[Tagging] landcover=trees definition

johnw johnw at mac.com
Thu Aug 20 07:35:25 UTC 2015


> On Aug 20, 2015, at 7:36 AM, Martin Koppenhoefer <dieterdreist at gmail.com> wrote:
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> sent from a phone
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>> Am 18.08.2015 um 22:54 schrieb John Willis <johnw at mac.com>:
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>> What if its grass along a (maintained) river embankment, but roped off so no one can walk on it, as it is not a park?
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> meadow? what's the use there? slow down the erosion?

I have lived in the extremes of both kinds of erosion control. 

In this instance, the grass is for erosion control during typhoons, and native weed control / beautification the rest of the time. The weeds in Japan are the most invasive thing I have ever seen. They will be 20cm tall one week and 2m tall the next. I've seen Kudzu top a 25m Cedar tree, then branch out and cover the entire stand. It is wicked stuff - roads and houses disappear under it - and it is only one kind of weed.


In Japan, it is usually weed control - there is so much water, anything left alone will be full of weeds in a few weeks and impassible in a few months. Even asphalt will be gone in a few years, if untravelled. The rain-weed-snow cycle is amazingly difficult on everything. Only the motorways have full-time weed control - every other road gets "thinner" in places as weeds encroach up to a meter into the road in summer. On trunk roads. Always fun to have the de-facto cycle lane disappear into a green wall. 

Places where grasses cant grow quickly (lack of rain, like Southern California), erosion is a huge issue. "erosion runoff" - Rain runnoff full of eroded materials that drains from construction sites - is considered hazardous pollution in California (yes, just water with a lot of silt in it), and has to be managed with rolled hay tubes staked into slopes to stop the water flow. so there is a lot of "landscaping" that is merely for erosion control, but is only called upon 3-4 times a year - like the iceplant along California freeway slopes. It also works as wildfire control. The wildfires leave entire mountains bare of anything growing, so winter rain storms lead to massive erosion, silty runnoff, and landslides, which are all mitigated with temporary hay rolls and permanent walls and other structures. 

Desert washes are dry year-round, except for 1-2 storms. They can erode 4 meters of the riverbank per storm, as there is no plants in the sand. So there is a lot of "gravel filled net bags" or "rock-filled wire boxes" stacked up that make porous "slowing" walls  at diagonal angles to trap silt and facilitate a stable spot for plants to grow.  

Recently Interstate 10 in California was severed in one direction because a bridge was not adequately protected from erosion, and a flash flood surge caused the bridge to collapse. 

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>> What about the grass surrounding an airport (Narita's is well trimmed)?
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> likely part of the airport?

Yep. The Jet engines would rip anything else out of the ground, and would blow away exposed dirt. 

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>> What about the landscaping lawns that cover the front of large industrial facilities?
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> landuse =industrial?
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Yep, Part of the factory land.

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> in all these cases, landcover=grass could be added (or maybe remain the only tag), grass doesn't become a sensible value for landuse in any of these cases 

Yes, I agree landuse would be a poor choice, natural (strictly defined as a naturally occurring or naturally taken over) would be too, so landcover is a good option for all of these.  


Javbw


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