Diameter distributions in Pinus sylvestris L.stands:evaluating modelling approaches including a machine learning technique

The diameter distribution of trees in a stand provides the basis for determining the stand’s ecological and economic value,its structure and stability and appropriate management practices.Scots pine(Pinus sylvestris L.)is one of the most common and important conifers in Turkey,so a well-planned management schedule is critical.Diameter distribution models to accurately describe the stand structure help improve management strategies,but developing reliable models requires a deep understanding of the growth,output and constraints of the forests.The most important information derived by diameter distribution models is primary data on horizontal stand structure for each diameter class of trees:basal area and volume per unit area.These predictions are required to estimate the range of products and predicted volume and yield from a forest stand.Here,to construct an accurate,reliable diameter distribution model for natural Scots pine stands in the Türkmen Mountain region,we used Johnson’s SBdistribution to represent the empirical diameter distributions of the stands using ground-based measurements from 55 sample plots that included1219 trees in natural distribution zones of the forests.As an alternative,nonparametric approach,which does not require any predefined function,an artificial intelligence model was constructed based on support vector machine methodology.An error index was calculated to evaluate the results.Overall,both Johnson’s SB probability density function with a three-parameter recovery approach and the support vector regression methodology provided reliable estimates of the diameter distribution of these stands.

Simulation of Haloxylon Ammodendron Stand Basic Diameter Structure Based on Fuzzy Distribution Function

Based on the investigation data of 12 Haloxylon ammodendron plots in the south edge of Gurbantunggut Desert, Fuzzy distribution was introduced into the study of Haloxylon ammodendron base diameter structure fitting according to the consistency between the characteristics of Fuzzy distribution function and the distribution series of cumulative percentage of stand base diameter, and the fitting precision and effect of Fuzzy distribution function were discussed. The root mean square error RMSE and determination coefficient R2 values showed that Fuzzy-Γ1, Fuzzy-Γ2, Fuzzy-Γ3, Fuzzy-Γ4 had good fitting performance, among which Fuzzy-Γ1 had relatively high fitting precision, and its parameters were closely related to stand age and density, Fuzzy-Γ2 distribution function was the second, and Fuzzy-Γ4 distribution function had the worst fitting effect. By introducing a parameter c from the similarity of four distribution function formulas, a generalized Fuzzy distribution function Fuzzy-Γ5 is obtained. This function shows the highest fitting accuracy. Most of the values of parameter c are near 1 or 2, which shows that the diameter distribution is mainly approximate to Fuzzy-Γ1 and Fuzzy-Γ2.

Sub-stand diameter distribution types vary along an old-growth Douglas-fir chronosequence into the horizontal diversification development stage

Managing mature Douglas-fir[Pseudotsuga menziesii(Mirb.)Franco]stands to emulate the structural complexity of natural old-growth forest requires identifying structural targets at the sub-stand level at which neighborhood dynamics and patchy disturbance shape structure.We therefore sought to describe the archetypal shapes of predominant sub-stand diameter distribution types(DDTs)observed in natural tree neighborhoods in stands comprising a chronosequence(ca.120-450+yrs)encompassing mature,vertical diversification,and horizontal diversification development stages.The ten 1.0 ha stands are located in the southcentral Oregon Cascades,USA.Building on the known spatial position of each tree,natural tree neighborhoods were identified using the floating neighborhood approach based on spatial tessellation connecting neighboring trees at the first-(mean 61 m2)through fifth-(mean 2058 m2)order scales.Cluster analysis was then used to objectively identify the most predominant DDTs among the relative tree size distributions observed in the trans-scale neighborhoods within each stand.Repeated measures regression was used to classify each DDT to one of six observed archetypal shapes:negative exponential,unimodal,rotated sigmoid,bimodal,concave,or multi-modal.Only three of the 81 observed DDTs deviated by<10%from the stand average,while every stand had at least one DDT that deviated by>50%(maximum 83%).Within each stand,five to ten predominant DDTs were observed,which deviated from the stand average by 30-48%and were characterized by two to five different archetypal shapes.Consequently,in some stands the majority of tree neighborhoods were best characterized by a different shape from that assigned at the stand level.Deviation from the stand average increased from the youngest stand in the mature development stage through the middle stands in the vertical diversification stage to the oldest stands in the horizontal diversification stage.The complexity of DDT shapes tended to increase along the chronosequence(from negative exponential and uniform toward concave and multi-modal),with shape richness highest mid-sequence and evenness peaking in the oldest stands.The high diversity of sub-stand structural complexity reduces the utility of standlevel diameter distributions as old-growth restoration targets.However,the presence in early-sequence stands of sub-stand diameter distributions common to later-sequence stands may facilitate active management at the neighborhood level to promote future old-growth condition.Restoration of substand diameter structures would likely require combining spatial perspectives,such as by augmenting tree-level croptree management with diameter distribution targets for the resulting tree neighborhoods.

Diameter distribution of trees in natural stands managed on polycyclic cutting system

Diameter frequency distribution in a specific stand provides basic information for forest resources management. In this study, four probability models were applied to analyze diameter distribution of natural forests after selective cutting with different intensities （low intensity of 13.0% in volume, medium intensity of 29.1%, high intensity of 45.8%, and extra-high intensity of 67.1%） The results show that the skewness and kurtosis of the four models are positive except that of low intensity selective cutting, which suggest that the number of small-size trees dominate the stand. The more intensity of selective cutting, the wider range of diameter distributions. The diameter structure of selective cutting with low intensity met Weibull and Beta distributions; that of medium intensity met Weibull, negative exponential as well as Gamma distributions; that of high intensity cutting met Weibull and negative exponential distributions, but that of extra-high intensity could not meet any above model. Weibull distribution model fits better than others regarding the structure of diameter distribution in natural forests managed on polycyclic cutting system. The results will provide basic information for sustainable management for mixed natural stands managed on a polycyclic cutting system.

Population structure of Araucaria angustifolia under distinct forest protection status:implications for management and conservation

Araucaria angustifolia is the dominant coniferous species in Brazil,a long-lived pioneer species and a supplier of valuable timber and non-timber products,which gives it key-species status.This study examines how A.angustifolia population structure affects the stand structure,and whether these relationships differ between protected and unprotected areas.The study was carried out on two protection status forests(national forest and urban forest)in a region of Atlantic mixed forest in ParanáState,southern Brazil.Skewness coefficient and the Weibull shape parameter described the population structure and its effects on species diversity and biomass stock.Population diameter distribution differed significantly between forests,with unbalanced structure in both,although regeneration was more abundant in the protected area.Skewness positively affected aboveground biomass whereas shape negatively affected it and species diversity.These relationships differed between protected and unprotected stands.The effect of A.angustifolia populations on stand structure was conditioned on protection status.Old-growth populations may have lower diversity and biomass stock even supporting large trees.Consequently,old-growth forests,can lead to wood loss through mortality,senescence,and declining populations,representing the waste of a valuable timber resource.These findings provide useful knowledge for forest management,species conservation,and the carbon market.

Measurement of respiration amount of white birch（Betula platyphylla）population in the mountainous region of Beijing

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Does variable stand structure associated with multi-cohort forests support diversity of ground beetle (Coleoptera, Carabidae) communities in the central Nearctic boreal forest？

Multi-cohort management （MCM） that retains a range of stand structures （age and size class） has been proposed to emulate natural disturbance and improve management in the Nearctic boreal forest. Although MCM forests contain both single- and multi-aged stands of mixed tree sizes, little is known about how variable stand structure affects associated fauna and biodiversity. Here, we examine the relationship between ground beetle （Coleoptera, Carabidae） communities and stand characteristics across a range of forest structure （=cohort classes）. Given that MCM classes are defined by the distribution of their tree-stem diameters, we ask whether parameters associated with these distributions （Weibull） could explain observed variation in carabid communities, and if so, how this compares to traditional habitat variables such as stand age, foliage complexity or volume of downed woody debris. We sampled carabids using weekly pitfall collections and compared these with structural habitat variables across a range of cohort classes （stand structure and age since disturbance） in 18 sites of upland mixed boreal forests from central Canada. Results showed that richness and diversity of carabid communities were similar among cohort classes. Weibull parameters from the diameter distribution of all stems were the strongest predictors of variation in carabid communities among sites, but vertical foliage complexity, understory thickness, and percentage of deciduous composition were also significant. The abundance of several carabid forest specialists was strongly correlated with tree canopy height, the presence of large trees, and high vertical foliage complexity. Our results demonstrate that variable forest structure, as expected under MCM, may be useful in retaining the natural range of ground beetle species across the central Nearctic boreal forest.

Inventory of aspen trees in spruce dominated stands in conserva-tion area

Background： The occurrence of aspen trees increases the conservation value of mature conifer dominated forests. Aspens typically occur as scattered individuals among major tree species, and therefore the inventory of aspens is challenging. Methods： We characterized aspen populations in a boreal nature reserve using diameter distribution, spatial pattern, and forest attributes： volume, number of aspens, number of large aspen stems and basal area median diameter. The data were collected from three separate forest stands in Koli National Park, eastern Finland. At each site, we measured breast height diameter and coordinates of each aspen. The comparison of inventory methods of aspens within the three stands was based on simulations with mapped field data. We mimicked stand level inventory by locating varying numbers of fixed area circular plots both systematically and randomly within the stands. Additionally, we also tested if the use of airborne laser scanning （ALS） data as auxiliary information would improve the accuracy of the stand level inventory by applying the probability proportional to size sampling to assist the selection of field plot locations. Results： The results showed that aspens were always clustered, and the diameter distributions indicated different stand structures in the three investigated forest stands. The reliability of the volume and number of large aspen trees varied from relative root mean square error figures above 50% with fewer sample plots （5-10） to values of 25%-50% with ]0 or more sample plots. Stand level inventory estimates were also able to detect spatial pattern and the shape of the diameter distribution. In addition, ALS-based auxiliary information could be useful in guiding the inventories, but caution should be used when applying the ALS-supported inventory technique. Conclusions： This study characterized European aspen populations for the purposes of monitoring and management of boreal conservation areas. Our results suggest that if the number of sample plots is adequate, i.e. 10 or more stand level inventory will provide accurate enough forest attributes estimates in conservation areas （minimum accuracy requirement of RMSE% is 20%-50%）. Even for the more ecologically valuable attributes, such as diameter distribution, spatial pattern and large aspens, the estimates are acceptable for conservation purposes

Appropriate search techniques to estimate Weibull function parameters in a Pinus spp.plantation

The Weibull function,a continuous probability distribution,is widely used for diameter distribution modelling,in which parameter estimation performance is affected by stand attributes and fitting methods.The Weibull cumulative distribution function is nonlinear,and classical fitting methods may provide a not optimal solution.Invoking the use of artificial intelligence by metaheuristics is reasonable for this optimisation task.Therefore,aimed and compared(1)the metaheuristics genetic algorithm and simulated annealing performance over the moment and percentile methods;(2)the hybrid strategy merging the metaheuristics tested and the percentile method and,(3)the metaheuristics fitness functions under basal area and density errors.A long-term experiment in a Pinus taeda stand subjected to crown thinning was used.According to our findings,all methods have a similar performance,independent of the thinning regimes and age.The pattern of the estimated parameters tends to be acceptable,as b increases over time and c increases after thinning.Overall,our findings suggest that methods based on metaheuristics have a higher precision than classical methods for estimating Weibull parameters.According to the classification test,the methods that involved simulated annealing stood out.The hybrid method involving this metaheuristic also stood out,with accurate estimates.Classical methods showed the poorest performance,and we therefore suggest the use of simulated annealing due to its faster processing time and high-quality solution.

Frost Resistance of Magnesium Oxychloride Cement Mortar Added with Highland Barley Straw Ash

In order to study the influence of highland barley straw ash (HBSA) prepared under certain conditions on the durability of magnesium oxychloride cement mortar (MOCM) under freeze-thaw damage,rapid freeze-thaw cycle tests were carried out firstly.The relative mass evaluation parameters and the relative compressive strength evaluation parameters,which represent the degradation of freeze-thaw resistance,were used as the indices to study the degradation rule of MOCM.Secondly,nuclear magnetic resonance (NMR) tests were carried out on MOCM under different freeze-thaw cycles to analyze the pore diameter changes in the freeze-thaw process.The microstructure of MOCM was tested by Fourier transform infrared spectroscopy (FTIR),X-ray diffraction (XRD) and scanning electron microscopy (SEM),and then the effect mechanism of HBSA on the anti-freezing performance of MOCM was revealed.Finally,the two-parameter Weibull distribution function was used to analyze the reliability of durability degradation of MOCM added with HBSA under freeze-thaw cycles.The specific conclusions are as follows:With the increase of HBSA's addition,the freeze-thaw resistance of MOCM increase firstly and then decrease.When the addition of HBSA is 10%,the decay rate of relative mass evaluation parameters and relative compressive strength evaluation parameters is the slowest,and the frost resistance is the best.The proportion of harmful pores and more harmful pores in MOCM added with 10% HBSA decreases by 25.11% and 21.34%,compared with that without HBSA before and after freeze-thaw cycles.A lot of magnesium silicate hydrate (M-S-H) gels are generated in MOCM with HBSA content of 10%,which fills part of the pores,so that the proportion of harmful pores and more harmful pores is the lowest.The Weibull function can be effectively applied to the reliability analysis of the freeze-thaw cycle of MOCM added with HBSA,and the theoretical results are in good agreement with the experimental results.

A Novel Method for Preparing Approximately Micron-sized Polymethyl Methacrylate Microspheres with Clear Surface

Polymethyl methacrylate (PMMA) microspheres with clear surface and diameter close to 1 祄 were synthesized by newly soap-free emulsion polymerization. The results showed that the presence of ethanol and NaCl made the increase of diameter and distribution, while the presence of toluene could avoid the problem of the increase of distribution, resulting a harvest of PMMA microspheres with a diameter close to 1 祄.

Determination of large diameter bored pile's effective length based on Mindlin's solution

The calculation equation of large diameter bored pile＇s effective length is connected with its distribution of pile shaft resistance. Thus, there is a great difference between the calculation results under the different distributions of pile shaft resistance. Primarily, this paper summarizes the conceptualized mode of pile shaft resistance under the circum- stance that the soil surrounding the piles presents different layer distributions. Secondly, based on Mindlin＇s displacement solution and in consideration of the effect of pile diam- eter, the calculation equation is optimized with the assumption that the pile shaft resis- tance has a parabolic distribution. The influencing factors are analyzed according to the calculation result of effective pile length. Finally, combined with an engineering example, the calculation equation deduced in this paper is analyzed and verified. The result shows that both the Poisson ratio of soil and pile diameter have impacted the effective pile length. Compared with the Poisson ratio of soil, the effect of pile diameter is more significant. If the pile diameter remains the same, the effect of the Poisson ratio of soil to the effective pile length decreases as the ratio of pile elastic modulus and soil share modulus increases. If the Poisson ratio of soil remains the same, the effect of the pile diameter to the effective pile length increases as the ratio of pile elastic modulus and soil share modulus increases. Thus the optimized calculation result of pile effective length under the consideration of pile diameter effect is more close to the actual situation of engineering and reasonably practicable.

Numerical simulation of multi-phase combustion flow in solid rocket motors with metalized propellant

Multi-phase flowfield simulation has been performed on solid rocket motor and effect of multi-phases on the performance prediction of the solid rocket motor(SRM) is investigation.During the combustion of aluminized propellant,the aluminum particles in the propellant melt and formliquid aluminum at the burning propellant surface.So the flow within the rocket motor is multi phase or two phase because it contains droplets and smoke particles of Al2O3.Flowsi mulations have been performed on a large scale motor,to observe the effect of the flowfield onthe chamber and nozzle as well.Uniform particles diameters and Rosin-Rammler diameter distribution method that is based on the assumption that an exponential relationship exists betweenthe droplet diameter,dand mass fraction of droplets with diameter greater thandhave been used for the si mulation of different distribution of Al2O3 droplets present in SRM.Particles sizes in the range of 1-100μm are used,as being the most common droplets.In this approachthe complete range of particle sizes is dividedinto a set of discrete size ranges,eachto be defined by single streamthat is part of the group.Roe scheme-flux differencing splitting based on approxi mate Riemann problem has been used to si mulate the effects of the multi-phase flowfeild.This is second order upwind scheme in which flux differencing splitting method is employed.To cater for the turbulence effect,Spalart-All maras model has been used.The results obtained show the great sensitivity of this diameters distribution and particles concentrations to the SRMflowdynamics,primarily at the motor chamber and nozzle exit.The results are shown with various sizes of the particles concentrations and geometrical configurations including models for SRM and nozzle.The analysis also provides effect of multi-phase on performance prediction of solid rocket motor.