Seasonal variation of environment and conspecific density-dependence effects on early seedling growth of a tropical tree in semi-arid savannahs
Different mechanisms have been proposed to explain species coexistence and maintainance of local species diversity in tree communities. Among the proposed mechanisms, negative density dependence theory (NDD) predicts that seedling growth rate declines at high conspecific densities. However, local en...
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| Format: | Article |
| Language: | English |
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Elsevier
2023-06-01
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| Series: | Global Ecology and Conservation |
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| Online Access: | http://www.sciencedirect.com/science/article/pii/S2351989423000902 |
| _version_ | 1797850293253177344 |
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| author | Sylvanus Mensah Christa J.M. Lokossou Achille E. Assogbadjo Romain Glèlè Kakaï |
| author_facet | Sylvanus Mensah Christa J.M. Lokossou Achille E. Assogbadjo Romain Glèlè Kakaï |
| author_sort | Sylvanus Mensah |
| collection | DOAJ |
| description | Different mechanisms have been proposed to explain species coexistence and maintainance of local species diversity in tree communities. Among the proposed mechanisms, negative density dependence theory (NDD) predicts that seedling growth rate declines at high conspecific densities. However, local environmental conditions and seasonality may also modulate the strength of NDD. We used data from dry and wet seasons in West African semi-arid savannas to explore the importance of NDD and environmental heterogeneity in predicting seedling growth of Afzelia africana Sm, a threatened species with high economic and cutural values. First, we analysed variation of seedling growth in dry and wet seasons, and between vegetation types (tree and shrub savannas). Next, we assessed the effects of environmental heterogeneity (soil type, slope and elevation) and biotic factors (conspecific/heterospecific seedling and adult densities, leaf fungal infection, herbivory) on seedling growth in dry and wet seasons, while controlling for initial seedling size. We predicted that seedling growth would be higher in the wet than in the dry season, and in shrub savannas than in tree savannas due to variation in stand density and intensity of competitive biotic interactions. We also hypothesized that slope and negative density dependence would influence seedling growth and that, the density-dependent effects would vary with environmental heterogeneity and seasonality. Results showed two distinct patterns of seedling growth primarily driven by seasonality: a higher growth rate in the wet season due to water availability and a smaller growth rate during the dry season, possibly because seedlings develop adaptation to drought and fire at the expense of their growth. Growth rate was also higher on flat and gentle slope. Density-dependent effects on seedling growth were only observed with conspecific adults. Seasonality modulated the strength of the density-dependent effect, which was significantly negative in the wet season and nonsignificant in the dry season. This study suggests that A. africana early seedling growth is modulated by interacting effects of seasonality, terrain slope and adult conspecific density. Campaigns for reforestation with A. africana in the semi-arid areas will require increased attention on the seedlings during the long periods of drought. |
| first_indexed | 2024-04-09T18:58:02Z |
| format | Article |
| id | doaj.art-4d495910f3684e30b24c8183524e4120 |
| institution | Directory Open Access Journal |
| issn | 2351-9894 |
| language | English |
| last_indexed | 2024-04-09T18:58:02Z |
| publishDate | 2023-06-01 |
| publisher | Elsevier |
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| series | Global Ecology and Conservation |
| spelling | doaj.art-4d495910f3684e30b24c8183524e41202023-04-09T05:47:51ZengElsevierGlobal Ecology and Conservation2351-98942023-06-0143e02455Seasonal variation of environment and conspecific density-dependence effects on early seedling growth of a tropical tree in semi-arid savannahsSylvanus Mensah0Christa J.M. Lokossou1Achille E. Assogbadjo2Romain Glèlè Kakaï3Laboratoire de Biomathématiques et d′Estimations Forestières, Faculté des Sciences Agronomiques, Université d′Abomey-Calavi, 04 BP 1525 Cotonou, Benin; Chair of Forest Growth and Dendroecology, Albert-Ludwigs-University Freiburg, Tennenbacher Str. 4, 79106, Freiburg im Breisgau, Germany; Corresponding author at: Laboratoire de Biomathématiques et d′Estimations Forestières, Faculté des Sciences Agronomiques, Université d′Abomey-Calavi, 04 BP 1525 Cotonou, Benin.Ecole Polytechnique d'Abomey-Calavi, Université d'Abomey-Calavi, 01 BP 2009 Cotonou, Bénin; Faculté des Sciences et Techniques, Université d′Abomey-Calavi, 01 BP 526 Cotonou, BeninLaboratoire de Biomathématiques et d′Estimations Forestières, Faculté des Sciences Agronomiques, Université d′Abomey-Calavi, 04 BP 1525 Cotonou, Benin; Laboratoire d′Ecologie Appliquée, Faculté des Sciences Agronomiques, Université d′Abomey-Calavi, 03 BP 1974 Cotonou, BeninLaboratoire de Biomathématiques et d′Estimations Forestières, Faculté des Sciences Agronomiques, Université d′Abomey-Calavi, 04 BP 1525 Cotonou, BeninDifferent mechanisms have been proposed to explain species coexistence and maintainance of local species diversity in tree communities. Among the proposed mechanisms, negative density dependence theory (NDD) predicts that seedling growth rate declines at high conspecific densities. However, local environmental conditions and seasonality may also modulate the strength of NDD. We used data from dry and wet seasons in West African semi-arid savannas to explore the importance of NDD and environmental heterogeneity in predicting seedling growth of Afzelia africana Sm, a threatened species with high economic and cutural values. First, we analysed variation of seedling growth in dry and wet seasons, and between vegetation types (tree and shrub savannas). Next, we assessed the effects of environmental heterogeneity (soil type, slope and elevation) and biotic factors (conspecific/heterospecific seedling and adult densities, leaf fungal infection, herbivory) on seedling growth in dry and wet seasons, while controlling for initial seedling size. We predicted that seedling growth would be higher in the wet than in the dry season, and in shrub savannas than in tree savannas due to variation in stand density and intensity of competitive biotic interactions. We also hypothesized that slope and negative density dependence would influence seedling growth and that, the density-dependent effects would vary with environmental heterogeneity and seasonality. Results showed two distinct patterns of seedling growth primarily driven by seasonality: a higher growth rate in the wet season due to water availability and a smaller growth rate during the dry season, possibly because seedlings develop adaptation to drought and fire at the expense of their growth. Growth rate was also higher on flat and gentle slope. Density-dependent effects on seedling growth were only observed with conspecific adults. Seasonality modulated the strength of the density-dependent effect, which was significantly negative in the wet season and nonsignificant in the dry season. This study suggests that A. africana early seedling growth is modulated by interacting effects of seasonality, terrain slope and adult conspecific density. Campaigns for reforestation with A. africana in the semi-arid areas will require increased attention on the seedlings during the long periods of drought.http://www.sciencedirect.com/science/article/pii/S2351989423000902Afzelia africanaBiotic neighborhood, conspecific adult densityDry seasonNegative density dependenceWest Africa |
| spellingShingle | Sylvanus Mensah Christa J.M. Lokossou Achille E. Assogbadjo Romain Glèlè Kakaï Seasonal variation of environment and conspecific density-dependence effects on early seedling growth of a tropical tree in semi-arid savannahs Global Ecology and Conservation Afzelia africana Biotic neighborhood, conspecific adult density Dry season Negative density dependence West Africa |
| title | Seasonal variation of environment and conspecific density-dependence effects on early seedling growth of a tropical tree in semi-arid savannahs |
| title_full | Seasonal variation of environment and conspecific density-dependence effects on early seedling growth of a tropical tree in semi-arid savannahs |
| title_fullStr | Seasonal variation of environment and conspecific density-dependence effects on early seedling growth of a tropical tree in semi-arid savannahs |
| title_full_unstemmed | Seasonal variation of environment and conspecific density-dependence effects on early seedling growth of a tropical tree in semi-arid savannahs |
| title_short | Seasonal variation of environment and conspecific density-dependence effects on early seedling growth of a tropical tree in semi-arid savannahs |
| title_sort | seasonal variation of environment and conspecific density dependence effects on early seedling growth of a tropical tree in semi arid savannahs |
| topic | Afzelia africana Biotic neighborhood, conspecific adult density Dry season Negative density dependence West Africa |
| url | http://www.sciencedirect.com/science/article/pii/S2351989423000902 |
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