# Remote Sensing Indicators of Spongy Moth (Lymantria dispar L.) Damage to Birch Stands in Western Siberia

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## Abstract

**:**

## 1. Introduction

- -
- What factors contribute to varying levels of insect attacks in nearby plantations?
- -
- How do the phases of leaf defoliation and refoliation relate to one another?
- -
- Does the condition of trees in sample plots with different levels of insect damage to their leaf apparatus correlate with the level of damage caused by phyllophagous insects?

## 2. Materials and Methods

#### 2.1. Satellite Data Acquisition and Processing

- -
- Availability of the calculated Normalized Difference Vegetative Index (NDVI) for all studied territories. In this paper, the NDVI is calculated using the standard formula:$$NDVI=\frac{NIR-Red}{NIR+Red}$$
- -
- Open access to the NDVI indicator time series via EO-browser analysis system of Sentinel-2 satellite data (https://apps.sentinel-hub.com/eo-browser/, accessed on 15 September 2023).
- -
- High spatial resolution up to 10 m per pixel.
- -
- Possibility of obtaining a sample of averaged NDVI time series for selected contours of the study sites directly through the EO-browser system.
- -
- In order to improve the accuracy of the obtained observations, we used images with the cloudiness level not exceeding 5%.

_{A}(t)−NDVI

_{C}(t))/NDVI

_{C}(t)

_{A}(t) is the value of the vegetative index of the damaged site at the moment t, and NDVI

_{C}(t) is the value of vegetative index of the control site at the moment t. This index characterizes the weakening of the trial site relative to the control site at the current moment. The dynamics of the DF index for the same PP06 is shown in Figure 5.

- MinDF—minimum DF value for the period: maximum stand damage.
- TMinDF—MinDF time point, which defines the moment of maximum stand damage.
- Integ(<MinDF)—integral sum of indicator during defoliation: defines the defoliation intensity for the whole time up to the moment of MinDF.
- Integ(>MinDF)—integral sum of the indicator during refoliation after MinDF has been reached.

#### 2.2. Assessing Tree Condition Using Biophysical Methods

_{0}and R

_{∞}, which represent the ohmic and capacitive components of the object’s impedance. Pathological processes in tree tissues modify these parameters. Specifically, the R

_{0}value [29,33] decreases as the quality of the cell membrane properties degrades. Later in the study, this index was employed to evaluate the condition of woody plant tissues in field conditions.

_{0}and R

_{∞}of the impedance hodograph were measured along with the value of the variable

_{0}(A) in damaged stands and the average characteristics R

_{0}(C) in control stands.

^{2}.

## 3. Results

_{d}and B

_{d}are coefficients, and ${B}_{d}=\frac{\partial (Integ(<MinDF))}{\partial (d{R}_{0})}$ indicates the susceptibility of trees to insect attack depending on their relative condition dR

_{0}. Experimental site PP05 differs significantly from the other trial sites. The dielectric values indicate a further decline in tree tissue functioning, which is likely due to drought conditions during the time of measurement, as observed at this trial site. The parameters of the equations of the relationship between Integ(<MinDF) and dR

_{0}, and between Integ(>MinDF) and dR

_{0}, are given in Table 3.

_{d}of susceptibility of trees to insect damage depending on their condition is significant at the level of p < 0.05, and the coefficient B

_{r}of susceptibility of trees to refoliation is significant at the level of p < 0.1.

_{1}is the date of damage onset, when the NDVI value in the outbreak becomes lower than this value in the control, D

_{2}is the date when the maximum crown damage is reached, and D

_{3}is the date when the NDVI value peaks during stand refoliation. By utilizing these dates, the following characteristics of the temporal dynamics of changes in NDVI were calculated: T

_{1}= D

_{2}−D

_{1}—period from the beginning to the maximum damage, and T

_{2}= D

_{3}− D

_{2}—period from the date of maximum damage to the maximum reforestation. For the specific values of D

_{1}to D

_{3}, T

_{1}, and T

_{2}, see Table 4.

_{1}and T

_{2}with the current state of trees in the stands, the same dielectric characteristics dR0 that were used to estimate the response of tree response amplitudes were used. Figure 10 and Figure 11 show the dependence of characteristic times T

_{1}and T

_{2}on the dR

_{0}state of trees in the outbreak area relative to the control.

_{1}and T

_{2}with increasing dR

_{0}values. The convergence of tree conditions in the outbreak zone and control leads to faster defoliation and refoliation processes, suggesting a correlation between tree condition and the rate of these processes. At the same time, for outbreak zones, the change in the duration of leaf removal period as a function of state change dR

_{0}$\frac{\partial {T}_{1}}{\partial (d{R}_{0})}\approx -44$ is smaller in absolute value than the same value for refoliation $\frac{\partial {T}_{1}}{\partial (d{R}_{0})}\approx -57$ (Table 5).

## 4. Discussion

_{1}and refoliation times T

_{2}is not clear, but it still exists. The chosen indicator to determine tree condition in the stands significantly influences the trees’ response to insect impacts. At high values of the condition index, the duration of both leaf defoliation and refoliation in trees decreases, resulting in decreased levels of insect impact on trees. Therefore, larger values of the tree state characteristic are correlated with decreased impact by insects. Additionally, there is an inverse relationship between the characteristic times T

_{1}and T

_{2}, where the duration of refoliation decreases as defoliation duration increases.

## 5. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 3.**Examples of established damaged and control plots, (

**a**) control is located in the nearest undamaged birch clump (PP05), (

**b**) control is located in an undamaged part of the same birch clump (PP06).

**Figure 4.**Typical curve of NDVI seasonal dynamics for pest-damaged and control intact trial plot PP06 (

**a**), PP04 (

**b**), PP05 (

**c**).

**Figure 5.**Dynamics of DF weakening indicator for PP06. MinDF—minimum value (maximum damage). Integ(<MinDF)—integral sum of indicator during defoliation. Integ(>MinDF)—integral sum of indicator during refoliation.

**Figure 7.**Relationships between defoliation and refoliation indicators of stands in 2020–2021 after damage by spongy moths. 1—stands in which Integ(>MinDF) ≈ Integ(<MinDF); 2—stands in which Integ(>MinDF) < Integ(<MinDF).

**Figure 9.**Relationship between the characteristics dR

_{0}(relative deviation in condition of trees) in damaged stands compared to the control and the level of defoliation Integ(<MinDF). 1—sample plots pp03, pp04, pp06–pp11; 2—sample plot pp05.

**Figure 10.**Dependences of characteristic times T

_{1}on the state dR

_{0}of trees in the outbreak area relative to the control. 1—plots with high levels of defoliation; 2—plots with low levels of defoliation.

**Figure 11.**Dependences of characteristic times T

_{2}on the state dR

_{0}of trees in the outbreak area relative to the control.

Year | Plot | MInDF | Date MInDF | Integ(<MinDF) | Integ(>MinDF) | Insect Attack |
---|---|---|---|---|---|---|

2020 | PP03 | −0.181 | 14.07.2020 | 2.898 | 4.162 | Possible |

2020 | PP04 | −0.157 | 22.07.2020 | 3.618 | 2.362 | Impossible |

2020 | PP05 | −0.021 | 27.07.2020 | 2.866 | 1.947 | Impossible |

2020 | PP06 | −0.009 | 24.08.2020 | 4.907 | 0.467 | Impossible |

2020 | PP07 | −0.014 | 30.07.2020 | 1.408 | 2.373 | Impossible |

2020 | PP08 | −0.152 | 09.08.2020 | 1.716 | 1.059 | Impossible |

2020 | PP09 | −0.037 | 04.08.2020 | 1.677 | 0.083 | Impossible |

2020 | PP10 | −0.081 | 16.08.2020 | 3.120 | 0.827 | Impossible |

2020 | PP11 | −0.031 | 15.06.2020 | 0.232 | 0.295 | Impossible |

2021 | PP03 | −0.145 | 02.07.2021 | 5.784 | 3.987 | Possible |

2021 | PP04 | −0.272 | 02.07.2021 | 5.150 | 5.050 | Possible |

2021 | PP05 | −0.363 | 02.07.2021 | 5.557 | 5.676 | Possible |

2021 | PP06 | −0.187 | 05.07.2021 | 3.260 | 5.055 | Possible |

2021 | PP07 | −0.208 | 03.07.2021 | 3.394 | 4.171 | Possible |

2021 | PP08 | −0.198 | 30.06.2021 | 3.821 | 4.216 | Possible |

2021 | PP09 | −0.058 | 05.07.2021 | 0.800 | 0.628 | Impossible |

2021 | PP10 | −0.031 | 20.07.2021 | 0.681 | 0.801 | Impossible |

2021 | PP11 | −0.073 | 27.07.2021 | 2.141 | 1.168 | Impossible |

2022 | PP03 | −0.143 | 31.08.2022 | 5.610 | 0.000 | Impossible |

2022 | PP04 | −0.022 | 10.07.2022 | 1.041 | 2.903 | Impossible |

2022 | PP05 | 0.150 | 09.08.2022 | 19.204 | 2.415 | Impossible |

2022 | PP06 | 0.023 | 22.07.2022 | 6.193 | 3.110 | Impossible |

2022 | PP07 | −0.129 | 04.08.2022 | 3.625 | 1.495 | Impossible |

2022 | PP08 | 0.004 | 31.08.2022 | 4.344 | 0.000 | Impossible |

2022 | PP09 | −0.069 | 17.07.2022 | 1.640 | 0.860 | Impossible |

2022 | PP10 | −0.039 | 20.06.2022 | 0.408 | 4.517 | Impossible |

2022 | PP11 | −0.146 | 09.08.2022 | 4.367 | 0.460 | Impossible |

**Table 2.**Characteristics of tree condition in the outbreak area and in control undamaged nearby stands.

Plots | Control | Damage | dR_{0} | Integ(<=MinDF) | Integ(>MinDF) | ||
---|---|---|---|---|---|---|---|

R_{0}(C) | R_{∞} (C) | R_{0}(A) | R_{∞} (A) | ||||

pp03 | 4.50 | 1.61 | 4.50 | 1.98 | −0.13 | 5.78 | 3.99 |

pp04 | 4.73 | 1.77 | 4.67 | 2.01 | −0.10 | 5.15 | 5.05 |

pp05 | 4.75 | 1.73 | 4.67 | 1.61 | 0.01 | 5.56 | 5.68 |

pp06 | 4.73 | 1.73 | 4.58 | 1.87 | −0.10 | 3.26 | 5.05 |

pp07 | 4.52 | 1.80 | 4.32 | 1.94 | −0.12 | 3.39 | 4.17 |

pp08 | 4.58 | 1.92 | 4.60 | 2.03 | −0.03 | 3.82 | 4.22 |

pp09 | 4.41 | 1.93 | 4.49 | 2.15 | −0.05 | 0.80 | 0.63 |

pp10 | 4.54 | 1.98 | 4.56 | 1.86 | 0.06 | 0.68 | 0.80 |

pp11 | 4.52 | 2.07 | 4.54 | 2.19 | −0.04 | 2.14 | 1.17 |

**Table 3.**Parameters of the coupling equations between Integ(<MinDF) and dR

_{0}and between Integ(>MinDF) and dR

_{0}.

Parameters | Values | Std.Err. | t-Test | p-Value |
---|---|---|---|---|

dR_{0}, Integ(<MinDF) | ||||

A_{d} | 1.68 | 0.74 | 2.28 | 0.06 |

B_{d} | −22.09 | 8.44 | −2.62 | 0.04 |

R^{2} | 0.53 | |||

adjR^{2} | 0.46 | |||

F-test | 6.86 | |||

dR0, Integ(>MinDF) | ||||

A_{r} | 1.72 | 0.82 | 2.11 | 0.08 |

B_{r} | −21.46 | 9.34 | −2.30 | 0.06 |

R^{2} | 0.47 | |||

adjR^{2} | 0.38 | |||

F-test | 5.28 |

**Table 4.**Temporal dynamics of tree defoliation and refoliation during the L.dispar outbreak in the Novosibirsk region in 2021.

Plot | D_{1}, Date | D_{2}, Date | D_{3}, Date | T_{1}, Days | T_{2}, Days |
---|---|---|---|---|---|

PP03 | 30.05.2021 | 09.06.2021 | 02.07.2021 | 10 | 23 |

PP04 | 31.05.2021 | 07.06.2021 | 05.07.2021 | 7 | 28 |

PP05 | 05.06.2021 | 07.06.2021 | 02.07.2021 | 2 | 25 |

PP06 | 07.06.2021 | 15.06.2021 | 02.07.2021 | 8 | 17 |

PP07 | 08.06.2021 | 15.06.2021 | 28.06.2021 | 7 | 13 |

PP08 | 05.06.2021 | 15.06.2021 | 30.06.2021 | 10 | 15 |

PP09 | 05.06.2021 | 12.06.2021 | 02.07.2021 | 7 | 20 |

PP10 | 05.06.2021 | 15.06.2021 | 25.06.2021 | 10 | 10 |

PP11 | 01.06.2021 | 06.06.2021 | 20.06.2021 | 5 | 14 |

**Table 5.**Parameters of regression equations of the relationships between T

_{1}, T

_{2}and dR

_{0,}and between T

_{1}and T

_{2}.

Parameters | Value | Std.Err. | t-Test | p-Value |
---|---|---|---|---|

T_{1} | ||||

Intercept | 3.16 | 0.90 | 3.53 | 0.02 |

Slope | −44.27 | 9.93 | −4.46 | 0.01 |

R^{2} | 0.80 | |||

F-test | 19.90 | |||

T_{2} | ||||

Intercept | 13.76 | 2.75 | 5.00 | 0.00 |

Slope | −56.81 | 31.53 | −1.80 | 0.12 |

R^{2} | 0.35 | |||

F-test | 3.2 | |||

T_{1}/T_{2} | ||||

Intercept | 27.88 | 5.30 | 5.26 | 0.00 |

Slope | −1.17 | 0.59 | −1.97 | 0.10 |

R^{2} | 0.39 | |||

F-test | 3.9 |

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**MDPI and ACS Style**

Kovalev, A.; Soukhovolsky, V.; Tarasova, O.; Akhanaev, Y.; Martemyanov, V.
Remote Sensing Indicators of Spongy Moth (*Lymantria dispar* L.) Damage to Birch Stands in Western Siberia. *Forests* **2023**, *14*, 2308.
https://doi.org/10.3390/f14122308

**AMA Style**

Kovalev A, Soukhovolsky V, Tarasova O, Akhanaev Y, Martemyanov V.
Remote Sensing Indicators of Spongy Moth (*Lymantria dispar* L.) Damage to Birch Stands in Western Siberia. *Forests*. 2023; 14(12):2308.
https://doi.org/10.3390/f14122308

**Chicago/Turabian Style**

Kovalev, Anton, Vladislav Soukhovolsky, Olga Tarasova, Yuriy Akhanaev, and Vyacheslav Martemyanov.
2023. "Remote Sensing Indicators of Spongy Moth (*Lymantria dispar* L.) Damage to Birch Stands in Western Siberia" *Forests* 14, no. 12: 2308.
https://doi.org/10.3390/f14122308