Trees have a remarkable urge to live. You can see it in the way they endure and how they resist the forces of opposition. They live long and die slow.

We have two aging mulberry trees on a hill in our pasture, and they have been dying for years. They are probably 95 percent dead now but they are still alive. This year, once again, they sprouted new leaves on a shrinking cluster of branches.

If those trees were growing in town, they would have been condemned and cut down a long time ago. Out here in the country, I am free to enjoy their remarkable uniqueness. Their tenacity inspires me, and even their dead limbs have a certain charm and beauty.

Mulberry trees live an average of 75 years, and our trees appear to be at least that old judging by their size. One of them has a trunk 21 inches in diameter. They have probably been growing on that hill since sometime in the 1940s.

How they got there is a mystery. Why were they growing on top of the hill instead of down in the draw where moisture is more abundant? How did they survive the cycles of drought and the browsing of cattle? And why were they the only trees we found growing in the pasture outside of the wooded area along the creek?

Those mulberry trees have apparently overcome much, but the true masters of tenacity are the Bristlecone Pines of the Great Basin. Growing near the timber line, they live in a condition of limited resources, battering winds and the frigid chill of a long harsh winter. And yet, some of those trees are over 5000 years old.

Some Bristlecones are hanging on to life by little more than a thread, the thread being a narrow strip of bark. Weathering has destroyed most of the bark in the older trees, exposing the bright red and orange color of the dead wood underneath. Bark protects the cambium, that thin lifeline of living cells underneath the bark.

One 3,000-year-old Bristlecone on Mt. Wheeler in the Great Basin National Park has a trunk with only a six-inch band of bark running up the tree. Yet, that tree is still alive and growing.

Once a tree has sprouted and taken root, it is committed to that place. It has no choice but to endure whatever may fall upon it, for tens, hundreds and sometimes thousands of years. Unfortunately, the worst threat comes from man himself.

Humans are ambivalent about trees. Much of the time we like them. We harvest the lumber, eat the fruit and enjoy the shade, but as soon as they become inconvenient or stand in the way of progress, our attitude changes.

We once lived in a tree house, sort of. The house was not in a tree, but the tree was making its way slowly into the house. It was an old house, and there was a huge burr oak growing by the front porch. When the tree grew big enough to make contact with the house, a previous occupant cut away part of the porch to make room for the tree.

The very thought of it still astonishes me. Who cuts down part of the house to make room for a tree? It smacks of a mythical heroism, the sort of thing that people long ago used to write stories about.

There are two pitfalls in describing a tree: one is to invest it with human traits, the other is to minimize or ignore its true nature. Tenacity seems to fit into a middle ground.

Unlike a stone, trees are invested with a life force. They persist. They engage with their environment and resist the physical powers of nature. They have the ability to continue in a course of action, not only in spite of opposition, but because of it.

Trees have what biologists call reaction wood. It’s what makes the limbs of a tree grow upward, against the pull of gravity. Stones fall, but trees reach for the sky. Perhaps it is not too much to think that, in persisting, they are also reaching for the future.

Feeling the wonder of that life force doesn’t humanize the tree. It humanizes us.

Richard Weber is a nature enthusiast living in Ellis County. rweber@gbta.net