Pinyon-juniper forests are hearty, drought-tolerant and ubiquitous across the West.
But climate change has put immense stress on the trees.
KNAU’s Adrian Skabelund spoke with researcher Kyle Rodman with Northern Arizona University’s Ecological Restoration Institute in a pinyon-juniper forest near Flagstaff.
KYLE RODMAN: What we're seeing generally is that there was a huge amount of dieback and die off in the early 2000s, particularly of pinyon pine. Eighty percent, or four out of five trees, have died since the late 90s in a lot of these places.
And because it's happened gradually over a couple of decades, if you're not intimately familiar with that place, you might not recognize that that change is happening. But in a lot of cases, it is.
The way we think about it, we have this term ‘background mortality,’ which is essentially: what is the normal rate of trees dying on the landscape if processes are, more or less, happening as they should.
And that number can be anywhere from zero to 1%, give or take. [That’s] a normal rate of background tree mortality. And obviously, you're going to have more in dry years and wet years, it fluctuates over time.
But that's what we look for is something in that range. And in a lot of places we were seeing around double that.
ADRIAN SKABELUND: So I think a lot of folks would imagine that pinyon pine and juniper would be maybe best adapted to prolonged periods of drought. Is that accurate, or do these findings challenge the layman's assumption about that?
RODMAN: Yeah, well, that's certainly true that pinyon and juniper both are very drought-tolerant, or at least tolerant of warm temperatures and dry conditions, more so than many other tree species in the West.
But the conditions we're seeing now, particularly over the past two decades or so, are much warmer and drier than the conditions that [the trees are] used to in those places. We're just talking about warming temperatures over the past century or so things have gone up by a couple of degrees.
SKABELUND: And it also sounds like those two species were impacted differently or had different rates of mortality. Can you speak to that?
RODMAN: Yeah, absolutely. So you know, there are a couple things going on there.
Pinyon pine in general has been a lot more susceptible to drought mortality over the past two decades.
We're definitely seeing mortality of juniper, particularly smaller juniper like seedlings. But pinyon pine has been a lot more susceptible.
SKABELUND: So are these classic pinyon-juniper forests just becoming largely just juniper forests?
RODMAN: Yeah, definitely. Around Flagstaff, we're definitely seeing a shift towards juniper dominance in a lot of places where pinyon and juniper used to co-dominate.
And I think that's generally true in places in New Mexico as well, where in some places 90% or more of the pinyon pine died in the early 2000s, but a lot of the juniper are still hanging out and surviving.
SKABELUND: Does this tell us anything, or give us any suggestions, as to what the next three decades will look like for these ecosystems and these kinds of woodlands?
RODMAN: I would say it definitely does. It's not like these things are going to disappear all at once right away. But they do seem to be on a trajectory of kind of a slow decline over several decades.
It's kind of a depressing thing to say, but I heard somebody put it this way recently, and I think it makes sense: The last 30 years might be the best climate that we'll see for the rest of our lives.
So not to get all doom and gloom, but these are kind of an indicator of where things are headed.
What we've seen over the past couple decades, which have been extremely warm and dry, it's likely to get more so.
So in my mind, as somebody that has a background in forestry and thinks a lot about what we can do about it in a forest management context, trying to move these [tree species] around to places that we think might be suitable for them moving forward.
We can be stewards of the land too, right, we can be actively involved in that process because we're causing a lot of the damage to begin with.
