Wednesday, 03 July 2019

How the Environment Affects Plants

Recently, I was asked by a young Asian student, “Do plants raised in a good environment flourish and grow bigger than plants raised in a bad environment?” At first, I wanted to dismiss what seemed like a silly question. As I headed for the creek to check on some honeysuckle and buckthorn that got treated last week, I thought more about that question. The more I though about it, the more interesting his became.

Broadly speaking, his assertion was probably true. The answer, however, changed with the species. Also, it depended on how the budding scholar defined the environment. Finally, the answer would hinge on what the young questioner thought was good and bad. Answering his question first meant understanding that the environment includes the soil, water and air.

Soil

Soil differs in its composition naturally from one place to another based on the underlying geology, as well as surface layer history like glaciation and floods. Soils fertility differs based on those factors. Human activities, most notably farming, have changed the characteristics of soil in many environments. Erosion and poor agricultural and horticultural practices have depleted many native soils. Likewise, resource extraction and industrial activities have polluted soils in many areas.

Water

We are all familiar with water pollution and its effects on plants. Acid rain harms plants, causing deforestation around the world. Toxic discharges from factories, leaking landfills, and pathogen laden runoff from factory farms pose threats to plants downstream.

Air

The air has several factors to consider. Increased CO2 from burning fossil fuels benefits some plant species, while others are unaffected or even suffer because they evolved to thrive in an atmosphere with less carbon dioxide. Toxins discharged from smoke stacks and tailpipes definitely injure most plants.

The reason I did not declare these impacts as good or bad is that under certain circumstances a particular plant species in a specific location might benefit from certain environmental degradation. Even if many native plants suffer, there are bound to be tough species that will move in and take their place.

This morning, I am walking along the floodplain of a small creek in the driftless area of Wisconsin. Because a large block of very hard rock split the southward advancing glaciers for millennia, glacial ice never scoured this part of Wisconsin like it did the rest of the state.

Farming Along the Creek

However, for the past century, farmers using poor practices caused erosion of tons of topsoil from surrounding hills. That topsoil landed in the valley below, covering the wetland adapted species and degrading the wetlands so they are far less capable of controlling flood events. The rains this spring, along with flooding last summer mean for a second year in a row, the farmers on either side of the creek will see disappointing harvests.

Aside from the money lost by the neighboring farmers, erosion has devastated those buried wetland plants and seeds. On the other hand, other plant species brought downhill with the soil, blown in by the wind or dropped by passing birds and animals now thrive in fertile topsoil with plenty of moisture. The creek corridor is a riot of growth, though most of it is invasive species that do little to recharge the groundwater or control flooding.

So what is the “correct answer” in this situation? It seems to me that the loss of topsoil from the uplands, as well as the loss of wetland plants, loss of groundwater recharge, and increased flooding downstream, more than offset any benefits.

Southern Wisconsin was a disturbance dominated ecosystem before Europeans settled here nearly two hundred years ago. Wildfire sparked by lightning and Native Americans burned the land every few years. The result was a landscape dominated by prairie and savannah. This kind of landscape is called an early successional ecosystem because it dominates soon after big disturbances like windstorms and fire.

Early Verses Late Succession Plant Communities

Today, most of the land is farmed, but woods and scrublands dominate the areas too steep or wet to crop. These woody species cannot tolerate fire. They are called late succession ecosystems because they move in after those first sun loving pioneer species. When fire disappears from the landscape, shade tolerant trees like cherry and maple are able to take over. They crowd out the scattered sun loving oaks, which cannot regenerate under the closed canopy of the darkened woodlands.

Many of the plants that once covered the prairies and savannah are now rare; with many threatened or endanger of extinction.

Effects of Farming

Because their root systems were so deep and they recycled nutrients so efficiently, those prairie and savannah plants built up fertile topsoils 3–8 feet thick. Now, through changed land use and erosion, most of that topsoil can be found more than a thousand miles south in the Gulf of Mexico.

Corn and soybeans still grow in tremendous abundance, thanks to chemical fertilizers and pesticides. That abundance allows farmers near my home to export their bounty around the world. Is that good or bad? Row crops suited for agriculture grow large and yield hundreds of tons per acre. That grain feeds millions of people around the world, How can that be bad?

Heading for Home

My notebook now holds the shrub kill observations that brought me here this morning. Almost without thinking, my entries show that the herbicide sprayed on the basal bark of those invasive shrubs is having its intended deadly impact. By fall they will be dead. In a few years their carcasses will fall over and their trunks will decay. If I continue to do my job, their offspring will join them. The native seeds I plant in their place will begin to stabilize the soil along this little trout stream.

Heading back to the truck my musings on plants, as well as good and bad environments come together. I think about the “land ethic” from A Sand County Almanac. Aldo Leopold first made this profound way of looking at the world popular. He wrote, “A thing is right when it tends to perserve the integrity, stability, and beauty of the biotic community. It is wrong when it tends otherwise.”

 

2018

December 2018

Monday, 03 December 2018

Natural Forests …

Picture of red cedar trees.

Seldom found growing so tall or close together, this grove of mature red cedars is at the UW Arboretum.

Someone recently asked, “How do the trees in forests grow by themselves?” I was stumped at first, because her question was so very broad. After collecting thoughts for a moment here is (more or less) what I came up with.

Where Forests Come From

Trees, like all plants, need: water, light, soil and shelter. In natural forests, new seedlings sprout from seeds that drop from trees above. Other seeds arrive on the wind dispersed from nearby trees. Still other trees arrive in the forest via animals such as squirrels who carry the seed from neighboring woodlands and bury them in the new forest. Chance determines which species arrive and what happens when they get there.

Managed woodlands grow by choice, not by chance. State nurseries provide seedlings. Woodland managers decide the species mix, the planting plan, thinning and management practices. The result is a healthy woodland that provides habitat for a wide range of wildlife. It also produces high quality forest products like timber, pulp and maple syrup.

Of course, natural regeneration needs to be included in forest management plans. Mature trees will produce seeds that sprout and help ensure the next generation. To the extent that mother nature does her bit, working with nature is a great strategy.

Wise landowners understand that the jeanie is out of the bottle. Climate change, habitat loss and invasive species mean “letting nature take care of things” no longer works. Understanding what makes a natural forest requires knowing where forests come from and why they are where they are. 

Plant Succession

Forests are the final stage in what biologists call natural plant community succession. It all begins with bare soil. The first plants to grow are grasses and forbs (wildflowers). They form plant communities called grasslands and prairies. If there are no serious disturbances (primarily wildfire) shrubs will find their way into the grasslands or prairie. As the percentage of shrub cover increases, tree seedlings follow. Trees use the shade of the shrubs to protected them from weather and soil moisture extremes. Some tree species, such as aspen, boxelder, birch and cottonwood do not need need shrub cover and can can colonized grasslands and prairies directly.

Picture of paper birch with cedar grove in the background.

Birch is an early succession species that grows fast and quickly replaced by more shade tolerant trees.

Pioneering tree species grow fast and need lots of sunlight. Because they cannot grow in shade, these early forest creators eventually are pushed out by more shade tolerant trees like maple and hemlock.

The final stage of plant community succession is the shade tolerant forest. These tree species can germinate and grow with very little light. They do well in the cool damp conditions created by the deep shade of a tightly closed canopy.

Fire Adapted Landscapes

Before pioneer settlement, much of America frequent “natural disturbance events.” The most common of these events was fire. Lightning caused many of these fires burning over the land and pushing back the plant community succession. Native Americans also used fire. By periodically setting fire to grasslands and prairies they kept most shrubs and trees from growing. This was desirable because grasslands and prairies were more productive for game and made travel easier. Fire prevented late succession forests from developing; creating the grasslands, prairies and savannahs that covered southern and western Wisconsin.

Some trees are fire adapted, which means that their bark is thick and can prevented them from being killed during by wildfire. Oak and hickory trees are the iconic fire adapted trees of the midwest. They can withstand prairie fires that kill species like cherry and maple. Several species of pine are also fire adapted. Some like the loblolly grow in the southeast. Others like lodgepole and ponderosa pine are common western forest species.

Because it takes time for the heavy protective bark to form on these fire adapted species, young seedlings would perish in prairie fires. Drought and animal browsing also take a heavy toll on seedlings For these reasons, woodlands created by these fire adapted species were sparse. They had open canopies that let light reach the ground between trees. The grasses and wildflowers that grew around the trees provided light fuels which caused fire to easily carry through the forests. Where fires were more frequent and trees even more widely spaced, the system that evolved was called a savannah.

Where Fire Rarely Visits

Picture of balsam fir branch.

Balsam fir is a classic northern forest tree. It grows as an understory tree in shade where other trees find hard to make a living.

Up north the snow pack is deeper and lasts later in the spring. Because of that soils are wetter and fire  less frequent. Trees that were more shade tolerant and less fire adapted could gain a foothold. Swamps, and shady northern slopes provide the similar conditions for isolated woodland pockets in southern Wisconsin.

What Does It Mean

Picture of oak hickory woodland.

Traditional Wisconsin oak hickory woodland. This would have been familiar to your parents of grandparents; before they got choked out by invasive shrubs and shade tolerant trees.

Today, with humans surpassing wildfire, much of the former oak and hickory savannah is moving toward late succession forests.  Wisconsin has lost more than 95% of its historic oak savannah. Oak and hickory are dying out of their historic woodlands replaced by more shade tolerant species. The closed canopy allows shade tolerant shrubs like buckthorn and honeysuckle to steel the remaining sunlight. The result is a serious decline of savannah and woodland wildflowers in Wisconsin. Likewise, western forests are becoming denser creating high fuel loads. This sets up conditions for the devastating wildfires that are plaguing the American west.

Private landowners and public land managers who put in place forest management plans are making a difference. They use selective thinning, forestry mowing and prescribed fire to reduce fire loading and let more sunlight reach the forest floor. Wise stewardship is restoring healthy forests, woodlands and savannas. This is how we take protect our natural heritage.

Forests, therefore, really do not grow by themselves. We steer its future; either by conscious management or benign neglect. It took 150 years of exploitation and total fire suppression to put our forests in their present condition. Wise stewardship and effective management can restore healthy forests over the next century. The choice is simple — it is, however, neither cheap nor easy.