Increased drought is forecasted for tropical regions, with severe implications for the health and... more Increased drought is forecasted for tropical regions, with severe implications for the health and function of forest ecosystems. How mature forest trees will respond to water deficit is poorly known. We investigated wood anatomy and leaf traits in lowland tropical forest trees after 24 months of experimental rainfall exclusion. Sampling sun‐exposed young canopy branches from target species, we found species‐specific systematic variation in hydraulic‐related wood anatomy and leaf traits in response to drought stress. Relative to controls, drought‐affected individuals of different tree species variously exhibited trait measures consistent with increasing hydraulic safety. These included narrower or less vessels, reduced vessel groupings, lower theoretical water conductivities, less water storage tissue and more abundant fiber in their wood, and more occluded vessels. Drought-affected individuals also had thinner leaves, and more negative pre‐dawn or mid‐day leaf water potentials. Future studies examining both wood and leaf hydraulic traits should improve the representation of plant hydraulics within terrestrial ecosystem and biosphere models, and help finetune predictions of how future climate changes will affect tropical forests globally.
Increased drought is forecasted for tropical regions, with severe implications for the health and... more Increased drought is forecasted for tropical regions, with severe implications for the health and function of forest ecosystems. How mature forest trees will respond to water deficit is poorly known. We investigated wood anatomy and leaf traits in lowland tropical forest trees after 24 months of experimental rainfall exclusion. Sampling sun‐exposed young canopy branches from target species, we found species‐specific systematic variation in hydraulic‐related wood anatomy and leaf traits in response to drought stress. Relative to controls, drought‐affected individuals of different tree species variously exhibited trait measures consistent with increasing hydraulic safety. These included narrower or less vessels, reduced vessel groupings, lower theoretical water conductivities, less water storage tissue and more abundant fiber in their wood, and more occluded vessels. Drought-affected individuals also had thinner leaves, and more negative pre‐dawn or mid‐day leaf water potentials. Future studies examining both wood and leaf hydraulic traits should improve the representation of plant hydraulics within terrestrial ecosystem and biosphere models, and help fine tune predictions of how future climate changes will affect tropical forests globally.
Aims Understanding succession in tropical forest is an important aspect of vegetation science, bu... more Aims Understanding succession in tropical forest is an important aspect of vegetation science, but to date, successional processes in seasonally dry tropical forests (SDTFs) have received much less attention than evergreen humid tropical forests. We aim to fill this knowledge gap.
Methods We investigated vegetation succession in SDTF areas consisting of three different successional stages (early, intermediate, late), and a SDTF-savanna ecotone in the municipal district of Juramento, north of Minas Gerais State, Brazil. Using twelve 400 m2 plots in each area, we compared vegetation parameters and structural variables (absolute density and basal area), and examined the floristic composition of the tree component to find gradients of change.
Important Findings We found evidence of species turnover along a successional gradient, with the intermediate stage showing the highest species richness and diversity. This was accompanied with a significant increase in the number of tree individuals and basal area from the early to intermediate successional stage. However, the intermediate and late SDTF successional stages were more similar in structure and floristics. The ecotone was the most species rich, and was similar to the intermediate SDTF and early successional stage in species richness and floristic composition respectively. These results will have implications for guiding SDTF management and recovery programs.
1. Understanding the anatomical basis of plant water transport in forest ecosystems is crucial f... more 1. Understanding the anatomical basis of plant water transport in forest ecosystems is crucial for contextualizing community-level adaptations to drought, especially in lifeform-rich tropical forests. To provide this context, we explored wood functional anatomy traits related to plant hydraulic architecture across different plant functional groups in a lowland tropical rainforest. 2. We measured wood traits in 90 species from six functional groups (mature-phase, understorey and pioneer trees; understorey and pioneer shrubs; vines) and related these traits to intrinsic water-use efficiency (WUEi) as a measure of physiological performance. We also examined vessel size distribution patterns across groups to determine tradeoffs in theoretical hydraulic safety versus efficiency. 3. Plant functional groups exhibited significant differences in vessel parameters and WUEi. Vessel diameters in vines and pioneer trees were two- to three-fold greater on average than in understorey trees and shrubs. Contrastingly, vessels in understorey-trees and -shrubs fell within the smaller size classes, suggesting greater safety mechanisms. In addition to these trends, large vessel dimensions were important predictors of WUEi among the functional groups. 4. We conclude that plant functional groups in tropical rainforest have distinctive functional anatomy profiles. These groups can therefore serve as a framework for further investigations on structure-function relationships, and a sound basis for modeling species responses to drought.
Graduação em Agronomia (UFLA) e membro do NPPJ,³ Estudante de graduação em engenharia florestal e... more Graduação em Agronomia (UFLA) e membro do NPPJ,³ Estudante de graduação em engenharia florestal e membro do Núcleo PPJ , 4 Mestre em Administração e membro do Núcleo PPJ. [email protected] Introdução A extensão universitária muitas vezes ocorre quando o conhecimento da universidade é levado para a sociedade. Freire (1975) considera o termo extensão carregado por significações como: transmissão, entrega, doação, messianismo, mecanicismo, invasão cultural, manipulação, entre outros. Isto mostra que a extensão pode ser realizada de várias maneiras. Através da análise da Lei Federal nº 5540, de 1968, percebe-se que a extensão é a princípio apenas uma forma de levar o conhecimento à sociedade. Esta lei traz no artigo 20 a seguinte consideração sobre o tema: "As universidades e os estabelecimentos de ensino superior estenderão à comunidade, sob a forma de cursos e serviços especiais, as atividades de ensino e os resultados das pesquisas que lhes são inerentes".
Seasonally Dry Tropical Forests (SDTF) were recently recognized as an important and unique biome,... more Seasonally Dry Tropical Forests (SDTF) were recently recognized as an important and unique biome, and remains under studied and poorly conserved. SDTF occurs in Africa, Asia, Australia and South America but the largest continuous occurrence of SDTF is in the Caatinga Biogeographical Domain in the northwest of Brazil. The Caatinga Biogeographical Domain was singled out by UNESCO in 2008 as a significant Biosphere reserve, and we present a synthesis of studies with special reference to the region. Landscape mapping of SDTF has only recently commenced, and floristic community classifications are ongoing. Biodiversity studies in SDTF are still in an exploratory phase, and new taxa of plants and animals continue to be described. While less species-rich than humid Amazonian and Atlantic rainforests, SDTF have comparably high and occasionally higher levels of beta-diversity, due to their inherent habitat heterogeneity. Vegetation structure studies on a number of SDTF tree species show pecu...
Introdution Studying fire effects on soil chemistry across rainforest – woodland boundaries is pa... more Introdution Studying fire effects on soil chemistry across rainforest – woodland boundaries is paramount for understanding fire – vegetation – soil interactions. Such vegetation boundaries are hypothesized to be zones of rapid change (Kark & van Rensburg 2006). Aims To understand if changes in soil chemistry after 11 years monitoring a rainforest – boundary zone transect: (a) can be related with fire, and whether (b) there are differences in the magnitude of soil chemistry change between burnt rainforest and burnt boundary zone. Results • Soil chemistry changed over the monitoring period • Some changes occurred due to unknown processes • Soil Ca change was pronounced in burnt rainforest • Soil P change was more pronounced in the boundary zone.
Full floristic data, tree demography, and biomass estimates incorporating non-tree lifeforms are ... more Full floristic data, tree demography, and biomass estimates incorporating non-tree lifeforms are seldom collected and reported for forest plots in the tropics. Established research stations serve as important repositories of such biodiversity and ecological data. With a canopy crane setup within a tropical lowland rainforest estate, the 42-ha Daintree Rainforest Observatory (DRO) in Cape Tribulation, northern Australia is a research facility of international significance. We obtained an estimate of the vascular plant species richness for the site, by surveying all vascular plant species from various mature-phase, remnant and open vegetation patches within the site. We also integrate and report the demography and basal areas of trees ≥ 10 cm diameter at breast height (dbh) in a new 1-ha core plot, an extension to the pre-existing forest 1-ha plot under the canopy crane. In addition, we report for the canopy crane plot new demography and basal areas for smaller-size shrubs and treelets subsampled from nine 20 m2 quadrats, and liana basal area and abundance from the whole plot. The DRO site has an estimated total vascular plant species richness of 441 species, of which 172 species (39%) are endemic to Australia, and 4 species are endemics to the Daintree region. The 2 x 1-ha plots contains a total of 262 vascular plant species of which 116 (1531 individuals) are tree species ≥ 10 cm dbh. We estimate a stem basal area of 34.9 m2 ha-1, of which small stems (tree saplings and shrubs <10cm dbh) and lianas collectively contribute c.4.2%. Comparing the stem density-diversity patterns of the DRO forest with other tropical rainforests globally, our meta-analysis shows that DRO forests has a comparatively high stem density and moderate species diversity, due to the influence of cyclones. These data will provide an important foundation for ecological and conservation studies in lowland tropical forest.
Understanding how tropical rainforest trees may respond to the precipitation extremes predicted i... more Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees). We characterised the species’ hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and ...
ABSTRACT The dry forest biome covers extensive areas of the global tropics. However, the understa... more ABSTRACT The dry forest biome covers extensive areas of the global tropics. However, the understanding of these forest formations from both human and biophysical perspectives varies widely both geographically and in terms of disciplinarity. While considerable resources have been made available for the sustainable management of the humid tropical forests, there has been a lack of comparable sustained attention on their dry forest equivalents. This special issue is an attempt to provide further insights into the state of the knowledge of global dry forests, and identify research gaps that could contribute to their long-term sustainability, both for human well-being and ecological integrity.
The dry forest biome covers extensive areas of the global tropics. However, the understanding of ... more The dry forest biome covers extensive areas of the global tropics. However, the understanding of these forest formations from both human and biophysical perspectives varies widely both geographically and in terms of disciplinarity. While considerable resources have been made available for the sustainable management of the humid tropical forests, there has been a lack of comparable sustained attention on their dry forest equivalents. This special issue is an attempt to provide further insights into the state of the knowledge of global dry forests, and identify research gaps that could contribute to their long-term sustainability, both for human well-being and ecological integrity.
Seasonally Dry Tropical Forests (SDTF) are gaining recognition as a significant biome and poorly ... more Seasonally Dry Tropical Forests (SDTF) are gaining recognition as a significant biome and poorly conserved tropical biodiversity refuge. Understanding floristic relationships within SDTF is essential for their effective conservation. This study examines the floristic variation within SDTF of the Caatinga Biogeographic Domain, in north-eastern Brazil. SDTF trees, shrubs and arborescent cacti were sampled in six localities in the Brazilian states of Minas Gerais and Bahia. A number of soil chemical attributes were also measured to analyse vegetation-soil relationships across the study sites. Five floristically distinct SDTF communities were delineated. Differences in these communities are attributable to influences from adjacent savanna and rain forest surrounding the study sites, and also to soil properties such as Al3+, base saturation and gravel content. The high species richness of, and species dissimilarity between communities reflect the need for judicious conservation planning for SDTF that account for biodiversity values and forest structural integrity.
Tropical biomes are species rich, but some biomes such as seasonally dry tropical forests (SDTFs)... more Tropical biomes are species rich, but some biomes such as seasonally dry tropical forests (SDTFs) are still inadequately studied compared to their co-occurring rain forest and savanna. SDTFs occur in areas of high environmental heterogeneity, resulting in high beta (β)-diversity or species turnover, but this has so far only been accessed using a single β-diversity measure, and at a spatial scale that is of limited applicability for reserve planning. The Caatinga Biogeographic Domain in Brazil contains the largest known extent of SDTF which are poorly studied and inadequately reserved. We therefore studied the variation in species richness and species turnover among SDTF between localities and between known floristic communities. From six localities within the Caatinga Biogeographic Domain we recorded all tree species with a circumference at breast height equaling or exceeding 10 cm within 106 400 m2 survey plots. From the species presence/absence data we calculated three measures of β-diversity between pairs of study localities and between different floristic communities representing: (i) species similarity, (ii) differences between species richness, and (iii) species gain and loss. Our results confirm the high β-diversity of SDTFs and species turnover between localities and also between floristic communities. The three indices were also complementary to each other and can be used to maximize accuracy in β-diversity studies. The implications of our study for conservation and reserve planning of SDTFs are discussed.
Understanding how tropical rainforest trees may respond to the precipitation extremes predicted i... more Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees). We characterised the species’ hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and leaf traits were poor predictors of sap flow measures. However, these traits exhibited different associations in multivariate analysis, revealing gradients in some traits across species and alternative hydraulic strategies in others. Trait differences across and within tree functional groups reflect variation in water transport and drought resistance strategies. These varying strategies will help in our understanding of changing species distributions under predicted drought scenarios.
ABSTRACT Tropical biomes are species rich, but some biomes such as seasonally dry tropical forest... more ABSTRACT Tropical biomes are species rich, but some biomes such as seasonally dry tropical forests (SDTFs) are still inadequately studied compared to their co-occurring rain forest and savanna. SDTFs occur in areas of high environmental heterogeneity, resulting in high beta (β)-diversity or species turnover, but this has so far only been accessed using a single β-diversity measure, and at a spatial scale that is of limited applicability for reserve planning. The Caatinga Biogeographic Domain in Brazil contains the largest known extent of SDTF which are poorly studied and inadequately reserved. We therefore studied the variation in species richness and species turnover among SDTF between localities and between known floristic communities. From six localities within the Caatinga Biogeographic Domain we recorded all tree species with a circumference at breast height equaling or exceeding 10 cm within 106 400 m2 survey plots. From the species presence/absence data we calculated three measures of β-diversity between pairs of study localities and between different floristic communities representing: (i) species similarity, (ii) differences between species richness, and (iii) species gain and loss. Our results confirm the high β-diversity of SDTFs and species turnover between localities and also between floristic communities. The three indices were also complementary to each other and can be used to maximize accuracy in β-diversity studies. The implications of our study for conservation and reserve planning of SDTFs are discussed.
ABSTRACT: Most studies on Seasonally Dry Tropical Forests (SDTFs) investigate phytogeographic pat... more ABSTRACT: Most studies on Seasonally Dry Tropical Forests (SDTFs) investigate phytogeographic patterns and floristic connections
of this disjunct biome. However, little is known about the structural characteristics of SDTFs. We aimed to describe the structure of
a SDTF in an ecotonal area between the Cerrado and Caatinga domains. In total, 79 tree species were recorded, and high values of
Shannon diversity index (3.6 nats/individual) and equability (0.83) were observed. The diameter distribution for the species with higher
cover values and for the entire community did not exhibit a reverse-J shaped distribution, which indicates the occurrence of different
growth strategies and ecological adaptations to water stress. The results did not indicate the formation of floristic groups, as the high
soil fertility in the study area results in a homogeneous environment. The structural characteristics of the study area associated with
the soil composition highlight its importance for conservation and emphasize the need for community structure studies in SDTFs.
Increased drought is forecasted for tropical regions, with severe implications for the health and... more Increased drought is forecasted for tropical regions, with severe implications for the health and function of forest ecosystems. How mature forest trees will respond to water deficit is poorly known. We investigated wood anatomy and leaf traits in lowland tropical forest trees after 24 months of experimental rainfall exclusion. Sampling sun‐exposed young canopy branches from target species, we found species‐specific systematic variation in hydraulic‐related wood anatomy and leaf traits in response to drought stress. Relative to controls, drought‐affected individuals of different tree species variously exhibited trait measures consistent with increasing hydraulic safety. These included narrower or less vessels, reduced vessel groupings, lower theoretical water conductivities, less water storage tissue and more abundant fiber in their wood, and more occluded vessels. Drought-affected individuals also had thinner leaves, and more negative pre‐dawn or mid‐day leaf water potentials. Future studies examining both wood and leaf hydraulic traits should improve the representation of plant hydraulics within terrestrial ecosystem and biosphere models, and help finetune predictions of how future climate changes will affect tropical forests globally.
Increased drought is forecasted for tropical regions, with severe implications for the health and... more Increased drought is forecasted for tropical regions, with severe implications for the health and function of forest ecosystems. How mature forest trees will respond to water deficit is poorly known. We investigated wood anatomy and leaf traits in lowland tropical forest trees after 24 months of experimental rainfall exclusion. Sampling sun‐exposed young canopy branches from target species, we found species‐specific systematic variation in hydraulic‐related wood anatomy and leaf traits in response to drought stress. Relative to controls, drought‐affected individuals of different tree species variously exhibited trait measures consistent with increasing hydraulic safety. These included narrower or less vessels, reduced vessel groupings, lower theoretical water conductivities, less water storage tissue and more abundant fiber in their wood, and more occluded vessels. Drought-affected individuals also had thinner leaves, and more negative pre‐dawn or mid‐day leaf water potentials. Future studies examining both wood and leaf hydraulic traits should improve the representation of plant hydraulics within terrestrial ecosystem and biosphere models, and help fine tune predictions of how future climate changes will affect tropical forests globally.
Aims Understanding succession in tropical forest is an important aspect of vegetation science, bu... more Aims Understanding succession in tropical forest is an important aspect of vegetation science, but to date, successional processes in seasonally dry tropical forests (SDTFs) have received much less attention than evergreen humid tropical forests. We aim to fill this knowledge gap.
Methods We investigated vegetation succession in SDTF areas consisting of three different successional stages (early, intermediate, late), and a SDTF-savanna ecotone in the municipal district of Juramento, north of Minas Gerais State, Brazil. Using twelve 400 m2 plots in each area, we compared vegetation parameters and structural variables (absolute density and basal area), and examined the floristic composition of the tree component to find gradients of change.
Important Findings We found evidence of species turnover along a successional gradient, with the intermediate stage showing the highest species richness and diversity. This was accompanied with a significant increase in the number of tree individuals and basal area from the early to intermediate successional stage. However, the intermediate and late SDTF successional stages were more similar in structure and floristics. The ecotone was the most species rich, and was similar to the intermediate SDTF and early successional stage in species richness and floristic composition respectively. These results will have implications for guiding SDTF management and recovery programs.
1. Understanding the anatomical basis of plant water transport in forest ecosystems is crucial f... more 1. Understanding the anatomical basis of plant water transport in forest ecosystems is crucial for contextualizing community-level adaptations to drought, especially in lifeform-rich tropical forests. To provide this context, we explored wood functional anatomy traits related to plant hydraulic architecture across different plant functional groups in a lowland tropical rainforest. 2. We measured wood traits in 90 species from six functional groups (mature-phase, understorey and pioneer trees; understorey and pioneer shrubs; vines) and related these traits to intrinsic water-use efficiency (WUEi) as a measure of physiological performance. We also examined vessel size distribution patterns across groups to determine tradeoffs in theoretical hydraulic safety versus efficiency. 3. Plant functional groups exhibited significant differences in vessel parameters and WUEi. Vessel diameters in vines and pioneer trees were two- to three-fold greater on average than in understorey trees and shrubs. Contrastingly, vessels in understorey-trees and -shrubs fell within the smaller size classes, suggesting greater safety mechanisms. In addition to these trends, large vessel dimensions were important predictors of WUEi among the functional groups. 4. We conclude that plant functional groups in tropical rainforest have distinctive functional anatomy profiles. These groups can therefore serve as a framework for further investigations on structure-function relationships, and a sound basis for modeling species responses to drought.
Graduação em Agronomia (UFLA) e membro do NPPJ,³ Estudante de graduação em engenharia florestal e... more Graduação em Agronomia (UFLA) e membro do NPPJ,³ Estudante de graduação em engenharia florestal e membro do Núcleo PPJ , 4 Mestre em Administração e membro do Núcleo PPJ. [email protected] Introdução A extensão universitária muitas vezes ocorre quando o conhecimento da universidade é levado para a sociedade. Freire (1975) considera o termo extensão carregado por significações como: transmissão, entrega, doação, messianismo, mecanicismo, invasão cultural, manipulação, entre outros. Isto mostra que a extensão pode ser realizada de várias maneiras. Através da análise da Lei Federal nº 5540, de 1968, percebe-se que a extensão é a princípio apenas uma forma de levar o conhecimento à sociedade. Esta lei traz no artigo 20 a seguinte consideração sobre o tema: "As universidades e os estabelecimentos de ensino superior estenderão à comunidade, sob a forma de cursos e serviços especiais, as atividades de ensino e os resultados das pesquisas que lhes são inerentes".
Seasonally Dry Tropical Forests (SDTF) were recently recognized as an important and unique biome,... more Seasonally Dry Tropical Forests (SDTF) were recently recognized as an important and unique biome, and remains under studied and poorly conserved. SDTF occurs in Africa, Asia, Australia and South America but the largest continuous occurrence of SDTF is in the Caatinga Biogeographical Domain in the northwest of Brazil. The Caatinga Biogeographical Domain was singled out by UNESCO in 2008 as a significant Biosphere reserve, and we present a synthesis of studies with special reference to the region. Landscape mapping of SDTF has only recently commenced, and floristic community classifications are ongoing. Biodiversity studies in SDTF are still in an exploratory phase, and new taxa of plants and animals continue to be described. While less species-rich than humid Amazonian and Atlantic rainforests, SDTF have comparably high and occasionally higher levels of beta-diversity, due to their inherent habitat heterogeneity. Vegetation structure studies on a number of SDTF tree species show pecu...
Introdution Studying fire effects on soil chemistry across rainforest – woodland boundaries is pa... more Introdution Studying fire effects on soil chemistry across rainforest – woodland boundaries is paramount for understanding fire – vegetation – soil interactions. Such vegetation boundaries are hypothesized to be zones of rapid change (Kark & van Rensburg 2006). Aims To understand if changes in soil chemistry after 11 years monitoring a rainforest – boundary zone transect: (a) can be related with fire, and whether (b) there are differences in the magnitude of soil chemistry change between burnt rainforest and burnt boundary zone. Results • Soil chemistry changed over the monitoring period • Some changes occurred due to unknown processes • Soil Ca change was pronounced in burnt rainforest • Soil P change was more pronounced in the boundary zone.
Full floristic data, tree demography, and biomass estimates incorporating non-tree lifeforms are ... more Full floristic data, tree demography, and biomass estimates incorporating non-tree lifeforms are seldom collected and reported for forest plots in the tropics. Established research stations serve as important repositories of such biodiversity and ecological data. With a canopy crane setup within a tropical lowland rainforest estate, the 42-ha Daintree Rainforest Observatory (DRO) in Cape Tribulation, northern Australia is a research facility of international significance. We obtained an estimate of the vascular plant species richness for the site, by surveying all vascular plant species from various mature-phase, remnant and open vegetation patches within the site. We also integrate and report the demography and basal areas of trees ≥ 10 cm diameter at breast height (dbh) in a new 1-ha core plot, an extension to the pre-existing forest 1-ha plot under the canopy crane. In addition, we report for the canopy crane plot new demography and basal areas for smaller-size shrubs and treelets subsampled from nine 20 m2 quadrats, and liana basal area and abundance from the whole plot. The DRO site has an estimated total vascular plant species richness of 441 species, of which 172 species (39%) are endemic to Australia, and 4 species are endemics to the Daintree region. The 2 x 1-ha plots contains a total of 262 vascular plant species of which 116 (1531 individuals) are tree species ≥ 10 cm dbh. We estimate a stem basal area of 34.9 m2 ha-1, of which small stems (tree saplings and shrubs <10cm dbh) and lianas collectively contribute c.4.2%. Comparing the stem density-diversity patterns of the DRO forest with other tropical rainforests globally, our meta-analysis shows that DRO forests has a comparatively high stem density and moderate species diversity, due to the influence of cyclones. These data will provide an important foundation for ecological and conservation studies in lowland tropical forest.
Understanding how tropical rainforest trees may respond to the precipitation extremes predicted i... more Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees). We characterised the species’ hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and ...
ABSTRACT The dry forest biome covers extensive areas of the global tropics. However, the understa... more ABSTRACT The dry forest biome covers extensive areas of the global tropics. However, the understanding of these forest formations from both human and biophysical perspectives varies widely both geographically and in terms of disciplinarity. While considerable resources have been made available for the sustainable management of the humid tropical forests, there has been a lack of comparable sustained attention on their dry forest equivalents. This special issue is an attempt to provide further insights into the state of the knowledge of global dry forests, and identify research gaps that could contribute to their long-term sustainability, both for human well-being and ecological integrity.
The dry forest biome covers extensive areas of the global tropics. However, the understanding of ... more The dry forest biome covers extensive areas of the global tropics. However, the understanding of these forest formations from both human and biophysical perspectives varies widely both geographically and in terms of disciplinarity. While considerable resources have been made available for the sustainable management of the humid tropical forests, there has been a lack of comparable sustained attention on their dry forest equivalents. This special issue is an attempt to provide further insights into the state of the knowledge of global dry forests, and identify research gaps that could contribute to their long-term sustainability, both for human well-being and ecological integrity.
Seasonally Dry Tropical Forests (SDTF) are gaining recognition as a significant biome and poorly ... more Seasonally Dry Tropical Forests (SDTF) are gaining recognition as a significant biome and poorly conserved tropical biodiversity refuge. Understanding floristic relationships within SDTF is essential for their effective conservation. This study examines the floristic variation within SDTF of the Caatinga Biogeographic Domain, in north-eastern Brazil. SDTF trees, shrubs and arborescent cacti were sampled in six localities in the Brazilian states of Minas Gerais and Bahia. A number of soil chemical attributes were also measured to analyse vegetation-soil relationships across the study sites. Five floristically distinct SDTF communities were delineated. Differences in these communities are attributable to influences from adjacent savanna and rain forest surrounding the study sites, and also to soil properties such as Al3+, base saturation and gravel content. The high species richness of, and species dissimilarity between communities reflect the need for judicious conservation planning for SDTF that account for biodiversity values and forest structural integrity.
Tropical biomes are species rich, but some biomes such as seasonally dry tropical forests (SDTFs)... more Tropical biomes are species rich, but some biomes such as seasonally dry tropical forests (SDTFs) are still inadequately studied compared to their co-occurring rain forest and savanna. SDTFs occur in areas of high environmental heterogeneity, resulting in high beta (β)-diversity or species turnover, but this has so far only been accessed using a single β-diversity measure, and at a spatial scale that is of limited applicability for reserve planning. The Caatinga Biogeographic Domain in Brazil contains the largest known extent of SDTF which are poorly studied and inadequately reserved. We therefore studied the variation in species richness and species turnover among SDTF between localities and between known floristic communities. From six localities within the Caatinga Biogeographic Domain we recorded all tree species with a circumference at breast height equaling or exceeding 10 cm within 106 400 m2 survey plots. From the species presence/absence data we calculated three measures of β-diversity between pairs of study localities and between different floristic communities representing: (i) species similarity, (ii) differences between species richness, and (iii) species gain and loss. Our results confirm the high β-diversity of SDTFs and species turnover between localities and also between floristic communities. The three indices were also complementary to each other and can be used to maximize accuracy in β-diversity studies. The implications of our study for conservation and reserve planning of SDTFs are discussed.
Understanding how tropical rainforest trees may respond to the precipitation extremes predicted i... more Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees). We characterised the species’ hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and leaf traits were poor predictors of sap flow measures. However, these traits exhibited different associations in multivariate analysis, revealing gradients in some traits across species and alternative hydraulic strategies in others. Trait differences across and within tree functional groups reflect variation in water transport and drought resistance strategies. These varying strategies will help in our understanding of changing species distributions under predicted drought scenarios.
ABSTRACT Tropical biomes are species rich, but some biomes such as seasonally dry tropical forest... more ABSTRACT Tropical biomes are species rich, but some biomes such as seasonally dry tropical forests (SDTFs) are still inadequately studied compared to their co-occurring rain forest and savanna. SDTFs occur in areas of high environmental heterogeneity, resulting in high beta (β)-diversity or species turnover, but this has so far only been accessed using a single β-diversity measure, and at a spatial scale that is of limited applicability for reserve planning. The Caatinga Biogeographic Domain in Brazil contains the largest known extent of SDTF which are poorly studied and inadequately reserved. We therefore studied the variation in species richness and species turnover among SDTF between localities and between known floristic communities. From six localities within the Caatinga Biogeographic Domain we recorded all tree species with a circumference at breast height equaling or exceeding 10 cm within 106 400 m2 survey plots. From the species presence/absence data we calculated three measures of β-diversity between pairs of study localities and between different floristic communities representing: (i) species similarity, (ii) differences between species richness, and (iii) species gain and loss. Our results confirm the high β-diversity of SDTFs and species turnover between localities and also between floristic communities. The three indices were also complementary to each other and can be used to maximize accuracy in β-diversity studies. The implications of our study for conservation and reserve planning of SDTFs are discussed.
ABSTRACT: Most studies on Seasonally Dry Tropical Forests (SDTFs) investigate phytogeographic pat... more ABSTRACT: Most studies on Seasonally Dry Tropical Forests (SDTFs) investigate phytogeographic patterns and floristic connections
of this disjunct biome. However, little is known about the structural characteristics of SDTFs. We aimed to describe the structure of
a SDTF in an ecotonal area between the Cerrado and Caatinga domains. In total, 79 tree species were recorded, and high values of
Shannon diversity index (3.6 nats/individual) and equability (0.83) were observed. The diameter distribution for the species with higher
cover values and for the entire community did not exhibit a reverse-J shaped distribution, which indicates the occurrence of different
growth strategies and ecological adaptations to water stress. The results did not indicate the formation of floristic groups, as the high
soil fertility in the study area results in a homogeneous environment. The structural characteristics of the study area associated with
the soil composition highlight its importance for conservation and emphasize the need for community structure studies in SDTFs.
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Papers by Deborah Apgaua
Methods We investigated vegetation succession in SDTF areas consisting of three different successional stages (early, intermediate, late), and a SDTF-savanna ecotone in the municipal district of Juramento, north of Minas Gerais State, Brazil. Using twelve 400 m2 plots in each area, we compared vegetation parameters and structural variables (absolute density and basal area), and examined the floristic composition of the tree component to find gradients of change.
Important Findings We found evidence of species turnover along a successional gradient, with the intermediate stage showing the highest species richness and diversity. This was accompanied with a significant increase in the number of tree individuals and basal area from the early to intermediate successional stage. However, the intermediate and late SDTF successional stages were more similar in structure and floristics. The ecotone was the most species rich, and was similar to the intermediate SDTF and early successional stage in species richness and floristic composition respectively. These results will have implications for guiding SDTF management and recovery programs.
2. We measured wood traits in 90 species from six functional groups (mature-phase, understorey and pioneer trees; understorey and pioneer shrubs; vines) and related these traits to intrinsic water-use efficiency (WUEi) as a measure of physiological performance. We also examined vessel size distribution patterns across groups to determine tradeoffs in theoretical hydraulic safety versus efficiency.
3. Plant functional groups exhibited significant differences in vessel parameters and WUEi. Vessel diameters in vines and pioneer trees were two- to three-fold greater on average than in understorey trees and shrubs. Contrastingly, vessels in understorey-trees and -shrubs fell within the smaller size classes, suggesting greater safety mechanisms. In addition to these trends, large vessel dimensions were important predictors of WUEi among the functional groups.
4. We conclude that plant functional groups in tropical rainforest have distinctive functional anatomy profiles. These groups can therefore serve as a framework for further investigations on structure-function relationships, and a sound basis for modeling species responses to drought.
of this disjunct biome. However, little is known about the structural characteristics of SDTFs. We aimed to describe the structure of
a SDTF in an ecotonal area between the Cerrado and Caatinga domains. In total, 79 tree species were recorded, and high values of
Shannon diversity index (3.6 nats/individual) and equability (0.83) were observed. The diameter distribution for the species with higher
cover values and for the entire community did not exhibit a reverse-J shaped distribution, which indicates the occurrence of different
growth strategies and ecological adaptations to water stress. The results did not indicate the formation of floristic groups, as the high
soil fertility in the study area results in a homogeneous environment. The structural characteristics of the study area associated with
the soil composition highlight its importance for conservation and emphasize the need for community structure studies in SDTFs.
Methods We investigated vegetation succession in SDTF areas consisting of three different successional stages (early, intermediate, late), and a SDTF-savanna ecotone in the municipal district of Juramento, north of Minas Gerais State, Brazil. Using twelve 400 m2 plots in each area, we compared vegetation parameters and structural variables (absolute density and basal area), and examined the floristic composition of the tree component to find gradients of change.
Important Findings We found evidence of species turnover along a successional gradient, with the intermediate stage showing the highest species richness and diversity. This was accompanied with a significant increase in the number of tree individuals and basal area from the early to intermediate successional stage. However, the intermediate and late SDTF successional stages were more similar in structure and floristics. The ecotone was the most species rich, and was similar to the intermediate SDTF and early successional stage in species richness and floristic composition respectively. These results will have implications for guiding SDTF management and recovery programs.
2. We measured wood traits in 90 species from six functional groups (mature-phase, understorey and pioneer trees; understorey and pioneer shrubs; vines) and related these traits to intrinsic water-use efficiency (WUEi) as a measure of physiological performance. We also examined vessel size distribution patterns across groups to determine tradeoffs in theoretical hydraulic safety versus efficiency.
3. Plant functional groups exhibited significant differences in vessel parameters and WUEi. Vessel diameters in vines and pioneer trees were two- to three-fold greater on average than in understorey trees and shrubs. Contrastingly, vessels in understorey-trees and -shrubs fell within the smaller size classes, suggesting greater safety mechanisms. In addition to these trends, large vessel dimensions were important predictors of WUEi among the functional groups.
4. We conclude that plant functional groups in tropical rainforest have distinctive functional anatomy profiles. These groups can therefore serve as a framework for further investigations on structure-function relationships, and a sound basis for modeling species responses to drought.
of this disjunct biome. However, little is known about the structural characteristics of SDTFs. We aimed to describe the structure of
a SDTF in an ecotonal area between the Cerrado and Caatinga domains. In total, 79 tree species were recorded, and high values of
Shannon diversity index (3.6 nats/individual) and equability (0.83) were observed. The diameter distribution for the species with higher
cover values and for the entire community did not exhibit a reverse-J shaped distribution, which indicates the occurrence of different
growth strategies and ecological adaptations to water stress. The results did not indicate the formation of floristic groups, as the high
soil fertility in the study area results in a homogeneous environment. The structural characteristics of the study area associated with
the soil composition highlight its importance for conservation and emphasize the need for community structure studies in SDTFs.