Effects of Climate Change on the Long Term Deterioration Trends of Wood in Cultural Heritage
This presentation is part of the A Century of Design in the Parks: Preserving the Built Environment in National and State Parks, June 21-23, 2016, Santa Fe, New Mexico.
Suzana Radivojevic : …and good morning everyone. It is a little bit of a change at least on the topic and this is the first, I believe, of two presentations at least touching on the effects of climate change on our parks. I think it’s important at this occasion to actually start thinking or at least talk about a lot of research that has been going on already, looking at long-term effects of climate change on our cultural and natural resources.
The effects are already dramatic worldwide and in the United States and that’s the only reason to highlight the range and the scale that I chose to start with showing a graph. So, this is where our comfort zone was in the past, somewhere around 1960’s we permanently start into zone which is warm and getting warmer, CO2 concentrations which are fueling temperatures are rising. Temperatures on this axis and this part was generated sometime around 2010. In 2016, we are outside of this plot with our CO2 and atmosphere around 460 ppm or so, maybe even more. For our cultural and natural resources the effects are not only large in terms of scale as is the case in the station with Mountain Pine Beetle, shown here further, the Rocky Mountain National Park. The research attempts to develop climate change adaptation strategies are extremely complex in terms of modeling, in terms of the number of variables and categories that we need to take into account and we’ll hear more about that from our research group from University of Oregon, Robert Melnick and Norah Kerr.
In contrast, the study or more of discussion that I want to talk about today has a very narrow focus: only on wood in our building environment, so thinking about the last presentation and all the wood in Many Glacier Hotel and most other park structures. I’m limiting or focusing only on wood in ground exposure or in-ground contact or above ground exposure, so not on wood that is buried, so no archeological artifacts or wood that is immersed in water. I also chose to consider only those deterioration mechanisms that are capable of creating structural damage and typically those are fungi and few insects. We will look at what we already know from our experience working with historic buildings but also from the science on these deteriorating organisms and then we’ll try to understand what is already happening at present. And based on that, try to come up with at least some understanding of what future has for wood in these buildings and maybe try to formulate some of the recommendations for how to address these problems already in a preventive way in our park structures.
Because fungi and insects are very different, I’ll try to keep them and talk about them separately. There are many different types of fungi. We usually refer to them in and distinguish them based on how they appear or what kind of decay pattern they produce in wood. What we see here is typical ground rot fungi, regardless of species they have very similar site of growth requirements. They require wood for food, they need oxygen, and most importantly they need moisture and temperature. That’s important because of environment change. They prefer moisture contents of around 30% based on wood weight in order to be able to infest wood, so we don’t see them as much here in New Mexico for example. Once they are established they can grow, I’d say, at 20% minimum moisture content. They also prefer optimum temperatures of around 80 Fahrenheit.
So, the relationship between those two environments, mainly temperature and moisture and wood decay in buildings is obvious but it is a little bit more complicated. I just wanted to talk about growth conditions, moisture, and temperature at three different levels that we usually refer to when talking about buildings. One being microclimate, mezoclimate, and macroclimate. Microclimate is typically determined by the conditions of the wood itself. So, moisture and temperature on the surface and within the wood. That is the critical level at which it will decay or not. At the very next level is mezoclimate which is determined by the surrounding, the setting of the building. If there is a lot of vegetation, if there is a water body close-by, if there are structural details that attract moisture, they are going to determine mezoclimate and also influence microclimate. But then at the very highest level there is the effect of macroclimate. Macroclimate is determined by temperature and precipitation. That’s where we see the effect of climate change.
For everyone working with wood that relationship between the climate and the amount of decay is kind of intuitive. In 1971, a wood scientist Theodore Scheffer, which was I believe Forest Product Lab in Madison, WI at the time, he tried and successfully developed an equation that describes this relationship. He used climate records of temperature and precipitation in this equation here, which is really not that complicated, he worked with annual averages, and he used, I think around 30 year record for the whole United States. That allowed him to calculate climate indexes, which described the potential for decay depending on the geographic region on the location of the building, which is related to the climate. Then he plotted all of the data for the United State and he distinguished three regions. He said if the climate index is less than 35 we have no decay. If the climate index is between 35 and 70 we see medium risk and then these dark regions, more than 70 there is high risk of decay. What that means is that, for instance this blue star is where approximately Las Vegas would be and that corresponds to the climate index of 0. So nothing ever happens in Las Vegas, at least with wood decay, but West Palm Beach, Florida 137.5.
This has been extremely useful and widely used. These maps were developed for other regions worldwide. They were used to model building performance. They are still used a lot. But around 2000, or maybe before that, scientists started realizing that there was a discrepancy between what they are observing in the field and what Scheffer’s indexes are saying. That was especially the case in Canada, because it’s North and global warming is kind of more pronounced, or we see more of a change, in the Northern parts. There government scientists in 2008 published a study, that what they actually did was they revisited and re-calculated Scheffer’s indexes but now using climate data from 1970-2000. We go back to that graph that we saw at the beginning, we already see global warming during that period. Not surprisingly, they saw an increase in Scheffer’s indexes. That explained their field observations.
So another study by Forest Products Lab followed and confirmed the effects in the United States. I’m sorry that these maps are not side-by-side, but basically we see increase in indexes and also shifts in these regions most notably in the North.
Both groups were careful not to say that this was due to climate change or so they left it open, but then there were other scientists throughout the world that followed and researchers were actually trying to figure out whether it was due to climate change and in the end there was a consensus, yes it was. Especially, there was a German group, which went even further and they said that the quantity and the quality of the change in decay indexes actually does depend on the geographic position and on the amount of climate change that will take place in the future. So, what that explains if you look at the climate change itself.
On this upper map we see what has already happened, this is observed temperature change throughout the country with apparent warming in red in the north and then in the Central parts. I’m not sure that everybody can see that there is a map in the left corner below, which shows one of the worst case scenarios for 2100. Here we see most of the warming taking place in the North and especially in the West of the country. If you look at what’s happening with precipitation, we see increase in rain fall, we already know that there has been more precipitation than what historic record was in the North mostly, but then there is kind of like a reverse scenario by 2100, where we will see a lot of precipitation, high increase in the Central part of the country. Very drastic difference in the past.
Knowing how fungi is like and what is happening with climate change we could make some kind of educated guess for each particular region. I’m sure everyone is looking at their state and their park and trying to figure out what is going to happen. What some researchers actually did, they plugged in all this data on points projection that we already had for their particular areas of interest and that has been done for Australia, European Union, Norway, so on and they have a pretty good idea what decay is potentially going to be like for their region.
Especially important is this map that I’m showing here. Let me see the full title of the project. This was the study that was done by European commissioner, on the project that is known as Noah’s Ark and probably many of us have come across that. The project was titled, Global Climate Change Impact on Built Heritage and Cultural Landscapes. So this research was done specifically to figure out what will happen in Europe and this is far future 2099. Interestingly, north and west of Europe are going to experience 50% increase in decay and south of Europe and west Europe 30% decrease, that’s what the modeling says. Based on that we can maybe guess that in the United States this decay risk potential will change for warmer and drier climates by actually going down and will increase in those regions, which will experience annual precipitation.
Moving to insects, while fungi generally shares similar life cycle and their deterioration patterns are kind of similar, wood wood-boring insects have a lot of diversity in terms of geographic ranges, decay patterns, distribution and so on. There are many different species that attack wood in North America but let’s focus just on those that are especially significant and those would be termites, carpenter, and dead-watch, and powderpost beetles and wood-boring beetles in general.
So what is unfortunate about insects is that the amount of available research for individual species is usually proportional to the economic damage they inflict and at the present our understanding of climate change effects and insect activity is usually limited to our understanding of their biology and ecology. So let’s just say what kind of changes we might see in the future. For example, wood-boring beetles are really diverse, they usually have very limited geographic ranges. We usually don’t consider them a big hazard in terms of structural damage. There are also exceptions, such as Pacific Northwest where we have this beetle here. Often, they have clear dietary restrictions, for this beetle here, which only feeds on the soft-wood species. But what is important to consider and to keep in mind when we talk about historic buildings is that these insects are very difficult to detect, to control, and to prevent their attack which makes them important pests to historic wood, fabric, and wood artifacts. Very special, important pests in museum collections.
Carpenter ants are present throughout the country. They can cause significant structural damage, mostly in the Pacific Northwest. What is interesting and why it is important to understand their habits and their life is that they are proportionately more active and frequent in maybe national parks because they like forests. That’s where they live regardless of whether it’s a historic building or just a deadwood.
Termites are ones that are really a concern. They cause billion dollar damage and we will only talk about subterranean termites. They are the most destructive. For those reasons, they also have been studied more extensively than other insects. National Park Service was also active in integrating research and cultural resource management by developing efficient treatments, for example Statue of Liberty National Monument control of termite infestation some years ago. We also have a better understanding of their requirements and their distribution. On this map we see infestation probability map that is used in building codes actually.
Earlier this year an interesting study came out of a research team from The University of Florida. What they looked at was what is the survival and the distribution of most important, termites in the United States going to be like and what is the wood consumption rate, which means the damage to wood in historic buildings in general, going to be like depending on climate change. The results were interesting. They confirmed the expectations and there are as many other insects moving northwards, so instead of having them only up to here, for example, certain species will slowly at least have a potential to move further north. The study also established that the critical parameter for most of those termites is going to be the low winter temperatures because those low winter temperatures are lethal to termites. And that’s what is critical for controlling their populations. So those are going to rise again, another indication that they are moving northward.
This study didn’t really look at formosan termites, which is just worth mentioning having this species on everyone’s map because this is the most destructive species, far more destructive than any of the native species. It was introduced to the United States sometime after the second world war and the distribution range has been just expanding ever since. They are also important because they have been destructing through all cultural resources. It is, I think, especially in historic French Quarter there are instances when they would attack, not only historic buildings but also Cypress trees and live Oak trees and just any wood.
With insects, based on what we know and what we understand and based on our experience with historic buildings, it is pretty certain that increased average temperatures, including annual average temperatures, summer temperatures, minimum winter temperatures, all of that is going to effect their activity, more activity, more deterioration. They will have longer productive season, which means a bigger population again, more damage, shorter biological cycle, which again means bigger population, a higher number of generations. In some instances, those climates that are going to become favorable for fungi infestations are going to be good for some insects such as carpenter ants, which like high moisture. Geographic range will move northward and then there is some elevated risk of non-native invasive species and what we already know is happening, not only for insects but for bears is appearance of new hybrid species that might be much more destructive than anything we already have.
So, based on what we know or at least the knowledge base that we already built that is accessible to us, at present what we can do in our parks, I think it is really important to understand that we’ve seen all of this just at someone else’s park. It is the communication and finding a way to share that knowledge and technologies which exist is really important when it comes to decay mechanisms to species distribution to growth requirements.
This is something that should be at least present as a concern as something to look for when doing regular inspection and maintenance, so these early signs of infestations don’t go unnoticed. It’s really important and these are preventive measures that everyone can incorporate. Then at some other level monitoring both short and long term, including non-destructive testing. Again, knowledge transfer dissemination is really important and use of preventive and remedial treatments that we already have and know a lot about.
About future, as we already saw climate based modeling is really a powerful tool. Apart from that looking at material resilience and not only material, but structural, because no matter how much we agree or not on that, structures were built or were not built for certain integration patterns that we see here and we need to revisit those material and structural properties. Also, to look at new materials and new ways of modifying structures if we have to. Monitoring of insects vectors is something that we should learn from biologists. What was done at the Noah’s Ark project was very interesting. They actually introduced classification for their historic buildings in European Union based on sensitivity to climate change. So they were classified as robust, or with high, medium, or low sensitivity. I don’t know how efficient or helpful that is but in combination with something as mapping it might maybe be for developing models and for future strategies. In the end, I still think that as with all the other issues that touch on climate change it’s really most important to ask good questions and those questions usually have to be important, well informed. So thank you and I would be glad to answer questions.
Dr. Suzana Radivojevic holds a Ph.D. in Wood Science from the University of Toronto, Canada, and a B.Sc.F.E. from the University of Belgrade, Serbia. She teaches at the University of Oregon, in the Historic Preservation Program, in the Department of Architecture, and at the UO Historic Preservation Pacific Northwest Field School. Her research interests are related to wood preservation technologies, wood building pathology, wood identification and dendrochronology. She has published her work in peer-reviewed journals and presented internationally. She serves as a referee for journals APT Bulletin and Studies in Conservation. She also works as an independent consulting researcher.