Effects of Forest Landscape Patterns on Bird Populations in the Rockies:

An Interview with Dr. Sallie Hejl.

From the Environmental Review Newsletter Volume One Number Four: April 1994


 Dr. Hejl has earned an M.A. in 1981 from the University of California at Davis and the Ph.D.in 1987 in Zoology from Northern Arizona University. She has worked as a wildlife biologist in western forests since 1978 and is currently a research wildlife biologist at the U.S. Forest Service Intermountain Research Station at Missoula Montana. Dr. Hejl has numerous refereed publications on the effects of forest structure on forest bird populations.

ER: Dr. Hejl, what is the main focus of your research?

SH: There are two issues that are important for forest birds in the West, particularly in the Rockies: are patterns of habitat across the landscape different now from what they were pre-settlement? And, if the landscape patterns in the forests are different, does that matter to the birds? And if so, which ones?

     A related question is, can we replicate natural disturbance patterns? The main natural disturbance in forests is fire but there are lots of other disturbances in Rocky Mountain forests, e.g. insects and disease and wind throw.

ER: How have the forest patterns in the Rockies changed since settlement?

SH: A lot of the ponderosa pine forests used to be open park-like old growth stands before they were logged in various ways. It's hard to summarize because every different logging treatment you can imagine has probably happened out there. Then by keeping out fire, the douglas firs have come in and filled those stands of ponderosa pine.

     There are also stands that were clear cut in the early 1900s and now they're all ponderosa pine again, but  very dense second growth.  In some places loggers selectively cut the biggest trees and those stands  may now appear similar to what old growth used to look like. Not necessarily park-like, but scattered big trees. However, in many places where fire was kept out, you now have this two story appearance with small douglas fir under the overstory of the ponderosa pine that was left.

ER:  Before, fires would come through and kill all those doug fir seedlings.

SH: Right. Every five to twenty-five years.

ER: Fire would clean out underneath...

SH: And leave the big old ponderosa pine.

     However, douglas fir-dominated forests here often burned at longer intervals, every 60 to 120 years. So keeping out fires has allowed those trees to become older.  So there may be more mature  douglas fir forest here than we had before in the Northern Rockies. The composition of the older forests has changed.

ER:  How old do the ponderosa pines get in the Northern Rockies?

SH: The old growth stands of ponderosa pine here in the Rockies vary between 200 and 450 years old.  They're old for that timber type but they aren't as old as douglas fir forests in the Pacific Northwest where you can have trees as old as 800 to 1,000 years.

ER: How has the overall structure of the forests changed since logging and fire suppression have come in?

SH: The age structures of the forest have changed and there's less old growth in general in the Rockies. There may be almost as much total old growth in some regions, but with different species of trees now.

ER: How does  changing the forest pattern affect forest dwelling birds?

SH: We don't know that at all. We have no idea if the different forest structure matters  for wildlife, or how much it matters, or in what way. For a well studied species there's some information for instance, in the Pacific Northwest with the northern spotted owl. In the Rockies, I've started to study landscape patterns and how they affect birds in the last five years.

     A lot of the studies I was first involved with were  getting distribution information of where birds were.  Then we realized the birds could be in a location but not reproducing there. There were even some indications of that from various studies - just as many of a bird species in one habitat as in another, but not reproducing in one of those areas.

ER: In forest fragmentation,  more birds may pack into a smaller area  and the long-term effects of that packing might not show up for several generations of birds.  Is that the idea?

SH: Exactly. That's the belief.

ER: Because nest predation might be increasing.

SH: Right. Or if the birds are packed into a small area, they may not be finding suitable nest sites.  They may be looking for them, but not be able to find them.  Or they may be having trouble finding enough food to bring up the young.  And you  don't know until you get reproductive success data .

     My early studies were based on point counts, which give distribution information. It's only in the last two years that I've tried to find nests and actually quantify if birds are successful in one habitat compared to another. That's the study I'm doing in Northern Idaho in western red cedar and western hemlock old growth forest. We're comparing bird reproductive success in  old growth forests that are surrounding clearcuts (i.e. fragmented old growth stands) to how birds are doing in unfragmented old growth.

ER: The unfragmented old growth is one big chunk. You compare bird nesting success in this unfragmented old growth to forest that has been fragmented. How do you do a nest survey in the these two types of woods?

SH: We hike in in the summer and try to find the nests in the study areas.  We put out several forty- or fifty hectare grids marked every 100 meters.  One person covers each grid, follows up clues and tries to follow birds and find their nests.  Sometimes you see a nest, other times you have to follow a bird for an hour before it leads you to a nest. [A hectare is an area of 10,000 square meters (2.5 acres). ed.]

Once we've found a nest, every three or four days we go back and check how it's doing.  Most of the nests we find are either so high up in trees or snags that we can't see into the nest so we watch the birds come to the nest and  try to determine what they're doing.

ER: If they keep bringing food?

SH: Right. Sometimes you can stay quite awhile, twenty minutes, and nothing happens and the nest could still be fine. So we try to stay at least a half an hour.  If the birds don't come at all in that time, perhaps in the next check in three or four days we'll see something.  

We're still figuring out this methodology for this habitat because birds come at different intervals.  It's a lot easier if you can look into the nest.  "OK, there's three eggs. Let's go." With ground nests, it's easy. You quickly go in from different directions, check the nest and leave, trying not to disturb the adults.

ER: How long will you have to do this to answer your question?

SH: We're probably only going to do this one more summer, three total summers.  One reason is we want to research other habitats, but also because it's such a difficult habitat to work in.  I think we've got a pretty good sample size on the few species that we can study effectively in this habitat.  But it may prove different this year.  We may figure out how to get more nests of other species and then I'm flexible to work longer in this habitat.

ER: Prior to your reproductive studies you were gathering information on how many and what kinds of birds were in the forests after different logging techniques were used.  What was your overall result? Are some forest birds declining there?

SH: For the point counts we compared three areas: unfragmented old growth, fragmented old growth (with fairly recent clearcuts interspersed)  and a third area that was fragmented, but with older clear cuts and selectively logged forest around it. The pattern of this third type was all chopped up, because that's how the forests in this area of Idaho had been treated in the past.

     In the three study areas there were four species of birds that were much more abundant in the continuous old growth compared to the other two areas: brown creeper, winter wren, golden-crown kinglet, and Swanson's thrush.

     Three of the four species were much more abundant in old growth, less abundant in the fragmented old growth, and much less abundant in the selectively logged fragmented forest. So at least three species were much more abundant in the two types of old growth, than they were in the selectively harvested forest. The brown creeper, the winter wren, and the golden-crown kinglet were less abundant in the fragmented old growth area but not necessarily less than one would expect based on less forest area. These birds were also less abundant in the selectively harvested forest - much less than you would predict based on the forest area that is there.

     So something about those selectively harvested forests is different to these birds than the true old growth or the old growth fragments.

ER: What do we know about the natural history of the creeper or the kinglet or the thrush that can explain their decline in selectively logged forest?

SH: When they selectively harvested, they probably removed either nesting or foraging sites for creepers. Creepers nest in trees that are large enough to have bark peeling away from the tree. Their nests are behind bark that's peeling away. I've never seen a creeper nest that wasn't this way. Removing the bigger trees is what I think would be important to that species. Smaller trees don't have exfoliating bark.

Richard Hutto, Charles Preston and Deborah Finch and I  just submitted a paper that summarized the effects of silvicultural practices across the Rocky Mountains, and the brown creeper was the species that came out clearly in all studies as being less abundant in treated areas.  I think that is the one species I  worry about trying to understand in time.

ER: In time before they're gone, you mean?

SH: It appears there are still lots of brown creepers around, but they are the one species that clearly is harmed by logging of the types we had in the past, which is taking out the biggest trees.

ER: Your study also found a decrease in golden-crowned kinglets in selectively logged forest. Is the negative impact on foraging or nesting habitat for kinglets?

SH: I don't think you can tell. It could be both. Kinglets nest and forage in foliage.  And they have been shown in many studies to be old growth associated. It may be foliage volume that is driving the numbers of them. In the Sierras the numbers of golden-crowned kinglets have increased since early in the century, at least in one area in Yosemite. And the author of that study (Ted Beedy) thought it was because they had kept out fire and  lots of true firs were moving in so there may be more foraging space for the kinglets. I wouldn't be surprised if their numbers are related to the foliage volume both for foraging and for nesting.

ER: Can you say that the kinglet population in the Rockies appears to be in good shape?

SH: I don't think we know those sorts of things. We don't know  - you mean compared to the past?

ER: Yes.

SH: We don't know because we didn't know what they were like in the past. We don't have much data to compare to. There is some Breeding Bird Survey data for the past twenty-four years, but we don't know if it adequately reflects trends in conifer forest birds.

ER: Are you concerned about this population of kinglets in the Northern Rockies?

SH: It seems like there are a lot of kinglets around. We don't know enough to say those sorts of things, but one thing the Forest Service is starting to do is to monitor these species. In the National Forest System they're setting up monitoring transects and they're putting them throughout the Northern Region so we can tell how populations of various species such as the kinglet are doing over time.  Of course the baseline starts now.

     I think for most of the bird species I study which are not the raptors or the species with huge territories (those are monitored different ways), there is no obvious species that I'd say we're in trouble with now in the Northern Rockies.

From the studies I've looked at, I'm most concerned about the brown creeper, nuthatches, and woodpeckers in general as the species that may be in trouble in the long run if we don't do things differently. There may be some uncommon species however, that may be dropping in numbers, and we do not have enough information to even realize that we should worry about them.

ER: You mean manage the woods differently?

SH: Yes because woodpeckers and nuthatches and creepers need big trees and big snags- elements that we systematically have taken out of the woods. Those are species that in general I would guess have decreased, if any have, in the past hundred years- the species that are associated with snags, old growth, and burns. We've logged old growth out - much of it.  We've taken out snags, and we've kept places from burning. [Snags are dead trees. ed.]

A big question we need to address is, can we live without fire? How do we use fire? Fire recycles nutrients back to the soil.  It creates snags, stimulates shrub regrowth and opens up forests.  Fire is a regenerating natural event that creates habitable areas for many plants and animals. The problem can be exacerbated by politicians who, because they don't know this (they're not scientists) think that timber that's left in a burned area is wasted. Instead, it's a key resource for say, black-backed woodpeckers.

ER: It's a resource for the forest itself.

SH: That's true too. For the health of the forest -  everything from the nematodes to the recycling of the materials for the trees.

ER: When we haul out the logs and burn the slash, we're removing material that ordinarily would stay in the woods and decompose.

SH: Right. It would be recycled.

ER: That recycling has built the forest structure that we're harvesting now.

SH: Yes. I don't think what we've done up to now is  necessarily irreversible. We know that we need to recycle or replenish nutrients. We put compost on our gardens. I don't know how many generations the forest will last if we continually take trees and snags off.

ER: What was the frequency and intensity of fires in pre-settlement times?

SH: That depends on which forest type you're in.

ER: In the North Rockies.

SH: It depends on which forest type in the Northern Rockies you're in. In the Rockies everything is so broken up that it's hard to generalize for any one forest type.

ER: You mean naturally broken up?

SH: Yes. There're mountains facing all different directions.  Lower elevation forests in general (like ponderosa pine) had fires fairly frequently, say every five to twenty-five years, so they had low intensity fires that mainly burned the small trees, grass and/or some of the trees.

At higher elevations or in wetter areas or on north facing slopes- those woods probably burned at much lower frequency, every 60 to 200 years, so fires were much more intense when they burned. Many of them were probably fires which burned up a whole stand of trees or most of the stand.

ER: How has fire suppression influenced the make up of the forests?

SH: Fire suppression has influenced both the structure and composition of the forest (the previously mentioned change to douglas fir in pine forests) and more older douglas fir stands as well. And in the ponderosa pine stands there are now trees that wouldn't have been there naturally.

In addition, fires that happen now are likely to be more intense and larger. That's the biggest change.  If we don't deal with fire suppression, we're going to be creating greater and greater fire threats  - if you think fires are a threat.

ER: We decided that fire is bad and fight it, so now we get it in spades when it gets out of control.

SH: Right. The direction current forest management is going is to re-introduce natural disturbance patterns or to let them happen.  One or the other. Unfortunately, you have to do a lot of manipulations before you can do that. We have to take out these smaller douglas firs or the ponderosa pine stands will go up in smoke, which they wouldn't have done very often since low intensity fires would have taken out small trees every five to twenty-five years and left the big trees.

ER: So you've got intermediary steps or forestry practices for ecosystem restoration.

SH: That's the hope. To get back to natural disturbance patterns.  If you're going to go back to natural fire patterns it entails logging smaller and different kinds of trees than used to be taken out.

ER: You're saying that you can incorporate selective logging into this restoration kind of pattern?

SH: Oh, definitely.  In the ponderosa pine forests here they're doing it. The Forest Service is trying to either restore old growth ponderosa pine or encourage it by taking mature stands and making them more like old growth ponderosa pine. This entails taking out the smaller douglas fir that would have naturally burned every five to twenty-five years and reintroducing fire into the systems.

We want to consider the forest landscape on a large scale and compare it to natural (pre-settlement) landscapes. We see that to maintain some bird species you need young successional stages of forest, to maintain other species you need old growth. We need to keep a mosaic of all different sorts of stands across the landscape. Once we know how landscape patterns matter to animals, we can  add that information into how it would be best to juxtapose those types of forest.  Up to now, all we can do is suggest how nature would have done it.  

In the eastern United States there are many bird species that are hurt by forest fragmentation. In much of the East there are patches of second growth forests surrounded by either urban areas, suburban areas, or agriculture.  In the western forests that I've studied there are forests next to forests.  They aren't little isolated patches.  There may be stringers of forests near a clearcut, but that may meld into another stand of timber and that may meld into a young forest right next to it.

ER: Right. The forest pattern is much different in the eastern U.S.

SH: So the natural patterns as well as the fragmented patterns are so different in the East and West that the concepts don't necessarily work the same way in the two areas. The issues may be the same. It may be important to have a lot of old growth for some species.  It may be important not to have these stark edges because more predators come in. We don't know all the answers.  

ER: Another difference is the scale of the forests is so much bigger in the West.  

SH: And it's mostly public forests in the West and hasn't been logged as much as the East yet and it's not been converted to other uses. When I talk to ornithologists from the East, they're worried about saving certain species or bringing them back - I  feel like we're ahead of the curve for most forest birds in the West (excluding hawks and owls). We're trying to be conservative about maintaining healthy forests and maintaining the species we have.

ER: We can learn from what's happened in the East. And edge effects are a big problem there.

SH: Right. That's why we know to look at that, but we still don't know if that matters here  - or which type of edges matter here. That's one thing I'm trying to figure out.  

Copyright 1994 Environmental Review