Park staff in southern Utah noticed something wrong with the landscape: some junipers, normally dark green against red rock, had turned orange. The trees were dying, in one of the driest periods in 1,800 years. An earlier drought, in 2002–2003, had already killed trees in the area's parks, and between them the two droughts took trees that had stood for centuries.
Sunrise over The Needles. Photo by Emily Ogden, National Park Service
That raised hard questions. Will it happen again? Could pinyon and juniper elsewhere be hit? Which other plant communities might change, where and when — and what can managers do? Scientists with the NPS Northern Colorado Plateau Network turned to satellite records to find out, starting with Canyonlands National Park.
Dying junipers in southern Utah raised the question of whether the same could happen elsewhere on the northern Colorado Plateau. Photo by D. Witwicki, National Park Service
Watching plants from orbit
Satellite images taken over years show:
- Phenology — the timing of growth: when the land turns green in spring (greenup) and brown in fall (browndown);
- Production — how much plants grow.
Linking both to climate reveals how sensitive each plant community is to weather — and, from climate projections, what may be coming. The team tracked 18 vegetation groups in and near the park from 2000 to 2019, from Douglas-fir and ponderosa pine to blackbrush, pinyon-juniper, grasslands, riparian areas and sparsely vegetated rock.
The vegetation groups analyzed at Canyonlands. Image from the National Park Service
What changed, 2000–2019
A longer growing season. On average, growth began 12.6 days earlier and ended 11.2 days later — a season 23.8 days longer.
More growth. Production trended up in 58% of the area studied, and down in only a small share. The biggest areas of increase were pinyon-juniper (44% of the study area) and sparsely vegetated land (7.6%). No group showed a downward trend in growing-season production.
Why? The Southwest has been in a long drought for 20–30 years, but it has wetter spells. 2000–2003 were among the driest years between 1980 and 2019, so the study began near a record low in precipitation; as rain recovered, plants grew more. That explains the gains.
A wet spring fills sandstone potholes at Canyonlands. Photo by Amy Washuta, National Park Service
Looking back to 1980, precipitation and other water measures have peaked in the middle of each decade. If that cycle holds, it could help managers time restoration projects that need several years of low drought stress for seeds to sprout and take hold.
What drives growth
- Annual production tracked precipitation and soil moisture most closely; two to three years of soil moisture was the best predictor.
- Douglas-fir, mixed montane shrubland and disturbed areas needed the most precipitation to keep producing; water, alkaline wet areas and ponderosa pine needed the least.
- The start of the season depended mainly on growing degree days and precipitation.
Most sensitive, most tolerant
Climate sensitivity is how much a plant community changes for a given change in climate — key to judging its vulnerability. Drought tolerance is how little water it needs.
| Most | Least | |
|---|---|---|
| Sensitive to precipitation | alkaline wet, water, wet shrubland, C3/C4 grassland, riparian | pinyon-juniper, geology, mixed montane shrubland, Douglas-fir |
| Drought-tolerant | water, alkaline wet, ponderosa pine, dry wash, sparsely vegetated | juniper, disturbed areas, mixed montane shrubland, Douglas-fir |
Wet shrubland, C3/C4 grassland and annual exotic grassland were the most sensitive to water deficit and drought. If the land dries, the area suited to drought-tolerant plants will likely grow, and room for the rest will shrink.
How strongly vegetation responds to precipitation; areas not shaded purple were more sensitive. Image from the National Park Service
Vegetation in purple areas is less drought-tolerant. Image from the National Park Service
Change is coming
Even these findings can't say exactly how Canyonlands' vegetation will change. But the junipers' death was caused by acute drought stress — a surprise, since junipers are not very sensitive to year-to-year rainfall — and under both best- and worst-case scenarios, the park is projected to become more arid.
Two recently dead pinyon pines near a long-term monitoring plot at Canyonlands. Photo by Amy Washuta, National Park Service
Projected soil moisture under best- and worst-case scenarios. Image from the National Park Service
The graph tracks soil moisture in the top meter at one pinyon-juniper patch in the middle of the park, against its pivot point — the level of drought stress a vegetation type can take and still persist. Below it, growth and survival suffer.
| Scenario | Soil moisture | Likely result |
|---|---|---|
| Warm and wet (best case) | reaches the historical pivot point only occasionally | not enough for today's vegetation there — probably a shift to a different plant community |
| Warm and dry (worst case) | lower still in most years | more intense, longer drought stress; the shift comes sooner, and toward more dry-adapted plants |
Either way, the time to plan is now.
Planning for change
Restoration succeeds more often when growing conditions favor the plants being established. Image from the National Park Service
- Climate Smart Conservation is the Park Service's roadmap for managing resources as the climate changes. It helps managers decide whether to resist, accept or direct vegetation change — and a key input is exactly what this study supplies: how sensitive and vulnerable each resource is.
- Timing restoration. Restoration is essential but costly and slow. Knowing how plant communities will likely respond to projected conditions lets managers choose the seed mix and timing that give desirable, climate-ready species the best chance to sprout and take hold.
The same data can help managers anticipate knock-on effects — on pollinators, or on wildlife movement — and answer questions such as:
- Where are the most and least sensitive plant communities, and when might they face conditions that force change?
- Will forests reach drought stress or transition sooner than shrublands?
- Which soils buffer drought best, and where are they?
- After wildfire or extreme drought, will the climate still support the original vegetation?
- Do sensitive animal species depend on climate-sensitive plant communities?
Plants shape a park's ecology and its views, and they respond when weather and climate change. Knowing where, when, what and why change may come lets managers plan for it.
Sources
Based on "Helping Managers Plan for Climate Change with Remote Sensing at Canyonlands National Park," Northern Colorado Plateau Network, National Park Service, summarizing D. Thoma, Landscape phenology, vegetation condition, and relations with climate at Canyonlands National Park, 2000–2019 (2023); a work of the United States government in the public domain. The article dates the juniper die-off to both 2018 and fall 2019, and gives the area of declining production as both 2% and 1.5%, so neither figure is given here; one picture's description is corrected to match its caption.
In these publicationsCanyonlands National Park
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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