Academic literature on the topic 'Seasonal dry tropical forests (SDTF)'
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Journal articles on the topic "Seasonal dry tropical forests (SDTF)"
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Rocha, Andre Medeiros, Marcos Esdras Leite, and Mário Marcos do Espírito-Santo. "MONITORING OF BRAZILIAN DECIDUOUS SEASONAL FOREST BY REMOTE SENSING." Mercator 19, no. 2020 (December 15, 2020): 1–20. http://dx.doi.org/10.4215/rm2020.e19022.
Full textAbstract:
Among the many characteristics that the Brazilian territory possesses, one precisely excel: the mentioned country hosts the second biggest forest resource of the planet, corresponding for approximately 10% of the total amount of global forest resources. In that scenario, the Seasonally Dry Tropical Forests (SDTF) perform the second less expressive forest type in Brazil, being situated mostly in non-forested biomes, such as Savannas and Scrublands. Thus, its conservation must rely on its correct identification, which becomes difficult because the SDTF areas are generally classified as other vegetation types. Therefore, the present study aimed to perform the land cover-land use monitoring for the years of 2007 and 2016 of the continuous area North of Minas Gerais - South Piauí, with the purpose of evaluating the current situation of Brazilian SDTFs and assessing the main drivers that affect its deforestation and natural regeneration. As a result, the study verified that the significant increase in crop areas and spatial mobility of parturelands contributed decisively for the changes presented by vegetation formations. HOWEVER, such drivers played differentiated roles in losses/gains. Especially, it was concluded that the changes in which deciduous forests have undergone were explained particularly by pasture. The other types of vegetation were also impacted by this class, but with a more incisive participation of the crops. Key-words: Mapping, Deciduous Forests, Remote Sensing, GIS.
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Power, M. J., B. S. Whitney, F. E. Mayle, D. M. Neves, E. J. de Boer, and K. S. Maclean. "Fire, climate and vegetation linkages in the Bolivian Chiquitano seasonally dry tropical forest." Philosophical Transactions of the Royal Society B: Biological Sciences 371, no. 1696 (June 5, 2016): 20150165. http://dx.doi.org/10.1098/rstb.2015.0165.
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South American seasonally dry tropical forests (SDTFs) are critically endangered, with only a small proportion of their original distribution remaining. This paper presents a 12 000 year reconstruction of climate change, fire and vegetation dynamics in the Bolivian Chiquitano SDTF, based upon pollen and charcoal analysis, to examine the resilience of this ecosystem to drought and fire. Our analysis demonstrates a complex relationship between climate, fire and floristic composition over multi-millennial time scales, and reveals that moisture variability is the dominant control upon community turnover in this ecosystem. Maximum drought during the Early Holocene, consistent with regional drought reconstructions, correlates with a period of significant fire activity between 8000 and 7000 cal yr BP which resulted in a decrease in SDTF diversity. As fire activity declined but severe regional droughts persisted through the Middle Holocene, SDTFs, including Anadenanthera and Astronium , became firmly established in the Bolivian lowlands. The trend of decreasing fire activity during the last two millennia promotes the idea among forest ecologists that SDTFs are threatened by fire. Our analysis shows that the Chiquitano seasonally dry biome has been more resilient to Holocene changes in climate and fire regime than previously assumed, but raises questions over whether this resilience will continue in the future under increased temperatures and drought coupled with a higher frequency anthropogenic fire regime. This article is part of the themed issue ‘The interaction of fire and mankind’.
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Reis, Geovany Heitor, Marcela de Castro Nunes Santos Terra, David Yue Phin Tng, Deborah Mattos Guimaraes Apgaua, Polyanne Aparecida Coelho, Rubens Manoel dos Santos, and Yule Roberta Ferreira Nunes. "Temporal vegetation changes in a seasonally dry tropical forest enclave in an ecotonal region between savanna and semiarid zones of Brazil." Australian Journal of Botany 65, no. 1 (2017): 85. http://dx.doi.org/10.1071/bt16188.
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Seasonally dry tropical forests (SDTFs) comprise a globally significant biome for biodiversity and conservation. Geographically, Brazilian SDTFs are primarily located within the country’s semiarid region (the Caatinga domain) in north-eastern Brazil. However, poorly studied and disjunct SDTF enclaves can occur within other regions, inside other Brazilian phytogeographical domains of vegetation such as savannas (i.e. the Cerrado domain) in central Brazil. These enclaves provide an opportunity to examine natural and non-anthropogenic edge effects on such vegetation. In 2007 and 2014, we studied a 120-ha SDTF enclave in the municipality of Januária in northern Minas Gerais, Brazil, to understand its (1) floristic composition and soil correlates, and (2) temporal variations in diversity, structure and dynamics. Three sets of 10 400-m2 plots were used to compare the vegetation at 0 m (edge), 100 m (middle) and 200 m (inner) into the forest. The edge plots were compositionally dissimilar from the interior plots because of soil fertility and soil textural gradients. Paradoxically also, the inner plots exhibited less stable vegetation-dynamic patterns than did both the middle and the edge plots, possibly owing to natural temporal fluctuations in vegetation dynamics. Overall, the SDTF enclave exhibited high diversity and structural complexity, likely because of its geographical setting within a matrix of savanna. These results highlight a conservation priority for further studies on such SDTF enclaves throughout their range.
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Saenz-Pedroza, Irving, Richard Feldman, Casandra Reyes-García, Jorge A. Meave, Luz Maria Calvo-Irabien, Filogonio May-Pat, and Juan M. Dupuy. "Seasonal and successional dynamics of size-dependent plant demographic rates in a tropical dry forest." PeerJ 8 (September 14, 2020): e9636. http://dx.doi.org/10.7717/peerj.9636.
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Tropical forests are globally important for biodiversity conservation and climate change mitigation but are being converted to other land uses. Conversion of seasonally dry tropical forests (SDTF) is particularly high while their protection is low. Secondary succession allows forests to recover their structure, diversity and composition after conversion and subsequent abandonment and is influenced by demographic rates of the constituent species. However, how these rates vary between seasons for different plant sizes at different successional stages in SDTF is not known. The effect of seasonal drought may be more severe early in succession, when temperature and radiation are high, while competition and density-dependent processes may be more important at later stages, when vegetation is tall and dense. Besides, the effects of seasonality and successional stage may vary with plant size. Large plants can better compete with small plants for limiting resources and may also have a greater capacity to withstand stress. We asked how size-dependent density, species density, recruitment and mortality varied between seasons and successional stages in a SDTF. We monitored a chronosequence in Yucatan, Mexico, over six years in three 0.1 ha plots in each of three successional stages: early (3–5 years-old), intermediate (18–20 years-old) and advanced (>50 years-old). Recruitment, mortality and species gain and loss rates were calculated from wet and dry season censuses separately for large (diameter > 5 cm) and small (1–5 cm in diameter) plants. We used linear mixed-effects models to assess the effects of successional stage, seasonality and their changes through time on demographic rates and on plant and species density. Seasonality affected demographic rates and density of large plants, which exhibited high wet-season recruitment and species gain rates at the early stage and high wet-season mortality at the intermediate stage, resulting in an increase in plant and species density early in succession followed by a subsequent stabilization. Small plant density decreased steadily after only 5 years of land abandonment, whereas species density increased with successional stage. A decline in species dominance may be responsible for these contrasting patterns. Seasonality, successional stage and their changes through time had a stronger influence on large plants, likely because of large among-plot variation of small plants. Notwithstanding the short duration of our study, our results suggest that climate-change driven decreases in rainy season precipitation may have an influence on successional dynamics in our study forest as strong as, or even stronger than, prolonged or severe droughts during the dry season.
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Apgaua, Deborah Mattos Guimarães, Polyanne Aparecida Coelho, Rubens Manoel dos Santos, Paola Ferreira Santos, and Ary Teixeira de Oliveira-Filho. "Tree community structure in a seasonally dry tropical forest remnant, Brazil." CERNE 20, no. 2 (June 2014): 173–82. http://dx.doi.org/10.1590/01047760.201420021540.
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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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Rodrigues, PMS, JO Silva, PV Eisenlohr, and CEGR Schaefer. "Climate change effects on the geographic distribution of specialist tree species of the Brazilian tropical dry forests." Brazilian Journal of Biology 75, no. 3 (August 25, 2015): 679–84. http://dx.doi.org/10.1590/1519-6984.20913.
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AbstractThe aim of this study was to evaluate the ecological niche models (ENMs) for three specialist trees (Anadenantheracolubrina, Aspidosperma pyrifolium and Myracrodruon urundeuva) in seasonally dry tropical forests (SDTFs) in Brazil, considering present and future pessimist scenarios (2080) of climate change. These three species exhibit typical deciduousness and are widely distributed by SDTF in South America, being important in studies of the historical and evolutionary processes experienced by this ecosystem. The modeling of the potential geographic distribution of species was done by the method of maximum entropy (Maxent).We verified a general expansion of suitable areas for occurrence of the three species in future (c.a., 18%), although there was reduction of areas with high environmental suitability in Caatinga region. Precipitation of wettest quarter and temperature seasonality were the predictor variables that most contributed to our models. Climatic changes can provide more severe and longer dry season with increasing temperature and tree mortality in tropics. On this scenario, areas currently occupied by rainforest and savannas could become more suitable for occurrence of the SDTF specialist trees, whereas regions occupied by Caatinga could not support the future level of unsustainable (e.g., aridity). Long-term multidisciplinary studies are necessary to make reliable predictions of the plant’s adaptation strategies and responses to climate changes in dry forest at community level. Based on the high deforestation rate, endemism and threat, public policies to minimize the effects of climate change on the biodiversity found within SDTFs must be undertaken rapidly.
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ANDRADE, EUNICE MAIA DE, GILBERTO QUEVEDO ROSA, ALDENIA MENDES MASCENA DE ALMEIDA, ANTONIO GIVANILSON RODRIGUES DA SILVA, and MARIA GINA TORRES SENA. "RAINFALL REGIME ON FINE ROOT GROWTH IN A SEASONALLY DRY TROPICAL FOREST." Revista Caatinga 33, no. 2 (April 2020): 458–69. http://dx.doi.org/10.1590/1983-21252020v33n218rc.
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ABSTRACT Seasonally dry tropical forests (SDTF) usually present dry seasons of eight or more months. Considering the concerns about the resilience of SDTF to climate changes, the objective of this study was to evaluate the effect of the rainfall regime on fine root growth in a SDTF. The experiment started at the end of the wet season (July 2015), when fine roots were evaluated and ingrowth cores were implemented. The temporal growth of fine roots in the 0-30 cm soil layer was monitored, considering the 0-10, 10-20, and 20-30 cm sublayers, through six samplings from November 2015 to July 2017. The characteristics evaluated were fine root biomass, fine root length, fine root specific length, and fine root mean diameter. The significances of the root growths over time and space were tested by the Kruskal-Wallis test (p<0.05). Fine roots (Ø<2 mm) were separated and dried in an oven (65 °C) until constant weight. The root length was determined using the Giaroots software. The fine root biomass in July 2015 was 7.7±5.0 Mg ha-1 and the length was 5.0±3.2 km m-2. Fine root growth in SDTF is strongly limited by dry periods, occurring decreases in biomass and length of fine roots in all layers evaluated. Fine root growth occurs predominantly in rainy seasons, with fast response of the root system to rainfall events, mainly in root length.
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Maia Andrade, Eunice, Wilner Valbrun, Aldênia Mendes Mascena de Almeida, Gilberto Rosa, and Antonio Givanilson Rodrigues da Silva. "Land-Use Effect on Soil Carbon and Nitrogen Stock in a Seasonally Dry Tropical Forest." Agronomy 10, no. 2 (January 22, 2020): 158. http://dx.doi.org/10.3390/agronomy10020158.
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Total organic carbon (TOC) and total nitrogen (TN) concentration in the soil are an indicator of soil degradation. To understand how land-use may impact these concentrations in seasonally dry tropical forests (SDTF), we analyzed the effect of four land-uses on TOC stocks (STK.TOC) and TN stocks (STK.TN) in a semi-arid region of Brazil. Soil samples were collected in 12 trenches (three sites × four land-uses—dense caatinga (DC), open caatinga (OC), pasture (PA) and agriculture (AG)), in the 0–10; 10–20 and 20–30 cm layers or as far as the bedrock. The data were compared by the Kruskal–Wallis test (p ≤ 0.05) and similarity investigated by cluster analysis. STK.TOC and STK.TN the surface layer (0–10 cm) showed no significant difference (p ≤ 0.05) between the DC; OC and PA land-uses. The similarity in STK.TOC and STK.TN values between DC, OC and PA, indicate that it is possible to explore SDTF to produce biomass and protein by adopting open caatinga and pasture land uses on Neosols with very low TOC stocks. The greatest reduction in STK.TOC and STK.TN in the agriculture land-use may lead to soil degradation and contribute to the addition of CO2 to the atmosphere.
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Mogni, V. Y., L. J. Oakley, and D. E. Prado. "THE DISTRIBUTION OF WOODY LEGUMES IN NEOTROPICAL DRY FORESTS: THE PLEISTOCENE ARC THEORY 20 YEARS ON." Edinburgh Journal of Botany 72, no. 1 (December 3, 2014): 35–60. http://dx.doi.org/10.1017/s0960428614000298.
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The Pleistocene Arc Theory (PAT) suggests that present-day disjunct fragments of dry forests in central tropical South America give evidence of a previously more continuous distribution during the Pleistocene that has been disrupted by dry-cold vs. humid-warm climatic cycles. This Arc extends from NE Brazil to NE Argentina and eastern Paraguay, through the Chiquitanía to NW Argentina and SW Bolivia and into the dry inter-Andean valleys in Peru and Ecuador, with intrusions into the Great Chaco. Seasonally Dry Tropical Forests (SDTFs) are floristically and physiognomically dominated by woody legumes, mostly deciduous in the dry season. In the last two decades field collection and research on legume taxa has greatly increased, with a significant number of taxonomic revisions and molecular phylogenetic studies, together with some paleoclimatic modelling studies. The evidence accumulated in the last 23 years has confirmed the integrity of the Chaco and Caatingas phytogeographical provinces, with an impressive and increasing level of botanical endemism discovered. The PAT pattern has also been supported, specifically through the mapping of five selected woody Leguminosae species (Anadenanthera colubrina, Enterolobium contortisiliquum, Pterogyne nitens, Amburana cearensis and Piptadenia viridiflora). The pre-existing nuclei of South American SDTF (Caatingas, Misiones and Piedmont) are now increased to four with the postulation of the Chiquitanía Nucleus in south-eastern Bolivia and bordering Paraguay. Some new endemisms are compiled from recent literature and mapped for the Misiones and Chiquitanía nuclei. The need for more botanical collections and further taxonomic, phylogenetic and demographic studies of South American legumes is emphasised.
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KÜLKAMP, JOSIMAR, JOÃO R. V. IGANCI, INÊS CORDEIRO, and JOSÉ FERNANDO A. BAUMGRATZ. "Ditaxis (Euphorbiaceae) from the Brazilian Caatinga, including a new species." Phytotaxa 455, no. 2 (August 10, 2020): 152–60. http://dx.doi.org/10.11646/phytotaxa.455.2.6.
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Ditaxis is a Neotropical genus with approximately 50 species, most of them in seasonally dry tropical forests of Brazil, Central America and the Antilles. The Brazilian Caatinga, the largest area of SDTF in South America, harbors three endemic species of Ditaxis, including the new Ditaxis grazielae, hereby described and illustrated. The new species is known from a few localities in the state of Bahia. We provide an identification key for the species occurring in the Caatinga, as well as comments on habitat, distribution and phenology. We also present amended descriptions and typifications for Ditaxis desertorum and D. malpighiacea, and propose D. gardneri as synonym of D. desertorum.
Dissertations / Theses on the topic "Seasonal dry tropical forests (SDTF)"
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Peña, José Luis Marcelo. "Diversidade florística, dendrologia e dendroecologia em florestas estacionais decíduas do Centro e Norte do Peru." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/11/11150/tde-04082017-143653/.
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Neste estudo analisamos a diversidade e endemismos da flora lenhosa das florestas estacionais decíduas (FEDs) do norte e centro do Perú. Caracterizamos a diversidade das plantas lenhosas ao longo dos vales, para definir os valores de conservação da área a nível nacional. Os resultados indicam que as FEDs do vale do Marañón apresentam valores significativamente altos em endemias em relação às outras FEDs do Perú e FEDs vizinhas e o padrão de endemismos e estrutura populacional das espécies variam no gradiente geográfico e altitudinal. Em constraste, as FEDs do vale do rio Tambo, centro do Perú, são moderadamente ricas em espécies do que a média das FEDs neotropicais e apresentam escassos endemismos. Esta região necessita de mais esforços de pesquisas para conhecer mais profundamente os elementos da biodiversidade. Neste estudo, também realizamos a caracterização dendro-anatômica do lenho das árvores de 87 espécies, sendo o primeiro registro da anatomia da madeira das árvores dos dois vales. Das análises do lenho das 183 espécies registradas nas florestas do norte e centro do Perú, só 157 apresentam anéis de crescimento e precisam ser analisadas em detalhe com outras pesquisas de desenvolvimento cambial e técnicas tradicionais de análises dendrocronológicas. A derivação desta informação pode alcançar alto impacto em estudos de variabilidade climática e aplicações na conservação. Assim mesmo, a análise preliminar dendrocronológica das taxas de crescimento do tronco revelam que as árvores de Cedrela kuelapensis apresentam as taxas de crescimento mais altas e ressaltam como um excelente recurso para programas de reflorestamento nos vales interandinos, além, das populações endêmicas de Cordia iguaguana e Esenbeckia cornuta são principalmente de exemplares jovens. Esperamos que as informações dos cinco capítulos constituam-se uma eficiente e importante ferramenta para melhorar a gestão dos recursos florestais dos vales estudados.In this study we analyzed the diversity and endemism of the woody flora of Seazonally dry tropical forests (SDTF) in northern and central Peru. We characterized the diversity of woody plants along the valleys to define the conservation values of the area at the national and international levels. The results indicate that the SDTF s of the Marañón Valley show surprisingly high values in endemics in relation to other SDTF s in Peru and neighboring SDTFs, and the pattern of endemism and population structure of the species varies in geographic and altitudinal grades. In contrast, the SDTFs of the Tambo River Valley, central Peru, are moderately rich in species that average the neotropical SDTFs and have scarce endemism. This region needs more efforts to get to know the elements of biodiversity more deeply. In this study, we also performed the dendroanatomic characterization of 87 species and is the first report of the anatomy of the wood for the two valleys. From the analysis of the wood of the 183 species recorded in the forests of northern and central Peru, only 157 have growth rings and need to be analyzed in detail with other studies of exchange rate development and traditional techniques of dendrochronological analysis. The derivation of this information can reach high impact in studies of climatic variability and conservation applications. Likewise, the preliminary dendrochronological analysis of growth rates reveals that Cedrela kuelapensis showed the highest growth rates and stands out as an excellent resource for reforestation programs in the inter-Andean valleys, in addition, Cordia iguaguana and Esenbeckia cornuta endemic populations are mainly from young individuals. We hope that the information in the five chapters constitutes in efficient and important tool to improve the management of forest resources in the valleys studied.
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Jones, Huw T. "Characterisation of neotropical savanna and seasonally dry forest ecosystems by their modern pollen rain." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/4257.
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At present there is uncertainty over the response of neotropical ecosystems to the climatic changes of the Quaternary. The majority of vegetation reconstructions from the region are derived from fossil pollen records extracted from lake sediments. However, the interpretation of these records is restricted by limited knowledge of the contemporary relationships between the vegetation and pollen rain of neotropical ecosystems, especially for more open vegetation such as savanna and dry forest. This research aims to improve the interpretation of these records by investigating the relationship between the vegetation and modern pollen rain of different savanna and seasonally dry tropical forest (SDTF) ecosystems in Bolivia using artificial pollen traps and surface lake sediments to analyse the modern pollen rain. Vegetation data is used to identify taxa that are floristically important within the different ecosystems and to allow modern pollen/vegetation ratios to be calculated. The modern pollen rain from the upland savanna is dominated by Moraceae/Urticaceae (35.1%), Poaceae (29.6%), Alchornea (6.1%) and Cecropia (4.1%), whilst the seasonally-inundated savanna sites are dominated by Moraceae/Urticaceae (30.7%), Poaceae (19.5%), Cyperaceae (14.0%) and Cecropia (7.9%). These two different savanna ecosystems are only slightly differentiated by their modern pollen rain. The main taxa in the modern pollen rain of the upland SDTF are Moraceae/Urticaceae (25.8%), Cecropia (10.5%), Acalypha (7.6%) and Combretaceae/Melastomataceae (6.7%). Seasonally-inundated SDTF is dominated by Cecropia pollen to the extent that it was removed from the pollen sum and the main non-Cecropia pollen types are Moraceae/Urticaceae (39.0%), unknown type df 61 (6.4%), Asteraceae (6.3%), Celtis (6.0%) and Physocalymma scaberrimum (4.9%). These two SDTF ecosystems are well differentiated by their modern pollen rain, implying that they may be defined in fossil pollen records. The modern pollen rain obtained from the surface lake samples is generally complementary to that obtained from the artificial pollen traps for a given ecosystem. All sites have a high Moraceae/Urticaceae pollen signal due to effective dispersal of this pollen type from areas of evergreen forest in close proximity to the study sites. The savanna sites show lower Poaceae percentages than have been previously reported in the literature by some authors and this raises the possibility than the extent of this ecosystem in the past may have been underestimated. Modern pollen/vegetation ratios show that many key vegetation types are absent/under-represented within the modern pollen rain.
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González-Rivas, Benigno. "Tree species diversity and regeneration of tropical dry forests in Nicaragua /." Umeå : Dept. of Silviculture, Swedish University of Agricultural Sciences, 2005. http://epsilon.slu.se/200558.pdf.
Full textBook chapters on the topic "Seasonal dry tropical forests (SDTF)"
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Stoner, Kathryn E., and Robert M. Timm. "Seasonally Dry Tropical Forest Mammals: Adaptations and Seasonal Patterns." In Seasonally Dry Tropical Forests, 85–106. Washington, DC: Island Press/Center for Resource Economics, 2011. http://dx.doi.org/10.5822/978-1-61091-021-7_6.
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"Fruit-Eating Bats and Birds of Three Seasonal Tropical Dry Forests in the Americas." In Tropical Dry Forests in the Americas, 191–238. CRC Press, 2013. http://dx.doi.org/10.1201/b15417-14.
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Bawa, Kamaljit S. "Impact of Global Changes on the Reproductive Biology of Trees in Tropical Dry Forests." In Biodiversity Conservation in Costa RicaLearning the Lessons in a Seasonal Dry Forest, 38–47. University of California Press, 2004. http://dx.doi.org/10.1525/california/9780520223097.003.0004.
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Lawrence, Deborah, and David R. Foster. "Recovery of Nutrient Cycling and Ecosystem Properties Following Swidden Cultivation: Regional and Stand-Level Constraints." In Integrated Land-Change Science and Tropical Deforestation in the Southern Yucatan. Oxford University Press, 2004. http://dx.doi.org/10.1093/oso/9780199245307.003.0014.
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The total area of agricultural systems in tropical Mexico increased by 64 per cent from 1977 to 1992—a mean annual deforestation rate of 1.9 per cent (Cairns et al. 2000). In all likelihood, this rate has continued for the past ten years. Dry tropical forest covers 8 per cent of Mexico and is subject to conversion for agricultural use (Trejo and Dirzo 2000). Because the southern Yucatán contains the largest contiguous block of dry tropical forest in Mexico and Central America, understanding the biogeochemical consequences of land-use change there is important for effective national and international conservation and development efforts. Over the past four decades the southern Yucatán peninsular region has undergone an increasing amount and intensity of land use (Chs. 3, 9, 10). These land uses, many focused on swidden practices, alter the structure and function of forested lands and often generate new feedbacks in terms of subsequent human use. Consequently, a major goal in assessing regional environmental change is to understand how biogeochemical processes respond to land-use change, emphasizing the potential of a human-dominated landscape to sustain continued human use. One of the greatest challenges in these studies is to untangle the effects of environmentally induced variation from, for example, climate, geology, or natural disturbance, from that induced by human activity. In the SYPR project the approach to this challenge has been to investigate variation in ecosystem processes in several study sites across the dominant environmental gradients while focusing on the influence of local, human-controlled factors within a given area. In the southern Yucatán peninsular region annual precipitation increases by more than 50 per cent over a distance of 120km. Median annual precipitation varies from about 900mm in the northern part of the study area to about 1,400mm in the southern part. This dramatic gradient overlies a seasonal pattern shared by all sites regardless of their total annual precipitation. Rainfall is highly variable, with a pronounced dry period lasting from four to six months, depending on latitude. The range in precipitation observed in the study area encompasses approximately 50 per cent of the variation in precipitation of dry tropical forests worldwide (Murphy and Lugo 1986).