvest residues plus forest floor litter placed on the soil surface was the most appropriate management to both reduce nutrient losses through leaching and increase height of seedlings at the end of the experimental period (two years). 相似文献
10.
? We describe the distribution and the ecology of three Armillaria species observed in silver fir (Abies alba) forests of the Pyrenees. ? We surveyed the presence and abundance of Armillaria above and belowground in 29 stands. Isolates were identified by the PCR-RFLP pattern of the IGS-1 region of their ribosomal DNA. We measured several ecological and management parameters of each stand in order to describe Armillaria infected sites. ? Armillaria cepistipes was the most abundant of three species observed. Armillaria gallica was dominant in soils with a higher pH and at lower elevations. Armillaria ostoyae seemed to be more frequent in stands where A. alba recently increased its dominance relative to other forest tree species. Thinning activities correlated with an increased abundance of Armillaria belowground. In 83% of the stands the same Armillaria species was observed above and belowground. ? It seems that in a conifer forest, A. cepistipes can be more frequent than A. ostoyae, a virulent conifer pathogen. Since logging is related to a higher abundance of Armillaria in the soil, the particular Armillaria species present in a given stand could be considered an additional site factor when making management decisions. 相似文献
11.
? Effects of overwinter storage regimes on seedling cold hardiness and physiological vigor are relatively unexplored, particularly for temperate deciduous forest tree species. ? We evaluated influence of storage duration (0, 66, 119, or 175 d) on electrolyte leakage of stem and root collar tissues following exposure to a series of freeze-test temperatures in black walnut (Juglans nigra L.) seedlings sampled from cold (3 °C) or freezer (?2 °C) storage. Seedlings were subsequently transplanted into a controlled growth chamber environment for two months. ? Regardless of storage temperature, mean LT50 was lowest for seedlings stored for 66 d (≤ ?34 °C) and increased dramatically after 119 d (≥ ?13 °C). ? Root collar tissue had lower LT50 than stem tissue after 119 d for cold-stored seedlings, reflecting importance of evaluative tissue type. Days to bud break shortened with increasing storage duration up to 119 d and stabilized thereafter for both storage regimes. Root growth potential was maximized after 119 d of storage, and subsequently declined for cold-stored seedlings. Height growth increased following storage, regardless of duration. ? To promote stress resistance and transplant growth response, we recommend that black walnut seedlings from this genetic source be outplanted after approximately 66–119 d of storage. 相似文献
12.
? To elucidate the application of natural regeneration to the restocking of evergreen broad-leaved forests in the subtropics, the characteristics of a 20-year-old evergreen broad-leaved forest restocked by natural regeneration after clearcut-burning were studied in Okinawa, Japan. Within a 0.87 ha clearcut area with four 10 m × 10 m sampling plots, two burned and two unburned ones, the tree composition, tree species diversity and vegetation changes were investigated. ? The results showed that the species diversity, basal area and density of woody stems ? 1.0 m in height differed significantly among phanerophyte types, while they were not significantly different between the burned and unburned treatments. A vegetation census also revealed no obvious differences between the treatments. ? The primary dominant species, Castanopsis sieboldii, continued to dominate the secondary forest with a broad height distribution. ? The structural complexity and high tree species diversity of the regenerating forest after clearcut-burning provides no evidence of degeneration. We can predict that the regeneration forest may gradually develop into stands similar to pre-clearcut primary forest, and that natural regeneration may restore the high tree species diversity of the evergreen broad-leaved forests in Okinawa. 相似文献
13.
? Mature, unmanaged forests in western North America provide important reference conditions for managers, yet little is known about fuel composition and the factors that influence fuel accumulation in such stands. Our objectives were to characterize fuels in a passively managed landscape of dry forests in central Oregon and identify environmental factors influencing fuel accumulation. ? Ordination techniques and analysis of variance revealed no statistical differences in total fuel loads across a wide range of environmental conditions. ? Individual fuel size classes, however, did vary by stand location and composition. Interior stands had more 1- to 100-h fuels and snags than stands at or near the edge, stands dominated by ponderosa pine had fewer small-diameter fuels and snags, lodgepole pine stands had more 1-h fuels and snags, and white fir stands had more 10-h fuels, duff, and snag basal area. ? Tree species, density and age, and years since last fire were the most important environmental variables, explaining 23% of the variation in fuels. ? Our results present further evidence that fuel composition is highly variable at many spatial and temporal scales. They also provide useful baseline information for managers of fire-prone western forests. 相似文献
14.
? Seedlings of seven pine species or hybrids, Pinus densiflora, Pinus thunbergii, Pinus virginiana, Pinus echinata, Pinus koraiensis, Pinus thunbergii × Pinus massoniana and Pinus × rigitaeda, were inoculated in a greenhouse with 100, 1 000 and 10 000 pathogenic nematodes, Bursaphelenchus xylophilus, to compare initial symptom development and to evaluate susceptibility to pinewood nematodes. ? Genetic types were significantly different in the starting day of needle discoloration (χ2 = 43.48; P < 0.001) and the period from nematode inoculation to seedling death (χ2 = 32.85; P > 0.001), but treatment groups were not statistically different in the days from inoculation to seedling death in any of the pine species. ? There was no relationship between seedling mortality and the number of nematodes recovered from infected seedlings. Only eight of the nematode-inoculated seedlings remained alive by day 83 after inoculation, including four seedlings each of P. echinata and P. × rigitaeda grown from bulked seed collections. ? Seedlings from the bulk lots were likely more genetically diverse than those from the single-source lots. A broader genetic representation of pine species or hybrids is suggested for screening for planting stocks resistant to B. xylophilus. 相似文献
15.
? Density dependence is a major mechanism for shaping plant communities. However, its role in regulating diverse, mixed natural tree communities is less certain. ? In this study we investigated density-dependent effects in a large-scale (25 ha) old-growth temperate forest in northeastern China. Spatial patterns of neighborhood distribution in the plot were analyzed using various methods for inferring competition, including (1) pair correlation function to determine spatial patterns of pre-mortality and post-mortality and (2) neighborhood analysis of individuals to examine the extent to which tree survival is correlated with other covariates. ? Results showed that, for common species, 3 of 5 canopy species and 3 of 8 midstory and understory species were random in mortality. Negative density-dependent mortality was not found when trees reach 1 cm in DBH. There was no significant correlation for canopy species between tree survival and conspecific abundance, but largely positive correlations for midstory and understory species. In contrast, tree survival was found to negatively correlate with conspecific basal area for most species, indicating strong intraspecific competition. No strong interspecific density dependence was found in the forest. 相似文献
16.
? In Mediterranean forestry, it is important to improve knowledge about mixed stands dynamics, including their productivity. Previous studies have focused on the interactions between different species (competition, reduction of competition and facilitation) depending on site, species composition and structure. ? At the centre of this research are the possible differences between pure and mixed stands of Pinus sylvestris and Quercus pyrenaica in terms of density-growth relationships and volume growth per species. ? Using data from the second and third Spanish National Forest Inventory (606 plots), volume increment models for these species were fitted. Both species displayed a similar density-growth pattern for pure and mixed stands, with a maximum volume growth at maximum density. Volume increment per occupied area was also found to be greater in mixed stands as opposed to pure stands, suggesting a species interaction with reduced levels of competition in the former. However, the total volume growth was generally lower in mixed stands since the growth rate of oak is much lower. ? The results highlight the expedience of favouring P. sylvestris-Q. pyrenaica mixed stands with higher proportions of pine trees in order to gain the benefits of a more complex forest whilst retaining an acceptable level of wood production. 相似文献
17.
? Understanding the effects of tree species diversity on biomass and production of forests is fundamental for carbon sequestration strategies, particularly in the perspective of the current climate change. However, the diversity-productivity relationship in old-growth forests is not well understood. ? We quantified biomass and above-ground production in nine forest stands with increasing tree species diversity from monocultures of beech to stands consisting of up to five deciduous tree species (Fagus sylvatica, Fraxinus excelsior, Tilia spp., Carpinus betulus, Acer spp.) to examine (a) if mixed stands are more productive than monospecific stands, (b) how tree species differ in the productivity of stem wood, leaves and fruits, and (c) if beech productivity increases with tree diversity due to lower intraspecific competition and complementary resource use. ? Total above-ground biomass and wood production decreased with increasing tree species diversity. In Fagus and Fraxinus, the basal area-related wood productivity exceeded those of the co-occurring tree species, while Tilia had the highest leaf productivity. Fagus trees showed no elevated production per basal area in the mixed stands. ? We found no evidence of complementary resource use associated with biomass production. We conclude that above-ground productivity of old-growth temperate deciduous forests depend more on tree species-specific traits than on tree diversity itself. 相似文献
18.
The concepts and principles in characterization of seedling performance potential are evaluated, the requirements of tests are discussed, and the guideline criteria presented in selected morphological and physiological tests are assessed. Further discussion follows concerning the development of proper concepts as a necessity for developing clear and operational devices, and problems in making predictions of survival and growth. When using a seedling performance potential test, the following features should be taken into an account: basis of assessment; empirical or mechanistic ability to accommodate changes in seedlings prediction span rules and scale of measurement possibility to use in statistical quality control applicability to different methods of characterization; single or sample sorting design for site specific conditions applicability for quality control during seedling raising in the nursery suitability to repeated sampling Clear practical requirements for a test are: yielding final results immediately, simple to understand and use at all levels of operation, inexpensive, accessible to all potential users, reliable, and of diagnostic value. Strong practicability of the performance potential tests require use of rigorous statistical analysis to find seedling tests with adequate prediction ability. 相似文献
19.
? Carabid beetles were investigated at five different forest types in the Ibaizabal basin (northern Spain). The landscape is characterized by the presence of remnants of native forest surrounded by conifer plantations. ? Carabids were trapped in 52 stands of mixed forest, beech forest, holm oak forest, mixed pine and Monterey pine plantations in 2005 and 2006. The main objectives of the study were: compare carabid diversity, recognise the characteristic species, and study the effects of ecological variables on carabid assemblages in the different forest types. ? No significative differences in species abundance, richness and diversity were found among the studied forests. Most of the trapped beetles were identified as forest generalists, nevertheless some native and non-native forest specialist species were also found. Distribution of carabid communities overlapped and, except for beech forest, no specific communities were distinguished. Altitude, percentage of grass coverage and temperature were the main variables influencing species distribution. ? The results suggest high habitat homogeneity, caused by regeneration in pine plantations of the indigenous understorey, and by poor habitat quality in native forest (patchy remnants enclosed in conifer plantations). This situation could explain the similar carabid diversity. 相似文献
20.
? We present the longest tree-ring chronology (141 y) of Quercus ilex L. (holm oak), and discuss the species climate-growth relationships and the influence of stand density on tree sensitivity to climate. ? Similarly to Quercus suber L., the most influential climatic variables upon holm oak growth were late spring and early summer precipitation, which enhanced growth, and high temperatures in the previous August and current July, which negatively affected growth. ? High density stands responded to similar climatic factors as low density stands, but their response was generally weaker. Holm oak sensitivity to climate has increased in recent decades, which might be related to increasing temperatures in the region. Sensitivity was higher in low density stands. Additionally, the effect of summer stress on growth seems to have increased during the same period, similarly to other species in the Iberian Peninsula, suggesting that trees are more vulnerable to climatic changes. ? Stand density could buffer the response to climate by smoothing climatic extremes. Nevertheless, the effect of competition might reverse this positive effect at the individual tree level. Precautions should be taken before providing management guidelines regarding the effect of climate change and stand density on holm oak. 相似文献
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