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Coupled Human-Environment Dynamics of Forest Pest Spread and Control in a Multi-Patch, Stochastic Setting.

Ali Q, Bauch CT, Anand M - PLoS ONE (2015)

Bottom Line: In particular, modest increases in the tree removal rate, modest increases in public concern for infestation, and modest decreases in the cost of locally purchased firewood, relative to baseline (current) values, cause very large increases in the average time until a patch becomes infested due to firewood transport from other patches, thereby better preventing long-distance spread.Patches that experience lower visitor volumes benefit more from firewood movement restrictions than patches that experience higher visitor volumes.Also, cross-patch infestations not only seed new infestations, they can also worsen existing infestations to a surprising extent: long-term infestations are more intense in the high volume patches than the low volume patches, even when infestation is already endemic everywhere.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Mathematics, Western University, London, Ontario, Canada.

ABSTRACT

Background: The transportation of camp firewood infested by non-native forest pests such as Asian long-horned beetle (ALB) and emerald ash borer (EAB) has severe impacts on North American forests. Once invasive forest pests are established, it can be difficult to eradicate them. Hence, preventing the long-distance transport of firewood by individuals is crucial.

Methods: Here we develop a stochastic simulation model that captures the interaction between forest pest infestations and human decisions regarding firewood transportation. The population of trees is distributed across 10 patches (parks) comprising a "low volume" partition of 5 patches that experience a low volume of park visitors, and a "high volume" partition of 5 patches experiencing a high visitor volume. The infestation spreads within a patch--and also between patches--according to the probability of between-patch firewood transportation. Individuals decide to transport firewood or buy it locally based on the costs of locally purchased versus transported firewood, social norms, social learning, and level of concern for observed infestations.

Results: We find that the average time until a patch becomes infested depends nonlinearly on many model parameters. In particular, modest increases in the tree removal rate, modest increases in public concern for infestation, and modest decreases in the cost of locally purchased firewood, relative to baseline (current) values, cause very large increases in the average time until a patch becomes infested due to firewood transport from other patches, thereby better preventing long-distance spread. Patches that experience lower visitor volumes benefit more from firewood movement restrictions than patches that experience higher visitor volumes. Also, cross-patch infestations not only seed new infestations, they can also worsen existing infestations to a surprising extent: long-term infestations are more intense in the high volume patches than the low volume patches, even when infestation is already endemic everywhere.

Conclusions: The success of efforts to prevent long-distance spread of forest pests may depend sensitively on the interaction between outbreak dynamics and human social processes, with similar levels of effort producing very different outcomes depending on where the coupled human and natural system exists in parameter space. Further development of such modeling approaches through better empirical validation should yield more precise recommendations for ways to optimally prevent the long-distance spread of invasive forest pests.

No MeSH data available.


Related in: MedlinePlus

Dynamics of infested trees, susceptible trees, and local strategists.Panels show a single realization of the number of infested trees (a); the average of 100 realizations of the number of infested trees (b), the number of susceptible trees (c), and the proportion of local strategists (d), over 300 years of simulated time. Only patch 1 was infested at time t = 0. Patches from 1 to 5 are in the low visitor volume Partition 1 while patches from 6 to 10 are in the high visitor volume Partition 2. The parametric values are given in Table 2.
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pone.0139353.g002: Dynamics of infested trees, susceptible trees, and local strategists.Panels show a single realization of the number of infested trees (a); the average of 100 realizations of the number of infested trees (b), the number of susceptible trees (c), and the proportion of local strategists (d), over 300 years of simulated time. Only patch 1 was infested at time t = 0. Patches from 1 to 5 are in the low visitor volume Partition 1 while patches from 6 to 10 are in the high visitor volume Partition 2. The parametric values are given in Table 2.

Mentions: The stochastic nature of the model dynamics is observed by simulating the number of infested trees against time in a single realization (Fig 2A, data available in the supplementary material: S1 Matlab Data File). Patch 1, where the infestation starts, experiences an outbreak that peaks rapidly. As the number of infested trees in patch 1 grows, the probability of infected firewood being transported from patch 1 to other patches increases. Eventually, after a few years, the other patches start to experience outbreaks as a few bundles of infested firewood make their way to those patches and a viable local population of forest pests is formed. In general, patches 2–5 (the high volume partition P1) experience outbreaks sooner than patches 6–10 (the low volume partition P2), except that patch 10 is the next patch to experience an outbreak, after patch 1, for this particular realization (Fig 2A). In contrast, patch 9 avoids infestation throughout the entire simulation. This illustrates the stochastic nature of long–distance forest pest spread. For all other patches, the infestation settles down to a steady state where the destruction of susceptible trees through infestation is balanced by the creation of susceptible trees through recruitment, in the long-term. We note that we ignore the impact of local control measures, since our focus is on long–distance establishment of new infestation sites. However, local control could be represented by increasing the parameter ε representing the probability of death of infested trees per unit time, and we investigate this change in the sensitivity analysis.


Coupled Human-Environment Dynamics of Forest Pest Spread and Control in a Multi-Patch, Stochastic Setting.

Ali Q, Bauch CT, Anand M - PLoS ONE (2015)

Dynamics of infested trees, susceptible trees, and local strategists.Panels show a single realization of the number of infested trees (a); the average of 100 realizations of the number of infested trees (b), the number of susceptible trees (c), and the proportion of local strategists (d), over 300 years of simulated time. Only patch 1 was infested at time t = 0. Patches from 1 to 5 are in the low visitor volume Partition 1 while patches from 6 to 10 are in the high visitor volume Partition 2. The parametric values are given in Table 2.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4592071&req=5

pone.0139353.g002: Dynamics of infested trees, susceptible trees, and local strategists.Panels show a single realization of the number of infested trees (a); the average of 100 realizations of the number of infested trees (b), the number of susceptible trees (c), and the proportion of local strategists (d), over 300 years of simulated time. Only patch 1 was infested at time t = 0. Patches from 1 to 5 are in the low visitor volume Partition 1 while patches from 6 to 10 are in the high visitor volume Partition 2. The parametric values are given in Table 2.
Mentions: The stochastic nature of the model dynamics is observed by simulating the number of infested trees against time in a single realization (Fig 2A, data available in the supplementary material: S1 Matlab Data File). Patch 1, where the infestation starts, experiences an outbreak that peaks rapidly. As the number of infested trees in patch 1 grows, the probability of infected firewood being transported from patch 1 to other patches increases. Eventually, after a few years, the other patches start to experience outbreaks as a few bundles of infested firewood make their way to those patches and a viable local population of forest pests is formed. In general, patches 2–5 (the high volume partition P1) experience outbreaks sooner than patches 6–10 (the low volume partition P2), except that patch 10 is the next patch to experience an outbreak, after patch 1, for this particular realization (Fig 2A). In contrast, patch 9 avoids infestation throughout the entire simulation. This illustrates the stochastic nature of long–distance forest pest spread. For all other patches, the infestation settles down to a steady state where the destruction of susceptible trees through infestation is balanced by the creation of susceptible trees through recruitment, in the long-term. We note that we ignore the impact of local control measures, since our focus is on long–distance establishment of new infestation sites. However, local control could be represented by increasing the parameter ε representing the probability of death of infested trees per unit time, and we investigate this change in the sensitivity analysis.

Bottom Line: In particular, modest increases in the tree removal rate, modest increases in public concern for infestation, and modest decreases in the cost of locally purchased firewood, relative to baseline (current) values, cause very large increases in the average time until a patch becomes infested due to firewood transport from other patches, thereby better preventing long-distance spread.Patches that experience lower visitor volumes benefit more from firewood movement restrictions than patches that experience higher visitor volumes.Also, cross-patch infestations not only seed new infestations, they can also worsen existing infestations to a surprising extent: long-term infestations are more intense in the high volume patches than the low volume patches, even when infestation is already endemic everywhere.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Mathematics, Western University, London, Ontario, Canada.

ABSTRACT

Background: The transportation of camp firewood infested by non-native forest pests such as Asian long-horned beetle (ALB) and emerald ash borer (EAB) has severe impacts on North American forests. Once invasive forest pests are established, it can be difficult to eradicate them. Hence, preventing the long-distance transport of firewood by individuals is crucial.

Methods: Here we develop a stochastic simulation model that captures the interaction between forest pest infestations and human decisions regarding firewood transportation. The population of trees is distributed across 10 patches (parks) comprising a "low volume" partition of 5 patches that experience a low volume of park visitors, and a "high volume" partition of 5 patches experiencing a high visitor volume. The infestation spreads within a patch--and also between patches--according to the probability of between-patch firewood transportation. Individuals decide to transport firewood or buy it locally based on the costs of locally purchased versus transported firewood, social norms, social learning, and level of concern for observed infestations.

Results: We find that the average time until a patch becomes infested depends nonlinearly on many model parameters. In particular, modest increases in the tree removal rate, modest increases in public concern for infestation, and modest decreases in the cost of locally purchased firewood, relative to baseline (current) values, cause very large increases in the average time until a patch becomes infested due to firewood transport from other patches, thereby better preventing long-distance spread. Patches that experience lower visitor volumes benefit more from firewood movement restrictions than patches that experience higher visitor volumes. Also, cross-patch infestations not only seed new infestations, they can also worsen existing infestations to a surprising extent: long-term infestations are more intense in the high volume patches than the low volume patches, even when infestation is already endemic everywhere.

Conclusions: The success of efforts to prevent long-distance spread of forest pests may depend sensitively on the interaction between outbreak dynamics and human social processes, with similar levels of effort producing very different outcomes depending on where the coupled human and natural system exists in parameter space. Further development of such modeling approaches through better empirical validation should yield more precise recommendations for ways to optimally prevent the long-distance spread of invasive forest pests.

No MeSH data available.


Related in: MedlinePlus