Lifestyles of High-Elevation Trees

Conifer trees in a mature, high-elevation forest. Conifers grow slowly and can live for hundreds of years. (Photo by Beth Cortright)

By Sanna Sevanto

Springtime in aspen and mixed-conifer forests brings many shades of green. On south-facing slopes, the dark shades of firs and spruces are contrasted by the bright, almost translucent green of the new leaves of aspens, while aspens on north facing slopes or in shady canyons might still have no leaves.

Firs and spruces, and also pines and junipers, belong to a group of plants called evergreen conifers or gymnosperms. Evergreen refers to the fact that they keep their leaves all year round. Conifer means that they carry their seeds in cones, and gymnosperm means that their seeds are bare, not enclosed in an ovary.

Aspens on the other hand, are deciduous angiosperms. Deciduous means that they drop their leaves every year, and angiosperm means that their seeds are covered. However, whether the seeds are covered or not is less relevant for the plant’s lifestyle than other differences that stem from these groupings.

All plants make their food in a process called photosynthesis where they take carbon dioxide from the air, and use sunlight and some water to produce sugars. This is the process that makes all the sugar we eat. To get the water up to the leaves, trees have developed a special tissue that we call wood. The young wood in the outer rings of the trees, below the bark, is called xylem, or sapwood, and can conduct water. The particular structure of this tissue determines how easy it is for the tree to get water to its leaves, and how fast it can grow.

Gymnosperms like spruces, pines, and firs, developed earlier in the evolutionary process than angiosperms like aspens. Gymnosperms existed for hundreds of millions of years before the dinosaurs, while angiosperms developed only just before dinosaurs went extinct. The wood of gymnosperms contains smaller tubes than the wood of angiosperms. Therefore, it is harder for gymnosperms to transport water from the soil to their leaves.

Mixed conifer trees growing in the shade of aspens. Eventually, the conifers will outgrow the aspens. (Photo by Craig Martin)

Gymnosperms also make sugars in their leaves at a slower rate than angiosperms, and consequently grow more slowly. When growing together with angiosperms, gymnosperms compensate for the slow growth rate by staying evergreen so that they can start photosynthesis as soon as air temperature rises above freezing even in the winter. They also can do photosynthesis at lower light levels than angiosperms. Therefore, you can see small spruce or fir saplings growing shaded under large trees, and slowly outgrowing aspens that need a lot of light.

Aspens, on the other hand, compete by growing tall very fast. This is made possible by the large water tubes in their wood, and the high photosynthesis rate their leaves can produce. But the fast growth rate comes with a cost. Their wood and leaf tissues are not as strong and sturdy as the wood and leaves of spruces and firs. Therefore, aspens don’t live as long as spruces and firs, and they have to drop their leaves every winter. The leaves wear out during the summer so much that they would not be functional next summer even if the plant tried to keep them. In the fall, aspens break down and pull the precious chlorophyll (the material that makes leaves green and is responsible for photosynthesis) back to their bark and roots for storage. As a result, the leaves turn yellow. In the spring, aspens use the stored chlorophyll components and sugars stored in their bark and roots to make the new leaves.

Because of the fast growth rate, aspens are one of the first trees to cover new openings in the forest, for example after a forest fire. Most of the aspen groves you see on the mountains cover old fire scars. 

Comparing the lifestyle of aspens and the conifers in our forests, aspens are like mice of the plant world: they grow and reproduce fast, cover new territory quickly, but also die quickly. Spruces and firs are like turtles, who live much longer, but move and grow slowly. This is all in relative terms of course! A typical age of dying aspen stems is over 100 years, while spruces and firs can easily live several hundred years.

But all is not quite as it seems. The aspen stems that you see in a grove are actually branches of the same tree growing from a very long-lived root system. It is said that Pando, an aspen grove in Utah, is among the oldest living organisms on Earth. This aspen tree covers an area of 106 acres and some estimates suggest it is over 80,000 years old.

Week 7, Day 3: Ponderosa Pines

Ponderosa pines are one of the most common trees found along the trails of Los Alamos and are an iconic tree of the West. (Photo by Craig Martin)

In this week of Take It Outside, we are exploring the forests of the Pajarito Plateau, from riverbank to mountaintop! Today, learn about the ponderosa pine, one of the most recognizable tree species in Western North America.

Blog Post:

PEEC volunteer Terry Foxx explores the beauty and resilience of ponderosa pine trees in today’s blog post. Read her post here.


Ponderosa pine cones are in ample supply on the Pajarito Plateau. Go on a walk to collect pine cones, and then paint them. You can arrange or connect your painted pine cones to make animals or art! Here is how to turn your pine cone collection into a snake!

If you don’t have pine cones where you live, painted dried sticks make great snakes too. Find one whose shape reminds you of a snake, peel off the bark, and paint patterns on it! Snakes often have patterns that help them camouflage into their environment or display bright colors to signal danger.

Pro Tip: Dried tree roots from dead plants make for extra squiggly-looking snakes.

Outdoor Challenge (Beginner):

Ponderosa pines are adapted to frequent fire. See if you can find some ponderosa pines, and look for the following fire adaptations:

  • Thick, fire-resistant bark
  • Puzzle-shaped bark flakes that easily exfoliate, carrying heat away from the tree
  • Tall trunks with few branches close to the ground, reducing the chance that heat reaches the needles at the top of the tree
  • New buds protected by thick scales and long needles

Can you find a tree with signs that it has survived a fire?

Outdoor Challenge (Advanced):

The ponderosa pine grows in community with several other species. Go outside and see if you can spot any signs of the following communities:

A female Acorn Woodpecker perched on a snag in Los Alamos. Do you see the small holes on the tree? Acorn Woodpeckers likely made them to store acorns! (Photo by Bob Walker)
  • Abert’s squirrels eat the seeds and inner bark of the ponderosa. You might find stripped pine cones that look a bit like chicken drumsticks lying on the ground. The squirrels also eat and distribute the spores of ectomycorrhizal fungi that grow in a symbiotic relationship with ponderosas: the fungus grows around the root tips of the tree, helping it to access nutrients in the soil. In exchange, the fungus gets sugars from the tree. The symbiosis between fungus and pine trees has been going on for 150 million years!
  • An Acorn Woodpecker’s favorite food is … acorns. Acorn-bearing gambel oaks tend to grow in the same areas as ponderosa pines, and the woodpeckers harvest acorns from the oaks in late summer and store the acorns for the rest of the year in standing dead ponderosa pines. These trees are called granaries, and can contain up to 50,000 acorns! You’ll see dead trees pocked with acorn-sized holes, and guarded by family groups of Acorn Woodpeckers.

Other Resources:

Share Your Experience:

Tell us about the trees and forested areas near you! We’d love to see your photos, too. Please send them to or share them on Facebook or Instagram with the hashtag #peectakeitoutside.

Join us tomorrow to explore aspen-mixed conifer forests!

The Rugged Ponderosa Pine

The history grove at Valles Caldera National Preserve serves as a reminder of how our forests looked before fire suppression. (Photo by Terry Foxx)

By Terry Foxx

One of my favorite tree species is the lofty ponderosa pine (Pinus ponderosa) with its straight trunk, vanilla and butterscotch scented bark, and branches with needle-like leaves that hover above my head. The trees appear to me to be like a person, standing tall and stately, with a straight trunk and branches reaching out like arms beckoning a hug.

Standing beneath a tree, I tip my head back to see what is living or foraging in the treetop. To my delight, I may observe an Abert’s squirrel chattering, a woodpecker searching for insects, or nuthatches hopping down the tree headfirst.

One of my favorite places in the Jemez Mountains is the history grove in the Valles Caldera National Preserve. The widely spaced ponderosas with the grassy understory are a reminder of how our forests looked before fire suppression. They were a mosaic of open stands, interspersed with meadows.

In the history grove, the ponderosa pines stand as witnesses to the past. The oval wounds in the bark are bark-peel trees from when Native Americans exfoliated sections of bark in the spring to obtain the sweet inner cambium for food. The trees marked with crosses remind us of sheepherders and their lonely existence. And the triangular wounds at the base of the tree, called “cat faces,” tell the story of fire and survival. Many of the large trees in the history grove are 200 to 300 years old. Within their growth rings are stories of fire, injuries, and people.

A Pygmy Nuthatch perched on the side of a ponderosa. (Photo by Sally King/NPS)

Loggers and ranchers called older and larger trees “yellow pine” because of the yellowish-orange puzzle-like bark and the young, darker trees “blackjacks.” It takes a tree about 40 years for the bark to change from black to yellow. The bark patterns also become furrowed and more puzzle-like as the tree ages. The thick bark protects the tree from low-intensity or surface forest fires. However, years of fire suppression have created conditions for hot-burning crown fires that kill the trees. 

Each natural growing tree is a miracle of nature. It takes many years before a ponderosa pine begins to produce cones that hold the seeds. Every three to five years the tree produces numerous cones. But from the countless seeds produced, only a few seeds sprout and grow. That tiny germinated tree must survive fires, insects, and competition for resources. I am amazed at the ruggedness of the species when I see a tree growing in harsh environments like rocky cliffs, dry canyons, and steep slopes. A mature tree represents resilience and survival!

In the past 20 years, the Cerro Grande and Las Conchas fires have burned over 200,000 acres of forest. The first two weeks of May is the twentieth anniversary of the Cerro Grande Fire of 2000, an event that changed the physical and emotional landscape of the community.

My upcoming book, Resilience and Renewal, a Landscape and Community Twenty Years After, will soon be published by the Los Alamos Historical Society in honor of the twentieth anniversary of the Cerro Grande Fire and its impacts on our community. When the museum opens, they will have a display entitled “Resilience and Recovery.” In the meantime, you can explore this exhibit online.

Week 2, Day 1: Trees Budding

These lambs at Los Luceros Historic Site want to say “Happy spring!” Learn more about Los Luceros here.

Welcome to week two of Take It Outside! This week, we are exploring the signs of spring. We are starting off the week by taking a closer look at budding trees.

We loved hearing your stories during week one! Check out some of our favorite quotes, pictures, and drawings from the week. Please continue to share your experiences with us!

If you haven’t already, please share your feedback on week one of Take It Outside by filling out this evaluation form.

Upcoming Event:

Join Jean Dewart of the Los Alamos Mountaineers tomorrow (Tuesday, March 24) at 7 PM for a live streamed talk! She will be speaking about visiting Churchill, Manitoba, Canada — the “Polar Bear Capital of the World.” Hear about highlights from her trip, see her polar bear pictures, and more at this virtual event. Learn more and find out how to join the livestream here.

Blog Post:

Arborist Chris Michel shares what’s going on with fruit trees as winter turns to spring. Learn why fruit trees flower in today’s blog post.


Trees are beginning to blossom at Los Luceros Historic Site! (Photo by Carly Stewart)

Make a nature journal to keep track of the changes you see throughout the spring. This is a great way to combine art, science, and written language. You can use an old or new notebook, or pieces of looseleaf paper folded in half and bound with string. Make a sturdy cover and decorate it with a collage of cut-out pictures from magazines, rubbings of leaves or other natural items, or your own drawings.

Here are some other journal ideas to experiment with:

A multimedia paper bag journal appropriate for kids who like to collect, and even for the youngest children. Instead of the four seasons, make a page for each day of this week of Take It Outside.

For adults and students, check out some pages from the nature journals of John Muir Laws. Notice how he combines sketches and notes, and includes questions and connections to extend his observations.

Outdoor Challenge (Beginner):

Go outside for a Signs of Spring scavenger hunt. Here’s our version. Make your own scavenger hunt using our ideas or yours, and see how many of these signs you can find today. Draw your favorite item in your nature journal.

Outdoor Challenge (Advanced):

Find a tree or bush in your neighborhood and monitor how it changes every day this week. Take photos or sketch its branches or leaves every day, and note what wildlife visits it. Start a nature journal to record your observations, and share your journaling tips with us.

Other Resources:

  • John Muir Laws has made his book, How to Teach Nature Journaling, available as a free download to support teachers and parents during the COVID-19 closures.
  • Are you starting to think about your garden as spring begins? Check out the Los Alamos Cooperative Extension Service page for lots of helpful hints about gardening in our climate. Their office is still answering questions by phone at (505) 662-2656 or by email at

Share Your Experience:

Tell us what signs of spring you notice this week! We’d love to see your photos, too. Please send them to or share them on Facebook or Instagram with the hashtag #peectakeitoutside.

Join us tomorrow to explore the sounds and smells of spring!

What Makes Fruit Trees Flower?

A peach tree blooming in White Rock last year. (Photo by Chris Michel)

By Chris Michel
ISA Certified Arborist, CM ArborCare

Fruit trees will be flowering soon. Apricots, peaches, and cherries should soon be showing their full glory, followed closely by pears and plums. Last, but not least, are our dear apples. We get to experience their beauty for a few weeks every year, but have you ever wondered how the tree decides when to flower? And what has to happen for these flowers to turn into fruit that can be enjoyed in the summer and fall?

Fruit trees begin their flowering process in the winter, while dormant. They require a certain amount of cold dormancy before the flowering process can begin in the spring. This exposure to cold temperatures is called vernalization and can be recorded by counting “chill hours”.

Flowering Adams Crabapple tree in the Los Alamos Master Gardeners’ Demonstration Garden. (Photo by Bob Walker)

Chill hours are the amount of time the trees endure temperatures between 32˚F and 45˚F. Based on the tree species they need to accumulate a certain number of chill hours before they begin to come out of dormancy. After the tree has chilled out for the winter it will need a certain number of warmer days before the flowering process begins. This is also species dependent and is why we have different types of fruit trees flowering at different times in the spring.

When the tree begins flowering it sends energy stored in the roots up through the branches to make the flowers grow. This is reserve energy that it has been holding onto all winter. It is also energy that the tree will not get back until it leaves out fully and can begin photosynthesis.

The tree does not gain any energy from the flowers, they are only there to attract pollinators and hopefully produce fruit. While some trees can be pollinated by wind, most fruit trees require bees or other insects to spread the pollen from flower to flower.

Apricots, peaches and sour cherries are self-pollinating, meaning they do not need another tree to pollinate. Most apples, pears, plums and sweet cherries will need another variety of the same type of tree to cross pollinate and get fruit. Historically, but not recently, New Mexico often gets a late freeze in the middle of spring which can eliminate the fruit crop from early blooming trees such as apricots.

Celebrate Arbor Day by having a new fruit tree planted on your property. CM ArborCare is collaborating with Petree Nursery and Garden Center to plant trees with local youth to honor National Arbor Day on April 24, 2020. We will be planting trees in Los Alamos and White Rock on this day. Fruit trees and ornamentals are available at discounted rates with this program. Call 500-4682 or visit for more details.

Why Do Leaves Change Color in Autumn? by Terry Foxx

As September begins, there are little hints of fall. The air temperature cools, and a leaf here and there begins to turn yellow, red, orange, or purple. By October, the mountain shimmers with the gold of the aspen. Although we don’t have a great variety of deciduous trees with leaves that transition in the fall, smatterings of different colors can be seen across the landscape.

Read more Why Do Leaves Change Color in Autumn? by Terry Foxx