By hemlines I'm referring to the trimmed bases of the foliage crowns of bushes and trees that feral herbivores like to munch on. A quick assessment of the height of a browse line and its severity provides real-time information about the impact of feral herbivores and the need for appropriate management.
It's the underneath part of the crown that can end up looking like a pudding bowl haircut as all foliage within reach is nibbled off along the horizontal plane. With feral goats, the line can be at the height they can reach when standing on their hind legs.
Even with severe hemlines, taller bushes and trees such as Quandongs (Santalum acuminatum) can produce seed for potential recruitment. However, seedlings and epicormic growth (having softer growing tips and being in easy reach) are highly vulnerable to being eaten.
Where there is ongoing browsing pressure, there's little or no successful recruitment. As the older trees and shrubs eventually die, there's nothing to replace them. Intense and ongoing browsing pressure can mean that even large trees quietly disappear from the landscape.
Bullock Bush (Alectryon oleifolius) is a small to medium-sized tree that cattle, goats and sheep find very palatable. Although it's a widespread species in South Australia, it's common to find these plants with severe haircuts and no recruitment (see images 1 and 2).
On our Boolcoomatta Reserve (a former sheep station, now under our conservation management for more than a decade) browse lines on Bullock Bushes are repairing themselves with lower hanging foliage from the crown and epicormic growth from the stems (images 3 and 4).
Also evident is recruitment through either seed germination or suckering, which is the result of committed and successful feral herbivore management over many years.
Yes we do concern ourselves with hemlines!