July 2008
Sun, 13 Jul 2008, 10:19am, Tinman said
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Ehrharta erecta is probably the most pernicious invasive we deal with at Edgehill. It is a perennial bunch grass that flowers and produces seed all year ‘round, unlike our native bunch grasses that only seed once per year. Ehrharta likes it wet, so in exposed areas (such as the eastern flank of Mt D), you don’t find it. However, the fog drip on Edgehill is sufficient that ehrharta is aggressive and exuberant.
The drought this year has really handicapped the ehrharta compared to the natives. In fact, our band of volunteers and staff have managed to keep the ehrharta quite well controlled in our principal work areas. This month’s workparty in fact pretty much eradicated all the ehrharta that was up, and things now look quite good:
Of course, the seed bank is lurking there and waiting for more wet in order to sprout away. Ehrharta will never be eradicated, just controlled. So we will always have motivation to return and pull again on another day.
This photo does reveal another of our major management headaches, though: the leaf litter from the blue gum eucalyptus. These trees shed high volumes of slowly-degrading leaves that cover up everything on the ground. Small seedlings of other plants are simply smothered by this leaf litter. This is one of the reasons why eucalyptus trees are rightly described as the biggest weeds in California. These particular trees were planted by Adolph Sutro over 100 years ago and are nearing the end of their expected lifetimes. Once they finally die and fall, well, good riddance.
This photo also shows (in the background) another problem found everywhere in San Francisco’s tree plantations that most people mistake for “forests”. Note the thick cylinders of ivy that encase the trunks of the trees. The ivy grows this way because of the fog drip from the trees. Eventually the ivy smothers the tree and its weight helps pull the tree over in the high winds we routinely get here. However, this is really a just end to the problem, as without these planted trees, the conditions that create these weedy monocultures wouldn’t exist. So in fact, this is merely an appropriate natural negative feedback loop that limits the damage inflicted by misguided human actions like Adolph Sutro’s those many years ago.
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