Thoughts on the Effects of Climate Change in Vermont Forests

David Paganelli 12-11-20

    It occurs to me that this complex topic can never be fully understood. There are too

many variables and not enough base knowledge and reliable data. Yet, there are some

things that we know, and from these small pieces of the puzzle, we can make broad

inferences, that advance our general understanding of the larger issues. Our

understanding of complex systems and mechanisms must start somewhere. When we

ultimately learn that certain assumptions were incorrect, we can adapt our climate

change/forest narrative, but in the meantime, we either form theories founded largely by

incomplete science and near complete ignorance, or we have no starting point at all.

So, with that in mind, we may not understand every mechanism of climate change, nor

see every small change taking place in the world around us, but we know that climate

change is real and that changes are occurring. Further, we know that small behavioral

changes made by a large number of people can make a substantial difference.

Specifically, with regard to climate change and Vermont forests, we may wish to

consider four apparently unrelated concepts.

1. A forest is more than trees.

2. Climate change effects in Vermont are unique to Vermont, and affect all

components of the forest.

3. Plants need light, water and carbon dioxide to photosynthesize, and the availability

of all of these critical inputs will change as climate changes.

4. Climate change is affecting Vermont forests and our active management can

improve the ability of forests to adapt to change.

A forest is more than trees

Trees are certainly the dominant vegetation that make up a forest, but there are other

plants in a forest. Shrubs, herbaceous plants, wildflowers, grasses, ferns, and each of

these plants has a life cycle and each has a niche in the ecological function of the forest.

There are fungi, lichens and mosses, amphibians, insects, birds, mammals, and microbes

in the soil, and many species of each, all with different lives and different functions. All

of these organisms interact and form a system. What they do, or how they specifically

impact all the other components of the ecosystem, is generally unknown, but we believe

(know?) that all species matter, that they all reach some complex balance together, and

that the complex interaction of the full suite of species is what makes a healthy forest.

Climate change effects in Vermont

We are experiencing warmer winters with less snow and more rain and ice. Our

summers are warmer too, with more precipitation, but that additional precipitation is

coming in heavy downpours rather than gentle rains. And the heavy rains are often

accompanied by violent winds.

Photosynthesis

Photosynthesis is the conversion of water and carbon dioxide to sugars that fuel plant

growth. The reaction takes place in chlorophyll (the green pigment in plants), is

powered by light from the sun and releases oxygen gas as a byproduct. Photosynthesis

provides the energy that drives all living processes in a forest. “Productivity” in a forest

ecosystem could be defined by how much photosynthesis takes place there, and in order

for photosynthesis to take place, there must be sufficient fuel for the reaction. Carbon

dioxide, sunlight and water from the soil are the fuels, and their abundance or shortage

regulates all plant life, and thus ecosystem productivity.

Carbon Dioxide - There is certainly no shortage of carbon dioxide, as excess carbon

dioxide resulting from the combustion of fossil fuels is the main driving factor in climate

change. While there is no shortage, excess carbon dioxide does favor certain plants over

others and vines such as Asiatic bittersweet, Virginia creeper, wild grape and poison ivy

are becoming more prevalent in our forests.

Sunlight - As long as the sun still shines there will be enough light to provide energy for

the photosynthesis reaction, but the density and species composition of canopy vegetation

affects the intensity of light that reaches the forest floor. As tree species shift in our

forests, the pattern and quality of light passing through the main canopy to the forest

floor, will change, and some species will be able to function better than others in the new

understory light conditions. This will lead to an understory species shift.

Water – Climate change is expected to increase total annual precipitation in Vermont.

But there is some question about how much of the additional water will actually be

available to plants. If the rain comes in the form of heavy downpours, with much of that

water running off, then there actually could be less water in the soil, where it is available

to plants. So, even with more water entering the system, drought conditions may increase

and the amount of water available to plants for photosynthesis may actually decline.

Some species of trees and other plants can tolerate drought better than others, and those

species will gain competitive advantage, while those that are less tolerant of drought, will

decline.

There is a direct relationship between winter snowpack and tree health. Snow

accumulates in winter, when trees are dormant and then melts in Spring, just as trees and

other plants are preparing to draw in large quantities of water from the soil to rehydrate

their stems and fill their leaves. If there is too little snow to fully saturate the soil, or it

melts a month before the plants are ready to use it and is lost from the soil, there may be

insufficient water available in Spring to bring the system back to full function.

Change and Equilibrium

The balance between all the organisms that make up a forest is in constant flux, but

always within certain bounds. There is constant change in the details, but the larger

forest ecosystem is constantly striving to reach equilibrium. That equilibrium may last

for hundreds or thousands of years, or may change dramatically over a short period (think

glaciation). Our forests had reached a particular equilibrium prior to European

settlement. Then, much of Vermont was cleared for agriculture. Later as the farms were

abandoned, the land returned to forest and a new equilibrium began to form. Now, a

hundred or more years into that process, the climate is changing and a newer, different

equilibrium is beginning to form. Climate change is obviously very bad news, but a

small bit of good news is that through our actions, we can positively impact the new

equilibrium.

Human Responsibility

As citizens, all of us can, and should, take actions to resist and counter climate change.

This may include promoting options that favor sequestration of carbon, or enhancing

carbon storage in forests. It is important for all of us to remember that while forests can

serve this purpose, they are much more than places to sequester or store carbon. And

while forests can grow sustainable crops of firewood, sawtimber and wood fiber, they are

much more than places to grow or store timber. Forests are living communities that are

home to thousands (perhaps millions) of all manner of living creatures. Those of us

privileged to own forest land, or to manage forest land for others, have the additional

responsibility to shepherd our forests, including all the living things within them, through

this period of great change, with the least loss possible. We can do that best by working

to maintain or create complex forest structure that emulates old forest conditions and that

maximizes habitat niches. This management approach may provide us the best chance to

properly balance our current need for sequestration and storage of carbon, with our

ongoing responsibility to maintain healthy forest ecosystems.