Temporal and Spatial Variation in Correspondence between Climate Proxies and Recorded Climate Data
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- Institutt for biologi 
Knowledge about effects of regional climate variation on the vegetation is important and will provide more insight into the impacts of global climate change. Tree growth and Normalized Difference Vegetation Index (NDVI) are commonly used as proxies of vegetation production and therefore indicators for response to climatic conditions. These correspondences between growth and climate may vary thorough time and space, and response to main growth-promotion climate variable seem to have been less pronounced during the late decades in boreal systems in the North Atlantic region. In this MSc thesis four sites, representing different climatic conditions along a coast-inland and a north-south gradient in Norway, were used to study effects of climatic conditions (temperature and precipitation) on growth (diameter and height) in Scots pine (Pinus sylvestris) for the period 1960-2012. In addition, the relationship between pine growth and NDVI for these sites was studied. Over the entire period a significant diameter growth response to temperature, is identified with the most consistent relationship shown for July. This relationship was positive for all study sites and significantly so for three. However, this relationship was not strongly consistent, neither in space nor in time. As it was less well expressed for parts of the study period, especially so at the beginning and/or end of the period for all study sites. For height growth, previous August temperature was identified as the most important factor, but with negative effect in north and positive in south. The relationships in north was most significant for the beginning of the study period, while in south they were more significant at the end. For precipitation a few significant positive relationships was shown for above average precipitation during non-growing season or early spring. The effects were evident for both diameter and height growth, but these were inconsistent both through time and space. NDVI was not found to be significantly correlated to either diameter or height growth at any of the included study sites. Even if diameter growth for Scots pine generally is well related to growing season temperature (June-August), this study indicate that diameter growth as a proxy for growing season temperature should be used with caution, because periods with low correlation between growth and growing season temperature may occur at varying spatial scales through time. It also implies that more detailed knowledge about tree growth climate correspondence is needed, e.g. in estimation of future changes in forest growth responses to climate. Relying solely on growing season temperature data could be of low predictable value, and preferably, diameter growth and height growth should be analyzed simultaneously.