Stem taper and bark functions for Norway spruce in Norway
Based on data from long-term experimental fields with Norway spruce (Picea abies (L.) H. Karst.), we developed new stem taper and bark functions for Norway. Data was collected from 477 trees in stands across Norway. Three candidate functions which have shown good performance in previous studies (Koz...
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| Format: | Article |
| Language: | English |
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Finnish Society of Forest Science
2019-09-01
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| Series: | Silva Fennica |
| Subjects: |
| _version_ | 1818544400119103488 |
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| author | Timo Pukkala Kjersti Holt Hanssen Kjell Andreassen |
| author_facet | Timo Pukkala Kjersti Holt Hanssen Kjell Andreassen |
| author_sort | Timo Pukkala |
| collection | DOAJ |
| description | Based on data from long-term experimental fields with Norway spruce (Picea abies (L.) H. Karst.), we developed new stem taper and bark functions for Norway. Data was collected from 477 trees in stands across Norway. Three candidate functions which have shown good performance in previous studies (Kozak 02, Kozak 97 and Bi) were fitted to the data as fixed-effects models. The function with the smallest Akaike Information Criterion (AIC) was then chosen for additional analyses, fitting 1) site index-dependent and 2) age-dependent versions of the model, and 3) fitting a mixed-effects model with tree-specific random parameters. Kozak 97 was found to be the function with the smallest AIC, but all three tested taper functions resulted in fairly similar predictions of stem taper. The site index-dependent function reduced AIC and residual standard error and showed that the effect of site index on stem taper is different in small and large trees. The predictions of the age-independent and age-dependent models were very close to each other. Adding tree-specific random parameters to the model clearly reduced AIC and residual variation. However, the results suggest that the mixed-effects model should be used only when it is possible to calibrate it for each tree, otherwise the fixed-effects Kozak 97 model should be used. A model for double bark thickness was also fitted as fixed-effects Kozak 97 model. The model behaved logically, predicting larger relative but smaller absolute bark thickness for small trees. |
| first_indexed | 2024-12-11T22:48:00Z |
| format | Article |
| id | doaj.art-0401b08b398549e4b1bde0f9bc17d432 |
| institution | Directory Open Access Journal |
| issn | 2242-4075 2242-4075 |
| language | English |
| last_indexed | 2024-12-11T22:48:00Z |
| publishDate | 2019-09-01 |
| publisher | Finnish Society of Forest Science |
| record_format | Article |
| series | Silva Fennica |
| spelling | doaj.art-0401b08b398549e4b1bde0f9bc17d4322022-12-22T00:47:33ZengFinnish Society of Forest ScienceSilva Fennica2242-40752242-40752019-09-0153310.14214/sf.10187Stem taper and bark functions for Norway spruce in NorwayTimo Pukkala0Kjersti Holt Hanssen1Kjell Andreassen2University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, FinlandNorwegian Institute of Bioeconomy Research, P.O. Box 115, NO-1431 Ås, NorwayNorwegian Institute of Bioeconomy Research, P.O. Box 115, NO-1431 Ås, NorwayBased on data from long-term experimental fields with Norway spruce (Picea abies (L.) H. Karst.), we developed new stem taper and bark functions for Norway. Data was collected from 477 trees in stands across Norway. Three candidate functions which have shown good performance in previous studies (Kozak 02, Kozak 97 and Bi) were fitted to the data as fixed-effects models. The function with the smallest Akaike Information Criterion (AIC) was then chosen for additional analyses, fitting 1) site index-dependent and 2) age-dependent versions of the model, and 3) fitting a mixed-effects model with tree-specific random parameters. Kozak 97 was found to be the function with the smallest AIC, but all three tested taper functions resulted in fairly similar predictions of stem taper. The site index-dependent function reduced AIC and residual standard error and showed that the effect of site index on stem taper is different in small and large trees. The predictions of the age-independent and age-dependent models were very close to each other. Adding tree-specific random parameters to the model clearly reduced AIC and residual variation. However, the results suggest that the mixed-effects model should be used only when it is possible to calibrate it for each tree, otherwise the fixed-effects Kozak 97 model should be used. A model for double bark thickness was also fitted as fixed-effects Kozak 97 model. The model behaved logically, predicting larger relative but smaller absolute bark thickness for small trees.Picea abiesforest managementKozak modelvariable-exponent taper function |
| spellingShingle | Timo Pukkala Kjersti Holt Hanssen Kjell Andreassen Stem taper and bark functions for Norway spruce in Norway Silva Fennica Picea abies forest management Kozak model variable-exponent taper function |
| title | Stem taper and bark functions for Norway spruce in Norway |
| title_full | Stem taper and bark functions for Norway spruce in Norway |
| title_fullStr | Stem taper and bark functions for Norway spruce in Norway |
| title_full_unstemmed | Stem taper and bark functions for Norway spruce in Norway |
| title_short | Stem taper and bark functions for Norway spruce in Norway |
| title_sort | stem taper and bark functions for norway spruce in norway |
| topic | Picea abies forest management Kozak model variable-exponent taper function |
| work_keys_str_mv | AT timopukkala stemtaperandbarkfunctionsfornorwayspruceinnorway AT kjerstiholthanssen stemtaperandbarkfunctionsfornorwayspruceinnorway AT kjellandreassen stemtaperandbarkfunctionsfornorwayspruceinnorway |