If one of the most important attributes for plants surviving frequent fire regimes is thick bark, then the growth rate of bark should be high in such systems. However, bark growth rate (bark production per year) has, as yet, been little investigated.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and their collaboratorsexamined the distribution of woody species in Hluhluwe-iMfolozi Park in South African over 253 sites, stratified by biome. They investigated the rate at which species produce bark and how bark growth rate influences their distribution and abundance in fire-prone environments.
The researchers tested the hypothesis that the bark growth rate of plants was less constrained by fire frequencies when they are capable of clonal spread by underground propagation structures, such as stems or adventitious buds on roots. They also compared bark protection of savanna and forest trees.
They found that bark growth rate was better correlated with the fire frequency at which species occur than bark thickness and relative bark thickness.
Species with a high bark growth rate were most common at sites with frequent fire. Conversely, species occurring in places with infrequent fires or no fire had low bark growth rates.
The results showed that the bark growth rate (bark production per unit time) is critical in environments with frequent fires. The survival during the juvenile period (minimum time from germination to sapling release from the fire trap) depends on the species ability to grow a sufficiently thick bark layer to resist the first fire event.
They also showed that fire frequency is one of the main factors controlling species distribution in the vegetation in Hluhluwe-iMfolozi. It acts as an environmental filter on trait distribution, with species having good bark protection (produced by high bark growth rate and bark thickness) distributed where the fires are frequent.