Relationships between climate, soil moisture and phenology of the woody cover in two sites located along the West African latitudinal gradient

The study quantifies the relationships at local scale between phenology and determinants of climate and soil water resources at two sites located along the latitudinal gradient of West Africa, one in the central Sahel (Mali), the other in the Sudanian bioclimatic zone (Benin). The aim is to improve our knowledge on possible vegetation response to possible climate change. Within the Sudanian site, average annual rainfall is 1200 mm, extending from April to October, while, in the Sahelian site, it is 370 mm, occurring from June to September. Physical data were collected from the African Monsoon Multidisciplinary Analysis research programme. The phenology of the dominant species was monitored in four types of vegetation cover at the wetter site, and in three types of vegetation cover at the drier site. For each sampled plant, leafing, flowering and fruiting were recorded as binary variables in terms of the presence/absence of phenophases. A small proportion of the variability of each phenophase occurrence is explained by the logit models. However, rainfall rise is significantly linked to leafing probability increase in the Sahelian site but not in the Sudanian site. Day length extension and temperature decrease are significantly correlated with an increase in leafing in the Sudanian site, but not in the Sahelian. On both sites, the increase in cumulative rainfall is not found to be linked to an increased probability of reproductive phenophases (negative or non-significant relationships). Air temperature is positively correlated with flowering rate in the Sudanian site, but, all other factors being constant, no climate factors are found to be highly significant of flowering occurrence in the Sahel. Fruiting probability is positively correlated mainly with temperature within the Sahelian site. Leafing occurrence is positively correlated with soil moisture in the 0–1 m layer for the Sudanian site, but not for the Sahelian site. Significant relationships between fruiting occurrence and soil moisture may reflect a prior selection of plants on fruiting period that maximizes seed dispersion and germination differently at the two sites. While vegetative and reproduction schedules may be determined by specific genetic factors, the physical environment controls the possibility of their expression. Reduction of the rainfall amount and intensity may increase reproduction rates in wet areas. Although this factor should decrease leafing rate, it does not influence reproduction at dry sites, except through the decrease in air humidity. In wetter areas, increasing temperature may reduce leafing, but may increase reproduction rates. Cover reduction may have an impact on local physical factors and, consequently, probably also affects vegetation phenology.

[1]  A. Aubréville.  Flore forestière soudano-guinéenne : A.O.F. - Cameroun - A.E.F. , 1950 .

[2]  A. Agresti.  An introduction to categorical data analysis , 1997 .

[3]  M. McDonald,et al.  Seasonal Patterns of Flowering and Fruiting in a Dry Tropical Forest in Jamaica 1 , 2005 .

[4]  S. Galle,et al.  Combined analysis of energy and water balances to estimate latent heat flux of a sudanian small catchment , 2009 .

[5]  T. Foucart.  Colinéarité et régression linéaire , 2006 .

[6]  Derek Eamus,et al.  Does irrigation affect leaf phenology in deciduous and evergreen trees of the savannas of northern Australia , 1998 .

[7]  Frédéric Baup,et al.  Woody plant population dynamics in response to climate changes from 1984 to 2006 in Sahel (Gourma, Mali) , 2009 .

[8]  The rooting patterns of woody and herbaceous plants in a savanna : are they complementary or in competition ? , 1995 .

[9]  S. Galle,et al.  Run-on contribution to a Sahelian two-phase mosaic system: Soil water regime and vegetation life cycles , 1999 .

[10]  H. Lieth.  Phenology and Seasonality Modeling , 1974, Ecological Studies.

[11]  Robert B. Jackson,et al.  THE GLOBAL BIOGEOGRAPHY OF ROOTS , 2002 .

[12]  J. Neter,et al.  Applied Linear Regression Models , 1983 .

[13]  H. Rita,et al.  Odds Ratio: An Ecologically Sound Tool to Compare Proportions , 2008 .

[14]  Dr. Henk Breman,et al.  Woody Plants in Agro-Ecosystems of Semi-Arid Regions , 2011, Advanced Series in Agricultural Sciences.

[15]  J. Terborgh,et al.  The Phenology of Tropical Forests: Adaptive Significance and Consequences for Primary Consumers* , 1993 .

[16]  P. Reich,et al.  Water stress and tree phenology in a tropical dry forest in the lowlands of Costa Rica. , 1984 .

[17]  D. Hosmer,et al.  Applied Logistic Regression , 1991 .

[18]  A. Lawin.  Analyse climatologique et statistique du régime pluviométrique de la haute vallée de l’Oueme à partir des données pluviographiques amma-catch benin , 2007 .

[19]  R. Borchert.  Induction of rehydration and bud break by irrigation or rain in decidous trees of a tropical dry forest in Costa Rica , 1994, Trees.

[20]  P. Jewell,et al.  Ecosystems of the World, 13: Tropical Savannas. , 1984 .

[21]  Samuel Alleaume,et al.  Sensitivity of African biomes to changes in the precipitation regime , 2006 .

[22]  Christian Floret,et al.  Plant phenology in relation to water availability: herbaceous and woody species in the savannas of northern Cameroon , 1995, Journal of Tropical Ecology.

[23]  Sylvie Galle,et al.  Assessing the water balance in the Sahel: Impact of small scale rainfall variability on runoff. Part 1: Rainfall variability analysis , 2006 .

[24]  R. B. Jackson,et al.  Rooting depths, lateral root spreads and below‐ground/above‐ground allometries of plants in water‐limited ecosystems , 2002 .

[25]  L. Diarra,et al.  Fluctuations saisonnieres de la feuillaison des arbres et des buissons saheliens. Consequences pour la quantification des ressources fourrageres , 1994 .

[26]  Frédéric Baup,et al.  Surface thermodynamics and radiative budget in the Sahelian Gourma: Seasonal and diurnal cycles , 2009 .

[27]  A. Aubréville.  Flore forestière : soudano-guinéenne , 1985 .

[28]  Ramakrishna R. Nemani,et al.  A generalized, bioclimatic index to predict foliar phenology in response to climate , 2004 .

[29]  Carlos A. Peres,et al.  Tree Phenology in Adjacent Amazonian Flooded and Unflooded Forests 1 , 2005 .

[30]  P. Ketner,et al.  Woody plant phenology in the West Africa savanna , 1998 .

[31]  D. Eamus,et al.  Reproductive Phenology of Woody Species in a North Australian Tropical Savanna 1 , 1999 .

[32]  P. Rosnay,et al.  Multi-scale soil moisture measurements at the Gourma meso-scale site in Mali , 2009 .

[33]  R. Borchert,et al.  Water status and development of tropical trees during seasonal drought , 1994, Trees.

[34]  Thierry Lebel,et al.  Rainfall climatology of the HAPEX-Sahel region during the years 1950–1990 , 1997 .

[35]  Steven W. Running,et al.  Effects of precipitation and soil water potential on drought deciduous phenology in the Kalahari , 2004 .

[36]  R. Borchert,et al.  Environmental control of flowering periodicity in Costa Rican and Mexican tropical dry forests , 2004 .

[37]  K. Tielbörger,et al.  Life history variation in an annual plant under two opposing environmental constraints along an aridity gradient , 2006 .

[38]  Derek Eamus,et al.  Ecophysiology of trees of seasonally dry tropics: Comparisons among phenologies , 2001 .

[39]  P. Kramer,et al.  Physiology of trees. , 1961 .

[40]  Peter B. Reich,et al.  PHENOLOGY OF TROPICAL FORESTS : PATTERNS, CAUSES, AND CONSEQUENCES , 1995 .

[41]  C. Thorncroft,et al.  African Monsoon Multidisciplinary Analysis: An International Research Project and Field Campaign , 2006 .

[42]  Ramakrishna R. Nemani,et al.  Canopy duration has little influence on annual carbon storage in the deciduous broad leaf forest , 2003 .