When I wrote my recent book on prairie management, I included a very short section at the end on climate change. Essentially, my advice to prairie managers was that managing prairies for biological diversity would help them be resilient enough to absorb climate change impacts. I still think that’s good advice, but it leaves out some other options.
One of the purposes of this blog is to allow me to expand upon the ideas from my book, so I’m taking this opportunity to do that with the issue of climate change. In this case, I asked for help from John Shuey, Director of Conservation Science for the Indiana Chapter of The Nature Conservancy. John is a good friend and someone I have tremendous respect for, and I can always count on him to cut through the fog and address issues directly.
What I like most about his ideas is that they are all things we can actually DO RIGHT NOW. One of the frustrating things about climate change is that it’s hard to design strategies when we don’t really know what climate conditions will be like in the future. But John suggests strategies that would be good ideas regardless of what the climate does. It feels good to have a map to follow, and this one points in the right direction – even if we don’t know exactly where we’re going.
“What do you see as the major threats to prairie and savannah conservation from climate change in your state?”
“Well, most models predict three key changes in Indiana’s climate change future. It will likely be hotter, with a slight increase in precipitation, and there will be more frequent severe weather events such as tornados, straight-line winds and ice storms. The increase in precipitation will be during the dormant season with predicted decreases during the summer. All that basically translates into three perceived threats: increased drought stress, increased fire frequency and intensity, and increased severe weather damage such as flash flooding and blow downs.”
“The central United States went through the Xerothermic Period between 8,000-5,000 BP, which was considerably warmer and drier than our present climate. Does the fact that our prairies have already survived that period give us hope for the next phase of climate change?”
“Based on paleobotanical data, expanses of grassland and savanna dominated much of Indiana during the Xerothermic Period, and wooded communities increased in abundance as climates became cooler and moister. Species compositions in today’s prairies will undoubtedly shift in response to climate change, but appropriate native species should be present at many sites to moderate those changes. Some species will increase in abundance and others will decrease – even disappear from sites altogether. The key for biodiversity conservation is to design strategies that will allow those changes to happen while minimizing species loss and preserving ecological functions. For example, we can help to ensure that the full range of habitat conditions will persist in our conservation areas by designing restoration projects now that meet the future needs of species most at risk from climate change.”
“Fortunately, prairies are pretty resilient communities, but we’ve put a lot of stress on them already – especially in landscapes where prairies are small and isolated from each other. How does that habitat fragmentation affect our conservation options?”
“The concept that ‘species will have to adjust northward’ as climate changes is very problematic in a landscape that is among the most developed in the world. Even if it is theoretically possible for species to respond to warming trends by moving northward, fragmented landscapes like those in Indiana will not permit much movement between conservation sites.
Because of that fragmentation, we need to do as much as we can to make habitat patches as internally resilient as possible. This can be done by maximizing the both the size and physical variation (e.g. slope, aspect, and soil moisture) of our natural areas. We can increase the size of, and even reconnect, fragmented habitats through restoration of adjacent areas where that’s feasible. Larger habitats can hold larger populations of species, which gives them a better chance of survival. In addition, larger sites usually provide more variation in topography and hydrologic gradients, which can increase the chance that species will find the conditions they need to survive somewhere in the conservation area. For example, shady microhabitats on north facing slopes may partially mitigate the impacts of regional increases of the evapotranspiration rates (a.k.a. drought stress). Some of the rare species found on these slopes today may not make it through the changes, but those microclimates will likely still be loaded with locally rare species in the future. Sadly, some of those ‘rare’ species may be abundant today but restricted to narrow ecological creases decades from now.
It’s also important for natural areas and to contain multiple examples of each habitat type, especially those most at risk from climate change – e.g. things like wet prairies and other moist habitats. This accomplishes two things; it maximizes habitats that are likely to mitigate drought impacts, and it creates a repeating mosaic of ecological gradients that is more likely to support metapopulations (multiple populations interacting with and supporting each other) of species pushed to the brink. As we design conservation areas and engage with private landowners in priority landscapes, we need to preserve as many examples of each habitat type as we can within regional landscapes. ”
“Talk more about wet prairies and other natural areas that rely on the proximity to groundwater or other hydrological features for their survival. Increasing drought stress sounds like a big deal for those sites…?”
“First, it’s important to know that many of our wetland systems in Indiana, such as bogs and fens, functioned though the Xerothermic Period in essentially the same manner as they do today. These sites are literally the source of the pollen records used to re-create paleoclimates such as the Xerothermic. It seems likely that their water budgets were reduced, and wetlands were probably smaller relative to their presettlement extent in Indiana, but they still survived.
It will be very important to protect groundwater and surface water inputs to natural areas wherever possible. Groundwater diversion, especially for irrigation, is already a concern at some of our most important sites, and needs to be addressed. If we really do get more precipitation during the dormant season, that might help recharge surface aquifers. However, increased droughts may counteract that, so we will need to help develop policies that help moderate surface and groundwater depletions and encourage wetland restoration and protection.
River flows will probably become more flashy because of increased storm intensity. The prevalence of channelized streams across the Midwest means that most run-off from big rains is lost quickly downstream. This creates unstable streambeds and increases non-point source pollution in rivers. It also means that most of that water is not captured in wetlands where it can provide habitat and help contribute to groundwater recharge. Implementing the increased use of two-stage ditches may be one way to help moderate flood damage while still preserving a more natural stream flow regime.
Finally, restoration of areas adjacent to wetlands and low prairies provides opportunities to improve hydrologic conditions in two ways. First, wetland restorations in formerly cropped areas can complement the hydroperiod of nearby natural wetlands. New wetlands can be designed to stay wet longer – or dry up sooner – depending upon what may be missing (or predicted) in existing sites. That full range of hydroperiod conditions is particularly important for successful breeding by reptile and amphibian populations. Second, restoring portions of the landscape surrounding small natural wetlands can help buffer them from the impacts of diversion ditches and other hydrologic alterations.”
“Are there other things we need to be thinking about relative to climate change?”
“Three things come to mind. First, invasive species will be moving into new areas as they, too, adjust to the changing climate. Unfortunately, invasives are more likely to be able to move around fragmented landscapes than many of our native species, and we need to be prepared for that. I think that the struggle to manage native grasslands will intensify in the future, and that we can never let our guard down.
Second, we tend to focus on the losers when we discuss climate change. It’s important to remember that there will be interesting winners as well. For example, in southern Indiana we are focusing heavily on small glade and barrens habitats surrounded by dense forest. I expect these glades and barrens – which, structurally, are just prairies that grow on very thin soils and bedrock – to thrive! We are aggressively restoring these habitats to their pre-fire suppressed condition so that they will be poised to take advantage of future harsh growing season droughts.
And finally, it’s important to remember that the predicted changes are PREDICTIONS. We have to be flexible in our strategies as we move forward. My guess is that I understand perhaps half of the future impacts to our sites – enough that we can take good ‘no regrets’ actions (productive strategies regardless of climate change) for the future. But we’ll need to continue adapting strategies as we learn more. If we are still following my current prescriptions 10 or 20 years from now we’re probably not paying attention to either changes on the ground or model refinements.”