A tale of two fires

In the last few years there have been two small fires on the front side of Cold Spring trail.

The first was the Cold Fire which burned on 6 Nov 2012 and was out by nightfall. It covered about 1 hectare. This fire burned at roughly 600 meters above sea-level.

The second was the Gibraltar Fire which started on 29 Oct. 2015 and was said to be fully contained on 3 Nov 2015. This was a bit bigger at about 10 flat hectares. This fire burned at roughly 950 meters above sea-level.

Both fires have a (roughly) west-facing hillside which I have watched recover.

I suspect that there are two significant differences in the way these slopes have recovered. The first is elevation (which affects what species can grow there) and the second is drought.

Both years were dry years, with only about  half to two-thirds the average rainfall, but in 2013 there was a relative abundance of rain in November and December, while in 2016 there had already been 4 years of drought and almost no rain fell in the fall.
RainYear2013

RainYear2016So after the Cold Fire there was moisture in the soil and forbs started growing in December. After the Gibraltar Fire there was no moisture and nothing grew until mid January.

Fires-Dec

In early January not much has changed. The Cold Fire had small, unidentifiable forbs, while the Gibraltar fire had nothing

Fires-Jan

In mid February the Cold Fire is lush, the hillside is covered with blooming Marah (wild cucumber) vines. The Gibraltar Fire also has Marah but only in patches, they do not cover the area the way they did below. There are also other small forbs. (the Gibraltar hillside is is the same as before, just seen from a different angle — it takes a while to figure what what views are best).

Fires-Feb

In March in the Cold Fire the Marah has stopped booming and been replaced by Calystegia macrostegia (Coastal Morning Glory). While in the Gibraltar Fire things look much as they did in February; the Marah continues to bloom, there are a few, very small, Calystegia purpurata (Pacific Morning Glory) vines, and some of the forbs have become identifiable as Phacelia and Eschscholzia (poppies), but only Marah is blooming.

Fires-Mar

In April the Cold Fire is at its peak with morning glory, phacelias, popcorn flower growing in lush abundance. But the Gibraltar Fire looks much as it did in March, except that the Marah has stopped blooming there too.

Fires-Apr

May brings drought to the Cold Fire, almost everything appears dead, though a few Phacelia grandiflora continue to bloom. While the Gibraltar Fire is lush in its turn. Phacelia distans, P. grandiflora, P. brachyloba, Emmenanthe pendulifora, Eschscholzia california, Calystegia purpurata are all in bloom.

Fires-May

In spite of the similarity in the fires, burning at approximately the same time in the calendar year, in close proximity, on the same trail, on the same side of the mountain, the first seven months have been very different.

Clearly the early rains in 2013 made for an early start in the Cold Fire, and then the subsequent drought dried everything up. While in the Gibraltar Fire the early drought meant nothing could start until much later, but the rains in January and March meant that plants could continue growing into May.

But there are other differences not easily explained by weather. I suspect some of the difference comes from the different behavior of the two Morning Glories. C. macrostegia was already taking over from Marah as those plants faded, but C. purpurata still is only in small patches. It has grown far more slowly, and spread far less. This might also be weather related, or altitude related, but in the White Fire along Aliso Trail C. purpurata was not as vigorous as C. macrostegia in the Cold Fire (though more vigorous than C. purpurata in the Gibraltar Fire). So I suspect that this elevation induced species difference is partly to blame.

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