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TROPICAL DRY DECIDUOUS FORESTS

TROPICAL DRY DECIDUOUS FORESTS Tropical deciduous forests cover extensive areas in climates with highly seasonal distribution of rainfall (Murphy and Lugo, 1986), characterized by the dominant proportion of deciduous woody components

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TROPICAL DRY DECIDUOUS FORESTS

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  1. TROPICAL DRY DECIDUOUS FORESTS Tropical deciduous forests cover extensive areas in climates with highly seasonal distribution of rainfall (Murphy and Lugo, 1986), characterized by the dominant proportion of deciduous woody components Proportion of deciduous species varies from 40 to100 % depending on the location within the rainfall gradient. Deciduousness is frequently facultative, duration of the leafless periods depending on soil water availability. The structural components change more or less monotonously as annual rainfall decreases - the proportion of deciduous trees and shrubs increases - epiphytes and hemiparasites frequency decreases - lianas (woody climbing plants) reach important proportion - proportion of succulent plants, including CAM performing cacti and stem succulents, increases

  2. Area and net primary production of organic matter (expressed as g C per unit area) of tropical forests and savannas estimated by direct measurements and using a process-based ecosystem simulation model Vegetation Units Area % NPP Total NPP % (x 106 km2) g C m-2 yr- 1 1015 g C yr-1 Whittaker and Likens (1973) World Total 149.0 58.8 Tropical Rain forest 17.0 11.4 1100 18.7 31.8 Tropical seasonal forest 7.5 5.0 800 6.0 10.2 Savanna 15.0 10.1 450 6.8 11.6 Total tropical 39.5 26.5 31.5 53.6 Melillo et al. (1993) World Total 127.3 53.2 Tropical evergreen forest 17.4 13.7 1098 19.1 35.9 Tropical deciduous forest 4.6 3.6 871 4.0 7.5 Tropical Savanna 13.7 10.8 393 5.4 10.2 Xeromorphic forests 6.8 5.3 461 3.1 5.8 Total tropical 42.5 33.0 31.6 59.4

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  4. Characteristic ecosystem processes regulated by seasonality of water availability and variability of growing period (begin to end of the rainy season) Primary Producers Decomposers Consumers Rainy Season Begin Leaf flushing and fine Rapid decomposition Activity of detritivores root production. of above- and below- herbivores, and seed- Carbohydrate and organic matter fruit eaters water transport Net losses of CO2 and to the shoots N oxides Middle Full canopy develop- Accumulation of Maximum herbivore ment, carbohydrate microbial biomass activity litter production End Growth stop Slow decrease of Reproduction and Leaf and fine root microbial activity begin of resting shedding phase. Faunal migrations Dry Season Carbohydrate Soil biological Pollinators expenditures for activity strongly and nectar consumers flowering and reduced or nil reproduction maintenance respiration of roots and stems

  5. Drought tolerance and ecological costs associated to contrasting phenological behaviors: deciduous and evergreen trees Deciduous trees Total or partial leaf abscision at moderate water potential values Associated costs Seasonal regeneration of leaf mass Productive capacity of limited duration Respiration losses of non photosynythetic organs remaining at high water potential during the dry season High requirement of nitrogen Evergreen Trees Protoplasmatic tolerance to low water potential maintaining metabolic activity. Many species are osmoregulators. Partial evasion to recurrent drought through development of deep root systems Associated costs Lower photosynthetic rates Requirement of thermotolerant tissues Protection against light damage of the photosynthetic system Development of deept roots

  6. Examples of life and growth-forms in tropical dry forests (includes tropical deciduous forest, thorn forest and thorn scrub). With data from Aristeguieta 1968, Wikander 1984, Bullock 1985, Ponce & Trujillo 1985 Trees and shrubs (woody plants) EvergreenCapparis, Casearia, Castela, Coccoloba, Guaiacum, Haematoxylon, Jacquinia Deciduous (obligate Acacia, Albizzia, Bumelia, Pisonia, Pithecelobium, or facultative) Prosopis, Swietenia, Tabebuia Green-stemmedCercidium Succulent deciduousBursera, Cochlospermum, Erythrina, Jatropha, Manihot Pereskia, Spondias CAM-type (cacti) Lemaireocereus, Opuntia, Pilosocereus, Ritterocereus Herbs & Rosettes Dicots C3 Bastardia, Croton, Melochia, Weddelia C4 Alternanthera, Atriplex, Euphorbia, Portulaca, Trianthema Grasses C4 Anthephora, Aristida, Cenchrus, Setaria, Sporobolus Bromeliads CAM Aechmea, Bromelia Lianes and creeping plants C3 Arrabidaea, Mansoa, Macfadyena, Cydista, Cissus (one species CAM inducible) CAM Acanthocereus, Selenicereus Epiphytes C3 Peperomia, Philodendron CAM Brassavola, Schomburgkia, Tillandsia Hemi-parasitesIxocactus, Phoradendron, Phtyrusa

  7. Anatomical characteristics associated with wind dispersion of reproductive units in trees and shrubs and climbers in a tropical dry forest (from Wikander 1980) Type of dispersal unit Trees and shrubs Lianes Feathery seeds Ceiba pentandra Marsdenia condensifloraCochlospermum vitifolium Matelea maritima Matelea planiflora Matelea urceolata Metastelma sp Winged seedsTabebuia ochracea Cydista equinoctialis Macfadyena unguis-cati Mansoa verrucifera Phryganocidia corymbosa Pithecoctenium crucigerum Prestonia exerta Very small seedsPogonopus speciosus Syncarpic fruitsCentrolobium paraense Heteropteris purpurea with one wing Fissicalix fendlerii Machaerium moritzianum Lonchocarpus dipteroneurus Nyssolia fruticosa Machaerium latialatum Securidaca diversifolia Machaerium robiniaefolium Securidaca sp. Myriospermum frustescens Schizocarpic,Beureria cumanensis Serjania sp winged fruitsBulnesia arborea Multi-winged fruitsPiscidia carthaginensis Combretum fruticosus Terminalia sp. Paullinia sp.

  8. Osmotic pressure of leaf sap and xylem tension measured in the field during the middle of the dry and rainy seasons in a dry tropical forest of the Paraguaná Penísula in Falcón State Venezuela Species Osmotic Pressure (MPa) Max. Xylem Tension (MPa) Dry Rain Dry Rain Evergreens Capparis odoratissima 4.31 2.96 5.49 3.57 Capparis linearis 3.66 2.95 5.99 4.50 Jacquinia aristata 4.09 1.51 4.96 2.76 Deciduous Casearia tremula 4.55 1.81 6.55 0.78 Pithecellobium dulcis 4.26 1.82 5.76 3.19 Prosopis juliflora 3.13 2.10 4.17 3.11 Succulent woody plants (deciduous) Jatropha gossypifolia 1.45 1.19 1.38 0.17 Pereskia guamacho 1.27 1.09 1.33 0.97 Malacophyllous shrub Croton cf. flavens 4.82 1.28 7.41 0.40

  9. Leaf size of the species studied in the tropical dry forest of Guánica. Leaf sizes classified according to Taylor (1975): Small, Medium and Big Species Average range Classification Morphological type (cm2) Exostemma caribaeum (Jacq.) R. & S. 6.5 - 13.8 Microphyll M-B Malacophyll* Bucida buceras L. 7.8 - 17.4 Microphyll M-B Sclerophyll Bursera simaruba (L.) Sarg. 13.9 - 23.7 Microphyll B - Mesophyll S Mesophyll, succulent stem Bourreria succulenta Jacq. 18.4 - 25.4 Microphyll B - Mesophyll S Sclerophyll Pisonia albida (Heimerl.) Britton 9.5 - 29.1 Microphyll B - Mesophyl S Mesophyll, succulent stem Thouinia portoricensis Radlk. 23.0 - 33.8 Mesophyll S Sclerophyll *Malacophylls: plants producing hygromorph, hairy leaves, resistant to low water potentials. They do not reduce tranpsiration at during the dry season, and osmotic pressure increase rapidly. By prolongued drought older leaves are shed, until only the buds remain active. Sclerophylls: plants producing hard, though, fiber rich leaves, capable of efficient transpiration control during drought Mesophylls: plants producing drought intolerant leaves, stomatal closure reduces transpiration at the onset of drought, and in so doing curtail photosynthesis too. Leaves are shed with high water content, and are yellow in color.

  10. Osmolality of the leaf vacuolar sap of woody species from a tropical dry forest in Guánica, Puerto Rico (Medina and Cuevas 1990) • Species mmoles kg-1 Rainy season Dry season • Bourreria succulenta 344 1343 • Bucida buceras 475 967 • Thouinia portoricensis 510 1232 • Pisonia albida 578 634 • Bursera simaruba 640 471 • Exostemma caribaeum 654 1491

  11. Photosynthesis (A), conductance (g), and intrinsic water use efficiency (IWUE) of woody species in a Tropical Dry forest, Guánica, Puerto Rico, during the rainy and dry seasons (Medina and Cuevas 1990) A max g max IWUE µmol m-2 s-1 mmol m-2 s-1 µmol/mmol x 10-2 Rain Dry Rain Dry Rain Dry Exostemma caribaeum 9.5 6.9 217 180 4.4 3.8 Bucida buceras 8.4 5.7 233 144 3.6 4.0 Bursera simaruba 8.6 6.2 190 142 4.5 4.4 Bourreria succulenta 9.0 6.9 224 177 4.0 3.9 Pisonia albida 7.5 5.6 205 142 3.7 3.9 Thouinia portoricensis 11.6 7.3 339 169 3.4 4.3 Species

  12. Osmotic behavior during leaf development among deciduous forests tree species (from Olivares and Medina 1992)

  13. Leaf composition of Evergreen Xerophytic and deciduos woody plants (Data from Pfundner 1993) Organic Quaternary SPECIES Water K Ca ∑ Cations Cl SO4 Acids NH4 comp. ∑cyclitols g/kg frwt. ------------------------------------- mmol kg-1 fresh weight-------------------------------------- Capparis linearis 498 177 141 540 114 283 125 82 6 Capparis odoratissima 444 142 166 418 68 533 63 123 61 Morisonia americana 396 222 94 362 18 329 53 428 8 Belencita nemorosa 416 363 246 801 1 1426 75 50 9 Jacquinia aristata 466 152 121 504 107 226 83 0 62 Jatropha gossypifolia 825 117 1 224 69 13 109 0 33 Pereskia guamacho 915 19 2 178 133 1 74 0 22 Prosopis juliflora 510 146 71 314 162 58 92 4 143

  14. Open fields of research related to the functioning of dry deciduous forests ecosystems 1. Factors regulating leaf shedding and leaf flushing Drought, photoperiodism, temperature 2. Synchronization of flowering during the rainy season - the role of pollinators (Janzen) - water relations (Borchert) 3. The contrast of evergreen and (facultative) deciduous trees - selecting factors: nutrients tolerance to low water potential duration of the dry season and carbohydrate balance control of respiration 4. Water and nutrient transport to aboveground growing meristems at the beginning of the rainy season 5. The physiological significance of high levels of soluble Ca in some families (Capparaceae) and the production of oxalate in others (Theophrastaceae)

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