Tropical Environments and Climate PDF

Introduction 1. Tropical climate 2. Biogeographical regions and geological changes 3. Tropical biomes; temperature and precipitation 1 1. Tropical climate Tropical climate characterised by: Where are the tropics? tropics of Cancer (23º 28’ N) &...

Introduction 1. Tropical climate 2. Biogeographical regions and geological changes 3. Tropical biomes; temperature and precipitation 1 1. Tropical climate Tropical climate characterised by: Where are the tropics? tropics of Cancer (23º 28’ N) & tropics of Capricorn (23º 28’ S) mean annual temperature > 18 ºC no seasonal fluctuations in temperature 2 Why are the tropics hotter than temperate areas? Angle of sun rays Concentration of sun rays Shorter distance through atmosphere 3  The intertropical convergence zone Are the tropics currently expanding? Yes, but why? Probably due to (1) an increase of O3 and black soot in the northern troposphere, which causes shifts of the Hadley cells, and (2) O3 loss above the Antartic stratosphere (CFC’s). 4 From: Heffernan 2016 January July 5 Normal Pacific pattern: equatorial winds gather warm water pool toward west. Cold water upwells along South American coast. El Niño due to chances in rainfall and seawater temperature El Niño Conditions: warm water pool approaches South American coast. Absence of cold upwelling increases warming. The La Niña condition is a more distinct form of the normal condition. 6 FYI: https://www.youtube.com/watch?v=tyPq86yM_Ic El Niño Southern Oscillation Index 7 A timeline of all the El Niño episodes between 1900 and 2016 (Wikimedia Commons) 2. Biogeographical regions 6 tropical biogeographical regions 8 9 10  Breakup of Gondwana MidOligocene Early Late LateMiocene Eocene (35 (20Ma) (50 Cretaceous KT (65 Cretaceous Pleistocene Jurassic PresentMa) Ma)Ma) Ma) (105Ma) (120Ma) (90 (150Ma) (50Ka) 11  Climate and vegetation in Australia during the Cretaceous and Tertiary Gondwana plants Araucariaceae Podocarpaceae Nothofagaceae Proteaceae tree ferns 12 Climate and vegetation in Australia during the Tertiary Dry forests: Eucalyptus (Myrtaceae), Acacia (Fabaceae), grasslands (C4 photosynthesis) 13  Climate and vegetation in Australia during the Tertiary: intrusion of Indo-Malay flora (rainforest) 14 15 3. Biomes: subdivisions of biogeograhical regions with characteristic forms of plants/animals Whittaker’s biome classification 16  Biome - Definition A biological subdivision that reflects the ecological character of the vegetation as well as the form and structure of natural communities. They are the largest geographical biotic communities that are convenient to recognize. They broadly correspond with climatic regions, and are equivalent to the concept of major plant formations in ecology. Which factors determine a biome? 1. Latitude 2. Altitude 3. Moisture levels; aridity; potential evapotranspiration 4. Temperature (average, maximum, minimum) 5. Prevailing wind direction and strength (on a global level) 6. Day length Where do biomes fit in the ecological hierarchy: – Biosphere: the part of the earth’s environment in which living organisms are found – Biomes: biogeographical area with characteristic forms of plants and animals – Ecosystem: a discrete unit of living and non-living organisms, interacting to form a stable system – Community: any grouping of populations of different organisms found living together in a particular environment; the biotic component of an ecosystem – Population: A group of organisms all of the same species, which occupies a particular area – Specimen: (Natural selection acts here) 17  Spatial and temporal hierarchy of processes that establish and maintain species diversity (modified from Haila, 1990 and Tracy and Brussard, 1994). 18 From: Hill & Hill (2001; DOI: 10.1177/030913330102500302) For a high resolution world map of forest cover, forest loss & gain: https://glad.earthengine.app/view/global-forest-change#bl=off;old=off;dl=1;lon=20 ;lat=10;zoom=3 19 ; 20 Which is a better prediction of plants traits? Temperature or rainfall? Note: SPEI values would be more useful than21 Moles et al. (2014; Journal of Vegatation Science); Mean Annual Precipitation: https://spei.csic.es/  What are the main differences in the water cycle between a healthy rainforest and a deforested area? 22 Drawing by A. Öfele (Institute of Systematic Botany and Ecology) Along the Eastern slopes of the Andes mountains in southern Peru, the Andean royal palm, Dictyocaryum lamarckianum (Mart.) H. Wendl., is narrowly distributed between approximately 1500 to 1800 m a.s.l. It is important to explore and understand the biotic and abiotic factors that limit the current and future geographic ranges of several Andean tree species including D. lamarckianum. From: Feeley K.J. (2015 Am J Bot). 23 Shelford’s law of tolerance (1913) states that for every organism there is an optimum in regard to environmental factors. When environmental factors are not favourable the number of individuals will decrease. (From: Kroone 2000) Climate variability hypothesis (Janzen 1967): Tropical species are locked into narrow temperature ranges, preventing them to spread over mountains into adjacent valleys, which limits the flow of genes and increases allopatric speciation and thus biodiversity in the tropics. Global warming in the tropics may 24 quickly put organisms outside their Thermal trouble in the tropics: why are tropical species more vulnerable to climate change than temperate ones? Or why are mountain passes „higher“ in the tropics? (from Perez et al-2016) 25 What is the adaptability or plasticity of climatic tolerances of species? Assume an average rate of phenotypic plasticity of 0.11 Haldanes (defined as the change of 1 phenotypic standard deviation) per generation Based on latitudinal transects (1 latitude = 0.45°C), and altitudinal transects (0.5°C per 100 m), we estimate that 1°C corresponds to ca. 0.3 Haldanes How many generations are needed for the following 2 scenarios? A. 2°C warming over 100 years = 0.6 Haldanes = 5.4 generations in 100 year = 18.3 years of life cycle B. 5°C warming over 100 years = 1.5 Haldanes = 13.6 generations in 100 years = 7.3 years of life cycle So species with short to medium generation times might be able to evolve rapidly enough to escape climate change, but species with longer generation times may only survive by migrating. Open questions based on the assumptions made: 1. Is the current distribution of a species really reflecting the full range of its tolerances? 2. Also, do all conspecific populations have the same tolerances or is there local adaptation? 26  Atmospheric carbon dioxide records indicate that the land surface has acted as a strong global carbon sink over recent decades, with a substantial fraction of this sink probably located in the tropics particularly in the Amazon. Nevertheless, it is unclear how the terrestrial carbon sink will evolve as climate and atmospheric composition continue to change. Here we analyse the historical evolution of the biomass dynamics of the Amazon rainforest over three decades using a distributed network of 321 plots. While this analysis confirms that Amazon forests have acted as a long-term net biomass sink, we find a long-term decreasing trend of carbon accumulation. Rates of net increase in above-ground biomass declined by one-third during the past decade compared to the 1990s. This is a consequence of growth rate increases levelling off recently, while biomass mortality persistently increased throughout, leading to a shortening of carbon residence times. Potential drivers for the mortality increase include greater climate variability, and feedbacks of faster growth on mortality, resulting in shortened tree longevity. The observed decline of the Amazon sink diverges markedly from the recent increase in terrestrial carbon uptake at the global scale, and is contrary to expectations based on models. From: Brienen et al. (2015) Trends in net above-ground biomass change, productivity and mortality across all sites. a–c, Black lines show the overall mean change up to 2011 for 321 plots (or 274 units) weighted by plot size, and its bootstrapped confidence interval (shaded area). The red lines indicate the best model fit for the long-term trends since 1983 using general additive mixed models (GAMM), accounting explicitly for differences in dynamics between plots (red lines denote overall mean, broken lines denote s.e.m.). Alternative analyses of subsets of plots that were all continuously monitored throughout shorter time intervals confirm that the observed trends are not driven by temporal changes in individual sample plot contributions. Estimated long-term (linear) mean slopes and significance levels are indicated, and are robust with regard to the statistical approach applied. Shading corresponds to the number of plots that are included in the calculation of the mean, varying from 25 plots in 1983 (light grey) to a maximum of 204 plots in 2003 (dark grey). The uncertainty and variation is greater in the early part of the record owing to relatively low sample size. 27 Tropical forests are a net carbon source based on aboveground measurements of gain and loss Fig. 1. Geography of carbon density change. (A to C) The figure depicts the spatial distribution of areas exhibiting gains, losses, and no change (stable). Values reported are the change from 2003 to 2014 within each 463 m by 463 m grid cell. Changes with a P value larger than 0.05 are identified as stable. Data in (A) to (C) have been aggregated to 5 km for display. Insets (a) to (c) are shown at full resolution and correspond to the black rectangles in (A) to (C), respectively. From: Baccini et al. (2017; Science 358, 230–234) 28  What is threatening (tropical) species? Disturbance due to land use change: 65% Agricultural use = 31% Biological resource use (logging, wood harvesting, hunting, fishing) = 21% Urbanisation = 13% Natural system modifications = 9% Invasiveness and new pests/diseases = 8% Climate change and severe weather < 4% 29