This morning I had to clear fast-growing weeds and young trees that were overwhelming a small dogwood tree that I had planted a few years back. Whether a natural or artificial clearing, the sunshine coming in through the freshly opened sky hole stimulates prolific growth. Cultivated dogwood trees are simply not up to the competition. Their situation reminds me of bullhorn acacia trees.
![]( "Bullhorn Acacia")
- Bullhorn Acacia
Most acacia trees grow in arid tropical regions where forage is scarce. As a defense against being eaten, most acacia trees have sharp thorns and produce bitter tasting alkaloids to prevent grazing. Bullhorn acacias (Acacia cornigera), native trees of Mexico and Central America, lack the chemical protection but benefit from an army of ant protectors. One species of ants called Pseudomyrmex ferruginea live in the hollow swollen thorns that are abundant on the succulent acacia tree. Not only does the tree provide housing for the ants through its thorns but it also provides nutritious nectar from glands o the stalk of its feathery leaves, and as a bonus, the tips of the leaftlets each produce a yellowish protein-lipid nodule called beltian bodies. There is no known function for these leaf tip delights except feeding the ants. So what do the ants do to earn the right to live symbiotically with the tree?
Once they reach the appropriate colony size, squad of Pseudomyrmex ants regularly patrol every inch of their tree including the space underneath and overhead. Anything too close to their tree is snipped off, pruned, or pulled up. If the branch of another tree so much as comes near their acacia tree, the ants will prune it away. Should another insect step foot on their tree or an herbivore nose in for a bite, the ants furiously attack. The ants quickly recruit more help by secreting a pheromone that rallies all the troops instantly. Some biologists report that grazing animals can smell the pheromone and save them grief by keeping their distance.