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Degeneration versus regeneration — logging in tropical rain forests
Abstract
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.
... Optimization of yield regulation parameters in this context is effectively facilitated by stand dynamics modelling and harvesting scenario simulations (Huth and Ditzer 2001;Van Gardingen et al. 2003, 2006Gourlet-Fleury et al. 2004, Kariuki et al. 2006). (Snook 1996;Fredericksen 1998;Brown 1998;Dawkins and Philip 1998;Ashton and Peters 1999) • Excessive exploitation impacts jeopardizing regeneration (Van Gardingen et al. 1998;Bruenig 1996;Dawkins and Philip 1998) 2. Unsustainable harvest levels • Harvesting all trees above relatively low MHD results in unsustainable harvest intensities; especially in the case of bell-shaped population structures (Lamprecht 1993;Snook 1996;Dawkins and Philip 1998;Sist 2000;Sist et al. 2003a;Van Gardingen et al. 2003;Grogan et al. 2008) • Species and quality selective overharvesting (Appanah et al. 1990;Dawkins and Philip 1998;Brown 1998;De Graaf 2000) • Associated high levels of logging damage (Dawkins and Philip 1998) 3. Inadequacy of residual growing stock • Decimation of seed sources (Weidelt 1989;Plumptre 1995;Snook 1996;Fredericksen 1998) • Low MHD/short felling cycles: premature removal of productive and value-producing trees (Rietbergen 1989;Bruenig 1996) • Repeated removal of fastest growers: leaving a residual growing stock of slower-growing trees or having dysgenic effects (Weidelt 1986;Appanah and Weinland 1992;Lamprecht 1993) • Residual growing stock consisting of trees of low growth performance (Thang 1987;Lamprecht 1993;Seydack et al. 1995;Bruenig 1996) ...
... Optimization of yield regulation parameters in this context is effectively facilitated by stand dynamics modelling and harvesting scenario simulations (Huth and Ditzer 2001;Van Gardingen et al. 2003, 2006Gourlet-Fleury et al. 2004, Kariuki et al. 2006). (Snook 1996;Fredericksen 1998;Brown 1998;Dawkins and Philip 1998;Ashton and Peters 1999) • Excessive exploitation impacts jeopardizing regeneration (Van Gardingen et al. 1998;Bruenig 1996;Dawkins and Philip 1998) 2. Unsustainable harvest levels • Harvesting all trees above relatively low MHD results in unsustainable harvest intensities; especially in the case of bell-shaped population structures (Lamprecht 1993;Snook 1996;Dawkins and Philip 1998;Sist 2000;Sist et al. 2003a;Van Gardingen et al. 2003;Grogan et al. 2008) • Species and quality selective overharvesting (Appanah et al. 1990;Dawkins and Philip 1998;Brown 1998;De Graaf 2000) • Associated high levels of logging damage (Dawkins and Philip 1998) 3. Inadequacy of residual growing stock • Decimation of seed sources (Weidelt 1989;Plumptre 1995;Snook 1996;Fredericksen 1998) • Low MHD/short felling cycles: premature removal of productive and value-producing trees (Rietbergen 1989;Bruenig 1996) • Repeated removal of fastest growers: leaving a residual growing stock of slower-growing trees or having dysgenic effects (Weidelt 1986;Appanah and Weinland 1992;Lamprecht 1993) • Residual growing stock consisting of trees of low growth performance (Thang 1987;Lamprecht 1993;Seydack et al. 1995;Bruenig 1996) ...
... Both can be negatively affected by the selective removal of conspecific neighbours (Guariguata and Pinard 1998). Tree harvesting based on relatively low MHDs results in the decimation or local extinction of adult trees of rare species and those with bell-shaped diameter class distributions (Snook 1996;Brown 1998;Sist et al. 2003a, b;Schulze et al. 2008). Declining regeneration capacities of logged-over forests have been recorded Snook 1996;Plumptre 1995). ...
Components of yield regulation systems are discussed which are required to ensure successful stand regeneration and sustainable
timber yield optimization in tropical and subtropical moist forests. Existing yield regulation/silvicultural systems were
classified into four groups: uniform systems, tropical shelterwood systems, manipulistic selection cutting systems and naturalistic
selection cutting systems. The performance of these systems, in particular of the relatively high impact systems generally
practiced in the tropics, was assessed and problems relating to inadequate regeneration, unsustainable timber harvest levels,
inadequacies of the residual growing stock and neglect of silvicultural interventions are identified. Most systems, as practiced,
are potentially subject to sustainability risks due to forest matrix destruction effects, disruption of functional interspecies
dynamics and disruption of regeneration processes. A forest matrix invasion model, which is considered to explain tropical
forest dynamics ecologically more closely than the successional disturbance model generally invoked for temperate forests,
is outlined. Based on this model, timber yield regulation characteristics for continuous cover primary forest management were
defined. They include large-tree productivity realization, relative high harvest maturity thresholds and residual growing
stock levels, and protection of the forest matrix through reduced impact logging.
... Logging areas tend to be larger than natural tree fall gaps and thus provide higher light availability at the forest floor . The high levels of disturbance caused by logging provide a competitive advantage to species that are responsive to high light levels and capable of rapid growth (Brown, 1998). In many cases these species are vines and other fast growing species that suppress the regeneration of commercially more valuable species . ...
... Another consequence of logging are locally high levels of soil disturbance and litter removal along skid trails and haul roads (Buckley et al., 2003). The extraction of logs rarely creates large gaps in the forest canopy but recovery is relatively rapid, since regeneration is enhanced in gaps and on skid trails in logged forest (Brown, 1998;. However, in the long term this change may not be a commercial advantage, if species composition is changing from shade-tolerant timber species to vines and noncommercial pioneer trees. ...
Terminalia oblonga (Ruiz et Pav.) Steud. is a common timber tree in lowland Latin America which is widely utilized and economically and ecologically valuable. The species suffers from reduced natural recruitment but the control of regeneration by environmental factors is incompletely understood. In the forest management plots of the BOLFOR project (La Chonta, Bolivia) we investigated the effects of soil disturbance, litter layer and canopy openness on seedling emergence and survival. Soil disturbance and a thin litter layer favoured seedling emergence, disturbance had also a positive effect on seedling survival, whereas canopy openness had no significant effect on emergence but influenced survival positively. The results are discussed with respect to the life history traits of T. oblonga and forest regeneration, which need to be considered for implementation of sustainable logging strategies and forest conservation. It is concluded that the regeneration of T. oblonga is favoured by moderate logging although the long-term effects need further research.
... This study found that loss of commercial species lost and decrease in number of species after logging was attributed to canopy opening. However, selective logging has both positive and negative effects on tree species diversity (Brown 1998, Van-Gemenden et al. 2003. Positive implications include efficient removal of one or two trees leaving the rest intact and canopy stratification. ...
... Conversely, T. macroptera is known to develop a fairly impressive crown (Arbonnier, 2008). There was competitive advantage for species that responded well to high light levels and which are capable of rapid growth (Brown, 1998). The shade created by the T. macroptera crown impeded normal growth of P. kotschyi individuals within 5 m of radius and may have led to removal of some individuals because more seedlings died in apparent low-light areas (Tesfaye et al., 2002;Schiøtz et al., 2006). ...
One of the major reasons for reforestation failure using tropical species is misunderstanding of the
neighbourhood relationship within tree populations. This study used the natural stand structures of
Terminalia macroptera and Pseudocedrela kotschyi, two socio-economically important species, to
design enrichment planting. A comparative analysis of the population structure of P. kotschyi and T.
macroptera in two regimes (pure and mixed) was performed. However, results indicated that young T.
macroptera individuals were predominant in both stand regimes. In the same way, no significant
difference was found between diameter size classes with respect to stand regime. Trees showed weak
density and a random pattern with the nearest neighbour distances varying between 5.67 (pure) and
7.01 m (mixed). P. kotschyi young individuals were also found to be predominant irrespective of stand
regime; yet, the diameter size class distributions revealed significant variations with respect to stand
regime. Trees had a higher density and stronger clumped pattern in pure stand as compared to mixed
stand. The nearest neighbour distances ranged from 2.97 (pure) to 4.87 m (mixed). Our findings
highlighted the relevance of taking into account relationships between stand regime and tree
population structure while designing artificial plantings.
Key words: Savanna woodland, density, spatial distribution, diameter class structure.
... Light levels are as important in regeneration after logging as they are in the natural regeneration cycle. Silvicultural systems used in Malaysia are designed to promote natural regeneration after logging (Dawkins and Philip, 1998), but modern mechanised extraction leads to considerable damage of natural regeneration Forest Ecology and Management 157 (2002) 65±75 (Brown, 1998). In areas where natural regeneration of valuable timber species is inadequate, enrichment planting with commercially important species can be used to restock the forest (ITTO, 1989). ...
Variation in forest canopy openness influences the growth and survival of seedlings below, and is therefore of practical importance when wishing to restock a forest with valuable timber species after logging. In this study, growth and light environment of dipterocarp seedlings in an enrichment planting project in secondary lowland forest in Borneo were analysed using geostatistics, in order to determine the spatial relationships between canopy openness and seedling performance. Seedling growth was correlated with canopy openness measures up to 50 m away along planting lines but was uncorrelated across planting lines, because the dense understorey between planting lines blocked lateral light. It is recommended that planting be conducted in patches rather than along lines, so that understorey clearance can allow light from canopy gaps in all directions to reach seedlings.
There is concern about economically excessive conversion of tropical forest land to alternative uses, such as agricultural production. In this thesis, a comprehensive review of the economics of forest land use in a tropical forest setting is presented. A theoretical model of tropical forest management for timber production, with non-timber forest benefits, insecure land tenure and evolving prices taken into account, is developed and numerically illustrated. The timber production model is extended to include alternative tropical forest land use options, such as conversion to agriculture. The decision to switch between alternative land uses over time due to changing prices and costs is also explored. The stand level model is extended to the forest level to examine the impact of stand interactions on forest land use decisions. The decision to convert forest land to alternative uses is empirically examined at the tropics wide level and at the country level for Mexico. The impacts of forest and related sector policies on forest land use decisions are explored. The theoretical and empirical analyses presented in this thesis provide important insights for a discussion of the policy options to promote greater tropical forest conservation.
Most studies valuation that have been described previously including forest ecosystems do not see the forest ecosystem services as natual capital / natural assets and even the socio-ecological context. The implication is that forest ecosystem services are considered as an economic asset / economic capital. the concept of value used in the valuation is the concept of the value of output. Though the forest ecosystem services has the characteristics of a sustainable dynamic and as part of the life supporting system including the ability resilience and self-terrific capacity. So that the forest ecosystem is no longer seen as economic assets, but with the characteristics of the dynamic and sustainable forest ecosystem is seen as natural or natural capital assets. The current perspective marginalize other forest ecosystem functions, such as socio-economic functions. Whereas the concept of an insurance value of forest ecosystems is not just the case as seen from the perspective as natural capital, but the role of social values in maintaining the sustainability of forest ecosystems is crucial, as reflected by the presence of heritage value, and existence value. So that the insurance value of the forest ecosystem occurs because the forest ecosystem serves as a natural asset / natural and social capital assets / social capital.
Climbing bamboos are extremely abundant in Deramakot Forest Reserve. The likelihood that a tree supported bamboo in its crown decreased with tree diameter; bamboos were not observed ascending trunks of trees >41.2cm dbh (Dinochloa scabrida) or 39.1 cm dbh (D. trichogona). The angle of ascent of twinning bamboo stems also decreased with increasing tree diameter. Free-standing culms attained heights of up to 3.45 m (D. scabrida) and 2.95 m (D. trichogona); unsupported culms of D. scabrida that twined around one another grew up to 4.68 m tall before toppling over. -from Authors
The damage occasioned by harvesting in a planned manner is assessed. The main features of the approach to damage reduction were: previous surveying and careful construction of roads and skidding trails, climber cutting and directional felling. Harvested volume was 20 m3 ha-1. The number of damaged trees over 10 cm in diameter was 5.3 per tree logged and the volume of damage was 0.27 m3 per cubic extracted. Damage caused to the canopy by road and trail cutting, provision of landings and felling damage amounted to a maximum canopy opening of 15%.
The diversity of many tropical forest ecosystems is thought to depend, in
part, on the variety of regeneration opportunities created by smallscale
disturbances such as tree-fall gaps. The authors tallied all tree
and shrub seedlings and saplings s 5 cm dbh in 39 hexagonal, 20-m2
plots in coastal hill dipterocarp forest of Penang, Malaysia. Ten plots
lVere located in closed-canopy forest; the rest were located in 21 natural
tree-fall gaps. The data obtained were analyzed using detrended correspondence
analysis. Virtually all species found in forest plots were also
found in gap plots, whereas at least 13 species were found only in gaps,
usually in association with obvious soil disturbance. Microhabitat differences
within and among gaps may influence local patterns ef species
success. However, the species composition of particular gaps is more
similar to that ef adjacent, undisturbed forest than to similar gap types
in different locations. This suggests that seedlings present at the time of
gap formation dominate the regenerating community, regardless of the
particular type of tree fall that created the gap.
The Reduced-Impact Logging (RIL) Project started in August 1992 when New England Electric System provided funds to Innoprise Corporation Sendirian Berhad (ICSB, Sabah, Malaysia) to implement a set of reduced-impact logging guidelines in 1400 hectares (ha) of its concession. The principal goal of the project was to reduce damage to both the soil and the residual stand during selective logging by harvest planning, prefelling vine cutting, directional felling, and other environmentally sound management techniques. The harvesting guidelines developed and adopted by the RIL project specify practices expected to reduce logging damage, thereby retaining more carbon in living trees and promoting post-logging biomass increments. -from Authors
The ways by which light gaps in the canopy are formed and the importance of buried seeds in treefall gap regeneration were studied in lowland forest in Pasoh Forest Reserve, Peninsular Malaysia. In the top 10 cm of soil under the mature forest canopy were 131 seeds/m, as determined by germinating seeds from the soil. This estimate of the buried seed population in Pasoh Forest Reserve is similar to estimates from several other Paleotropical forests but is lower than most buried seed population estimates reported for Neotropical forests. The density of buried seeds was significantly lower in 2- to 5-year-old treefall gaps than under the canopy of mature forest. Flats of sterilized soil and flats of soil containing a natural complement of buried seeds were set out in recent treefall gaps to compare the rates of seedling emergence from buried seeds and from seeds that arrived after the gaps were formed. Although less abundant than in many other tropical forests, buried seeds give rise to seven times more seedlings during the first nine months than freshly dispersed seeds. Pioneer trees contributed a smaller fraction of the buried seeds (29%) than observed in other lowland tropical rain forests. We believe this results from the relative scarcity of pioneer trees in Pasoh Forest Reserve and the relatively large size of their seeds compared, for example, with seeds of pioneer trees in the mature forest on Barro Colorado Island, Panama. The number of pioneer trees is relatively low at least in part because most canopy trees in Pasoh Forest Reserve have small crowns and because many of the trees that die remain standing (45%); trees with small crowns and trees that die standing open small canopy gaps when they fall.
Population dynamics and height growth of colonizing seedlings were
monitored for three years in newly created artificial gaps and beneath
intact canopy in primary lowland rain forest in Sabah, Malaysia. The
effects of gap size, soil surface conditions and competition from
advance regeneration were assessed. Recruitment during the first two
years was less than 100 seedlings m-2, or less than 5% of the
estimated seed bank in the top 5 cm of the soil prior to disturbance.
Overall, germination was not obviously affected by gap size, but was
increased markedly by soil exposure or disturbance. The diversity of the
colonizing vegetation at the end of two years appeared to be negatively
related to gap size. Seedling mortality was less both at larger gap size
and in the absence of competition from advance regeneration, whereas the
opposite appeared true for seedling growth. The results indicate that
gap size is unlikely to influence the composition of colonizing
vegetation by controlling seed germination, but an effect operating
through differential mortality cannot be discounted.
Three stages of selective commercial logging in a 0.54 km2 catchment in the Ulu Segama caused great changes in the output of sediment and water over a 27-month period from June 1988. The ratio of monthly suspended sediment yield from the logged catchment to that from a nearby undisturbed catchment changed from the order of 1:1 before disturbance; to 4:1 after a logging road had been built across the head of the catchment; to 5:1 after logging within 37 m of the road; and to 18:1 in the five months after logging of the remainder of the catchment. A year after logging had ceased the largest monthly sediment yields of the whole period were only 3.6 times those of the undisturbed catchment, indicating a degree of recovery. Sediment accumulated in the channel bed and on the narrow flood plain remained to be evacuated, and gullies on abandoned logging trails continued to supply sediment to the Drainage system.
Information available concerning all but the most common timber species in the Guianas is scattered and difficult to obtain. Very little is known of the ecological requirements of these timber species. Over 170 tree species in Guyana, Suriname and French Guiana were found to have useable timber properties. Three-quarters of these are currently harvested in one of the three countries and less than 20% account for greater than 90% of production.
Most timber species are mammal-dispersed,(51%), followed by bird and wind dispersal (21 and 20%,respectively). The seeds of less than 8% of the species are transported through unassisted modes, though several of these are important timber trees. The largest seeds are associated with mammal dispersed and unassisted species. Most bird and wind dispersed species have seed sizes below the median for all timber species. The seeds of timber species in Guyana were significantly larger than non-timber species.
Dispersal is important in maintaining timber tree population structures and avoiding inbreeding depression. Maintaining adequate dispersal of timber species in the Guianas depends largely on the conservation of mammals. Many species cannot be dispersed by smaller animals because their seeds are too large. Wind and bird dispersed species are at a relative advantage since their seeds are smaller and can be effectively dispersed by wind and mammals in the absence of their primary agents. Available data suggest that disproportionate harvesting of mammal-dispersed species relative to their contribution to total estimated standing volumes occurs in Guyana, while bird and wind dispersed species are the most disproportionately harvested in Suriname and French Guiana, respectively. Groups of species with the same dispersal mode should be exploited in relative proportion to their availability to avoid altering resources for animals. Maintaining the widest spectrum of resources available to animals will increase the likelihood that they continue to act as effective dispersal agents of valuable timber trees in the Guianas.
Only a small percentage of tropical forests are legally protected and so, if we are to conserve tropical forest species we must encourage sustainable exploitation of unprotected forest areas. Selective timber harvesting is frequently cited as a sustainable use of tropical forests and the authors studied the effects of this kind of exploitation on natural treefall rates, an important regulative process, in the Kibale Forest, Uganda. Their results indicate that levels of destruction typical of capital intensive mechanised timber harvesting seriously disrupt the dynamic balance of the forest. They discuss alternative methods for selective timber harvesting that would be less disruptive and present an objective method which may help rain forest managers determine which multiple-use options are compatible with rain forest conservation.
Published work on the dynamics of forest tree recruitment, growth and mortality in natural tropical forest is reviewed. In most forests studied, annual mortality is between 1% and 2% and is independent of size class in trees >10 cm dbh; mortality is negatively correlated with growth rate and crown illumination; growth rate is highly variable between individual trees, but shows strong autocorrelation between successive measurements on the same tree.
Differences in the rate of dynamic processes can be detected between some species at a site, but data are presently insufficient to determine whether these differences are preserved at other sites where the species occur. None of the studies discussed are of sufficient duration to permit us to draw any conclusions about the equilibrium or non-equilibrium of floristic composition.
The abundance of all tree and shrub species has been monitored for eight years in a 50 ha census plot in tropical moist forest in central Panama. Here we examine population trends of the 219 most numerous species in the plot, assessing the impact of a long-term drying trend. Population change was calculated as the mean rate of increase (or decrease) over eight years, considering either all stems ≥10 mm diameter at breast height (dbh) or just stems ≥100 mm dbh. For stems ≥10 mm, 40% of the species had mean growth rates <1% per year (either increasing or decreasing) and 12% had changes ≥5% per year. For stems ≥100 mm, the figures were 38% and 8%.
Species that specialize on the slopes of the plot, a moist microhabitat relative to the plateau, suffered significantly more declines in abundance than species that did not prefer slopes (stems ≥10 mm dbh). This pattern was due entirely to species of small stature: 91% of treelets and shrubs that were slope-specialists declined in abundance, but just 19% of non-slope treelets and shrubs declined. Among larger trees, slope and non-slope species fared equally. For stems ≥100 mm dbh, the slope effect vanished because there were few shrubs and treelets with stems ≥100 mm dbh. Another edaphic guild of species, those occurring preferentially in a small swamp in the centre of the plot, were no more likely to decline in abundance than non-swamp species, regardless of growth form. Species that preferentially colonize canopy gaps in the plot were slightly more likely to decrease in abundance than non-colonizing species (only for stems ≥10 mm dbh, not ≥100 mm). Despite this overall trend, however, several colonizing species had the most rapidly increasing populations in the plot.
The impact of a 25-year drying trend and an associated increase in the severity of the 4-month dry season is having an obvious impact on the BCI forest. At least 16 species of shrubs and treelets with affinities for moist microhabitats are headed for extinction in the plot. Presumably, these species invaded the forest during a wetter period prior to 1966. A severe drought of 1983 that caused unusually high tree mortality contributed to this trend, and may also have been responsible for sharp increases in abundance of a few gap-colonizers because it temporarily opened the forest canopy. The BCI forest is remarkably sensitive to a subtle climatic shift, yet we do not know whether this is typical for tropical forests because no other large-scale censuses exist for comparison.
This booklet is a popularized account of the soil and water impacts of timber harvesting in tropical moist forests aimed at the general public and practitioners and published as part of the IHP-Humid Tropics Programme Series of UNESCO as no. 7
Large portions of the rain forests of Borneo (mainly in Indonesian Kalimantan and in the Malaysian state of Sabah) were heavily damaged by fire in 1982 and 1983. Accurate and timely assessments of the extent and dynamics of the 'Borneo fires' have been difficult, however, owing to the size and geography of the area. The authors report on a series of observations made using the Advanced Very High Resolution Radiometer (AVHRR) carried on-board the NOAA-7 satellite. Such observations obtained daily by this sensor provide valuable information on the occurrence of the fires and on their impact on the vegetation.-from Authors
This article describes the waste associated with logging and log processing in eastern Amazonia and suggests methods for reducing both waste and forest damage as a result of logging.
Ranching and logging operations are transforming the moist tropical forests of an eastern Amazonian landscape into a mosaic of pastures and regrowth forests. The new ecosystems of this region are agriculturally unproductive, biologically impoverished, and far more flammable than the mature forests they replace. In the absence of fire, the forest regrows on abandoned sites, accumulating biomass and species at a rate that is inversely related to the intensity of use prior to abandonment. Forest regrows slowest on those rare abandoned pastures that were once scraped with bulldozers. The grass- and shrub-dominated old fields that form on some of these sites resist forest regrowth because of numerous barriers to tree establishment and growth. Knowledge of these barriers provides a basis for developing inexpensive techniques to restore agricultural productivity in old fields by implanting tree-based agricultural systems or to restore forest regenerative capacity in old fields by establishing trees that attract seed-carrying animals and ameliorate harsh environmental conditions. These restoration techniques will be needed over large areas of Amazonia if current attempts to reform degraded pastures fail. -from Authors
As the humid tropics may contain some humid forested areas which were very little affected by Quaternary climatic changes and sea-level fluctuations, they represent a particularly important area for the study of geomorphological processes. Many writers have viewed the humid tropics as an area where denudation proceeds much more rapidly than elsewhere but, as much of the energy in the humid tropical ecosystem is used in the development of a highly productive plant community with a massive internal circulation of nutrients, there may be relatively little energy left to carry out geomorphological work. Precipitation is the chief factor affecting denudation rates in the humid tropics, where rivers with torrential run-off derived from cyclone rains carry higher suspended sediment loads than those in the equatorial humid tropics experiencing less prolonged and less intense rainfalls. Differences between the suspended sediments loads of humid tropical and humid temperate rivers may be less than previously thought. The difference between suspended sediment yields of rivers in humid tropical north-east Queensland and the Snowy Mountains of Australia is significant at the 0.05 level only and is thought to arise from the contrast in erosive effectiveness of rainfall and snow. Contrasts in dissolved loads might be expected to be greater, but silica loads of tropical and temperate rivers with the same run-off are shown to be similar. It is concluded that humid tropical denudation processes act less rapidly than had previously been held, save in areas where man or volcanoes destroy the vegetation which plays such an important part in the evolution of humid tropical landscapes.
(1) This study tests the hypothesis that photosynthetic performance of seedlings in a tropical forest depends on the successional status of the species. According to this hypothesis, pioneers display an enhanced capacity to utilize the high photon flux density associated with a gap. (2) Data were collected from nine species representing three ecological groupings: weeds of gaps, pioneer trees and climax trees. Pioneer trees had photosynthetic attributes similar to weeds. Compared to climax trees, both groups had higher stomatal conductances, higher light compensation points, higher rates of dark respiration, much higher mesophyll conductances, and often higher quantum efficiencies. (3) In a fluctuating light regime, there was no support for the hypothesis that species growing in shade show rapid stomatal responses to sunflecks, all species showed fluctuating rates of photosynthesis with little or no adjustment of stomata during the 20-min test.
Amazon logging has been traditionally restricted to floodplain forests, but the Amazon highway system now permits the logging of the interfluvial forest. In an assessment of a mechanized, selective logging operation in Para state, eastern Amazonia, 30-50 m of wood volume were removed per ha. This amounted to four to eight trees per ha, or one to two percent of all tree stems 10 cm dbh. The profits were considerable (the land owner made 9000 in the logging of 52 ha over a 21-day period); but in the process of extraction, 26 percent of all the pre-harvest trees 10 cm dbh were killed or damaged (e.g., 12% lost their crowns, 11% were uprooted by bulldozers, and 3% suffered substantial bark scarring). Total canopy cover was reduced by almost one-half (from 80$% to 45%) and 8% of the forest area was scarred by logging roads. If logging continues at its present rate, all of Para state could easily be logged within the next 80 years. Strategies to promote the responsible use of Para's forest do exist; all that is lacking is the political will to bring them to life.
The influence of vegetation litter on a variety of geomorphological and hydrological processes is stressed, notably as regards retention of rainfall, evaporation and drought in soils, overland flow, rainsplash erosion, weathering, soil characteristics, frost processes and ground vegetation. Results of a laboratory study of retention of rainfall by the litter of two contrasting species, pine (Pinus sylvestris) and beech (Fagus sylvaticus), are presented. The retention properties of immersed single leaves and needles, and of aggregate litters under simulated rainfall conditions are described. Individual beech leaves retain (wt. for wt.) one and a half times the amount of water that pine needles do. This is related to the contrasting physical characteristics of dead leaves and needles, and notably to the much higher surface area/weight ratio of beech leaves. The chief factors controlling absolute amounts of retention of rainfall by aggregate litters are the type of litter (beech retains substantially more water than does pine), and the amount of litter, since the greater the amount of litter, the greater the retention. The retention capacity of litter was soon reached in most of the experiments, and so the percentage of rainfall retained by litter shows a strong inverse relationship with rainfall amount. Differences in percolation in pine litter as compared to beech litter are stressed. Percolation is more direct in pine litter, whereas defined streams of water tend to develop in beech litter. Finally, a tentative model of the retention of rainfall by litter is presented, laying emphasis on the following factors: the amount of litter; type of litter; rainfall characteristics; and evaporation rates. The great variability in amounts (and hence effects) of litter as between different climatic regions of the world is discussed and stressed.
1 We report growth and photosynthetic characteristics of seedlings of two contrasting climax tree species (Shorea leprosula Miq. and Dryobalanops lanceolata Burck., Dipterocarpaceae) growing in three differing forest light environments (ranging from 2.4-21.8 mol photon m-2 day-1) in lowland rain forest in Sabah, Malaysian Borneo. 2 Our aim was to determine whether interspecific differences in seedling ecology reflected differences in the ability of the photosynthetic apparatus to acclimate to light (assessed by measuring photosynthetic light response curves in the field). 3 S. leprosula has been described as a fast growing light-demander whose seedlings will not survive in deep shade whereas D. lanceolata is slower growing with seedlings that can survive a range of light conditions from deep shade to large canopy gaps. 4 Light environments were characterized by analysis of hemispherical photographs taken in the position of each leaf used for photosynthesis measurements, such that we could analyse both within and between site variation. Growth, seedling architecture and mortality were recorded. 5 D. lanceolata showed a greater ability to acclimate to shade, where it had the greater net carbon assimilation rate of the two species at low instantaneous photon flux densities (PFD). Conversely, S. leprosula had a greater ability to acclimate to high light and had greater assimilation rates at high instantaneous PFDs in all environments. 6 Photosynthetic performance, growth and light availability showed strong correlation across environments. Although there were small interspecific differences in photosynthesis within each forest environment, differences in growth and survival were more clearly related to the differing carbon allocation patterns of the two species. 7 D. lanceolata showed an increasing allometric shift in low light in favour of the growth of long branches which are likely to increase sunfleck interception. S. leprosula maximizes height growth and thus has a competitive advantage in more open sites. 8 Although photosynthetic performance paralleled that of growth, we conclude that rates of carbon dioxide fixation alone cannot define the seedling ecology of a species in the absence of information on photosynthate allocation.
Mechanized selective logging in tropical rain forest typically removes only a small percentage of timber trees, but incidental damage may be severe. In a West Malaysian dipterocarp forest, extracting 3.3 percent of trees destroyed 50.9 percent, and damage was spread equally among all tree taxa and all size classes. The overall availability of food sources for frugivores and folivores is thus drastically reduced, even where timber trees are not themselves used by animals. To some extent, the initial loss of food sources may be buffered by increased reproductive and vegetative activity of those trees that remain.
In the Atlantic lowland tropical rainforests of the Rio San Juan region, Nicaragua, we are conducting applied vegetation community analyses within an attempt to integrate non-timber forest products with natural forest management. Two long-term sampling plots were evaluated: one primary tropical rainforest plot before and 1 yr after selective logging, and another plot 9 yr after selective logging with and without Hutchinson Liberation Silviculture treatment (in which selected young trees are released from competition for light). The purpose of the study was to evaluate changes in community ecology variables with logging, damage, regeneration, and silviculture, both for useful plant species and for the plant community as a whole, and to evaluate the potential for incorporating non-timber forest product management with silvicultural management. One year after logging there was an increase in species (from to species/) and density (from to plants/) due to establishment or increase of secondary species (vines, grasses, balsa, cecropia) and to seedling regeneration after logging. The more severe the logging damage the more severe were the effects on some variables, particularly increased densities of vines and secondary species. Forest plots 9 yr post-harvest appeared to be returning to pre-harvest levels of species ( species/) and density ( plants/). Hutchinson Liberation Silviculture, while promoting growth of desired timber, did not significantly affect either non-timber forest products or the basic physiognomy of the forest. These results are contrasted with other silvicultural systems, particularly the Hartshorn Strip Clearcut, in which regeneration was dominated by resprouts and the proportion of vines was even higher. Hutchinson Liberation Silviculture provides the potential for simultaneous management of non-timber forest products, and moreover, non-timber forest product management holds the potential for significantly reinforcing silvicultural management.
Hurricane Hugo struck Puerto Rico on 18 September 1989 and radically altered the canopy structure of forests in the Luquillo Mountains. We measured canopy structure before and after the hurricane in hectare-sized plots of "tabonuco forest" (subtropical wet forest) at 350 m elevation, "colorado forest" (lower montane wet forest) at 750 m, and "cloud forest" (lower montane rain forest) at 1000 m. In all three plots the chief effect of the hurricane was to reduce significantly the vegetation cover in upper height intervals. Foliage profiles (showing percent vegetation cover in height intervals above ground) changed significantly, average maximum canopy height decreased (by as much as 50%), and the amount of low canopy area (vegetation 2 m high) markedly increased (up to 60-fold) in all three plots. In the colorado forest plot the hurricane caused more damage on ridges than in valleys; whereas, the cloud forest plot sustained equal damage on windward and leeward slopes. Overall, the hurricane altered forest structure so much that forest composition and dynamics could be affected for many years. Local variation in hurricane damage can contribute to forest complexity in the Luquillo Mountains.
This study was undertaken to establish whether selective felling and the existence of large forest gaps influence the dynamics of tree and branch falls. Censuses of fallen trees and large branch falls in uncut, lightly cut and heavily cut forest tracts were conducted for 20 months. Dead-standing trees in the study compartments were enumerated only three times at 6-month intervals.In lightly cut forest, the densities of live and dead tree and branch falls were similar but monthly tree snaps were more than uproots. However, for heavily cut forest, total tree falls (snap + uproot) involved more live than dead trees. There were more live than dead tree snaps and the rate of tree uproots was low. in contrast to the above, the density of tree snaps and uproots in uncut mature forest was similar. For total tree falls and live tree or large branch falls, the heavily selectively cut forest exhibited higher rates than uncut and lightly cut forest tracts. The annual rates of live tree falls ha−1 were 1.30 for lightly cut, 3.30 for heavily cut and 1.74 for uncut mature forest. It appears that heavy logging increases tree mortality rates through falls where more live tree snaps than uproots are involved.
Many human activities have impacted genetic diversity in forests (species diversity and genetic diversity within species) by their influence on the evolutionary processes of extinction, selection, drift, gene flow, and mutation, sometimes increasing diversity, as in the case of domestication, but often reducing it. Even in the absence of changes in diversity, mating systems were altered, changing the genetic structure of populations. Demographic changes (conversion of old-growth to younger, even-aged stands) influenced selection by increasing the incidence of disease. Introduction of exotic diseases, insects, mammalian herbivores, and competing vegetation has had the best-documented effects on genetic diversity, reducing both species diversity and intraspecific diversity. Deforestation has operated on a vast scale to reduce diversity by direct elimination of locally-adapted populations. Atmospheric pollution and global warming will be a major threat in the near future, particularly because forests are fragmented and migration is impeded. Genetic inventories of indicator species can provide the baselines against which to measure changes in diversity. -from Author
In lowland dipterocarp forest in Sabah, Malaysia, most primary forest bird species were present in areas selectively logged eight years previously. However, certain taxa, notably flycatchers, woodpeckers, trogons and wren-babblers, became comparatively rare. In contrast, nectarivorous and opportunistic frugivorous species were significantly more abundant. Few species appeared to change foraging height, but netting rates suggest that the activity of some species had increased, or that some birds ranged over larger areas after logging. Although there is still much to be learned about the survival of birds in logged forest, large areas of this habitat are important for bird conservation. However, the susceptibility of logged forest to fire, and our present incomplete understanding of bird behaviour and population dynamics in logged forests mean that they should not be considered by conservationists as alternatives to reserves of primary forest.
The research was carried out from January 1981 to December 1983, in a small watershed of 1.3 km2 surface area located at INPA's Ducke Forest Reserve. This watershed is drained by the Barro-Branco stream, and its vegetation cover is characterized by a typical tropical rain forest of the central Amazon region.In order to estimate its real evapotranspiration, transpiration and other hydrological parameters, the precipitation and the discharge yielded by the Barro-Branco stream were measured during the experimental period.A mean precipitation of 2209 mm year−1 was recorded, from which 67.6% was lost to the atmosphere through evapotranspiration. This result was similar to that calculated by the modified Penman's method (1479.2 mm year−1).If the average rain water interception by the forest canopy is assumed to be 11.3% of the total precipitation amount, as estimated by Gash's model, the transpiration was 1243.7 mm year−1, representing 56.3% of the total rainfall observed for the 1981–1983 period.
Figs Ficus spp. are of exceptional importance to many frugivorous bird species in Malaysian forests. During selective logging operations epiphytic and strangling Ficus are particularly prone to loss because of their tendency to grow on commercial timber species of harvestable size. The conservation of important Ficus species within logging concession areas or other areas of degraded forest is recommended as a measure to assist the survival of vulnerable fig-eating bird species.
We present the results of an experiment to assess the damage caused by logging a 19 ha plot of upland rainforest under the Queensland Selective Logging System. Logged trees were concentrated along ridges and mean removals were 6.6. stems, 4.9 m2 basal area and 37 m3 logs ha−1. Losses from the whole stand were highest in the smallest and largest size classes and averaged 146.7 stems ha−1 and 12 m2 ha−1. No tree species were eliminated by logging. Twenty two percent of the canopy was lost and fish eye photography showed that the amount of light reaching the ground was even altered on areas that received no overhead canopy loss. Changes in canopy profiles were complex not just a simple reduction of the upper layers. Logging tracks occupied 5% of the area. These results are compared with a range of other studies in Queensland and overseas. The Queensland system appears to cause less incidental damage than those reported from South East Asia. Recommended improvements to the Queensland system include extracting more timber from the crowns of felled trees, increasing winching and improving erosion control from major roads. Most importantly, enhancing the skills, sensibilities and cooperation of field personnel is considered to be vital in further reducing damage.
It is suggested that evolution in plants may be associated with the emergence of three primary strategies, each of which may be identified by reference to a number of characteristics including morphological features, resource allocation, phenology, and response to stress. The competitive strategy prevails in productive, relatively undisturbed vegetation, the stress-tolerant strategy is associated with continuously unproductive conditions, and the ruderal strategy is characteristic of severely disturbed but potentially productive habitats. A triangular model based upon the three strategies may be reconciled with the theory of r- and K-selection, provides an insight into the processes of vegetation succession and dominance, and appears to be capable of extension to fungi and to animals.
Published observations on adaptations for seed disperal and seedling establishment are consistent with the hypothesis that rainforest trees partition forest clearings as establishment sites for offspring. Gaps vary importantly in two ways. The size of the opening affects the microclimate of the gap and therefore the conditions for seedling establishment. For any individual tree, the frequency of occurrence of gaps of a particular size range affects the probability that its propagules will reach a gap of suitable size for germination and establishment. In most rainforests large gaps (involving the death of several trees) are probably more rare than small gaps (involving single trees or branches). Interspecific competition for establishment sites has resulted in adaptive compromises in the regeneration strategies of each species. Traits that increase the probability of establishing seedlings in gaps of a particular size range appear to lower establishment in gaps outside this size range. I suggest that the coexistence of many rainforest tree species is at least partially due to their partitioning of canopy gaps by size. Therefore the size-class frequency distribution of gaps peculiar to a given rainforest is expected to influence the types and diversity of species present. Examination of vegetation data from New and Old World rainforests reveals many patterns consistent with this hypothesis. This framework provides a mechanism for predictive and experimental studies of competitive interactions among rainforest trees.
summarySeedlings of four species of the genus Shorea section Doona were examined. All co-exist in the moist evergreen rain forest of southwestern Sri Lanka. Experiments were designed to investigate some physiological and anatomical attributes of leaves under different light conditions. The attributes considered were net photosynthesis, transpiration, stomatal conductivity, blade and cuticle thickness, stomatal frequency, thickness of upper epidermis and palisade mesophyll, and number of palisade layers. Results demonstrate the close association between anatomical adaptation and efficiency in physiological processes. Results also elucidate some of the relationships between distribution patterns of species across the forest topography and their differences in light and drought tolerance. This indicates that an important period determining site specialization of a species occurs during regeneration establishment. These relationships are not as simple or as ecologically noticeable though as for those relationships documented in many previous studies between tree species of markedly different successional stages or taxonomy.
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This concluding survey1 of the problems considered in the Symposium naturally falls into three sections. In the first brief section certain of the areas in which there is considerable difference in outlook are discussed with a view to ascertaining the nature of the differences in the points of view of workers in different parts of the field; no aspect of the Symposium has been more important than the reduction of areas of dispute. In the second section a rather detailed analysis of one particular problem is given, partly because the question, namely, the nature of the ecological niche and the validity of the principle of niche specificity has raised and continues to raise difficulties, and partly because discussion of this problem gives an opportunity to refer to new work of potential importance not otherwise considered in the Symposium. The third section deals with possible directions for future research.
The Demographic
There was fruiting of the dipterocarps of Pantai Aceh Forest Reserve, Penang, Peninsular Malaysia in September 1986. The opportunity was taken to investigate the establishment and seedling survival of Shorea curtisii, Shorea multiflora and Shorea pauciflora over the subsequent year. The germination and seedling survival of Shorea curtisii was compared between canopy gaps and forest understorey sites.
Under the shaded conditions none of the species grew beyond the two leaf stage over their first year. Shorea multiflora seedlings suffered a 72% mortality, significantly lower than that of Shorea pauciflora (89%) and Shorea curtisii (93%). The major cause of mortality appeared to be drought, though Shorea curtisii was also prone to predation by small mammals.
In a gap, Shorea curtisii seeds probably germinated less well but seedling survival (28% versus 7%) and growth was better than canopy-shaded conspecifics. Seedlings in gaps escaped small mammal predation.
The Kibale Forest, western Uganda, is the only site where studies have compared the impact of elephants on rainforest regeneration in logged and unlogged control areas. Elephants used heavily logged areas more than lightly logged and unlogged areas. Forest gaps were used more by elephants than closed-canopy areas and large gaps more than small ones. Gaps were larger in logged than unlogged forest. There were lower densities of young trees (saplings and poles) and a higher incidence of elephant damage to them in heavily logged forest than in lightly logged and unlogged sites. Elephant use of an area and damage to young trees was inversely or unrelated to the density of young trees and directly related to the density of herbaceous tangle. Heavy logging resulted in large areas of herbaceous tangle, which attracted elephants who suppressed forest regeneration by damaging young trees and perpetuating the herbaceous tangle. The tangle directly competed with regeneration of young trees while also attracting elephants and rodents (seed and seedling predators) and facilitating increased windthrow of trees. Selective browsing of young trees by elephants affected rates of regeneration, growth form and species composition. Rather than remove elephants, a more effective and humane approach to long-term management of logging is to reduce logging offtake and incidental damage caused by timber extraction.