Mixed-effects modeling for tree height prediction models of Oriental beech in the Hyrcanian forests

Height–diameter relationships are essential elements of forest assessment and modeling efforts.In this work,two linear and eighteen nonlinear height–diameter equations were evaluated to find a local model for Oriental beech（Fagus orientalis Lipsky） in the Hyrcanian Forest in Iran.The predictive performance of these models was first assessed by different evaluation criteria： adjusted R^2（R^2_（adj））,root mean square error（RMSE）,relative RMSE（%RMSE）,bias,and relative bias（%bias） criteria.The best model was selected for use as the base mixed-effects model.Random parameters for test plots were estimated with different tree selection options.Results show that the Chapman–Richards model had better predictive ability in terms of adj R^2（0.81）,RMSE（3.7 m）,%RMSE（12.9）,bias（0.8）,%Bias（2.79） than the other models.Furthermore,the calibration response,based on a selection of four trees from the sample plots,resulted in a reduction percentage for bias and RMSE of about 1.6–2.7%.Our results indicate that the calibrated model produced the most accurate results.

Effect of canopy gap size and ecological factors on species diversity and beech seedlings in managed beech stands in Hyrcanian forests

We studied the species diversity of the herb layer and ecological factors in harvest-created gaps in beech stands under a single-tree selection system in Northern Iran. To determine diversity, the number of beech seedlings, and other ecological factors, 16 gaps were selected and subplots of 5 m2 were positioned at the centre and at the cardinal points of each gap. Species richness and Simpson diversity index increased with increasing gap area as did numbers of seedlings. With increasing humus layer thickness, species richness declined but the Hill evenness index increased. Species richness increased with increasing light availability. There was no relationship between crown radii of beech trees and diversity indices. Correlations between environmental factors and numbers of individuals of some species in the herb layer were not significant except in a few cases. The results help explain the effects of man-made gaps on the dynamics of managed beech stands and this benefits evaluation of silvicultural operating plans.

Spatial correlation of pit and mound topography with canopy gaps in a virgin mixed beech forest, northern Iran

In a reserved forest parcel in a virgin eastern Hyrcanian mixed beech forest,80 ha was surveyed to determine the pit and mound topography,canopy gaps and dead trees.The aim was to investigate the spatial patterns and correlation of pit and mound features with canopy gaps.Seventy-five canopy gaps and 61 pit and mound features were identified.The univariate first order nearest neighbor(R_(CE))and bivariate second order test(Ripley’s K)statistic were applied.R_(CE) statistics highlighted a general aggregation pattern for canopy gaps and pits and mounds,while pits and mounds alone were more clumped.Distances between canopy gaps were 130 m average,whereas distances between pit and mound features and dead trees were 60 and 78 m,respectively.Spatial positive correlation of canopy gaps with pits and mounds were observed with all distances.The result of spatial correlations between canopy gaps with pits and mounds confirmed that windthrows cause micro successions in fallen tree ecosystem-scale correlated with gap phase dynamics in the forest community-scale.

Drought can favour the growth of small in relation to tall trees in mature stands of Norway spruce and European beech

Background: Climate change triggered many studies showing that trends and events of environmental conditions can reduce but also accelerate growth at the stand and individual tree level. However, it is still rather unknown how climate change modifies the growth partitioning between the trees in forest stands.Methods: Based on long-term girth-tape measurements in mature monospecific and mixed-species stands of Norway spruce(Picea abies(L.) Karst.) and European beech(Fagus sylvatica L.) we traced the effect of the severe droughts in 2003 and 2015 from the stand down to the tree level.Results: Stand growth of Norway spruce decreased by about 30% in the once-in-a-century drought 2015, while European beech was much more drought resistant. Water availability generally amplified size-asymmetric growth partitioning. Especially in case of Norway spruce water availability primarily fostered the growth of predominant trees, whereas drought favoured the growth of small trees at the expense of the predominant ones. We could not detect significant differences between mixed and monospecific stands in this regard.Conclusions: The drought-induced reallocation of growth in favour of small trees in case of spruce may result from its isohydric character. We hypothesize that as small trees are shaded, they can benefit from the reduced water consumption of their sun-exposed taller neighbours. In case of beech, as an anisohydric species, tall trees suffer less and smaller trees benefit less under drought. The discussion elaborates the consequences of the water dependent growth allocation for forest monitoring, growth modelling, and silviculture.

Biomass and nutrients allocation in pot cultured beech seedlings:influence of nitrogen fertilizer

Allocation of biomass and nutrient elements including Nitrogen to above and belowground compartments of beech seedlings （Fagus sylvatica L.） treated by labeled nitrogen fertilizer in the form of 15NH4 and 15NO3 were investigated at the end of two successive growing seasons. Pot cultured beech seedlings were grown at a green house on intact soil cores sampled from three adjacent stands including beech, Norway spruce and mixed beech-spruce cultures of Soiling forest, Germany. Comparing biomass allocation and nutrients concentrations of the seedlings between the control and 15N-fertilized treatments revealed no significant effect of N fertilization on nutrients uptake by seedlings over the experiment. The form of N input influenced its movement into plant pools. It was demonstrated that beech seedlings take up nitrogen mainly in the form of nitrate, which is then reduced in the leaves, although the differences between the retention of NO3^--N and NH4^＋-N in plants were not statistically significant. Percent recoveries of 15N in trees were typically greater after 15NO3 than after 15NH4 additions. It was indicated that immobilization of ~SN tracer in fine roots was a slower process comparing other plant compartments such as stem and coarse roots, but a powerful sink for N during the course of study.

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.

Forest structure and woody plant species composition after a wildfire in beech forests in the north of Iran

Beech （Fagus orientalis Lipsky） forest covers about 565,000 ha of land in Guilan province, north of Iran and forms a major carbon pool. It is an important economic, soil protection and recreation resource. We studied long-term effects of fire on the structure and composition 37 years after fire occurrence in these forests. To do this research, we selected 85 ha burned and 85 ha unburned beech forests）. The results indicated that the fire had not changed the overall uneven-aged structure, but it changed forest composition from pure stands to mixed stands that now include species such as Carpinus betulus, Acer cappadocicum and Alnus subcordata. The density of trees and regeneration was significantly increased, while the density of shrubs significantly decreased. The main reasons for increased tree regeneration were attributed to （1） reduction of litter depth, and （2） increase in available light from opening of the canopy and reduction in shrub competition. It is apparent that the forest is on a path to return to its natural state before the fire after 37 years.

Natural regeneration of oriental beech(Fagus orientalis Lipsky)trees in canopy gaps and under closed canopy in a forest in northern Iran

For developing nature-based silvicultural practices in a beech forest to promote, abundance, height, vitality, and preferred growth form, regenerated trees growing in gaps were compared with those under closed canopies. A systematic 50 ×50 m grid was plotted in a beech stand in the Kheyrud Experimental Forest for selecting trees to measure variables in gaps and under closed canopies. Abundance and mean height of regenerated beech trees were significantly higher in closed canopies than in canopy gaps. Beech seedlings with excurrent growth were significantly taller within regeneration patches under closed canopy. Moreover, regenerated trees with high vitality were more abundant in closed canopy areas than in gaps. Thus, beech regeneration should improve under closed canopies; hence, gaps in a near natural forest should be created only after adequate regeneration and appropriate growth under the parent tree in a closed canopy area is ensured. The results of this research have profound implications for the sustainable management of the forest and for ensuring sustainable beech regeneration. The presence of a closed canopy cover likely will reduce potential stresses on oriental beech regeneration.

Effects of thinning on stand structure and tree stability in an afforested oriental beech(Fagus orientalis Lipsky) stand in northeast Turkey

We studied relationships between stand structure and stand stability according to thinning intensity in an afforested oriental beech stand. Various thinning intensities were applied in sample stands. We sampled eight plots in stands that were lightly thinned, eight plots in heavily thinned stands and eight plots in unthinned stands as a control. Height and diameter distributions of the stands were measured to assess stand structure. We quantified individual tree stability and collective stability. Heavy thinning during the first thinning operation damaged the storied structure of the stand in thicket stage and affected collective structuring ability. While most control plots had multi-storied stands, after light and heavy thinning two-storied structure became more common.Large gaps occurred in the canopy after heavy thinning. On average, nine tree collectives were formed per sampling plot in the untreated stand, seven collectives after thinning in 2008 and four collectives after thinning in 2009. Stable trees accounted for 17 % of trees in control plots, 24 % in lightly thinned plots, and 15 % in heavily thinned plots. Collective stability values were 83 % in control plots, 82 % in lightly thinned plots and 36 % in heavily thinned plots. We conclude that it is necessary to retain collective structuring capacity during thinning operations for sustaining stand stability.

Study of the Single Shear Performance of a Joint with a New Beech and Self-Tapping Screw Composite Dowel

A new beech and self-tapping screw composite dowel is proposed and studied,its performance being compared with that of beech dowels and self-tapping screws alone.The single shear performance of components connected by composite dowels was tested.Results show that the dowels are a good choice for components requiring high stiffness.Screws remain a good choice for components requiring excellent seismic performance.Combination group presents similar maximum load stiffness to those of composite dowels,but other ductility parameters are superior for composite dowels.The best connection mode was provided by two composite dowels.Based on connecting two points,structural elements with two composite dowels showed much better load bearing ability than when joined by two beech dowels or by two self-tapping screws separately.The structural element with two composite dowels not only presented better initial stiffness,but also exhibited a better ductility coeffi-cient and less energy consumption.So,the composite dowels can be used for beam column connection,dowel laminated timber,and restoration or enhancement of ancient buildings.

Distribution of stem decay in the beech trees of the Azerbaijan and its impact on the output of commercial wood

To determine the distribution of stem decay in the beech stands of Azerbaijan, we sought to identify the species, number, and height of attachment of fruiting bodies;the extent of decay in tree trunks growing under different conditions;and its influence on the trees’ commercial wood. The research was conducted on three farms representing the most common forest types of the Greater Caucasus within Azerbaijan. Examination of the presence of fruiting bodies in the tree trunk revealed that stem decay is the most common infection in beech (Fagus orientalis) stands, especially in fresh, moist areas, with less infection under dry growing conditions. In this work, the length, diameter, and volume of decay were studied by infecting the trunks of 93 model trees affected with mushrooms in 1–4 m cuttings. Our results showed that as the age of the stand increased, extent, diameter, and volume of decay increased significantly: the extent of decay from 1.47 to 6.43 m;the diameter of the decay from 8.15 to 32.7 cm;and the volume of decay from 2.5 to 13.2%. The relationship between age and the specified indicators is presented graphically. Using data obtained from the same sample of trees, we determined the expected and actual yield of commercial wood by age class. We determined that stem decay in beech stands leads to a decrease in the yield of commercial wood on average from 25.1% in the middle-aged to 14.8% in overmature plantations, respectively, with an estimated yield of 40.8–62.7%. Here we present mathematical models of the output of commercial wood from the infected part of the stands by age classes with the use of average data on the extent of decay in model trees.

Residual tree damage along skidding trails in beech stands in Greece

We studied the damage caused to unfelled trees during skidding operations in four beech stands of northern and central Greece that were managed under differing harvesting systems.After timber was harvested we recorded and analyzed all damage to a width of 2 m along both sides of the skid trails.The percentage of damaged residual trees was 17–28 %.Higher numbers of saplings were uprooted or destroyed in parts of the stands with high natural regeneration.Most damaged trees suffered 1.33–1.90 wounds that were inflicted up to a height of 1 m above ground level.At all sites mean wound sizes were large,89–1190 cm2,and caused elevated risk of future fungal infection.The damage caused by skidding during timber harvesting can be minimized by better planning the harvest operations,and training forest workers in reduced impact logging.

Long-term effect of fire on herbaceous species diversity in oriental beech (Fagus orientalis Lipsky) forests in northern Iran

We studied the long-term impacts of natural burning on herbaceous species diversity 37 years after a fire occurred in the Roudbar forests of Guilan Province, northern Iran. Numerous studies have examined short-term changes in understory vegetation following wildfire; however, very few long-term studies are available or changes inferred from retrospective studies based on chro- nosequences. For this study, 170 ha of forest （85 ha, burned areas; 85 ha, unburned areas） were surveyed. Because the 1000 m2 plots were too large for detailed measurements of herbaceous species, we determined a sub-sample size according to the Whittaker＇s nested plot sampling protocol and minimal areas method. Hence, sub-plots of 32 m2 were used for herbaceous species measurements, which consisted of percent cover of each species based on the Domin criterion. We measured plant diversity （Shannon-Wiener index）, spe- cies richness （Margalef＇s index）, and evenness （Smith-Wilson index）. Mean percent cover, together with diversity, richness and even- ness, increased markedly in burned areas compared to unburned controls. This suggests that the biodiversity of these forests could be restored within 37 years after fire. However, the abundance of invasive species such as Rubus fruticosus and Bromus benekenii increased significantly in burned areas, but these could be controlled by relevant silvicultural operations.

How do soil fauna and soil microbiota respond to beech forest growth?

The dynamics and performance of soil biota during forest rotation were studied in monoculture beech stands forming a chronosequence of four different age-classes(30,62,111,153 yr).Biomass was monitored in major groups of microflora,microfauna,mesofauna,and macrofauna.Resource availability(litter layer,soil organic mater),biomass of the two dominant decomposer groups(microflora,earthworms)as well as the biomass of mesofauna and microfauna were found to remain quite stable during forest succession.Nevertheless,the marked increase of the biomasses of primary decomposers(fungi,saprophagous macroinvertebrates)in the 62-year-old stand,followed by an increase of the biomasses of macropredators in the 111-year-old stand,indicate substantial changes of several components of edaphic communities during forest development.However,constant values of soil respiration suggest that the overall performance of the soil food web does not change during beech forest succession.Thus,the decomposer system of lowland managed beech forests on calcareous soils seems to be very stable over time.We suggest that earthworm activity might have masked impacts of forest development on other soil biota and led to an astounding stability of decomposer assemblages during beech forest rotation.

The fate of ^(15)N-labeled nitrogen inputs to pot cultured beech seedlings

The partitioning of nitrogen deposition among forest soil （including forest floor）, leachate and above- and belowground biomass of pot cultured beech seedlings in comparison to non-cultured treatments were investigated by adding 1.92 g.m^-2 ^15N tracer in throughfall for two successive growing seasons at a greenhouse experiment. Ammonium and nitrate depositions were simulated on four treatments （cultured and non-cultured） and each treatment was labeled with either ^15N-NH4^＋ or ^15N-NO3^-. Total recovery rates of the applied ^15N in the whole system accounted for 74.9% to 67.3% after ^15N-NH4^＋ and 85.3% to 88.1% after ^15N-NO3^-in cultured and non-cultured treatments, respectively. The main sink for both ^15N tracers was the forest soil （including forest floor）, where 34.6% to 33.7% of ^15N-NH4^＋ and 13.1% to 9.0% of ^15N-NO3^-were found in cultured and non-cultured treatments, respectively, suggesting strong immobilization of both N forms by hetero- trophic microorganisms. Nitrogen immobilization by microorganisms in the forest soil （including forest floor） was three times higher when ^15N-NH4^＋ was applied compared to ^15N-NO3^-. The preferential heterotrophic use of ammonium resulted in a two times higher retention of deposited ^15N-NH4^＋ in the forest soil as compared to plants. In contrast, nitrate immobilization in the forest soil was lower compared to plants, although statistically it was not significantly different. In total the immobilization of ammonium in the plant-soil system was about 60% higher than nitrate, indicating the importance of the N-forms deposition for retention in forest ecosystems.

Soil Microbial Activity and Functional Diversity in Primeval Beech Forests

Virgin forests are unique ecosystems, which can be used as etalon for basic biocoenotic investigation. Soil microorganisms are very sensitive reagents on influence of biotical factors, and at the same time are the active producers of phytotoxic and phytostimulating exometabolites. Studies of soil microbiota were conducted in virgin beech forests of Shyrokoluzhansky massif of the Carpathian Biosphere Reserve. It was found the ratio and the number of different ecological-trophic groups of soil microorganisms changes with altitude. So the number of ammonificators with increasing of altitude above sea level was reduced. The soil at altitude of 1,100 meters above sea level was characterized by minimum content of organotrophes -1.22 × 10^6 （CFU-colony forming units/lg.a.d.s.）. At the altitude of 500 meters content of ammonificators increased at six times and was 7.07 ×10^6 CFU/lg.a.d.s., which indicates to accumulation of the soil organic matter. Similar changes occurred with the number of bacteria which are using mineral forms of nitrogen for their nutrition. Their maximum quantity （4.32 × 10^6 CFU/lg.a.d.s.） was in the soil of biotope disposed at altitude of 500 meters above sea level. Fluctuations in the number of soil micromycetes of virgin forest ecosystems have not been as significant as the bacterial microbiota （within 17 ×10^3-28 × 10^3 CFU/lg.a.d.s.）. Among a wide spectrum of bacterial microbiota were isolated strains with high phytostimulating action.

Analysis of Dose--Thickness Interaction with X-Rays Energy of 6 and 18 MeV for Beech Wooden Materials

In this study, dose and thickness interrelation is analyzed by using photon rays with an energy of 6 MeV and 18 MeV on wooden type materials made of beech trees with different surface area. We studied the dose measurements on the surface area of 5 cm × 5 cm, 8 cm× 8 cm, 10 cm × 10 cm, 12 cm × 12 cm with different thicknesses. X-ray with an energy of 6 MeV is applied at 0° gantry angle; and solid phantom is adjusted. Dose measurements are carried out on beech type of wooden materials with different thicknesses, and stopping power of these materials are compared.

Drought events influence nutrient canopy exchanges and green leaf partitioning during senescence in a deciduous forest

The increase in the frequency and intensity of drought events expected in the coming decades in Western Europe may disturb forest biogeochemical cycles and create nutrient deficiencies in trees.One possible origin of nutrient deficiency is the disturbance of the partitioning of the green leaf pool during the leaf senescence period between resorption,foliar leaching and senesced leaves.However,the effects of drought events on this partitioning and the consequences for the maintenance of tree nutrition are poorly documented.An experiment in a beech forest in Meuse(France)was conducted to assess the effect of drought events on nutrient canopy exchanges and on the partitioning of the green leaf pool during the leaf senescence period.The aim was to identify potential nutritional consequences of droughts for trees.Monitoring nutrient dynamics,including resorption,chemistry of green and senesced leaves,foliar absorption and leaching in mature beech stands from 2012 to 2019 allowed us to compare the nutrient exchanges for three nondry and three dry years(i.e.,with an intense drought event during the growing season).During dry years,we observed a decrease by almost a third of the potassium(K)partitioning to resorption(i.e.resorption efficiency),thus reducing the K reserve in trees for the next growing season.This result suggests that with the increased drought frequency and intensity expected for the coming decades,there will be a risk of potassium deficiency in trees,as already observed in a rainfall exclusion experiment on the same study site.Reduced foliar leaching and higher parititioning to the senesced leaves for K and phosphorus(P)were also observed.In addition,a slight increase in nitrogen(N)resorption efficiency occurred during dry years which is more likely to improve tree nutrition.The calcium(Ca)negative resorption decreased,with no apparent consequence in our study site.Our results show that nutrient exchanges in the canopy and the partitioning of the green leaf pool can be modified by drought events,and may have consequences on tree nutrition.

The rate of deadwood decomposition processes in tree stand gaps resulting from bark beetle infestation spots in mountain forests

Decaying wood is an essential element of forest ecosystems and it affects its other components.The aim of our research was to determine the decomposition rate of deadwood in various humidity and thermal conditions in the gaps formed in the montane forest stands.The research was carried out in the Babiog orski National Park.The research plots were marked out in the gaps of the stands,which were formed as a result of bark beetle gradation.Control plots were located in undisturbed stands.The research covered wood of two species–spruce and beech in the form of cubes with dimensions of 50 mm×50 mm×22 mm.Wood samples were placed directly on the soil surface and subjected to laboratory analysis after 36 months.A significant influence of the wood species and the study plot type on the physicochemical properties of the tested wood samples was found.Wood characteristics strongly correlated with soil moisture.A significantly higher mass decline of wood samples was recorded on the reference study plots,which were characterized by more stable moisture conditions.Poorer decomposition of wood in the gaps regardless of the species is related to lower moisture.The wood species covered by the study differed in the decomposition rate.Spruce wood samples were characterized by a significantly higher decomposition rate compared to beech wood samples.Our research has confirmed that disturbances that lead to the formation of gaps have a direct impact on the decomposition process of deadwood.

乙二醛法脱水加固饱水榉木的机制研究和温度对性能的影响

乙二醛法是我国目前应用最广的脱水加固木质文物保护方法。采用傅里叶红外光谱(FTIR)、扫描电镜(SEM)和X射线衍射(XRD)等方法研究了乙二醛法脱水加固饱水榉木的试验过程,分析了脱水填充机制以及温度对脱水加固饱水榉木性能的影响规律。结果表明:乙二醛进入饱水榉木内部后交联聚合形成乙二醛聚合物直接作用于细胞内部,与细胞壁结合,支撑细胞加固细胞壁;试样的增重率升高,收缩率降低,色差明显增加。乙二醛法处理的温度升高(40℃相对于20℃)能提高乙二醛在榉木试样内部的扩散和浸入量,增加乙二醛聚合物在榉木内部的含量,提高试样增重率和弯曲强度,降低收缩率,有利于木材细胞形状的恢复和保持,缩短脱水加固工艺处理的时间,对表面活性剂的效果影响较轻。