How do trees at treeline respond to fire?

We planted seedlings in burned and unburned areas to determine how fire will affect their growth and survival.

We will also put miniature greenhouses on top of the seedlings (to simulate warming) in 1999 to see how both fire and warming affect tree growth.

 

Fire and spruce forests

People have known for some time that fire has a positive effect on spruce forest regeneration: competing shrubs are removed and the organic (top) layer of soil is burned down to mineral soil, where spruce germinate best. But fire may also have a negative impact, particularly at or above treeline: once the surrounding trees are removed, the harsh conditions may prevent seedlings from surviving.

With these two possibilities in mind, what does fire do to spruce at treeline? We want to know this because it probably has some effect on how spruce will respond to global warming.

To help figure this out, we traveled to the edge of a fire that burned both at treeline and above treeline-- so where there's forest and tundra and there are places that have burned and haven't burned. At each of these places, we planted spruce seedlings that we will monitor over the next 3 years.

Why plant seedlings in these places?

During the 3 years, we can look at each group to make comparisons. For instance, how do the seedlings in burned areas compare to the seedlings in unburned areas? In making this comparison, we may learn more about how fire effects spruce seedlings: if the burned ones do considerably better than the unburned ones, we may suspect that fire has a positive effect on early seedling growth. If the unburned seedlings grow better, we may suspect that fire has a negative impact. Once we learn more about if burning or not burning is best for early seedling growth, we can also compare treeline with above treeline. Which place-- above treeline or treeline-- is better for spruce growth? Again, what we learn from the seedling planting experiment will help us figure out how both fire disturbance and warming affect treeline. Although we've planted over 640 seedlings, we still need to travel to other burns to replicate our study so we can have more confidence in our findings.

Fire and warming

During the 1999 field season, we will warm different groups of the planted seedlings. Why? We hope that artificial warming will mimic global warming so that we can see how fire and warming interact to affect spruce growth. These two things together may have a different effect than either of the two (fire, warming) separately.

What did we do?

Follow the descriptions and listen to the audio below to further understand what we did.

Listen to Dr. Andrea Lloyd describe how we planted seedlings. Click here for text.

Click here to download a free RealPlayer so you can listen.

We carried the seedlings up to be planted in and around an area that burned in 1989. Here, we planted seedlings where the fire burned (right) and where it didn't burn (left). But since the fire burned in tundra (above treeline) and forest (treeline), we planted seedlings in four main places: at treeline in burned areas, at treeline in unburned areas, above treeline in burned areas, and above treeline in unburned areas.

First we visited the tundra to plant the seedlings. To do so, we dug small holes, put in the small spruce seedlings, gave them some water, and put the soil and tundra back around each seedling. Again, we did this in both burned and unburned areas. We planted seedlings in small groups of 10. Here's a group of planted seedlings in the tundra.

 
Then we visited the forest to plant seedlings. Here is an unburned forest where we planted...  ... and here is a burned forest where we planted. By following closely how each seedling grows over the next 3 years, we can make comparisons to help determine how fire disturbance affects seedling growth.

One way to keep track of how the seedlings grow is to take pictures of them each year. We are careful to take the picture from the same height and angle each year to make the best comparisons. These pictures will not tell us exactly how much growth has happened each year, but with the help of a computer, we will be able to get a good estimate. We will also collect, dry, and weigh them after 3 years to estimate "biomass," which is the total amount of living tissue. This is what the pictures of the seedlings looked like: all 641 had their own numbers. We mapped them all so that we can find them next year.

How does fire affect spruce at treeline? Click logo for audio description. Click here for text.

 

What will the greenhouses do? Click logo for audio description. Click here for text.

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