Maija Salemaa, Eeva-Liisa Jukola-Sulonen, Martti Lindgren. (1991). Forest condition in Finland, 1986-1990. Silva Fennica vol. 25 no. 3 article id 5451. https://doi.org/10.14214/sf.a15605

Keywords: needle age; Finland; defoliation; discolouration; cones; needle cast; air pollution; leaves

Abstract | View details | Full text in PDF | Author Info

The results of the Finnish forest condition survey carried out during 1986–90 in background areas are presented. The same 3,388 forest trees (1,897 Scots pines (Pinus sylvestris L.), 1,289 Norway spruces (Picea abies (L.) H. Karst. And 202 broadleaves) on 450 mineral soil sample plots were examined annually. Growth characteristics (defoliation, the number of needle age classes, branch damage and needle discolouration), fertility and abiotic and biotic damage express the general vitality of the trees and are not specific for air pollutants. A correlative approach was applied in analysing the factors which may explain the regional pattern and changes in defoliation.

Average tree-specific degree of defoliation was 9% in pine, 21% in spruce and 12% in broadleaves in 1990. Altogether 11% of the pines, 42% of the spruces and 16% of the broadleaves have lost over 20% of their needles or leaves. Defoliation in spruce was the same as in the previous year, but in pine and broadleaves it had slightly decreased. Defoliation had increased by 5 %-units in pine, 16 %-units in spruce and 7 %-units in broadleaves during the whole study period 1986–90.

High stand age and different weather and climatic factors greatly affected forest defoliation in background areas in Finland. Pine cancer (Ascocalyx abietina) has enhanced defoliation in pine in the western part of the country. Air pollutants have evidently contributed to the increase of defoliation in the most polluted parts of Southern Finland. In pine a significant positive correlation was found between modelled sulphur deposition and the average stand-specific degree of defoliation as well as with the increase in average 5-year defoliation in Southern Finland. It is suspected that green algae growing on needles of spruce in Southern Finland indicates elevated nitrogen deposition levels.

The PDF includes an abstract in Finnish.

Salemaa, E-mail: ms@mm.unknown
Jukola-Sulonen, E-mail: ej@mm.unknown
Lindgren, E-mail: ml@mm.unknown

article id 5147, category Article

J. Eriksson, J. Bergholm, K. Kvist. (1981). Injury to vegetation caused by industrial emissions of boron compounds. Silva Fennica vol. 15 no. 4 article id 5147. https://doi.org/10.14214/sf.a15374

Keywords: Betula pendula; boron; soil; Sweden; toxicity; emissions; air pollution; leaves; fiberclass factory

Abstract | View details | Full text in PDF | Author Info

At immediate surroundings of a fiberglass plant in Central Sweden, vegetation shows toxicity symptoms. Soils and birch (Betula pendula Roth) leaves were sampled. The soil was analysed for water soluble and organic bound boron, carbon, nitrogen, and pH. Vegetation was analysed for total boron. Both fractions of boron in the soils increased towards the factory. Organic bound boron increased irregularly because of its strong correlation to carbon content which varied in the area. The C/N ratio increased nearer the industry due to the harmful effect of boron on the decomposition of organic matter. No relation between pH and the distance from the emission source was visible, but B/C ratio was found to increase with increasing pH of the soil. Boron levels in birch leaves were elevated very much close to the factory. The geographical distribution of high levels of boron in birch, corresponded well with high values in soils, and also with the main wind directions. The limit values for visible injury on birch were found to be around 5 ppm of water-soluble boron in soil and around 200 ppm in leaves.

Eriksson, E-mail: je@mm.unknown
Bergholm, E-mail: jb@mm.unknown
Kvist, E-mail: kk@mm.unknown

article id 5141, category Article

Lisbeth Mortensen, Knud V. Weisberg. (1981). A method for measurement of actue leaf injury on tobacco indicator plants. Silva Fennica vol. 15 no. 4 article id 5141. https://doi.org/10.14214/sf.a15368

Keywords: damages; photography; measuring methods; air pollution; bioindicators; Nicotiana tabacum; leaves; damaged leaf area; ozone

Abstract | View details | Full text in PDF | Author Info

A technique for instrumental scoring of damaged leaves on tobacco (Nicotiana tabacum) indicator plants caused by ozone in the lower atmosphere is being developed. The leaves are photographed in situ with an integrated unit, which illuminates the leaf from behind and keeps the camera in a well-defined position. By using microfilm and a minus green filter, it is possible to obtain negatives where the necrotic flecks appear as dark spots on a white leaf. The negatives are scanned in a TV-system and the size of the damaged fraction of the leaf is calculated by a microprosessor and is shown as a percentage of the leaf.

Mortensen, E-mail: lm@mm.unknown
Weisberg, E-mail: kw@mm.unknown

Category : Research article

article id 26012, category Research article

Alwin A. Hardenbol, Hans Ole Ørka, Terje Gobakken, Joel Kostensalo. (2026). Optimising rare tree species detection for large-area mapping: a case study on European aspen (Populus tremula). Silva Fennica vol. 60 no. 3 article id 26012. https://doi.org/10.14214/sf.26012

Keywords: Bayesian statistics; biodiversity conservation; base rate problem; broadleaves; individual tree map; model transferability

Highlights: Balancing false discovery and false negative rates improves rare tree species detection; Preferring volume- over count-based approaches makes ecological sense for rare tree species; We detected 70% of aspen volume and classified this volume with 31% false discovery rate and 54% false negative rate; Base rates of rare tree species have been overlooked in remote sensing literature.

Abstract | Full text in HTML | Full text in PDF | Author Info

Some locally rare tree species – like European aspen (Populus tremula L.) – contribute disproportionately to forest biodiversity, making their accurate monitoring important for conservation. However, most remote sensing studies of rare tree species ignore their low prevalence/base rate, necessary for model transferability. We aimed to assess European aspen classification under realistic landscape prevalence and find methods to improve classification performance. Across 253 plots from field data in Våler, Norway we detected and segmented 5455 living trees, including 55 European aspens (ca. 1% prevalence), from high-density airborne laser scanning (ALS) data merged with multispectral aerial imagery. Individual segments were then classified as European aspen or non-aspen using random forest and synthetic minority oversampling (SMOTE). We evaluated classification based on tree counts and summed tree volumes. To underpin the importance of prevalence consideration and compare our results, we also re-analysed published Fennoscandian European aspen classification studies. Contrary to a perfect balance, we found an optimal SMOTE-ratio at ca. 0.07 (European aspen–non-aspen ratio). Our count-based classification achieved 32% (16–52) false discovery rate (FDR) and 73% (60–83) false negative rate (FNR), whereas volume-based classification achieved 31% (11–51) FDR and 54% (38–71) FNR. Re-analysed studies averaged 66% FDR and 33% FNR at a 1% prevalence. Our results demonstrate that rare tree species classification benefits from optimising majority–minority ratios and, given the ecological value of larger trees, volume-based approaches are warranted. Finally, we urge reporting landscape prevalence and adjust classification metrics to reflect these to enable transferability to real-world applications in rare tree species classification.

Hardenbol, Natural Resources Institute Finland (Luke), Natural Resources Unit, Yliopistokatu 6B, FI-80100 Joensuu, Finland https://orcid.org/0000-0002-0615-505X E-mail: alwin.hardenbol@luke.fi
Ørka, Norwegian University of Life Sciences (NMBU), Faculty of Environmental Sciences and Natural Resource Management, P.O. Box 5003, NO-1432 Ås, Norway https://orcid.org/0000-0002-7492-8608 E-mail: hans-ole.orka@nmbu.no
Gobakken, Norwegian University of Life Sciences (NMBU), Faculty of Environmental Sciences and Natural Resource Management, P.O. Box 5003, NO-1432 Ås, Norway https://orcid.org/0000-0001-5534-049X E-mail: terje.gobakken@nmbu.no
Kostensalo, Natural Resources Institute Finland (Luke), Natural Resources Unit, Yliopistokatu 6B, FI-80100 Joensuu, Finland https://orcid.org/0000-0001-9883-1256 E-mail: joel.kostensalo@luke.fi

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