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The spatial distribution of canopy gaps was analysed on three sites (total 71 ha) in the tropical moist forest of Tal National Park, Ivory Coast. Pattern analysis revealed a clustered distribution of gaps for two of the three sites. Catena dependent gap formation processes might explain local differences in the occurrence and distribution of gaps. Gap densities, sizes and percentage forest area in gap phase are higher on the upper and middle slope than on the crest or lower slope. As a consequence, regeneration of gap dependent tree species might be directed to the catena positions with the highest disturbance regime. The spatial distribution of gap dependent species can be clumped, not only due to the regeneration within gaps, but also due to the clustered nature of gap distribution on its own.
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... There is also a much longer history of research on the lower end of the canopy-height distribution (Hubbel and Foster 1986, Jans et al. 1993, Poorter et al. 1994, Kellner, Clark and Hubbell 2009, Lobo and Dalling 2014, Hunter et al. 2015. This work has focused on the spatial extent and rate of occurrence and disappearance of low-canopy microsites, usually termed "gaps". ...
... Intersite comparisons therefore require a common gap definition or an empirically-based correction between definitions. In studies in old-growth tropical rainforests that were based on the definition we used at La Selva (a patch with top vegetation height < 2 m; Brokaw 1982), total gap extent was estimated as 0.8-1.5% of the forest area (Hubbell and Foster 1986, Jans et al. 1993, Poorter et al. 1994, Van der Meer and Bongers 1996. ...
Article
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The distribution of canopy heights in tropical rainforests directly affects carbon storage and the maintenance of biodiversity. We report results from a unique 20‐year record of annual monitoring of canopy‐height distributions across an old‐growth tropical rainforest landscape at the La Selva Biological Station in Costa Rica. Canopy heights to 15 m were measured annually in 18 0.50 ha plots at 231 points on a 5 x 5 m grid from 1999‐2018 (9 plots in 1999), and heights >15 m were classified as “high canopy”. During the study two major disturbance events (one immediately prior to the study) dominated the landscape‐scale distribution of canopy heights. Height recovery from the 1997‐1998 strong El Niño disturbance took approximately 15 years. Frequency of canopy gaps varied an order of magnitude among years, and 96% disappeared in ≤2 years. High‐canopy coverage and gap frequency varied substantially across the local gradients of soil nutrients and topography, and plot‐level conditions and trends frequently differed from the landscape‐level patterns. In contrast to the two major landscape‐level disturbances, significant plot‐level disturbances were common throughout two decades. Including a similar data set taken in 1992, canopy‐height distributions for the last three decades over this old‐growth tropical rainforest landscape are most parsimoniously interpreted as showing local disturbance and recovery and no unidirectional trends over time. Together these results suggest that understanding the landscape‐ and plot‐level dynamics of tropical rainforest canopy‐height distributions will require repeat sampling for multiple decades, while accurately measuring gap frequency and recovery will require sample intervals of ≤2 years.
... Shallow soils and high windspeed also lead to more canopy gap [152] Dynamics [153] formation (Poorter et al. 1994) [153] ...
... In addition, near to the crest soils tend to be shallow, which in combination with high wind speed leads to a more stunted vegetation (Lawton and Putz 1988) where many small trees may provide more trellis for lianas. Shallow soils and high windspeed also lead to more canopy gap formation (Poorter et al. 1994) and light, and hence more opportunities for liana recruitment and growth. ...
... Curzon and Keeton (2010) found clustering of canopy gaps in Tsuga canadensis-northern hardwood stands and McNab et al. (2004) found clusters of large canopy openings following hurricane disturbance in stands of the Appalachian Highlands. In addition to storm-related characteristics, a range of biophysical site conditions may also explain the underlying mechanisms of opening patterns including topography, soil conditions or neighborhood effects (Poorter et al., 1994). ...
Article
Mixed Quercus-Pinus stands are increasingly desired by forest managers to achieve a range of objectives, including biodiversity enhancement and resilience to global change. To create and perpetuate desired mixed Quercus-Pinus stand composition and structure, quantitative information on natural disturbance impacts on stand development and succession is necessary. Wind is the most common natural canopy disturbance in eastern North America, and impacts vary in severity and spatiotemporal scales. Intermediate-severity disturbance (ISD; events that occur along a classification gradient between frequent gap-scale and infrequent, stand-replacing events) is hypothesized to be an important driver of mixed Quercus-Pinus creation and maintenance. Our overarching goal was to quantify patterns of intermediate-severity wind disturbance in a mixed Quercus-Pinus echinata Mill. forest on the Cumberland Plateau in Tennessee, USA. Specifically, our objectives were to: 1) quantify post-disturbance species composition, stand structure, and residual tree spatial patterns, 2) infer individual-tree, neighborhood, and site-specific impacts on tree mortality, and 3) describe frequency, size, shape, and spatial distribution of ISD-created canopy openings. We inventoried plots in Pinus echinata-dominated, disturbance-impacted portions of the forest. To infer individual-tree and spatially-explicit neighborhood characteristics that influenced survival probability, we applied a random forest classification algorithm. To document changes in tree spatial distribution before and after disturbance, we used spatial point pattern analysis. To characterize forest-scale disturbance patterns, we classified canopy gaps from high-resolution orthoimagery. The most important predictors of survival were basal area, taxonomic group, and distance to nearest neighbor. Pre-disturbance trees and residuals were spatially randomly distributed. Most detected openings were 50-150 m 2 , and the opening size-frequency distribution exhibited a reverse J-shape. Openings were spatially clustered within the forest at distances < 200 m and complex in shape. We provide quantitative recommendations on the frequency, size, shape, and spatial distribution of silvicultural entries patterned after natural disturbance. To emulate natural disturbance patterns, we recommend patch seedtree harvests with reserves or patch clearcuts with reserves, and these harvest-created openings should be concentrated (i.e., clustered) in portions of the stand in which P. echinata is most dominant and/or most competitive. Site preparation with prescribed fire, herbicide, and/or mechanical thinning may also be necessary to prepare the seedbed and reduce hardwood competition to favor Pinus establishment in openings.
... Mortality in old-growth forests is frequently density independent and do not change the spatial pattern of surviving trees (Larson et al., 2015). Putting these facts together, the interplay between the aggregated nature of the many phenomena causing the mortality of canopy trees, vertical stand structure and canopy heterogeneity is not obvious and as such has been an interesting area for scientific exploration in the forest ecosystems of tropical (Lawton and Putz, 1988;Poorter et al., 1994;van der Meer and Bongers, 1996;Trichon et al., 1998;Salvador-van Eysenrode et al., 2000) and temperate zones (Runkle and Yetter, 1987;Runkle, 1990;Frelich and Lorimer, 1991;Hessburg et al., 1999;Nuske et al., 2009). ...
Article
The action of many agents causing the mortality of overstory trees may potentially induce the formation of an aggregated distribution of canopy gaps. In this study we tested the hypothesis that natural stand dynamics generates an aggregated pattern of canopy openness in old-growth forests formed by Fagus sylvatica L., Abies alba Mill. and Picea abies (L.) H. Karst. We compared canopy openness and its spatial heterogeneity in five stands in the Western Carpathians (Central Europe) and three stands in the Dinaric Mountains (Southeast Europe). The stands were between 4.48 and 9.24 ha in size. In each stand we took hemispheric photographs in a regular 20 × 20 m grid in the leafless period to minimize coverage by the understory. Tree species and the dbh of live trees of dbh ≥7 cm were recorded on circular plots with a radius of 7 m centered at the grid points. At the stage of picture processing, understory trees of dbh <25 cm and polar coordinates recorded during field measurements were removed from the pictures, and for every grid point the local canopy openness of the overstory layer was determined in the sky region defined by a zenith angle of 15°. We characterized the spatial pattern of canopy openness by using variograms and Moran’s I coefficients and tested the spatial dependence in the distribution patterns of grid points characterized by different levels of canopy openness. Depending on the stand, mean canopy openness varied between 17.5 and 41.0%, with the greatest values recorded in the Carpathian stands with a considerable proportion of Norway spruce and a more severe disturbance regime. Relationships between canopy openness and the overall number, basal area or volume of trees forming the overstory were strongly modified by variation in the density and species percentage in the mid-canopy zone. In all the stands small-scale variation determined for inter-point distances of 20 m accounted for the majority of the total variation in canopy heterogeneity and ranged between 61 and 100%. We found a tendency to form random patterns of canopy openness in the Dinaric stands, which were characterized by a greater basal area and probably also lower frequency of severe disturbances, and aggregated patterns in the Carpathian stands, which were characterized by a smaller basal area driven by more severe disturbances. The revealed spatial dependence in canopy openness may suggest that in the studied ecosystem canopy gaps are not only a legacy of the mortality of canopy trees but also self-organizing structural elements which, under a more severe disturbance regime, can affect the mortality rate in their neighbourhood. Nonetheless, the percentage of spatially structured variability in canopy openness observable at scales larger than the grid spacing used in our study was insignificant (83% on average). The close-to-random pattern of canopy heterogeneity may weaken the spatio-temporal synchronization of the juvenile growth, maturation and senescence of neighbouring trees and counteract the formation of coarse-grained patch mosaics.
... African forest was ascribed to changes in soil characteristics over a larger elevational gradient than present at Noh Bee (Poorter et al. 1994). ...
Thesis
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... In Côte d'Ivoire, three protected areas were selected for Dosso et al. 2010), the lowland evergreen seasonal forest in Taï National Park (a locality with yellow-brown, often waterlogged soils: Poorter et al. 1994), and the evergreen Banco National forest located Northwest of Abidjan (a forest with old trees, sandy and drainable soils bordered by wild banana trees and three access roads). One additional location, an oil palm plantation, was selected for sampling along the Dabou-Youhouli road. ...
Article
Termites are dominant organisms of tropical ecosystems. Their success is partly due to the diversity of their feeding substrates, from dead plant tissues to mineralised soils. The Apicotermitinae is one of the richest subfamilies of soil-feeding termites, which are traditionally classified in feeding groups according to anatomical criteria, deemed to the reveal whether species feed on organic-rich layers (group III) or on mineralised soil (group IV). Previous studies based on δ15N isotopic values showed that this subfamily's niche covers a broad range along the gradient of humification. We hypothesised that this broad feeding range could be reflected in the crop-gizzard (Cr-Gi) content and volume. We investigated 17 African species distributed between the two feeding groups. Our results showed a variation of Cr-Gi volume and a consistent composition of content among Apicotermitinae species. Some small-bodied species had a very large Cr-Gi volume relative to their size, indicating a difference in foraging behaviour. These species might use this enhanced storage capacity to forage for longer periods of time. Cr-Gi content was dominated by clay (kaolinite) suggesting that a dietary specialisation could be based on the quality of organic compounds from organo-mineral aggregates. Variations in crystalline solids (quartz) between species indicate either differences in the abundance of mineral grains between feeding patches or active discrimination among particles by foragers. The similar composition of Cr-Gi contents in afrotropical Apicotermitinae suggests that the anatomical criteria used to assign species to feeding groups III or IV are not appropriate.
... On the contrary, mature forests are located in the upper and middle slopes, and have high spatial and structural complexity (e.g., an uneven canopy; Grau, 2002;Malizia & Grau, 2008). Upper and middle slopes usually have high gap density and size (Poorter, Jans, Bongers, & Rompaey, 1994), which facilitate liana proliferation in these mature forests. Although this study is limited in space and time, we believe that these findings could be extended to other subtropical montane areas undergoing late stages of succession, because treefall gaps play a major role on liana dynamics in montane regions (Mohandass, Campbell, Hughes, Mammides, & Davidar, 2017). ...
Article
Liana dynamics in secondary and mature forests are well known in tropical areas dominated by native tree species. Outside the tropics and in secondary forests invaded by exotic species, knowledge is scarce. In this study, we compare liana communities between secondary and mature forests dominated by native species in a subtropical montane area of Sierra de San Javier, Tucuman, Argentina. Additionally, we evaluate changes of liana communities in secondary forests with increasing densities of Ligustrum lucidum and Morus alba, two of the most invasive exotic trees of the area. We surveyed liana species richness and density in three 30‐year secondary patches, four 60‐year secondary patches, and four mature patches dominated by native tree species, to analyze changes in liana communities with forest age. Within each patch, we sampled 10–25 20 × 20 m quadrats. Additionally, we surveyed liana density and species richness in secondary forest patches with different densities of L. lucidum and M. alba. In native‐dominated forests, liana species richness increased and showed a tendency of increasing basal area from 30‐year secondary forests to mature forests. Liana density was highly variable, and most of the species were shared between native‐dominated secondary and mature forests. Liana density and species richness decreased with L. lucidum density, whereas in secondary forests highly dominated by M. alba, lianas increased in density. Overall, lianas followed different pathways influenced by native forest succession and exotic tree invasions. Abstract in Spanish is available with online material. La dinámica de lianas en bosques secundarios y maduros es bien conocida en áreas tropicales dominadas por especies de árboles nativos. Fuera de los trópicos y en bosques secundarios invadidos por especies exóticas la información es escasa. En este estudio se comparan las comunidades de lianas entre bosques secundarios y maduros dominados por árboles nativos en un área subtropical montana de la Sierra de San Javier, Tucumán, Argentina. Adicionalmente se evalúan cambios en las comunidades de lianas en bosques secundarios hacia mayores densidades de Ligustrum lucidum y Morus alba, dos de los árboles exóticos más invasores del área. Muestreamos las especies de lianas y su densidad en tres parches de bosque secundario de 30 años, cuatro parches de bosque secundario de 60 años, y cuatro bosques maduros dominados por especies de árboles nativos, para analizar cambios en las comunidades de lianas con la edad del bosque. Dentro de cada parche, muestreamos entre 10 y 25 cuadrantes de 20 × 20 m. Adicionalmente, muestreamos la densidad y riqueza de lianas en parches de bosque secundario con diferentes densidades de L. lucidum y M. alba. En los bosques nativos, las lianas incrementaron en riqueza de especies y mostraron una tendencia a incrementar en área basal desde los bosques secundarios de 30 años a los bosques maduros. La densidad de lianas fue altamente variable, y la mayoría de las especies fueron compartidas por los bosques secundarios y maduros dominados por árboles nativos. La densidad y riqueza de especies de lianas disminuyeron con la densidad de L. lucidum, mientras que la densidad de lianas incrementó hacia bosques secundarios altamente dominados por M. alba. Las lianas siguieron caminos alternativos influidos por la sucesión de bosques nativos y por las invasiones de árboles exóticos.
Chapter
The disturbance is one of the most common and widespread phenomena shaping natural and man-made environments. Disturbance modifies land mosaic, shapes individual patches, and spreads across a broad range of temporal and spatial scales. Snow cover, flooding, gap disturbance in forest, fires, pathogens, animals, and human activity concur with create and maintain landscape patchiness.
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Teak, the most valuable timber species of tropics, covers about 4.346 million ha of forest and represents 75% of high tropical hardwood plantations. Considering its importance, the species is now introduced in large areas outside its natural ranges such as Indian subcontinent and south eastern Asia. Due to large natural range, the local factors vary significantly. Teak is a light adoring species and found in areas with rainfall varying from 500 mm to 5000 mm and in temperature ranges of 2°C to 48°C. Well drained alluvial soil with acidic pH (6.5), made of volcanic origin and with high limestone content is good for better growth of the species. The productivity of a plantation can be largely improved through the selection of a correct site for the plantation programme. Presence of different macro and micronutrients affect the anatomical properties of wood of this species. According to its growth performance in different countries different sites qualities are present like poor, moderate and good. Teak is a species of tropical summer rain climate is generally absent in dipterocarp forest. Due to huge profitability of the timber species sometimes the agriculture lands are converted into plantation area. It is found that factors like climate (rainfall, temperature, light etc.) and edaphic (soil physical and chemical properties, topography etc.) should be taken in to consider before selection of site, as its rotation period is too long.
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Neotropical forest dynamics are reviewed by focusing on four questions: (1) What is a mature neotropical forest? (2) How long does it take to attain maturity? (3) How important are gaps to species regeneration? and (4) What are the important equilibrium processes in neotropical forest dynamics? The absence of regeneration of dominants has often been used as a distinguishing feature of late secondary forest; however, the abundance of shade-intolerant species in mature forest suggests that local absence of regeneration is an inadequate criterion for distinguishing between late secondary and mature forest. Recent studies estimate forest turnover rates of 75-150 years, indicating tropical forests are much more dynamic than thought previously. The dependence on gaps by almost half of the 320 tree species in a Costa Rican wet forest for successful regeneration illustrates the importance of gaps in tropical forest dynamics. Factors important in determining which species successfully colonize a gap are: time of gap occurrence; proximity and dispersal of seeds; size of gap; substrate conditions; and plant-herbivore interactions.
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Recognizing that sound information is vital to the progress of conservation, IUCN have gathered together a visual portfolio of maps of rain forests in Africa. The accompanying text analyzes the extent and causes of deforestation and points a way towards sustainable forest development.
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