Land-use impact on the growth and survival of seedlings and saplings in West African savannas
In frequently disturbed habitats such as savannas, survival of seedlings and saplings depends on the species-specific ability to persist for a long time and to re-sprout following disturbances that are damaging to individuals. This physiological ability increases with increasing stem diameter, as re-sprouting requires sufficient nutrient reserves. Are survival and growth of seedlings and saplings of woody savanna species related to habitat conditions and land-cover type?
Semi-arid savannas representing different site conditions and land-use practices in North Benin, West Africa.
For individuals of 18 common woody species <1-m tall, basal diameter and height were repeatedly measured in five censuses from 2008 to 2010 in the land-cover types non-arable sites, fallows and protected areas. We used multistate capture–recapture models to estimate survival and transition probabilities between diameter classes.
We detected six groups of species with similar survival and transition probabilities. For one of these groups we found no correlation to land use, whereas the other groups comprise species with distinct preferences for different land-cover types. Most species developed better in the communal area compared to the protected area. For five species (one shrub and four trees), we detected an extremely low transition probability for the latter land-cover type.
For some species groups, differences in plant performance were explained by a human-caused opening of the canopy that is beneficial for germination of seeds and enhances survival of juveniles by reducing the competition for light, water and nutrients. Other species showed their best demographic performance in the communal area on non-arable sites with unfavourable environmental conditions and resulting small-scale heterogeneity (mosaic of bare ground and areas with low herbaceous cover), whereas five species are likely to decline in the protected area.