Felling Cycle Research Articles

Evaluation of the management potential of timber resources in clearwater floodplain forests in the Amazon using growth models

The Amazonian clearwater igapós are poorly studied floodplain ecosystems that are mainly covered by forests and are undergoing massive threats due to changes in land use and climate. Their hydrochemical characteristics and edaphic conditions fall between those of the eutrophic várzea floodplains on whitewater rivers and those of the oligotrophic igapós on blackwater rivers. Previous studies have indicated the management potential of timber species in the highly dynamic várzea floodplains due to the fast tree growth and high forest productivity. Timber resource management, however, is not recommended for the blackwater ecosystem because of its slow dynamics and high vulnerability to disturbances. For clearwater igapós, information on the potential for sustainable management of timber resources is lacking. In this study, we modeled the growth in diameter, height, and volume to derive species-specific minimum logging diameters (MLD) and felling cycles (FC) for eight merchantable species in the clearwater igapós of the Branco and Tapajós rivers in the northern and southern Amazon Basin, respectively. Diameter growth was modeled by analyzing the tree rings that are annually formed in the Amazonian floodplains as a consequence of the regular and predicable long-term flooding. Growth modeling followed the guidelines of the Growth-Oriented Logging (GOL) concept, with the adjustment of diameter growth improved by applying nonlinear mixed-effects regression. MLDs varied from 36 to 90 cm and FCs ranged from 6 to 21 years, which diverges from the standards of Brazilian logging regulations (MLD: 50 cm; FC: 25–35 years). This indicates the potential for timber resource management, which should be tested and introduced at small scales, integrated in protected areas to stepwise promote the sustainable management of these natural resources by traditional communities to increase their income and the conservation of this ecosystem.

Turberaied ja nende ökonoomiline hindamine pohla kasvukohatüübi männiku näitel

Abstract The article provides an overview of the experience of using shelterwood systems in Estonia and the methodological aspects of their economic assessment. The methodology is tested with calculations made on the management alternatives of pine (Pinus sylvestris L.) stand in Rhodococcum site type. Based on the Estonian forest management rules and the results of previous silvicultural studies, the management models were elaborated for different types of shelterwood harvesting. The difference model was used when predicting stand development, the actual prices of different wood assortments and the actual cost of management activities were used in calculations. The net present value of cash flows is used as a criterion, which allows comparing management periods of different lengths. Calculations were performed for three different periods: one regeneration felling cycle, two regeneration felling cycles and perpetual management cycles. The results of different types of shelterwood systems are compared with the results of clear-cutting scenarios. The calculations indicate that in the short term, the net present value of the different types of shelterwood harvesting and clear-cutting are quite similar. The results of the first cycle of regeneration felling are most affected by the costs of cultivation and tending of a plantation and young forest. In the long run, clear-cutting will have an advantage over shelterwood harvesting, as the stand regeneration period is shorter.

Follow the forest: Slow resilience of West African rainforest frog assemblages after selective logging

Assessing resilience of ecological communities, the ability of species assemblages to return to a previous state following disturbance, is an essential task when designing biodiversity friendly concepts for silvicultural management regimes. However, ecological communities may demonstrate resilience only after long time periods, and long-term data, collected on permanent study sites within standardized sampling frameworks, are scarce. We assessed the resilience of amphibian assemblages to disturbance via selective logging within the largest remaining rainforest in Ivory Coast, the Taï National Park. We analyzed extensive amphibian and habitat data obtained during two major assessment periods > 15 years apart (period P1 = in 2000, period P2 = in 2016–2017) and spanning 45 years post-logging recovery (period P1 = 30 years post-logging). We revisited identical sites and used identical, standardized methodology in both study periods. Forest structure in formerly selectively logged sites slowly recovered towards old growth forest structure over the course of 45 years, with most visible changes occurring between P1 and P2. While species richness and diversity in both old growth and secondary forests remained largely unchanged across the study periods, frog assemblage composition in formerly disturbed sites followed the forest recovery process. Yet, their composition was still distinctly different from old growth forest assemblages. The different levels of resilience over time indicate that the slowest organisms in our system (forest trees) set the pace for the recovery of associated taxa (frogs). Effective post-harvesting restoration schemes need to incorporate these delayed response times. Thus, significantly longer felling cycles than those commonly applied in regular harvesting schemes are needed if the goal is to conserve and restore original forest diversity in logged forest ecosystems.

Measures for sustainable forest management in the tropics – A tree-ring based case study on tree growth and forest dynamics in a Central Amazonian lowland moist forest

The conservation of tropical forests is recognized as one of the most important challenges for forestry, ecology and politics. Besides strict protection, the sustainable management of natural forests should be enhanced as a key part of the foundation for the maintenance of tropical rain forest ecosystems. Due to methodological reasons it has been complicated to attain reliable growth data to plan sustainable felling cycles and rotation periods. Tree ring analyses enable the estimation of growth rates over the entire life span of trees and their age as well as giving hints from forest dynamics in previous centuries. For tree ring analysis, stem disk samples were taken from three important commercial tree species (Cariniana micrantha, Caryocar villosum and Manilkara huberi) in the upland (terra firme) forests of the Precious Woods Amazon logging company near Itacoatiara, Brazil. Based on radiocarbon estimates of individual growth zones, the annual nature of tree rings was proven for the three species. Tree rings were measured and the results used together with height estimates to model diameter, height and volume growth. The age of the eldest tree, a C. micrantha, was 585 yrs with 165 cm in diameter. The species’ diameter increments range from 0.20±0.12 cm yr-1 to 0.29±0.08 cm yr-1. At first sight, this is considerably lower than increments reported from other Amazonian or African timber species. Considering the respective wood density there is no significant difference in growth performance of dominant timber species across continents. The interpretation of lifetime tree ring curves indicate differences in shadow tolerance among species, the persistence of individuals in the understory for up to 150 years and natural stand dynamics without major disturbances. Management criteria should be adapted for the measured growth rates as they differed considerably from the Brazilian standards fixed by laws (felling cycle of 25–35 years and a common minimum logging diameter of 50 cm). Felling cycles should be increased to 32–51 years and minimum logging diameters to 63–123 cm depending on the species.

Growth models for two commercial tree species in upland forests of the Southern Brazilian Amazon

Despite all efforts to promote sustainable use of timber resources in tropical forests, the current management criteria still require adjustments at a species level, considering specific growth patterns and ecological features. Forest management in upland forests (terra firme) of the Brazilian Amazon region generally applies for all commercial tree species a common minimum logging diameter (MLD) of 50 cm and a felling cycle (FC) varying according to the harvest intensity between 25 and 35 years.. In this study, we define species-specific FCs and MLDs for the two commercial tree species Hymenaea courbaril L. (Fabaceae) and Handroanthus serratifolius (Vahl) S.O. Grose (Bignoniaceae) from the terra firme of the Southern Brazilian Amazon, applying growth models based on the relationships between estimated tree age, diameter, height and volume. A total of 37 transversal cross-sections (20 stem discs from Hymenaea and 17 from Handroanthus) were obtained at a height of 20–60 cm above soil level in a private forest concession close to the municipality of Novo Aripuanã in the southern region of the Amazonas state. The two species are common in terra firme forests and have high wood densities of 0.76–0.96 g cm−3 (H. courbaril) and 0.85–1.08 g cm−3 (H. serratifolius). The mean age of H. courbaril and H. serratifolius, estimated by ring counting, varied from 104 to 241 years and both species had similar mean diameter increments of 3.9 ± 0.5 mm year−1 and 4.1 ± 0.6 mm year−1, respectively. Both species present similar tree growth in diameter, height and volume resulting in a FC of 24.2 years and a MLD of 64.9 cm for H. courbaril, and a FC of 26.0 years and a MLD of 69.5 cm for H. serratifolius. These results demonstrate the need to adjust the selective logging systems practiced in the Brazilian Amazon region towards a species-specific management of timber species to increase the sustainability of selective logging.

Volume increment modeling and subsidies for the management of the tree Mora paraensis (Ducke) Ducke based on the study of growth rings

First study that demonstrated the formation of annual growth rings in Amazonian Estuary trees. Growth patterns of Mora paraensis and specific management criteria, such as felling cycle, are presented. The aim of the present study was to contribute to increased sustainability in the timber management of Mora paraensis, through the estimation of minimum logging diameter (MLD) and felling cycle, using volume increment models based on tree-ring analysis and allometric relationships. We collected stem discs from 17 trees of five diameter classes. The diameters and heights of the trees were also measured. We estimated tree ages by ring-counting and the radial increment rates by measuring the ring widths with a digital analysis system. We built growth models based on relationships between age, diameter and tree height to estimate volume increment along the tree’s whole life cycle. The maximum current diameter increment in M. paraensis occurs at an age of around 26 years, reaching 4.91 mm year-1. The MLD was 46.4 ± 0.6 cm (standard error), which trees achieve at an age of about 115 years. The felling cycle, estimated by the mean passage time through 10 cm diameter classes until achieving the MLD, was 24.7 ± 1.3 years. These results corroborated the norms of the current Brazilian legislation that regulates forest management of high intensity in the Amazon basin. In future, more specific growth models are needed for other commercial tree species in the Amazonian Estuary to define the optimal harvest rate to maintain sustainable timber resource management practices. Through such practices, the conservation of these ecosystems and their multiple services and functions, as well as the welfare of the forest-dependent human populations can be secured.

Mortality of stocking commercial trees after reduced impact logging in eastern Amazonia

Forest harvest causes disturbances in the forest and affects the mortality of residual trees. The effects of this activity on trees of the residual stocking for future felling cycles are poorly known in post-harvest situations. Detecting mortality patterns and comprehending the factors that rule the post-harvest tree mortality may offer important subsidies for future sustainable harvests. In this study, the mortality of trees under Reduced Impact Logging (RIL) was assessed in a chronosequence of 13years in logging areas (2002–2015) in eastern Amazonia. The data were collected in five Units of Annual Production (UAP) and in a control plot. In each UAP, a Working Unit (WU) of 100ha was divided into 20 plots of 50m×1000m (5ha). Trees≥45cmDBH were inventoried one year before forest harvest and again in 2015. The mortality rates were calculated and compared among: (a) ecological groups; (b) different logging intensities and (c) diameter classes. The mortality rate is higher in the first five years (5.87%) and the effects of RIL are perceived up to seven years post-harvest (3.18%). The logging intensity, 3–40m3ha−1, did not affect the mortality of trees≥45cmDBH. Pioneer species are more susceptible to impacts of forest harvest than species of other ecological groups. In RIL plots, as well as in the non-logged plot, the mortality rate was not influenced by the size of trees≥45cmDBH.

Recruitment, growth and recovery of commercial tree species over 30 years following logging and thinning in a tropical rain forest

Sustainable production of timber from commercial species across felling cycles is a core challenge for tropical silviculture. In this study, we analysed how the intensity and type (harvesting and thinning) of silvicultural interventions affect: (a) recruitment of small stems (5cm⩽DBH<15cm), (b) increment of future crop trees (15cm⩽DBH<50cm) and (c) recovery of harvestable growing stocks (DBH⩾50cm) of 52 commercial timber species in the Tapajós National Forest, Brazil. Intervention intensities comprised logging (on average 61m3ha−1) and associated damage to remaining trees (1982) and thinning (refinement) to reduce basal area at the stand level (1993/1994). These interventions together resulted in a gradient of reduction in basal-area from 19 to 53% relative to pre-logging stocks. Trees (DBH⩾5cm) were measured on eight occasions in 41 permanent sample plots of 0.25ha each. The dynamics were analysed at the stand level over 30years and compared among treatments (including unlogged forest) and to pre-logging stands. Recruitment and growth temporarily increased following interventions and recovery of harvestable growing stock decreased with intervention intensity. Harvesting substantially increased recruitment of small stems relative to the unlogged forest, but recruitment rates decreased over time and did not increase following thinning. Gross increment of future crop trees was higher in logged than in unlogged forest and increased over time with high intensity of follow-up thinning, where it remained significantly higher than in control plots over time. Increased recruitment rates and volume increments were mainly driven by long-lived pioneer species, changing the composition of the growing stock. In 2012, recovery of harvestable growing stock of the 22 species harvested in 1982 varied between 19% and 57% in logged treatments relative to pre-logging levels. When considering an additional group of 30 species that were not harvested in the permanent sample plots but are now potentially commercial, relative recovery increased enough to support a second harvest under the present regulations (maximum harvest of 30m3ha−1), except for treatment with high thinning intensity where stocks were still less than 30% relative to pre-harvest levels. In contrast, light and medium thinning intensity promoted recovery of harvestable growing stock. These findings indicate that intensive thinning should be avoided and silvicultural interventions oriented towards future crop trees of target species should be adopted. This may enhance recovery and reduce unintended changes in composition of the commercial growing stock.

Short term impact of selective logging on a western lowland gorilla population

Selective timber production is implemented over a large proportion of the world’s tropical forests. Within these forest ecosystems, the frugivore community contributes important ecological services through animal-mediated seed dispersal. However, there is no clear understanding of the impacts of logging on wildlife or of the extent to which seed dispersal is preserved in logged forests. Given its tendency for nesting in light gaps, the western lowland gorilla is likely to provide directed-dispersal services to a wide range of tree species. Production forests preserved from poaching have been reported to harbor high densities of gorillas, but the monitoring of gorilla populations subjected to logging is poorly documented. This study investigated gorilla density and nesting behavior after timber exploitation in a logging concession in southeast Gabon. Nest count censuses were performed on line transects, before and after the second felling cycle. Gorilla density dropped from 1.5 (116.7 nests km−2, 95% CI=83.4–163.5) to 1.0 (64.9 nests km−2, % CI=32.6–129.5) weaned gorilla km−2 4–6months after logging, then rose to 2.6 (176.3 nests km−2, 95% CI=113.5–274.1) gorillas km−2 9–11months after logging. A consistent preference for nesting in open canopy terra firma forest was observed during all censuses. This study demonstrates the short-term resilience of the western lowland gorilla to selective timber harvesting, and argues that they offer a continued contribution to directed-dispersal services within months after logging. Although a long-term monitoring of gorillas in a logged forest should be undertaken, the role of this species in logged forest recovery is thought to be important. The preservation of gorilla should receive particular consideration by forest managers.

Tropical forest recovery from logging: a 24 year silvicultural experiment from Central Africa

Large areas of African moist forests are being logged in the context of supposedly sustainable management plans. It remains however controversial whether harvesting a few trees per hectare can be maintained in the long term while preserving other forest services as well. We used a unique 24 year silvicultural experiment, encompassing 10 4 ha plots established in the Central African Republic, to assess the effect of disturbance linked to logging (two to nine trees ha−1 greater than or equal to 80 cm DBH) and thinning (11–41 trees ha−1 greater than or equal to 50 cm DBH) on the structure and dynamics of the forest. Before silvicultural treatments, above-ground biomass (AGB) and timber stock (i.e. the volume of commercial trees greater than or equal to 80 cm DBH) in the plots amounted 374.5 ± 58.2 Mg ha−1 and 79.7 ± 45.9 m3 ha−1, respectively. We found that (i) natural control forest was increasing in AGB (2.58 ± 1.73 Mg dry mass ha−1 yr−1) and decreasing in timber stock (−0.33 ± 1.57 m3 ha−1 yr−1); (ii) the AGB recovered very quickly after logging and thinning, at a rate proportional to the disturbance intensity (mean recovery after 24 years: 144%). Compared with controls, the gain almost doubled in the logged plots (4.82 ± 1.22 Mg ha−1 yr−1) and tripled in the logged + thinned plots (8.03 ± 1.41 Mg ha−1 yr−1); (iii) the timber stock recovered slowly (mean recovery after 24 years: 41%), at a rate of 0.75 ± 0.51 m3 ha−1 yr−1 in the logged plots, and 0.81 ± 0.74 m3 ha−1 yr−1 in the logged + thinned plots. Although thinning significantly increased the gain in biomass, it had no effect on the gain in timber stock. However, thinning did foster the growth and survival of small- and medium-sized timber trees and should have a positive effect over the next felling cycle.

Silvicultural disturbance has little impact on tree species diversity in a Central African moist forest

Timber production is an important economic sector in most forested countries of Central Africa, where about 14 million hectares of lowland moist forests are now planned for management. This production is expected to be sustainable, but the actual impact of logging on biodiversity is still questioned.To answer this question, we used a unique long-term controlled experiment implemented more than 20years ago in an old-growth semi-deciduous moist forest of the Central African Republic (CAR). We tested whether (i) anthropogenic disturbances associated with silvicultural operations had an effect on the composition and diversity of tree communities, and (ii) there is a relationship between diversity and disturbance intensity in those forests.For this, we botanically identified all trees⩾10cm DBH in 28 1-ha plots where no treatment (controls), logging and logging+thinning operations were implemented 24years ago and created a strong gradient of disturbance. We investigated the relationships between five diversity indices and a disturbance index calculated for each 1-ha plot, for all species and separately for three regeneration guilds.We found a strong positive monotonic relationship between the intensity of disturbance and the percentage of pioneer species in the tree communities, which proved to be equally detrimental, in terms of relative abundance, to the non-pioneer light-demanding and the shade-bearing species.Overall, disturbance appeared to have a weak monotonous negative effect on diversity, irrespective to the index considered. The diversity of shade-bearers slightly decreased along the disturbance gradient without significant decrease in species density; disturbance had no effect on non-pioneer light demanders, but a clear significant negative effect on the diversity of pioneers, with a significant decrease in species density. This negative effect was associated with the massive recruitment of the early-successional, fast-growing Musanga cecropioides R. Br. (Urticaceae), which rapidly preempted space and resources in the most disturbed plots. Despite this effect, disturbance did not significantly affect the local heterogeneity in species distribution.These results suggest that the semi-deciduous moist forests of CAR are locally resilient to small-scale disturbances associated with silvicultural operations. This may be a consequence of the past anthropogenic and/or climatic disturbances, which have been stronger and more long-lasting than elsewhere within the tropical forest biome, and would have removed the most vulnerable species. Because logging intensity in these forests is usually low, we do not expect any direct major impact on tree species diversity, at least after the first felling cycle.

La stratégie de modélisation empirique « cohort » et son application pour l¿aménagement de la forêt de Tapajós, Pará, Amazonie brésilienne

La stratégie de modélisation empirique est ici revue et présentée ainsi que son application à l'Amazonie orientale. Le modèle de croissance Cafogrom élaboré au cours de la période 1994-1998 a pu être testé grâce aux récentes mesures de 2003 et 2007 en Forêt nationale de Tapajós dans deux zones expérimentales dénommées km67 et km114 au long de l'autoroute BR 163 reliant Santarém à Cuiabá. Le modèle montre un accroissement annuel de la forêt avec un écart annuel de moins de 15 % au cours de la période 1981-2007 sur le km67 et avec la même précision sur km114, un site moins productif, mais avec un biais accru de sous-estimation d'environ 32 % en 26 ans. L'accroissement moyen annuel du volume des arbres de plus de 50 cm de diamètre (DBH) a été de 2,2 m3/ha/an en 26 ans, dont 1,2 m3/ha/an (54 %) pour les essences commerciales. Les parcelles étudiées sur le site km114, le moins productif, ont eu un accroissement moyen de 1,07 m3/ha/an au cours de vingt ans couvrant la période 1983-2003. En considérant les règles du gouvernement brésilien dont l'intensité maximale d'exploitation est de 30 m3/ha avec une rotation de passage en coupe de 35 ans (0,86 m3/ha/an), la viabilité de ce régime conservateur est confirmée à condition que l'exploitation comprenne une gamme variée d'espèces commerciales. La stratégie de mise à jour de Cafogrom est détaillée, elle devra être réécrite sous la forme d'une application en langage Python dans le cadre contextuel Myrlin/ Fmt (www.myrlin.org, www.eofmt.com).

Allometry, above-ground biomass and nutrient distribution in Ceriops decandra (Griffith) Ding Hou dominated forest types of the Sundarbans mangrove forest, Bangladesh

The Sundarbans, the world’s largest single expanse of natural mangroves located in southern Bangladesh, is the most productive mangrove ecosystem in the world. Ceriops decandra (Griff.) Ding Hou is the dominant shrub in the strong saline zone of the Sundarbans and is mainly extracted for fuel wood, charcoal and tannin. The harvest of C. decandra has decreased by about 50 % in the Sundarbans during the last 10 years creating a major concern. This study derived allometric models of above-ground biomass and estimated of above-ground standing and harvestable biomass and nutrient stock in C. decandra in dominant forest types (C. decandra and C. decandra–Excoecaria agallocha) in the Sundarbans. Allometric relationships between collar girth (CG) and biomass of plant parts (leaf, branch and stem) were tested using linear, power and logarithmic equations. The power equation was found to be most suitable. The density and the estimated total aboveground biomass of C. decandra in C. decandra and C. decandra–E. agallocha forest types were 33,237 and 965 stems/ha (density) and 33.49 and 14.36 t/ha (biomass), respectively. Also, 13.56 and 6.61 t/ha of harvestable biomass were estimated, from C. decandra and C. decandra–E. agallocha forest types, respectively. Nitrogen, potassium and phosphorus concentrations in the leaves, branches and stems showed significant (p < 0.05) variation. The findings of the present study will help to quantify the impact of present harvesting techniques and alteration of different silvicultural intervention like fixation of felling cycle, felling criterion, and regeneration and slash treatment.

Stock recovery rates are not the panacea to assess timber yield sustainability: Evidence from managed Central African forests

After the change of the forestry laws in six Central African countries in the 1990s, the stock recovery rate—the ratio of the exploitable timber stock at the end of a felling cycle over the initial pre-felling stock—has become the standard index to assess timber yield sustainability. The Dimako formula, that is the legal expression of the stock recovery rate, is not necessarily the best estimate of this index. In particular, it accounts for only a limited knowledge on vital rates, it does not always increase with the diameter cutting limit, and it is negatively sensitive to the number of trees above the cutting limit, which may promote heavy initial logging when assessing forest management over several felling cycles. Here, we show that the Dimako formula can be generalised by using a more detailed model of forest dynamics, or a finer description of logging damage, and we demonstrate that an alternative formula has better properties. We used four species with contrasted initial diameter distribution, inventoried in the Dimako forest, eastern Cameroon, to illustrate the behaviour of alternative formula. If an increased level of details had to be incorporated in the Dimako formula, boosted post-logging growth should be considered at first. Because the stock recovery rate results from the combined influence of the initial dbh distribution of the species, which is a history-dependent feature of the population, and of its vital rates, which is an ecological species-specific feature of the population, its interpretation must at least take account of the autecology of the species. Particular caution must be taken when applying the formula to groups of species rather than to single species. The stock recovery rate alone gives a reductionist insight into yield sustainability.

TIEMPOS Y RENDIMIENTOS DEL APROVECHAMIENTO FORESTAL EN EL SALTO, DURANGO, MÉXICO

Timber harvesting operations in four ejidos in the El Salto region of Durango, Mexico, were analyzed using a time and motion study to determine the operational productivity of manual felling, delimbing, bucking, skidding and mechanized loading. A total of 704 cycles for felling, 900 for mechanical skidding and 1,294 for mechanical loading were timed. The results indicate that the operational productivity in the manual felling cycle is 28.67 m3•h-1. Crane skidding was 19.83 m3•h-1 at an average distance of 43.13 m. Mechanized loading productivity was 35.27 m3•h-1. Productivity was shown to be sensitive to variations in the diameter and length of the trees and logs, as well as the distances found in the work cycles analyzed.

Growth and population structure of the tree species Malouetia tamaquarina (Aubl.) (Apocynaceae) in the central Amazonian floodplain forests and their implication for management

The long-term success of forest management depends primarily on the sustainability of timber production. In this study we analyse the population structure, tree age and wood increment of Malouetia tamaquarina (Aubl.) (Apocynaceae) to define a species-specific minimum logging diameter (MLD) and felling cycle by modelling volume growth. Contrary to other timber species in the nutrient-rich white-water floodplains forests (várzea), M. tamaquarina grows in the subcanopy of old-growth várzea forests. The wood of this species is utilized by local inhabitants in the floodplains for handicraft. In 35 plots of 25 m × 50 m we measured diameter at breast height (DBH) and tree height of all trees taller than 150 cm height. From 37 individuals with DBH > 15 cm we sampled two cores by increment borers to determine the wood density, tree age and diameter increment rates. In the management area of a várzea settlement with about 150 ha recently harvested trees of M. tamaquarina have been recorded and DBH was measured. The species presents an inverse J-shaped diameter distribution indicating that the species is obviously regenerating in the old-growth forests. Tree-ring analysis indicates a mean age of 74.5 years for a DBH of 22.7 cm for a studied population comprising 37 trees with maximum ages of up to 141 years for an individual with a DBH of 45.7 cm. The tree species has low annual diameter increment rates (3.16 ± 0.6 mm) despite a low wood density (0.36 ± 0.05 g cm −3). The volume growth model indicates a MLD of 25 cm and a felling cycle of 32.4 years. In the management area 35 trees with a mean DBH of 24 cm were recorded, similar to the defined MLD. The abundance of trees above the MLD is 2.7 trees ha −1, or 405 trees, when extrapolated to the whole management area. Considering a felling cycle of 32.4 years (annual production unit of 4.63 ha) this results in total of 12.5 harvestable trees, almost three times less than actually harvested. The actual practice of harvesting M. tamaquarina risks the overexploitation of this slow-growing species.

Comparison of two working methods for small tree harvesting with a multi tree felling head mounted on farm tractor

In this study, the efficiency of a small multi-tree felling head, mounted on a farm tractor with a timber trailer was studied, when harvesting small trees for energy in thinnings. Both separate loading and direct loading of the felled trees was studied. Time studies were carried out in a mixed stand of Norway spruce (Picea abies (L.) Karst) and birch (Betula pubescens Ehrh.). The time consumption of the work elements in the different work methods was formulated by regression analysis, where the independent variables were tree size and degree of accumulation. The average size of the harvested trees was 0.035 m3. The time consumption for the harvesting and loading were similar for the two studied methods, 20 minutes per m3 at a tree size of 0.035 m3, but the two methods showed different characteristics for different tree sizes and level of accumulation. The direct loading method had the highest productivity when more than 0.1 m3 were collected in the felling cycle, whereas the separate loading method had the highest productivity when less than 0.05 m3 were collected in the felling cycle. The total effective time consumption for harvesting and forwarding the biomass 300 meters to roadside landing was 27 minutes per m3. The efficiency of the initial felling and collecting of the small trees was the main challenge. Both the harvesting technique and harvesting technology needs further development to provide a feasible production chain for woodfuel from energy thinning.

The stock recovery rate in a Central African rain forest: an index of sustainability based on projection matrix models

The stock recovery rate is used in most natural forests of the Congo Basin to assess logging sustainability. This rate is computed using the so-called Dimako formula. Although this formula has been used for many years now in management plans, its mathematical properties have not been closely reviewed. We show that the Dimako formula corresponds to a Leslie matrix model, and then we propose an extension of it as a Usher matrix model. The stock recovery rate at the end of the first felling cycle for six commercial species in the Central African Republic varied between 21.7% and 99.9%. As felling cycles follow each other, the stock recovery rate converged towards a limit that is the asymptotic stock recovery rate. This limit varies between 27.2% and 158.4% for the same six species. Comparing felling scenarios reveals that increasing the minimum harvest diameter was as efficient at increasing the stock recovery rate at the end of the first felling cycle as decreasing the logging intensity. The results for the other parameters of the felling scenarios varied among species, with changes in the stock recovery rate ranging from 0% to 180% at the end of the first felling cycle, and changes in the asymptotic rate ranging from 0% to 685%.

Influence of Thinning on Soil CO 2 Efflux in Chinemse Fir Plantations

ABSTRACT Forest management is expected to influence soil CO 2 efflux ( F CO 2 ) as a result of changes in microenvironmental conditions, soil microclimate, and root dynamics. Soil F CO 2 rate was measured during the growing season of 2006 in both thinning and non-thinning locations within stands ranging from 0 to 8 years after the most recent thinning in Chinese fir ( Cunninghamia lanceolata (Lamb.) Hook) plantations in Huitong Ecosystem Research Station, Hunan, China. Soil temperature and moisture were also measured to examine relationships between F CO 2 and soil properties. Forest thinning resulted in huge changes in F CO 2 that varied with time since cutting. Immediately following harvest (year 0) F CO 2 in thinning area increased by about 30%, declined to 20%–27% below pre-cutting levels during years 4–6, and recovered to pre-cutting levels at 8 years post-cutting. A similar temporal pattern, but with smaller changes, was found in non-thinning locations. The initial increase in F CO 2 could be attributed to a combination of root decay, soil disturbance, and increased soil temperature in gaps, while the subsequent decrease and recovery to the death and gradual regrowth of active roots. Strong effects of soil temperature and soil water content on F CO 2 were found. Forest thinning mainly influenced F CO 2 through changes in tree root respiration, and the net result was a decrease in integrated F CO 2 flux through the entire felling cycle.

Wood growth of Tabebuia barbata (E. Mey.) Sandwith (Bignoniaceae) and Vatairea guianensis Aubl. (Fabaceae) in Central Amazonian black-water (igapó) and white-water (várzea) floodplain forests

Tree growth is a fundamental indicator for conservation plans of Amazonian floodplain forests. In this study we use dendrochronology to analyze wood growth patterns of Tabebuia barbata and Vatairea guianensis, two tree species occurring in nutrient-rich white-water (várzea, Mamirauá Sustainable Development Reserve, MSDR) and nutrient-poor black-water (igapó, Amanã Sustainable Development Reserve, ASDR) floodplain forests of Central Amazonia. From 20 trees per species and floodplain system (total of 80 trees) growing under a similar flooding regime with a mean inundation height of about 4 m we measured diameter at breast height (dbh). We sampled two cores per tree with an increment corer at the height of dbh to determine wood density (WD), tree age and mean radial increment (MRI) rates. The wood samples were macroscopically analyzed. Both tree species show distinct annual tree rings characterized by marginal parenchyma tissues. MRI was measured by a digital measuring device and WD was determined by the ratio dry mass/fresh volume. MRI of both tree species was significantly higher in the várzea than in the igapó, which can be traced back to the contrasting nutrient status. WD showed no difference comparing both floodplain forest types. Tree ages of a species for the same diameter are more than twofold higher in the igapó than in the várzea. To insure a sustainable harvest, felling cycles in these forests should be adjusted according to rates of growth.