Strolling the sandy paths of Fort Ord Natural Reserve, on the coast of Monterey County, feels a bit like wandering through Lilliput. In place of head-high hedges and broad oak boughs grow Mother Nature’s own bonsais. Sandmat manzanita forms a leafy carpet underfoot, interspersed with California lilac the size of cantaloupe and mature oaks that resemble mere saplings. The close-packed foliage and rounded shapes of the shrubs bring to mind a garden pruned by gnomes.
According to Laurel Fox, the concept of resident tree trimmers isn’t far off the mark. For the past 15 years, she has studied the ecological relationships between these diminutive plants and their animal neighbors. A UC Santa Cruz professor of ecology and evolutionary biology, Fox has been the faculty director of the Fort Ord Natural Reserve since its inception in 1996.
On this late October morning, enough sun filters past the marine layer to lend a movie-set glow to the land. Red-brown manzanita trunks gleam through masses of olive-green leaves, set against a backdrop of golden dune sand.
Fox picks her way through the low-slung greenery toward several clusters of metal stakes encircled by wire mesh. These are her experimental plots. When first erected, each contained four components of classic Central Coast maritime chaparral — California lilac (Ceanothus cuneatus rigidus), manzanita (Arctostaphylos pumila), mock heather (Ericameria ericoides), and open sand. The fencing protects the plants from herbivores, allowing Fox to observe how grazing affects community dynamics.
Fox pauses along the way to point out a ceanothus with fingernail-sized leaves. Half of this miniature Monterey ceanothus consists of bare twigs, bristly as a hedgehog’s back. “These dense, intermeshed branches are very typical of heavy browse. It’s so heavily eaten, it’s almost topiaried,” Fox says.
We stop at the first exclosure plot, which features wide mesh above and finer mesh below. This plot is designed to exclude both deer and rabbits; others fence out only deer. Fox threads her fingers through the wire and looks fondly at the plants inside. She knows each one well, having tracked its growth very closely. “I put these up in the summer of ’96. By the summer of ’97, the ceanothus inside was growing.” Now half again as tall as Fox, this shrub’s long shoots and abundant leaves make it a giant in this Lilliputian landscape. Fox now gestures toward a cluster of twigs at its base. “You can just about see the old architecture of the plant. It was less than a foot and a half tall, very chewed on.”
It is said that nature abhors a vacuum, and plants are no exception to this rule. Where ceanothus outside the fences showed almost no growth — many had suffered reductions in leaf coverage or up and died — new shoots from protected plants flourished. Areas of open sand around each plant shrank apace. This loss of bare ground, Fox found, hurt populations of two rare annual wildflowers. As the years progressed, exclosured ceanothus grew larger, while the manzanita and mock heather shrank. Monterey spineflower (Chorizanthe pungens pungens) and sand gilia (Gilia tenuiflora arenaria) also disappeared from the plots entirely, but maintained a presence in unfenced control sites.
The caged ceanothus enjoyed other benefits of protection: they could devote more energy to setting seed. For more than a year, UCSC undergraduate Adrian Deveny painstakingly counted the seeds below both protected and unprotected plants. He found seed numbers beneath control plants remained fairly steady at 1 seed per square meter year round, with a modest spike to 1.5 seeds per square meter in June. Meanwhile, protected plants set many times more seed than unprotected plants. These dropped at least three times as many seeds on the ground as unprotected plants by July, a number that declined slowly over the next six months.
Live traps revealed the fate of the seeds. Small rodents ranging from deer mice to the California pocket mouse were twice as abundant near the deer exclosures. And dishes stocked with seeds that excluded seed harvesters, such as ants and birds, revealed rodents took virtually all of the bait.
The rodents were commuting to the plots to take advantage of abundant food. Dusky-footed woodrats, for example, raided the lush manzanita and ceanothus branches inside the cages, but tended to build their ramshackle nests of duff and sticks under nearby oak groves.
Fox describes the three-way interactions between ceanothus and local herbivores: “It’s a chain. The deer are suppressing seed production by feeding on the leaves. That results in fewer seeds and less rodent activity. But when the plants are protected from deer, you get so many more seeds that it attracts rodents and, over six to ten months, they reduce the seedbank back to what it was,” Fox says.
Her findings have implications for conserving maritime chaparral in a warming future. Like many other chaparral plants, Monterey ceanothus does not resprout after fire. Instead, it relies on seeds remaining in the soil to replenish populations. Excluding deer increases the number of ceanothus seeds on the ground during peak fire season. If fire frequency increases as predicted, it is most likely to flare up during late summer and fall. In this situation, having a seedbank fortified in late summer with the help of human fencing may become a lifeline for this species of special concern.
And where will that leave the local “gardeners”? They’ll have lots of other local plants to trim with their gnawing teeth. — KMW
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