Plant Functional Traits and the Distribution of West African Rain Forest Trees along the Rainfall Gradient

Plant morphological and physiological traits affect the way plants tolerate environmental stresses and therefore play an important role in shaping species distribution patterns in relation to environmental gradients. Despite our growing knowledge on the role of functional traits in structuring plant communities, few studies have tested their importance at large scales in the wet tropics. Here, we describe the distribution patterns of the most important West African rain forest timber species along the regional rainfall gradient and relate them to their functional traits. We found that the distribution patterns of 25 out of the 31 studied species (80%) were significantly related to mean annual rainfall. Shade tolerance and drought resistance were identified as the main strategy axes of variation. Wood density and leaf deciduousness emerged as the best predictor traits of species position along the rainfall gradient, explaining respectively 32 and 15 percent of the variation. Species traits tended to show stronger relationships with estimated optimum annual rainfall for each species than to the extreme rainfall conditions where they occur. The significant role of rainfall in shaping timber species distribution and the strong relationships between species traits and rainfall indicate that changes in climate, especially declining rainfall, could have strong effects on species composition and abundance in these tropical forests

[1]  L. Poorter.  The relationships of wood-, gas- and water fractions of tree stems to performance and life history variation in tropical trees. , 2008, Annals of botany.

[2]  P. Campanello,et al.  Coordination of leaf and stem water transport properties in tropical forest trees , 2008, Oecologia.

[3]  M. Swaine,et al.  Responses of tropical forest tree seedlings to irradiance and the derivation of a light response index , 1999 .

[4]  J. P. Grime.  Vegetation classification by reference to strategies , 1974, Nature.

[5]  G. Parker,et al.  Seasonal balance and vertical pattern of photosynthetically active radiation within canopies of a tropical dry deciduous forest ecosystem in Mexico , 2005, Journal of Tropical Ecology.

[6]  L. Poorter.  Leaf traits show different relationships with shade tolerance in moist versus dry tropical forests. , 2009, The New phytologist.

[7]  A. Gentry,et al.  Patterns of neotropical plant species diversity. , 1982 .

[8]  S. Hubbell,et al.  Seed size, growth rate and gap microsite conditions as determinants of recruitment success for pioneer species , 2002 .

[9]  Frans Bongers,et al.  Ecological differentiation in xylem cavitation resistance is associated with stem and leaf structural traits. , 2011, Plant, cell & environment.

[10]  L. Poorter,et al.  Seedling root morphology and biomass allocation of 62 tropical tree species in relation to drought‐ and shade‐tolerance , 2009 .

[11]  J. Conroy,et al.  Wood density and anatomy of water-limited eucalypts. , 2004, Tree physiology.

[12]  C. Baraloto,et al.  Seed size, seedling morphology, and response to deep shade and damage in neotropical rain forest trees. , 2007, American journal of botany.

[13]  Bettina M. J. Engelbrecht,et al.  Tolerance to low leaf water status of tropical tree seedlings is related to drought performance and distribution. , 2009 .

[14]  F. Bongers,et al.  The forests of Upper Guinea: gradients in large species composition , 2004 .

[15]  Paul A. Keddy,et al.  Assembly and response rules: two goals for predictive community ecology , 1992 .

[16]  P. Reich,et al.  Strategy shifts in leaf physiology, structure and nutrient content between species of high‐ and low‐rainfall and high‐ and low‐nutrient habitats , 2001 .

[17]  H. Muller‐Landau.  Interspecific and Inter‐site Variation in Wood Specific Gravity of Tropical Trees , 2004 .

[18]  V. J. G. Houba,et al.  A novel digestion technique for multi-element plant analyses , 1983 .

[19]  Mark Westoby,et al.  A leaf-height-seed (LHS) plant ecology strategy scheme , 1998, Plant and Soil.

[20]  Thomas J. Givnish,et al.  Adaptation to Sun and Shade: a Whole-Plant Perspective , 1988 .

[21]  F. Ewers,et al.  Relationships among xylem transport, biomechanics and storage in stems and roots of nine Rhamnaceae species of the California chaparral. , 2007, The New phytologist.

[22]  S. H. Bullock.  Seasonally Dry Tropical Forests: Plant reproduction in neotropical dry forests , 1995 .

[23]  P. Grubb.  A reassessment of the strategies of plants which cope with shortages of resources , 1998 .

[24]  David D. Ackerly,et al.  FUNCTIONAL STRATEGIES OF CHAPARRAL SHRUBS IN RELATION TO SEASONAL WATER DEFICIT AND DISTURBANCE , 2004 .

[25]  M. Westoby,et al.  The Evolutionary ecology of seed size , 2000 .

[26]  J. P. Grime,et al.  Evidence for the Existence of Three Primary Strategies in Plants and Its Relevance to Ecological and Evolutionary Theory , 1977, The American Naturalist.

[27]  R. Villar,et al.  Relative Growth Rate and Biomass Allocation in Ten Woody Species with Different Leaf Longevity Using Phylogenetic Independent Contrasts (PICs) , 2005, Plant biology.

[28]  Stephen P. Hubbell,et al.  Drought sensitivity shapes species distribution patterns in tropical forests , 2007, Nature.

[29]  Jacob McC. Overton,et al.  Shifts in trait‐combinations along rainfall and phosphorus gradients , 2000 .

[30]  E. Veenendaal,et al.  Responses of West African Forest Tree Seedlings to Irradiance and Soil Fertility , 1996 .

[31]  M. Swaine,et al.  Rainfall and soil fertility as factors limiting forest species distributions in Ghana , 1996 .

[32]  M. Swaine,et al.  Classification and ecology of closed-canopy forest in Ghana. , 1976 .

[33]  N. Batjes.  A world dataset of derived soil properties by FAO–UNESCO soil unit for global modelling , 1997 .

[34]  Y. Malhi,et al.  Spatial patterns and recent trends in the climate of tropical rainforest regions. , 2004, Philosophical transactions of the Royal Society of London. Series B, Biological sciences.

[35]  L. Poorter,et al.  Does a ruderal strategy dominate the endemic flora of the West African forests? , 2007 .

[36]  Louis S. Santiago,et al.  Coordinated changes in photosynthesis, water relations and leaf nutritional traits of canopy trees along a precipitation gradient in lowland tropical forest , 2004, Oecologia.

[37]  L. Poorter,et al.  Wood mechanics, allometry, and life-history variation in a tropical rain forest tree community. , 2006, The New phytologist.

[38]  R. Borchert,et al.  Soil and Stem Water Storage Determine Phenology and Distribution of Tropical Dry Forest Trees , 1994 .

[39]  F. Bongers,et al.  West African forests; introduction , 2004 .

[40]  Frederick C Meinzer,et al.  Dynamics of transpiration, sap flow and use of stored water in tropical forest canopy trees. , 2004, Tree physiology.

[41]  Lars Markesteijn,et al.  Seedling Traits Determine Drought Tolerance of Tropical Tree Species , 2008 .

[42]  Wilfried Thuiller,et al.  RELATING PLANT TRAITS AND SPECIES DISTRIBUTIONS ALONG BIOCLIMATIC GRADIENTS FOR 88 LEUCADENDRON TAXA , 2004 .

[43]  O. Phillips,et al.  Continental-scale patterns of canopy tree composition and function across Amazonia , 2006, Nature.

[44]  K. Kitajima.  Relationship between photosynthesis and thickness of cotyledons for tropical tree species , 1992 .

[45]  K. Kitajima,et al.  Carbohydrate storage enhances seedling shade and stress tolerance in a neotropical forest , 2007 .

[46]  S. Davies,et al.  The role of desiccation tolerance in determining tree species distributions along the Malay–Thai Peninsula , 2008 .

[47]  F. Bongers,et al.  Patterns and Determinants of Floristic Variation across Lowland Forests of Bolivia , 2011 .

[48]  Ülo Niinemets,et al.  GLOBAL-SCALE CLIMATIC CONTROLS OF LEAF DRY MASS PER AREA, DENSITY, AND THICKNESS IN TREES AND SHRUBS , 2001 .

[49]  M. Huston,et al.  A theory of the spatial and temporal dynamics of plant communities , 1989, Vegetatio.