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Deer Grazing- Oak Challenge Number Four
Abundant herds of deer can also nibble away at the seedling oaks as they struggle up through the grasses. In areas fenced to exclude deer and gophers, on Hastings and elsewhere, oak seedlings thrive. In areas where deer can browse on oak seedlings, like cattle, they will kill or stunt the oaks. Why does biting the tender tip off an oak seedling cause harm?
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| Blue Oak, Red Hill, Hastings Reserve. Tagged No. 765 in 1965, this oak continues to be eaten only by deer. Growth is shown in the chart above. Over 35 years, and as can be seen in the figure, such deer browsing ALONE means very slow growth. This area was probably a blue oak woodland, cleared for agriculture in the early 1900s. Poor agricultural practices lead to the erosion of all topsoil, and the farm was abandoned in 1935. A group of 78 blue oak seedlings were tagged in 1965 in this field and they have been periodically measured. No new seedling have been found since 1965.Stick in photo is 1 meter. |
In 1965, Keith White, the former plant ecologist here, found 78 blue oak seedlings along the edges of what we call North Field, just above the offices. All these tiny seedlings were given a metal tag and then periodically measured. Even though these seedlings are not grazed by cattle, and are only grazed by deer and the occasional rabbit, they have remained small. In nearly 40 years of monitoring, they have only grown about 12 inches! Apparently deer alone can bonsai blue oak. Of the 78 once present, now only about 30 survive. One of these, #765, is shown in the accompanying photos with it’s slow growth charted.
Plants typically make a hormone that causes the twig to elongate, and that hormone is made in the bud, often on the terminal tip. Cut off (or bite off) that tender tip, and the twig stops elongating. Not all oaks stop growing if they are trimmed, but the valley oak and blue oak certainly stop growing. Removing the terminal tips of these oaks has a dramatic effect that is often most apparent in the second or third year after clipping.
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Jim Griffin, about 1989, with seedling valley oaks in garden plot protected from gophers. All acrorns planted in 1975 survivied and grew into saplings. In 1985, the oak seedlings near Jim had terminal buds removed. Note very short ones near Jim. These remain just below wire mesh fence even today. By 2000, the oaks in foreground, that had never been trimmed, were over 10 feet tall. |
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So, here, we took a photo of the same plot in 2000 from what appears as the left side in the picture above. The tall oaks now dwarf the fence posts. Those in the lower left, clipped in 1985, remain dwarfed, even without further grazeing by deer or cows. |
In one of Jim Griffin’s first gopher-proof gardens at Hastings, he showed that all the acorns in the plot grew into seedlings inside the fence keeping out gophers and deer. All the seedlings outside the fence (with gophers and deer) died by the third year. Then, Jim clipped all the leaves from the green trees in late summer, and from some others, he clipped off the first three branches (center, left and right twig). Even now, some 10 years later, the effects of this clipping remain evident. Although protected from any further injury, the valley oak seedlings that were both clipped and stripped of leaves in one year remain stunted, under 12 inches tall. Those never clipped or stripped (opposite corner) are now saplings 10 feet tall. It remains a mystery why the Valley oak and Blue oaks do not sprout when they are cut back or why they remain stunted for years after they have been clipped.
In
1969, Jim Griffin planted a Valley Oak acorn, kept it free from gophers
and grazing until it reached about 8 feet in height. Then, the fences
were removed and the tree continued to grow, tolerating gopher attacks,
deer, insects and drought. Now, some 30 years later, it is a graceful
addition to the Hastings Ranch House (photo). It is clear that once the
terminal buds of the Valley oaks and Blue oaks reach over 6 feet tall,
they are able to survive pretty much on their own.
For those of you who know these woodlands, the Coast live oak (Quercus agrifolia) comes to mind. They are certainly reproducing very well. Scrub jays also plant Coast live oak, but for some reason, gophers pretty much leave them alone. Even as tiny seedling, the crisp, tough leaves have sharp spines and show much less damage by deer, rabbits and cattle. A handshake with a Coast live oak is painful, while a handshake with a Blue oak or Valley oak is velvet. Coast live oak seedlings, (and mature trees!) can be cut to the ground and they will form bushy sprouts. The prickly bushy branches grow out and eventually are large enough so deer cannot reach an interior twig. No longer eaten off, and protected by a ring of thorny branches, a central twig can elongate, and soon bear acorns. Center stem quickly shoot up above the growing tree’s bushy bottom parts. Eventually, this main stem bears enough top branches to shade out the bushy basal branches that then die and fall off, leaving a lovely, winding Coast live oak.