Forest Tree Height Research Articles

Tree diameter, height and stocking in even-aged forests

• Empirical observations suggest that in pure even-aged forests, the mean diameter of forest trees (D, diameter at breast height, 1.3 m above ground) tends to remain a constant proportion of stand height (H, average height of the largest trees in a stand) divided by the logarithm of stand density (N, number of trees per hectare): D = β(H − 1.3)/ ln(N). • Thinning causes a relatively small and temporary change in the slope β, the magnitude and duration of which depends on the nature of the thinning. • This relationship may provide a robust predictor of growth in situations where scarce data and resources preclude more sophisticated modelling approaches. Mots-cles : monoculture / index de densite de peuplement / modele de croissance / diagramme de gestion de la densite

Mapping Height and Biomass of Mangrove Forests in Everglades National Park with SRTM Elevation Data

We produced a landscape scale map of mean tree height in mangrove forests in Everglades National Park (ENP) using the elevation data from the Shuttle Radar Topography Mission (SRTM). The SRTM data was calibrated using airborne lidar data and a high resolution USGS digital elevation model (DEM). The resulting mangrove height map has a mean tree height error of 2.0 m (RMSE) over a pixel of 30 m. In addition, we used field data to derive a relationship between mean forest stand height and biomass in order to map the spatial distribution of standing biomass of mangroves for the entire National Park. The estimation showed that most of the mangrove standing biomass in the ENP resides in intermediate-height mangrove stands around 8 m. We estimated the total mangrove standing biomass in ENP to be 5.6 � 10 9 kg.

Structure and floristics of an old secondary rain forest in Central Kalimantan, Indonesia, and a comparison with adjacent primary forest

The study of tropical secondary forests, and of the time taken for them to revert to ‘primary’ forest, is of increasing importance given the current global destruction of tropical rain forests. We describe a 55-year-old secondary rain forest at Barito Ulu, Central Kalimantan, Indonesia, and compare it with the adjacent, undisturbed, primary forest. Three 0.25 ha plots were set up in each forest type and all stems over 10 cm dbh were measured and identified, soil samples were taken and analysed, and the composition of the seed bank was examined. Although the basal area, tree height and biomass of the old secondary forest approached that of the primary forest (82% for basal area, 88% for tree height and 74% for biomass), there were still major differences in the floristics and species diversity. The old secondary forest was dominated by Cratoxylon arborescens (Hypericaceae) and Pternandra caerulescens (Melastomataceae), whereas the primary forest was dominated by dipterocarps. The Shannon–Wiener diversity index was 3.40 for the old secondary forest plots and 4.17 for the primary forest plots; the Jaccard’s coefficient of similarity was 24%. Mortality, recruitment, turnover and tree growth rates were greater in the old secondary forest. The seed bank of the old secondary forest contained more than double the number of seeds of the primary forest seed bank and many more seeds were of shrub species; there were the same number of species in the two forests seed banks. There were no major differences between the two forest types in terms of soil chemistry. Despite the close proximity to potential seed sources, succession in the Barito Ulu area has proceeded more slowly than in some other tropical areas. This may be due to the low concentrations of soil nutrients and/or the poor dispersal of dipterocarp seeds. Fifty-five years of succession is concluded to be insufficient time for the return of most primary forest species. However, the forest structure of the old secondary forest shows a closer resemblance to the primary forest than does the floristic composition.

A comparison of forest structure among old-growth, variable retention harvested, and clearcut peatland black spruce (Picea mariana) forests in boreal northeastern Ontario

Harvesting techniques that retain structural elements of the original forest may help to preserve the characteristic ecological features and biological diversity of old-growth forests. Harvesting with advance regeneration protection (HARP) is one such technique practised in the Lake Abitibi Model Forest of northeastern Ontario on peatland sites. In this system, winter harvesting operations clear trees in strips about 5–7 m wide and using a minimum diameter limit cut extract trees from the adjacent residual forest rows, 5–9 m wide. In order to assess the effectiveness of HARP in retaining forest structure, we quantified forest and understorey structural features in 24 1.65-ha plots spanning a wide range of forest retention, including clearcuts, three levels of HARP, and the edge and interior of unharvested forest (logging had occurred 2.5–3.5 years before the study). Mean tree age, diameter, and height in HARP forests in all cases exceeded 68% of the mean values found in unharvested forest, which was strikingly higher than the percent retention of basal area (20–43%). Also, unlike clearcuts, HARP forests retained the inverse-J curves between stem density and size class observed in unharvested forests, although stem densities in all size classes were lower. The percentage of black spruce regeneration originating from seed versus vegetative layering was directly related to the amount of forest basal area retained, averaging 2–5% in unharvested forests, 9–38% in HARP forests, and 67% in clearcuts. Many understorey characteristics closely followed the harvest intensity gradient, with amounts of moss, lichen, and Ledum highest at the unharvested end of the gradient and amounts of decaying moss, coarse and fine downed woody debris, exposed soil, and sedge highest at the clearcut end of the gradient. When the structural features were combined into a single composite variable using Principal Components Analysis (PCA) and the scores plotted against basal area, the relationship was curvilinear, with HARP treatments retaining greater amounts of structural characteristics than expected based solely on the basal area of wood harvested. This research suggests that the retention and redevelopment of old-growth features in peatland black spruce forests will be better under a HARP system than under a traditional clearcut system. Longer-term research, specifically on the edge habitats created by the HARP system, is required. Key words: boreal, peatland, black spruce, alternative harvesting methods, forest ecology

Estimation of forest parameters using CARABAS-II VHF SAR data

The use of airborne CARABASII VHF (20-90 MHz) SAR data for retrieval of forest parameters has been investigated. The investigation was performed at a test site located in the southwest of Sweden consisting mainly of Norway spruce forests. Regression models predicting forest parameters from radar backscattering amplitude were developed and evaluated. The results showed a linear relationship between backscattering amplitude and forest stem volume, stem diameter, and tree height. The analysis also showed that the radar signal is strongly affected by ground slope conditions. The root mean square errors from the regression analysis, restricted to forest stands on near-horizontal ground, were found to be 66 m/sup 3/ ha/sup -1/, 3.2 cm, and 2.3 m for stem volume, stem diameter, and tree height respectively. No saturation of the backscattered signal was observed up to the maximum stem volume of 625 m/sup 3/ ha/sup -1/, corresponding to a biomass of 375 tons ha/sup -1/. The results imply that VHF SAR data have significant potential for operational use in forestry.

Estimating Stem Volume and Basal Area in Forest Compartments by Combining Satellite Image Data with Field Data

The weighted k - nearest neighbour (kNN) method was used for estimating stem volume (m3 ha?1) and basal area (m2 ha?1) on a compartment level (average 19 ha) by combining satellite image data with measurements from Swedish National Forest (NFI) inventory plots. In the kNN method each estimation location (target plot) is assigned a value that is an average, which is weighted, of the attribute data from the k closest reference plots (NFI plots). The distance between target and reference plot was measured on different scales, which were transforms of spectral values and/or ancillary data. The standard error (assuming bias with no trend) of stem volume estimates in the compartments was 36% using only spectral data. This estimation accuracy improved to 17% if site index, age of the forest and mean tree height (ancillary data) were known for the compartments. Low volumes were overestimated and high volumes underestimated. This bias was reduced if ancillary data were added but was also dependent on the transform of the original scales.

Determination of mean tree height of forest stands using airborne laser scanner data

The mean tree height of forest stands is a crucial stand characteristic in forest planning. Currently, the mean tree height is determined by field measurements or by photogrammetric measurements utilizing aerial photographs. In this study, mean tree height of 36 test stands is derived from tree canopy heights measured by means of an airborne laser scanner. On the average the laser recorded 505–1070 canopy heights per stand. First, the laser mean height is computed as the arithmetic mean of the canopy heights within each stand. The laser mean height underestimates the ground truth mean height by 4.1–5.5 m. Second, a weighted mean of the laser canopy heights is computed. The individual height values are used as weights. The weighted mean height underestimates the true height by 2.1–3.6 m. Finally, the laser mean height is computed as the arithmetic mean of the largest laser values within square grid cells with cell sizes of 15–30 m. The bias of the laser estimates is in the range −0.4 m to 1.9 m. The standard deviation for differences between the laser mean heights and the ground truth mean height is 1.1–1.6 m.

Determination of heat and water vapour fluxes above a spruce forest by eddy correlation

Heat and water vapour fluxes have been measured by eddy correlation at three levels above a spruce forest (tree height 31 m) in central Germany. A number of methodical problems are discussed, and necessary data corrections are presented. Stationarity of the fluxes is proven by cospectral analysis, confirming that averaging times of 10–30 min are adequate to describe the transport processes. Sensible and latent heat fluxes do not vary with height in the layer from ( z − d) = 6.5 z 0 to ( z − d) = 11.7 z 0. Based on footprint estimates it is concluded that, in general, the measured fluxes may be taken as representative of the spruce canopy. Even in the worst-case situations, when the wind comes from a beech-spruce transition 200 m away, no height dependence of the fluxes is detected. On the selected days, which were mainly bright, a Bowen ratio near one is found during the hours of highest available energy, whereas at night no evapotranspiration is observed. The turbulent diffusion coefficients of heat and water vapour follow a distinct diurnal pattern, with a maximum of about 10 m 2 s −1 shortly after noon. The heat diffusion coefficient tends to exceed that of water vapour by a factor of about 1.2, showing daytime-dependent variations. Owing to some unexplained deficits in the energy balance this value is not very certain, but the results are consistent with some other published data. At least they demonstrate that uncritical application of the similarity hypothesis ( D h = D v) above high vegetation may lead to erroneous flux calculations.

An empirical approach to the analysis of forest stratification

Natural forest communities consist of different overlapping elementary subpopulations. Using the results of forest stratification in the preceding study, the properties of mean tree height for subpopulation in a stratified forest stand were examined. Mean tree height decreased as tree density per subpopulation increased. This relation was described by a simple mathematical model consisting of a power equation of tree density and two coefficients. The first coefficient or exponent of tree density was close to −1/2 in its expectation, while the other coefficient depended on life forms, especially in tropical forests. For tropical deciduous forests which suffered from seasonal forest fires, the latter coefficient was smaller than those for tropical evergreen and Japanese forests. This difference of the coefficient was not clear between tropical evergreen and Japanese forests and between deciduous and evergreen forests in Japan. In conclusion, the proposed model is similar to the 1/2 power law of tree height in man-made forests with simple architecture, and is designated the quasi-1/2 power law of tree height.