Mapping the Growing Stem Volume of the Coniferous Plantations in North China Using Multispectral Data from Integrated GF-2 and Sentinel-2 Images and an Optimized Feature Variable Selection Method

Accurate measurement of forest growing stem volume (GSV) is important for forest resource management and ecosystem dynamics monitoring. Optical remote sensing imagery has great application prospects in forest GSV estimation on regional and global scales as it is easily accessible, has a wide coverage, and mature technology. However, their application is limited by cloud coverage, data stripes, atmospheric effects, and satellite sensor errors. Combining multi-sensor data can reduce such limitations as it increases the data availability, but also causes the multi-dimensional problem that increases the difficulty of feature selection. In this study, GaoFen-2 (GF-2) and Sentinel-2 images were integrated, and feature variables and data scenarios were derived by a proposed adaptive feature variable combination optimization (AFCO) program for estimating the GSV of coniferous plantations. The AFCO algorithm was compared to four traditional feature variable selection methods, namely, random forest (RF), stepwise random forest (SRF), fast iterative feature selection method for k-nearest neighbors (KNN-FIFS), and the feature variable screening and combination optimization procedure based on the distance correlation coefficient and k-nearest neighbors (DC-FSCK). The comparison indicated that the AFCO program not only considered the combination effect of feature variables, but also optimized the selection of the first feature variable, error threshold, and selection of the estimation model. Furthermore, we selected feature variables from three datasets (GF-2, Sentinel-2, and the integrated data) following the AFCO and four other feature selection methods and used the k-nearest neighbors (KNN) and random forest regression (RFR) to estimate the GSV of coniferous plantations in northern China. The results indicated that the integrated data improved the GSV estimation accuracy of coniferous plantations, with relative root mean square errors (RMSErs) of 15.0% and 19.6%, which were lower than those of GF-2 and Sentinel-2 data, respectively. In particular, the texture feature variables derived from GF-2 red band image have a significant impact on GSV estimation performance of the integrated dataset. For most data scenarios, the AFCO algorithm gained more accurate GSV estimates, as the RMSErs were 30.0%, 23.7%, 17.7%, and 17.5% lower than those of RF, SRF, KNN-FIFS, and DC-FSCK, respectively. The GSV distribution map obtained by the AFCO method and RFR model matched the field observations well. This study provides some insight into the application of optical images, optimization of the feature variable combination, and modeling algorithm selection for estimating the GSV of coniferous plantations.

Distribution of mixed coniferous stands in the Luzhsko-Volkhovsky landscape district

Смешанные древостои с преобладанием сосны и ели занимают территории с оптимальными лесорастительными условиями, в отличие от монодоминантных насаждений. Условно чистые древостои в большинстве случаев приурочены к экстремальным условиям местообитания или обусловлены созданием лесных культур. Среди смешанных древостоев с преобладанием хвойных пород однозначно только хвойно-лиственные, а именно – елово-лиственные древостои, связываются с антропогенным воздействием на географический ландшафт. В каждом отдельно взятом ландшафте будет формироваться отличное распределение типов хвойных насаждений по лесопокрытой площади в зависимости от почвенно-гидрологических условий. Оценка пространственного распределения смешанных хвойных древостоев в различных типах леса позволяет дать точную экологическую характеристику и оценку ландшафта и оценить его антропогенную изменённость. Рассматриваются особенности распространения смешанных древостоев с преобладанием сосны и ели в наиболее представленных типах леса в основных ландшафтах Лужско-Волховского ландшафтного округа Ленинградской области. Проведён анализ ландшафтов по распределению покрытой лесом площади по почвенно-гидрологическим условиям и основным обобщённым группам типов леса. Присутствие сложного комплекса холмисто-моренных, камовых, озовых урочищ, чередующихся с заболоченными котловинами и озёрами практически во всех рассмотренных ландшафтах, позволяет сделать заключение, что приуроченность смешанных хвойных древостоев связана с фактором переходных форм рельефа от одной ландшафтной группы к другой. Типологическая приуроченность хвойных полидоминантных древостоев является закономерной для зеленомошной серии типов леса данного ландшафтного округа. Mixed woodlands with a predominance of pine and spruce occupy territory with optimal forest-growing conditions, unlike monodominant plantations. Conditionally clean woodlands are in most cases shortened to extreme habitat conditions or due to the creation of forest crops. Among mixed woodlands with a predominance of conifers, unambiguously only coniferous-deciduous, namely spruce-deciduous woodlands, are associated with anthropogenic effects on the geographical landscape. In each individual landscape, an excellent distribution of the types of coniferous plantations along the covered area will be formed, depending on soil and hydrological conditions. The assessment of the spatial distribution of mixed coniferous trees in different types of forest allows to give an accurate ecological characteristic and assessment of the landscape and to assess its anthropogenic variation. The article considers the distribution features of mixed woodlands with a predominance of pine and spruce in the most represented types of forest in the main landscapes of the Luga-Volkhov landscape district of the Leningrad region. An analysis of landscapes was carried out on the distribution of forest-covered area according to soil-hydrological conditions and the main generalized groups of forest types. The presence of a complex of hilly-moraine, stone, oze tracts alternating with swampy basins and lakes in almost all the landscapes considered allows us to conclude that the confluence of mixed coniferous woodlands is associated with the factor of the transition forms of relief from one landscape group to another. The typological confluence of coniferous polydominant woodlands is natural for a green-haired series of forest types of this landscape district.

To the study of formation of phytophagous true bugs (Insecta: Heteroptera) complex on introduced coniferous in Donbass

Three species of true bugs: Dichrooscytus gustavi Josifov, 1981 (Miridae), Gonocerus juniperi HerrichSchaeffer, 1839 (Coreidae) and Chlorochroa pinicola (Mulsant & Rey, 1852) (Pentatomidae) was firstly found during the reconnoiter surveillance of specialized phytophagous Hemiptera (Heteroptera) on introduced coniferous in the territory of Donbass for the period 2019–2020. Two species (G. juniperi and C. pinicola) are recorded for the first time for the southeast of Ukraine, D. gustavi - for the first time for Ukraine. The paper presents information on the distribution, biology and ecology of the recorded species. Dichrooscytus gustavi and G. juniperi are trophically associated with junipers (Juniperus spp.), C. pinicola – with pines (Pinus spp.). The expansion of phytophagous species composition on pines in Donbass is a consequence of active forest management activities. In addition to the nearby invaders, which include C. pinicola, an increase in the number of dangerous alien invasive pests such as Leptoglossus occidentalis Heidemann, 1910 (Heteroptera: Coreidae) has recently been observed on pines. The invasion of the sucking-feeders species on junipers into Donbass may be the result of massive import potted crops of this breed from nurseries and independent dispersal of this insects from adjacent territories. An increase of the number of sucking pests - the main vectors of viral and phytoplasmic diseases on pines and junipers can negatively affect the decorative and sanitary condition of coniferous plantations in Donbass. To develop a forecast of harmfulness and a complex of protective measures, it is necessary to control the appearance of new phytophagous species on introduced coniferous and to constantly monitor the state of their populations.

Influence of anthropogenic pollution on morphological-anatomical parameters and spectral characteristics of Scots pine needles

The research paper demonstrates a comprehensive comparative analysis of the state of coniferous plantations in Minsk in areas with a favourable and predominantly unfavourable ecological situation and control trees growing in relatively clean territories. The morphological-anatomical and bilateral (in terms of fluctuating asymmetry) patterns of needles of Scots pine (Pinus sylvestris L.) change were revealed, reflecting the severity of anthropogenic press on the urban environment. The possibility of using the FTIR spectroscopy method combined with chemometric analysis algorithms for the differentiation of needles is shown. Using the method of principal components, the test samples were divided into clusters reflecting the extent of their anthropogenic load.

Insect pests in the forests of Bulgaria and their economic importance

Based on the forest-pathological inventories for the last 30 years, the economic importance of the insect pests in the Bulgarian forests and its dynamics for the periods 1990–2002 and 2003–2018 were determined. Insect pest attacks have declined sharply in the last sixteen years- in coniferous forests they have decreased three times and in deciduous ones - almost six times. Generally, the health status of the forests, with regard to pest status, after 2003 is improving, and this is more clearly expressed in the deciduous forests. As a result of this development, the pest control measures areas gradually shifted from deciduous to coniferous forests. Since 2003, deterioration in the health status of ageing coniferous plantations has been identified, however, with the attacks of two major groups of pests escalating- pine sawflies and bark beetles.

Violation of the structure of the forest biocenosis under the action of stem pests and methods of controlling their numbers

The study of the forest ecosystem as an integral part of the erosion system is associated with a number of issues. The forest is the most powerful and effective tool in the fight against soil erosion, droughts and hot winds, as well as an environmental stabilising factor in general. Human forestry activities in the fight against the drying of coniferous plantations from an outbreak of mass reproduction and spread to large areas of stem pests under the influence of a complex of ecological and climatic factors, is one of the serious factors disrupting the structure of the forest biocenosis. The search for alternative solutions to the localisation of this problem requires a detailed study of the behaviour of the most common bark beetles of coniferous trees in climatic and environmental conditions that developed during 2011-2020. During the period of active temperatures in 2019, namely from the second decade of April to the third decade of October, work on stationary supervision and laboratory field work was carried out to solve the problem of localisation of stem pests of Polissya and Forest-Steppe pine plantations. Methods of laying out hunting trees and pheromone traps were used. In practice, the pest did not inhabit hunting trees and only a few representatives and very small entomophagous traps fell into the traps. Instead, it inhabited healthy stands of trees, where the catchers were located. It is established that from the scientific and practical standpoint, the studied regularity of pine drying centres is clearly confined to highways and timber roads, as well as the area of distribution of relevant species of trunk pests and weakening zones of pine stands in some areas for other reasons. It is proved that to preserve the ecological potential of coniferous plantations and reduce the negative impact of xylophagous insects, it is necessary to design preventive and biological methods of control of the main trunk pests of coniferous trees