Boletim do Museu Paraense Emílio Goeldi, Jul 31, 2017
In order to test the effect of the lower availability of water for vegetation in a tropical Amazo... more In order to test the effect of the lower availability of water for vegetation in a tropical Amazonian forest, a long-term research project was created in 2001 called Projeto Seca Floresta (ESECAFLOR). The main objective of the project is to determine how a significant reduction of the available water in the soil, in the long term, can affect the biota. The ESECAFLOR consists of two 1-hectare plots, the experimental plot is covered with 6,000 plastic panels reducing precipitation by 50%. The objective of this work is to compare the floristic and plant structure (< 2 meters high) between the experimental and control of ESECAFLOR plots. There was a significant reduction in species richness and diversity, plant density and height, and a significant change in species composition between experimental plot compared to control. The plant community clearly responded to the reduction of soil moisture in the experimental plot, corroborating the results of some climate models that say rainfall reduction in the Amazon will negatively affect the plant community.
Tree growth of Nectandra amazonum (Lauraceae) in the Central Amazonian floodplains does not respo... more Tree growth of Nectandra amazonum (Lauraceae) in the Central Amazonian floodplains does not respond to the annual long-term flooding but responds to variation of minimum temperature and potential evapotranspiration. During the last two decades, the Central Amazon region has been impacted by increasingly frequent and more severe floods and droughts and increasing temperature. Little is known about the effects of these climate trends on tree growth in floodplain forests. In this study, we analysed Nectandra amazonum (Lauraceae), an evergreen and flood-adapted tree species, dominant not only in the nutrient-rich Amazonian floodplains (varzea), but also occurring in other environments within and outside the Amazon basin. For the period from 2001 to 2017, intra- and interannual climate–growth relationships of N. amazonum were analysed applying a combination of conventional dendrochronological (cross-dating) and densiometric techniques to construct a robust tree-ring chronology. Six wood parameters were derived from the chronology (ring width, width of earlywood and latewood and corresponding wood density values) and correlated with local climate and hydrologic data. The analysed 32 trees did not show correlation between wood parameters and variation of the hydrological regime. Climate–growth relationships indicated that potential evapotranspiration and minimum temperature play an important role in tree growth mainly during the period of transition between the dry and the wet seasons, and during the aquatic phase affecting physiological processes such as photosynthesis and respiration, respectively. We discuss these results in the background of changing hydroclimatic conditions induced by climate and land-use change in the Amazon basin. Based on our findings, we emphasize the need for more dendroclimatic studies in the tropics applying a multiproxy approach. This will deepen our understanding of tree growth responses, helping to elucidate the dynamic processes of tropical forests that grow under global change impacts.
Successional sequences from open sites to closed forests may take different pathways depending on... more Successional sequences from open sites to closed forests may take different pathways depending on the initially established vegetation. In Amazonian whitewater floodplains, we analysed encroachment by a monodominant shrub, the native fast - growing woody Senna reticulata . We analysed the impact of S. reticulata on woody pl ant diversity and the development of successional stages of deforested areas. The main hypothesis was that there is a difference in species abundance, diversity, composition and biomass between S. reticulata stands aged 2 and 6 years, and that with increas ing stand age species abundance, diversity and biomass increase. We determined all woody plants in plots dominated by S. reticulata , two years and six years old. Our results showed that in the first two years S. reticulata is highly encroaching and forms almost monodominant stands by outshading other species including competing C4 grasses. Within six years the result was a positive balance for native species d...
Understanding and predicting vegetation patterns in floodplains are essential for conservation an... more Understanding and predicting vegetation patterns in floodplains are essential for conservation and/or restoration of river floodplains subject to hydrological alterations. We propose a conceptual hydroecological model to explain the disturbance mechanisms driving species diversity across large river floodplains. These ecosystems harbor a unique set of flood-tolerant species different from the surrounding upland vegetation. In elevation gradients across pristine floodplains, the greater the flooding, the fewer the number of plant species. As terrain elevation increases, flood depth and duration decrease and it is more likely that species composition is influenced by external natural or humandriven disturbances. The spatial interaction between the natural flood regime and upland factors creates patterns of disturbance gradients that influence how floodplain vegetation establishes. In regions where upland conditions are subject to strong external disturbances, species diversity peaks at intermediate stages along the disturbance gradient. We demonstrate this concept with observations from the Central Amazon and Pantanal in Brazil, the Mekong's Tonle Sap in Cambodia, and the Okavango Delta in Botswana. We discuss how this model could be further elaborated and validated to inform management of large river basins under the impact of upstream-induced flood pulse alterations.
QuestionThe encroachment of woody species has been globally reported over much of arid and semi‐a... more QuestionThe encroachment of woody species has been globally reported over much of arid and semi‐arid biomes, and has been associated with a decrease in cover and number of herbaceous species. How does the encroachment of a woody shrub affect herbaceous community structure and species composition in grasslands of a wetland ecosystem?LocationSeasonally flooded grasslands in a Neotropical Hyperseasonal Savanna, the Pantanal wetland, Brazil.MethodsWe investigated the effect of the encroaching plant Combretum laxum on a herbaceous community from seasonally flooded grasslands in the Pantanal wetland using 29 vegetation samples representing encroachment at different spatio‐temporal stages. The point quadrat method was used to acquire vegetation data, as plant cover, species richness (S) and Shannon‐Wiener diversity index (H’). We evaluated the existence of stages of encroachment related to differences in vegetation structure and species composition using non‐metric multidimensional scaling...
Boletim do Museu Paraense Emílio Goeldi, Jul 31, 2017
In order to test the effect of the lower availability of water for vegetation in a tropical Amazo... more In order to test the effect of the lower availability of water for vegetation in a tropical Amazonian forest, a long-term research project was created in 2001 called Projeto Seca Floresta (ESECAFLOR). The main objective of the project is to determine how a significant reduction of the available water in the soil, in the long term, can affect the biota. The ESECAFLOR consists of two 1-hectare plots, the experimental plot is covered with 6,000 plastic panels reducing precipitation by 50%. The objective of this work is to compare the floristic and plant structure (< 2 meters high) between the experimental and control of ESECAFLOR plots. There was a significant reduction in species richness and diversity, plant density and height, and a significant change in species composition between experimental plot compared to control. The plant community clearly responded to the reduction of soil moisture in the experimental plot, corroborating the results of some climate models that say rainfall reduction in the Amazon will negatively affect the plant community.
Tree growth of Nectandra amazonum (Lauraceae) in the Central Amazonian floodplains does not respo... more Tree growth of Nectandra amazonum (Lauraceae) in the Central Amazonian floodplains does not respond to the annual long-term flooding but responds to variation of minimum temperature and potential evapotranspiration. During the last two decades, the Central Amazon region has been impacted by increasingly frequent and more severe floods and droughts and increasing temperature. Little is known about the effects of these climate trends on tree growth in floodplain forests. In this study, we analysed Nectandra amazonum (Lauraceae), an evergreen and flood-adapted tree species, dominant not only in the nutrient-rich Amazonian floodplains (varzea), but also occurring in other environments within and outside the Amazon basin. For the period from 2001 to 2017, intra- and interannual climate–growth relationships of N. amazonum were analysed applying a combination of conventional dendrochronological (cross-dating) and densiometric techniques to construct a robust tree-ring chronology. Six wood parameters were derived from the chronology (ring width, width of earlywood and latewood and corresponding wood density values) and correlated with local climate and hydrologic data. The analysed 32 trees did not show correlation between wood parameters and variation of the hydrological regime. Climate–growth relationships indicated that potential evapotranspiration and minimum temperature play an important role in tree growth mainly during the period of transition between the dry and the wet seasons, and during the aquatic phase affecting physiological processes such as photosynthesis and respiration, respectively. We discuss these results in the background of changing hydroclimatic conditions induced by climate and land-use change in the Amazon basin. Based on our findings, we emphasize the need for more dendroclimatic studies in the tropics applying a multiproxy approach. This will deepen our understanding of tree growth responses, helping to elucidate the dynamic processes of tropical forests that grow under global change impacts.
Successional sequences from open sites to closed forests may take different pathways depending on... more Successional sequences from open sites to closed forests may take different pathways depending on the initially established vegetation. In Amazonian whitewater floodplains, we analysed encroachment by a monodominant shrub, the native fast - growing woody Senna reticulata . We analysed the impact of S. reticulata on woody pl ant diversity and the development of successional stages of deforested areas. The main hypothesis was that there is a difference in species abundance, diversity, composition and biomass between S. reticulata stands aged 2 and 6 years, and that with increas ing stand age species abundance, diversity and biomass increase. We determined all woody plants in plots dominated by S. reticulata , two years and six years old. Our results showed that in the first two years S. reticulata is highly encroaching and forms almost monodominant stands by outshading other species including competing C4 grasses. Within six years the result was a positive balance for native species d...
Understanding and predicting vegetation patterns in floodplains are essential for conservation an... more Understanding and predicting vegetation patterns in floodplains are essential for conservation and/or restoration of river floodplains subject to hydrological alterations. We propose a conceptual hydroecological model to explain the disturbance mechanisms driving species diversity across large river floodplains. These ecosystems harbor a unique set of flood-tolerant species different from the surrounding upland vegetation. In elevation gradients across pristine floodplains, the greater the flooding, the fewer the number of plant species. As terrain elevation increases, flood depth and duration decrease and it is more likely that species composition is influenced by external natural or humandriven disturbances. The spatial interaction between the natural flood regime and upland factors creates patterns of disturbance gradients that influence how floodplain vegetation establishes. In regions where upland conditions are subject to strong external disturbances, species diversity peaks at intermediate stages along the disturbance gradient. We demonstrate this concept with observations from the Central Amazon and Pantanal in Brazil, the Mekong's Tonle Sap in Cambodia, and the Okavango Delta in Botswana. We discuss how this model could be further elaborated and validated to inform management of large river basins under the impact of upstream-induced flood pulse alterations.
QuestionThe encroachment of woody species has been globally reported over much of arid and semi‐a... more QuestionThe encroachment of woody species has been globally reported over much of arid and semi‐arid biomes, and has been associated with a decrease in cover and number of herbaceous species. How does the encroachment of a woody shrub affect herbaceous community structure and species composition in grasslands of a wetland ecosystem?LocationSeasonally flooded grasslands in a Neotropical Hyperseasonal Savanna, the Pantanal wetland, Brazil.MethodsWe investigated the effect of the encroaching plant Combretum laxum on a herbaceous community from seasonally flooded grasslands in the Pantanal wetland using 29 vegetation samples representing encroachment at different spatio‐temporal stages. The point quadrat method was used to acquire vegetation data, as plant cover, species richness (S) and Shannon‐Wiener diversity index (H’). We evaluated the existence of stages of encroachment related to differences in vegetation structure and species composition using non‐metric multidimensional scaling...
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