Treebeard's Stumper Answer
We had an unusual snow storm on March 15. We usually get some snow in the mountains behind Santa Barbara, but this storm dumped as much as 10 inches and completely covered the upper Santa Ynez Valley. There was even snow at Dunn Middle School in Los Olivos. I got to take my first ever snow day from work, but Ry and I spent most of it chain sawing a path through the broken trees along our road. What a mess. I made an album of snow pictures.
Snow at the Middle School was a fun surprise last week! It wasn't so much fun at my home on San Marcos Pass. We had seven inches of heavy snow on the ground by noon. Then the oak trees started to break under the weight. It sounded like artillery! Our house survived, but the woods are a mess. As the snow melted, I noticed California poppies near school and yellow buttercups in the mountains that went through the storm without damage. How can the snow snap the oak trees, yet leave these delicate wildflowers unharmed?
Storm damage in front of our house.
Note the widow-makers hanging from the tree.
Snow falls flake by flake, so it builds up around wildflowers and actually protects them. They don't have large surfaces, and their delicate stems bend easily to shake off any snow that accumulates. Trees are different. The oaks have rigid horizontal branches that collect large amounts of heavy snow. Try holding a weight out at arm's length for a full minute to appreciate the effect! Pines are more protected by their shape and didn't suffer as much damage. The forest will recover, but it will be different. I think of this as evolution in action.
The storm brought widow-makers for us, but it was a windfall for the tree trimmers. Our road is now cleared (at great expense), but the woods are still a tangle of fallen branches. The view from our house is changed. I'm worried about summer fires with all the ladder fuel on the ground that can carry fire up into the trees. I feel vulnerable and exposed. Check out my snow pictures to see why.
I filled a kitchen measuring cup with snow from our porch and let it melt: 500 ml of snow made about 100 ml of water. I have nothing to compare this to. We had big fluffy snowflakes, but they were not classic hexagons. Later in the day (after the trees broke), it turned to corn snow. There was no wind during our storm, which increased the damage since wind would help shake the snow from the trees.
I noticed that different kinds of trees respond to the snow event in different ways. These are first impressions. My trail into the woods needs a lot of work before I can do more research! The links are to my flora which is under construction and may not work yet. Visit CalFlora for more species info.
It's not surprising that pines and large-leafed deciduous trees with a pyramidal shape are dominant in the high mountains and further north. Regular snow storms could change the makeup of our forest surprisingly fast since the replacement trees are already here. This must be a reminder of past climates.
- The Coast Live Oaks (Quercus agrifolia) were the hardest hit, no doubt because of their broad stature and hard wood. Virtually every tree in the forest suffered some damage. It was interesting that all the trees began to break about the same time, suggesting that this is a simple matter of mechanical load. Most branches snapped clean and either fell or made a hinge that left a widow-maker high in the tree.
- Our native Coulter Pines (Pinus coulteri) came through the storm with little damage. Pine needles don't accumulate much snow and the flexible branches can bend under the weight to shake it off. The pyramidal shape allows the upper branches to clear the lower when they drop their load. Wind would help this process, though our storm was still. Be careful walking under pines with snow!
- Madrones (Arbutus menziesii) suffered some damage, especially near our house where they are in the open. Most trees survived intact. This surprised me at first since madrone wood is so hard and brittle. These beautiful trees also have larger leaves than the oaks. It's my guess that the individual leaves bend and drop their snow before damage occurs, whereas the smaller oak leaves overlap and collect more snow en masse. The surface area of a leaf is a function of size squared, but the snow accumulation is cubic. Slightly larger leaves collect much more snow individually, which can help the tree give before it is broken. Being able to give might be a better strategy than brute strength.
- Tanbark Oaks (Lithocarpus densiflora) came through the storm without much damage. They also have larger leaves than live oaks and a more pyramidal shape.
- Bay Trees (Umbellularia californica) and Willows (Salix sp.) are so flexible that whole trees were bent down to the ground across our road, but they didn't usually break. I discovered the hard way that bay trees spring up with tremendous force when cut free. This is pretty unnerving when working with a chain saw!
- Bigleaf Maples (Acer macrophyllum) and Western Sycamores (Platanus racemosa) are deciduous trees that didn't have their Spring leaves yet. They had no problems.
- Shrubs suffered most damage from falling oak branches. I did notice some snow damage on the Greenbark Ceanothus (Ceanothus spinosus), which has particularly hard and brittle wood.
We had a similar snow storm on San Marcos Pass about 20 years ago in 1981 (also late spring? also La Niña?) that did comparable damage. Our recent storm would have been more damaging to our trees without this previous storm. Old timers remember another heavy snow storm about 25 years before that. The oak woodland is still here, so maybe this is a natural pruning cycle. I hope it's not also part of a natural fire cycle.
I did an Alta Vista search on <"snow damage" and tree> and got some hits, but nothing definitive.
- The most interesting site I found is the The STORMS Project, "Silvicultural Techniques Offering Risk Minimising Strategies - Predicting damage to forests from wind, fire and snow." This site has a nice photo page and links to research abstracts, much of it from Sweden and Finland. A mechanistic model of storm damage to trees based on physics seems possible.
- There is a Tree Care FAQ with advice about how to deal with storm damage to trees at home.
- We've had interesting weather here in central California for the last few years! I have other stumpers about our local weather and natural history: Scarcity and Abundance (22 May 98), Pastures of Plenty (10 April 98), The Rain and the Wind (27 Feb 98), and Fall or Spring? (21 Nov 97). Also check out the About the Flora page at my treebeard.org server for more deep questions about the Santa Barbara flora.
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