[Geezer (OP)]

It's high-summer in the Selkirk mountains. We had an unusually wet June, and the trees seem to be loving it. The tops of the fir trees are actually more yellow than green.

Why is that?

[CliffordK]

Didn't you ask this question last year?

http://www.thenakedscientists.com/forum/index.php?topic=39913.0

[Geezer (OP)]

Yes, but (obviously) I still didn't get a satisfactory answer 

[Don_1]

Apart from the answer Clifford gave you last year, if the ground has become too wet and is not draining very well, this can cause a yellowing of leaves. You may see this in any plant which is getting too much water.

Looking at our pelargoniums, they have been suffering from too much water and soil which cannot drain fast enough. These sun loving plants we put in because they are quite resistant to drought.

Since drought is the one thing we haven't seen so far this year, many leaves have turned yellow. It could be that the soil in the US Selkirk Mountains became waterlogged. In which case, perhaps you should be thankful, since the middle states are burning to a crisp.

Spare a thought for those farmers who have seen their crops wither and die in the relentless burning sun.

[Geezer (OP)]

Thanks Don.

I think Clifford probably nailed it last year (I may have to change my handle to Señor Moment).

Yes, things are pretty grim in large chunks of the US. We have been spared (this time) but it's always a worry when you are surrounded by honking great pines and firs. Officially, this is rain forest, but that does not mean it can't all go up in smoke like it did 100 years ago. http://en.wikipedia.org/wiki/Great_Fire_of_1910