A Walk in What Used to be Woods

I drove up to the Niobrara Valley Preserve this week and arrived in time for a long hike before dark on Monday evening.  It was the kind of opportunity to wander and think that is critically important (but unfortunately rare) for land managers and ecologists.  I focused my time north of the river where steep ridges and “foothills” full of pines, bur oaks, prairie, and lots of eastern red cedar trees had experienced an intense summer wildfire during the severe drought of 2012.  Since the fire, our staff has been having lots of discussions about how we should be managing the site and its recovery.  It was great to have a few hours to just hike around, observe, and think.  I took some notes in my field notebook as I walked.  Here are a few of those notes (in italics), fleshed out with some of the further thoughts.

fallen ponderosa pine in 2012 wildfire area at TNC's Niobrara Valley Preserve, Nebraska.
A rare fallen ponderosa pine in 2012 wildfire area at TNC’s Niobrara Valley Preserve, Nebraska.  Most of the trees killed by the fire are still standing, and probably will be for many years to come.  This photo is looking southeast from the hills on the north side of the Niobrara River, where fire intensity was very high and killed nearly every pine and cedar tree.

No young cedar or pine trees anywhere.

As we started to assess the impacts of the wildfire, many of my biggest questions had to do with the future of this area north the river, where ponderosa pine and bur oak trees had been abundant, along with an extensive population of eastern red cedar.  I knew the Sandhills prairie would recover just fine (and it has), and I figured we wouldn’t see much pine re-establishment for a long time (none so far), but I was most concerned that cedars would re-infest the slopes north of the river faster than we could control them.  Because the pines and cedars had been so thick in many areas, I guessed it would be a while before grass colonized sufficiently to support a prescribed burn hot enough to kill cedar trees, and I worried that we’d end up right where we’d been within 10-15 years (except with all cedars and no pines).  As it happens, the grass is filling in pretty well in many places, but I haven’t seen a single young cedar tree yet.  Researchers from the University of Nebraska-Lincoln, who are helping us study the area, have apparently seen a couple, but they are exceedingly rare.  (One of those researchers, graduate student Amanda Hefner, is working to answer many of the questions we have about the recovery of these wooded areas.)

I’ve been talking to other people about their experiences with hot prescribed fires or summer wildfires that wiped out cedar trees in Nebraska grasslands.  Typically, without follow-up fire, a dense regrowth of cedars reaches head high or so within about 10 years.  Based on what I’m seeing so far, I don’t think we’re going to see that kind of rapid reestablishment.  So, why?  Did the fire scorch the seed bank?  Is the area far enough away from other fruiting cedar trees that it is temporarily safe from reinvasion?  I really need to spend some time walking near the edge of the big wildfire to see what the cedar re-invasion looks like there.

 

The wildfire didn’t appear to affect sumac, plum, or other deciduous shrubs – even in hottest areas.

A big topic in the prescribed fire circles here in Nebraska has been the proposal that we should consider conducting burns in hotter and drier conditions than we usually do.  University of Nebraska Range Ecologist, Dirac Twidwell, has been leading this push.  Research that Twidwell and others conducted in the southern Plains showed some dramatic positive results from summer burning under severe drought conditions – including mortality of some re-sprouting tree species that hadn’t previously been thought to be susceptible to fire.  I’ve been wondering about using hotter summer fires, perhaps during drought conditions, as a way to combat high populations of deciduous trees and shrubs in prairies.  Maybe burning under more stressful conditions (for the trees) would reduce their populations?  I’m still thinking about that idea, but what I saw at the Niobrara Valley Preserve makes me question how likely we are to see success.  Even in areas where cedars and pines experienced crown fires, and fire intensity was at its highest during the July 2012 wildfire (in hot weather, during a severe drought), I don’t see any evidence that sumac or wild plum were hurt at all.  I can see the outline of the shrub patches that burned during the fire, and today’s patches are even bigger – and maybe more dense – than they were before the wildfire.

Eastern red cedar skeleton in 2012 wildfire area at the Niobrara Valley Preserve, Nebraska.
There is a lot to see in this photo.  In the foreground, you see strong growth of grasses beneath what had been a big spreading cedar tree that had been shading the ground prior to the fire.  If you look closely, you can also see stems of smooth sumac beneath the tree and behind it to the left – a healthy spreading population.  In the background, you can see skeletons of pines, oaks, and cedars on grassy hills above the river.

 

Most bur oaks in steep draws were single trunks before the 2012 wildfire, but out in the open, many were multi-trunk trees.  They must have seen at least one big fire in the past?

People who spend more time than I do along the Niobrara may find this to be old news, but I was surprised at how many old bur oaks had multiple trunks prior to the 2012 wildfire – evidence that they’d likely been through a relatively severe fire that had caused them to respond by resprouting from their bases.  We should cut a few of those old trunks apart to date that fire.   Interestingly, however, those multi-trunk trees seemed to be mainly (exclusively?) outside of the steep draws.  Those draws were full of pines and cedars, along with oaks and a few other deciduous trees, and there wasn’t much herbaceous vegetation (grasses, sedges, and forbs) beneath those trees.  The combination of steep terrain, lack of herbaceous fuel for fires, and high soil moisture (shade from trees and steep terrain), probably kept previous fires from being intense enough in those areas to top-kill oak trees.  However, the 2012 wildfire was a completely different animal, and now nearly all the bur oaks north of the river are starting their growth over from the base.  It will be very interesting to see if they all turn into big trees with 4-5 trunks again.

Bur oak with resprouts in 2012 wildfire area at TNC's Niobrara Valley Preserve, Nebraska.
A bur oak at the top edge of a draw.  The tree had been growing with five big separate trunks prior to the 2012 wildfire, and is now has many resprouts from its base again.  Further down into the draw, all the oaks I found had only one single trunk.

 

The steepest slopes at the top of ridge are still dominated by annuals.  Perennial grasses are filling in well elsewhere, except steep slopes under (formerly) dense cedars and pines.

In general, I’ve been pleasantly surprised by the density of herbaceous vegetation in much of the 2012 wildfire area north of the river.  Even where pine and cedar density was fairly high, perennial grasses and sedges are filling in pretty quickly.  The thinnest vegetation is in places where topography is particularly steep and where big pines and cedars had been growing most thickly.  Where trees were thin or non-existent before the fire, the vegetation responded just as I’d expect prairie to do – there is great plant vigor and species diversity.  Where the vegetation had been thinner prior to the fire because shade from trees, today’s plant diversity seems lower, and many patches are dominated by one or two grass species.  Species such as sand lovegrass (Eragrostis trichodes) and Scribner’s panicum (Panicum oligosanthes), for example, have formed near monocultures in many places.  I think these will diversify over time, so I think it’s great (and interesting) to see them for now.

Grazed sedge in 2012 wildfire area at the Niobrara Valley Preserve, Nebraska.
On this steep east-facing slope of a draw, there is still a lot of bare ground, though perennial sedges and grasses occur here and there.  Whatever the particular sedge species in this photo is, it is apparently a favorite of deer because every plant I found had been cropped very short.

However, in those steeper areas, especially near the top of the ridge, perennial grasses and sedges are still very thin, and most vegetation is annuals.  This isn’t necessarily a problem, and the annuals seem to do a pretty good job of holding the soil, but it makes me wonder about the speed and eventual trajectory of the plant community recovery in these areas.  Mostly, I’m just curious to see what happens, but I’m also a little concerned that we might see some invasive species fill in before native perennials get a foothold.  As an example, smooth brome is common in the flats above the ridge, and it’d be a shame if it also gained dominance on the steep slopes below.  I’m hopeful that the soil conditions won’t favor brome, but we’ll have to just wait and see.

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Overall, these observations just add further complexity to discussions our staff has been having about how to manage this area in the future.  We still need to decide what we want the area to become so we can guide it in that direction.  It’s all fine and good to say we’ll just let it develop however it wants to, but if the site trends toward a cedar woodland with a smooth brome understory, for example, that’s not really going to be very positive for wildlife or biological diversity.

We’d really like to encourage the bur oak trees to survive and thrive but aren’t sure what kind of fire frequency or intensity might best facilitate that.  What about deciduous shrubs?  Are we ok with letting the current clones become so large and dense that they eliminate grasses beneath them?  They would essentially be fireproof at that point, and we’d have no easy way of thinning or otherwise managing them – especially in really steep areas.  More importantly, those shrub patches would likely provide safe haven for cedars and other trees to establish and grow within those fireproof shrub clones.  Is that what we want?  If not, what are our management options?  We have lots of ideas, but still have a lot of discussing, researching, and observing to do.

These kinds of questions and challenges are why land management is interesting and fun.  I’m really looking forward to watching this area (and all the others I get to help with) continue to develop over the next few decades.

Wildfire Recovery at The Niobrara Valley Preserve – Asking The Big Questions

Most of you are familiar with the wildfire that affected our Niobrara Valley Preserve this summer.  Well, we’re still trying to regain our footing after that event.  A great deal of time and money has already been spent on rebuilding and redesigning infrastructure (especially fences), but there’s still much to do.  In addition, the staff of the Preserve, along with a few of us from around the state, has taken this opportunity to do some deep thinking about what the Preserve can be in the future.  It’s an incredible place, and we want to be sure it lives up to its potential.  I’ll share more about that process as the picture becomes more clear.

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The Niobrara River continues to flow through the Preserve, but much of the landscape looks pretty different since the fire.  Open grassy slopes such as this one will recover quickly, but more wooded areas will come back much more slowly.

In the meantime, we’re also trying to learn what we can from the 2012 wildfire so that we and others can be more prepared the next time something like this happens.  I’ve been asked to help organize this effort, which is an intriguing task for me since most of our questions are about woodlands – not exactly my area of expertise.  Fortunately, I’ve had some great advice from others, particularly Dr. Dave Wedin at the University of Nebraska, who is also generously helping us line up researchers and funding.  Other advice has come from a wide spectrum of foresters, ecologists, and others, and I appreciate it all.

I was up at the Preserve last week for another bison roundup (the west herd this time) and had some time to poke around in the hills and think about our current list of research ideas.  I think we’re honing in on a few important research directions, but we still have some thinking to do about how to ask and answer the right questions.  Since we’re at a good point to get feedback from others, I thought I’d lay out some of what we’re thinking and see if any of you have suggestions for us to consider.  If nothing else, those of you who are familiar with the Preserve, and concerned about the impacts of the fire, can get an update on the situation and a feel for where we’re going next.

Yucca are starting to regrow across the burned portions of the Preserve.  Many show signs of being eaten - there's not much else green out there!
Yucca are starting to regrow across the burned portions of the Preserve. Many show signs of being browsed by deer and other wildlife – there’s not much else green out there!

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Wild rose is another of the plants regrowing in the burned areas.  These woody plants, perennial grasses, and sedges make up the bulk of the surviving plants.
Wild rose is another of the plants regrowing in the burned areas. These and other perennials, including grasses, sedges, and wildflowers, are most abundant in open areas without dense stands of trees.

Our primary research objective is to learn lessons that will help us and others adapt our pre- and post-wildfire management in the future.  It would certainly be interesting to simply document the way in which plant and animal communities recover from the fire, but that has been done elsewhere.  With very limited resources, we’ll spend a little effort documenting how the Niobrara Valley Preserve recovers from the fire (including the use of time-lapse and other photography) but we want to focus most of our effort on learning things that we and others can actually use down the road.

Impacts of Tree Density

The first thing we want to know is how the density of eastern red cedar and ponderosa pine trees affected the way the fire burned  and (more importantly) the way the areas beneath the trees will recover.  In addition to the perennial plants that survived the fire, much of the future plant community in our former pine woodland will depend upon the seed bank (the collection of seeds sitting in the soil, ready to germinate when given the chance).  Unfortunately, areas under dense tree stands are also the most vulnerable to soil erosion.  Especially on steep slopes, wind and water erosion can quickly remove both seed and soil, leaving very little to support plant community recovery.  Since there were few herbaceous (non-woody) plants under dense tree stands, there is little to hold the soil (and the precious seeds in it) from washing and blowing away.  If seeds and soil go, it’s going to be a very long time before anything grows in those places.

Soil erosion will probably be an issue on steep slopes and under formerly dense stands of trees.
Soil erosion will probably be an issue on steep slopes and under formerly dense stands of trees.

We hope to correlate the amount of soil erosion with tree density and slope, and see how those factors affect plant community recovery.  Ideally, we can combine our data with what others have learned elsewhere and develop recommendations for future management.  We want to know how densely can we allow trees to grow before the site becomes vulnerable to severe erosion in the aftermath of a potential wildfire.  Hopefully, that information can help managers decide how to prioritize tree thinning operations.

Much of the erosion that's occurred so far appears to be wind erosion.  A 70 mph wind storm got sand moving in some areas.
Much of the erosion that’s occurred so far appears to be wind erosion. A 70 mph wind storm really got sand moving in some areas.

On a related topic, we want to see how cedar and pine density affected the survival of bur oak trees.  It’s clear that we’re going to have varying degrees of recovery among the oaks growing on the lower slopes of our pine woodlands.  Some of the oaks have already re-sprouted from the base, but others haven’t.  Those others are either completely dead or waiting to resume growth from the tips of their branches next year.  What could we have done as land managers to prevent oak mortality by thinning the cedars and pines near those oaks?

Many of the bur oaks in the burned area are re-sprouting from the base.
This oak is re-sprouting from the base – it’s still alive, but has to start it’s growth over from the ground.

Aiding Recovery

We also have questions about how best to manage the recovery of burned sites.  Some people are advocating seeding burned areas to speed up the establishment of herbaceous and/or woody plants.  There are numerous concerns about this, including what kind of seed would be used and whether or not it would actually make any difference.  We certainly want to avoid introducing plant species that could cause more problems than they solve, but the bigger question is whether or not seeding will make a difference when the most problematic areas are those where soil erosion rates are high.  Putting seed in those erodible areas probably won’t do much good. However, while we and most of our neighbors will probably not be doing large-scale seeding, we might consider a few small-scale trials to test the idea.  We could broadcast seeds in a few trial plots and see if the plant community establishes differently within those plots than elsewhere.

Aside from any seeding efforts, the recovery of ponderosa pines in large swaths of burned woodland is likely going to be dependent upon seed coming from unburned areas.  Because of the size of burned areas, that could take a very long time.  Is it worth trying to speed up that recovery by planting small patches of ponderosa pines in various locations, with the idea that as they mature, those trees would be seed sources for nearby establishment – thus speeding overall woodland recovery?

A few mature ponderosa pines may have survived along the very top of the ridge north of the river.  If so, new pines may be able to spread from these pockets of survivors.
A few mature ponderosa pines may have survived along the very top of the ridge north of the river. If so, new pines may be able to spread from these pockets of survivors.

The answer to that question is related to another big question.  How do we manage these burned woodlands over the next couple of decades – especially in terms of prescribed fire?  At first glance, it might seem that we’ve had enough fire to last quite a while.  On the other hand, prescribed fire might be pretty important to help prevent cedars from coming right back in, and to give us some control over the overall recovery trajectory.  If we do employ prescribed fire, that’s going to impact where pines will be able to survive – including any we plant and those that come back on their own.

Very few pine cones can be found away from the very top of the ridge.  A few isolated exceptions like this might produce a few trees, but future prescribed fires may not allow many of those to mature.
Not many pine cones can be found away from the very top of the ridge. A few isolated exceptions like this might produce a few trees, but future prescribed fires may not allow many of those to mature.

Grassland recovery from the wildfire comes with questions too.  We have choices to make about whether to graze some of those drought and fire-stricken prairies immediately or to rest them for several months or longer first.  In our bison pastures, bison are never removed, so grazing resumed immediately after the fire.  We could build some exclosures to look at how immediate grazing impacts grassland production and species diversity.  In addition, we can manage our cattle pastures in several different ways and measure the results.  What we learn could help us and others make informed decisions after future wildfires.

The last big question we’re struggling with has to do with invasive species, especially in burned woodlands.  I’m not sure yet how to formulate a research question on this topic because we don’t yet know what kinds of invasives we’ll be dealing with.  Some plant species will be much quicker to colonize burned woodlands than others, but whether they will include truly invasive species – and which ones they might be – will be unknown until it happens.  We may just have to be ready to react as quickly as possible when we see what happens, and try to learn from our experience as we attempt to contain any invasions that occur.

We don't yet know what will be growing here in the coming years, but something will - and it will continue to be a beautiful and ecologically important place.
We don’t yet know what will be growing here in the coming years, but something will – and it will continue to be a beautiful and ecologically important place.

There are plenty of questions we could ask about the impacts of this wildfire.  We’re hoping to focus on those that might be the most useful to us and others when dealing with future wildfires.  We have our draft list, but would be happy to hear from anyone with suggestions of other questions we should consider or how we should prioritize among the questions we have.  Thanks for your help and support!

I'm smiling here, but as a prairie ecologist, I'm pretty far out of my element trying to help restore pine woodland.
I’m smiling here, but as a prairie ecologist, I’m pretty far out of my element trying to help restore pine woodland.

If you’re interested in contributing toward the recovery of the Niobrara Valley Preserve, please click here.

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