Bobcat Fire Burn Scar Update: 295 Days Post-Fire
Updated: Jul 12, 2021
(Disclaimer: I am not a bonanist; I'm a pastoralist. So although I'm doing my best to document what's happening in our burn scar, I might get some things wrong. I welcome corrections!)
Goats foraging amongst piñon pines and Joshua trees in 2018. Sadly this especially beautiful area of the forest was lost in the fire.
I last wrote about our Joshua trees way back in November 2020 for Issue #4 of The Obligate Resprouter. At the time we had several blackened stands to the southwest of the barn already showing some green resprouting from their branches. I’ve since been checking up on those trees frequently and providing updates on the ranch’s social media accounts.
Resprouting and falling over simultaneously.
Most of the trees that had vigorous green growth on their branches in the months following the fire have since died. Last night I took a walk in the area and only found 2 branches still making an effort, and one was on a young trunk leaning heavily, its damaged root crown unable to hold up the weight of the new growth. I suspect that these too will give up soon.
But in May I started to notice new sprouts coming up near some of these dead or dying stands. The goats had been in the area nibbling on post-fire annuals like pussypaws, but after seeing the seedlings I started chasing the goats out of the area when their GPS tracker alerted me to their presence. Our technique of chasing the goats out of the burn scar is about as effective as Jack’s buck apron, which is to say it’s mostly effective but not entirely. I can see that there have been some experimental bites taken from the tips of leaves here and there, but these experiments must have been unsuccessful, because there are very few. This is good news and also makes sense. The leaves of Joshua tree sprouts are no more tender and no less pointy than the leaves of mature plants, which the goats don’t eat. In the burn scar, they prefer to eat the fibrous parts of the dead plants. My conclusion from these observations is that Joshua tree seedlings in general are safe from foraging pressure from both goats and deer. The only part of the living plant they find palatable is the blossom, which are only rarely low enough to be reached.
These beauties, spared by the fire, might have come from seed, since there aren't any mature JTs in the immediate area.
There are 3 different ways that Joshua trees can repopulate after fire. If any seeds survive the burn, they can sprout. There is no literature about the effects of fire on Joshua tree seeds in the ground, but lab experiments have shown germination rates increase with temperature treatment. I’m not finding any sprouts more than a few feet from the burned stands. If new sprouts were coming from seeds, I’d expect to see clumps of seedlings coming up away from the mature trees, for example out of wood rat dens. But I’m not. I’m guessing that seed survival in the soil is very low.
Possible resprouting from root crown, photographed yesterday.
They can also resprout from their root crowns in response to trunk damage, including from fire. I have observed multiple sprouts coming up directly from the base of some burned trunks. Whether or not this resprouting occurs depends on many factors including the severity of the fire and age of the tree. Reports from several test sites indicate that resprouting is most common on mid-sized trees. I haven’t specifically counted yet, but it looks like about 1 out of 15 or 20 trunks show sprouting at the base, and in each case, there are 3 – 5 sprouts clustered together.
Possible resprouting from rhizomes, photographed in May.
The third way that Joshua trees can regrow after fire is via rhizome production and clonal growth. Not all Joshua trees produce rhizomes, but it’s more common at higher elevations. I think this is the primary pre-fire reproduction mechanism here at 5200 feet, as evidenced by the huge round rooms formed in the interior of the largest Joshua trees, where our goat Opal tries to have her kids if I don’t get her into a kidding pen early enough. It is suspected that montane conditions including cold temperatures, high winds and heavy snowfall limit aerial development, thereby encouraging growth underground. It has also been suggested that fire stimulates rhizome production. Rhizomes spread out from the base 2 or 3 feet and then send up sprouts, and I’ve observed a few sprouts matching this description in the burn scar.
View from inside a JT "room" about 10 feet long and 6 feet wide, created over time by clonal growth. The original tree that must have occupied the center is long gone, and the large trees in the circle comprising the walls of the room must be over 100 years old. Along with the giant piñons like Big Mama, these rooms provide evidence that the ranch hadn't burned for a very long time before the Bobcat Fire.
Given the shrinking range of the Joshua tree, I’m thrilled to see these sprouts. Most of the existing studies of post-disturbance Joshua tree population density are from low elevation sites in the Mojave Desert, where rhizome production is probably rare. In those cases, medium term population density is significantly reduced as a result of the disturbance. It’s possible that recovery at high elevation sites is more encouraging, but there’s really no reason to believe that the fire will result in more Joshua trees as in the case of, for example, flannelbush or spiny poppy, whose long-lived seeds survive fire and germinate in response. If 100 joshua trees are replaced by 50 new ones, it would be a significant improvement over the 10 – 20% repopulation typical at lower elevations.
This baby was probably 30-40 years old when it bloomed for the first time in the spring before the fire. Sadly this area was burned and this tree didn't make it.
Joshua tree seedlings grow about 3” per year in the first ten years, and then at about half that rate once they start branching. Based on this, these seedlings might reach 15 feet, a typical height in the pre-burn stand, in about 100 years. But in 100 years it’s unclear if this location will still be suitable for their survival. Increasing atmospheric CO2 causes a reduction in the freezing tolerance of Joshua trees. This threat, combined with increasing fire frequency and severity, is why the Joshua tree is temporarily protected by the Endangered Species Act while the petition is in review. I’ve written about the gift the fire has been to the land in many respects, but for Joshua trees, fire doesn’t do any favors.
Exposed root crown of a large toppled tree in the burn scar.
I’ll be watching these little guys and documenting their growth for the next 30-40 years if luck graces both my health and theirs. Then, someone else will have to take over the job.
The information about Joshua tree plant reproduction and fire effects, with the exception of my personal observations, is from the USFS Fire Effects Information System listing.
The largest JTs on the property grow on the hillside between Big Pines Hwy and Lake Caldwell. Thankfully these were spared by the fire.
You can see more of my observations along with those of others in this part of the Bobcat Fire burn scar by searching zip code 93563 at https://www.inaturalist.org.