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The effect of logging in natural forests
... Instead, crawler tractor operators simply search the area for commercial trees to harvest (Pinard et al., 2000b). Hence, previous studies have shown that up to 50% larger areas of forest ground may be damaged during CL operations that when RIL methods are applied (Bertault and Sist, 1995;Pinard et al., 2000b). ...
Rainforests in Southeast Asia are enormously important, both ecologically and socio-economically, but their sustainability is severely threatened by various forms of disturbance that perturb the dynamics of forests here and elsewhere. To help efforts to counter such threats, this thesis focuses on two of the most important forms of disturbance that currently affect tropical rainforests: logging and extreme climatic events. It is based on research conducted in the Gunung Rara Forest Reserve, in Sabah, Malaysia (approx. 4°33´N, 117°02´E). The project started in 1992 in a mixed dipterocarp lowland rainforest, involving establishment of a long-term experiment with a 2 x 2 factorial randomized block design, where slope was the blocking factor. Two selective logging methods, supervised logging (SL) and conventional logging (CL), both with (CC) and without (NCC) pre-harvest climber cutting, and a control treatment (C), were applied to evaluate their effects on key parameters of forest dynamics, including: ingrowth of new trees (≥ 10 cm diameter at breast height, DBH), growth of standing trees (survivor growth), tree mortality, and overall development of the stands. Analysis of data covering 18 years of subsequent stand development shows that SL with CC resulted in consistently higher stand volume recovery and ingrowth of dipterocarps, while suppressing establishment of pioneer species by up to 40%, compared to either CL treatment, especially at high harvest intensities In addition, CC reduced overall mortality, suggesting that it can effectively reduce negative effects of harvest operations. Using linear mixed effect models, I also found that the stand level growth rate of dipterocarps was two times higher following SL with CC than following the CL treatment. Furthermore, diversity patterns of naturally regenerating trees (≥ 10 cm DBH) were studied over 10 years after selective logging, using the gradient of harvest intensity (0-16 trees ha-1). Species richness peaked at intermediate levels of extraction, corroborating the intermediate disturbance hypothesis (IDH), and suggesting that moderate levels (< 8 trees ha-1) of harvesting may maintain tree biodiversity. Finally, I studied the effects of El Niño Southern Oscillation events on uncut forests and found that both the intensity and duration of these events strongly influenced the forest dynamics. However, long periods of moderate-intensity El Niño-associated drought had stronger effects on tree mortality and subsequent growth of survivor trees than peak intensities. The results also indicate that cumulative effects of multiple events, rather single events, should be considered. However, although fluctuations in basal area were observed over 19 years of repeated events, the findings suggest that the uncut tropical rainforest was quite resilient and has fairly good capacity to withstand repeated extreme climatic fluctuations
... Ž . 1990;Bertault and Sist, 1995 ; iii the non-conformity and relative brevity of the periods studied also pose a problem because short-term forest dynamics Ž . is influenced by climatic events; iv lastly, the accuracy of the increment measurements is not the same in the two compartments: it is about 10 times better in compartment B, a point which can partly explain the strong dispersion of the data from compartment A. ...
Within the framework of a programme on the functioning of dense moist evergreen forests of the Western Ghats, the French Institute of Pondicherry, in collaboration with the Karnataka Forest Department, installed permanent plots to monitor the dynamics of a low elevation forest. The preliminary results of the comparison of the demographic processes in two compartments are presented: one compartment had never been harvested, while the other was selectively felled in 1979–1980. They are compared in terms of species composition, recruitment, mortality and individual growth, in order to describe the natural forest dynamics and evaluate the impact of selective felling. In both compartments, the mortality rate, around 0.9% yr−1, is lower than in other tropical moist evergreen forests, while the average diameter increment, at 2.1 (unlogged stand) and 2.9 mm yr−1 (logged stand), is higher. The impact of selective felling, 10 to 15 years after the harvest, is mainly noticeable: (i) on mortality of trees with dbh>40 cm belonging to lower canopy and intermediate stratum species which died about four times more in the logged compartment; and (ii) on diameter increment of emergent and upper canopy tree species whose growth is still stimulated by about 50%. Despite the general trend of a reduction in the difference between the density and the basal area of the two compartments, medium-term modification of the demographic processes among the various structural ensembles in the logged compartment, indicates that selective felling may not be sustainable in the long-term without consequences on the forest structure and composition.
... Forest within the study area is designated a permanent production forest, and is managed for timber according to the Indonesian Selective Cutting and Planting (TPTI) system. Approximately 10 trees per ha are removed, but up to 50% of the trees left remaining in the stand may be damaged or destroyed during extraction, leaving behind a mosaic of undisturbed and disturbed patches of forest (Bertault and Sist, 1995). ...
Hemispherical canopy photographs are now widely used to estimate the proportion of above canopy PPFD (photosynthetic photon flux density) that is transmitted to the forest understorey. Some studies have obtained good results, while others have found that predictions are not always independent of forest type or condition, and that errors are sometimes large beneath very dense canopies. Lack of repeatability can make it difficult to compare sites, studies, or photographs taken at different times. In this study the method for calibrating predictions from photographs was tested in logged and undisturbed tropical broadleaf forest in Borneo, during both the wet and dry seasons. During the dry season a regional smoke ‘haze’ caused by widespread forest fires provided very uniform diffuse conditions and thus a unique test of the calibration. Total transmission (the ‘global transmission factor’, Tt) was modelled as the weighted average of direct and diffuse transmission, with the weighting on diffuse transmission (fd′) determined as the value which maximised the correlation between Tt and measured PPFD. fd′ is an indirect measure of fd, the actual proportion of above canopy PPFD that is diffuse. fd′ should increase with cloudiness or smoke haze. Accurate determination of fd′ is important for prediction of transmission over short time-scales, such as days or weeks. fd′ was modelled for each day and was correlated (r2 = 0.65) with daily shadow band measurements of the above canopy diffuse component during the wet season. During the dry season, fd′ initially decreased with the expected increase in sunshine hours, then the smoke haze halved above canopy PPFD and fd′ increased from less than 0.5 to 1.0, thus validating this method of calibration. After calibration, predictions of Tt from photographs in logged forest were repeatable, accurate (r2 > 0.96) and linear for sites with PPFDs ranging from less than 5% of above canopy PPFD to sites with more than 50% of above canopy PPFD. fd′ modelled from monthly or longer averages of transmission factors and PPFD was within 0.12 of fd. Results were more variable (r2 = 0.68) if calibration was based on data from undisturbed forest only. Overall accuracy and repeatability between sites were attributed to increased digitised image resolution, the use of a spot meter with a narrow field of view to set photograph exposure times, and other improvements in methodology.
Penelitian keragaman jenis tumbuhan (pohon) tingkat pancang pada kawasan bekas pembalakan dengan sistem konvensional dan Reduced Impact Logging (RIL) di PT. Inhutani I Labanan dilakukan pada dua buah plot masing masing seluas satu hektar, yang dibagi menjadi sub plot seluas 5 m x 5 m. Semua jenis pancang yang berukuran diameter kurang dari 10 cm dan tinggi ≥ 1,5 diidentifikasi dan diukur. Data dikumpulkan sebelum dan sesudah penebangan. Tujuan penelitian untuk mendapatkan informasi tentang keragaman dan komposisi jenis-jenis pohon tingkat pancang yang masih tertinggal dalam tegakan tinggal setelah kegiatan pembalakan dengan sistem pembalakan ramah lingkungan (RIL) dan konvensional. Hasil penelitian memperlihatkan bahwa terjadi penurunan jumlah suku 6,25 %, genus 6,78 %, dan jenis 5,4 % pada sistem pembalakan ramah lingkungan; dan penurunan genus 12,79 %, jenis 3,60 % pada sistem konvensional. Penurunan 31,26 % semua jenis sesudah pembalakan dengan RIL dan 24,6 % dengan sistem konvensional. RIL menyebabkan kerusakan yang lebih tinggi dibandingkan dengan sistem konvensional.
We introduce a volume recovery index (VRI), the fraction of inventoried (alternatively felled) tree volume that can be recovered and commercialized. The new index improves on the traditional marketing coefficient used in the Congo Basin, through a systematic assessment of wastage at logging and preprocessing stages. Statistically, the new index is more reliable: its two proposed versions are both accurate (absence of bias) and precise (small mean square error). Practically, VRI gauges the ATO/ITTO indicator 2.3.4 stating that “[wastage should be] minimized at all stages of production and processing”. VRI actually encapsulates three sub-indicators of that indicator and complements a fourth sub-indicator on using “felling methods [that] optimize the volume of usable timber”. Thus, VRI is useful in assessing the ecological and socioeconomic sustainability of timber production of all forest types, with particular relevance for reduced-impact logging (RIL) and carbon (or biomass) storage. We examine the qualities of VRI as sustainability indicator, set forth a principle for sustainable logging, and discuss the limitation effects of (i) ecology (species growth conditions, spatial distribution, and stand structure), (ii) management (polycyclic logging, species selection and diversification, logging operations, logging intensity, and conservation constraints) and (iii) policy (legislation on timber processing and export products, incentive allocation, property rights definition and enforcement) on volume recovery, together with possible remedies. We recommend: (i) using the spatialized VRI jointly with other pressure indicators in discriminating between genuine environmental limitations and mining exploitation; (ii) adopting RIL techniques to their fullest potential, given current low logging intensities in Congo Basin; (iii) allowing transfer of user rights in salving damaged trees and low quality timber; (iv) promoting recovery and utilization of residue to increase timber transformation rate, curb resource dissipation, reduce the rate of desertification, improve distribution of forest benefits, and contribute to poverty alleviation.
Tropical rain forests are widely regarded as being very ancient climax ecosystems composed of highly specialized organisms.
This has encouraged a view that they are potentially extremely fragile and that human intervention will inevitably lead to
their destruction. As a consequence, many of those who are concerned about the loss of this important ecosystem have campaigned
against the use of tropical rain forests for timber production. Despite this pressure, it is almost certain that within the
next few decades virtually all tropical rain forest not set aside exclusively for conservation will be logged. This chapter
examines the assertion that tropical rain forests are fragile and that their use for timber production is ecologically incompatible
with their conservation. The process of natural regeneration in tropical rain forests is reviewed in order to understand the
likely consequences of a logging operation.
In East Kalimantan (Indonesia), impacts of conventional (CNV) and reduced-impact logging (RIL) on forest ecosystems were compared on the basis of pre- and post-harvesting stand inventories. There was a positive and significant correlation between the proportion of trees damaged by felling and the density of trees felled. Logging intensity ranged from 1 to 17 trees ha−1(9–247 m3 ha−1) and averaged 9 trees ha−1 (86.9 m3 ha−1). The study has shown that with RIL techniques, logging damage on the original stand can be significantly reduced by 50% compared with conventional logging. However, this 50% reduction in logging damage, was dependent on the felling intensity. With a felling intensity of 8 stems ha−1 or less, RIL techniques only damaged 25% of the original tree population whereas 48% were damaged with conventional techniques. Above this felling intensity (i.e. 8 stems ha−1), the effectiveness of RIL in limiting forest damage was significantly reduced, mainly because of the increasing felling damage. Moreover, the removal of all harvestable timber trees, leaving only few potential crop trees, will result in a seriously depleted residual stand. Because of the high damage involved by high felling intensity, leaving few potential crop trees, and the yield capacity of the remaining stand, acceptable harvesting volume will not be reached within the felling rotation of 35 years. It is concluded that silvicultural system based on diameter limit alone, as is the Indonesian system (TPTI), cannot be compatible with sustainability and more sophisticated harvested-selection rules are needed.
Timber harvesting was investigated both in terms of commercial timber volume extracted and impact on residual stand. Conventional (CNV) and reduced impact logging (RIL) techniques were compared on the basis of pre- and post-harvesting stand inventories. The timber volume extracted averaged 87 m3 ha−1 and the resulting commercial volume was 46 m3 ha−1 (i.e. 53.7% of the felled volume). On average, logging damage affected 40% of the residual trees (diameter at breast height (dbh) over 10 cm); injured and dead trees were recorded in equivalent proportions (21% and 19%, respectively). Generally, felling operations caused injury to trees, crown damage being most common, whereas skidding caused death to trees, essentially by uprooting. Tree injury and death from RIL in contrast, was substantially lower (30.5%) than from conventional methods (48.1%). This study demonstrated that the impact of logging on trees can be substantially reduced by strict supervision and planning of logging operations and limit of harvesting intensity, which should not exceed 80 m3 ha−1. If these technical recommedations are followed, it is possible to reduce the damage by 20% which is equivalent to about 100 stems ha−1 (dbh over 10 cm).
"Selected Proceedings of an International Workshop 17-19 November 1997" Incluye bibliografía
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