Clearcutting

The system involves clear felling and burning of forest patch that is cropped for a few years and thereafter abandoned for restoring soil fertility.

From: Forest Resources Resilience and Conflicts, 2021

SITE-SPECIFIC SILVICULTURE | Silviculture in Mountain Forests

W. Schönenberger, P. Brang, in Encyclopedia of Forest Sciences, 2004

Clear-Cutting

Clear-cutting is a silvicultural system that removes an entire stand of trees from an area of 1 ha or more, and greater than two tree heights in width, in a single harvesting operation (Figure 5). It can be highly profitable. However, its application in mountain forests often involves unacceptable risks, or impairs landscape values.

Figure 5. A clear-cut and subsequent planting in Austria. On steep slopes clearcutting may lead to serious erosion problems.

Clear-cutting mountain forests can initiate erosion processes which may result in a complete loss of the soil. On a regional scale, higher altitudes in mountain areas usually receive higher precipitation. Steep slopes are prone to surface erosion (gullying, rill erosion), nutrient leaching, landslides, and debris flows. Clear-cutting often contributes to reductions in root strength and soil water-holding capacity, due to soil compaction and reduced transpiration. Moreover, the removal of the forest cover exposes the soil surface to heavy precipitation and large variations in temperature. If natural hazards are to be prevented, the size of clear-cut areas in protection forests must be kept small. Thus, clear-cutting is often not an option.

Unstocked, even slopes steeper than about 30° at high altitudes are prone to avalanche release. If a slope exceeds 45°, snow avalanches can start in canopy gaps exceeding 30 m perpendicular to the contour line. Any rough surface structure, such as a rock, trunk, or tree, reduces the risk of snow movement by creating heterogeneity in the snow layer and ‘nailing’ the snow to the ground. While forests can rarely stop flowing snow avalanches, they are highly effective in preventing avalanche release. Surface roughness is also important for impeding rockfalls. However, in this case, forests serve not to prevent rockfall starting, but rather stop falling rocks.

If clear-cutting is not properly applied as a silvicultural system and is the first step to permanent deforestation, it usually has a negative impact on the fresh water supply. More than half of the world's population relies on clean water from mountains. While the demand is increasing, the supply is endangered. Mountains are the sources of most rivers, and mountain forests help to ensure that the water supply is seasonally balanced and that the water is of high quality. Clear-cutting large mountain forests without restoration cannot, therefore, be considered at all sustainable.

The impact of clear-cutting will obviously depend on the size of the clear-cut area. Large clear cuts in environments with pronounced climatic extremes, where tree regeneration depends on the beneficial effects of adult trees, must be avoided. This means that clear-cutting is not appropriate on very dry, very cold, or very wet sites, as it can lead to failures in stand renewal, even with repeated plantings. A system of small patch cuts is similar to the selection system, whereas leaving seed-dispersing trees to facilitate natural regeneration (the seed tree system) is comparable to the shelterwood system.

Not all damage attributed to clear-cutting is caused by the unwanted side-effects of the silvicultural system itself. The damage may actually be the result of inadequate road construction, of inappropriate site preparation treatments such as burning, or of careless logging practices, which damage the advance regeneration. However, even careful clear-cutting should not be used in those mountain forests where protection from natural hazards is needed, where erosion is a matter of major concern, and where the sites do not restock easily.

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TEMPERATE ECOSYSTEMS | Fagaceae

R. Rogers, in Encyclopedia of Forest Sciences, 2004

Southern Beech (Nothofagus)

Clear-felling has been the common way of harvesting southern beech in New Zealand and other areas across its distribution in the southern hemisphere. However, research is ongoing in New Zealand to find out if group selection (an uneven-aged silvicultural method) could be used to sustain southern beech forests. The group selection method is a modification of the single-tree selection method whereby openings larger than the crowns of the largest trees are made in the forest canopy. Typical openings range from 0.1 to 0.25 hectare. In large part, this method requires adequate advance regeneration to successfully regenerate the stand.

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Separation of Source Components of Soil Respiration

Yiqi Luo, Xuhui Zhou, in Soil Respiration and the Environment, 2006

Clear-cutting in forests, clipping and shading in grasslands

Clear-cutting in forests and clipping in grasslands share the same features by cutting and clearing the aboveground parts of vegetation to create vegetation-free soils. As a consequence, live roots and carbohydrate supply to the soil from aboveground is reduced, and resultant soil respiration decreases (Brumme 1995, Striegl and Wickland 1998). Shading in grasslands blocks light to reduce carbohydrate supply to root systems (Craine et al. 1999, Wan and Luo 2003). Clear-cutting creates gaps in forest stands and forms root-free patches when the forest gap sizes range from several square meters at the minimum to tens of square meters. In grasslands, clipping of areas of one or a few square meters is adequate to study root contribution to the total soil respiration.

Ohashi et al. (2000), for example, cut four trees and created a gap of 2.5 m × 2.5 m in a 10-year-old Japanese cedar (Cryptomeria japonica) in southwest Japan in March 1996. Four types of measurement plots are set up at the center of the gap, at 0.8 m (edge of the gap), at 1.6 m (edge of the surrounding stand, and at 6.0 m (in the forest as control) from the center of the gap (Fig. 9.2). Measured soil respiration does not differ among the four plots in the first year. In the second year, soil respiration measured at the center of gap decreases by approximately 50% compared with that in the control. The root respiration that is estimated from the differences between soil respiration in the center of the gap and that in the control correlates with soil surface temperature. The correlation illustrates a seasonal trend of higher proportional rates of root respiration in the summer than in the winter.

FIGURE 9.2. Location of measurement plots, (a) side view, (b) plan view. Dashed rectangles are for measurement plots, (×) measurement point; (o) felled tree; (○) living tree.

(Redrawn with permission from Ecological Research: Ohashi et al. 2000).

Clipping and shading are used to manipulate substrate supply to soil respiration in a tallgrass prairie of the U.S. Great Plains (Wan and Luo 2003). Reduced substrate supply significantly decreases soil respiration by 33, 23, and 43% for the clipping, shading, and clipping plus shading treatments respectively (Fig. 5.1). Root and rhizosphere respiration, respiration from decomposition of aboveground litter, and respiration from oxidation of SOM and dead roots contribute 30, 14, and 56% respectively to annual mean soil respiration. Similarly, two days after clipping in a Kansas tallgrass prairie, soil respiration decreases by 21 to 49%, despite the fact that clipping increases soil temperature (Bremer et al. 1998). The rate of rhizosphere respiration in planted barrel medic (Medicago truncatula Gaertn. Cv. Paraggio) decreases immediately after defoliation (Crawford et al. 2000). In a Minnesota grassland, two days of shading causes a 40% reduction in soil respiration, while clipping reduces soil respiration by 19% (Craine et al. 1999).

Several biological and environmental factors can confound estimation of root contributions to soil respiration with the clear-cutting, clipping, and shading methods. The forest cutting and grassland clipping may temporarily increase soil respiration due to accelerated decomposition of dead roots and/or stored carbohydrate (Toland and Zak 1994). Accelerated decomposition of dead roots occurs in a tropical forest (Tulaphitak et al. 1985), a hardwood forest (Londo et al. 1999), and a northern mixed forest (Hendrickson et al. 1989). It may take a long time for microorganisms to decompose dead roots fully. The relative decomposition rate of dead roots is 0.13 year−1 in a Japanese plantation (Nakane 1995). Dead root decomposition contributes 50 g C m−2 yr−1 to the soil respiration in the second year of the cutting experiment (Ohashi et al. 2000). In addition, forest cutting or grassland clipping may stimulate growth of roots of the remaining plants.

The death of live roots may decrease rhizospheric microbes and microbial respiration, leading to an overestimation of root respiration per se. Decomposition of dead roots may change soil nutritional environments, affecting microbial respiration indirectly. Elimination of rhizosphere activity changes microbial community composition and alters uses of soil carbon substrates.

Clear-cutting, clipping, and shading potentially alter soil temperature and moisture. As a result of the removal of a substantial portion of the canopy, the treatment plots receive more incoming shortwave radiation during the daytime but trap less long-wave radiation at night than the control plots. Temperature is higher by day and lower at night, and upper layers of litter and soil become drier in the treatment plots than in the control plots. The absence of roots, however, can decrease plant water uptake and transpiration, resulting in increases in soil moisture. Changes in temperature and moisture affect respiration rates, compromising the estimation of root contributions to soil respiration. To minimize the changes in environmental conditions, Nakane et al. (1983, 1996) used a frame box covered with nets in clear-cut areas to maintain similar environments as in the controls. Ohashi et al. (2000) used the small gaps that do not result in much change in environmental conditions. Wan and Luo (2003) used correction functions to account for the effects of altered temperature and moisture on soil respiration.

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Forest responses to soil disturbance due to machine traffic

Iwan Wästerlund, in Soil and Root Damage in Forestry, 2020

Trafficated area

At clearfellings of forest areas with the tree-length method, the skid trails are reported to take up 15%–35% of the site area but the total area influenced may run as high as 80% (Lull, 1959; Froehlich, 1978; Martin, 1988; Reisinger et al., 1988; Davis, 1992). More than half of the skid trail area (50%–75%) has been classified as disturbed and compacted. By using designated skid trails and increased spacings to 125 ft (37 m), the disturbed area could be limited from 15%–20% to 8% according to Stewart et al. (1988). In that case, a grapple skidder cannot be used. In a controlled logging operation in Malaysia, trails after skidders covered 24% of the area, whereas trails after manual extraction covered only 4% (Malmer and Grip, 1990). One interesting thing is that very few seem to bother about the feller-bunchers or harvesters. However, in a study by Lee et al. (1990), it was found that a frame-mounted feller-buncher caused more soil disturbance and compaction than a boom-mounted because the first machine type has to travel to each tree. Martin (1988) recommends the use of forwarders rather than dragging the whole tree to reduce exposure of mineral soil. He also recommends delimbing of conifers on the site and placing the slash in the trails to reduce compaction.

In Europe, the traffic during clearfelling appears to be a forgotten topic. Roughly estimated, about 30% of the area is used for forwarding or skidding of the timber. With use of a feller-buncher or a harvester the influenced area could be much higher especially if the machines are traveling different routes.

Generally, the clearfelling is followed by some kind of site preparation before planting which may further increase the traffic on the site. The site preparation for the next tree generation could imply slash removal, soil scarification, etc. A heavy work well suited for mechanization which means machines traveling back and forth over the area. Slash piling is often included in the total effects of the logging operation, but Davis (1992) argues that alternatives to tractor slash piling should be considered to reduce the trafficated area. Gent and Morris (1986) concluded that windrowing and chopping of slash added only little added effect to the total soil bulk density partly because of all traffic before that treatment. The organic matter content after slashing may be in the same (low) level as in the skid trails (Snider and Miller, 1985).

However, if the soil preparation is done with, for example, a powered two-row disc trencher or a similar device, the soil is loosened behind the machine. There appears to be no remaining soil compaction due to the machine wheels and previously compacted soil is loosened at least near the surface (Froehlich and McNabb, 1984; Gyldberg, 1993). Martin (1988) recommends “Scarification should be planned carefully and not be a by-product of an otherwise haphazard skidding arrangement.”

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SITE-SPECIFIC SILVICULTURE | Silviculture in Polluted Areas

M.V. Kozlov, in Encyclopedia of Forest Sciences, 2004

Site preparation

Soil ploughing after clear-cutting is a common forestry practice, which has positive effects on the first phases of forest regeneration. In the Upper Silesian Industrial Region, full tillage of the sandy soil promoted better growth of nearly all tree species in their juvenile period than other methods of soil preparation (plowing or disk cultivation). Full tillage decreased soil acidity, reduced metal contents, enhanced microbiological activity, and decreased infections of young trees by root-rot fungi (Heterobasidion annosum). However, plowing also decreased mycorrhyzal infestation of Scots pine roots and the soil content of N, K, and Mg, requiring compensatory measures.

During the reforestation of clear-cuts exposed to acidic deposition, diagnostic fertilization and liming were applied in the same way as for the revitalization of damaged stands in Germany and the Czech Republic. Current recommendations are that liming be conducted at least twice, before the mechanical preparation of soils and after planting of seedlings. Fertilization should be restricted to planting holes or planting rows so as to minimize competition from weeds. Herbicide application may enhance seedling establishment in habitats covered by grasses (Calamagrostis villosa or Agropyron repens) but others recommend that herbicides be avoided during site preparation in polluted regions. Bulldozing of areas covered by C. villosa, the grass species that makes the replanting of forest trees extremely difficult or even impossible, promoted the establishment of pioneer trees and therefore accelerated the natural succession leading to the establishment of a full forest cover.

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Large-Scale Ecology: Model Systems to Global Perspectives

E. Chauvet, ... M.O. Gessner, in Advances in Ecological Research, 2016

3.5 Forest Clear Cutting

The effects of forest clear cutting on leaf litter decomposition were assessed in northern Sweden (Table 6). Leaf litter decomposition was stimulated in streams flowing through forest clear-cuts (altered streams) compared with streams flowing through old mixed boreal forests (reference streams), mostly for alder in coarse-mesh bags (McKie and Malmqvist, 2009*). No significant differences were found for macroinvertebrate abundance, diversity, assemblage composition or functional feeding groups abundances and species densities between reference and altered streams (except for scraper species density that was higher in reference streams), suggesting that macroinvertebrate community structure was not tightly coupled to variability in leaf litter decomposition (McKie and Malmqvist, 2009*). Rather, higher decomposition rates in the clear-cut streams were associated with an increase in decomposition efficiency by microbes and shredders compared with reference streams (McKie and Malmqvist, 2009*). Notably, this increase in decomposition efficiency occurred even though mean temperatures were actually lower in the clear-cut sites during the study period. This can be explained by the joint effects of three variables that differed between clear-cut and forested streams: increased nutrient concentrations, a shift in the composition of litter inputs, and increased shredder biomass. Firstly, phosphate concentrations were slightly greater in the clear-cut streams (McKie and Malmqvist, 2009*), which might have stimulated decomposition from the bottom-up by favouring increased microbial activity (Ferreira et al., 2006c*, 2015a; Gulis and Suberkropp, 2003; Robinson and Gessner, 2000). Secondly, benthic litter standing stocks in the clear-cut streams were dominated by broadleaf (Betula spp.) litter, while the forested streams were dominated by refractory conifer needles, reflecting the dominance of birch saplings in the recovering riparian vegetation of the clear-cut streams. This greater incidence of broadleaf litter coupled with higher phosphorus concentrations together likely resulted in greater availability of nutrient rich and palatable litter in the clear-cut streams, in turn explaining why shredder biomass was overall higher in these streams (McKie and Malmqvist, 2009*). Higher shredder biomass in turn increased the resource-processing potential of detritivore assemblages, providing a further potential explanation for elevated decomposition rates in the clear-cut streams. Additionally, the potential increase in primary production in clear-cut streams may have stimulated litter decomposition by the release of labile carbon that could have stimulated the use of leaf litter by decomposers in a case of priming effect (Danger et al., 2013). Increased primary production may have also contributed to the increased shredder biomass at clear-cut streams if these were feeding on algal resources associated with decomposing litter (Franken et al., 2005).

Table 6. Summary Table of the Literature Assessing the Effects of Forest Logging on Litter Decomposition in Streams

ReferenceaRegionLitter SubstrateDecomposer CommunitybNo. Reference/Altered Streams or SitesResponse to Forest Changec
Benfield et al. (1991)South Appalachian Mountains, USADogwood leavesTotal1–3/1+
Red maple leavesTotal1–3/1+
White oak leavesTotal1–3/1+
Rhododendron leavesTotal1–3/1+
Kreutzweiser et al. (2008)CanadaSpeckled alder leavesTotal9/12
*McKie and Malmqvist (2009)Northern SwedenAlder leavesMicrobial5/5+
Total5/5+
Oak leavesMicrobial5/5+
Total5/5+
Lecerf and Richardson (2010b)CanadaRed alder leavesTotal13/3
a
References marked with an ‘*’ are derived from the RivFunction project.
b
Total decomposer community: microbes + macroinvertebrates.
c
Response of litter decomposition to forest change: −, significant inhibition of litter decomposition in altered streams and +, significant stimulation of litter decomposition in altered streams.

Again, there are conflicting results among studies addressing the effects of forest harvest on litter decomposition in streams (Benfield et al., 1991, 2001; Kreutzweiser et al., 2008; Lecerf and Richardson, 2010a; McKie and Malmqvist, 2009*; Table 6) suggesting that effects are context dependent and in particular related to the clear-cut type (deciduous/broadleaf vs coniferous). A recent meta-analysis addressing the effects of forest harvest on several stream parameters also found contradictory results among primary studies, i.e. negative and positive responses of the same parameter to forest harvest among studies, highlighting the ‘need to consider site-specific mechanisms by which such changes occur’ (Richardson and Béraud, 2014).

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Ecology Processes

Brian J. McGill, in Encyclopedia of Biodiversity (Third Edition), 2013

Indicators

Extreme human impacts such as clear cutting, building roads, or plowing fields have rather obvious impacts on the natural ecosystem, allowing for an informed debate about the pros and cons of such development in a particular situation. However, many development and management practices are much more subtle. Such practices include exurbanization (low-density housing development outside the suburbs), selective logging, roads in wild areas, etc. The ecological consequences of such actions can often be subtle and even counterintuitive. For example, clear cutting that leaves behind patches of original forest habitat can actually increase species diversity in the retained patches in some cases and for some taxa, but this is mostly because it mixes forest with edge species. More nuanced measures of the impact of ecosystems are clearly needed. Advanced multivariate statistics are clearly one approach. But such approaches have limited available expertise within the scientific community and great difficulty in translation to managers and policy makers. The tools of describing assemblages given in this entry can provide a useful toolkit for measuring changes.

Fig. 6 provides two examples of using assemblage descriptions as indicators as applied to a breeding bird survey route in late secondary forest. Fig. 6(a) builds on the techniques from the section Mean Descriptions of an Assemblage, and also from a recent study, (McGill, 2011b) which showed that using three distinct univariate measures, one to represent total assemblage abundance, one to represent total assemblage diversity and one to represent assemblage evenness provided a good description of assemblages and separated multiple assemblages well in ordinations. Specific measures depend on sampling methodologies and sizes. Fig. 6(b) builds on the techniques of the section Variation Within an Assemblage (Distributions or Histograms) by using a particular way of plotting species abundance distributions to control for total assemblage abundance and richness and which highlights the proportion of rare species in the assemblage. Both figures suggest that this assemblage initially improved and then leveled off to a noisy equilibrium by several key indicators of healthy ecosystems (higher richness, abundance, evenness, and proportions of rare species). Other aspects of assemblages can be tracked as well. For example, studies of fisheries show that the average mass of individuals being caught and the average trophic level (as measured by isotope analysis) have decreased over recent decades. The relative proportions of different size classes (basically the frequency distribution of body size) can be an important indicator of successional stage in forests and an indicator of ecosystem health. Some studies have also shown that α diversity may increase or be unchanged under human disturbances, but the β diversity may drop considerably – in short humans are homogenizing the landscape, which will reduce overall (γ) diversity even if simplistic α-diversity measures fail to show this.

Fig. 6

Fig. 6. Two examples of how our understanding of assemblages can be used to help in assessing human-caused impacts on assemblages. Both datasets are for birds (see Fig. 5(b)). (a) Each point represents one year (1975–2007) with darker points representing later years. A simple ordination is performed by plotting these points vs. species richness, total abundance and evenness (McGill, 2011b). Overall the system has moved from low richness and high abundance to the opposite (high richness and low abundance), then returned to settle around a region intermediate in both abundance and richness. Evenness has also increased. This suggests that this one site near Orono ME has actually shown improvement especially from the 1970s to the mid 1980s, possibly with some overshoot but appears stable at the present time. (b) The same data plotted as species abundance distributions. This plot is a new way of plotting species abundance distributions (McGill et al., 2007). The x-axis shows abundance as a percentage of all individuals in the assemblage (i.e., relative abundance) on a log scale. The y-axis shows the percentage of species with an abundance equal or less than that shown by where a horizontal line intersects the curve. Thus, for the dark 2005 line, 80% of species have an abundance of 2% or less. As a result rare species appear on the left side and common (high relative abundance) species appear on the right, making it easy to determine the relative proportions of rare species (higher line on the left side). This graph allows for easy comparison between assemblage with different numbers of species or individuals. This data suggest that the proportion of rare species was lowest in 1975 and 1981, generally increased, with an extreme deviation in 1993 and is the highest it has ever been in the last year of 2005. Again this is suggestive of an assemblage that has become less detrimentally impacted by humans in the past 35 years.

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Logged Forests

Reinmar Seidler, Kamaljit S. Bawa, in Encyclopedia of Biodiversity, 2001

II.A.2. Selective Logging Systems

In many species-diverse tropical forests, clear-cutting is neither an economically nor an ecologically interesting option, since only a few tree species are commercially accepted. Moreover conspecifics are widely scattered, and infrastructure including roads and rural mills may be sparse. In such managed forests, trees are selectively logged. Selective logging is a general term encompassing a wide array of management systems that vary widely with respect to spatial and temporal scale, harvesting intensity, planning, and oversight. Selectivity of species to be removed does not necessarily translate into selectivity of overall impact, so the residual forest may be affected indiscriminately even by the selective extraction of only a few trees per hectare.

Tropical forest management systems were adapted from the German forestry tradition, which was exported, to India and Burma during the 19th century. Natural regeneration systems, or polycyclic systems, minimize silvicultural interventions by relying on natural regeneration after the harvest of a relatively low number of trees per hectare. These systems result in uneven-aged and multispecies stands, which are thought to provide the best opportunities for biodiversity conservation as part of the management plan. However, a variety of assumptions about regeneration patterns must be made, many of which have been questioned by some foresters, and conclusive evidence of long-term sustainability is lacking.

Natural regeneration systems with adaptations to regional conditions have been developed in Malaysia (selection management system), Ghana (modified selection system), Suriname (Celos silvicultural system), Trinidad (periodic block system), and Queensland, Australia (Queensland selective logging system). Each of these has made important strides toward solving technical silvicultural problems, but in many cases sociopolitical obstacles have been more severe.

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Biodiversity in Logged and Managed Forests

Reinmar Seidler, Kamaljit S. Bawa, in Encyclopedia of Biodiversity (Second Edition), 2013

Selective Logging Systems

In many species-diverse tropical forests, clear-cutting is neither an economically nor an ecologically appropriate option, since only a few tree species are commercially accepted – although the number of accepted species is rising fast in response to a number of technical and industrial drivers. Moreover, conspecifics are widely scattered, and infrastructure including roads and rural mills may be sparse. In such managed forests, trees are selectively logged. Selective logging is a general term encompassing a wide array of management systems that vary widely with respect to spatial and temporal scale, harvesting intensity, planning, and oversight. Selectivity of species to be removed does not necessarily translate into selectivity of overall impact, so the residual forest may be affected indiscriminately even by the selective extraction of only a few trees per hectare.

Tropical forest management systems were adapted from the Central European forestry tradition, which was exported to India and Burma during the nineteenth century. Natural regeneration systems, or polycyclic systems, minimize silvicultural interventions by relying on natural regeneration after the harvest of a relatively low number of trees per hectare. These systems result in uneven-aged and multispecies stands, which are thought to provide the best opportunities for biodiversity conservation as part of the management plan. However, a variety of assumptions about regeneration patterns must be made, many of which have been questioned by foresters, and conclusive evidence of long-term sustainability is lacking.

Natural regeneration systems with adaptations to regional conditions have been developed in Malaysia (selection management system), Ghana (modified selection system), Suriname (Celos silvicultural system), Trinidad (periodic block system), and Queensland, Australia (Queensland selective logging system). Each of these has made important strides toward solving technical silvicultural problems, but in many cases sociopolitical obstacles have been more severe. Nevertheless, research is showing that where careful reduced-impact logging (RIL) is carried out, the impacts can be much smaller than in conventional logging (e.g., Smith et al., 2005; Meijaard et al., 2006; Lagan et al., 2007; Putz et al., 2008), and guidelines for tropical and temperate zone forests are being published (e.g., Thorpe and Thomas, 2007).

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Humans & Conservation

Reinmar Seidler, in Encyclopedia of Biodiversity (Third Edition), 2024

Selective Logging Systems

In many species-diverse tropical forests, clear-cutting is neither an economically nor an ecologically appropriate option – since only a few tree species are commercially accepted is neither an economically nor an ecologically apng fast in response to a number of technical and industrial drivers. Moreover, conspecifics are widely scattered, and infrastructure including roads and rural mills may be sparse. In such managed forests, trees are selectively logged. Selective logging is a general term encompassing a wide array of management systems that vary widely with respect to spatial and temporal scale, harvesting intensity, planning, and oversight. Selectivity of species to be removed does not necessarily translate into selectivity of overall impact, so the residual forest may be affected indiscriminately even by the selective extraction of only a few trees per hectare.

Tropical forest management systems were adapted from the Central European forestry tradition, which was exported to India and Burma during the nineteenth century. Natural regeneration systems, or polycyclic systems, minimize silvicultural interventions by relying on natural regeneration after the harvest of a relatively low number of trees per hectare. These systems result in uneven-aged and multispecies stands, which are thought to provide the best opportunities for biodiversity conservation as part of the management plan. However, a variety of assumptions about regeneration patterns must be made, many of which have been questioned by foresters, and conclusive evidence of long-term sustainability is lacking.

Natural regeneration systems with adaptations to regional conditions have been developed in Malaysia (selection management system), Ghana (modified selection system), Suriname (Celos silvicultural system), Trinidad (periodic block system), and Queensland, Australia (Queensland selective logging system). Each of these has made important strides toward solving technical silvicultural problems, but in many cases the sociopolitical obstacles to implementation have been significant. Where careful reduced-impact logging (RIL) is carried out, the impacts can be much smaller than in conventional logging (e.g., Smith et al., 2005; Meijaard et al., 2006; Lagan et al., 2007; Putz et al., 2008), and guidelines for tropical and temperate zone forests are being published (e.g., Thorpe and Thomas, 2007). However, reported outcomes vary widely across forest types, harvest intensity level, and many other factors, some of which (e.g., weather during harvest) cannot easily be controlled under commercial conditions. Gatti et al. (2015), working very carefully in tropical forests of Sierra Leone, Ghana, Cameroon and Gabon, found that significant reductions in biomass, loss of carbon storage capacity and reduced biodiversity values could only be avoided at the lowest-intensity harvest levels.

Recent publications are now able to examine the impact of different harvesting systems on tropical forests after intervals of 30 years or more. (Landburg et al., 2003), for instance, compared indicators of forest structure and vegetation composition after three different logging systems (plus unlogged forest) in Suriname. They found that differences between conventional and RIL plots in forest structure variables (such as canopy openness) were less than expected. Some of the RIL plots, including a Celos Management System plot from the 1980s, showed surprisingly high openness indices allowing establishment of secondary forest species and a dense palm layer. Landburg et al. suggest that this may have been the result of incorrect application of the RIL guidelines, emphasizing once again that even when felling personnel are trained and supervised, there may be practical challenges in applying best practices.

In hindsight it is probably fair to say that most of the tropical silvicultural systems that have been developed over the decades have suffered from too little analytical attention to the sociopolitical and sociocultural contexts within which the systems are meant to be carried out. Poudyal et al. (2018) point out (1) that studies are largely concentrated in just a few countries, while other tropical countries that have also practiced selective logging remain understudied, and (2) that the needs and constraints of forest managers, and the capacity of stakeholders to adopt improved techniques, have received too little research attention. These non-technical issues constitute the principal obstacles to success in improved forest management going forward.

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