Banking on seeds: long-lived seed banks enable invasive Australian Acacias to survive in time and space

Mass recruitment of Acacia after fire

Figure 1: Mass recruitment of Acacia after fire

Mass production of seed even in the presence of biological control

Figure 2: Mass production of seed can occur even in the presence of biological control

Viable seeds of Australian Acacia remain in the soil long after the parent plants have died or have been removed. These ‘seed banks’ enable stands of Australian Acacia to re-establish and makes their permanent removal extremely difficult. This leads to land managers having to repeatedly visit cleared sites to remove seedlings that have germinated from the seed bank, leading to lower cost effectiveness of clearing operations. Despite the significance of Australian Acacias in South Africa and the importance of seed banks to their successful management, there is a general lack of knowledge on their seed bank dynamics. Much of the information relating to aspects of the seed bank dynamics, of the more well studied species, has been collected in isolation or has used different sampling methods making it difficult to generalise to new sites and situations. Consequently there is a wide gap in our understanding in relation to the seed bank dynamics of Australian Acacia in South Africa. This case in relation to a global context is not unique and only a few studies on the seed bank dynamics of alien invasive plants have been completed (see Gioria et al., 2012).

Seed retrieved from a single soil sample

Figure 3: A large number of seed retrieved from a single soil sample

The seed banks of the most prominent ant-dispersed invasive Australian Acacia in the fynbos biome are the focus of C·I·B funded PhD candidate, Matthys Strydom (co-supervised by Karen Esler, Ruan Veldman and John Wilson), who is no stranger to seed bank work. During the final year of his BSc, Matthys, in collaboration with Prof Karen Esler and Alan Wood (Plant Protection Research Institute), found that even after biological control agents had been present at the study sites for 21 years, seed banks were large and still posed a serious challenge for management. This shows that control operations need to include longer term management of the seed bank in their planning and costing (Strydom et al. 2012). During his MSc (co-supervised by Karen Esler and Alan Wood), Matthys determined the seed rain and seed bank status of Acacia saligna across its distribution in South Africa. By assessing the influence of different abiotic and biotic factors he was able to predict under which conditions the seed bank of this species will be most problematic for control and management.

Read the papers:

Gioria, M., Pyšek, P. and Moravcová, L. 2012. Soil seed banks in plant invasions: promoting species invasiveness and long-term impact on plant community dynamics. Preslia 84: 327350.

Strydom, M., Esler, K.J., Wood, A.R. (2012) Acacia saligna seed banks: sampling methods and dynamics, Western Cape, South Africa. South African Journal of Botany, 79:140-147.

For more information, contact Matthys Strydom or Karen Elser