Tuesday, January 18, 2011

Do Trees REALLY Prevent Mudslides?

The rain keeps falling and the mud keeps sliding. 

It has been almost a year since I wrote an article for another of my blogs entitled, "Trees and Mudslides." It describes what we learned in Seattle during the mid-90s about what does, and does not, contribute to mudslides. Much of what we discovered observing the aftermath of many, many slides during that time ran completely contrary to what we believed and taught homeowners.

Unfortunately, it does not appear that this new information has come to the attention of very many people. So after a slide occurs, when people are upset and emotions are running high, there's a lot of arguing and finger-pointing that goes on about trees on slopes (among other things). Some people are angry because trees have been cut down. Some are angry because none were planted to hold the slope in the first place.

However, from what we know now, we can see that planting trees on a particular slope might have been a terrible choice and cutting down existing trees might have kept the slide from being far worse. Sometimes trees help and sometimes they don't. When you have all the information, you'll see that there are no easy answers.

If you live in an area on or near a slope, I highly recommend that you read this post. In it you will find links to the USGS survey and reports commissioned by the city of Seattle to investigate the causes of slides that occurred during the winter of 1996-7. Specific areas of the city are described in detail, which you may find very useful if you live in those areas or are considering living there.

Saturday, January 15, 2011

What the Heck is a Joshua Tree?

I just came back from a trip to Southern California, where a friend and I spent part of a day hiking and taking in the sights at Joshua Tree National Park. I grew up in California and have seen a lot of the Golden State, but this was my first visit to this particular park.

We entered the park at its southern edge, just off I-10. After driving for miles through typical barren dessert terrain, we began to see, here and there, small specimens of the famous Joshua Trees. They look to me like a cross between a palm and a dracaena.

As we drove further still, we began to see extraordinary rock formations and larger Joshua Trees.

We stopped to hike in the Hidden Valley area amid more stunning rock and mature trees.

Here you see four sizes of Joshua Trees silhouetted against the blue sky and rock.

Of course, Joshua Trees don't grow in Seattle, but plant people like me are curious. I wanted to know more about these trees after our day in the park. So I looked them up. As it happens, they are related to a plant that we see often in Seattle. The flower stalk in the photo below offers a hint.


Joshua Trees are in the Yucca family (Y. brevifolia) and they are related to those spiky plants that we see all over the city (Y. filimentosa) that sport 4-7' tall spikes of creamy white flowers in spring. Strange as it might seem, an echo of the dessert blooms right here in our own front yards.

Related post:

How Do You Say Yucca?