Course:CONS200/2019/Links between climate change and insect outbreaks in BC: Past trends and future outlook

Introduction

The links between climate change and Bark Beetles population

Climate change are predicted to play a vital role to shape the forest ecosystems by affecting the frequency and disturbances.  In recent decades, forest disturbances were starting to show evidence of the dangers such as the unpredictable droughts and insect outbreaks are relative to climate change. In the fact, changes in weather are simultaneously influences the species ranges, life cycles, and interactions of the native bark beetles with their important agents of conifers in Canada. Species range expansions as well as success of population dynamics in response to the direct affects such as the changing of temperature, developmental timing and cold tolerance, moreover, the indirect affect such as community associates, host-tree physiology and host-tree distribution are rewarding the abundance to bark beetles at the same level. One example is the mountain pine beetles which has extend their range as the result of increased temperatures and has achieved higher densities as the result of increased survival and availability of host plants, consequently bring massive damage to forests in North America. However, the insects’ outbreaks have a complex and symbiotic relationship with weather.

The present climate change

Temperature influences almost all insects reproduce processes such as off-springs rate, species range and weather-tolerances. The seasonal temperatures in North America plays a key role in limiting populations of bark beetles by directly affecting their growth and survival. During twenty-first century, average global temperatures are evident to increase between 2 and 4 degrees as the result of growing green gas concentration in atmosphere, particularly across North America, the rise of temperature is projected to exceed global mean increases. Associated changes in precipitation may result in the dry seasons with a duration of droughts. Conifers and other floras provide essential ecosystem services and host of many fungi and animals, however, are predictably affected by change in temperature, precipitation and gases. Due to the fact that the direct link between insect success of population and seasonal temperature, the insects are processing the evolution to acquire the genetic adaptation of insects. In the next century the climatic changes will significantly affect the condition, composition and distribution of ecosystems.  The native bark beetles of western North America

The native bark beetles of western North America

Native bark beetles which evolved within the coniferous forest ecosystems of western North America, are key agents of change in these systems, in the meanwhile, Insect outbreak will bring irreversible damage and missed up in these ecosystem. In recent decades, billions of coniferous trees have been killed by native bark beetles. For example, the mountain pine beetle Dendroctonus ponderosa is one of the tree-killing bark beetle responsible for mature pine trees, their range of population is from northern Mexico through the Pacific Northwest to northwestern Alberta in Canada, most frequently occurring at elevations of 1500-2600 m above mean sea level. In another case, lodge pole pine Pinus contorta var. latifolia and several other species of pine are also attacked by native bark beetles.

Categories of Actors

Images from Wikimedia Commons can be embedded easily.

Direct effects of climate change on bark beetles

Although among the hundreds of native bark beetles species in Canada, only few species attack and reproduce in living trees, the rest of aggressive bark beetles can kill healthy trees and cause the increasing death rate of trees in those areas. Actually, host trees selection and colonization by adult bark beetles are complex processes, but depends on their experiences, they can recognize the host trees species whether they are suitable to live or not, even solve the issues about the defensive ability of the host trees. Once select the host trees, adult bark beetles lay eggs in the phloem, and the babies eating trees’ tissue and eventually results in the mortality of the host tree. Many bark beetles species invisibly kill trees because of their survival, the direct effects of climate change on bark beetles population will occur distinctly from the influence of temperature on life strategies includes: a), maintain adaptive developmental timing leading to population, and b), modification of cold tolerance due to reproduce in the low temperature.

Developmental timing

The time required to complete a generation varies among bark beetles within the species, population and even the individuals. Some species such as some western pine beetles produce more than one generation per year. And then some mountain pine beetles need even more than three years to produce a single generation, depending on the temperature at a particular land-scale. Moreover, as the result of the evolution, the adaptation of bark beetles cause their success of fertilization rapidly increase. Although it is little known about specific temperature-dependent developmental processes of bark beetles species, diapause and direct temperature control, have evolved to maintain appropriate life-cycle timing, and each modification of adaptation of bark beetles is affected differently by climate change.  

Cold tolerance

In addition to climate controls on adaptive developmental timing, mortality from cold is another key temperature-related factor in bark beetles. Similar to the adaptation in developmental timing, cold tolerance will undoubtedly different among the populations of the same bark beetle species. Cold tolerance of those insects can be safely alive during the winter or the periods of low temperature, and similarly, it will reduce the insects’ mortality.

Indirect effects of climate change on bark beetles

Bark beetle population success will be influenced indirectly by the effects of climate on community associates, host-tree vigor, and host abundance.

Community associates

After colonizing a tree, the bark beetles start a symbiotic relationship with fungi, bacteria and even nematodes that can significantly influence their fitness, as many bark beetles have evolved adaptations to assist in the transport of specific associates, derive nutritional and defensive benefits. For example, spruce beetles have specialized body structures to carry associated nematodes, and mountain pine beetles and western pine beetles have structures to transport symbiotic fungi. Moreover, benefits to the insects are not the same for each fungi species, shifts in temperature and precipitation associated with climate change could indirectly affect bark beetles population success.

Host-tree distribution

The distribution of coniferous trees across western North America resulted from climatic shifts in the past millions of years. In a rapidly changing environment, coniferous trees will persist through migration or adaptation to new conditions, or they will extinct.

The evidence for the problem

Recent research of forest health in relation to climate change reveal that BC's forests have already faced two globally significant epidemics: the Dothistroma needle blight and the massive mountain pine beetle throughout the BC interior. Rapid genetic adaptation of insects to seasonal changes in temperature has already been documented . Many new species are moving into new environment because of increasing temperatures, new species invasion has been proved that it makes insect outbreaks happened. Furthermore, insect outbreaks success would occur directly and indirectly negative effects in BC, such as fungi or bacteria breeding .

Trees would take several generations (100 to 1000 plus years) to adapt to a new climate. Insects outbreak happens, trees would take more generation to adapt the new climate. Even trees belongs to insects invasion areas is possibly to be endangered, and the soil becomes barren, it would be a vicious circle between climate, tree growth and insects survival.

Forest insects

The warming climate causes the greater accumulation of heat and increase the diversity of insects with a wider range of latitudes and altitudes, the diversified classification of insects parasitize on the tree hosts brings more pressure. Furthermore, once the droughts occur more frequently, the stressed trees are facing a starts of pest outbreaks. Besides, extreme weather will cause the larger scale of damage in which provide the opportunity for pest outbreaks.

Bark beetles

Bark beetles are quite sensitive of the changing of climate and their population record as exceeded population compared with the original number. The life circle and dynamics of bark beetle is complex with many different factors, and they would substantially increase in population when all inductors coincide and surpass the threshold. The reason why bark beetles outbreak is threatened to the environment is that new generation of bark beetle need to excavate outward the host tree, and search a new host tree to lay new eggs.This process is fatal for the host trees.

MPB(mountain pine beetles)

The warming winter are facilitating the outbreak of MPB(mountain pine beetles). The three-fold increase in susceptible pine seen in the latter half of the 20th century provided ideal conditions for MPB to spread across BC and into Alberta (Carroll et al. 2006). In the research, foresters predict that the coming decades is a continuing spread of MPB.

Douglas-fir beetles

Douglas- fir beetle is often affected by the weather-related events; such as drought and windtrow(Furniss and Carolin 1977, McMullen 1984). As climate change suggest a more frequent summer drought and winter windstroms than earlier time, it would facilitate the growth of the Douglas- fir beetle. It is expected to see a worsen situation of outbreaks in many areas in BC with a warm dry condition and a reduced resilience to the budworm trees. Evidence has announced that the situation is occurring in the eastern chilcotin region of BC(L. Rankin, Forest Entomologist, BC Ministry of Forests and Range, personal communication, Sept 29, 2009).

Spruce beetles

Spruce beetle is one of most detrimental pest among the mature spruce forests in Western North America. They are induced by the warming climate and wind-throw and drought as well. Heat accumulation is increasing and helps to form a one year life cycle which in turn could potentially produce larger population then causes more intensive outbreaks (Furniss and Carolin 1977). As well as the wind-throw events, their capability of survival is enhanced when the downed trees are left to be removed, because the beetles can successfully attacking and killing this material and later to influence the standing spruce extensively.

Options for remedial action(s)

One way that we can prevent climate change from harming insects in British Columbia’s forests is to preserve the old growth forests of BC to keep carbon stored in the forest and that way the insects will not be as harmed. We can also try to make the forests’ climate appropriate for the insects being affected by using a technical way with the help of the government. Since the living conditions fluctuate all year around in Canada, it is hard for the insects and other species to adapt to the current climate. If humans are able to move the insects population over to a better climate for them, it will help the insects a lot but it seems almost impossible to move all the insects. What seems to be the best and most possible way to remedy this situation is that if we can limit climate change to change the temperature to a maximum of 5 degrees Celcius so that the climate change will not be too harsh for the insects like beetles to adapt to (Carrington, 2018). It is estimated that the cumulative impact of the mountain pine beetle outbreak in the affected regions from 2000 to 2020 may be approximately 270 megatonnes (Mt) of carbon alone (Kurz, 2008). That is approximately 36 grams of carbon m^-2yr^-1 which is on average 374,000 km squared (Kurz, 2008). If the world does not take action to this situation right away, this impact will convert the forest from a small net carbon sink to an extremely large net carbon sink. This will have a very negative effect while this is happening and immediately afterwards (Kurz, 2008). In one of the worst years, the impact that was coming from the mountain pine beetle outbreak in British Columbia was nearly equivalent to approximately 75 percent of the average annual direct forest fire emissions from all of Canada from 1959 to 1999 (Kurz, 2008). During this time, the resulting net reduction of the net primary production was of a similar outcome of the increases that was observed in the 1980’s and the 1990’s for global change (Kurz, 2008).

The presence of the mountain pine beetle infestation in the British Columbia forests are ranked among one of the largest ecological disturbances that are recorded in Canada so far (Maness, 2013). Some of the most recent outbreaks may be occurring due to the large scale climatic shifts in the ecosystem. The outbreaks has expanded the population a lot over the past 10 years (Parkins, 2007; Ministry of Forests (MoF), 2005). Due to a combination of older age class forests which are more vulnerable to the diseases and infestation and the above average seasonal temperatures of forests. The outbreaks are also related to the change of the climate conditions if the climate conditions begin to favour the beetles rapid population growth (Parkins, 2007). This will affect the forests for a long period of time (parkins, 2007). These outbreaks of the mountain pine beetles do not look like they are expected to stop or slow down any time soon, so humanity must try to find a way to help relieve this situation. These recent outbreaks may be foreshadowing some of the near future outbreaks of mountain pine beetles or different insects of British Columbia with a very similar magnitude of the forests in North America over the upcoming decades (Maness, 2013). The British Columbia provincial government estimates that approximately 30 communities and 25,000 families are being affected by the beetle infestation already (Parkins, 2007; Ministry of Forests, 2004a). The local surface energy balance of the ecosystem may be altered due to the associated dieback of the forests which could result in substantial shifts in evapo transition and albedo. This will then also affect the regional temperature and climate of the ecosystem. A typical decrease in the summertime climate temperature is 19 percent of the affected forests that are over 170,000 km squared. This will then result in a fluctuation of heat that will increase by 8 percent and 1 percent and these changes are comparable to other types of disturbances like forest fires and climate change (Maness, 2013). If the climate change increases the temperature in British Columbia, then there will most likely be more forest fires that will kill off more insects.

Conclusion

Form the collected research, the result shows that the bark beetle response to the climate change with an uncertain and complex outcome. Since there are many other factors working together to generate the issue of pasts trends, for instance, the changing of development timing, cold tolerance within beetles and differentiated level of community associates and host-tree distribution. Those are factors might potentially effect the mortality of the trees. In order to possibly eliminate the cost toward the pasts trends, researchers in forest management realm have evaluate strategy which is assisting the migration of seed sources and species.

Implication for forest management

With the fast evolving pace among the forest pest outbreaks, the enlarged difficulty and complexity of the challenges are more noticeable, at the same time, forest management need to making effort on adapting the practices that not only fulfill the present ones, but also manage it into future. Several key assessment, monitoring and modeling are required to better clarify the connections between climate change and pest outbreaks.

Timber supply forecasting

“Timber supply is based on the predictions of the productivity and on the the current assumptions associated with juvenile stands”( Alex J. Woods,2010). Besides, supply of the timer is largely depends on the physiology of the trees which means that the greater destructiveness the problem is the less supplying of the timer. At this point, the changes in insect outbreaks impact are exceed the imagination in which lowering the accurateness of assess the timber supply.

Monitoring and modeling

More adequate of monitoring in terms of both scale and frequency is at vital demand. Even though the aerial overview could capture the insect and disease to some extent, many problems found out to be irreversible which is detrimental to the health of the forest. So, monitoring insects should across the special scale and insists on a long term records with a more frequent level. “An effective monitoring program adds to our understanding of how pests affect forests and how climate change is influencing ecosystem dynamics and managed stand productivity” ( Alex J. Woods,2010). In addition, the synthesizing of climate models with environmental envelopes might accomplish the goal of forecast the potential regional biotic change related to global warming.

Assisted migration and genetic diversity

Increasing the diversity of species and genetic in corporate with facilitate the migration is regarded as an effective and efficient way of maintaining the healthy plantation when facing the climate change (Millar et al. 2007, O’Neill et al. 2008). In other word, the increasing number of species on a landscape might exerts a buffer effect as each types of insects or trees are slightly different in climatic adaptation (Ledig and Kitzmiller 1992, Millar et al. 2007). However, the majority of forest need to adapt a new environmental condition without human intervention. And we have to admit that the redistribution of seedlots and the level of genetic gain in growth is hard to accomplish simultaneously. With the higher risks of pest outbreaks in BC, it is more appropriate to focus on the resistance traits first.

References

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