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Climate change, forest insects and the fossil record : knowing the past is the key to our future Hill, Lindsay 2015-09

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   CLIMATE CHANGE, FOREST INSECTS AND THE FOSSIL RECORD:  KNOWING THE PAST IS THE KEY TO OUR FUTURE  Lindsay Hill      FRST 497 September 2015  1  Abstract  From enhancing nutrient cycling, promoting soil formation and controlling the population size of other organisms, insects have an important role in all forested ecosystems. Insects have had naturally occurring life cycles within forests for millennia. However, due to climate change these cycles are becoming interrupted. In order to fully understand how insects contribute to the health of forests, it is necessary to look at historical life patterns related to insects and climate change. By using the fossil record, we can learn about the natural occurrences of forest insects and how their life cycles vary with a changing climate. From studying the fossil record we have learned that: a change in climate can drive a change in forest composition, impacting insect behaviour; there is increased insect feeding with increased temperature; and insect diversity tracks plant diversity. This is significant because what we can learn from historical evidence can help inform management decisions by forest professionals in a time when climate change is creating patterns that humans have not observed before. Despite the limitations of using this method, the fossil record is overall a source of abundant and useful information that should not be ignored. Key words: Climate change, fossil record, forest, forest insects, forest management, feeding, diversity   2  Table of Contents  Abstract ......................................................................................................................................................... 1  Introduction .................................................................................................................................................. 3  Discussion ...................................................................................................................................................... 5 A change in climate can drive a change in forest composition ......................................................... 6 There is increased feeding with increased temperature .................................................................. 8 Insect diversity tracks plant diversity ................................................................................................ 9  Limitations ................................................................................................................................................... 11  Conclusion ................................................................................................................................................... 13  Works Cited ................................................................................................................................................. 15     3  Introduction   Due to media, much of the public associate forest insects with large scale insect outbreaks and forest mortality, even going so far as to label forest insects as “forest pests”. However, this misconception is not necessarily true. An insect should not be considered a “pest” if it is not an invasive or alien species. A common image when thinking about forest insects is mountain pine beetle (Dendroctonus ponderosae Hopkins), causing unprecedented levels of forest mortality across British Columbia. However, with around 35,000 documented insects species in British Columbia alone (Carroll, 2015), there is more to the insect/forest association than just large scale outbreaks and mortality.  Forest insects have important roles in maintaining the proper function of an ecosystem. Decomposers, like carrion beetles (Silphidae), promote the cycling of nutrients, thus the availability of nutrients for plants and formation of soil (Galante & Marcos-Garcia, 2008). Some insects prey on others, potentially controlling the population size of the prey species. An example of this are checkered beetles (Cleridae) which prey on bark beetles (Moeck & Safranyik, 1984). Even an innocuous mountain pine beetle population is a natural aspect of a forest stand in British Columbia. Populations will attack weak trees (Safranyik & Carroll, 2006), which will create gaps, promote nutrient cycling and contribute to the overall complexity of a stand. Some forest insects, like mountain pine beetle, will even have outbreak populations occur intermittently (Safranyik & Carroll, 2006). However, when these outbreaks occur at unprecedented sizes, new locations and increased or decreased frequencies is when a forest insect becomes a forest pest. An insect species becomes problematic when it deviates from its natural life cycle pattern. This includes a species with an unprecedented outbreak, like mountain pine beetle, an introduced species, like Asian long-horned beetle (Anoplophora glabripennis Motschulsky), and species whose outbreak patterns are disrupted. Larch budmoth (Zeiraphera diniana Hübner) has had a regular outbreak cycle for at least 4  1,200 years in the European Alps. Due to the changing climate though, these outbreak populations have been absent since the 1980s (Esper et al., 2007). These changes can affect the functioning of a forest ecosystem. However, with the relative newness of these changes, how the ecosystem will be affected remains to be seen. One of the major determining factors of an ecosystem is climate. Climate is an influencing factor on where a species can survive. This is due to the fact that every species has certain climatic thresholds that it can exist within (Cowie, 2012). This means that if the climate changes in a specific area, the species able to establish in that area may change as well. With five of the warmest decades in the last 2,000 years occurring between 1950 and 2000 (Cowie, 2012), anthropogenic caused climate change could be creating environments and conditions that are novel to us at this time. As a consequence of this, how forest managers make decisions relating to insect management may need to be reconsidered. If ecosystems evolve into states that have not been seen by us, the decisions that we are currently making in order to manage our forests need to be reassessed. Review of these decisions will ensure that management practices are up to date and well-informed. However, the question then becomes: how do we ensure management decisions are well-informed if the ecosystems being managed are novel to us? The fossil record can provide considerable information regarding forest composition and insect feeding patterns throughout climate shifts. By looking at the fossil record, it may be possible to get the information needed to make knowledgeable management decisions when ecosystems are changing in ways that we have not seen before. In this essay, I will look at how we can use the fossil record to inform forest insect management decisions in the face of climate change. To do this, I will highlight three conclusions that have been found when looking at the fossil record and the corresponding implications for forest management.   5  Discussion   Despite common perceptions, the fossil record can be remarkably informative when considered broadly; this means that the fossil record does not reveal specific information over small time scales. What the fossil record does show, however, are general biotic and abiotic trends through time (Trexler, 2006). The fossil record can show animal histories, fossilized pollen remnants can show dominant plant species from which overall ecosystem types can be inferred and the presence of charcoal and burn scars can show fire disturbance histories. Past climates can be projected by comparing past forest composition, plant physiology and paleosols (preserved soils) with current conditions (National Park Service, 2010). There is a developing interest in what the fossil record shows regarding historical forested landscapes and the information that has been gathered could be useful for forest management. Research into the fossil record has shown three general trends with regards to climate change and forest/insect interactions: 1. A change in climate can drive a change in forest composition, impacting insect behaviour 2. There is increased feeding with increased temperature 3. Insect diversity tracks plant diversity By applying these trends that were found within the fossil record to current forest insect management strategies, forest managers may have the knowledge that is needed in order to respond to changing insect life cycles as climate changes. Here I will discuss these three trends and the ideal management actions in response to each.   6   A change in climate can drive a change in forest composition, impacting insect behaviour Approximately 8,200 years ago a climate event occurred, referred to as the 8,200 year event. It was an abrupt cooling event with estimates of it lasting from 200 years to it being a more prolonged event, upwards of 600 years (Hu et al., 1999; Rohling & Pälike, 2005; Brunelle et al., 2008). The 8,200 year event was an interglacial event that saw periods of dramatic cooling (Morrill & Jacobsen, 2005). A swift and radical change in temperatures would have a remarkable impact on forested ecosystems, potentially changing dominant plant species. If the dominant plant species were to change, then insect behaviours would change as well. This means that specialized insects, such as mountain pine beetle, would be impacted by the changing plant dominance; becoming abundant or scarce depending on whether or not the preferred host species was available. Brunelle et al. (2008) prepared paleoecological reconstructions from two lakes in the United States that looked for pollen remnants and Dendroctonus body fragments, likely mountain pine beetle, from the time surrounding this period, approximately 7,000 – 9,000 years ago. During periods where Dendroctonus fragments were present, the lodgepole pine (Pinus contorta Douglas) vs. whitebark pine (Pinus albicaulis Engelmann) pollen accumulations were recorded. It was found that in the middle of the 8,200 year event, whitebark pine populations dominated the forest composition; as opposed to lodgepole pine, which dominated before and after. Along with this, they found that bark beetle outbreak populations were associated with the whitebark pine dominance. Outbreak populations of mountain pine beetle would not necessarily succeed in colder and wetter conditions. These conditions, however, will support a healthy whitebark pine forest, which will support a mountain pine beetle outbreak. It was shown that the changing climate was not necessarily the most important factor leading to an insect outbreak. The changing forest composition, resulting from the changing climate, was a major determining factor (Brunelle et al., 2008). 7  Forest management is a broad spectrum of actions varying from doing nothing to applying intensive silviculture practice. The reason that doing nothing to regulate forest insects is an unreasonable forest management decision is because timber is one of our chief resources. Consequently, management needs to focus on maintaining the structure, function and overall health of forests while still promoting valuable timber. The natural interactions between forests and insects that are crucial to a healthy forest is information that can be used to support management decisions (Edmonds, Agee & Gara, 2000). The fossil record is one method we can use to better understand these interactions. Several pieces of information are necessary in order to make management decisions. In a managed forest, it is essential to differentiate between latent insects and insects that are pests causing economic damage (Edmonds, Agee & Gara, 2000). Knowing the life histories of key pests and their potential for economic damage is information that we can gather from current situations, but can then be supplemented from the fossil record, as Brunelle et al. (2008) showed. Looking back through time will ensure that an insect’s life history is fully understood. Once this is understood, it can then be decided when management requires suppression. This involves understanding how an insect population will develop and react to the environment and determining at which point insect damage has become great enough to warrant suppression. This is essentially determining when to do nothing and when to do something. Once the environment and consequences are fully understood silvicultural practises can then be implemented in order to control damage (Edmonds, Agee & Gara, 2000). Knowing that climate change has historically impacted forest composition, and in turn, insect feeding, is important for forest managers. This means that our current climatic condition could have implications to current forest/insect interactions. Brunelle et al. (2008) showed that the climatic environment is not the only factor that will influence the likelihood of an insect outbreak. Knowing this, it is important for forest professionals to understand the environments and compositions that promote insect outbreaks. Once this is understood more thoroughly, determining which insects are key pests and the acceptable level of 8  damage they produce will allow us to determine when suppression efforts are not only advisable, but necessary. Studying the fossil record can provide much of the information needed to gain a deeper understanding of this. There is increased feeding with increased temperature Temperature has a significant impact on insect life cycles, affecting survival and reproduction rates, abundance and range (Bale et al., 2002). This is due to the fact that insects are ectotherms; their body temperature, functions and life cycle events are influenced by external temperature (Paaijmans et al., 2013). This means that not only are insects influenced by daily temperature fluctuations, but climate change as well; which could have larger impacts on an entire population. Climate change can directly impact survivability, abundance and range.  Studies have shown that historical climate changes have resulted in increased feeding by herbivorous insects. Wilf and Labandeira (1999), recognized that insect feeding increases with a decreased latitude, so they suggested that with increased temperatures at a constant latitude, insect feeding would increase as well. The Paleocene-Eocene Thermal Maximum (PETM) was an event beginning approximately 54 - 56 million years ago which lasted 100,000 - 200,000 years. The PETM saw an increase in temperatures by 5 - 10°C (Wing et al., 2005). Wilf and Labandeira (1999), studied insect damage on fossil plants from the time surrounding the PETM in order to analyse whether herbivorous insect feeding increased or remained static at a constant latitude. What they found was that there was an increase in insect damage on fossil leaves from the early Eocene compared to the late Paleocene. This supports the idea that when temperatures rise, as they did during the PETM, insect feeding also increases (Wilf & Labandeira, 1999).  By the end of 2100, it is anticipated that global temperatures will rise by up to 4°C (Alley et al., 2007; Currano et al., 2008). This makes the Paleocene-Eocene Thermal Maximum comparable to the change in 9  climate we are currently seeing and the resulting insect feeding behaviour even more relevant to current conditions. Integrated Pest Management (IPM) aligns well with what the fossil record shows in a warming environment; the increase of insect feeding with an increase in temperature.  IPM is a process of forest insect management that involves three steps. First, as mentioned previously, determining the level of acceptable economic damage. Or in other words, when pest suppression is necessary. Next, insect populations need to be monitored. This ensures that suppression is implemented neither too early, disturbing healthy forest interactions, nor too late, resulting in the timber supply being damaged to an unacceptable level. Finally, once the situation requires control, silviculture techniques can be implemented to inhibit further loss. These techniques will vary from insect to insect, but will generally involve controlling host suitability and susceptibility (Edmonds, Agee & Gara, 2000). If we can expect temperatures to increase, and thus insect feeding to increase as well, there is another management strategy to consider. By directing harvesting to infested and high risk stands we would be able to utilize the timber supply in a proactive way by minimizing loss and controlling the outbreak (McLean, van der Kamp & Behennah, 2005). Insect diversity tracks plant diversity Using the fossil record to understand large scale spatial and temporal trends shows that insect diversity tracks plant diversity (Wilf, 2008). While at first this seems like a minor aspect of forest ecology to understand, this information is key to understanding insect/plant relationships during extinction and recovery events, or even recovery after large scale insect outbreaks. As nearly three quarters of insect herbivores are specialists, meaning that they utilize only one or very few host species, they would be particularly vulnerable to host plant extinctions or large scale mortality (Bernays & Chapman, 1994; Novotny et al., 2002; Schoonhoven, van Loon & Dicke, 2005; Wilf, 2008). If a forest has a high or low plant diversity it will then have an effect on insect diversity, and further ecosystem interactions.  10  An ecosystem with a high plant diversity means that numerous insect types can be supported, allowing for naturally occurring plant and insect population cycles to occur with efficient recovery. However, Wilf et al. (2006) looked at impacts on the ecosystem when plant and insect diversity  was lowered after mass extinction events. It was found that after a mass extinction, when plant diversity was low, insect diversity was typically impacted as well. The reduction in plant diversity and subsequent lowering of insect diversity, resulted in unbalanced and simplified food webs and ecological landscapes that required up to 4 million years to recover. Historical mass extinctions are relevant to our current ecological situation owing to the fact that substantial insect outbreaks and climate change are occurring, along with forest licensees’ tendency to reforest harvested areas with single species. We know that an increased plant diversity is still linked to an increased insect diversity (Siemann et al., 1998; Wright & Samways, 1998; Hawkins & Porter, 2003; Wilf et al., 2006); this tendency has not changed from what has been observed in the fossil record. Since this historical trend is still relevant today, it needs to help inform decisions being made for managed stands. While managing a forest, it is important to not let harvesting effect the diversity of the stand. By harvesting only one or few timber types, or replanting post-harvest with a single species, the overall diversity of the landscape could be lowered. As Wilf et al. (2006) showed, this simplified landscape can create unstable relationships between forests and insects that could take substantial time to recover. An ecosystem with high diversity is more likely to maintain healthy ecosystem processes. Not only that, but a highly diverse forest is more resilient to change and disturbances, such as climate change and insect outbreaks (Convention on Biological Diversity, 2011). Harvesting a variety of timber types, utilizing a variety of harvesting methods, such as partial cuts, and replanting with a mixture of seedling species, not just lodgepole pine, are all ways that can help ensure that biodiversity will not be impacted because of forest management. 11  Limitations   While utilization of the fossil record is beneficial for informing forest management decisions, there are limits as to how effective it can be. The principal limitation is the unpredictability caused by climate change. Climate change does not signify simply that a raise in temperature is occurring. What will be seen is a general rise in temperatures, with an increase in major climatic events, an increase in climatic variability and climate types that we have not seen before. Even now, locations that have seen an overall decrease in precipitation, have seen an increase in major rainfall events (Karl et al., 2009). This means that due to the variable nature of climate change, there is a certain risk associated with the conclusions that we draw. The decisions that are made by forest professionals in order to maintain a healthy relationship between forests and forest insects need to be based on the most reliable information possible. However, due to the unpredictability of climate change, there will still be an unknown aspect to some forest management decisions that are made. Another perceived limitation to this methodology is the use of the fossil record itself. First, the fossil record can only provide long term, general trends (Trexler, 2006). This means that there is difficulty with gathering information about specific, short term phenomena. This will constrain how we can use the fossil record. It would be difficult to answer how an insect population would be affected by one small aspect of change over a short time. Instead, we have to look at how a population would react to broad scale, long term change. However, some might argue that this would actually encourage long term forest management decisions, to the benefit of the forest landscape. Second, the reliability of the entire fossil record is sometimes questioned owing to its perceived “bias”. The odds of any individual organism becoming fossilized are extremely small. An organism would need to be in the right environment with the right timing and then maintain its physical integrity throughout the fossilization process (Lieberman & Kaesler, 2010). Some say that the rare conditions required for fossilization to occur indicates that the 12  fossil record does not provide us with an accurate view into historical environments. This is also not necessarily a vaild argument. Invertebrates, such as insects, have a large fossil record owing to their generally large population sizes and their broad distribution ranges. Plants also have a very detailed fossil record. This is due to their sheer abundance in forested ecosystems; their population sizes increase the odds of fossilization. Fossilized pollen is another facet of the fossil record that can contribute to our understanding of past ecological conditions (Lieberman & Kaesler, 2010).  Considering this, despite initial concerns, the fossil record can provide enough information to help inform management practices. The final limitation I would like to discuss is the likelihood of forest management practices being implemented that are aligned with what we can learn from the fossil record. As an example, the British Columbia (B.C.) Forest Stewardship Action Plan for Climate Change Adaptation (2012) acknowledges that climate change is affecting the dynamic relationship between forests and insects. With the intention of reducing this impact, it states that one of the aims of forestry in B.C. is “to avoid undue simplification of ecosystems at the stand and landscape levels”. British Columbia has over fifty native tree species (Klinkenberg, 2013). This, combined with B.C.’s goal of maintaining forest diversity, would make it logical to assume planting programs post-harvest would encompass a wide variety of native tree species. However, it takes nothing more than a walk through a planted cutblock to see the glaring error in this. In 2013, approximately 47% of the 238 million seedlings produced for planting in BC were lodgepole pine (Kolotelo, 2015). Reforesting landscapes with predominantly one species goes against the goal of diversity; it is in direct conflict with what we have learned about the effects of plant diversity on insect diversity. Using the fossil record to strengthen our knowledge of how the forest/insect relationship will be effected by climate change is only valuable if forest management applies the information that has been gathered. 13  Conclusion   The fossil record is a reliable source of information regarding the state of past ecosystems and how they reacted to change, including changes in climate. If this were to be ignored, forest professionals may miss out on an important point of reference which would lead to holes in the understanding of the integrity of our forested ecosystems. Through the fossil record, we have learned that climate change has an effect on insect populations; either directly, by influencing the behaviours of insects, or indirectly, by influencing the environment and host availability. What the fossil record means for forest management is the development of longer term management decisions. Maintaining diversity and a focus on more than just the current forest rotation requires a long term focus. However, it is important to remember the difference between having the fossil record inform decisions and completely decide our management practices. By focusing entirely on the fossil record, current and never before seen conditions could be overlooked. Climate change is having a great effect on many aspects of the environment. Arctic ice and forest cover have been decreasing around the globe while temperature and atmospheric carbon levels are increasing. Saying that the current temperature is above average may be a little misleading; what is the “average” temperature after all? What is significant, however, is that 2014 was the hottest year on record (NASA/GISS, 2015) and 2015 is on track to be even warmer (NCEI, 2015). This is a substantial change that poses is a real threat to the health and functioning of our forests. Which is why a short term, business-as-usual approach to forest insect management is not an appropriate method of action. A comprehensive understanding of how climate change effects the complex relationship between insects and forests is needed in order to help establish these long term management choices. This is information that we can learn from the fossil record. 14  As nutrient cyclers, predators and promoters of stand complexity, insects have an important role in forested landscapes. While managing a stand for objectives such as timber supply or recreation, forest professionals have an obligation to maintain the function of the forest; whether that means controlling an invasive pest outbreak or not wholly repressing a naturally occurring insect outbreak. For harvestable lands, there is a responsibility to ensure the timber supply remains valuable while still protecting the health of the ecosystem, and insects are a part of that system. Using the fossil record to find out more about forest insects and climate change will only strengthen our understanding, which will enable professionals to make the most informed management decisions possible.                   15  Works Cited  Alley, R., Berntsen, T., Bindoff, N. L., Chen, Z., Chidthaisong, A., Friedlingstein, P., . . . al., e. (2007). Climate Change 2007: The Physical Science Basis, Summary for Policymakers. Intergovernmental Panel on Climate Change Secretariat. Geneva. Bale, J. S. (2002). 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New York: Cambridge University Press. Klinkenberg, B. (2013). E-Flora BC: Electronic Atlas of the Flora of British Columbia. University of British Columbia, Vancouver. Retrieved July 15, 2015 Kolotelo, D. (2015, July 3). Tree Seed Use in British Columbia: Current Practices and Future Directions. Retrieved from Ministère des Forêts, de la Faune et des Parcs: Lieberman, B. S., & Kaesler, R. (2010). Prehistoric Life: Evolution and the Fossil Record. Chichester: Wiley-Blackwell. McLean, J. A., van der Kamp, B., & Behennah, A. L. (2005). Forest Pest Management. In S. B. Watts, & L. Tolland (Eds.), Forestry Handbook for British Columbia (5th ed., pp. 528-554). University of British Columbia. 17  Ministry of Forests, L. a. (2012). Forest Stewardship Action Plan for Climate Change Adaptation. British Columbia. Moeck, H. A., & Safranyik, L. (1984). Assessment of Predator and Parasitoid Control of Bark Beetles. Victoria: Environment Canada. Morrill, C., & Jacobsen, R. M. (2005). 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The Biology and Epidemiology of the Mountain Pine Beetle in Lodgepole Pine Forests. In L. Safranyik, & B. Wilson, The Mountain Pine Beetle – A Synthesis of 18  Biology, Management, and Impacts in Lodgepole Pine (pp. 3-66). Victoria: Pacific Forestry Center. Schoonhoven, L. M., van Loon, J. J., & Dicke, M. (2005). Insect-Plant Biology. Oxford: Oxford University Press. Siemann, E., Tilman, D., Haarstad, J., & Ritchie, M. (1998). Experimental Tests of the Dependence of Arthropod Diversity on Plant Diversity. The American Naturalist, 738-750. Trexler, D. (2006). Fossil Record. In H. J. Birx, Encyclopedia of Anthropology (pp. 983-995). Thousand Oaks: SAGE Publications Inc. Wilf, P. (2008). Insect-Damaged Fossil Leaves Record Food Web Response to Ancient Climate Change and Extinction. New Phytologist, 486-502. Wilf, P., Labandeira, C. C., Johnson, K. R., & Eillis, B. (2006). Decoupled Plant and Insect Diversity after the End-Cretaceous Extinction. Science, 1112-1115. Wilf, P., & Labandeira, C. C. (1999). Response of Plant-Insect Associations to Paleocene-Eocene Warming. Science, 2153-2156. Wing, S. L., Harrington, G., Smith, F. A., Bloch, J. I., Boyer, D. M., & Freeman, K. H. (2005). Transient Floral Change and Rapid Global Warming at the Paleocene-Eocene Boundary. Science, 993-996. Wright, M. G., & Samways, M. J. (1998). Insect Species Richness Tracking Plant Species Richness in a Diverse Flora: Gall Insects in the Cape Floristic Region, South Africa. Oecologia, 427-433.   


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