The Experts below are selected from a list of 2205 Experts worldwide ranked by ideXlab platform
Thomas T Veblen - One of the best experts on this subject based on the ideXlab platform.
-
structure and tree fall Gap Dynamics of old growth nothofagus forests in tierra del fuego argentina
Journal of Vegetation Science, 1993Co-Authors: Alan J Rebertus, Thomas T VeblenAbstract:Tree size and age structure, tree-fall and Gap char- acteristics, and regeneration in Gaps were studied in Nothofagus-dominated old-growth forests in Tierra del Fuego, Argentina. Gap-phase regeneration has resulted in all-aged populations for N. pumilio, N. betuloides, and Drimys winteri, and regeneration in Gaps appears to be maintaining coexist- ence between species in mixed stands. N. betuloides fills many Gaps via advance regeneration and some individuals persist for > 150 yr in the understory. Multiple periods of release and suppression indicate that N. betuloides may take advantage of several Gap events to reach the main canopy. Likewise, Drimys grows well under closed canopy and can rapidly respond to Gap formation, sometimes impeding the regeneration of N. betuloides. In contrast, N. pumilio regen- erates in Gaps mainly from seed or from advance regenera- tion of small, ephemeral seedlings. Gap turnover times in Fuegian forests were estimated at 300 - 500 yr, although Gap formation was highly episodic and possibly associated with regionally extensive windstorms, earthquakes, and stand-level dieback. 92 % of Gaps involved multiple tree-falls, and at least 53 % involved secondary expansion. Gap and tree-fall characteristics in Tierra del Fuego were similar to results from northern Patagonia, Chile, and New Zealand; however, we emphasize that regeneration of Nothofagus spp. and Drimys winteri in Gaps depends on associated vegetation and varies along both local and regional environmental gradients.
-
Structure and tree‐fall Gap Dynamics of old‐growth Nothofagus forests in Tierra del Fuego, Argentina
Journal of Vegetation Science, 1993Co-Authors: Alan J Rebertus, Thomas T VeblenAbstract:Tree size and age structure, tree-fall and Gap char- acteristics, and regeneration in Gaps were studied in Nothofagus-dominated old-growth forests in Tierra del Fuego, Argentina. Gap-phase regeneration has resulted in all-aged populations for N. pumilio, N. betuloides, and Drimys winteri, and regeneration in Gaps appears to be maintaining coexist- ence between species in mixed stands. N. betuloides fills many Gaps via advance regeneration and some individuals persist for > 150 yr in the understory. Multiple periods of release and suppression indicate that N. betuloides may take advantage of several Gap events to reach the main canopy. Likewise, Drimys grows well under closed canopy and can rapidly respond to Gap formation, sometimes impeding the regeneration of N. betuloides. In contrast, N. pumilio regen- erates in Gaps mainly from seed or from advance regenera- tion of small, ephemeral seedlings. Gap turnover times in Fuegian forests were estimated at 300 - 500 yr, although Gap formation was highly episodic and possibly associated with regionally extensive windstorms, earthquakes, and stand-level dieback. 92 % of Gaps involved multiple tree-falls, and at least 53 % involved secondary expansion. Gap and tree-fall characteristics in Tierra del Fuego were similar to results from northern Patagonia, Chile, and New Zealand; however, we emphasize that regeneration of Nothofagus spp. and Drimys winteri in Gaps depends on associated vegetation and varies along both local and regional environmental gradients.
Alan J Rebertus - One of the best experts on this subject based on the ideXlab platform.
-
structure and tree fall Gap Dynamics of old growth nothofagus forests in tierra del fuego argentina
Journal of Vegetation Science, 1993Co-Authors: Alan J Rebertus, Thomas T VeblenAbstract:Tree size and age structure, tree-fall and Gap char- acteristics, and regeneration in Gaps were studied in Nothofagus-dominated old-growth forests in Tierra del Fuego, Argentina. Gap-phase regeneration has resulted in all-aged populations for N. pumilio, N. betuloides, and Drimys winteri, and regeneration in Gaps appears to be maintaining coexist- ence between species in mixed stands. N. betuloides fills many Gaps via advance regeneration and some individuals persist for > 150 yr in the understory. Multiple periods of release and suppression indicate that N. betuloides may take advantage of several Gap events to reach the main canopy. Likewise, Drimys grows well under closed canopy and can rapidly respond to Gap formation, sometimes impeding the regeneration of N. betuloides. In contrast, N. pumilio regen- erates in Gaps mainly from seed or from advance regenera- tion of small, ephemeral seedlings. Gap turnover times in Fuegian forests were estimated at 300 - 500 yr, although Gap formation was highly episodic and possibly associated with regionally extensive windstorms, earthquakes, and stand-level dieback. 92 % of Gaps involved multiple tree-falls, and at least 53 % involved secondary expansion. Gap and tree-fall characteristics in Tierra del Fuego were similar to results from northern Patagonia, Chile, and New Zealand; however, we emphasize that regeneration of Nothofagus spp. and Drimys winteri in Gaps depends on associated vegetation and varies along both local and regional environmental gradients.
-
Structure and tree‐fall Gap Dynamics of old‐growth Nothofagus forests in Tierra del Fuego, Argentina
Journal of Vegetation Science, 1993Co-Authors: Alan J Rebertus, Thomas T VeblenAbstract:Tree size and age structure, tree-fall and Gap char- acteristics, and regeneration in Gaps were studied in Nothofagus-dominated old-growth forests in Tierra del Fuego, Argentina. Gap-phase regeneration has resulted in all-aged populations for N. pumilio, N. betuloides, and Drimys winteri, and regeneration in Gaps appears to be maintaining coexist- ence between species in mixed stands. N. betuloides fills many Gaps via advance regeneration and some individuals persist for > 150 yr in the understory. Multiple periods of release and suppression indicate that N. betuloides may take advantage of several Gap events to reach the main canopy. Likewise, Drimys grows well under closed canopy and can rapidly respond to Gap formation, sometimes impeding the regeneration of N. betuloides. In contrast, N. pumilio regen- erates in Gaps mainly from seed or from advance regenera- tion of small, ephemeral seedlings. Gap turnover times in Fuegian forests were estimated at 300 - 500 yr, although Gap formation was highly episodic and possibly associated with regionally extensive windstorms, earthquakes, and stand-level dieback. 92 % of Gaps involved multiple tree-falls, and at least 53 % involved secondary expansion. Gap and tree-fall characteristics in Tierra del Fuego were similar to results from northern Patagonia, Chile, and New Zealand; however, we emphasize that regeneration of Nothofagus spp. and Drimys winteri in Gaps depends on associated vegetation and varies along both local and regional environmental gradients.
Debra P C Peters - One of the best experts on this subject based on the ideXlab platform.
-
plant species dominance at a grassland shrubland ecotone an individual based Gap Dynamics model of herbaceous and woody species
Ecological Modelling, 2002Co-Authors: Debra P C PetersAbstract:Abstract Transition zones or ecotones between biomes are predicted to be particularly sensitive areas to directional changes in climate. However, for many ecotones, there is little understanding of the key processes that allow dominant species from adjacent biomes to coexist at transition zones and how differences in these processes affect species responses to changes in environmental conditions. The objective of this study was to examine the relationship between plant life history traits and patterns in dominance and composition at a grassland–shrubland transition zone in order to predict shifts in dominance with directional changes in climate. It was hypothesized that differences in life history traits allow species from adjacent biomes to coexist at this transition zone, and that these dominance patterns are dynamic through time as a result of species-specific responses to changes in climate. A mixed lifeform individual plant-based Gap Dynamics model (ECOTONE) was developed to examine consequences of differences in recruitment, resource acquisition, and mortality to patterns in species dominance and composition under a variety of soils and climatic conditions. This model is unique because it represents interactions among multiple potential dominant species that include congeneric species of one lifeform as well as herbaceous and woody lifeforms across multiple spatial scales. Similar to other Gap models, ECOTONE simulates the recruitment, growth, and mortality of individual plants on a small plot through time at an annual timestep. ECOTONE differs from other Gap models in the degree of detail involved in determining successful recruitment by each species and in the simulation of belowground resources. Individual plant root distributions and resource availability by depth are dynamic. Soil water content is simulated on a daily timestep and nitrogen is simulated monthly. Multiple spatial scales can be simulated using a grid of plots connected by seed dispersal. ECOTONE was parameterized for two soil types at the Sevilleta National Wildlife Refuge (SEV), a site located within the transition zone between two major biomes in North America. Shortgrass steppe communities are dominated by the perennial grass Bouteloua gracilis (blue grama) and Chihuahuan desert communities are dominated by the perennial grass Bouteloua eriopoda (black grama) or the shrub Larrea tridentata (creosotebush). Experiments were conducted to provide key parameters related to recruitment and growth that were supplemented with information from the literature for remaining parameters. Model output was verified using field estimates of cover and biomass for the three dominant species as well as other groups of species. Simulation analyses were conducted under current climate and for a directional change in climate. Nitrogen was assumed constant for all runs to allow a focus on water availability constraints as affected by climate. Under current climatic conditions, simulated biomass on sandy loam soils was dominated by B. eriopoda with smaller biomass of B. gracilis and other species groups. By contrast, simulated biomass on a loamy sand soil was codominated by B. eriopoda and L. tridentata with very small biomass attributed to other species groups. Under a GFDL climate change scenario of increased year-round temperatures and increased summer precipitation, vegetation patterns shifted to a clear dominance of biomass by B. eriopoda on both soil types. These results show that temporal partitioning of soil water is important to codominance by the two Bouteloua species, and that spatial and temporal partitioning of soil water is important for grass–shrub interactions. The results also suggest that global climate change may provide a mechanism for the recovery of B. eriopoda following shrub invasion in the Southwestern U.S. Thus, an individual-based modeling approach is capable of representing complex interactions among herbaceous and woody species as well as between congeneric species with different life history traits at a biome transition zone. This modeling approach is useful in improving our understanding of key processes driving these vegetation Dynamics as well in predicting shifts in dominance as environmental conditions change in the future.
-
Plant species dominance at a grassland–shrubland ecotone: an individual-based Gap Dynamics model of herbaceous and woody species
Ecological Modelling, 2002Co-Authors: Debra P C PetersAbstract:Abstract Transition zones or ecotones between biomes are predicted to be particularly sensitive areas to directional changes in climate. However, for many ecotones, there is little understanding of the key processes that allow dominant species from adjacent biomes to coexist at transition zones and how differences in these processes affect species responses to changes in environmental conditions. The objective of this study was to examine the relationship between plant life history traits and patterns in dominance and composition at a grassland–shrubland transition zone in order to predict shifts in dominance with directional changes in climate. It was hypothesized that differences in life history traits allow species from adjacent biomes to coexist at this transition zone, and that these dominance patterns are dynamic through time as a result of species-specific responses to changes in climate. A mixed lifeform individual plant-based Gap Dynamics model (ECOTONE) was developed to examine consequences of differences in recruitment, resource acquisition, and mortality to patterns in species dominance and composition under a variety of soils and climatic conditions. This model is unique because it represents interactions among multiple potential dominant species that include congeneric species of one lifeform as well as herbaceous and woody lifeforms across multiple spatial scales. Similar to other Gap models, ECOTONE simulates the recruitment, growth, and mortality of individual plants on a small plot through time at an annual timestep. ECOTONE differs from other Gap models in the degree of detail involved in determining successful recruitment by each species and in the simulation of belowground resources. Individual plant root distributions and resource availability by depth are dynamic. Soil water content is simulated on a daily timestep and nitrogen is simulated monthly. Multiple spatial scales can be simulated using a grid of plots connected by seed dispersal. ECOTONE was parameterized for two soil types at the Sevilleta National Wildlife Refuge (SEV), a site located within the transition zone between two major biomes in North America. Shortgrass steppe communities are dominated by the perennial grass Bouteloua gracilis (blue grama) and Chihuahuan desert communities are dominated by the perennial grass Bouteloua eriopoda (black grama) or the shrub Larrea tridentata (creosotebush). Experiments were conducted to provide key parameters related to recruitment and growth that were supplemented with information from the literature for remaining parameters. Model output was verified using field estimates of cover and biomass for the three dominant species as well as other groups of species. Simulation analyses were conducted under current climate and for a directional change in climate. Nitrogen was assumed constant for all runs to allow a focus on water availability constraints as affected by climate. Under current climatic conditions, simulated biomass on sandy loam soils was dominated by B. eriopoda with smaller biomass of B. gracilis and other species groups. By contrast, simulated biomass on a loamy sand soil was codominated by B. eriopoda and L. tridentata with very small biomass attributed to other species groups. Under a GFDL climate change scenario of increased year-round temperatures and increased summer precipitation, vegetation patterns shifted to a clear dominance of biomass by B. eriopoda on both soil types. These results show that temporal partitioning of soil water is important to codominance by the two Bouteloua species, and that spatial and temporal partitioning of soil water is important for grass–shrub interactions. The results also suggest that global climate change may provide a mechanism for the recovery of B. eriopoda following shrub invasion in the Southwestern U.S. Thus, an individual-based modeling approach is capable of representing complex interactions among herbaceous and woody species as well as between congeneric species with different life history traits at a biome transition zone. This modeling approach is useful in improving our understanding of key processes driving these vegetation Dynamics as well in predicting shifts in dominance as environmental conditions change in the future.
Tibor Standovár - One of the best experts on this subject based on the ideXlab platform.
-
Natural Gap Dynamics in a Central European mixed beech-spruce-fir old-growth forest.
Ecoscience, 2020Co-Authors: Kata Kenderes, Kamil Král, Tomáš Vrška, Tibor StandovárAbstract:Abstract: We provide a study on long-term canopy Gap Dynamics in the Žofin Virgin Forest (total area 98 ha), which has been strictly protected since 1838. Our aims were i) to describe the size distribution of Gaps at a given time; ii) to determine the area where dynamic processes occurred within a given period; and iii) to determine the role of deciduous versus coniferous trees in Gap formation. The fate of individual Gaps was followed in a 47-ha beech-dominated part of the reserve by analyzing aerial photographs taken in 1971, 1983, 1991, and 2004. The role of individual trees in canopy Gap Dynamics was studied by combining Gap distribution maps with stem position maps of 1975 and 1997 for a 10-ha sample plot. We showed that i) total Gap area (9–11%) and average Gap size (88–99 m2) was stable during the 33-y study period; ii) canopy Dynamics occurred in 0.1% of the area annually; iii) most Gaps were created by the simultaneous death of 1–3 canopy trees; iv) death of deciduous trees played a more importan...
-
thirty years of Gap Dynamics in a central european beech forest reserve
Forestry, 2008Co-Authors: Kata Kenderes, Barbara Mihok, Tibor StandovárAbstract:Summary Investigation of Gap characteristics and tree regeneration patterns is central for our understanding of forest Dynamics. By integrating aerial photograph analyses and ground surveys, we provide a study of long-term canopy Gap Dynamics and tree regeneration patterns in a Hungarian beech forest reserve. We found (1) that in spite of the overall increase of Gap area during the investigated 30-years (from 2.5 to 7.7 per cent), total Gap area and average Gap size (40 – 93 m 2 ) were remarkably similar to those found in other temperate and tropical forests, (2) if the fate of individual Gaps was followed, two to three times more intensive canopy Dynamics (Gap creation, closure and expansion) could be recognized than simple change of Gap area indicated, and (3) average seedling density was considered to be suffi cient for natural regeneration. However, it was apparent that recent increased deer browsing had prevented establishment of younger trees of 1 – 2 m in height, as taller saplings were recorded only in old Gaps. Our results not only provide useful information on forest Dynamics but can also contribute to understanding the potential roles that small forest reserves can play in providing essential reference data for nature-based forest management of this forest type.
J. Demsar - One of the best experts on this subject based on the ideXlab platform.
-
Probing superconducting Gap Dynamics with THz pulses
2015 Conference on Lasers and Electro-Optics (CLEO), 2015Co-Authors: M. Beck, M. Klammer, I. Rousseau, G. N. Gol'tsman, I. Diamant, Y. Dagan, J. DemsarAbstract:We studied superconducting Gap Dynamics in a BCS superconductor NbN and electron doped cuprate superconductor PCCO following excitation with near-infrared (NIR) and narrow band THz pulses. Systematic studies on PCCO imply very selective electron-phonon coupling.
-
energy Gap Dynamics of superconducting nbn thin films studied by time resolved terahertz spectroscopy
Physical Review Letters, 2011Co-Authors: Matthias Beck, Maximilian Klammer, S Lang, Paul Leiderer, V V Kabanov, G N Goltsman, J. DemsarAbstract:Using time-domain terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting Gap in a conventional BCS superconductor NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare quasiparticle recombination rate, the Cooper pair-breaking rate and the electron-phonon coupling constant, � ¼ 1:1 � 0:1, which is in excellent agreement with theoretical estimates.
