Showing papers on "Tree canopy published in 2005"

Estimates of forest canopy height and aboveground biomass using ICESat

Abstract: Exchange of carbon between forests and the atmosphere is a vital component of the global carbon cycle. Satellite laser altimetry has a unique capability for estimating forest canopy height, which has a direct and increasingly well understood relationship to aboveground carbon storage. While the Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud and land Elevation Satellite (ICESat) has collected an unparalleled dataset of lidar waveforms over terrestrial targets, processing of ICESat data to estimate forest height is complicated by the pulse broadening associated with large-footprint, waveform-sampling lidar. We combined ICESat waveforms and ancillary topography from the Shuttle Radar Topography Mission to estimate maximum forest height in three ecosystems; tropical broadleaf forests in Brazil, temperate broadleaf forests in Tennessee, and temperate needleleaf forests in Oregon. Final models for each site explained between 59% and 68% of variance in field-measured forest canopy height (RMSE between 4.85 and 12.66 m). In addition, ICESat-derived heights for the Brazilian plots were correlated with field-estimates of aboveground biomass (r(2) = 73%, RMSE = 58.3 Mgha(-1)).

Disturbance history and historical stand dynamics of a seasonal tropical forest in western thailand

Abstract: Disturbances influence forest dynamics across a range of spatial and temporal scales. In tropical forests most studies have focused on disturbances occurring at small spatial and temporal scales (i.e., gap dynamics). This is primarily due to the difficulty of reconstructing long-term disturbance histories of forests in which most tree species lack annual growth rings. Consequently, the role of past disturbances in tropical forests is poorly understood. We used a combination of direct and indirect methods to reconstruct the his- torical disturbance regime and stand development patterns in mature and regenerating seasonal dry evergreen forest (SDEF) in the Huai Kha Khaeng Wildlife Sanctuary in western Thailand. Direct estimates of long-term establishment and growth patterns were obtained from 12 tree species that form annual growth rings as a consequence of the region's strong intra-annual rainfall seasonality. Indirect estimates of establishment patterns were obtained from analyses of stand structure and individual tree architecture and application of age- estimation models to 10 dominant canopy-tree species using demographic data from a large- scale, permanent forest-dynamics plot. The combination of direct and indirect methodologies revealed a complex disturbance history in the seasonal evergreen forest over the past 250 years. In the mid-1800s, 200-300 ha of forest were destroyed by a catastrophic disturbance, which led to the synchronous es- tablishment of many of the trees that presently dominate the forest canopy. Since then wide- spread disturbances of variable intensity have occurred at least three times (1910s, 1940s, and 1960s). These disturbances created discrete temporal pulses of establishment in small to large gaps in the forest matrix across several square kilometers. Background mortality and gap formation were evident in every decade since 1790, but these varied in intensity and frequency. The SDEF retains a distinct structural and floristic legacy from the catastrophic dis- turbance of the mid-1800s. The single-age cohort that established after the disturbance has developed a complex three-dimensional structure as a consequence of differences in in- terspecific growth patterns of the canopy-tree species and subsequent disturbances of mod- erate and low intensity. While no single methodological approach provided a complete picture of the disturbance history and stand development patterns of the seasonal evergreen forest, taken together they offered new insights into the long-term dynamics of a primary tropical forest. In particular, the study highlighted the role of disturbance at multiple spatial and temporal scales and varying intensities in determining the structure and composition of a complex, species-rich tropical forest and raises important questions about the role of rare, catastrophic events on tropical forest dynamics.

Beyond the regeneration phase: differentiation of height–light trajectories among tropical tree species

Abstract: 1 A heightlight trajectory (HLT, a fitted curve relating canopy exposure to tree height) was determined for populations of individuals of each of 47 tree species in a Liberian lowland rainforest. The HLTs were compared and related to tree allometry and adult stature. Crown exposure was measured for 7460 trees and related to tree height using a multinomial regression analysis. Individual trees were followed for 2.89.8 years. 2 The trajectories of the 47 species were compared with the average vertical light profile in the forest canopy. Evidence was found for the existence of all nine trajectories hypothesized on the basis of three possible light environments (high, intermediate and low) for juveniles and adults. The classical paradigm of pioneer vs. shade tolerant, based on seed and seedling responses, does not therefore apply to post-seedling stages. 3 The majority of the species followed the vertical light profile in the forest canopy, starting in low light environments in the juvenile stage and ending up in high light environments in the adult stage. Only two species complied with the classic notion of whole-life shade tolerants and whole-life shade intolerants (one each). 4 The predictable vertical light gradient in the forest canopy has led to a close association between adult height, light trajectories and allometric traits. Large-stature species tend to have relatively slender stems and narrow crowns, and therefore realize a faster temporal and height-related increase in crown exposure. 5 Tree species have different heightlight trajectories when they grow from seedling to adulthood. This may have profound repercussions for our current views on plasticity and adaptation, light partitioning and species coexistence, and on silviculture and management

Seedling recruitment in a hurricane-driven tropical forest: light limitation, density-dependence and the spatial distribution of parent trees

Abstract: Summary 1 We used inverse modelling to parameterize spatially-explicit seedling recruitment functions for nine canopy tree species in the Luquillo Forest Dynamics Plot (LFDP), Puerto Rico. We modelled the observed spatial variation in seedling recruitment following Hurricane Georges as a function of the potential number of seedlings at a given location (based on local source trees and the potential contribution of parents from outside of the mapped area) and of light levels and density-dependent mortality during establishment. We adopted the model comparison paradigm and compared the performance of increasingly complex models against a null model that assumes uniform seedling distribution across the plot. 2 Our data supported a model in which parents must reach a threshold size before any seedling production will occur. Once parents attain that size, the relationship between tree diameter and the number of seedlings produced is fairly flat for the majority of species. These results contradict previous analyses that simply assumed a linear relationship between biomass and seedling production and a uniform size threshold for seedling production across species. 3 The majority of species tested supported models that included at least one of a bath term (contribution from non-local trees), conspecific density dependence and light availability after the hurricane. Density dependence shifted the mode of the effective dispersal kernel away from potential parent trees and significantly reduced the number of seedlings established near parent trees. Recruitment from non-local sources accounted for 6‐81% of observed seedling recruitment depending upon the tree species. Light availability appeared to divide species into three groups that showed more successful seedling establishment at low ( 30% full sun). 4 Differences between individual species in the importance of local vs. bath recruitment and the intensity of density dependence suggest the existence of distinct recruitment syndromes that go beyond the traditional focus of tropical tree life histories. Understanding these syndromes will provide valuable insights into the spatial distribution of tropical tree species and the maintenance of tropical forest diversity.

Airborne laser scanning: Exploratory data analysis indicates potential variables for classification of individual trees or forest stands according to species

Abstract: Understanding your data through exploratory data analysis is a necessary first stage of data analysis particularly for observational data. The checking of data integrity and understanding the distributions, correlations and relationships between potentially important variables is a fundamental part of the analysis process prior to model development and hypothesis testing. In this paper, exploratory data analysis is used to assess the potential of laser return type and return intensity as variables for classification of individual trees or forest stands according to species. For narrow footprint lidar instruments that record up to two return amplitudes for each output pulse, the usual pre-classification of return data into first and last intensity returns camouflages the fact that a number of the return signals have only “single amplitude” (singular) returns. The importance of singular returns for species discrimination has received little discussion in the remote sensing literature. A map view of the different types of returns overlaid on field species data indicated that it is possible to visually distinguish between vegetation types that produce a high proportion of singular returns, compared to vegetation types that produce a lower proportion of singular returns, at least when using a specific laser footprint size. Using lidar data and the corresponding field data derived from a subtropical woodland area of South East Queensland, Australia, map scatterplots of return types combined with field data enabled, in some cases, visual discrimination at the individual tree level between White Cypress Pine (Callitris glaucophylla) and Poplar Box (Eucalyptus populnea). While a clear distinction between these two species was not always visually obvious at the individual tree level, due to other extraneous sources of variation in the dataset, the observation was supported in general at the site level. Sites dominated by Poplar Box generally exhibited a lower proportion of singular returns compared to sites dominated by Cypress Pine. While return intensity statistics for this particular dataset were not found to be as useful for classification as the proportions of laser return types, an examination of the return intensity data leads to an explanation of how return intensity statistics are affected by forest structure. Exploratory data analysis indicated that a large component of variation in the intensity of the return signals from a forest canopy is associated with reflections of only part of the laser footprint. Consequently, intensity return statistics for the forest canopy, such as average and standard deviation, are related not only to the reflective properties of the vegetation, but also to the larger scale properties of the forest such as canopy openness and the spacing and type of foliage components within individual tree crowns.

Successional dynamics of woody seedling communities in wet tropical secondary forests

Abstract: Summary 1 Chronosequence studies have found that shrubs and lianas are generally more abundant in early stages of tropical forest succession, whereas canopy trees and palms become more abundant and species-rich in older stages and mature forests. 2 We analysed changes in woody seedling communities over 5 years in four secondgrowth forests (initially 13‐26 years after pasture abandonment) in Costa Rica. We recorded community-level changes in woody seedling density, species density, species richness and composition in six woody life-forms: canopy trees, subcanopy trees, canopy palms, understorey palms, shrubs and lianas. We evaluated these changes in relation to annualized recruitment and mortality rates for each life-form. 3 Seedling density declined in all four sites over the 5 years, whereas Shannon diversity and the proportion of rare species increased. Species richness and evenness increased in all but the oldest site. 4 Canopy palm, understorey palm and canopy tree seedlings increased in species richness and relative abundance, whereas shrub and liana relative abundance declined. Canopy trees accounted for 34‐42% of all new recruits. Detrended correspondence analysis showed that species composition was initially highly distinct within each forest site and remained distinct over the 5-year period. 5 Shifts in life-form were correlated with declining light availability during succession. Across sites, median light availability at the end of the study period in 2003 was positively correlated with recruitment rates of understorey palms, shrubs and lianas, and was negatively correlated with mortality rates of canopy trees and palms. 6 Observed changes among seedling communities mirrored those described in chronosequence studies on plants in larger size classes, lending support to the assumptions of chronosequence studies in Neotropical forests. 7 The results demonstrate the importance of seedling recruitment and mortality in determining the course of succession. Convergence occurs in some community properties, such as relative abundance within life-forms, but not in others, such as species composition. Finally, the results illustrate the value of studying plant community dynamics at the level of woody life-forms, especially in hyperdiverse systems such as tropical forests.

Estimating forest canopy bulk density using six indirect methods

Abstract: Canopy bulk density (CBD) is an important crown characteristic needed to predict crown fire spread, yet it is difficult to measure in the field. Presented here is a comprehensive research effort to evaluate six indirect sampling techniques for estimating CBD. As reference data, detailed crown fuel biomass measurements were taken on each tree within fixed-area plots located in five important conifers types in the western United States, using destructive sampling following a series of four sampling stages to measure the vertical and horizontal distribution of canopy biomass. The six ground-based indirect measurement techniques used these instruments: LI-COR LAI-2000, AccuPAR ceptometer, CID digital plant canopy imager, hemispherical photography, spherical densiometer, and point sampling. These techniques were compared with four aggregations of crown biomass to compute CBD: foliage only, foliage and small branchwood, foliage and all branchwood (no stems), and all canopy biomass components. Most techniques had the best performance when all canopy biomass components except stems were used. Performance dropped only slightly when the foliage and small branchwood canopy biomass aggregation (best approximates fuels available for crown fires) was employed. The LAI-2000, hemispherical photography, and CID plant canopy imager performed best. Regression equations that predict CBD from gap fraction are presented for all six techniques.

Estimates of‘relative pollen productivity’ and‘relevant source area of pollen’ for major tree taxa in two Norfolk (UK) woodlands

Abstract: Surface sample pollen assemblages and vegetation data collected from two East Anglian fen carr sites with adjacent dry woodland belts are analysed to estimate the relevant source area of pollen (RSAP) and the relative pollen productivity (RPP) values for the major canopy trees. The‘relevant source area of pollen’ is found to be on the order of 50-150 m, comparable with but slightly greater than estimates for forest hollow contexts in dry woodlands. Estimates of pollen productivity relative to Quercus are then compared with published values from south Sweden. Betula and Corylus values are similar, but some values estimated for taxa characteristic of wetter habitats, and therefore competitively advantaged in the fen carr system (Alnus, Salix and Fraxinus), are substantially higher at one or both sites. The results suggest that palaeoecological records from fen carr systems should be interpreted as reflecting predominantly local vegetation signals once the tree canopy is established.

Tropical Forest Measurement by Interferometric Height Modeling and P-Band Radar Backscatter

Abstract: A new approach to tropical forest biomass monitoring with airborne interferometric X and P-band synthetic aperture radar (SAR) data is presented. Forest height, basal area, and aboveground biomass are modeled from remote sensing data for a study site in the Brazilian Amazon. Radar data quality has improved: A novel digital model of vegetation height from X- and P-band interferometry is available along with the usual P-band backscatter information. The digital vegetation height model is derived from the interferometric surface models of the ground (from P-band) and the forest canopy (from X-band). The difference between the surface models is called "interferometric height," and is used as a measure of vegetation height. Interferometric height is shown to relate to a subset of the forest trees that changes according to the forest successional stages. The suitability of radar backscatter and interferometric height as a means for forest and biomass monitoring was explored by relating forest parameters as measured in the field to remote sensing data. Basal area and biomass were related to radar backscatter with limited precision of r 2 0.19 and r 2 0.34, respectively. Mean forest height is shown to relate to interferometric height with good precision (r 2 0.83, RMSE 4.1 m). A statistical model for forest biomass as a function of both P-band backscatter and interferometric height information not only arrives at high values of precision (with r 2 0.89 and a RMSE from cross-validation of only 46.1 t/ha), but also overcomes the well-known issue of backscatter saturation. This research shows that tropical forest biomass can be quantified and mapped over large areas for a range of forest structures with reasonably tight and similar errors. FOR .S CI. 51(6):585-594.

Light limitation creates patchy distribution of an invasive grass in eastern deciduous forests.

Abstract: Species interactions and their indirect effects on the availability and distribution of resources have been considered strong determinants of community structure in many different ecological systems. In deciduous forests, the presence of overstory trees and shrubs creates a shifting mosaic of resources for understory plants, with implications for their distribution and abundance. Determination of the ultimate resource constraints on understory vegetation may aid management of these systems that have become increasingly susceptible to invasions by non-native plants. Microstegium vimineum (Japanese grass) is an invasive annual grass that has spread rapidly throughout the understory of forests across the eastern United States since it was first observed in Tennessee in 1919. M. vimineum occurs as extensive, dense patches in the understory of eastern deciduous forests, yet these patches often exhibit sharp boundaries and distinct gaps in cover. One example of this distributional pattern was observed relative to the native midstory tree Asimina triloba (pawpaw), whereby dense M. vimineum cover stopped abruptly at the drip line of the A. triloba patch and was absent beneath the A. triloba canopy. We conducted field and greenhouse experiments to test several hypotheses regarding the causes of this observed pattern of M. vimineum distribution, including allelopathy, seed dispersal, light limitations, and soil moisture, texture, and nutrient content. We concluded that light reduction by the A. triloba canopy was the environmental constraint that prevented establishment of M. vimineum beneath this tree. Whereas overstory tree canopy apparently facilitates the establishment of this shade-tolerant grass, the interaction of overstory canopy with midstory canopy interferes with M. vimineum by reducing the availability of sunflecks at the ground layer. It is likely that other midstory species influence the distribution and abundance of other herb-layer species, with implications for management of understory invasive plant species.

Effect of forest canopy on GPS‐based movement data

Abstract: The advancing role of Global Positioning System (GPS) technology in ecology has made studies of animal movement possible for larger and more vagile species. A simple field test revealed that lengths of GPS-based movement data were strongly biased (P<0.001) by effects of forest canopy. Global Positioning System error added an average of 27.5% additional length to tracks recorded under high canopy, while adding only 8.5% to open-canopy tracks, thus biasing comparisons of track length or tortuosity among habitat types. Other studies may incur different levels of bias depending on GPS sampling rates. Ninety-nine percent of track errors under high canopy were ≤7.98 m of the true path; this value can be used to set the scale-threshold at which movements are attributed to error and not biologically interpreted. This bias should be considered before interpreting GPS-based animal movement data.

Effects of tree species composition on within‐forest distribution of understorey species

Abstract: Question Do tree species, with different litter qualities, affect the within-forest distribution of forest understorey species on intermediate to base-rich soils? Since habitat loss and fragmentation have caused ancient forest species to decline, those species are the main focus of this study.Location: Three ancient forests, along a soil gradient from acidification-sensitive to base-rich, were studied: Limbrichterbosch and Savelsbos in The Netherlands and Holtkrat in Denmark.Methods: Canopy and soil surveys along transects generated data for Redundancy Analysis on tree - humus relationships. We analysed the distribution of forest plant species with Canonical Correspondence Analysis. The explanatory factors were soil characteristics (pH, organic matter, loam content and thickness of the humus layers), external crown projection, groundwater and canopy data. We further analysed the relationship between forest species and humus characteristics with Spearman correlations.Results: Tree species have a significant impact on humus characteristics through the nature of their litter. Humus characteristics significantly explain the distribution of forest understorey species. The pH of the first 25 cm mineral soil and the thickness of the F- (fermentation) layer are the primary factors affecting the distribution of ancient forest species.Conclusion: This study indicates that the species composition of the forest canopy affects the distribution of forest understorey species. Ancient forest species are more abundant and frequent underneath trees with base-rich litter. On acidification-sensitive soils these relationships were stronger than on more base-rich, loamy soils.Abbreviations: Ah = Soil horizon consisting of mineral soil with a high organic matter content; CEC = Cation exchange capacity; F = Fermenting litter (layer); Ah = Humus-rich mineral soil (layer); L = Litter (layer); RDA = Redundancy analysis.

Extensive observations of CO2 carbon isotope content in and above a high-elevation subalpine forest

Abstract: [1] The dynamics of forest-atmosphere CO2 carbon isotope exchange were examined in a coniferous forest in Colorado, United States. Tunable diode laser absorption spectrometry provided extensive characterization of the carbon isotope content (δ13C) of CO2. Observed patterns in δ13C of forest air were associated with photosynthesis, respiration, and atmospheric boundary layer dynamics. Similar relationships between δ13C and CO2 were observed at all forest heights and confined to a relatively narrow envelope. Substantial variation was observed in the isotope ratio of nocturnal ecosystem respiration (δ13CR, calculated from isotopic mixing lines). A systematic bias was identified when estimating δ13CR from data sets with small range in CO2 in the samples, leading us to restrict analysis of δ13CR to periods with CO2 range >40 μmol mol−1. Values of δ13CR varied from −28.1 to −25.2‰, with variation from one night to the next as large as 1.7‰. A consistent difference was observed between δ13CR calculated near the forest floor (<2 m height) versus the upper canopy (5–11 m) on the same nights. δ13CR was more enriched in the upper canopy than near the ground on 34 of 43 nights, with a mean enrichment of 0.6‰ and a maximum of 2.3‰. A similar pattern was observed comparing δ13CR at night with the analogous quantity calculated during daytime, but only a few daytime periods met the 40 μmol mol−1 criterion. Comparisons between air samples measured (1) 10 m above the forest canopy, (2) 3 km away, and (3) within the convective boundary layer 125 km distant showed CO2 differences between sites as large as 5–6 μmol mol−1 even at midday. These results suggest that attempts to use flask measurements at remote monitoring stations as a proxy for the air directly interacting with a vegetation canopy should be made with caution. However, our results also suggest that substantial information about biosphere-atmosphere isotopic exchange can be obtained by simultaneous examination of CO2 and δ13C at multiple spatial scales.

Variable rate nitrogen application in florida citrus based on ultrasonically-sensed tree size

Abstract: Most Florida citrus groves are still managed as large contiguous uniform blocks, despite significant variation in fruit yield and tree canopy size. Site-specific grove management by variable rate delivery of inputs such as fertilizers on a tree size basis could improve horticultural profitability and environmental protection. Tree canopy sizes were measured real-time in a typical 17-ha Valencia grove with an automated ultrasonic sensor system equipped with Differential Global Positioning System (DGPS). Prescription maps for variable application of nitrogen fertilizer were generated from ultrasonically scanned tree sizes on a single tree basis using ArcView GIS and Midtech Fieldware. Leaf samples from trees with different canopy sizes, which had been fertilized at a conventional uniform rate of 270 kg N/ha/y, were analyzed for nitrogen concentration. Analysis of 2980 tree spaces in the grove showed a skewed size distribution, with 62% in the 0- to 100-m3/tree volume classes and a median volume of 79 m3/tree. The tree volumes ranged from 0 to 240 m3/tree. Regression analysis showed that trees with excess leaf nitrogen (>3%) had canopies less than 100 m3. These trees receiving excess nitrogen are likely to have lower fruit yields and quality, and wasted fertilizer nitrates may leach beyond the root zone to groundwater. In order to rectify the excess fertilization of smaller trees, a granular fertilizer spreader with hydraulically powered split-chain outputs controlled with a MidTech Legacy 6000 controller was used for variable rate application of nitrogen in one-half of the grove. A 38% to 40% saving in granular fertilizer cost was achieved for this grove when variable N rates were implemented on a per-tree basis ranging from 135 to 270 kg N/ha/y.

Early performance predicts canopy attainment across life histories in subalpine forest trees

Abstract: Few individuals in canopy tree species attain the canopy and reproduce. Understanding why these select few succeed is fundamental to tree population ecology and forest community dynamics. Yet our understanding remains poor, because the time required to reach the canopy is long relative to experimental and demographic studies. We used a simple, yet powerful, approach to examine the long-term process of canopy recruitment. We compared early growth in proven "winners" (extant canopy trees) with that of "con- tenders" (extant saplings 75 cm tall to 5 cm dbh). The resulting analyses relate early radial growth (after reaching 50 cm height) to survival, implicit in the long-term persistence of winners. We focused on the three major tree species of subalpine forests in the northeastern United States: shade-intolerant mountain birch (Betula cordifolia), shade-tolerant balsam fir (Abies balsamea), and highly shade-tolerant red spruce (Picea rubens). For all species, extant canopy trees grew faster than extant saplings at equivalent ages and sizes. For shade-intolerant B. cordifolia, no surviving canopy trees, or even saplings, had slow early growth. Even in shade-tolerant A. balsamea and P. rubens, surprisingly few individuals with slow early growth were represented in the canopy, even though both saplings and canopy trees survived slow growth for up to 50 years later in life. Thus, long- term success in reaching the canopy was strongly determined by fast early growth rates, across all species and life histories. We discuss implications for understanding the physi- ology of shade tolerance and for modeling forest dynamics. Most current models of forest tree population and community dynamics ignore individual growth history, but our results suggest that failure to account for growth history may overestimate long-term survival of shade-tolerant species.

Radiative transfer model for microwave bistatic scattering from forest canopies

Abstract: A bistatic forest scattering model is developed to simulate scattering coefficients from forest canopies. The model is based on the Michigan Microwave Canopy Scattering (MIMICS) model (hence called Bi-MIMICS) and uses radiative transfer theory, where the first-order fully polarimetric transformation matrix is used. Bistatic radar systems offer advantages over monostatic radar systems because of the additional information provided by the diversity of the geometry. By simulating the forest canopy scattering from multiple viewpoints, we can better understand how the forest scatterers' shape, orientation, density, and permittivity affect the canopy scattering. Bi-MIMICS is parametrized using selected forest stands with different canopy compositions and structure. The simulation results show that bistatic scattering is more sensitive to forest biomass changes than backscattering. Analyzing scattering contributions from different parts of the canopy gives us a better understanding of the microwave's interaction with the tree components. The ground effects can also be studied. Knowledge of the canopy's bistatic scattering behavior combined with additional synthetic aperture radar measurements can be used to improve forest parameter retrievals. The simulation results of the model provide the required information for the design of future bistatic radar systems for forest sensing applications.

Tree mortality, canopy turnover, and woody detritus in old cove forests of the southern appalachians

Abstract: A long-term study of tree mortality, canopy turnover, and coarse woody detritus inputs was conducted in cove forests of the Great Smoky Mountains, Tennessee, USA. Seven old-growth stands were studied over a 10-yr period using 0.6–1.0 ha plots. Annual mortality of trees >10 cm dbh was 0.5–1.4% among stands (mean 0.7%). The highest mortality rate among canopy trees was exhibited by trees >80 cm dbh. An increase in mortality rate with canopy tree size was evident for two (Tsuga canadensis and Acer saccharum) of the three most abundant species in the forest. The increase in mortality with tree size had implications for canopy turnover and detritus input. Gap disturbance frequency was estimated at 0.008–0.019 forest area/yr, giving a return interval of ∼130 yr or less. Standing death was the most common mode of mortality (59%). Annual rates of snag formation were 1.4 snags/ha for trees >10 cm dbh and 0.4 snags/ha for trees >50 cm dbh. The density of large snags (>50 cm dbh) was 5 snags/ha. Snags accounted for ...