Seppo Nevalainen

Detection of dead or defoliated spruces using digital aerial data

Abstract The purpose of this study was to develop a method for detecting dead and defoliated spruces and defoliated stands in remote-sensing material using a semi-automatic pattern-recognition technique, spectral properties of trees, and different degrees of defoliation. The study material included two mapped defoliation stands in the municipality of Juupajoki (61°50′N, 24°18′E) in southern Finland. The ground truth data were collected during 1996–1997. The aerial color infrared (CIR) photographs, scaled to 1:5000, were taken on 28 June 1995 and on 19 June 1997. The degree of defoliation was visually estimated for every conifer in the defoliation stands. Individual trees in the digital aerial photographs were segmented using a robust segmentation method based on the recognition of tree crown patterns at a sub-pixel accuracy. The images were filtered with a Gaussian N × N smoothing operator, and local maxima above a threshold level were segmented using a directional derivate with some constraints. The segments were placed into defoliation classes using linear Fisher classification models, the parameters of which were estimated by cross-validation. Discriminant analysis was used to find variables for the segment classification. Defoliated tree segments and stands were classified satisfactorily. The accuracy of the pattern-recognition method proved adequate for detecting dead or heavily defoliated trees and heavily defoliated stands. The method described provides an interesting approach to using digital aerial data for automatically detecting severely defoliated spruce stands or individual trees.

Gremmeniella abietina in Finnish Pinus sylvestris stands in 1986-1992: a study based on the National Forest Inventory.

Data from 24544 pine-dominated plots of the Eighth National Forest Inventory (NFI) in southern Finland were used in this study. The most commonly identified cause of damage was Gremmeniella abietina (10.6% of the stands). Disease assessments by NFI groups were reliable at the stand level. The disease was spatially clustered, being almost twice as common on peatland as on mineral soil plots. However, there was no difference between undrained peatlands and mineral soils. The more the original peatland site type had changed after drainage, the more common was the disease. On mineral soil, disease frequencies were highest on alluviated plots or on the most fertile plots. Naturally regenerated stands were affected more than artificially regenerated stands, but the difference was significant only on the richer sites. The proportion of diseased plots increased with stand density up to 25-28 m

Extensive tree health monitoring networks are useful in revealing the impacts of widespread biotic damage in boreal forests

We surveyed the regional distribution of conifer defoliation in Finland with an extensive monitoring network during 1995–2006 (EU Forest Focus Level I). The average defoliation in the whole Finland was 10.3% in pine and 19.9% in spruce. The sharp changes were often related to abiotic and biotic factors. The mean age of the stand explained more than one half of the between-plot variance in defoliation. In a variance component analysis, the main effect of years was negligible, while most of the random variation was due to plot main effect and plot × year interaction. About one fifth of the defoliation could be attributed to abiotic or biotic damage, and there were strong local correlations, e.g., between the changes in defoliation and degree of pine sawfly (Diprionidae) damage. There were clear temporal and spatial patterns in the incidence of the most important causes [Scots pine: Scleroderris canker (Gremmeniella abietina), pine shoot beetles (Tomicus sp.), and pine sawflies (Diprion pini, Neodiprion sertifer); Norway spruce: rust fungi (primarily Chrysomyxa ledi)]. Our results suggest that extensive monitoring networks can reveal useful information about the widespread outbreaks of pest organisms (insects and fungi) already in their increase phases, giving some time for management decisions. In a changing climate, large-scale, regular monitoring of tree health, including abiotic and biotic causes, is more important than ever before.

Exceedance of critical loads and of critical limits impacts tree nutrition across Europe

Key messageExceedance of critical limits in soil solution samples was more frequent in intensively monitored forest plots across Europe with critical loads for acidity and eutrophication exceeded compared to other plots from the same network. Elevated inorganic nitrogen concentrations in soil solution tended to be related to less favourable nutritional status.ContextForests have been exposed to elevated atmospheric deposition of acidifying and eutrophying sulphur and nitrogen compounds for decades. Critical loads have been identified, below which damage due to acidification and eutrophication are not expected to occur.AimsWe explored the relationship between the exceedance of critical loads and inorganic nitrogen concentration, the base cation to aluminium ratio in soil solutions, as well as the nutritional status of trees.MethodsWe used recent data describing deposition, elemental concentrations in soil solution and foliage, as well as the level of damage to foliage recorded at forest plots of the ICP Forests intensive monitoring network across Europe.ResultsCritical loads for inorganic nitrogen deposition were exceeded on about a third to half of the forest plots. Elevated inorganic nitrogen concentrations in soil solution occurred more frequently among these plots. Indications of nutrient imbalances, such as low magnesium concentration in foliage or discolouration of needles and leaves, were seldom but appeared more frequently on plots where the critical limits for soil solution were exceeded.ConclusionThe findings support the hypothesis that elevated nitrogen and sulphur deposition can lead to imbalances in tree nutrition.

Vulnerability to pine sawfly damage decreases with site fertility but the opposite is true with Scleroderris canker damage; results from Finnish ICP Forests and NFI data

Key messageThe probability of pine sawfly damage was highest in drier sites, while Gremmeniella abietina damage showed an opposite pattern. ICP Forests and rolling National Forest Inventory (NFI) data have good potential for quantifying patterns in damage occurrence, but region-wise NFIs may produce biased results.ContextFactors affecting the occurrence of important biotic damage on Pinus sylvestris were studied with data from large-scale forest monitoring networks.AimsWe tested how much the probability of damage caused by pine sawflies (Neodiprion sertifer Geoffr. and Diprion pini L.) and G. abietina (Lagerb. (Morelet)) differed between different forest site types and the effects of relevant climatic factors on damage probabilities.MethodsLong-term damage observations from ICP Forests Level 1 monitoring and National Forest Inventory (NFI) data were used. In addition to the traditional frequentist approach, we used a hierarchical Bayesian (HB) framework with the ICP Forests data to model the probabilities of pine sawfly outbreaks starting and continuing.ResultsThe probability of pine sawfly damage was highest in drier sites while the probabilities for G. abietina damage showed an opposite pattern. The HB analysis revealed clear differences between forest site types in the probability of outbreak starting, but the differences in the probabilities of outbreaks continuing were not clear.ConclusionICP Forests and rolling NFI data have good potential for quantifying patterns in damage occurrence, but annually region-wise NFIs may produce biased results.

Extent of abiotic damage and its relation to defoliation of conifers in Finland

Abstract Data from the eighth National Forest Inventory (NFI) and annual surveys of the vitality of forests was used in this study. Abiotic damage (wind, snow, frost or edaphic factors) was present on 8.4% of forest land, on 1.68 million hectares during 1986–1994. It decreased the silvicultural quality of the stand in 5.2% of forest land. Abiotic damage was more frequent in northern than in southern Finland. Especially snow damage was important in northern Finland in Scots pine stands. The defoliation of conifers and various damage forms showed significant co-occurrence. Temporal and spatial patterns were evident in the occurrence and importance of different causal agents. Abiotic damage increased the defoliation in Picea abies more than in Pinus sylvestris, but in the latter species the damage was locally more severe. Sudden changes in defoliation were related to abiotic and biotic damage, and the effect of these injuries can be so remarkable that they mask the possible trend in defoliation. The analysis of these injuries may aid monitoring of forest condition by simplifying interpretation of national and regional patterns of forest damage.

The Occurrence of Abiotic and Biotic Damage and its Relation to Defoliation (Needle Loss) of Conifers in Finland (1985–1988)

The data from permanent and temporary plots of the 8th National Forest Inventory were used in this study. Some form of abiotic or biotic damage was registered in roughly one third of the stands or sample trees. The proportion of damage that greatly reduced the stand quality or was likely to cause the death of trees was considerably low, in the range of 1–3%. In Lapland the frequency of damage (broken stems, crown injuries etc.) was higher than in southern Finland. Damage caused by abiotic factors and fungi, especially Ascocalyx abietina were the most important types of identified damage. Damage frequencies were higher in defoliated than non-defoliated conifers, but most of the observed defoliation could not be directly attributed to specific biotic or abiotic causes. Ascocalyx caused some increase in defoliation in western Finland. Other biotic/abiotic damage was only locally important in this respect.

Distribution and frequency of Cronartium flaccidum on Melampyrum spp. in permanent sample plots in Finland

Abstract In 2006, the distribution and frequency of pine stem rust Cronartium flaccidum was studied on Melampyrum spp. in permanent sample plots of an EU forest health monitoring program and of a BioSoil program in Finland. The frequency of Melampyrum spp. infected with C. flaccidum was low, but the rust was recorded in new locations of eastern Finland. No uredinia of C. flaccidum were observed in samples collected from over 700 plots. Telia were common on Melampyrum sylvaticum but were occasionally also found on Melampyrum pratense and Melampyrum nemorosum. Melampyrum pratense was the most common species growing in plots on mainly dry sites. Melampyrum sylvaticum was seldom detected, suggesting that alternate hosts are absent from northern Finland or that the current sample plot network is too sparse for effective disease monitoring in the north. No relationship between C. flaccidum, Melampyrum spp. and rust incidence in host trees was observed, which implies that the autoecious Peridermium pini is a more likely pathogen than C. flaccidum locally. Because plots containing M. sylvaticum occur almost solely in southern Finland, the plots with M. sylvaticum reflect the best changes in rust epidemics in that area. In the future, nutrient-rich sites containing M. sylvaticum may serve as a source of rust epidemics. It is unlikely that C. flaccidum will spread to dry sites via M. pratense.

Dynamics of Defoliation, Biotic and Abiotic Damage During 1986–1998

The estimation of tree defoliation, widely used to depict forest condition, has, despite its practicality, several disadvantages. Needle or leaf biomass in the crown is strongly affected by tree age, climatic and genetic factors, shading and a variety of abiotic or biotic stresses. Very little empirical information is available about the natural variation in leaf biomass (Westman and Lesinski 1986, McKay 1988). The reasons for an increase in defoliation must therefore be elucidated separately, e.g. with the help of statistical analysis. According to the ICP Forests recommendations, abiotic and biotic damage (especially that caused by snow, wind, ice, game, defoliating insects, needle cast and decay fungi) should be recorded in the forest health surveys (Manual on... 1994). In the reports from some countries, a rapid deterioration in forest vitality has been attributed to abiotic or biotic damage (Strelezki 1985, Roloff 1985, Hutte 1986, Innes et al. 1986, Keane et al. 1989, Innes and Schwyzer 1994). It has even been suggested that, apart from some special years when the growing conditions have been extremely poor, the results of forest health surveys merely reflect the effects of abiotic and biotic damage (Kandier 1989).