“To improve is to change; to be perfect is to change often.” ― Winston S. Churchill

By DR. CAMERON BARROWS

My guess is that most people prefer stability in their world. Seeing the same species and abundance of plants, birds, and lizards each time you hike a trail might give a sense of healthy stability. Except nature isn’t stable. Every year is different, different rainfall patterns, different temperatures, different wildflowers, different pollinators, different weeds in my yard. Those year-to-year changes (except the non-native weeds in my yard) have fostered new species as individuals adapt to seemingly subtle differences in temperature and rainfall. If every year was a carbon copy of the years preceding and the years following, there would be fewer species, less biodiversity. Those relatively fine scale, year-to-year differences create more niches to fill with the abundance of species we know today.

At larger time scales the effects of change are even greater. Arizona’s Petrified Forest National Park today is a desert grassland, but that wasn’t always the case. During the Triassic Period, 250-200 million years ago, that piece of ground was part of the Pangea supercontinent and was shifted south, similar in latitude to where Costa Rica and Panama occur today. This was before the age of dinosaurs, before flowering plants. The climate was tropical, and crocodilians, lizards, and amphibians dominated the land and land-water interfaces. Plant life included ferns, horsetails, cycads, and conifers. All groups that survive and thrive today, except the ferns and horsetails back then were much bigger. Horsetails today are typically about the diameter of a pencil and maybe two to three feet tall, whereas back then some were the diameter of your arm or lower leg and could reach 20-40 feet high. Conifers were about the same size as a Jeffrey pine.

The same piece of ground where the National Park sits today was back then probably an estuary. It was likely near a river mouth, a river that was eroding upland habitats and then depositing layers of silt in the delta over tens of thousands of years or perhaps millions of years. Just like today, sometimes such rivers flooded, ripping the vegetation from their banks and depositing trees as logjams in the estuary. The flood waters then covered the trees in silt, creating an anaerobic tomb before fungi and bacteria could break down the trees. Over the years, maybe thousands or millions of years, silica in the entombing silt replaced the trees’ cellulose, turning each tree into rock, or more precisely agates, in the exact shape and size of the original trees. In some even the conifer’s tree rings were agatized, allowing people today to estimate growth rates and ages of the trees when they were entombed.

Given enough time, the rivers eroded the mountains away. The continents we know today broke free from Pangea’s grip, and what would become North America shifted north. The estuary was no more. Its landscape became increasingly arid, its giant ferns, horsetails, and conifers were replaced by cacti, grasses, pinyon pines, junipers, and Mormon tea. There are still lizards and at least one amphibian (a toad). The crocodilians are gone, but their descendants eventually evolved into birds, and birds are common. Strong winds eroded the finer silts, exposing the agatized conifer trunks that became the focus for protecting this landscape as a National Park.

Change created that landscape, albeit at a time scale that makes a human lifespan seem imperceptible. Add enough human lifespans together and you can see when this landscape was not quite so arid, during the waning years of the Pleistocene Epoch. Rivers flowed more regularly. People lived here then; the foundations of their pueblos still exist, and their petroglyphs still stand as testimony to the creatures and ideas that captured their imaginations. The earliest people living here may have even seen mammoths or giant ground sloths. Taking a hike in nature back then would have been like a walk across some of the remaining wild areas of Africa today, both exhilarating and dangerous.

The problem with change is being able to distinguish between change that supports biodiversity and change that erodes that richness. Occasional floods create habitat for seedling willows and cottonwoods, which then support an abundance of bird and insect life as they mature. Except when those floods are too frequent, in which case the trees can never mature. Wildfires in chaparral, grasslands, and some conifer forests can rejuvenate those habitats and stimulate greater seed/fruit production, benefiting wildlife and people alike. The sequence of post-fire re-establishment creates new habitats and fosters higher levels of biodiversity. However, too large or too frequent wildfires or wildfires across landscapes without adaptations for re-establishing those habitats (deserts, pinyon forests) will destroy biodiversity. So, change is good, except when it’s not. As naturalists, the more we understand the complexities of nature the better we will be at knowing the difference.