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.

Spatiotemporal variation and correlation of soil enzyme activities and soil physicochemical properties in canopy gaps of the Tianshan Mountains,Northwest China

The study of the heterogeneity of soil enzyme activities at different sampling locations in canopy gaps will help understand the influence mechanism of canopy gaps on soil ecological processes.In this paper,we analyzed the spatiotemporal variation of soil enzyme activities and soil physicochemical properties at different sampling locations(closed canopy,expanded edge,canopy edge,gap center)in different sampling time(December,February,April,June,August,and October)on the northern slope of the Tianshan Mountains,Northwest China.The results showed that soil catalase,cellulase,sucrase,and acid phosphatase activities were relatively high from June to October and low from December to April,and most of soil enzyme activities were higher at closed canopy than at gap center.Soil urease activity was high during December-February.The soil temperature reached the highest value during June-August and was relatively high at gap center in October,December,and February.Soil water content was significantly higher in December and April than in other months.Soil bulk density was higher at gap center than at closed canopy in December.Soil pH and soil electrical conductivity in most months were higher at closed canopy than at gap center.Soil organic carbon,soil total nitrogen,and soil total phosphorus were generally higher at gap center than at closed canopy.Furthermore,sampling time played a leading role in the dynamic change of soil enzyme activity.The key factors affecting soil enzyme activity were soil temperature and soil water content,which were governed by canopy gaps.These results provide important support for further understanding the influence mechanism of forest ecosystem management and conservation on the Tianshan Mountains.

An environmental gradient change of Picea mongolica seedling from the center of a forest canopy gap in forest-steppe ecotone in Inner Mongolia Autonomous Region of China

In sandy forest with a forest canopy gap for a period of over 30 years, the spruce（Picea mongolica） seedlings were monitored on two 5-m- wide transects from the center of a large gap into the surrounding forest. The farther they were to the far center, the taller grew the seedling and the more is the number of seedling. There were many seedlings under the canopy but almost all seedlings died before they grow up. Along the forest edge, growth of seedlings was temporarily enhanced by lateral penetration of light from the gap. The implications for natural forest regeneration dynamics are discussed. Our results prove that in P mongolica forest a gap disturbance creates a non-uniform environment for regeneration of the species, and determines that the forest was a non-even aged forest.

Canopy gap characteristics and spatial patterns in a subtropical forest of South China after ice storm damage

The divergent gap characteristics and spatial patterns of canopy gaps created by natural or artificial disturbances can exert a dominant influence on forest structure and composition.However,little research has been conducted on the effects of ice storm damage on canopy gaps in subtropical mature forests of South China.In this study,one semi-natural site was dominated by a broad-leaf forest and two managed sites were representative of plantations with coniferous forests.Based on airborne laser scanning data and field evidence across sites,statistical analyses were used to examine gap characteristics following ice storms of moderate severity.Generalized Ripley’s K-function analysis was applied to test gap spatial patterns at a range of scales,and spatial point pattern analysis was used to quantitate the relative importance of specific influences on patterns of gap occurrence.The results revealed that the average gap size was 75.7 m^2 and that 12.2 gaps occurred per hectare.Most gaps were single-tree fall events.In addition to more gaps,the mean gap size was smaller and the shape was more complex in the semi-natural site than in two managed sites.Large differences in gap characteristics were observed among snapped,uprooted,snag,and artificial gap damage types.Gaps generally showed a clustered distribution at large scales(e.g.70 m),whereas spatial patterns varied with gap damage types at different sites.The occurrence of gaps was strongly related to slope and topographic position at the semi-natural site,whereas slope,stem density,and human accessibility(proximity to pathways)were the most important factors affecting gap occurrence at the managed sites.We suggest that gap-based silvicultural treatments and natural disturbances regimes conjoin,highlighting interactions with other factors such as microsite conditions,non-tree vegetation and more.

Afforestation,restoration and regeneration——Not all trees are created equal

Undulations in weather patterns have caused climate shifts of increased frequency and duration around the world. The need for additional research and model data on this pressing problem has resulted in a plethora of research groups examining a particular tree species or biome for negative effects of climate change. This review aims to （1） collect and merge recent research data on regeneration within old- and new-growth forests, （2） highlight and expand upon selected topics for additional discussion, and （3） report how shade tolerance, drought toler- ance, and inherent plasticity affect tree growth and development. Al- though shade and drought tolerance have been well studied by a number of research groups, this review reveals that in-depth analysis of a single or a few species in a given area will not generate the data required to implement a successful regeneration plan. Studies using historical accounts of previous species composition, information regarding site sea- sonality, species competition, and individual responses to drought and shade are needed to （1） develop best management plans and （2） ensure future modeling experiments are focused on a greater variety of species using more innovative methods to evaluate climate change effects.

Species diversity and regeneration of old-growth seasonally dry Shorea robusta forests following gap formation

Diversity and regeneration of woody species were investigated in two ecological niches viz. gap and intact vegetation in old-growth seasonally dry Shorea robusta （Gaertn. f.） forests in Nepal. We also related varieties of diversity measures and regeneration at- tributes to gap characteristics. Stem density of tree and shrub components is higher in the gap than in the intact vegetation. Seedling densities of S. robusta and Terminalia alata （B. Heyne ex Roth.） are higher in the gap than in the intact vegetation, while contrary result is observed for T. bellirica （Gaertn. ex Roxb.） and Syzigium cumini （L. Skeels） in term of seedling density. The complement of Simpson index, Evenness index, and species-individual ratio in the seedling layer are lower in the gap than the intact vegetation. Gap size can explain species richness and species establishment rate. Gaps created by multiple tree falls in different years have higher seedling density of S. robusta than gaps created by single and/or multiple tree falls in the same year. In conclusion, gaps maintain species diversity by increasing seedling density, and favor regeneration of Sal forests. In addition to gap size, other gap attributes also affect species diversity and regeneration.

Disturbance history,species diversity,and structural complexity of a temperate deciduous forest

Stand structural complexity enhancement is an increasingly popular management objective,especially on public lands.Complex stand structures are hypothesized to support a relatively high degree of native forest diversity and be more resistant and resilient to disturbances.Complex structures are characterized by the presence of deadwood and heterogeneity of tree-size classes and tree architecture.Relatively little is known about how discrete disturbance events affect structural complexity and compositional diversity in Quercus-dominated stands at fine spatial scales(i.e.neighborhoods).We established 200.05 ha fixed-radius plots on the Sipsey Wilderness of William B.Bankhead National Forest in northern Alabama to quantify woody plant species composition and structure.Trees were mapped on each plot to quantify overstory structural complexity and compositional diversity.We extracted two cores from all canopy Quercus spp.C 5 cm diameter at breast height to quantify age,recruitment pulses,and reconstruct canopy disturbance history.Shannon species diversity in the sampled area was 1.75 for trees,2.08 for saplings,and 1.69 for seedlings.Quercus alba had the greatest basal area,and Ostrya virginiana had the highest density.The stand exhibited a reverse J-shaped distribution with a q-factor of 1.72.The oldest Quercus dated to 1795,and the largest recruitment pulse occurred in the 1870s.The mean return interval for intermediateseverity disturbance was 38 years.Although we documented no relationships between disturbance frequency and compositional diversity at the neighborhood scale(0.05 ha),less frequent disturbance was associated with higher structural complexity(r^2=0.258,p=0.026)at the neighborhood scale.We suggest that localized disturbance increases species diversity and structural complexity,but these processes are manifest at the stand level and not at the neighborhood scale.We conclude that the spatial variability(i.e.size,shape,orientation,microsite conditions)is likely more influential on diversity and complexity than the temporal variation(frequency)of these processes at the neighborhood scale.

Differential modulation of crown allometry and stem growth at gap edges in five European tree species by drought conditions

Background In Central Europe,forests are increasingly affected by various disturbances,resulting in an increasing gap formation in the canopy.In order to support goal-oriented management,more knowledge is required about the acclimation of the crown and its effects on the basal area growth of trees at the edge of a gap.Methods This work compared trees'growth and crown structure at the edge of a transient gap,with a gap size of more than 80​m^(2),with trees in the stand that were at least 30​m away from the gap.A total of 249 European beeches(Fagus sylvatica L.),Norway spruces(Picea abies L.Karst),Scots pines(Pinus sylvestris L.),oaks(Quercus spp.;Quercus petraea(Matt.)Liebl.,Quercus robur L.),and silver firs(Abies alba Mill.)were examined on long-term experimental plots in southern Germany.Various crown measures were developed and calculated using high-resolution terrestrial laser scanning(TLiDAR)to capture the three-dimensional crown structures.Growth responses to edge conditions were measured based on tree rings.Using linear mixed models,we predict the basal area increment of edge trees relative to trees in the stand under wet and dry soil moisture conditions after the gap formation.Results We identified i)species-specific acclimation of the crown of edge trees after the gap formation,ii)under wet soil moisture conditions a growth increase of 25%–45%for beech,pine,and oak edge trees and growth losses of 5%–60%for spruce and fir and iii)coniferous tree species benefited from the edge position regarding their basal area increment under dry soil moisture conditions and deciduous tree species grew regardless of the soil moisture conditions at the edge of a gap.Conclusion Gaps have a species-specific effect on the habitus and growth of edge trees and can have both positive and negative impacts on silviculture.

Gap characteristics and their effects on regeneration,dominance and early growth of woody species

Aims We aim to examine the canopy gap characteristics and evaluate their influence on regeneration,dominance and the early growth of woody species in seasonally dry Shorea robusta forests(Sal forests).Methods Sixty canopy gaps were surveyed in six randomly located transects belts in seasonally dry subtropical Sal forests of central Nepal.Each transect belt was followed until 10 gap sites were encountered.The equation for the area of an ellipse was used to calculate the size of canopy gap,measuring the longest axis and its perpendicular shorter axis.Number,sizes,ages and causes of tree falls creating canopy gaps along with number and sizes of border trees were identified and recorded.Detailed gap inventories were carried out using square 25-m2 quadrats placed in the middle of each gap.All individuals>2 m in height within the quadrat were identified at the species level and their diameter at breast height was measured.We assigned a nested 4-m2 quadrat to the corner of each 25-m2 quadrat,within which all woody individuals>10 cm tall were identified at the species level,and counted them and their regeneration mechanisms were identified.The height and collar diameter of the tallest individuals were measured.Descriptive statistics was calculated for the variables of interests and Pearson correlation,linear regression,independent-sample t-test and chi-square test were used to relate them and to test for their associations.Important Findings The study found mean gap size of 283 m2 and;50%gaps of 10–15 years old.Gaps created by natural single-tree falls were significantly more numerous,and their mean size was significantly smaller than those resulting from artificial causes or multiple-tree falls.Gap size correlated with the basal area of felled trees,but it did not correlate with the number of tree falls.While tree fall basal area was significantly positively correlated to the seed-originated seedling to resprout ratio,it was negatively correlated,along with gap area and the basal size of retained trees,to seedling growth.The relative seedling density of Terminalia alata increased with increases in gap areas,while that of S.robusta decreased with increases in tree fall basal area,thereby lowering the plot-level dominance.However,the relative seedling densities of Eugenia operculata and Syzigium cumini were negatively and positively correlated,respectively,with tree fall basal area.

Sap flow for beech(Fagus sylvatica L.)in a natural and a managed forest—effect of spatial heterogeneity

Aims Beech(Fagus sylvatica L.)is an important species in natural and managed forests in Europe.This drought-sensitive species dominates even-aged stands as well more natural stands composed of a mixture of tree species,age and size classes.This study evaluates the extent that heterogeneity in spacing and tree diameter affect the seasonal availability and use of water.Methods Two stands were evaluated:(i)a heterogeneous forest remnant(NAT)with trees up to;300 years old,a mean top height of 28.4 m and a total of 733 stems ha
1with stem diameters averaging 18 cm and(ii)an even-aged 80-year old stand(MAN),with a height of 25 m,and a total of 283 stems ha
1 with diameters averaging 38 cm.Stem sap flow,Js(g m
2 s
1),was continuously measured in 12(MAN)and 13(NAT)trees using 20-mm long heat dissipation sensors.Individual tree measures of sap flow were correlated using non-linear statistical methods with air vapour pressure deficit(D,hPa)and global radiation(Rg,J m
2 day
1),along with constraints imposed by reductions in soil water content(SWC).SWC was measured as volumetric%using time domain reflectometry.Important Findings The daily integrated Js(Js-sum)for trees growing in the evenly spaced MAN stand and trees in canopy and closed forest positions in NAT stand decreased as the availability of soil moisture was reduced.In the heterogeneous NAT stand,SWC in a recently formed canopy gap remained high throughout the vegetation period.Based on regression models,the predicted relative decrease in Js-sum for dry relative to moist soil water conditions in the closed forest(at mean daily D=10 hPa)was 7–11%for trees near the gap and 39–42%for trees in the closed forest.In MAN,the reduction in Js-sum was 29%in dry relative to moist conditions.Js-sum in the outer 20 mm of the xylem in NAT was lower than that in MAN and the rate of decline in Js with xylem depth was less in NAT than in MAN.In MAN,Js-sum in deep and outer xylem was negatively affected at low soil moisture availability;in NAT,this was the case for only the outer xylem indicating that deep roots could be important in supplying water at times of low soil moisture in the upper soil.

Effect of Gap Size on Seedling Establishment of Tsuga longibracteata

Effects of three gaps which are large (118 m2), medium (86 m2) and small (20 m2), respectively, and under canopy of Tsuga longibracteata forest on the seedling establishment of T. longibracteata were studied through seed burial experiments from December 2003 to January 2005 in Tianbaoyan National Nature Reserve of Fujian, China. The results showed that the area of gap had an evident effect on the seedling establishment of T. longibracteata. The seedling emergence rates of T. longibracteata in plots of large gap, medium gap, small gap and under canopy were 10%, 10%, 4% and 6%, representing an increasing trend along with the gap size increasing without a significant difference. Rain eroding and insects feeding were two main factors leading to seedling death. The larger the gap size was, the more seedlings were killed by rain erosion and the fewer seedlings were killed by insects feeding. The emergence time of seedlings was almost same in all plots while their death time was different respectively. The gap size had a significant impact on seedling survival rate. The seedling survival rate was highest in the medium gap plot (27.0%) and next to the highest in large gap plot (7.3%), and seedling in small gap plot and under canopy plot died out after one growing season. Increased light supply in gaps was favorable for the seedlings growth and survival. Increased light supply in the large gap could enhance the growth of seedling leaf and root of T. longibracteata, and the seedling in turn allocated more dry mass to root and leaf, but it has little impact on the growth of stem. This research indicates that T. longibracteata is a pioneer species and its seedling establishment need a medium or large gap (>50 m2).