Determinants of stem form: Application to Tectona grandis (Linn. F) stands

ABSTRACT

Stem form information can enhance rapid estimation of stem volume. Studies on important determinants of stem form in pure stands are scanty. This study aimed at identifying determinants of stem form using Tectona grandis stands in Omo Forest Reserve, Nigeria. Twenty 0.04 ha square plots were randomly selected across four stand ages. Crown diameter, total and merchantable heights (MH), diameters at breast height (DBH), at 5.27 m tree height and at midpoint from breast height to tip of tree were measured in each plot. Measured trees were classified into four canopy layers (CL)—dominant, codominant, intermediate, and suppressed. Merchantable volume, basal area (BA), form factor (F_f), normal form quotient (Q_n), Girard form class (Q_G), absolute form quotient (Q_a), ratio of diameter at merchantable limit to diameter at the base (D_t/D_b), and tree slenderness coefficient were derived from the data. Analysis of variance, correlation, and regression analyses were used to analyze the data. Significant differences were observed in stem form and tree size variables under different canopy layers. The DBH, BA, MHT, and CL were identified as important variables associated with stem form. Inclusion of Q_a improved most the predictive ability of the selected stem volume equation.     

Stand characteristics of mixed oriental beech (<Emphasis Type="Italic">Fagus orientalis</Emphasis> Lipsky) stands in the stem exclusion phase,northern Iran

The structure of forest stands changes through developmental phases. This study is carried out in the unmanaged, oriental beech (Fagus orientalis Lipsky) stands in the north of Iran. The aim of this research was to quantify structural characteristics of stands in the stem exclusion phase using common structural indices, which include mingling, tree–tree distance, stem diameter, and tree height differentiation. According to our measurements from three stands, naturally regenerated stands tend to be mixed in species composition have slightly heterogeneous diameter distributions and uniform tree height. The average distance between trees was 3.3 m. Stocking volume of the stands had an average of 540 m³ ha^?1 and 412 stem ha^?1. Dead wood volume was 24 m³ ha^?1, and as a standing volume, the most frequent species in dead wood pool was oriental beech (F. orientalis) (48 %). The common form of dead trees was snag (41 %). The mean value of mingling and tree-to-tree interval indices revealed that beech was mixed intensively with hornbeam and appears to be a more successful competitor for space and light compared with hornbeam; moreover, we found relatively high evidence of inter-species competition in this phase. A better understanding of stand characteristics in the stem exclusion phase as a critical part of the natural dynamics of forest ecosystems could facilitate predictions about the future changes within the stand.     

The effects of different types of management,functions, and characteristics of stands in Polish forests on the amount of coarse woody debris

In the modern forestry paradigm, many factors influence the amount of coarse woody debris (CWD). The present paper analyzes the effects of both local (national) programs (special functions of forests) and European programs (Natura 2000 sites), as well as the individual characteristics of forest stands. The study was conducted on 2,752 sampling plots distributed over an area of about 17,500 ha and located in lowland stands having a species composition typical of large areas in central Europe. Natura 2000 areas contained significantly more CWD (8.4 m³/ha) than areas not covered by the program (4.8 m³/ha). However, this is due to the fact that Natura 2000 sites involve well-preserved forest areas, such as nature reserves (26.6 m³/ha). In the managed forests that have been covered by the Natura 2000 program over the past several years, the volume of CWD has not increased. Forests with ecological and social functions differed slightly in the amount of CWD. More CWD occurred in protected animal areas (8.7 m³/ha) than in stands damaged by industry (3.9 m³/ha). Intermediate CWD levels were found in water-protection forests and in forests located around cities and military facilities. In managed forests, the lowest CWD volume was observed in middle-aged stands. The species composition of the stand had little effect on the volume of CWD. Only stands with a predominance of ash and alder had higher CWD levels (13.5 m³/ha). More CWD was found in stands whose species composition did not represent the potential site quality (6.4 m³/ha) than in habitats with the optimum species composition (3.8 m³/ha). CWD volume should be systematically increased taking into consideration local natural conditions. Such efforts should be focused on particularly valuable regions, and especially on Natura 2000 sites, where the threshold values reported from other European forests should be reached. Leaving some trees to die naturally and retaining reasonable amounts of such trees ought to be incorporated into CWD management practice in Poland.     

Allometry, biomass, and chemical content of Novel African Tulip Tree (Spathodea campanulata) Forests in Puerto Rico

The African tulip tree, Spathodea campanulata, the most common tree in Puerto Rico, forms novel forest types with mixtures of native and other introduced tree species. Novel forests increase in area in response to human activity and there is no information about their biomass accumulation and nutrient cycling. We established allometric relationships and chemically analyzed plant parts of African tulip trees to determine the concentration and standing stock of chemical elements (C, N, P, K, Ca, Mg, S, Mn, Al, Fe, Na), and ash. Trees ranged in diameter at breast height from 8 to 85 cm and in height from 8.8 to 28 m. The concentrations of N, P, K, and Ca in leaves of the African tulip tree were similar to those of the native pioneer Cecropia schreberiana and higher than those of mature forest tree species in Puerto Rico. The over bark wood volume of African tulip trees in nine forest stands where it was dominant ranged from 163 to 849 m³/ha. Aboveground biomass ranged from 60 to 296 Mg/ha, and N and P stocks ranged from 190 to 988 and 32 to 137 kg/ha, respectively. Novel forests on abandoned agricultural lands can store more biomass and elements than native and plantation forest stands of similar age.     

Growing stock variation in different teak （Tectona grandis） forest stands of Mizoram,India

The growing stock assessment of three different teak forest stands （Tuirial： 500 m asl, Sairang： 200 m asl and Phunchawng： 550 m asl） was done in 2006 in Mizoram, India. Five diameter classes were arbitrarily established for knowing the volume attribute data and population structure, viz. a （10-20 cm）, b （20-30 cm）, c （30-40 cm）, d （40-50 cm）, and e （50-60 cm）. Results revealed that the density of the individuals among the studied stands varied from 280 stems/ha to 620 stems/ha. The average diameter of all the individuals ranged between 27.48 cm and 35.43 cm. Similarly, the average height was oscillated between 17.87 m and 22.24 m. The total basal area was recorded between 24.28 m2.ha-1 and 45.80 m2.ha＂l. The maximum and minimum values of total growing stock under all the diameter classes were 669.01 m3.ha-1 and 284.7 m3.ha-1, respectively. The representation of population structure of different stands explained that the perpetuation of this species was ensured for a quite long time.     

Litterfall,decomposition and nutrient release of <Emphasis Type="Italic">Shorea robusta</Emphasis> and <Emphasis Type="Italic">Tectona grandis</Emphasis> in a sub-tropical forest of West Bengal,Eastern India

We studied leaf litter fall, decomposition and nutrient release patterns of Shorea robusta and Tectona grandis by using a litter bag technique to better understand the release pattern of nutrients to soil from leaf litter. Annual litterfall varied from 13.40 ± 2.56 t ha^?1 a^?1 for S. robusta to 11.03 ± 3.72 t ha^?1 a^?1 for T. grandis and the decay constant (k) of decomposed leaf litter was distinctly higher for T. grandis (2.70 ± 0.50 a^?1) compared to S. robusta (2.41 ± 0.30 a^?1). Biomass loss was positively correlated with the initial litter C, WSC, C/N and ash content in S. robusta and N, P and K concentration for T. grandis. Biomass was negatively correlated with lignin and L/N ratio for S. robusta and L, WSC, L/N and C/N ratio for T. grandis (P < 0.01). Nutrient use efficiency (NUE) and nutrient accumulation index (NAI) of S. robusta was higher than for T. grandis. The retranslocation of bioelements from senescent leaves ranked as P > N > K. Annual N, P and K input to soil through litterfall differed significantly between the two species in the following order: N>K>P. S. robusta was superior in terms of K and P return and T. grandis was superior in terms of N return. The two tree species showed a similar patterns of nutrient release (K > P > N) during decomposition of their leaf litter. Nutrients of N, K and P were the primary limiting nutrients returned to soil through litterfall with important roles in soil fertility and forest productivity.     

Floristic diversity,carbon storage and ecological services of eucalyptus agrosystems in Cameroon

Although agrosystems are recognized for their socio-economic value, few works have been conducted to assign its sequestration potential and ecological services. Accordingly, this study aimed to evaluate the ecological services of the eucalyptus stands in order to permit to small producers the access in carbon credit market. Three stands were selected according to age. Data were compared to that of a savannah (control). In total, 12,817 individuals belonging to 30 families, 53 genera and 70 species were identified in the plantations against 7107 individuals belonging to 24 families, 36 genera and 42 species in the savannah. Gmelina, Annona, Hymenocardia, Allophyllus, Daniellia, Terminalia and Piliostigma were the most represented genera. There was no significant difference between Savannah and plantations in terms of diversity (p > 0.05). The largest stock of carbon was found in oldest stands (108.51 ± 26.46 t C/ha) against 13.62 ± 3.03 t C/ha in Savannah. Eucalyptus saligna stored 39.66 t C/ha (4 t C ha^?1year^?1) in young stands; 57.28 t C/ha (6 t C ha^?1year^?1) in medium stands and 85.46 t C/ha (9 t C ha^?1year^?1) in old stands. The sequestration potential was higher in eucalyptus stands (398.25 t CO_2eq/ha) than savannah (50.05 t CO_2eq/ha). In total 956.82 t CO_2eq/ha were sequestered for an economic value of $9568.45/ha against 50.05 t CO_2eq/ha corresponding to $500.56/ha in Savannah. Eucalyptus stands are carbon sinks and could be an opportunity for financial benefits in the event of payment for environmental services in the context of the CDM process.     

Productivity of mixed versus pure stands of oak (Quercus petraea (Matt.) Liebl. and Quercus robur L.) and European beech (Fagus sylvatica L.) along an ecological gradient

The mixture of beech (Fagus sylvatica L.) and oak (sessile oak, Quercus petraea (Matt.) Liebl., and pedunculate oak, Q. robur L.) is of considerable importance in Europe and will probably become even more important under climate change. Therefore, the performance of oak and beech in mixture was compared with the species’ growth in pure stands. Data from 37 long-term mixing experiments in Poland, Germany and Switzerland were pooled for analysis of mixing effects on stand productivity and possible interrelationships with mixing portions or site conditions. We found that on average, mixed stands of oak and beech exceeded biomass productivity in pure stands by 30 % or 1.7 t ha^?1 year^?1, as the growth of both species was benefitted by the mixture. However, that the interaction actually ranged from facilitation and overyielding on poor sites to underyielding on fertile sites triggered by competition. An empirically derived interaction model showed volume and dry mass growth changing in mixed stands from gains of 50 % to losses of 10 % depending on site conditions. It is concluded that the analysed mixture grows in accordance with the stress-gradient hypothesis and that our results suggest a site-specific relationship between species mixture and biomass productivity. As a consequence, an adequate species mix should result in increased productivity under steady state as well as climate change.     

Variation in post-wildfire regeneration of boreal mixedwood forests: underlying factors and implications for natural disturbance-based management

To test the direct regeneration hypothesis and support natural disturbance-based forest management we characterized the structure and composition of boreal mixedwood forests regenerating after large wildfires and examined the influence of pre-fire stand composition and post-fire competing vegetation. In stands which had been deciduous (Populus sp.)-dominated, conifer (white spruce)-dominated, or mixed pre-fire we measured regeneration stocking (presence in 10 m² plots), density and height 10–20 years post-burn in five wildfires in Alberta, Canada. Most plots regenerated to the deciduous or mixed stocking types; plots in the older fire and in stands that were pure conifer pre-fire had higher amounts of conifer regeneration. Surprisingly, regeneration in pre-fire ‘pure’ white spruce stands was most often to pine, although these had not been recorded in the pre-fire inventory. Pre-fire deciduous stands were the most resilient in that poplar species dominated their post-fire regeneration in terms of stocking, density and height. These stands also had the highest diversity of regenerating tree species and the most unstocked plots. High grass cover negatively affected regeneration density of both deciduous and conifer trees. Our results demonstrate the natural occurrence of regeneration gaps, pre- to post-fire changes in forest composition, and high variation in post-fire regeneration composition. These should be taken into consideration when developing goals for post-harvest regeneration mimicking natural disturbance.     

Prediction of tree height,basal area and stem volume in forest stands using airborne laser scanning

The aim of this study was to develop prediction models using laser scanning for estimation of forest variables at plot level, validate the estimations at stand level (area 0.64 ha) and test the effect of different laser measurement densities on the estimation errors. The predictions were validated using 29 forest stands (80×80 m²), each containing 16 field plots with a 10 m radius. For the best tested case, mean tree height, basal area and stem volume were predicted with a root mean square error of 0.59 m (3% of average value), 2.7 m² ha^?1 (10% of average value) and 31 m³ ha^?1 (11% of average value), respectively, at stand level. There were small differences in terms of prediction errors for different measuring densities. The results indicate that mean tree height, basal area and stem volume can be estimated in small stands with low laser measurement densities producing accuracies similar to traditional field inventories.     

Effects of Wheeled Cable Skidding on Residual Trees in Selective Logging in Caspian Forests

There are increasing demands on silvicultural practices to reduce the adverse impacts of harvesting. Damage to residual trees caused by ground-based skidding was assessed in stands with low [3.4 stems per hectare (sph), 14.36 m³/ha], medium (5.2 sph, 21.61 m³/ha), and high (7.1 sph, 25.95 m³/ha) harvest intensities. Skidding was conducted using a cable skidder. After the skidding operation, a field survey was conducted to collect data on all residual trees (species, dbh, height) and on tree wounds (size class, location, intensity of damage). It was hypothesized that increased harvest intensity leads to increased injury rates. The treatment with the highest harvest intensity was found to cause the highest percentage of damage and the largest stem wounds. The most common types of damage were stem wounds to the cambium layer and bark scrapes. In all three harvest intensity treatments the probability of individual tree damage decreased as skid-trail cross slope decreased and distance to skid-trail edge increased. It is concluded that harvesting intensity should be limited to 5 trees/ha during each harvesting operation to reduce extent of tree damage and thus future financial loss.     

Timing and intensity of precommercial thinning in Pinus sylvestris stands

The effects of timing and intensity of precommercial thinning were studied in three Scots pine artificially regenerated stands on Vaccinium forest sites in southern Finland. A two-level factorial design (3×3) was used in each stand: thinning at dominant height of 3, 6 and 9 m to 1000, 1600 and 2200 stems ha^?1. The effects of the treatments were analysed after a period of 23–25 yrs when the dominant height was 14–15 m. Early thinning resulted in the highest standing volume and amount of merchantable wood, and also in slightly accelerated height development. Thinning to 1000 stems ha^?1 caused a considerable production loss, but there were no differences between the densities of 1600 and 2200 stems ha^?1. Branches became thicker after early thinning, but the differences between the treatments were negligible for crop trees. Crown ratio was lowest as the result of early or moderate thinning (2200 stems ha^?1).     

Effect of thinning on growth of Acer velutinum Boiss. in northern forests of Iran

It has become necessary to develop stands of fast growing endemic species in the Caspian forests because of their reduction in area and the domestic demand of timber processing industries in Iran. Acer velutinum, an en- demic species in Iran, is often planted in monocultures or in a mixture with other endemic species. Our study was con- ducted on A. velutinum planted in Berenjestanak （control plots） and Chaibagh （thinned plots） in northern Iran in 1991. A randomized sampling method with circular sampling plots of 100 m2 was used to measure diameter and height of trees. The results show that the diameter of trees in thinned stands was 19.98 cm and in the control stands 13.84 cm, while the mean heights were 18.33 and 17.46 m, respectively. The mean basal area in thinned stands was 30.74 m2 and in the control 15.70 m2 per ha. The results of Student＇s t tests indicate that there are significant differences at a probability level of 99.9% between the two variously treated stands in diameter （d）, height （h）, basal area, volume growth and the stabil- ity coefficient. We conclude that tending operations with suitable intensity in different time periods are recommended to obtain stable stands.     

A comparative assessment on regeneration status of indigenous woody plants in Eucalyptus grandis plantation and adjacent natural forest

Diversity, density and species composition of naturally regenerated woody plants under Eucalyptus grandis plantation and the adjacent natural forest were investigated and compared. Twenty plots, with an area of 20 m × 20 m for each, were established in both of E. grandis plantation and adjacent natural forest, independently. In each plot, species name, abundance, diameter and height were recorded. Numbers of seedling were collected in five sub-plots (4 m²) within each major plot. A total of 46 species in the plantation, and 52 species in the natural forest, which belongs to 36 families were recorded. The diversity of species (H′) is 2.19 in the plantation and 2.74 in the natural forest. The density of understory woody plant was 3842 stems/ha in the plantation and 4122 stems/ha in the natural forest. The densities of seedlings in the natural forest and the plantation were 8101 stems/ha and 4151 stems/ha, respectively. High similarity of woody species composition was found between the natural forest and the plantation. The E. grandis plantation was found favoring the regeneration and growth of Millitia ferruginia and Coffea arabica in a much better way than other underneath woody species.     

Estimation of shrub biomass by airborne LiDAR data in small forest stands

The presence of shrub vegetation is very significant in Mediterranean ecosystems. However, the difficulty involved in shrub management and the lack of information about behavior of this vegetation means that these areas are often left out of spatial planning projects. Airborne LiDAR (Light Detection And Ranging) has been used successfully in forestry to estimate dendrometric and dasometric variables that allow to characterize forest structure. In contrast, little research has focused on shrub vegetation. The objective of this study was to estimate dry biomass of shrub vegetation in 83 stands of radius 0.5 m using variables derived from LiDAR data. Dominant species was Quercus coccifera, one of the most characteristic species of the Mediterranean forests. Density of LiDAR data in the analyzed stands varied from 2 points/m² to 16 points/m², being the average 8 points/m² and the standard deviation 4.5 points/m². Under these conditions, predictions of biomass were performed calculating the mean height, the maximum height and the percentile values 80th, 90th, and 95th derived from LiDAR in concentric areas whose radius varied from 0.50 m to 3.5 m from the center of the stand. The maximum R² and the minimum RMSE for dry biomass estimations were obtained when the percentile 95th of LiDAR data was calculated in an area of radius 1.5 m, being 0.48 and 1.45 kg, respectively. For this radius, it was found that for the stands (n = 39) where the DTM is calculated with high accuracy (RMSE lower than 0.20 m) and with a high density of LiDAR data (more than 8 points/m²) the R² value was 0.73. These results show the possibility of estimating shrub biomass in small areas when the density of LiDAR data is high and errors associated to the DTM are low. These results would allow us to improve the knowledge about shrub behavior avoiding the cost of field measurements and clear cutting actions.     

Growth,stem quality and nutritional status of Betula pendula and Betula pubescens in pure stands and mixtures

The growth, technical quality and nutritional status of pure and mixed silver birch (Betula pendula Roth) and downy birch (Betula pubescens Ehrh.) plantations were studied 21 and 22 years after planting on afforested organic soil arable land and on upland forest soil. In mixtures, 50% of both birch species was planted. Silver birch trees grew better, but had higher mortality than downy birch trees on both sites. Mortality of both species was highest, and the difference in their growth smallest, on organic soil. In pure stands on organic soil, downy birch dominant height, diameter and mean volume were 96%, 92% and 82% of those of silver birch and on mineral soil 87%, 84% and 60%, correspondingly. On mineral soil, silver birch had a higher mean annual increment (MAI) (5.8 m³ ha^?1a^?1) than downy birch (3.9 m³ ha^?1a^?1), but on organic soil the MAI of both species was similar (3.3–3.4 m³ ha^?1 a^?1). Planting birches in mixture did not affect the growth of the trees on organic soil. On mineral soil, the mean diameter and mean volume of silver birch trees were higher in mixed than in pure plantations. The technical stem quality of both tree species was low. On mineral soils, pure silver birch is more productive than mixture, but on peat soil the higher growth of silver birch could contribute to increased productivity and downy birch would ensure sufficient survival for future timber production.     

Effect of gap size on mid-rotation stand structure and species composition in a naturally regenerated mixed broadleaf forest

This paper is an assessment of the effect of gap size on stand structure and species composition 48 years following treatment in a mixed broadleaf upland forest. Established in 1960, the study tests three circular openings, 15.2 m (0.02 ha), 45.7 m (0.16 ha), and 76.2 m (0.46 ha). Forty-eight years following treatment (2008) basal area, top height, and quadratic mean diameter were significantly lower in 15.2 m openings. Maple (Acer spp.) species had the highest mean importance value across treatments (0.40). Trends suggest that species composition of dominant and codominant trees among opening sizes may have been influenced by shade tolerance adaptations of the species groups present. Whereas 15.2 m openings were dominated by shade tolerant maple species, 45.7 and 76.2 m openings produced a mixture of commercial species including shade intolerant species such as yellow-poplar (Liriodendron tulipifera L.), trees of intermediate shade tolerance like oak (Quercus spp.), and shade tolerant maple. Data further suggest the density of overstory oak was highest in the intermediate opening size (45.7 m), while yellow-poplar increased in the larger opening sizes. Evaluation of species shifts between 1981 and 2008 showed that relative basal area of maple increased across all treatments. Relative basal areas from 45.7 to 76.2 m openings suggest declines in yellow-poplar and other non-commercial species were balanced by increases in oak and maple.     

Comparing volume growth in pure and mixed stands of Pinus sylvestris and Quercus pyrenaica

? In Mediterranean forestry, it is important to improve knowledge about mixed stands dynamics, including their productivity. Previous studies have focused on the interactions between different species (competition, reduction of competition and facilitation) depending on site, species composition and structure.

? At the centre of this research are the possible differences between pure and mixed stands of Pinus sylvestris and Quercus pyrenaica in terms of density-growth relationships and volume growth per species.

? Using data from the second and third Spanish National Forest Inventory (606 plots), volume increment models for these species were fitted. Both species displayed a similar density-growth pattern for pure and mixed stands, with a maximum volume growth at maximum density. Volume increment per occupied area was also found to be greater in mixed stands as opposed to pure stands, suggesting a species interaction with reduced levels of competition in the former. However, the total volume growth was generally lower in mixed stands since the growth rate of oak is much lower.

? The results highlight the expedience of favouring P. sylvestris-Q. pyrenaica mixed stands with higher proportions of pine trees in order to gain the benefits of a more complex forest whilst retaining an acceptable level of wood production.

     

Effect of silvicultural practices on fibre properties of Eucalyptus wood from short-rotation plantations

The effect of nitrogen addition and weed management on fibre properties of wood from 6.5-year-old Eucalyptus grandis and E. tereticornis from intensively managed short-rotation plantations were investigated. Trees for analyses were sampled from plots with zero nitrogen input (n = 4), plots with high level (187 kg N ha^?1) nitrogen input (n = 4), plots from which weed growth was not removed throughout the rotation (n = 4) and plots from which weeds were removed periodically (n = 4). Fibre characteristics were evaluated on wood samples collected from base, breast height, 50, 75 and 100 % of merchantable bole height of trees. Though N input and weed management improved tree growth significantly irrespective of species, the treatment effects did not cause any significant change in fibre characteristics such as fibre length, fibre diameter, lumen width and wall thickness. Longest and widest fibres were observed at the outer most radial portion of wood in all cases. In general, within tree fibre length varied significantly along the radial direction of wood. Fibre diameter, lumen width and wall thickness lacked any specific pattern between species and treatments. Runkel ratio and felting and flexibility coefficients values showed high pulping quality of wood irrespective of species and treatments. The study concluded that the fibre properties that influence pulpwood quality of Eucalyptus have not been affected by silvicultural practices, like fertilizer input and weed management, aimed at improving productivity of short-rotation eucalypt plantations.