Characterising wide spatial variation in population size structure of a keystone African savanna tree

摘要: Abstract Elephant impact on trees is of conservation concern in African savannas, but it’s effect population size structure heavily utilised species has received little attention. Although studies have shown that the and density Sclerocarya birrea subsp. caffra (marula), a savanna tree species, varies widely across its range, causes this variation are poorly understood. This study aimed to describe compare these divergent structures develop an understanding relationship between site characteristics, specifically disturbance. Four distinct groups were identified: (1) adult dominated populations consisting only adults no juveniles or seedlings. The class distributions (SCDs) group bell-shaped, indicating unstable which may come about through circumstances longer occur areas, for example human settlement massive episodic recruitment event. High impala utilisation seedlings rodent seed predation proposed be main cause lack recruitment; (2) rotated sigmoid (or negative J shaped) curves, representing stable structures, when protected from elephants, as well at high rainfall sites with without elephants suitable habitats marulas able attain relatively instability not inherent; (3) juvenile almost adults. Adults relegated few refugia, where unable reach them; (4) mostly These populations, all exposed fire “missing classes” varying 5 40 cm stem diameter 2–8 m height. was most likely caused by suppression combined elephant individuals classes”. Consistent application pressure postulated result progression class” structure, finally local extirpation, increasing densities concomitant utilisation, interacting fire, soil type.