When spring comes unsprung

Spring is here!

In theory.

It's just that spring here isn't like spring in Other Places.

You can forget the rising sap, unfurling leaves and frolicking bunnies and chicks (alright, I admit I've never actually experienced a Northern Hemisphere spring, but I've seen the Easter cards...)

Here spring is more like an intense bout of schizophrenia.
At night winter has a monopoly, with temperatures dropping to 8 C

(46 F), but as soon as the sun sneaks over the horizon, summer leaps in and the mercury rockets to the mid 30s C (95 F).

And the weather's not the only one refusing to take its meds.
After five months without rain, the bush is leafless, parched and grey. As you'd expect. Then whoosh (that's a figurative whoosh, not an audible whoosh), all the knob thorns burst into flower.



Knob thorns (Acacia nigrescens) are the dominant tree species here, so if they decide to bloom prolifically, when everyone else is playing dead, it's rather startling.



The knob thorn gets its name from its... er... knobs, which grow on the trunk and branches of young trees. Each knob is tipped with a single thorn, presumably to spike large herbivores.

 



In Africa, acacias are called thorn trees (rather than wattles) because of their weaponry. My tree guide (South African) puts it bluntly: 'Australian acacias are always spineless'. Even I feel that this is a trifle harsh.



All the local browsers (giraffe, kudu, bushbuck and impala) enjoy munching knob thorns, but I hadn't realised how sought-after the species was until I tried to take a close-up photo of its flowers. No go. Despite an exhaustive search, I couldn't find a single branch growing within my reach (kudus are considerably taller than me!). I trust you appreciate my dedication to blogging, as I had to dodge speeding traffic to snap an un-nibbled, highway-side specimen.



Hard-won knob thorn flowers.







With such a profusion of blossom, the local giraffes are looking rotund and smug. During the brief (2-3 week) flowering period, knob thorn flowers make up 25% of their diet, and they're currently swanning around dusted in golden pollen, and sometimes wreathed with creamy blooms. It's been suggested that giraffes may act as pollinators for the knob thorn, since the trees produce many more flowers than they need for seed production. However, research undertaken in Kruger National Park found that knob thorns growing in giraffe-free localities produced more seed than their giraffe-nibbled counterparts. And within trees munched by giraffes, seed-production was far greater in branches located above the giraffe's reach than in the branches they could access.



Munching knob thorn flowers isn't as pleasant as you'd think. They contain three times more tannin than the leaves. Tannins (which have that awful drying, astringent effect in your mouth) bind with the plant's proteins, making them indigestible.



Are giraffes pollinators or flower predators of Acacia nigrescens in Kruger National Park, South Africa? P.A. Fleming, S.D. Hofmeyr, S.W. Nicolson and J.T. du Toit. Journal of Tropical Ecology (2006) 22:247–253.

 

NB: I wrote this post a couple of weeks ago, but I was so busy emulating decapitated poultry (during the lead up to my overseas trip) that I didn't get around to posting it. Sorry!