380 the conifers concerned (over 1000 years in some Podocarp forest species) means that only very... more 380 the conifers concerned (over 1000 years in some Podocarp forest species) means that only very infrequent catastrophic dynamics disturbance would be required to maintain their abundance in the landscape (Read & Hill 1988; Stewart & Rose 1989). Most of the recent New ...
Some plant traits may be legacies of coevolution with extinct megafauna. One example is the conve... more Some plant traits may be legacies of coevolution with extinct megafauna. One example is the convergent evolution of "divaricate" cage architectures in many New Zealand lineages, interpreted as a response to recently-extinct flightless avian browsers whose ancestors arrived during the Paleogene. Although experiments have confirmed the divaricate habit deters extant browsers, its abundance on frosty, droughty sites appears consistent with an earlier interpretation as a response to cold, dry Plio-Pleistocene climates. We used 45 protein-coding sequences from plastid genomes to reconstruct the evolutionary history of the divaricate habit in extant New Zealand lineages. Our dated phylogeny of 215 species included 91% of New Zealand eudicot divaricate species. We show that 86% of extant divaricate plants diverged from non-divaricate sisters within the last 5 Ma, implicating Plio-Pleistocene climates in the proliferation of cage architectures in New Zealand. Our results, combined with other recent findings, are consistent with the synthetic hypothesis that the browser-deterrent effect of cage architectures was strongly selected only when Plio-Pleistocene climatic constraints prevented woody plants from quickly growing out of reach of browsers. This is consistent with the abundance of cage architectures in other regions where plant growth is restricted by aridity or short frost-free periods.
In south-central Chile, the dynamics of southern beech (Nothofagaceae) stands vary predictably al... more In south-central Chile, the dynamics of southern beech (Nothofagaceae) stands vary predictably along climatic gradients. Beeches form persistent stands at high elevations, but their establishment on lowland sites depends mainly on catastrophic disturbances. In New Zealand, nearly all studies of beech forest dynamics to date have reported all-sized, persistent populations. However, previous work has focused largely on the South Island or on North Island mountains, where beeches are widespread and often dominant. Little is known about beech dynamics in the warm North Island lowlands, where beeches are less common. We aimed to clarify the circumstances that enable beeches to establish on lowland sites in the North Island. We measured population structures of beeches and associated species on 11 plots distributed across a range of climate, lithology and topography. On sites where the most shade-tolerant broadleaved trees were absent or uncommon, all-sized populations showed that beech regeneration did not depend on major disturbances. These stands were located mostly on steep faces or ridges with soil carbon:nitrogen ratios &gt; 18, usually with ericaceous understoreys. On sites with higher N availability, where shade-tolerant broadleaved trees were abundant, beech populations were generally sparser, with restricted age ranges. One of these ± even-aged beech stands appeared to have established after windthrow, the other four after fires. Recent dieback of <i>Weinmannia racemosa</i> associated with insect attack had resulted in another wave of beech regeneration in one of the post-fire stands. Establishment on landslides appears to only rarely enable beeches to capture new sites in the lowland North Island. We conclude that beeches form stable self-replacing stands on lowland North Island sites with low nitrogen availability, but that exogenous disturbances occasionally enable beeches to establish as pioneers on sites with higher nitrogen availability. The early successionalrole commonly seen in lowland south-central [...]
Safeguarding Earth’s tree diversity is a conservation priority due to the importance of trees for... more Safeguarding Earth’s tree diversity is a conservation priority due to the importance of trees for biodiversity and ecosystem functions and services such as carbon sequestration. Here, we improve the foundation for effective conservation of global tree diversity by analyzing a recently developed database of tree species covering 46,752 species. We quantify range protection and anthropogenic pressures for each species and develop conservation priorities across taxonomic, phylogenetic, and functional diversity dimensions. We also assess the effectiveness of several influential proposed conservation prioritization frameworks to protect the top 17% and top 50% of tree priority areas. We find that an average of 50.2% of a tree species’ range occurs in 110-km grid cells without any protected areas (PAs), with 6,377 small-range tree species fully unprotected, and that 83% of tree species experience nonnegligible human pressure across their range on average. Protecting high-priority areas fo...
It has been suggested that divaricate plants are an anachronism in contemporary New Zealand, beca... more It has been suggested that divaricate plants are an anachronism in contemporary New Zealand, because of the extinction of browsing birds (moa) that may have influenced their evolution, and because the divaricate form is not an effective defence against introduced browsing mammals. This article infers the relative susceptibilities of divaricate, broadleaved and conifer species to ungulate browsing, by measuring tree diameter distributions in a forest remnant fenced in the late 1970s after a century of unimpeded access by livestock. The 26 ha remnant, at Pehiri in the eastern North Island, spans a range of landforms from river flats (favoured by podocarps and divaricates) to hillslopes where broadleaved species predominate. The commonest broadleaved species (Alectryon excelsus, Melicytus ramiflorus , Hedycarya arborea) had empty or under-represented diameter classes in the 5 to 20 cm range, consistent with reduced regeneration during the century of unrestricted browsing. In contrast, ...
A trade-off between shade tolerance and growth in open conditions is widely believed to underlie ... more A trade-off between shade tolerance and growth in open conditions is widely believed to underlie the dynamics of humid forests. Little is known about how the growth versus shade tolerance trade-off interacts with other major trade-offs associated with differential adaptation to major environmental factors besides light. We asked whether the growth versus shade tolerance trade-off differed between subtropical rainforest tree assemblages native to basaltic (fertile) and rhyolitic (infertile) soils in northern New South Wales, because of the allocational costs of adaptation to low nutrient availability. Seedling relative growth rates of six basalt specialists and five rhyolite specialists were measured in a glasshouse and the minimum light requirements of each species were quantified in the field by determining the 10th percentile of juvenile tree distributions in relation to understorey light availability. A similar range of light requirements was observed in the two assemblages, and ...
Background/Question/Methods Shade tolerance is often assumed to be a fixed trait of a species, th... more Background/Question/Methods Shade tolerance is often assumed to be a fixed trait of a species, though recent work has indicated that larger individuals are less able to tolerate shade than smaller individuals of the same species. We hypothesized that whole-plant light compensation points and carbon flux per gram plant of shade tolerant species will be more stable during juvenile ontogeny than those of shade intolerant species. The whole-plant light compensation point (WPLCP) has been suggested as a conceptually simple measure of the light requirements of species, and is estimated as the x-intercept of the relationship between growth and light environment over a long time interval. Here we compare WPLCP for growth and survival of four size classes (<50 cm, 50-100 cm, 100-150 cm, and >150 cm) of juvenile evergreen tree species differing in shade tolerance. We also examine ontogenetic variation in light capture and simulated whole-plant carbon gain by combining 3D-digitizing with...
Los bambus del genero Chusquea son colonizadores agresivos de claros en los bosques lluviosos tem... more Los bambus del genero Chusquea son colonizadores agresivos de claros en los bosques lluviosos templados en el sur de Chile. Los matorrales de Chusquea, que se desarrollan tras la formacion de los claros, suprimen la regeneracion de las especies arboreas, llevando a pensar que los niveles luminicos bajo los bambu podrian ser inferiores a los que prevalecen bajo el bosque cerrado. Se usaron dos analizadores de doseles LAI-2000 para comparar disponibilidad de luz difusa bajo cinco matorrales de Chusquea quila y cinco rodales aledanos de bosque cerrado, en un bosque lluvioso antiguo ubicado ubicado a una elevacion de E 400 m s.n.m. en el Parque Nacional Puyehue (40o39'S). Ademas se comparo el indice de area foliar de estos dos tipos de vegetacion. El nivel promedio de la luz difusa bajo los matorrales de C. quila (1,5 %) fue levemente menor que el medido bajo el bosque cerrado (1,7 %). Asimismo, se midio mayor indice de area foliar para los bambus (6,1) comparado con el bosque cerrado (5,3). Sin embargo, las mediciones de indice de area foliar con el LAI-2000 probablemente sobreestiman la superficie asimilatoria efectiva de los matorrales de bambu, debido a la retencion de hojas muertas por los culmos de C. quila. Por otra parte, el indice de area foliar del bosque es subestimado, debido a la omision de la vegetacion del piso (< 50 cm en altura). La abundancia de los matorrales de Chusquea spp. en los bosques antiguos, y su capacidad de retener los sitios mediante la supresion de la regeneracion de los arboles, sugiere que un modelo bifasico de retroalimentacion positiva es apropiado para la dinamica de estos bosques
380 the conifers concerned (over 1000 years in some Podocarp forest species) means that only very... more 380 the conifers concerned (over 1000 years in some Podocarp forest species) means that only very infrequent catastrophic dynamics disturbance would be required to maintain their abundance in the landscape (Read &amp; Hill 1988; Stewart &amp; Rose 1989). Most of the recent New ...
Some plant traits may be legacies of coevolution with extinct megafauna. One example is the conve... more Some plant traits may be legacies of coevolution with extinct megafauna. One example is the convergent evolution of "divaricate" cage architectures in many New Zealand lineages, interpreted as a response to recently-extinct flightless avian browsers whose ancestors arrived during the Paleogene. Although experiments have confirmed the divaricate habit deters extant browsers, its abundance on frosty, droughty sites appears consistent with an earlier interpretation as a response to cold, dry Plio-Pleistocene climates. We used 45 protein-coding sequences from plastid genomes to reconstruct the evolutionary history of the divaricate habit in extant New Zealand lineages. Our dated phylogeny of 215 species included 91% of New Zealand eudicot divaricate species. We show that 86% of extant divaricate plants diverged from non-divaricate sisters within the last 5 Ma, implicating Plio-Pleistocene climates in the proliferation of cage architectures in New Zealand. Our results, combined with other recent findings, are consistent with the synthetic hypothesis that the browser-deterrent effect of cage architectures was strongly selected only when Plio-Pleistocene climatic constraints prevented woody plants from quickly growing out of reach of browsers. This is consistent with the abundance of cage architectures in other regions where plant growth is restricted by aridity or short frost-free periods.
In south-central Chile, the dynamics of southern beech (Nothofagaceae) stands vary predictably al... more In south-central Chile, the dynamics of southern beech (Nothofagaceae) stands vary predictably along climatic gradients. Beeches form persistent stands at high elevations, but their establishment on lowland sites depends mainly on catastrophic disturbances. In New Zealand, nearly all studies of beech forest dynamics to date have reported all-sized, persistent populations. However, previous work has focused largely on the South Island or on North Island mountains, where beeches are widespread and often dominant. Little is known about beech dynamics in the warm North Island lowlands, where beeches are less common. We aimed to clarify the circumstances that enable beeches to establish on lowland sites in the North Island. We measured population structures of beeches and associated species on 11 plots distributed across a range of climate, lithology and topography. On sites where the most shade-tolerant broadleaved trees were absent or uncommon, all-sized populations showed that beech regeneration did not depend on major disturbances. These stands were located mostly on steep faces or ridges with soil carbon:nitrogen ratios &gt; 18, usually with ericaceous understoreys. On sites with higher N availability, where shade-tolerant broadleaved trees were abundant, beech populations were generally sparser, with restricted age ranges. One of these ± even-aged beech stands appeared to have established after windthrow, the other four after fires. Recent dieback of <i>Weinmannia racemosa</i> associated with insect attack had resulted in another wave of beech regeneration in one of the post-fire stands. Establishment on landslides appears to only rarely enable beeches to capture new sites in the lowland North Island. We conclude that beeches form stable self-replacing stands on lowland North Island sites with low nitrogen availability, but that exogenous disturbances occasionally enable beeches to establish as pioneers on sites with higher nitrogen availability. The early successionalrole commonly seen in lowland south-central [...]
Safeguarding Earth’s tree diversity is a conservation priority due to the importance of trees for... more Safeguarding Earth’s tree diversity is a conservation priority due to the importance of trees for biodiversity and ecosystem functions and services such as carbon sequestration. Here, we improve the foundation for effective conservation of global tree diversity by analyzing a recently developed database of tree species covering 46,752 species. We quantify range protection and anthropogenic pressures for each species and develop conservation priorities across taxonomic, phylogenetic, and functional diversity dimensions. We also assess the effectiveness of several influential proposed conservation prioritization frameworks to protect the top 17% and top 50% of tree priority areas. We find that an average of 50.2% of a tree species’ range occurs in 110-km grid cells without any protected areas (PAs), with 6,377 small-range tree species fully unprotected, and that 83% of tree species experience nonnegligible human pressure across their range on average. Protecting high-priority areas fo...
It has been suggested that divaricate plants are an anachronism in contemporary New Zealand, beca... more It has been suggested that divaricate plants are an anachronism in contemporary New Zealand, because of the extinction of browsing birds (moa) that may have influenced their evolution, and because the divaricate form is not an effective defence against introduced browsing mammals. This article infers the relative susceptibilities of divaricate, broadleaved and conifer species to ungulate browsing, by measuring tree diameter distributions in a forest remnant fenced in the late 1970s after a century of unimpeded access by livestock. The 26 ha remnant, at Pehiri in the eastern North Island, spans a range of landforms from river flats (favoured by podocarps and divaricates) to hillslopes where broadleaved species predominate. The commonest broadleaved species (Alectryon excelsus, Melicytus ramiflorus , Hedycarya arborea) had empty or under-represented diameter classes in the 5 to 20 cm range, consistent with reduced regeneration during the century of unrestricted browsing. In contrast, ...
A trade-off between shade tolerance and growth in open conditions is widely believed to underlie ... more A trade-off between shade tolerance and growth in open conditions is widely believed to underlie the dynamics of humid forests. Little is known about how the growth versus shade tolerance trade-off interacts with other major trade-offs associated with differential adaptation to major environmental factors besides light. We asked whether the growth versus shade tolerance trade-off differed between subtropical rainforest tree assemblages native to basaltic (fertile) and rhyolitic (infertile) soils in northern New South Wales, because of the allocational costs of adaptation to low nutrient availability. Seedling relative growth rates of six basalt specialists and five rhyolite specialists were measured in a glasshouse and the minimum light requirements of each species were quantified in the field by determining the 10th percentile of juvenile tree distributions in relation to understorey light availability. A similar range of light requirements was observed in the two assemblages, and ...
Background/Question/Methods Shade tolerance is often assumed to be a fixed trait of a species, th... more Background/Question/Methods Shade tolerance is often assumed to be a fixed trait of a species, though recent work has indicated that larger individuals are less able to tolerate shade than smaller individuals of the same species. We hypothesized that whole-plant light compensation points and carbon flux per gram plant of shade tolerant species will be more stable during juvenile ontogeny than those of shade intolerant species. The whole-plant light compensation point (WPLCP) has been suggested as a conceptually simple measure of the light requirements of species, and is estimated as the x-intercept of the relationship between growth and light environment over a long time interval. Here we compare WPLCP for growth and survival of four size classes (<50 cm, 50-100 cm, 100-150 cm, and >150 cm) of juvenile evergreen tree species differing in shade tolerance. We also examine ontogenetic variation in light capture and simulated whole-plant carbon gain by combining 3D-digitizing with...
Los bambus del genero Chusquea son colonizadores agresivos de claros en los bosques lluviosos tem... more Los bambus del genero Chusquea son colonizadores agresivos de claros en los bosques lluviosos templados en el sur de Chile. Los matorrales de Chusquea, que se desarrollan tras la formacion de los claros, suprimen la regeneracion de las especies arboreas, llevando a pensar que los niveles luminicos bajo los bambu podrian ser inferiores a los que prevalecen bajo el bosque cerrado. Se usaron dos analizadores de doseles LAI-2000 para comparar disponibilidad de luz difusa bajo cinco matorrales de Chusquea quila y cinco rodales aledanos de bosque cerrado, en un bosque lluvioso antiguo ubicado ubicado a una elevacion de E 400 m s.n.m. en el Parque Nacional Puyehue (40o39'S). Ademas se comparo el indice de area foliar de estos dos tipos de vegetacion. El nivel promedio de la luz difusa bajo los matorrales de C. quila (1,5 %) fue levemente menor que el medido bajo el bosque cerrado (1,7 %). Asimismo, se midio mayor indice de area foliar para los bambus (6,1) comparado con el bosque cerrado (5,3). Sin embargo, las mediciones de indice de area foliar con el LAI-2000 probablemente sobreestiman la superficie asimilatoria efectiva de los matorrales de bambu, debido a la retencion de hojas muertas por los culmos de C. quila. Por otra parte, el indice de area foliar del bosque es subestimado, debido a la omision de la vegetacion del piso (< 50 cm en altura). La abundancia de los matorrales de Chusquea spp. en los bosques antiguos, y su capacidad de retener los sitios mediante la supresion de la regeneracion de los arboles, sugiere que un modelo bifasico de retroalimentacion positiva es apropiado para la dinamica de estos bosques
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