Complex Forest Research Articles

International benchmarking of terrestrial laser scanning approaches for forest inventories

The last two decades have witnessed increasing awareness of the potential of terrestrial laser scanning (TLS) in forest applications in both public and commercial sectors, along with tremendous research efforts and progress. It is time to inspect the achievements of and the remaining barriers to TLS-based forest investigations, so further research and application are clearly orientated in operational uses of TLS. In such context, the international TLS benchmarking project was launched in 2014 by the European Spatial Data Research Organization and coordinated by the Finnish Geospatial Research Institute. The main objectives of this benchmarking study are to evaluate the potential of applying TLS in characterizing forests, to clarify the strengths and the weaknesses of TLS as a measure of forest digitization, and to reveal the capability of recent algorithms for tree-attribute extraction. The project is designed to benchmark the TLS algorithms by processing identical TLS datasets for a standardized set of forest attribute criteria and by evaluating the results through a common procedure respecting reliable references. Benchmarking results reflect large variances in estimating accuracies, which were unveiled through the 18 compared algorithms and through the evaluation framework, i.e., forest complexity categories, TLS data acquisition approaches, tree attributes and evaluation procedures. The evaluation framework includes three new criteria proposed in this benchmarking and the algorithm performances are investigated through combining two or more criteria (e.g., the accuracy of the individual tree attributes are inspected in conjunction with plot-level completeness) in order to reveal algorithms’ overall performance. The results also reveal some best available forest attribute estimates at this time, which clarify the status quo of TLS-based forest investigations. Some results are well expected, while some are new, e.g., the variances of estimating accuracies between single-/multi-scan, the principle of the algorithm designs and the possibility of a computer outperforming human operation. With single-scan data, i.e., one hemispherical scan per plot, most of the recent algorithms are capable of achieving stem detection with approximately 75% completeness and 90% correctness in the easy forest stands (easy plots: 600 stems/ha, 20 cm mean DBH). The detection rate decreases when the stem density increases and the average DBH decreases, i.e., 60% completeness with 90% correctness (medium plots: 1000 stem/ha, 15 cm mean DBH) and 30% completeness with 90% correctness (difficult plots: 2000 stems/ha, 10 cm mean DBH). The application of the multi-scan approach, i.e., five scans per plot at the center and four quadrant angles, is more effective in complex stands, increasing the completeness to approximately 90% for medium plots and to approximately 70% for difficult plots, with almost 100% correctness. The results of this benchmarking also show that the TLS-based approaches can provide the estimates of the DBH and the stem curve at a 1–2 cm accuracy that are close to what is required in practical applications, e.g., national forest inventories (NFIs). In terms of algorithm development, a high level of automation is a commonly shared standard, but a bottleneck occurs at stem detection and tree height estimation, especially in multilayer and dense forest stands. The greatest challenge is that even with the multi-scan approach, it is still hard to completely and accurately record stems of all trees in a plot due to the occlusion effects of the trees and bushes in forests. Future development must address the redundant yet incomplete point clouds of forest sample plots and recognize trees more accurately and efficiently. It is worth noting that TLS currently provides the best quality terrestrial point clouds in comparison with all other technologies, meaning that all the benchmarks labeled in this paper can also serve as a reference for other terrestrial point clouds sources.

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 20 0.05 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. ≥ 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 intermediate-severity 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 (r2 = 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.

Growth Variations of Tree Saplings in Relation to Species Diversity and Functional Traits in a Tree Diversity Pot Experiment

Despite the accumulating evidence of the beneficial effects of diverse mixed species forests on ecosystem functioning and services, foresters in subtropical forest cultivation in China still prefer easily managed monocultures, which is also due to the complexity of mixed forests and the unknown underlying mechanisms related to relationships between biodiversity and forest growth. In a designed pot experiment, we selected two early-successional tree species (Pinus massoniana Lamb., Liquidambar formosana Hance.) and two late-successional tree species (Schima superba Champ., Elaeocarpus decipiens Hemsl.) and planted four saplings in one pot with regard to tree species diversity (monoculture, two species and four species mixtures), each combination replicated four times. In this three-year duration experiment, the effect of tree species diversity, tree identity, and functional traits on sapling growth (tree height, ground diameter, crown projection area), were analyzed. The results showed that the increments of ground diameter and crown projection area increased with tree species richness, whereas the mean tree height increment showed the opposite effect. This growth variation was species specific and related to functional traits (early or late succession), as the increments of the early successional tree species (P. massoniana Lamb. and L. formosana Hance.) had a positive correlation with tree species richness, while the late successional tree species (E. decipiens Hemsl. and S. superba Champ.) showed negative effects. In addition, our study provided evidence for the allometric differences between mixtures and monocultures, which have an important reference value on mixed-species forests.

Changes in forest structural complexity followed by selection cutting: An analysis using multi-temporal UAV imagery

Changes in forest structural complexity followed by selection cutting: An analysis using multi-temporal UAV imagery

The environmental triangle of the Cerrado Domain: Ecological factors driving shifts in tree species composition between forests and savannas

Abstract The Cerrado Domain of central Brazil houses the largest extent of savanna in the Neotropics, but despite its simple characterization as a giant savanna, it contains considerable vegetation heterogeneity that is poorly understood. We aimed to determine how vegetation types in the Cerrado diverge in their tree species composition and what role ecological factors play in driving compositional patterns. We used a dataset of 1,165 tree species inventories spread across the Cerrado Domain, which come from six vegetation types that have a substantial arboreal component: woody savannas, dystrophic cerradão, mesotrophic cerradão, seasonally dry tropical forests, semideciduous forests and evergreen forests. We found three extremes in terms of tree species composition, with clear underlying ecological drivers, which leads us to propose a ternary model, the Cerrado Vegetation Triangle, to characterize woody vegetation in the Cerrado. At one extreme, we found that semideciduous and evergreen forests are indistinguishable floristically and are found in areas with high water availability. At another extreme lie seasonally dry tropical forests which are found on more fertile soils. At the third extreme, we found that all types of savanna, and dystrophic cerradão, are highly similar in tree species composition and are commonly found in areas of poor soils and high flammability. Mesotrophic cerradão is transitional in tree species composition between savannas and seasonally dry tropical forest. The lack of variation in tree species composition attributed to climatic variables indicates that within homogeneous macroclimatic zones, many types of forest and savanna co‐exist due to complex mosaics of local substrate heterogeneity and fire history. Synthesis. Our findings highlight the complexity of forest–savanna transitions in the Cerrado Domain, with relevance for understanding the future of Cerrado vegetation under environmental change. If nitrogen deposition is extensive, some savannas may be more likely to transition to mesotrophic cerradão or even seasonally dry tropical forest, whereas if water availability increases these same savannas may transition to semideciduous or evergreen forest. Our “Cerrado Vegetation Triangle” model offers a simple conceptual tool to frame discussions of conservation and management.

Leaf damage and functional traits along a successional gradient in Brazilian tropical dry forests

Herbivory has significant impacts on individual plants and plant communities, both at ecological and evolutionary time scales. In this context, this study aims to evaluate herbivore damage and its relationship with leaf chemical and structural traits, nutritional status, and forest structural complexity along a successional gradient. We predicted that trees in early successional stages support conservative traits related to drought tolerance (high specific leaf mass and phenolics), whereas trees in light-limited, late successional stages tend to enhance light acquisition strategies (high nitrogen content). We sampled 261 trees from 26 species in 15 plots (50 × 20 m; five per successional stage). From each tree, twenty leaves were collected for leaf trait measures. Phenolic content increased whereas specific leaf mass and nitrogen content decreased from early to late stages. However, leaf damage did not differ among successional stages. Our results partially corroborate the hypothesis that early successional plants in tropical dry forests exhibit leaf traits involved in the conservative use of water. The unexpected decrease in nitrogen content along the chronosequence is likely related to the fact that thinner leaves with low specific leaf mass could have less nitrogen-containing mesophyll per unit area. Mechanisms affecting herbivory intensity varied across scales: at the species level, leaf damage was negatively correlated with tannin concentration and specific leaf mass; at the plot level, leaf damage was positively affected by forest structural complexity. Herbivory patterns in tropical forests are difficult to detect because abiotic factors and multiple top-down and bottom-up forces directly and indirectly affect herbivores.

Spatial Dynamics and Structure of Human Disturbed Mangrove Forests in Contrasting Coastal Communities in Eastern Africa

The spatial dynamics and structure of mangrove forests in peri-urban, rural and rural island settings in Mozambique was investigated to test the hypothesis that peri-urban forests are more impacted. LandSat images from 1991, 2002 and 2013 were analysed for changes in area cover and forest structural data were collected in the field. At the peri-urban site, mangrove cover increased by 22.7%, while at the rural site 23.2% were lost. The small area of the rural island was not assessed, but losses are expected given the high density of stumps. All forests are structurally small, with height and diameter of species varying significantly among sites (p < 0.001). The forest complexity index varied from 1.61 (rural island), to 0.90 (peri-urban) and 0.39 (rural). The communities harvested all diameter classes at the rural island, while class 5.1–8 cm was preferred at the peri-urban and rural sites. The proportion of stumps:live trees were 1:11 (peri-urban site); 1:9 (rural) and 1:4 (rural island). The proportions of regenerating classes were 16:4:1 (peri-urban); 76:16:1 (rural) and 8:1:0 (rural island). This study provided important insights to mangrove forest structure and uses in an understudied region and showed that management plans are required at all sites for sustainable use.

Mapping multi-scale vascular plant richness in a forest landscape with integrated LiDAR and hyperspectral remote-sensing.

The central role of floristic diversity in maintaining habitat integrity and ecosystem function has propelled efforts to map and monitor its distribution across forest landscapes. While biodiversity studies have traditionally relied largely on ground-based observations, the immensity of the task of generating accurate, repeatable, and spatially-continuous data on biodiversity patterns at large scales has stimulated the development of remote-sensing methods for scaling up from field plot measurements. One such approach is through integrated LiDAR and hyperspectral remote-sensing. However, despite their efficiencies in cost and effort, LiDAR-hyperspectral sensors are still highly constrained in structurally- and taxonomically-heterogeneous forests - especially when species' cover is smaller than the image resolution, intertwined with neighboring taxa, or otherwise obscured by overlapping canopy strata. In light of these challenges, this study goes beyond the remote characterization of upper canopy diversity to instead model total vascular plant species richness in a continuous-cover North Carolina Piedmont forest landscape. We focus on two related, but parallel, tasks. First, we demonstrate an application of predictive biodiversity mapping, using nonparametric models trained with spatially-nested field plots and aerial LiDAR-hyperspectral data, to predict spatially-explicit landscape patterns in floristic diversity across seven spatial scales between 0.01-900m2 . Second, we employ bivariate parametric models to test the significance of individual, remotely-sensed predictors of plant richness to determine how parameter estimates vary with scale. Cross-validated results indicate that predictive models were able to account for 15-70% of variance in plant richness, with LiDAR-derived estimates of topography and forest structural complexity, as well as spectral variance in hyperspectral imagery explaining the largest portion of variance in diversity levels. Importantly, bivariate tests provide evidence of scale-dependence among predictors, such that remotely-sensed variables significantly predict plant richness only at spatial scales that sufficiently subsume geolocational imprecision between remotely-sensed and field data, and best align with stand components including plant size and density, as well as canopy gaps and understory growth patterns. Beyond their insights into the scale-dependent patterns and drivers of plant diversity in Piedmont forests, these results highlight the potential of remotely-sensible essential biodiversity variables for mapping and monitoring landscape floristic diversity from air- and space-borne platforms.

Ecological Structure of a Tropical Urban Forest in the Bang Kachao Peninsula, Bangkok

Rapid urbanization has changed the structure and function of natural ecosystems, especially floodplain ecosystems in SE Asia. The ecological structure of vegetation stands and the usefulness of satellite images was investigated to characterize a disturbed tropical urban forest located in the Chao Phraya River lower floodplain, Thailand. Nine sample plots were established on the Bang Kachao Peninsula (BKP) within 4 tropical forest types in an urban area: rehabilitation forest, home-garden agroforestry, mangrove and park. The tree habitats were beach forest, swamp forest, moist evergreen forest, dry evergreen forest, mangrove forest and abandoned orchard or home-garden. Normalized difference vegetation index (NDVI) values obtained from Landsat 7 satellite images were correlated with plant structure from field surveys. NDVI had the highest relationship with stand factors for number of families, number of species, Shannon-Weiner index and total basal area. Linear regression predicted well the correlation between NDVI and stand factors for families and basal area. NDVI trends reflected urban tropical forest typing and biodiversity, being high in rehabilitation and mangrove forests, moderate in home-gardens and low in parks. We suggest that the application of NDVI for assessments can be useful for future planning, monitoring and management of the BKP and hence may contribute for increasing biodiversity and complexity of these urban forests.

Nearest Neighborhood Characteristics of a Tropical Mixed Broadleaved Forest Stand

Structural complexity and local biodiversity of species-rich tropical forests can be characterized by their spatial patterns, which contribute to species intra- and interspecific interactions. Aiming to describe spatial patterns of species at fine spatial scales, we applied the quantitative analyses based on the relationships of nearest neighbors of conspecific and heterospecific trees. In a two-hectare plot of a tropical broadleaved forest stand in central Vietnam with minimal human influence, all tree individuals with diameter at breast height ≥ 2.5 cm were mapped and their characteristics were recorded. We applied two different types of analyses: (1) Intraspecific structural characteristics using nearest neighbor statistics; (2) overall interspecific associations through a classification scheme based on bivariate nearest neighbor distribution function D12(r) and Ripley’s K function K12(r). The findings showed that: (1) Most of studied species in the forest were highly mixed with other species, while conspecifics were regular to aggregated distribution at small spatial scales. Tree individuals with different diameter values were surrounded by heterospecific trees; (2) The majority of 306 species-species pairs showed spatial independence (66.7%), whereas 29.8% of all species showed an overall positive association and negative association consisted only a small percentage (3.5%) up to spatial scales of 50 m. We found significant evidences of the main ecological theories such as dispersal limitation, Neutral theory, Janzen-Connell hypothesis, and other effects like the stochastic dilution. We suggest using both the bivariate distribution of the structural parameters and the spatial point pattern analysis based on nearest neighbor distance as advantageous approaches for further understanding of population structure, as well as discovering and protecting biodiversity in the future.

Structural complexity and tree species composition of mangrove forests of the Andaman Islands, India

This study reports the mapping, structural characteristics and distribution of mangrove species of the Andaman Islands. 79 mangrove patches were identified using Thiessen polygons of which, 53 accessible patches were surveyed during 2014–2015. Multiple linear transects were laid at each of the mangrove patches and data pertaining to diameter at breast height, basal area and height were recorded for all mangrove trees within a 10 × 10 m quadrat laid along the transects at 50 m intervals. Altogether, 178 quadrats were laid and 25 mangrove species representing 11 families and 14 genera were recorded. Of the 3073 mangrove plants enumerated in the present study, 96.06% were composed of trees (>4 m height), 1.99% of saplings (>1 m to ≤4 m height) and 1.95% of seedlings (≤1 m height). The number of species per quadrat ranged from 1 to 9 and majority of the quadrats had 2–3 species. Density and basal area of mangrove trees ranged from 1252 ha−1 to 2200 ha−1 and 30.8 m2/ha to 59.6 m2/ha, respectively. High diversity indices (Shannon-Wiener index ranged from 1.65 to 2.24; Simpson index from 0.74 to 0.85 and Pielou’s evenness index from 0.66 to 0.84) indicated greater diversity and even dispersion of mangroves in the Islands. The study also revealed that the mangrove forests of Andaman Islands were characterized by a mixed species composition. Most of the sites were represented by different combinations of dominant and co-dominant species, all from the family Rhizophoraceae. The present study highlights the need for conserving the mixed species mangrove forests of Andaman and Nicobar Islands and development of location-specific management plans for biodiversity conservation.

Tropical and Highland Temperate Forest Plantations in Mexico: Pathways for Climate Change Mitigation and Ecosystem Services Delivery

Forest plantations are a possible way of increasing forest productivity in temperate and tropical forests, and therefore also increasing above- and belowground carbon pools. In the context of climate change, monospecific plantations might become an alternative to mitigate global warming; however, their contribution to the structural complexity, complementarity, and biodiversity of forests has not been addressed. Mixed forest plantations can ensure that objectives of climate change mitigation are met through carbon sequestration, while also delivering anticipated ecosystem services (e.g., nutrient cycling, erosion control, and wildlife habitat). However, mixed forest plantations pose considerable operational challenges and research opportunities. For example, it is essential to know how many species or functional traits are necessary to deliver a set of benefits, or what mixture of species and densities are key to maintaining productive plantations and delivering multiple ecosystem services. At the same time, the establishment of forest plantations in Mexico should not be motivated solely by timber production. Forest plantations should also increase carbon sequestration, maintain biodiversity, and provide other ecosystem services. This article analyzes some matters that affect the development of planted forests in the Mexican national context, and presents alternatives for forest resources management through the recommendation of mixed forest plantations as a means of contributing to climate change mitigation and the delivery of ecosystem services.

Associations between canopy openness, butterfly resources, butterfly richness and abundance along forest trails in planted and natural forests

Increasing the biodiversity in plantations of trees is an important issue because plantations have replaced many natural and semi-natural ecosystems worldwide. Therefore, identifying appropriate management techniques and key factors for enhancing biodiversity in plantations is required. We surveyed butterfly assemblages along forest trails in both plantations and natural forests and measured various environmental variables, including canopy, sub canopy and shrub stem densities, percentage of deciduous trees, flower plant richness, host plant richness, canopy openness and distance to forest edge. We hypothesized that (1) flower and host plant richness increase with an increase in the percentage of deciduous trees and canopy openness; (2) butterfly richness and abundance increase with an increase in forest structural complexity, butterfly resources, canopy openness and distance to forest edge; (3) the responses of plants and butterflies to canopy openness differ in plantations and natural forests; and (4) in plantations, tree-feeding butterflies respond to canopy openness less strongly than herbaceous plant feeding butterflies do because of the low diversity of trees in plantations. Our results generally support these hypotheses. Butterfly resources and butterfly richness and abundance all increase with increasing canopy openness; however, the increases were usually more dramatic in natural forests than in plantations and other factors are less important. In plantations, herbaceous plant feeding butterflies responded to increasing canopy openness more strongly than tree-feeding butterflies. The results of the present study indicate the importance of sunlit forest trails in enhancing butterfly resources, butterfly richness and abundance in plantations. Because at the stand-level management is labour- and cost-intensive, labour- and cost-saving trail management options need to be explored further in terms their effectiveness in increasing biodiversity in plantations.

Structural Complexity and Ecosystem Functions in a Natural Mixed Forest under a Single-Tree Selection Silviculture

The objective of forest management has become broader, and it is essential to harmonize timber production with conservation of the forest ecosystem. Selection cutting is recognized as a major alternative of clear-cutting, because it can maintain the complexity and heterogeneity of a natural forest; however, its long-term evaluations are limited. This study compared various attributes of stand structures, which are indicators of biodiversity and ecosystem carbon stock between managed and unmanaged blocks (12.6 ha area in total) in a natural mixed forest in Hokkaido, the northernmost island of Japan. We found that 30 years’ implementation of single-tree selection did not affect the volume, size structure, species diversity nor spatial distribution of overstory trees in the managed stands. Also, the total carbon stock in the managed stands was almost equal to that of the unmanaged stands. In contrast, several structural attributes and indicator elements that are significant for biodiversity (such as large-diameter live trees, dead trees, cavities, epiphytic bryophytes, and some avian guilds) showed marked decrease in the managed stands. We conclude that it is required to leave these structures and elements to some extent for deriving the merit of the management as an alternative silvicultural regime in the region.

Species-specific spatial structure, species coexistence and mortality pattern in natural, uneven-aged Scots pine (Pinus sylvestris L.)-dominated forest

Complexity of uneven-aged forests results from the heterogeneity of their structure reflected among others by the spatial pattern of their components. Forest structure is usually modified by various processes operating at different scales and time. Structure and processes are not independent, and both are important drivers of forest dynamics. The impact of natural processes on forest structure manifested in the specific spatial pattern of trees can be quantified by point pattern analysis applied to long-term repeatedly measured stem-mapped plots. Such studies are relatively scarce in the literature although they provide better insight into the mechanisms affecting forest dynamics. Our study is focused on the spatiotemporal analysis of the structure of mixed uneven-aged Scots pine-dominated forest located at the Kampinoski National Park (Poland). Univariate analysis showed that the initial pattern of all live trees was initially random and it shifted toward more uniform with forest aging. Spatial patterns of individual tree species varied from that stated for all forest community. We observed changes in spatial pattern of Scots pine and common oak from random toward more clumped (pine) or uniform (oak) pattern. In case of black alder and common birch, the initial aggregated pattern was maintained over the examined 14-year period of the forest succession. Bivariate analysis showed that the most common interspecific association between pairs of tree species was spatial segregation (pine vs. alder, alder vs. birch and oak vs. birch) followed by spatial independence (pine vs. oak and oak vs. alder). The positive association was stated only for pine and birch and only for certain spatial scales (> 5 m). Simultaneously, at small distances they showed reciprocal repulsion. Changes in spatial relationships between tree species were negligible over 14-year period of forest succession. Our results confirmed the density-dependent mortality process in the uneven-aged Scots pine-dominated forest over 14-year period of forest development. Our study showed that spatial interactions between individuals along with species-specific ecological requirements should be incorporated into realistic models of forest development, helping to manage the forest ecosystems toward their greater structural complexity.

More ways than one: Mixed-severity disturbance regimes foster structural complexity via multiple developmental pathways

Abstract Mixed-severity disturbance regimes are prevalent in temperate forests worldwide, but key uncertainties remain regarding the variability of disturbance-mediated structural development pathways. This study investigates the influence of disturbance history on current structure in primary, unmanaged Norway spruce (Picea abies) forests throughout the Carpathian Mountains of central and eastern Europe, where windstorms and native bark beetle outbreaks are the dominant natural disturbances. We inventoried forest structure on 453 plots (0.1 ha) spanning a large geographical gradient (>1,000 km), coring 15–25 canopy trees per plot for disturbance history reconstruction (tree core total n = 11,309). Our specific objectives were to: (1) classify sub-hectare-scale disturbance history based on disturbance timing and severity; (2) classify current forest structure based on tree size distributions (live, dead, standing, downed); (3) characterize structural development pathways as revealed by the association between disturbance history and current forest structural complexity. We used hierarchical cluster analysis for the first two objectives and indicator analysis for the third. The disturbance-based cluster analysis yielded six groups associated with three levels of disturbance severity (low, moderate, and high canopy loss) and two levels of timing (old, recent) over the past 200 years. The structure-based cluster analysis yielded three groups along a gradient of increasing structural complexity. A large majority of plots exhibited relatively high (53%) or very high (26%) structural complexity, indicated by abundant large live trees, standing and downed dead trees, and spruce regeneration. Consistent with conventional models of structural development, some disturbance history groups were associated with specific structural complexity groups, particularly low-severity/recent (very high complexity) and high-severity/recent (moderate complexity) disturbances. In other cases, however, the distribution of plots among disturbance history and structural complexity groups indicated either divergent or convergent pathways. For example, multiple disturbance history groups were significantly associated with the high complexity group, demonstrating structural convergence. These results illustrate that complex forest structure – including features nominally associated with old-growth – can be associated as much with disturbance severity as it is with conventional notions of forest age. Because wind and bark beetles are natural disturbance processes that can induce relatively high levels of tree mortality while simultaneously contributing to structural complexity and heterogeneity, we suggest that forest management plans allow for the stochastic occurrence of disturbance and variable post-disturbance development trajectories. Such applications are especially appropriate in conservation areas where biodiversity and forest resilience are management objectives, particularly given projections of increasing disturbance activity under global change.

A Large-Scale Emulation System for Realistic Three-Dimensional (3-D) Forest Simulation

The realistic reconstruction and radiometric simulation of a large-scale three-dimensional (3-D) forest scene have potential applications in remote sensing. Although many 3-D radiative transfer models concerning forest canopy have been developed, they mainly focused on homogeneous or relatively small heterogeneous scenes, which are not compatible with the coarse-resolution remote sensing observations. Due to the huge complexity of forests and the inefficiency of collecting precise 3-D data of large areas, realistic simulation over large-scale forest area remains challenging, especially in regions of complex terrain. In this study, a large-scale emulation system for realistic 3-D forest Simulation is proposed. The 3-D forest scene is constructed from a representative single tree database (SDB) and airborne laser scanning (ALS) data. ALS data are used to extract tree height, crown diameter and position, which are linked to the individual trees in SDB. To simulate the radiometric properties of the reconstructed scene, a radiative transfer model based on a parallelized ray-tracing code was developed. This model has been validated with an abstract and an actual 3-D scene from the radiation transfer model intercomparison website and it showed comparable results with other models. Finally, a 1 km $\times$ 1 km scene with more than 100 000 realistic individual trees was reconstructed and a Landsat-like reflectance image was simulated, which kept the same spatial pattern as the actual Landsat 8 image.

Spatial aspects of structural complexity in Sitka spruce – western hemlock forests, including evaluation of a new canopy gap delineation method

Structural complexity in long-lived forests where stand-replacing disturbances are rare is thought to emerge from chronic small-scale disturbances and competitive interactions between trees. We analyzed tree size distributions, tree spatial patterns, and canopy gap attributes in ten 1.42 ha stem mapped plots in old-growth Sitka spruce (Picea sitchensis (Bong.) Carrière) – western hemlock (Tsuga heterophylla (Raf.) Sarg.) forests in southeast Alaska. Most plots had rotated sigmoid or reverse-J-shaped diameter distributions. Overstory tree patterns were uniform at short distance (&lt;5 m) and random or aggregated at larger distances (&gt;5 m); understory trees were spatially random or aggregated at most scales. Tree patterns were highly variable across plots. Overstory and understory tree populations were spatially independent in most medium canopy cover (40%–70%) plots but spatially repelled in most high canopy cover (&gt;70%) plots. Canopy gap delineation using a traditional geometric approach identified more gaps and greater forest area in gaps compared to a new method based on canopy tree shadow lengths. We recommend defining the lower limit of canopy gap size using overstory tree crown diameter; gap delineation based on overstory tree shadow length is overly conservative at higher latitude sites. Our analyses show that, despite their low species richness, the temperate rainforests of southeast Alaska are highly structurally diverse.

I Coleotteri Carabidi (Coleoptera, Carabidae) come indicatori di passati interventi selvicolturali in foreste vetuste del Parco Nazionale della Sila (Calabria, Italia)

Abstract: Old-growth forests are terrestrial ecosystems with the highest level of biodiversity and the main environments for the study of conservation and dynamics of the forest system. In Mediterranean Europe, two millennia of human exploitation deeply altered the structural complexity of the native forests. Some animal groups, including insects, may be used as a proxy of such changes. In this paper we explored the possible effects of forest management on the functional diversity (species traits) of carabid beetle communities. Three old-growth forests of the Sila National Park were sampled by pitfall traps set up in pure beech, beech-silver fir and Calabrian black pine forests. In each forest, five managed vs. five unmanaged stands were considered. Managed sites were exploited until the sixties of the past century and then left unmanaged. More than 6000 carabid specimens belonging to 23 species were collected. The functional diversity in carabid groups is influenced by forest management especially in beech and beech-silver fir stands. Body size, specialized predators, endemic species and forest species were negatively affected by stand management. On the contrary, omnivorous ground beetles populations (or species) with a high dispersal power (macropterous) and large geographic distribution were positively influenced by stand management. In pine forests the old-growth community seems less sensitive to past management and more affected by soil evolution. Soil erosion and disturbance may reduce species diversity of ground beetles. Anyway, the composition of the carabid community shows that 50-60 years of forest restoration are enough for the reconstruction of a fairly diverse assemblage reflecting a “subclimax” situation.

Stand structural complexity of mixed old-growth and adjacent selection forests in the Dinaric Mountains of Bosnia and Herzegovina

Research results on the structure of European OGF are often contradictory; while some researchers stress equilibrium structures, others suggest that this rarely happens due to biomass accumulation. If the former were the case, then there would be a fairly strong argument that OGF should serve as natural references for selection management. At the same time, mountain mixed selection forests are in many regions considered to be the most “natural” type of MF, and thus to a large extent similar to corresponding OGF. However, because there are few old-growth forests (OGF) left in Europe, comparisons between OGF and selection-managed forests (MF) are rare. Since nature-based silviculture should follow natural processes and not exclude any species from its natural range, in this study we compared two mixed OGF and neighboring MF (Piceo-Abieti-Fagetum illyricum) in the Dinaric Mountains of Bosnia and Herzegovina. The MF were managed by the single-tree selection system for almost a century. The results indicated that this management approach yielded a statistically significant difference in tree species composition and presence of large-diameter trees. The cumulative diameter distributions, however, were similar in OGF and MF as both exhibited the shapes that are considered to provide demographic equilibrium. On the species level, though, this was the case only for beech. Species occurrence matrices indicated significant dominance of young European beech (Fagus sylvatica L.) trees over silver fir (Abies alba Mill.) and Norway spruce (Picea abies L. Karst) in OGF. Nevertheless, based on the results from MF, the study highlights the crucial role of silvicultural measures that may potentially provide targeted long-term coexistence of the studied broadleaved and coniferous tree species.