Oak decline analyzed using intraannual radial growth indices, δ13C series and climate data from a rural hemiboreal landscape in southwesternmost Finland |
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Authors: | S Helama A Läänelaid J Raisio H M Mäkelä E Hilasvuori H Jungner E Sonninen |
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Institution: | 1. Arctic Centre, University of Lapland, P.O. Box 122, 96101, Rovaniemi, Finland 6. Finnish Forest Research Institute, Northern Unit, Rovaniemi, Finland 2. Department of Geography, University of Tartu, Vanemuise St. 46, 51014, Tartu, Estonia 3. The Public Works Department, Street and Park Division, P.O. Box 1515, 00099, City of Helsinki, Finland 4. Finnish Meteorological Institute, P.O. Box 503, 00101, Helsinki, Finland 5. Dating Laboratory, Finnish Museum of Natural History, University of Helsinki, P.O. Box 64, 00014, Helsinki, Finland
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Abstract: | Decline of pedunculate oak (Quercus robur L.) was studied in SW Finland. This is a region where the species is growing near its northern distributional limit globally and a recent decline of mature trees has been described regionally. Tree rings of declining oaks were compared to the chronologies of healthy and oaks that died, climate series and stable isotope discrimination of carbon (δ13C) of comparable mature trees. The radial growth (earlywood, latewood, and annual ring width) of declining oaks was clearly deteriorated in comparison to healthy oaks, but recuperated, compared to oaks that died, through all index types. Comparison of climate relationships between growth and δ13C, expected to reflect oaks’ intrinsic water use efficiency, indicated enhancing resistance to droughts through the growing season. The growth and the climatic growth response was differentiated in declining oaks as compared with the healthy and oaks that died revealing that: (1) declining oaks exhibited decreasing competitive strength as indicated by reduced overall growth relative to healthy oaks, (2) the growth of declining oaks was more sensitive to winter conditions, but less restricted by summer droughts than the growth of other oaks, and (3) healthy oaks were seen having benefitted from the ongoing lengthening of the growing season. Lack of correlativity between growth and δ13C became evident as their responses to temperature and precipitation variations deviated drastically during the other but summer months. Our results indicate that several different ecological factors, rather than a single climatic factor (e.g., drought), are controlling the oak decline in the studied environment. |
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