共查询到20条相似文献,搜索用时 31 毫秒
1.
Georges Kunstler Robert B. Allen David A. Coomes Charles D. Canham Elaine F. Wright 《Annals of Forest Science》2013,70(3):287-298
Context
There is strong interest in sustainable forest management systems that preserve characteristics of forests close to naturalness. Assessing the effectiveness of these systems is difficult because defining “natural” baselines from which impacts are estimated is challenging and because the influence of harvesting can have complex interactions with major natural disturbances.Aims
We used SORTIE/NZ, an individual tree-based forest dynamics model, to understand how harvesting and earthquake disturbance affect the dynamics of a New Zealand podocarp–angiosperm forest.Methods
Having parameterized SORTIE/NZ with extensive field data, we ran simulations for three natural dynamics scenarios (no disturbance and two earthquake scenarios) and then added podocarp harvesting scenario to each of these.Results
Simulations suggest that this forest is experiencing transient dynamics, with a natural rise in the dominance of one species of slow-growing podocarp with and without earthquake. Harvesting podocarps strongly affected its increase in basal area.Conclusion
Our results indicate that transient dynamics may occur in mixed podocarp forests and major disturbances may have complex interactions with management. Evaluating management impacts without accounting for these complex dynamics may be misleading. Models make predictions about transient trajectories that may help to evaluate these impacts. 相似文献2.
Context
Clustering forest harvest stands reduces the movements of the harvesters, forwarders and staff. Moreover, it simplifies the subsequent log transport, when compared with dispersed stands.Aims
Harvesting activities are generally based on silvicultural motivated planning data. The development of an analytical method to cluster harvest stands with respect to the spatial network of roads should improve the harvesting effort.Material and method
The clustering of harvest stands was developed for Aracruz (Brazil) in 2004, where it is used there successfully since. The hierarchical method ??single linkage cluster analysis?? is applied. As a distance function, the Euclidian distance was substituted by the shortest path on the spatial network.Result
The clustering method is based on the minimum spanning tree, which is the spatial equivalent to the dendrogram of an ordinary cluster analysis. Applying the Delaunay triangulation to fill the distance matrix reduces the distance calculation time from O(n 2) to O(n). The method is illustrated by a planning district of the Aracruz enterprise.Conclusion
Harvesting units are properly clustered spatially by the discussed method. Topographic obstacles are automatically avoided and the need to relocate machinery is reduced as well as the total driving distance. 相似文献3.
Valentine Lafond Guillaume Lagarrigues Thomas Cordonnier Benoît Courbaud 《Annals of Forest Science》2014,71(2):173-186
Context
Climate change is expected to increase forest vulnerability through disturbances such as windstorms and droughts. Forest managers are therefore investigating strategies to increase forest resistance and resilience, especially by promoting uneven-aged and mixed forests through group selection, and by reducing stand stocking and large trees proportion. However, there is little information on the long-term impacts of these two practices.Aims
The objectives of this study were (1) to develop an original silviculture algorithm designed for uneven-aged management and (2) to use it to assess the effects of the above-mentioned management methods in long-term simulations.Methods
We simulated individual and group selection techniques in order to study the effects of group size, harvesting intensity and their interactions on wood production, stand heterogeneity, and regeneration in mountain spruce–fir forests. We used the spatially explicit individual-based forest model Samsara2 to simulate forest dynamics.Results
Our simulation results confirmed the positive effect of group selection practices on structure diversity and regeneration but not on spruce maintenance. Increasing harvesting intensity enabled forest destocking but decreased structure diversity and led to non-sustained yields for the most intensive scenarios.Conclusion
As adaptation measure, we thus recommend moderate group selection harvesting creating 500 m2 gaps. 相似文献4.
Giovanni Di Matteo Irene Tunno Pierfrancesco Nardi Paolo De Angelis Giada Bertini Gianfranco Fabbio 《Annals of Forest Science》2014,71(8):885-895
Context
Harvesting of Mediterranean oak coppice forests has been progressively suspended on a share of cover over the last decades. Positive growth trend in outgrown coppices no longer harvested on short rotations now drives natural forest restoration on wide areas, and it represents a potential carbon sink in view of global warming.Aims
Our goals were to estimate carbon (C) and nitrogen (N) content per compartment in two deciduous oak outgrown coppice forests, aged differently and growing under unequal site quality, to verify whether C concentration across compartments is in agreement with the conventional conversion rate of 0.5.Methods
Ecosystem C and N pools were assessed by multiplying the whole coppice mass (combining specific allometric functions, root-to-shoot ratio, and soil sampling) by respective C and N concentrations.Results
The results point out that the largest percentage of N was stored in 15-cm topsoil (84.06 and 73.34 % at the younger and older site, respectively), whereas the proportion of organic ecosystem C pool was more variable, as a consequence of the amount and allocation of phytomass. We found that, in most cases, C concentration was less than the conventional conversion rate of 0.5, especially in deadwood, O layer, and root compartments.Conclusion
The findings provide further knowledge of C and N storage into these new built-up forest types and the evidence that a detailed analysis may get higher accuracy in the pools estimate, producing a more reliable outlook on dynamics and climate change mitigation ability of these systems. 相似文献5.
Regeneration strategies influence ground bryophyte composition and diversity after forest clearcutting 总被引:1,自引:0,他引:1
Xiao Li Yan Wei Kai Bao Xue Yong Pang Ning Xuan Zhang Jiquan Chen 《Annals of Forest Science》2013,70(8):845-861
Context
Natural regeneration with broadleaved species and reforestation with coniferous trees are two widely practiced forest regeneration strategies after timber harvesting. They lead to different tree species composition and may cause different understory biodiversity, but the effects on ground bryophyte composition and diversity are not well-known.Aims
We tested whether natural regeneration with broadleaved species and reforestation with spruce induced different diversities of the ground bryophyte populations 20–40 years after old-growth spruce forest clearcutting in the subalpine regions of southwestern China.Methods
Differences between natural stands and plantations were compared through the analysis of 13 paired stands, with 78 plots, 390 shrub/herb quadrats, and a total of 1,560 bryophyte quadrats.Results
Naturally regenerated forests were characterized by lower density and cover and lower tree height but higher herbaceous plant height, shrub cover, and bryophyte diversity. They also harbored many more ground bryophytes. The species richness of pleurocarpous mosses and fans, mats, and turfs were significantly higher in naturally regenerated forests. Frequency difference analysis demonstrated that more bryophyte species preferred ground habitats in naturally regenerated forests than in plantations (116 vs. 48 species). The canonical correspondence analysis indicated that stand structure attributes were more important determinants of ground bryophyte diversity and abundance.Conclusion
Natural regeneration and reforestation resulted in large differences in ground bryophyte populations. A larger diversity was observed in the former case, and natural regeneration practices can be an effective measure for the protection of ground bryophyte diversity after clearcutting. 相似文献6.
? Context
The knowledge of how shrub–seedling interactions vary with summer drought, canopy opening, and tree species is crucial for adapting forest management to climate change.? Aims
The aim of this study was to assess variation in shrub–oak recruitment associations along a south–north drought climate gradient and between two levels of canopy cover in coastal dune forest communities in a climate change-adapted forest management perspective.? Material and methods
Mapped data of associational patterns of seedlings of three oak species with interspecific pooled shrubs were analyzed using a bivariate pair correlation function in 10 (0.315 ha) regeneration plots located in forest and recent gap sites along the climate gradient. An index of association strength was calculated in each plot and plotted against a summer moisture index.? Results
The association strength increased with increasing summer drought from wet south to dry north and from closed forests to gaps.? Conclusion
Consistent with facilitation theory, our results suggest that climate change may shift associational patterns in coastal dune forest communities towards more positive associations, in particular in canopy gaps. In a perspective of climate change, foresters may need to conserve understory shrubs in gaps in order to promote oak species regeneration. 相似文献7.
Shrub biomass estimation in the semiarid Chaco forest: a contribution to the quantification of an underrated carbon stock 总被引:1,自引:0,他引:1
Georgina Conti Lucas Enrico Fernando Casanoves Sandra Díaz 《Annals of Forest Science》2013,70(5):515-524
Context
The quantification of biomass of woody plants is at the basis of calculations of forest biomass and carbon stocks. Although there are well-developed allometric models for trees, they do not apply well to shrubs, and shrub-specific allometric models are scarce. There is therefore a need for a standardized methodology to quantify biomass and carbon stocks in open forests and woodlands.Aims
To develop species-specific biomass estimation models for common shrubs, as well as a multispecies shrub model, for the subtropical semiarid Chaco forest of central Argentina.Methods
Eight shrub species (Acacia aroma, Acacia gilliesii, Aloysia gratissima, Capparis atamisquea, Celtis ehrenbergiana, Larrea divaricata, Mimozyganthus carinatus, and Moya spinosa) were selected, and, on average, 30 individuals per species were harvested. Their total individual dry biomass was related with morphometric variables using regression analysis.Results
Crown area as well as crown-shaped variables proved to be the variables with the best performance for both species-specific and multispecies shrub models. These allometric variables are thus recommended for standardized shrub biomass assessments.Conclusion
By accounting for the shrub component of the vegetation, our models provide a way to improve the quantification of biomass and carbon in semiarid open forest and woodlands. 相似文献8.
Annabelle Amm Christian Pichot Philippe Dreyfus Hendrik Davi Bruno Fady 《Annals of Forest Science》2012,69(7):845-856
? Context
Dispersal and recruitment play a critical role in determining the abundance and the spatial structure of regeneration.? Aim
In this study, we estimated landscape scale seed dispersal using the inverse modeling method by fitting seedling counts to seed tree location and fertility in the European silver fir Abies alba Miller.? Methods
Seed trees and seedlings from three age cohorts were counted in 30 plots on Mont Ventoux (southeastern France) at elevations from 995 to 1,605?m, where the following ecological variables were measured: elevation, slope, aspect, light availability, and tree density. We developed and fitted a dispersal model, including a new parameter, recruitment rate, which depended both on the ecological characteristics of the plots and on seed production.? Results
Elevation was the factor that affected seedling recruitment the most, with an optimum value at around 1,200?m. Estimated A. alba seed dispersal distances were short (median values for the three cohorts, respectively, 16.4?C13.2?C19.6?m).? Discussion
We demonstrated that including the ecological characteristics of plots and post-dispersal recruitment processes realistically reduced estimates of seed dispersal distances which are otherwise grossly over-estimated using inverse modeling procedures. 相似文献9.
Context
Although adventitious shoots are produced in many tree species in response to injury, little is known about the effects of salinity on sprouting.Aims
The main objective was to examine the sprouting capacity of Pinus leiophylla seedlings in relation to injury and physiological changes induced by NaCl.Methods
Seedlings were grown in controlled-environment growth rooms and treated with 0, 100, 150, and 200 mM NaCl. Numbers of adventitious shoots were recorded and growth and physiological parameters measured after 64 days of treatments and following a 30-day recovery period.Results
NaCl treatments triggered sprouting of adventitious shoots, mainly in the lower parts of the stems. However, fewer sprouts were induced by 200 mM NaCl compared with the lower concentration treatments. These changes were accompanied by needle necrosis, decreased chlorophyll concentrations, seedling dry mass, and stem diameter. Stomatal conductance, net photosynthesis, and root hydraulic conductance decreased with increasing NaCl concentrations and did not return to the control levels after 30 days of stress relief.Conclusions
Pinus leiophylla has the regeneration potential when exposed to salinity. However, very high salt concentrations induce severe physiological impairments and, consequently, a decrease of this regeneration potential. 相似文献10.
Fire severity as a key factor in post-fire regeneration of Pinus pinaster (Ait.) in Central Portugal
Context
Mediterranean pine woodlands are strongly affected by wildfires; however, there are knowledge gaps in the role of fire severity on Pinus pinaster Ait. regeneration.Objectives
The principal questions were: (a) does post-fire regeneration of Maritime Pine differ where canopies were consumed to a low vs. high degree and (b) which factors, besides fire severity, could explain these differences.Methods
Pine recruitment was monitored from 2 to 36?months after a summer wildfire in 18 25?m2 plots, equally divided over two fire severity classes based on crown consumption. Besides the degree of crown consumption, three quantitative fire severity indices as well as post-fire site conditions, seed input and understory vegetation recovery were measured.Results
Pine seedling densities were consistently higher in the plots with low than high crown consumption but due to marked spatial variability, they were only significantly different at two out of the eight sampling occasions. This variability could be explained by a quantitative index based on the diameter of twigs, as well as by seed input and post-fire site conditions (ash and litter cover).Conclusion
Fire severity was found to strongly affect the pine recruitment following wildfire, using both a qualitative visual severity index and a quantitative, more labour-intensive one. 相似文献11.
Context
Fine scale regeneration patterns of coexistent species are influenced by regeneration mechanisms and microsite requirements. Spatial patterns may be either disjunct or overlapping, which will determine competitive effects and microsite dominance, and future forest composition.Aims
Using American beech (Fagus grandifolia Ehrh.) and sugar maple (Acer saccharum Marshall) as an example, three hypotheses were tested: (1) random beech spatial patterns, (2) clumped spatial patterns of small sugar maple seedlings, and (3) disjunct beech and sugar maple patterns.Methods
Individual stems were sampled in a contiguous grid of 1-m2 quadrats across a 576-m2 area at three sites. Densities were separated into three height classes (≤30 cm, 30–90 cm, and?>?90 cm, ≤4 cm diameter at breast height). Spatial statistics and regression were used to analyze spatial patterns and correlations.Results
Beech and seedling sugar maple patterns were patchy, rejecting the first and not rejecting the second hypotheses. Hypothesis three was rejected because patches of the two species overlapped with advance regeneration beech overtopping sugar maple.Conclusion
Patchy patterns of advance regeneration beech and post-harvest sugar maple establishment suggest spatiotemporal niche partitioning. Beech had a competitive height advantage following harvest, but sugar maple still occurred in beech-free patches and beneath overtopping beech at a fine scale. Self-replacing beech patterns will ensure the species will continue dominance unless a selective chemical or manual treatment is applied that removes beech and releases sugar maple. 相似文献12.
Context
Implementing nature-based silviculture requires understanding the structural and compositional changes that occur in forested stands under known disturbance types and intensities.Aims
The objectives were to assess the (a) resistance of hardwood forests to change, (b) their trajectory of recovery following disturbance, and (c) how closely resulting forests resemble original forests.Methods
We characterized tree structure and composition at three points in time (pre-disturbance, 1-year post-disturbance, and ~15 years following disturbance) along a harvesting disturbance gradient created by removing trees in different forest canopy strata.Results
Significant differences to pre-disturbance conditions were noted immediately post-harvest for tree basal area, density, species richness, and tree species composition; treatment differences were observed for all parameters except diversity. Plots exposed to the least extreme harvesting disturbances (cutting small and intermediate trees) had returned to pre-disturbance conditions for most parameters after 15 years, while the most extreme harvesting disturbance (cutting large trees) had not yet recovered.Conclusions
Although not initially resistant, Central Appalachian eastern hardwoods are fairly resilient to the removal of trees in the subcanopy or a mixture of the subcanopy and canopy; only the removal of solely canopy trees (i.e., high grading) and complete removal (i.e., clearcutting) appear to impose harvesting disturbances to which these forests may not be resilient. 相似文献13.
Mar��a Jos�� Leiva Juan Manuel Mancilla-Leyton ��ngel Mart��n-Vicente 《Annals of Forest Science》2013,70(1):11-20
Context
??Dehesas?? are savanna-like ecosystems of human origin that extend broadly in the Mediterranean area of the Iberian Peninsula. They consist of scattered oaks (mainly Quercus ilex subsp. ballota L. holm-oak), an annual grassland layer and interspersed shrubs. These ecosystems, used for grazing and wild game, support high plant and animal biodiversity and provide important environmental services. At present, Mediterranean ??dehesas?? are endangered by the lack of oak regeneration.Aims
This paper analyses the efficiency of: (1) using shrubs as nurse plants; (2) drip irrigation of seedlings during summer; and (3) a combination of the two methods for the restoration of a ??dehesa?? in a mid-mountain Mediterranean area of southern Spain.Methods
Different techniques were tested to improve the recruitment of holm-oak seedling during a 3-year field experiment: (1) acorn plantation in open spaces, irrigating seedlings during the first dry season; (2) acorn plantation beneath the canopy of Myrtus communis L. and (3) both methods combined.Results
There was a large facilitative effect of myrtle for the recruitment of holm-oak seedlings, regardless of the supply of irrigation. This effect was associated with a large decrease in air temperature and photosynthetically active radiation beneath myrtle canopies. By contrast, summer irrigation of seedlings planted in open spaces did not improve seedling survival after 3 years despite a small and transient positive effect on seedling survival during the 1st year.Conclusion
The use of evergreen shrubs, such as myrtle, as nurse plants may be considered to restore ??dehesas?? instead of expensive seedling irrigation techniques. Several studies have promoted abandoning grazing to increase holm oak self-regeneration in ??dehesas??. However, creating closed patches of naturally occurring evergreen shrubs could provide suitable sites for oak planting when necessary, thus enhancing seedling recruitment without damaging the environmental and economic value of these ecosystems. 相似文献14.
Florian Delerue Maya Gonzalez Anne Atlan Sylvain Pellerin Laurent Augusto 《Annals of Forest Science》2013,70(3):219-228
Context
While many woody perennials grow and reproduce in varying environments, their ability to modify their reproductive allocation under varying resource availability is unclear.Aims
This study aimed to demonstrate the occurrence of plasticity of reproductive allocation in a pioneer woody species (Ulex europaeus).Methods
We studied seed production in 144 plants under different irradiance and population densities. We measured their basal area, their whole shoot biomass and photosynthetic biomass, and their reproductive output (number of fruits per individual and number of seeds per fruit).Results
We found that newly produced photosynthetic biomass was influenced by environmental variation, which in turn determined its reproductive output. In addition, in low light conditions investment in reproduction was more reduced than investment in growth indicating plasticity of reproductive allocation.Conclusion
These results provide the first evidence for plasticity of reproductive allocation of a woody plant. It may lead to the ability of this pioneer species to survive and to continue to reproduce even at low rates in non-optimal shady habitats and to maintain a non-empty seed bank in forest systems with long unfavourable periods between two disturbances. 相似文献15.
Dehai Zhao Michael Kane Robert Teskey Daniel Markewitz Dale Greene Bruce Borders 《Annals of Forest Science》2014,71(8):843-851
Context
To sustainably manage loblolly pine plantations for bioenergy and carbon sequestration, accurate information is required on the relationships between management regimes and energy, carbon, and nutrient export.Aims
The effects of cultural intensity and planting density were investigated with respect to energy, carbon, and essential nutrients in aboveground biomass of mid-rotation loblolly pine plantations, and the effects of harvesting scenarios on export of nutrients were tested.Methods
Destructive biomass sampling of a 12 years-old loblolly pine culture/density experiment, and analysis of variance were used to assess the effects of cultural intensity (operational vs. intensive) and six planting densities ranging from 741 to 4,448 trees ha?1. Two harvesting scenarios (stem-only vs. whole-tree harvesting) were assessed in terms of energy, carbon, and nutrient export.Results
The concentrations of energy, carbon, and nutrients varied significantly among stem wood, bark, branch, and foliage components. Cultural intensity and planting density did not significantly affect these concentrations. Differences in energy, carbon and nutrient contents among treatments were mainly mediated by changes in total biomass. Nutrient contents were affected by either cultural intensity or planting density, or both. Stem-only harvesting removed 71–79 % of aboveground energy and carbon, 29–45 % of N, 28–44 % of P, 44–57 % of K, 51–65 % of Ca, and 50–61 % of Mg.Conclusions
Stem-only harvesting would be preferred to whole-tree harvesting, from a site nutrient conservation perspective. 相似文献16.
Aims
This study aims to evaluate the effects of wood ash application on nutrient dynamics and soil properties of an acidic forest soil (Arenosol).Methods
Treatments were loose and pelleted ash application (11?Mg?ha?1), alone or together with N fertiliser, and control treatment in a lysimeter experiment. Nutrient leaching was followed during a 2-year period and soil chemical and biological properties were evaluated at the end of the experiment.Results
Wood ash increased leaching of total N, NH 4 + -N, base cations and P, mainly during the first months, the effect being more pronounced for the loose formulation. At the end of the study period, a positive effect on soil nutrient availability and soil acidity reduction was seen. The application of loose and pelleted ash alone decreased N leaching and increased N microbial biomass at the end of the experiment. The C dynamics was weakly affected.Conclusion
Wood ash can be used to improve nutrient availability and balance nutrient exported by tree harvesting in acid forest soils, the effects at short-term being stronger for loose than for pelleted ash. However, their application should be carried out when vegetation is established to minimise nutrient losses at short-term and reduce the potential risk for water bodies. In N-limited soils, wood ash should be applied with N fertilisers to counteract N immobilisation. 相似文献17.
? Context
Soil temperature can limit tree growth and function, but it is often unaddressed in understanding the successional status of trees.? Aims
We tested how soil temperature affected carbon allocation strategies of two dominant co-occurring boreal conifer species, Pinus contorta and Picea mariana.? Methods
We measured nonstructural carbon (NSC) concentrations, biomass, and photosynthesis of dormant and actively growing 2-year-old seedlings in response to three soil temperatures (5, 10, and 20 °C) under a common ambient air temperature.? Results
For both species, variation in carbon reserves with soil temperature was more pronounced following seedling growth than during dormancy. For both species and all organ types (roots, needles, and stems), NSC concentrations were highest when seedlings were grown at 5 than 20 °C. Mass adjusted for NSC content was negatively correlated with NSC concentration for all organ types of both species. Soil temperature had a marginally significant effect on photosynthesis of pine; seedlings grown at 10 or 20 °C acquired more carbon than seedlings grown at 5 °C. Spruce seedlings photosynthesized more when grown at 20 °C than at 5 or 10 °C.? Conclusion
Interspecific differences in allocation of carbon may underlie the responses of P. mariana and P. contorta to cold soils and consequently their successional status. 相似文献18.
Context
Loss of woodlands and degradation of vegetation and soil have been described for all Mediterranean-type ecosystems worldwide. In the Western Iberian Peninsula, overexploitation of evergreen cork oak land use systems has led to soil erosion, failures in oak recruitment, and loss of forests. Degraded and dry sites are quickly colonised by pioneer heathland rockrose (Cistus spp.) shrubs forming highly persistent patches.Aims
Although traditionally shrublands have been considered as a transient successional state, we present evidence that they can represent persistent alternative states to former cork oak forests.Review trends and conclusions
We first describe how Mediterranean vegetation evolved in the Iberian Peninsula and the role of fire and long-term human management as main disturbances. We then discuss alternative pathways through state-and-transition models indicating the ecological and land use variables that halt cork oak regeneration and recruitment and drive vegetation transitions towards persistent shrublands. Unless concerted management actions and restoration programmes are undertaken, the cork oak land use systems will not be sustainable. 相似文献19.
Context
Although drought is generally considered the main environmental constraint in Mediterranean environments, the ability to acclimate to and tolerate frost in early developmental stages can be a determinant for seedling survival of many Mediterranean tree species like stone pine (Pinus pinea L.).Aims
The aim of this study was to assess the impact of the developmental stage of naturally regenerated stone pine individuals on tolerance to low temperature (LT) from summer to late autumn and in spring, at a highly continental site in central Spain. Specifically, we tested to what extent the differences in tolerance are related to shoot heteroblasty.Methods
We assessed LT tolerance of needles from individuals at three age classes (class C1: seedlings, class C2: 4- to 8-year-old saplings and class C3: >9-year-old saplings) over nine dates from summer to spring.Results
LT tolerance displayed severe seasonal trends and differed between age classes. It usually increased with sapling age. Such differences were tightly related to heteroblasty of the shoots. Our results point to a higher LT tolerance associated with larger leaf dry mass per unit area (LMA) values. No impact of late frosts on shoot growth rates was detected during this study.Conclusions
Developmental changes during early plant growth seem to play a role in frost tolerance of stone pine seedlings, a finding which furthers our understanding of regeneration dynamics in this species in areas with continental influence. 相似文献20.