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Heat and hope: climate change on Sonoma Mountain

By Arthur Dawson

Go anywhere on Sonoma Mountain and you’re bound to discover something that speaks of the past. It might be a thousand-year-old redwood or the sawed-off stump of one, the tumbled-down stone wall of an early homesteader, a strand of rusty barbed wire on a rotting fence post, or an obsidian shard glinting in the dust. They’re good reminders of how things change over time and the many conditions under which humans have lived here. People were already living here at the close of the last Ice Age, 10,000 or more years ago, when the climate was several degrees cooler than it is today. Sonoma Mountain probably supported trees and plants that are now more common farther north in California and the Pacific Northwest.

The mountain’s time magic works on a smaller scale too. Hike up the mountain in April and you’ll find yourself walking back the season as you ascend. By that time, wildflowers like buttercup, paintbrush, and hound’s tongue are already faded and going to seed lower down. But high up they’re still brightly colored and in full bloom. Modest as it is, Sonoma Mountain’s elevation makes the difference. Following the laws of physics, the air temperature drops about 3.5 degrees (all temperatures in this article are in Fahrenheit) for every thousand feet of elevation, so the upper mountain tends to be six or seven degrees cooler than nearby valleys (days of summer fog are an exception – Petaluma can be swathed in bone-chilling gray while the mountain’s summit is blisteringly hot and sunny).

Just a few years ago, climate change’s more serious effects were predicted to be decades away. But we’re already living in the world of heat waves and megafires I feared my grandkids might face much later in this century. It’s a sobering time, and this is the effect of just two degrees of warming. By 2050, Santa Rosa is expected to be another two degrees warmer. By 2100, there’s a good chance our regional climate will average nine degrees higher than in 2000. Of course, the future remains unknown. But even the most optimistic scenarios, with high levels of human cooperation and technological advancement, predict the temperature will rise by three or four degrees over the next 80 years.

For comparison, it took 10,000 years after the end of the last Ice Age for the climate to warm seven degrees. Things are heating up much faster now. One way to imagine Sonoma Mountain’s future is to identify a “climate analog” – a place where the current climate closely matches what is projected for the future. Depending on the model used and on how things play out, Sonoma Mountain’s climate analog for 2050 could be as distant as the mountains of San Diego County, or as close as the San Jose/Watsonville area.

What might Sonoma Mountain look like in the future?

Sonoma Mountain supports a wide range of habitats, from grassland to forests with various combinations of oak, madrone, bay, Douglas fir, redwood, and other species. These habitats, in turn, support the mountain’s diverse and abundant wildlife. The vegetation patterns we see today were created by many complex factors. No one knows exactly how climate change will alter these patterns, but modeling changes in these factors offers a glimpse of the mountain’s possible futures.

In 2010, Sonoma County’s Pepperwood Preserve and U.C. Berkeley’s Department of Integrative Biology formed the Terrestrial Biodiversity Climate Change Consortium (TBC3) to investigate changes in the natural world. In one study, which included the bioregion of Sonoma Mountain, they modeled how four future scenarios – warmer/ dryer; warmer/wetter; hotter/dryer; and hotter/wetter – might affect habitats on the mountain.

The changes may happen quite gradually; established trees can survive a long time even when conditions grow less ideal. On the other hand, major disturbances, like wildfire or severe drought, could speed up the process. Over time, oak woodlands may convert to California bay forest; the mountain’s extensive grasslands may shift to shrublands of chamise, manzanita and coyote bush; and Oregon oaks will likely retreat upslope toward cooler, moister conditions. For a time, live oak, Douglas fir and redwood trees may hold their own.

Sonoma Mountain has a vital role to play in protecting biodiversity during the com- Climate change – from page 11

ing years. The mountain itself has a strong influence on local climate and resilience. Its rugged terrain encompasses cool, shady, north-facing slopes and canyons; hot, dry, south-facing ones; and everything in between. Cool, moist locations will serve as “climate refugia.” If conditions lower down become unsuitable for Oregon oaks, hound’s tongue, scarlet warriors, and other species, they should be able to hold on, for a while, higher on the mountain. The wildlife corridor not only offers a pathway for animals to adapt to seasonal change by moving; it also allows plants to do the same thing in the long term.

In the future, I can imagine families hiking up the mountain to see flowers that have disappeared from the valley. “I remember when these were all over the regional park,” a parent might say to their kids. “Now we have to climb up here just to see them.” There is some comfort in thinking of Sonoma Mountain as a refuge, a place where the natural world can find safekeeping amid the coming changes. But my deepest longing is that the human world will soon set itself on a path to net zero carbon emissions and allow us to slowly begin to turn the tide.

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