Harvesting intensity affects forest structure and composition in an upland Amazonian forest

Forest structure and floristic composition were studied in a series of 0.5 ha natural forest plots at four sites near Porto Trombetas in Pará State, Brazil, 11–12 years after being subjected to differing levels of above-ground biomass harvest and removal. In addition to undisturbed control plots, experimental treatments included: removal of most trees ≥45 cm DBH (low intensity harvest); removal of trees <20 and ≥60 cm DBH (moderate intensity harvest); clear-cutting (100% above-ground biomass removal). Post-harvest basal area growth generally increased with harvest intensity, and total basal areas for trees ≥5 cm DBH were, at the time of our study, 60% (in the clear-cut) to about 80% of those in the control plots. Biomass harvests stimulated recruitment and growth of residual trees, particularly in the smaller diameter classes, but had little effect on species richness for small trees, seedlings, vine, herbs, and grasses. Species richness for trees ≥15 cm DBH was greater in the control and low-intensity (74–75 species) than in the moderate intensity (47 species) and clear-cut (26 species) treatment plots. While the tree flora within all harvest treatments was broadly similar to the undisturbed (control) plots and included similar numbers of species of the major plant families typical of the surrounding forests, the more intensive harvest treatments, especially the clear-cut, were dominated by a higher proportion of short-lived, early successional tree species.     

Seasonal leaf dynamics in an Amazonian tropical forest

The ecological consequences of climate change for large tropical forests such as the Amazon are likely to be profound. Amazonian forests strongly influence regional and global climates and therefore any changes in forest structure, such as deforestation or die-back, may create positive feedback on externally forced climate change. Monitoring, modelling and managing the impacts of anthropogenic climate change on forest dynamics is therefore an important objective of forest researchers, and one that requires long-term data on changes at the level of community, populations and phenotypes. In this paper we provide the most comprehensive study yet on the seasonal dynamics of various leaf traits: leaf area index (LAI), leaf mortality (LM), leaf biomass (LB), leaf growth rate (LG), and leaf residence time (TR) from 50 experimental plots in a forest site at Belterra, Pará State, Brazil. From this study we estimate annual mean leaf area index (LAI) to be 5.07 m² m⁻² and annual mean leaf dry biomass to be 0.621 kg m⁻². The typical leaf grew at 0.049 kg m⁻² month⁻¹ and remained on the tree for 12.7 months. We compare these results to other similar studies and critically discuss the factors driving leaf demographics in Amazonia.     

The influence of windthrow microsites on tree regeneration and establishment in an old growth mountain forest

The Rothwald forest in Lower Austria represents one of the few never logged old growth forests in Central Europe. Here, the influence of windthrow pits and mounds on tree regeneration in a spruce-fir-beech mountain forest was studied. Two main factors for recolonisation of sites after disturbance were investigated: (i) the trapping ability of microsites for seeds and (ii) the ability of particular tree species to establish and grow on different microsites. On two one hectare permanent sample plots, pits resulting from windthrow with existing tree trunks were recorded. At each windthrow three microsites were determined: pit, pitwall and undisturbed forest floor. If the windthrow plate already collapsed and formed a mound, this microsite was recorded as well. Furthermore, a control site was established at each windthrow. For two years the development of seedlings at four different microsites and the according control sites were monitored. To describe the variability of environmental factors possibly influencing seedling establishment and survival, litter, humus and soil attributes, herb vegetation cover as well as light availability (GSF) were assessed. In addition, soil temperature, chemical soil properties and water content were recorded at randomly selected windthrows. The distribution of the seedlings was assessed with a Redundancy Analysis, its occurrence modelled with a logistic regression and the mortality analysed with the Kaplan-Maier lifetime function. In contrast to the assumption of seed accumulation in concave microsites because of secondary dispersal, the pit microsites show comparable seed rain to the control site. However, pits have the lowest seedling numbers and by far the highest mortality rates of seedlings. The thickness of leaf litter was identified as a major driver of suitability of a microsite for recolonisation. Through its thickness, it inhibits germination and smothering of seedlings poses a particular high hazard during the winter period. Also different establishment patterns of the investigated tree species were detected. The results indicate that windthrows create microsite heterogeneity and plant species richness but limit tree population size and spatial distribution of the occurring tree species.     

Bamboo dieback and tree regeneration responses in a subtropical forest of South America

Bamboos’ vegetative growth are frequently associated to negative effects on tree recruitment and survival and despite this process, the effects of bamboo dieback after flowering events are poorly understood due the rarity of these events. 2 years after the massive flowering of the woody bamboo Merostachys multiramea in a southern South America subtropical forest, we compared changes in environmental conditions; tree species regeneration and production of new culms in canopy gaps resulted from bamboo dieback and areas of continuous canopy allowed by sparse bamboo cover. We observed sharp differences in environment conditions mainly resulted from differences in canopy openness and a NPMANOVA revealed differences among the stands regeneration directions (species composition and density). Average density, number of culms per sapling and total height of M. multiramea did not differ between stands, although slight differences were detected with increasing values toward opened sites.     

Timber tree regeneration along abandoned logging roads in a tropical Bolivian forest

Sustainable management of selectively logged tropical forests requires that felled trees are replaced through increased recruitment and growth. This study compares road track and roadside regeneration with regeneration in unlogged and selectively logged humid tropical forest in north-eastern Bolivia. Some species benefited from increased light intensities on abandoned logging roads. Others benefited from low densities of competing vegetation on roads with compacted soils. This was the case for the small-seeded species Ficus boliviana C.C. Berg and Terminalia oblonga (Ruiz & Pav.) Steud. Some species, e.g. Hura crepitans L., displayed patchy regeneration coinciding with the presence of adult trees. Our results suggest that current management practices could be improved by intensifying logging in some areas to improve regeneration of light demanding species. Sufficient seed input in logged areas should be ensured by interspersing large patches of unlogged forest with logged areas. This may also assist regeneration of species that perform poorly in disturbed areas.     

The influence of storm-induced microsites to tree regeneration patterns in boreal and hemiboreal forest

We reviewed studies dealing with regeneration under variable conditions in boreal and hemiboreal forests as affected by different microsite types by tree species functional groups. Generally, the importance of storm-induced microsites for regeneration dynamics in boreal forests depends on several factors: (1) distribution and type of microsites (generated by storm characteristics and stand conditions); (2) viable seed supply (stand history, species dispersal traits and status of surviving trees) and their species’ life history strategy; (3) climatic and site conditions (pre-storm conditions and storm-induced changes); and (4) delayed storm effects, such as retarded falling of trees, favoured vegetation growth, etc. Studies acknowledging the significance of microsites were mostly related to intermediate or severe events, causing sufficient changes in resource levels and growth conditions, and influencing extrinsic factors such as frost heaving, erosion and browsing. Also, the dispersal traits of available tree species, including sprouting and response of surviving trees, such as canopy expansion, should be considered in evaluating microsite importance in individual cases. In intermediate to severe windstorm events, pioneer species are generally profiting most from the additional offer in microsites, requiring bare mineral soil and elevated locations for their establishment and growth. Under gap dynamics, shade-tolerant species benefit from dead wood and elevated locations as these offer safe sites in stands with abundant understorey vegetation.     

Mechanical cleaning and prescribed burning for recruiting commercial tree regeneration in a Bolivian dry forest

A critical component of sustainable forest management is the regeneration of commercially valuable tree species. Mechanical cleaning with machetes and chainsaws, prescribed burning, and a combination of both treatments were applied to recently-created logging gaps in a Bolivian dry forest to evaluate their impact on the natural regeneration of commercial tree species and on control of competing vegetation. The three treatments and an untreated control were applied to logging gaps during the dry season of 1998 and replicated ten times. Eight months following burning, the density of commercial tree regeneration in gaps did not differ statistically among treatments. Relative height growth of total commercial regeneration also did not differ among treatments, although it did vary by species. Reduction in competing vegetation following the application of site preparation treatments was significantly higher, but competing plant cover was beginning to converge among treatments after eight months. Despite better control of competing vegetation, early recruitment and growth responses to burning and cleaning of vegetation in logging gaps do not appear to justify application of these treatments in this forest, especially considering their high costs.     

Nitrogen uptake from 15N-enriched fertilizer by four tree crops in an Amazonian agroforest

Mixed tree cropping systems have been proposed for sustainable nutrient management in the humid tropics. Yet, the nutrient interactions between intercropped trees have not been addressed sufficiently. In the present study we compare the temporal and spatial patterns of the uptake of applied ¹⁵N by four different tree crops in a mixed tree cropping system on a Xanthic Ferralsol in central Amazônia, Brazil, during one year. Most of the N uptake occurred during the first two weeks. Very little N was recovered by peach palm (Bactris gasipaes), more by cupuassu (Theobroma grandiflorum) and annatto (Bixa orellana) and most by Brazil nut (Bertholletia excelsa). Due to tree pruning the total accumulation of applied ¹⁵N in the above-ground biomass of annatto decreased throughout the year. It remained constant in cupuassu and peach palm and increased in Brazil nut. Brazil nut showed an extensive root activity and took up more fertilizer N applied to neighboring trees than from the one applied under its own canopy in contrast to the other three tree crops. Therefore, trees with wide-spread root systems may not need to receive N fertilizer directly but can take up N applied to other trees in the mixed cropping system. This means that such trees may effectively decrease N leaching when intercropped with trees that have dormant periods or places with low N uptake, but also exert considerable resource competition.This revised version was published online in November 2005 with corrections to the Cover Date.     

Logging and topographic effects on tree community structure and habitat associations in a tropical upland evergreen forest,Ghana

We determined the response of tree community structure to logging disturbance and topography,and the patterns of tree-habitat associations in Tano Offin Forest Reserve,Ghana.We sampled trees in 27 20 m× 20 m plots randomly and equally distributed in three topographic habitats(slope,valley,and hilltop) in each of two forests:logged and unlogged.Two topographic features,altitude and degree of slope,were measured and related with species composition.Overall,there were significant effects of logging and topographic habitat and their interaction on species diversity and composition,with the unlogged forest and valley habitat supporting higher diversity.Tree diversity varied among the topographic habitats in the logged but not in the unlogged forest.There were topographic effects on abundance of individual species but not on tree community abundance and basal area.Logging and its interaction with topographic habitat showed significant effects on tree abundance and basal area.Some species were associated with specific topographic habitats or a combination in the logged and unlogged forests.However,the patterns of habitat associations of the species differed between the logged and unlogged forests.     

Photosynthetic capacity in a central Amazonian rain forest

The vertical profile in leaf photosynthetic capacity was investigated in a terra firme rain forest in central Amazonia. Measurements of photosynthesis were made on leaves at five levels in the canopy, and a model was fitted to describe photosynthetic capacity for each level. In addition, vertical profiles of photosynthetic photon flux density, leaf nitrogen concentration and specific leaf area were measured. The derived parameters for maximum rate of electron transport (J(max)) and maximum rate of carboxylation by Rubisco (V(cmax)) increased significantly with canopy height (P < 0.05). The highest J(max) for a single canopy level was measured at the penultimate canopy level (20 m) and was 103.9 &mgr;mol m(-2) s(-1) +/- 24.2 (SE). The highest V(cmax) per canopy height was recorded at the top canopy level (24 m) and was 42.8 +/- 5.9 &mgr;mol m(-2) s(-1). Values of J(max) and V(cmax) at ground level were 35.8 +/- 3.3 and 20.5 +/- 1.3 &mgr;mol m(-2) s(-1), espectively. The increase in photosynthetic capacity with increasing canopy height was strongly correlated with leaf nitrogen concentration when examined on a leaf area basis, but was only weakly correlated on a mass basis. The correlation on an area basis can be largely explained by the concomitant decrease in specific leaf area with increasing height. Apparent daytime leaf respiration, on an area basis, also increased significantly with canopy height (P < 0.05). We conclude that canopy photosynthetic capacity can be represented as an average vertical profile, perturbations of which may be explained by variations in the environmental variables driving photosynthesis.     

Effects of grazing on natural regeneration of tree and herb species of Kheyroud forest in northern Iran

We investigated the effects of grazing on natural regeneration, quantity, and diversity of woody species and dominant herb species in Kheyroud forest in northern Iran. We sampled vegetation in 5m2 plots in custom units, which are demarcated resource areas traditionally used by local livestock producers. The authors quantified number of species, height of seedlings, and diameter of seedlings. Height classes were 0-30 cm, 30-130 cm, and >130 cm, and diameter classes were 0-2.5 cm, 2.5-5 cm and 5-7.5 cm. The density of seedlings declined with distance from corral until reaching the custom unit boundary. Most seedlings had diameters of 0-2.5 cm and heights of 0-30 cm. Predominant species, Carpinus betulus and Acer capadocicum, were in plots near the centers of custom units, Fagus orientalis, Acer velutinum, Quercus castanifolia species were dominant in plots near the custom unit boundary. Plant species such as Oplismenus undulatifolius, Euphorbia amygdaloides, Rubus fruticos and Pteridium aquilinum were dominant in plots nearer to forest corral. Healthy seedlings were more numerous in plots nearest the corral, while defective and deformed seedlings were more abundant away from the corral. We conclude that grazing had negative effects on the quantity and quality of vegetative regeneration. Continuation of overgrazing will not only endanger the sustainability of forest ecosystems, but also will increase the challenge of sustainable forest management.     

Does the herb Acanthus pubescens and/or elephants suppress tree regeneration in disturbed Afrotropical forest?

As a result of extensive deforestation, the survival of many tropical forest species may depend on disturbed forests. However, recent studies demonstrate that tree regeneration following logging can be slow, decreasing the conservation value of disturbed forests. Here we test whether the dominating herb, Acanthus pubescens, in the understory of logged forest, suppresses tree regeneration in Kibale National Park, Uganda. We compare the establishment, growth, and survival of tree seedlings over 2.5 years between sites cleared of A. pubescens and controls. We also consider the role of elephants (Loxodonta africana) in inhibiting tree regeneration. Seedling abundance and species richness was greater in cleared than control plots at the start of the study. Seedling abundance decreased over the study, but remained greater in cleared than control plots. Species richness did not vary over the study. However, species composition of the cleared plots was marginally different from control plots at the start, but converged on the composition of control plots by the end of the study. This suggests a common regeneration assemblage derived from reorganisation of species, rather than recruitment of new species. There was no difference in recruitment rates between cleared and control plots. These findings suggest no strong direct effects of the herb on tree regeneration in this disturbed forest. However, when we modelled (i.e., removed) the effect of elephants on regeneration, the abundance of seedlings increased in both plot types and remained reasonably constant over time. The decline in density of regenerating stems over the study was most likely caused by elephants visiting the plots. We conclude that elephants have a far greater effect in suppressing tree regeneration at Kibale than the herb stratum and are ultimately responsible for arresting succession in disturbed forest. However, as intensive logging creates conditions favourable for A. pubescens, which is eaten by elephants, the best management intervention is to constrain logging intensities to below levels above which widespread establishment of A. pubescens is promoted, thus limiting elephant activity in regenerating areas.     

The ecology of tree regeneration in mature and old forests: combined knowledge for sustainable forest management

We focused our attention on quantifying the factor complex of forest regeneration in 423 mature and old stands with contrasting environmental conditions. We recorded the microhabitat selection of tree recruits, the frequency of tree seedlings, and evaluated the drivers of sapling abundance and diversity. The majority of forest regeneration was established on undisturbed forest floor. Dead wood was a frequent substrate in spruce-(co)dominated forests. Seedling frequency within a stand was related to the site-type specific productivity gradient of stands—pine seedlings were common in low-productivity and spruce in high-productivity boreal forests. Seedlings of temperate broad-leaved trees dominated in productive boreonemoral forests, except for oak, which showed a uniform distribution of abundance in all forest site-types. Sapling abundance was dictated by forest site-type, and facilitated by stand diversity, variability in stand closure, lying dead wood, abundant moss, and a thick organic layer. Only in boreal forests was sapling abundance suppressed by the abundant spruce and younger trees. Upon considering the relationship between sapling abundance and species richness, sapling diversity was dependent on forest site-type, suppressed by stand density and dead wood (old gap) abundance, and facilitated by stand diversity. In addition, boreonemoral stands, competition from herbs, and facilitation by mosses occurred. The observed pattern of tree recruitment points to the importance of top-down effects of the overstory, competing or facilitating interactions with forest floor vegetation, and availability of regeneration microhabitats, which in complex make their ecology comparable with forest herbs. Natural forest regeneration can be enhanced if silvicultural methods support mixed stands and enhance field layer diversity. Oak can provide the universal tree species to improve stand structure over a wide range of habitats.     

The composition and diversity of natural regeneration of tree species in gaps under different intensities of forest disturbance

The positive ecological interaction between gap formation and natural regeneration has been examined but little research has been carried out on the effects of gaps on natural regeneration in forests under different intensities of disturbance.This study evaluates the composition,diversity,regeneration density and abundance of natural regeneration of tree species in gaps in undisturbed,intermittently disturbed,and disturbed forest sites.Bia Tano Forest Reserve in Ghana was the study area and three gaps each were selected in the three forest site categories.Ten circular subsampling areas of 1 m2 were delineated at 2 m spacing along north,south,east,and west transects within individual gaps.Data on natural regeneration 350 cm height were gathered.The results show that the intensity of disturbance was disproportional to gap size.Species diversity differed significantly between undisturbed and disturbed sites and,also between intermittently disturbed and disturbed sites for Simpson's(1-D),Equitability(J),and Berger-Parker(B-P) indices.However,there was no significant difference among forest sites for Shannon diversity(H) and Margalef richness(MI) indices.Tree species composition on the sites differed.Regeneration density on the disturbed site was significantly higher than on the two other sites.Greater abundance and density of shade-dependent species on all sites identified them as opportunistic replacements of gap-dependent pioneers.Pioneer species giving way to shade tolerant species is a natural process,thus make them worst variant in gap regeneration.     

Forest gap dynamics and tree regeneration

When one or a few canopy trees die (or are injured) in a forest, small openings, which are called ‘gaps,’ are formed in the forest canopy and are then filled with other trees. This sort of forest dynamics is termed gap dynamics; a large number of papers and data on gap dynamics have been accumulated since the 1970’s, and gap dynamics has been described in many forest types. In this review, I introduce the basic concepts of gap dynamics and summarize major issues on gap dynamics relating to tree regeneration, with many references. Although enormous studies on gap dynamics of natural forests have been conducted, applications of gap dynamics to forest practice are limited. However, accumulated knowledge on gap dynamics should be useful for sustainable forest ecosystem management, as much of the literature suggests. Recipient of the Japanese Forestry Society Award 2000.     

Increased forest production through forest tree breeding

Forest tree breeding started in the middle of the twentieth century and since then the use of improved forest regeneration material has become an essential part of forestry in many countries. This review describes methods and achievements of tree breeding programmes, which aim at increasing the quantities and improving qualities of wood-based raw materials through selection, field testing and controlled crossings. Most improved materials currently deployed are seed crops from first-generation phenotypic or tested seed orchards, which offer 10–25% gains in yield depending on the selection intensity of parent trees. Methods of vegetative propagation are developed intensively so that it could be applied to a larger range of species, because it offers high genetic gain and uniformity of the material. Genomic tools are also developed to enhance the efficacy of selection. Applications of genetic engineering are currently limited to research purposes. Forest tree breeding will be an integral part of bioeconomy in securing the production of good quality raw materials in large quantities and will have a significant economic impact on the profitability of forestry in the long term.     

Characterization and antioxidant activity of Amazonian woods

The heartwood and sapwood characteristics of 11 Amazonian trees were investigated. Whereas 7 of the specimens had densities greater than 0.7 g/cm³, the heartwood density of ipê amarelo (Tabebuia serratifolia), maçaranduba (Manilkara huberi), cumaru-ferro (Dipteryx odorata), and guarita (Astronium lecointei) exceeded 1.0 g/cm³. Jatobá contained small amounts of Klason lignin and α-cellulose, and large amounts of holocellulose and alkali extract, suggesting that it has a high polysaccharide content that can be dissolved in an alkaline medium. The difference in the syringyl/guaiacyl (S/G) ratios of the samples before and after alkali extraction suggests that alkali extracts contain syringyl-type polyphenols. In all of the samples, the heart-wood methanol extracts were larger in volume than the sapwood methanol extracts, and the sapwood alkali extracts were larger in volume than the heartwood alkali extracts. The antioxidant activities of the methanol and alkali extracts were assayed by measuring the levels of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and super oxide dismutase (SOD)-like activity, respectively. The heart-wood methanol extract of jatobá (Hymenaea courbaril) exhibited the highest level of activity (EC₅₀ = 44 mg/l), which exceeded that of α-tocopherol (EC₅₀ = 48 mg/l), and the heartwood alkali extracts of jatobá and ipê amarelo had high SOD-like activity comparable with red wine.