Transcript DryFor
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 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 (x 106 km2) Whittaker and Likens (1973) World Total Tropical Rain forest 17.0 Tropical seasonal forest Savanna Total tropical 149.0 11.4 7.5 15.0 39.5 Melillo et al. (1993) World Total Tropical evergreen forest Tropical deciduous forest Tropical Savanna Xeromorphic forests 6.8 Total tropical 127.3 17.4 4.6 13.7 5.3 42.5 % NPP Total NPP g C m-2 yr- 1 1015 g C yr-1 % 58.8 1100 5.0 10.1 26.5 13.7 3.6 10.8 461 33.0 18.7 800 450 1098 871 393 3.1 31.8 6.0 6.8 31.5 19.1 4.0 5.4 5.8 31.6 10.2 11.6 53.6 53.2 35.9 7.5 10.2 59.4 ? 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 Begin Leaf flushing and fine root production. Carbohydrate and water transport to the shoots Rapid decomposition of above- and beloworganic matter Net losses of CO2 and N oxides Activity of detritivores herbivores, and seedfruit eaters Middle Full canopy development, carbohydrate litter production Accumulation of microbial biomass Maximum herbivore activity End Growth stop Leaf and fine root shedding Slow decrease of microbial activity Reproduction and begin of resting phase. Faunal migrations Rainy Season Dry Season Carbohydrate Soil biological expenditures for activity strongly flowering and reduced or nil maintenance respiration of roots and stems Pollinators and nectar consumers reproduction 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 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) Evergreen Capparis, Casearia, Castela, Coccoloba, Guaiacum, Haematoxylon, Jacquinia Acacia, Albizzia, Bumelia, Pisonia, Pithecelobium, Prosopis, Swietenia, Tabebuia Cercidium Bursera, Cochlospermum, Erythrina, Jatropha, Manihot Pereskia, Spondias Lemaireocereus, Opuntia, Pilosocereus, Ritterocereus Deciduous (obligate or facultative) Green-stemmed Succulent deciduous CAM-type (cacti) Herbs & Rosettes Dicots Grasses Bromeliads C3 C4 C4 CAM Bastardia, Croton, Melochia, Weddelia Alternanthera, Atriplex, Euphorbia, Portulaca, Trianthema Anthephora, Aristida, Cenchrus, Setaria, Sporobolus Aechmea, Bromelia Lianes and creeping plants C3 CAM Arrabidaea, Mansoa, Macfadyena, Cydista, Cissus (one species CAM inducible) Acanthocereus, Selenicereus C3 CAM Peperomia, Philodendron Brassavola, Schomburgkia, Tillandsia Epiphytes Hemi-parasites Ixocactus, Phoradendron, Phtyrusa 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 condensiflora Cochlospermum vitifolium Matelea maritima Matelea planiflora Matelea urceolata Metastelma sp Winged seeds Tabebuia ochracea Cydista equinoctialis Macfadyena unguis-cati Mansoa verrucifera Phryganocidia corymbosa Pithecoctenium crucigerum Prestonia exerta Very small seeds Pogonopus speciosus Syncarpic fruits with one wing Centrolobium paraense Heteropteris purpurea Fissicalix fendlerii Machaerium moritzianum Lonchocarpus dipteroneurus Nyssolia fruticosa Machaerium latialatum Securidaca diversifolia Machaerium robiniaefoliumSecuridaca sp. Myriospermum frustescens Schizocarpic, winged fruits Beureria cumanensis Bulnesia arborea Serjania sp Multi-winged fruits Piscidia carthaginensis Terminalia sp. Combretum fruticosus Paullinia sp. 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) Dry Rain Evergreens Capparis odoratissima Capparis linearis Jacquinia aristata 4.09 4.31 3.66 1.51 Deciduous Casearia tremula 4.55 Pithecellobium dulcis Prosopis juliflora 1.81 4.26 3.13 2.96 2.95 Max. Xylem Tension (MPa) Dry Rain 5.49 3.57 5.99 4.50 4.96 2.76 6.55 0.78 1.82 2.10 5.76 3.19 4.17 3.11 Succulent woody plants (deciduous) Jatropha gossypifolia 1.45 1.19 Pereskia guamacho 1.27 1.09 1.38 0.17 1.33 0.97 Malacophyllous shrub Croton cf. flavens 7.41 0.40 4.82 1.28 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 (cm2) Morphological type Exostemma caribaeum (Jacq.) R. & S. 6.5 - 13.8 Microphyll M-B Malacophyll* Bucida buceras L. Microphyll M-B Sclerophyll Bursera simaruba (L.) Sarg. 7.8 - 17.4 13.9 - 23.7 Bourreria succulenta Jacq. 18.4 - 25.4 Pisonia albida (Heimerl.) Britton Thouinia portoricensis Radlk. Microphyll B - Mesophyll S Microphyll B - Mesophyll S 9.5 - 29.1 23.0 - 33.8 Sclerophyll Microphyll B - Mesophyl S Mesophyll S Mesophyll, succulent stem Mesophyll, succulent stem 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. 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 caribaeum654 1491 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) Species A max µmol m-2 s-1 Rain Dry g max mmol m-2 s-1 Rain Dry IWUE µmol/mmol x 10-2 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 11.6 7.3 339 169 3.4 4.3 Thouinia portoricensis Osmotic behavior during leaf development among deciduous forests tree species (from Olivares and Medina 1992) Leaf composition of Evergreen Xerophytic and deciduos woody plants (Data from Pfundner 1993) Organic Quaternary SPECIES Capparis linearis Capparis odoratissima Morisonia americana Belencita nemorosa Jacquinia aristata Water g/kg frwt. 498 177 444 396 416 825 Pereskia guamacho 915 510 141 114 283 125 82 6 166 418 68 533 63 123 61 222 94 362 18 329 53 428 8 246 152 117 19 146 540 142 363 466 Jatropha gossypifolia Prosopis juliflora K Ca ∑ Cations Cl SO4 Acids NH4 comp. ∑cyclitols ------------------------------------- mmol kg-1 fresh weight-------------------------------------- 801 121 1 2 71 504 224 178 314 1 107 69 133 162 1426 75 226 13 1 58 50 83 109 74 92 9 0 0 0 4 62 33 22 143 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)