Analysis of forest structural complexity using airborne LiDAR data and aerial photography in a mixed conifer–broadleaf forest in northern Japan

Determining forest structural complexity,i.e.,a measure of the number of different attributes of a forest and the relative abundance of each attribute,is important for forest management and conservation.In this study,we examined the structural complexity of mixed conifer–broadleaf forests by integrating multiple forest structural attributes derived from airborne Li DAR data and aerial photography.We sampled 76 plots from an unmanaged mixed conifer–broadleaf forest reserve in northern Japan.Plot-level metrics were computed for all plots using both field and remote sensing data to assess their ability to capture the vertical and horizontal variations of forest structure.A multivariate set of forest structural attributes that included three Li DAR metrics(95 th percentile canopy height,canopy density and surface area ratio) and one image metric(proportion of broadleaf cover),was used to classify forest structure into structural complexity classes.Our results revealed significant correlation between field and remote sensing metrics,indicating that these two sets of measurements captured similar patterns of structure in mixed conifer–broadleaf forests.Further,cluster analysis identified six forest structural complexity classes includingtwo low-complexity classes and four high-complexity classes that were distributed in different elevation ranges.In this study,we could reliably analyze the structural complexity of mixed conifer–broadleaf forests using a simple and easy to calculate set of forest structural attributes derived from airborne Li DAR data and high-resolution aerial photography.This study provides a good example of the use of airborne Li DAR data sets for wider purposes in forest ecology as well as in forest management.     

Role reversal in the stand dynamics of an angiosperm–conifer forest: Colonising angiosperms precede a shade-tolerant conifer in Afrotemperate forest

In mixed angiosperm–conifer forests worldwide, infrequent landscape-level catastrophic disturbances create a mosaic of persistent and different aged forest stands in the landscape with varying levels of dominance by the conifer component. In the ‘temporal stand replacement model’ (TSRM), disturbance creates conditions favouring a colonising cohort that is replaced by a suite of relatively shade-tolerant canopy species, which establish following the synchronous senescence of the pioneer canopy. In most southern hemisphere mixed angiosperm–conifer forests, with the exception of those in southern Africa, the establishing cohort is usually a large and very long-lived (550–650 years) conifer that is gradually replaced by angiosperms. As an explanation of the apparent dominance of the conifer Podocarpus latifolius, we examine the efficacy of the TSRM in mixed Afrotemperate forests where the establishing cohort is not a conifer. Forest succession in Afrotemperate forests was deterministic with the successive replacement of species determined first by their establishment success in shaded environments, and second, by their relative longevity. Several angiosperm species that were common canopy dominants established a pioneer cohort but were gradually replaced by P. latifolius, a shade-tolerant species. Continuous regeneration beneath the angiosperm canopy by P. latifolius eliminates synchronous canopy senescence, a key feature of the TSRM, as a mechanism driving the temporal replacement of canopy species. Senescing angiosperms created canopy gaps that were colonised by grasses and ferns, which suppressed canopy tree regeneration. In contrast, with continuous regeneration beneath the shaded canopy, P. latifolius gains a critical advantage over angiosperms at gap formation. Thus, in the absence of fairly large-scale natural disturbances, conifers come to dominate Afrotemperate forests. Commensurate with the latter, conifers in Podocarpus-forest were dated to approximately 320 years, more than 100 years older than the oldest P. latifolius in angiosperm-dominated forest. Tree life-history differences (shade tolerance, longevity) and the time since disturbance drive successional change from an angiosperm-dominated system to a stage dominated by P. latifolius. In general, the TSRM is a plausible explanation for the observed canopy tree structure and dynamics in mixed Afrotemperate forests. South African Afrotemperate forest is unusual among other southern hemisphere mixed angiosperm–conifer forests in that a suite of angiosperm canopy species, rather than a single conifer species, forms the colonising cohort.     

Elevated CO₂ enhances leaf senescence during extreme drought in a temperate forest

In 2007, an extreme drought and acute heat wave impacted ecosystems across the southeastern USA, including a 19-year-old Liquidambar styraciflua L. (sweetgum) tree plantation exposed to long-term elevated (E(CO(2))) or ambient (A(CO(2))) CO(2) treatments. Stem sap velocities were analyzed to assess plant response to potential interactions between CO(2) and these weather extremes. Canopy conductance and net carbon assimilation (A(net)) were modeled based on patterns of sap velocity to estimate indirect impacts of observed reductions in transpiration under E(CO(2)) on premature leaf senescence. Elevated CO(2) reduced sap flow by 28% during early summer, and by up to 45% late in the drought during record-setting temperatures. Modeled canopy conductance declined more rapidly in E(CO(2)) plots during this period, thereby directly reducing carbon gain at a greater rate than in A(CO(2)) plots. Indeed, pre-drought canopy A(net) was similar across treatment plots, but declined to ～40% less than A(net) in A(CO(2)) as the drought progressed, likely leading to negative net carbon balance. Consequently, premature leaf senescence and abscission increased rapidly during this period, and was 30% greater for E(CO(2)). While E(CO(2)) can reduce leaf-level water use under droughty conditions, acute drought may induce excessive stomatal closure that could offset benefits of E(CO(2)) to temperate forest species during extreme weather events.     

Incorporation and remobilization of ¹³C within the fine-root systems of individual Abies alba trees in a temperate coniferous stand

Forest ecosystems have a large carbon (C) storage capacity, which depends on their productivity and the residence time of C. Therefore, the time interval between C assimilation and its return to the atmosphere is an important parameter for determining C storage. Especially fine roots (≤2 mm in diameter) undergo constant replacement and provide a large biomass input to the soil. In this study, we aimed to determine the residence time of C in living fine roots and the decomposition rates of dead fine roots. Therefore, we pulse-labelled nine 20-year-old individual silver fir trees (Abies alba Miller; ～70 cm tall) with 13CO? in situ to trace the assimilated C over time into the fine-root systems. Whole trees were harvested at different time points after labelling in autumn, biomass was determined and cellulose and starch of fine roots were extracted. Moreover, soil cores were taken and ingrowth cores installed, in which fine roots were genetically identified, to assess incorporation and remobilization of 13C in the fine roots of silver fir trees; litterbags were used to determine fine-root decomposition rates. The 13C label was incorporated in the fine-root system as cellulose within 3 days, with highest values after 30 days, before reaching background levels after 1 year. The highest δ13C values were found in starch throughout the experiment. 13C recovery and carbon mean residence times did not differ significantly among fine-root diameter classes, indicating size-independent C turnover times in fine roots of A. alba trees of ～219 days. Furthermore, carbon was remobilized from starch into newly grown fine roots in the next spring after our autumn labelling. One year after installation, litterbags with fine roots revealed a decrease of biomass of ～40% with relative 13C content in fine-root bulk biomass and cellulose of ～50%, indicating a faster loss of 13C-labelled compounds compared with bulk biomass. Our results also suggest that genetic analysis of fine-root fragments found in soil and ingrowth cores is advisable when working in mixed forest stands with trees of similar fine-root morphology. Only then can one avoid dilution of the labelling signal by mistake, due to analysis of non-labelled non-target species roots.     

On the use of phloem sap δ¹³C as an indicator of canopy carbon discrimination

In this study we measured δ13C in various carbon pools along the basipetal transport pathway in co-occurring Pinus pinaster and Acacia longifolia trees under Mediterranean climate conditions in the field. Overall, species differences in photosynthetic discrimination resulted in more enriched δ13C values in the water-conserving overstory P. pinaster relative to the water-spending understory invasive A. longifolia. Post-photosynthetic fractionation effects resulted in differences in δ13C of water-soluble organic matter pools along the plant axis with progressive depletion in δ13C from the canopy to the trunk (～6.5‰ depletion in A. longifolia and ～0.8‰ depletion in P. pinaster). Regardless of these fractionation effects, phloem sap δ13C in both terminal branches and the main stem correlated well with environmental parameters driving photosynthesis for both species, indicating that phloem sap δ13C has potential as an integrative tracer of changes in canopy carbon discrimination (Δ13C). Furthermore, we illustrate that a simple model based on sap flow estimated canopy stomatal conductance (G(S)) and phloem sap δ13C measurements has significant potential as a tool for estimating canopy-level carbon assimilation rates.     

Fuel loads,snag abundance,and snag recruitment in an unmanaged Jeffrey pine–mixed conifer forest in Northwestern Mexico

Management of downed woody fuels and snags (standing dead trees) is receiving increasing attention because of their ecosystem values and effects on potential fire behavior. Research has correlated the abundance of many wildlife species with snags and downed woody material but very little information exists of the abundance and arrangement of these forest structures, particularly in unmanaged forests. Conifer forests in northwestern Mexico have not experienced systematic fire suppression or harvesting making them unique in western North America. In 1998, average snag density in Jeffrey pine–mixed conifer forests in the Sierra San Pedro Martir (SSPM) National Park was 3.95 snags/ha but 35% of inventoried plots had no snags. In 2002, average snag density significantly increased to 5.10 snags/ha after a multiple-year drought. Average surface and ground fuel loads were 15.8 and 8.7 t/ha, respectively. High variability characterized all snag and fuel attributes measured in this forest. This high amount of variation is probably the result of the relatively intact frequent surface fire regime and because no harvesting has occurred in the sampled area. The patchy distribution of snags observed argues against the application of uniform targets for snag retention across similar forested landscapes. An improvement in management guidelines would be to manage for snag density and large fuels over moderate spatial scales (hundreds of hectares) instead of on a per hectare basis. Forest fragmentation and diverse ownerships in many western United States forests complicates this recommendation. Conservation of the forests in the SSPM is critical because it is the last landscape-scale, old-growth mixed conifer forest in western North America with a relatively intact frequent fire regime.     

Allelopathic effect of larch leaching on ash growth in mixed forest

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Effective rainfall seasons for interannual variation in δ13C and tree-ring width in early and late wood of Chinese pine and black locust on the Loess Plateau, China

We studied the importance of effective rainfall for interannual variation in water use efficiency (WUE) and tree-ring growth of Chinese pine (Pinus tabulaeformis Carr.) and black locust (Robinia pseudoacacia L.) by examining correlations of seasonal precipitation with annual values of stable carbon isotope ratio (δ¹³C) and tree-ring width in early and late wood. The correlations with precipitation were examined for each month and for periods of all possible lengths from 2 to 22 months starting from January of the previous year to October of the current year. The period with the highest correlation was adopted as the most effective rainfall season for interannual variations in WUE and tree-ring width. In early wood, precipitation during the dry season (October to May) before the growing season was negatively correlated with δ¹³C in pine trees and positively correlated with ring width in pine and locust trees. In late wood, rainfall during the growing season in the current year was negatively correlated with δ¹³C in pine and locust trees, and positively correlated with ring width in locust trees. Our results demonstrated the differences in the water use strategies of pine and locust trees. The δ¹³C in pines indicated higher WUE and more conservative water use than in locust trees. Precipitation during the dry season affected the interannual variation in WUE and tree-ring growth in pine and locust trees, indicating that rainfall during the dry season is important for carbon gain and tree-ring growth during the following growing season.     

Carbon balance in a cool–temperate deciduous forest in northern Japan: seasonal and interannual variations, and environmental controls of its annual balance

We monitored variation in seasonal and annual net ecosystem production (NEP), gross primary production (GPP), and ecosystem respiration (R _E) based on 7-year eddy covariance measurements above a cool?Ctemperate deciduous broad-leaved forest (Japanese beech forest). The 7-year means (±SD) of annual NEP, GPP, and R _E were 312?±?64, 1250?±?62, and 938?±?36?g?C?m^?2?year^?1, respectively. Variation in NEP was much larger than variation in GPP and R _E. During the growing season, the main factor controlling carbon balance was air temperature; variation in seasonal integrated NEP was regulated by accumulated air temperature (degree-day) with a significant negative correlation, whereas the seasonal ratio of R _E to GPP was correlated positively with accumulated air temperature. Because the deviation of seasonal NEP was also significantly correlated with seasonal R _E/GPP, NEP was controlled by R _E/GPP, depending on air temperature during the growing season. Seasonal R _E in the defoliation and snow seasons was also important for evaluating the annual carbon balance, because the total number of days in the two seasons was quite large owing to a long snowy winter. In the defoliation and snow seasons, we found defoliation season length was a major factor determining seasonal integrated R _E, illustrating the positive correlation between R _E and defoliation season length. The major factors controlling interannual variations in forest carbon balance are discussed.     

Time course of δ1¹³C in poplar wood: genotype ranking remains stable over the life cycle in plantations despite some differences between cellulose and bulk wood

Genetic differences in δ13C (isotopic composition of dry matter carbon) have been evidenced among poplar genotypes at juvenile stages. To check whether such differences were maintained with age in trees growing in plantations, we investigated the time course of δ13C as recorded in annual tree rings from different genotypes growing at three sites in southwestern France and felled at ～15-17 years. Wood cores were cut from tree discs to record the time course of annual basal area increment (BAI). The isotopic ratio δ13C was recorded in bulk wood and in extracted cellulose from the annual rings corresponding to the period 1996-2005. Discrimination against 13C between atmosphere and tissues (Δ13C) was computed by taking into account the inter-annual time course of δ13C in the atmosphere. Annual BAI increased steadily and stabilized at about 8 years. An offset in δ13C of ～1‰ was recorded between extracted cellulose and bulk wood. It was relatively stable among genotypes within sites but varied among sites and increased slightly with age. Site effects as well as genotype differences were detected in Δ13C recorded from the cellulose fraction. Absolute values as well as the genotype ranking of Δ13C remained stable with age in the three sites. Genotype means of Δ13C were not correlated to annual BAI. We conclude that genotypic differences of Δ13C occur in older poplar trees in plantations, and that the differences as well as the genotype ranking remain stable while trees age until harvest.     

Spatial pattern of trees influences species productivity in a mature oak–pine mixed forest

Spatial pattern has a key role in the interactions between species in plant communities. These interactions influence ecological processes involved in the species dynamics: growth, regeneration and mortality. In this study, we investigated the effect of spatial pattern on productivity in mature mixed forests of sessile oak and Scots pine. We simulated tree locations with point process models and tree growth with spatially explicit individual growth models. The point process models and growth models were fitted with field data from the same stands. We compared species productivity obtained in two types of mixture: a patchy mixture and an intimate mixture. Our results show that the productivity of both species is higher in an intimate mixture than in a patchy mixture. Productivity difference between the two types of mixture was 11.3 % for pine and 14.7 % for oak. Both species were favored in the intimate mixture because, for both, intraspecific competition was more severe than interspecific competition. Our results clearly support favoring intimate mixtures in mature oak–pine stands to optimize tree species productivity; oak is the species that benefits the most from this type of management. Our work also shows that models and simulations can provide interesting results for complex forests with mixtures, results that would be difficult to obtain through experimentation.     

Future orientation and planning in forestry: a comparison of forest managers’ planning horizons in Germany and the Netherlands

Long range (or strategic) planning is an important tool for forest management to deal with the complex and unpredictable future. However, it is the ability to make meaningful predictions about the rapidly changing future that is questioned. What appears to be particularly neglected is the question of the length of time horizons and the limits (if any) to these horizons, despite being considered one of the most critical factors in strategic planning. As the future creation of values lies within individual responsibility, this research empirically explored the limits (if any) of individual foresters’ time horizons. To draw comparisons between countries with different traditions in forest management planning, data were collected through telephone surveys of forest managers in the state/national forest services of the Netherlands and Germany. In order to minimize other cultural differences, the research in Germany concentrated on the federal state of Nordrhein-Westfalen, which has considerable similarities with the Netherlands, e.g. in topography, forest types and forest functions. The results show that, in practice, 15 years appears to be the most distant horizon that foresters can identify with. This is in sharp contrast to the time horizons spanning decades and even generations that are always said to exist in forestry. The “doctrine of the long run”—the faith in the capacity of foresters to overcome the barriers of the uncertain future and look ahead and plan for long-range goals—which in many countries still underlies traditional forest management, can therefore be rejected.

The Austrian domestic forest policy community in change? Impacts of the globalisation and Europeanisation of forest politics

The interest intermediation system has always attracted the attention of forest policy scientists. However, research on this subject has focused on the national level, despite the fact that forest issues are increasingly prominent on international and European agendas, both in the EU and the Pan-European Process on the Protection of Forests in Europe. Accordingly, the impacts of the globalisation and Europeanisation of forest policy and the peculiarities of multi-level policy processes have not been sufficiently taken into account. This article examines how international forest politics and the integration of national actors in the EU multi-level system of joint decision-making affect national actor constellations. To this end, I draw on the advocacy coalition framework to depict the Austrian forest policy network and its actors’ dispute on forest certification, as well as on hypotheses and empirical results of multi-level governance scholars and on my own preliminary results to investigate the likely effects of the evolving EU forest policy. The discussion provides some hypotheses and indications that national forest policy networks might be subject to significant change.     

Concentrations and seasonal dynamics of dissolved organic carbon in forest floors of two plantations （Castanopsis kawakamii and Cunninghamia lanceolata） in subtropical China

The concentrations and seasonal dynamics of DOC in forest floors of monoculture plantations ofCastanopsis kawakamii and Chinese fir (Cunninghamia lanceolata) were assessed in Sanming, Fujian, China (26°11′30″N, 117°26′00″E). Forest floor samples were taken in January, April, July and October in 2002 and divided into undecomposed material (horizon Oi), partially decomposed organic material (horizon Oe), and fully decomposed organic material (horizon Oa). Upon collection, DOC concentrations of samples were analyzed by a High Temperature TOC. The results showed that the annual average DOC concentration of Chinese fir (1341.7 mg·kg⁻¹) in the forest floor was higher than that ofCastanopsis kawakamii (1178.9 mg·kg⁻¹). Difference in DOC concentrations was observed among three horizons of the forest floor. DOC concentration of forest floor in the two forests was the highest in horizon Oe. Seasonal trends of DOC concentrations in different horizons of forest floors were similar and the maximal value occurred in autumn (or winter). The concentration and temporal change of DOC in studied forests were probably related to the variation in moisture, temperature, biological activity and quantity of organic matter in the forest floor. Foundation item: This study was supported by the Teaching and Research Award program for MOE P.R.C. (TRAPOYT) Biography: ZHANG Jiang-shan (1946-), male, Researcher in Fujian Normal University, Fuzhou 350007, P.R. China. Responsible editor: Zhu Hong     

Oak loss increases foliar nitrogen, δ15N and growth rates of Betula lenta in a northern temperate deciduous forest

Oak forests dominate much of the eastern USA, but their future is uncertain due to a number of threats and widespread failure of oak regeneration. A sudden loss of oaks (Quercus spp.) could be accompanied by major changes in forest nitrogen (N) cycles with important implications for plant nutrient uptake and tree species composition. In this study, we measured the changes in N use and growth rates of black birch trees (Betula lenta L.) following oak girdling at the Black Rock Forest in southeastern New York, USA. Data were collected from nine experimental plots composed of three treatments: 100% oaks girdled (OG), 50% oaks girdled (O50) and control (C). Foliar N concentration and foliar (15)N abundance increased significantly in the oak-girdled plots relative to the control, indicating that the loss of oaks significantly altered N cycling dynamics. As mineralization and nitrification rates increase following oak loss, black birch trees increase N absorption as indicated by higher foliar N content and increased growth rates. Foliar N concentration increased by 15.5% in the O50 and 30.6% in the OG plots relative to the control, while O50 and OG plots were enriched in (15)N by 1.08‰ and 3.33‰, respectively (P?相似文献   

Distribution of the timber quality attribute ‘knot surface’ in logs of Fagus sylvatica L. from pure and mixed forest stands

European Journal of Forest Research - Research on mixed forests has mostly focused on tree growth and productivity, or resistance and resilience in changing climate conditions, but only rarely on...     

Spatial variation of local stand structure in an Abies forest, 45 years after a large disturbance by the Isewan typhoon

Heterogeneity of forest stand structure often results from repeated small disturbances, but structural variation also arises in a stand that has regenerated after a single large stand-replacing disturbance. We explored the structural variation within a subalpine Abies forest in Japan that regenerated after a large typhoon in 1959. In 2004, four 50 × 50 m plots were established at two sites in the regenerated forest. To characterize local stand structure within each plot, we determined the stem density, stand basal area, mean diameter at breast height (DBH), and coefficient of variation (CV) of DBH in 10 × 10 m subplots. We analyzed the spatial distribution pattern of the trees in each subplot using the L(t) function and categorized the distributions as clumped or non-clumped. The analysis revealed marked variation among subplots in the stand’s structural characteristics. Although the spatial distribution patterns of the trees in all plots were clumped, 11 of 50 subplots at one site and 39 of 50 subplots at the other site were non-clumped. Subplots with a clumped distribution pattern generally had a smaller basal area, smaller mean DBH, and greater CV of DBH than subplots with the same density but a non-clumped pattern. These results illustrated the spatial heterogeneity of forest structure that can arise in Abies forest that has experienced a large disturbance, probably because of the different densities and distribution of saplings surviving the disturbance and the different forest growth dynamics that result.     

Can methyl jasmonate treatment of conifer seedlings be used as a tool to stop height growth in nursery forest trees?

A plant's induced defense system can be triggered by the application of the plant hormone methyl jasmonate (MeJA), and recent research suggest that MeJA treatment may become a tool for protection of conifer seedlings against insect herbivory (e.g. by the pine weevil Hylobius abietis). A side-effect of MeJA application is temporarily reduced height growth. This has generally been considered as negative, but in forest tree nurseries this could instead be beneficial since it is commonly desired to stop the growth of nursery seedlings in late summer. Artificially longer dark periods (long nights/short days) are widely used in high-latitude nurseries to terminate height growth and induce freezing tolerance. However, long night treatment requires specialized nursery equipment and are labor intensive. Therefore alternatives are sought after. We compared long-night and MeJA treatments by following the growth of Norway spruce (Picea abies) seedlings throughout one season. The regulatory effect of MeJA on height growth was similar if not even better than that of long nights, i.e. it was terminated faster. However, MeJA treatment also reduced root growth and delayed the development of freezing tolerance. MeJA may therefore not replace long-night treatments, but it could facilitate a more flexible application of long nights by gaining a longer time interval during which this treatment can be used without risking the seedlings growing too large.