Relationship between seed size and related functional traits in North Saharan Acacia woodlands

Background and aims - North Saharan Acacia woodland is a fragile ecosystem altered by desertification and human activities. Little research has been conducted on the ecology of North Saharan Acacia woodland species. Seed size is a key trait to determine germination success, survival rate and establishment of Acacia woodland species under desert constraints. Methods - We analysed seed-size relationships in 42 selected woody plants in four different types of Acacia woodland vegetation which correspond to 26 plant species. We examined the correlation among seed size, fruit size, plant height, leaf size and flowering time and we tested seed size and fruit size variation among growth forms, dispersal modes and mechanisms to prevent dispersal. Key results - Close relationships were found between seed size and fruit size (r = 0.77**), between fruit size and plant height (r = 0.51**) and between seed size and flowering duration (r = -0.46*) and a weak positive relationship was found between fruit and leaf size. Species with restricted spatial dispersal tended to have smaller seeds and fruits compared to those with well-developed spatial dispersal. Species which disperse and germinate throughout the year tended to have large diaspores, whereas species with seasonal germination tended to have small diaspores. The relationship between seed size and growth form/plant height was strong for gravity-dispersed (barochorous) species secondarily dispersed by vertebrates (Ziziphus lotus), seeds with secondary wind-assisted dispersal (Zilla spinosa subsp. macroptera) and for restricted-dispersal species (Tetraena gaetula). Precocious, short-flowering species that spread dispersal and germination over time (Acacia tortilis subsp. raddiana) tended to have large seeds. Early- and long-flowering herbaceous species tended to have small seeds (Brocchia cinerea). Conclusion - Close relationships are found between seed size and fruit size, between fruit size and plant height and between seed size and flowering duration in Moroccan Acacia woodland species.