IUFRO/Seoul 2010: FORESTS AND CLIMATE CHANGE FINNISH STUDIES WITH CLIMATIC GRADIENTS

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2 XXIII IUFRO World Congress, August 2010, Seoul, Republic of Korea "Forests for the Future: sustaining Society and the Environment" IUFRO/Seoul 2010: FORESTS AND CLIMATE CHANGE SESSION: CLIMATIC GRADIENTS IN MOUNTAINS: OPPORTUNITIES FOR STUDYING FORESTS FACING CLIMATE CHANGE Abstract FINNISH STUDIES WITH CLIMATIC GRADIENTS Kari Mielikäinen Finnish Forest Research Institute, Vantaa, Finland Mauri Timonen Finnish Forest Research Institute, Rovaniemi, Finland Samuli Helama Arctic Centre, Rovaniemi, Finland Climatic gradients have been investigated in Finland from historical, cyclic, latitudinal, altitudinal and regional perspectives. Current temperature of July and, to a lesser degree, precipitation of May limit tree growth in Northern Finland. According to our studies, based on the Finnish 7644-yr supralong tree-ring chronology of timberline Scots pine, long-term Holocene June-July temperature during the last 7600 years has varied within the range of o C and 2-3 o C compared to today's mean temperature. About 5000 years ago pine timberline was some 400 m higher and 85 km more north than today. Since then it has retreated and also fluctuated. Now it is, however, again advancing. Concerning the fluctuating pattern of timberline, spectral and wavelet analysis of tree-ring indices suggest that more emphasis should be paid to the cyclic nature of climatic events. Growth studies crossing latitudes in north-south direction clearly show the effect of a "Hazard factor". It is an expression of increasing variability in biological productivity as moving from favorable climate to extreme conditions. It can be quantified by "Coefficient of Variation" (CV). The CV of tree-ring index of Scots pine within a 1100 km north-south distance in Finland increases from 28 % in the south to 45 % at the pine timberline. That means dramatic changes not only in climate but also in the ecosystem conditions. Altitudinal (elevation) and regional (e.g. marinity-continentality) gradients of climate may also show drastic trends. Conclusions: 1) study of forests facing climatic gradients provides a powerful and simple way for testing forest behaviour in changing climate. 2) A more detailed analysis of CV and related characteristics probably will improve our understanding of ecosystem responses under changing climate. More to read: 2

3 FINNISH STUDIES WITH CLIMATIC GRADIENTS We look climate gradients on the historical, altitudinal, latitudinal and regional basis. I. Historical view. Based on the locations of the samples used in reconstructing the Finnish supra-long timberline pine chronology, Kultti et al. (2006) estimated that Holocene summer climate ca years ago was 2.6 o C, 3000 years ago 1 o C and during the Medieval warm period 0.5 o C warmer than today. Hence historical timberlines fluctuated beyond and below the present pine timberline on a latitudinal range of 100 km and altitudinal range of 500 m (from 400 m to 900 m a.s.l.). II. Cyclic view. Analysis of the Finnish supra-long tree-ring chronology of timberline pine suggests that more emphasis should be paid to the cyclic nature of climate. According to Wavelet and spectral analysis, a cycle of about 80 (60-95) years has dominated tree growth in Northern Finland for more than the last 500 years and less regularly over 2000 years. Our tree-ring studies also indicate that climate change should be considered as a cyclic phenomenon driven mainly by solar activity and local climate dynamics. III. Altitudinal view. Sutinen et al. (200x) have established gradient lines across several hill sides in Finnish Lapland. One of the targets is to monitor regeneration of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris L). According to these studies Finnish pine and spruce timberlines have advanced altitudinally about 100 m and latitudinally some 25 km. One gradient study (unpublished) was done at mt. Kukastunturi; a 480 m high small mountain in Western Finnish Lapland. Lines reaching from valley bottom (220 m a.s.l.) to the top (480 m a.s.l.) were investigated for testing differences in tree-ring index. According to the IPCC (xxx), climate warming can first be observed at high elevations as increased growth. Our pilot study showed a recent increase in ring-width and treering index of the hill top trees of Mt. Kukastunturi. Our test data, however, was too small for reliable conclusions. In addition, we consider this more as a hypothesis and want to test it at several locations in Finnish Lapland. IV. Latitudinal view. Instead of trying to estimate the characteristics of future climate, we suggest just investigating the parameters of the existing climate. We focus on looking at different parameters of variation. We have found the Coefficient of Variation (CV) or the Hazard factor to be a useful tool in studying all kinds of impacts in a changing climate. Based on our large tree-ring data (thousands of samples), we know that CV varies from 28 % in the south to 45 % at pine timberline. Correlating these numbers with forest ecosystem parameters or models, provides a lot of information about the ongoing processes. Climatic signals were extracted from ring-width chronologies of Scots pines (Pinus sylvestris L.) from natural stands of the northern, middle, and southern parts of the boreal forest belt in Finland. The strength of the common growth signals (forcing factors) were quantified as a function of time. This was achieved by mean interseries correlations, calculated over a moving 30-year window, both within and between the regional chronologies. Strong regional signals and also evidence for common forcings were found, especially between northern and central, central and eastern, as well as central/eastern and southern chronologies. 3

4 Response function analyses revealed that growing season temperatures govern the growth rates of northern pines, while towards south, pine growth becomes less affected by temperatures, and more affected by e.g. precipitation. During some periods, growing conditions seem to have been favorable in the south, while they have been unfavorable in the north (growth inversions). Going from the north to the south, the variability of radial growth clearly decreases, and the variance of ring-width series becomes smaller. Growth variability in the four regions was compared during the common interval of the chronologies, from 1806 to The spectral densities of the northern, central, eastern and southern chronologies were also compared as functions of frequency, viz. cycles per year. The variance is much greater and there is more periodic behavior in the north than in the south in high, medium, as well as lower frequencies. V. Regional view. Multivariate techniques (PCA in particular) have proven to be very useful in tree-ring studies when applied to a climatic gradient. The combined interpretation of loadings, eigenvalues and cumulative variance expressed by the analysis has allowed a detailed description of the information tree rings in the area contain about the climatic gradient. When studying climatic gradients, it is basic to take into account that these gradients fluctuate, they are time variable, and they can increase or decrease in intensity during the period under study. This is why an analysis by subperiods is strongly recommended and widely used (Tardif et al. 2003). In the Macias et al. (2004) study, chronology statistics and multivariate analyses was used for a spatiotemporal analysis of a network of 21 Scots pine (Pinus sylvestris) ringwidth chronologies in northern Fennoscandia. Chronologies wew chosen from the both sides (western and eastern) of the Scandes Mountains (678N 708N, 158E 298E). Growth relationships with temperature, precipitation, and North Atlantic Oscillation (NAO) indices were calculated for the period A subperiod analysis of the relationships between chronologies along the gradient has revealed a general decrease in the variability they hold in common, especially in the second half of the 20th century. This decrease is coinciding with a significant loss of correlation between the chronologies and the NAO indices. In a study on wood density/air temperature relationships, Briffa et al. (1998) already described a loss of sensitivity of wood density to temperature changes during the late 20th century. To determine whether this is a result of NAO active/passive phase dynamics, a consequence of an anthropogenic induced climatic change, or if it is caused by a combined effect of both, is something beyond the scope of this paper, but it is without doubt one of the main lines of our future research in this topic. Identifying which of the NAO-affected climatic parameters has been changing in the area will help us to answer these questions. However, the change is most probably affecting not one but many combined precipitation and temperature parameters. Describing and understanding such temporal changes in the strength with which NAO affects tree rings in the area is of vital importance when using tree rings as proxy data in dendroclimatic reconstructions. This study also reveals the fact that NAO/tree-ring relationships are not continuous along all range of NAO values. It is important to realize that NAO can affect tree growth in a given season only if it is positive (i.e. end of previous fall) or negative (i.e. end of spring/ beginning of summer). Current July temperature and, to a lesser degree, May precipitation are the main growth limiting factors in the whole area of study. Differences in radial growth between both sides of the Scandes Mountains were attributed to the Oceanic-Continental climatic 4

5 gradient in the area. The gradient signal is temporally variable and has strengthened during the second half of the 20th century. Northern Fennoscandia Scots pine growth is positively related to early winter NAO indices previous to the growth season and to late spring NAO. NAO/growth relationships are unstable and have dropped in the second half of the 20th century. Moreover, they are noncontinuous through the range of NAO values: for early winter, only positive NAO indices enhance tree growth in the next growing season, while negative NAO does not. For spring, only negative NAO is correlated with radial growth. (1) In accordance with previous studies (Briffa et al., 1990; Lindholm, 1996), the main limiting climatic factor in the northern Fennoscandian forests is July temperature. May precipitation is another key factor for tree growth, and it is caused by rain inducing early snowmelt and soil warming, enabling an early start of the vegetation period (Kirchhefer, 2001). (3) The second half of the period studied, corresponding to , is characterized by an enhancing of the east-west differences in northern Fennoscandia. (4) Northern Fennoscandia forests are most sensible to previous early winter and end of the springsummer NAO indices. They show significant positive relationships with these NAO season values. (5) During the first half of the period analyzed ( ), NAO indices and residual chronologies are very highly correlated, while in the second half ( ), the correlations of radial growth with NAO indices drop, especially in the west. (6) Positive previous early winter NAO indices enhance tree growth in the next growing season, while negative previous early winter NAO indices do not have any correlation with tree growth. On the other hand, positive NAO spring values are not correlated with radial growth, while negative NAO spring values show a significant correlation with them. VI. Global view. THE EURACLIMATES PROJECT: General outlines for Eurasian wide climate change research, based on the networks of climatically sensitive conifer chronologies. Some approaches to study climate changes in the whole Eurasia: 1. The EuraMountainClimates Project: Eurasian mountain timberlines climate change research. 2. The Boreal Zone Biome Climates Project: Eurasian climate change research in the Boreal humid and semiarid zones. 3. The SpineaClimates Project: climate change research based on Scots pine (Pinus sylvestris) tree-ring chronologies 4. The TaigaClimates Project: climate change research based on the all sensitive northern timberline conifer species A. Vaganov s suggestion to be considered in our joint EU proposal (based on negotiation in Ekaterinburg, June 7 th, 2006) B. A suggestion from Shiyatov and his group. Fig. 1. Transect measurements based on Pinus sylvestris Fig. 2. Transect measurements based on all climatically sensitive Taiga conifer species 5

6 Papers: Helama, S., Mielikäinen, K., Timonen, M.& Eronen, M Finnish supra-long tree-ring chronology extended to 5634 BC. Norsk Geografisk Tidsskrift - Norwegian Journal of Geography,62:4, Abstract / Pdf Kultti, S., Mikkola, K., Virtanen, T., Timonen, M. & Eronen, M Past changes in the Scots pine forest line and climate in Finnish Lapland: a study based on megafossils, lake sediments, and GIS-based vegetation and climate data. The Holocene 16(3): Pdf Macias, M.,Timonen, M., Kirchhefer, A., Lindholm, M., Eronen, M. & Gutierrez, E Growth variability of Scots pine along a West-East Gradient across Northern Fennoscandia: A Dendroclimatic Approach. Arctic, Antarctic, and Alpine Research, 36: Pdf Eronen, M., Zetterberg, P., Briffa, K., Lindholm, M., Meriläinen, J. & Timonen M Part 1: The supra-long Scots pine tree-ring record for northern Finnish Lapland; Chronology construction and initial inferences. The Holocene 12(6): Abstract / Pdf Helama, S., Lindholm, M., Timonen, M., Eronen, M. & Meriläinen, J Part 2: Interannual-to-centennial variability in summer temperatures in northern Fennoscandia during the last 7500 years extracted from tree-rings of Scots pine. The Holocene 12(6): Pdf More to read: 6

7 Ver MT A. Vaganov s suggestion to be considered in a joint EU proposal (based negotiation in Ekaterinburg, June 7 th, 2006) Subprojects: 1. Climate Change and its impact on the growth of pine (and some other conifers?) - three transects south - north (Fennoscandia, Ural mountains, Krasnojarsk) - one transect east - west close to arctic tree (forest) line Objectives: a) Analysis of age-growth curves and classifications b) Sensitivity: spatial and temporal changes of climate c) Analysis of response functions and their classification (periods and ) d) Parametrisation of process-based model (Vaganov-Shaskin) e) Ratio (portioning) of climatic - non-climatic variability over territory of pine distribution in Eurasia f) Temporal changes in ratio: climatic/non-climatic variability g) Spatial analysis of growth trends 2. Growth of pine on forested area boundaries as an indicator of potential migration of pine - "How fast can pine occupy new habitats?" a) What provenances will be optimally adapted to new habitat? b) Climate-induced variability in growth and mortality (regeneration) c) Spatial analysis of growth trends (climatic effects) through boundaries d) Analysis of climatic response change in last decades (statistical and process-based modeling) 3. Holocene multi-millenial chronologies in Northern Eurasia: a potential for long-term and high-frequency climate change analysis and a unique source of multi-proxy data a) Inter-comparison of Fennoscandia, Ural, Taimyr and Yakutia millenial chronologies as an indicator of lond-term temperature changes b) low-frequency climatic signal from chronologies c) Combined multi-records (TRW, max. density, cell dimensions, isotope composition) to indicate and extract climatic signals d) Analysis of links between millennial chronologies with other long-term low-resolution proxy records (lake sediments, speleotherms, pollen spectra etc.) - coincidence in the values of reconstructed temperature inferred from different proxies - can tree ring data be used to calibrate those proxies on longer time scales. 7

8 B. A suggestion from Shiyatov and his group Possible collaboration with METLA (Laboratory of Dendrochronology IPAE, Ekaterinburg) Climate changes in Eurasia and their impact on growth of coniferous trees (Pinus sylvestris, Larix sibirica, Picea obovata) (S.G. Shiyatov, V.S. Mazepa, R.M. Hantemirov, L.I. Agafonov, V.M. Goryachev, M.A. Gurskaya, V.V. Kukarskih). 1. Areas (regions) Material will be collected within the West-Siberian Plane, along one latitudinal (west-east) transect (from the Yamal Peninsula to the Lower Enysei) and one longitudinal (north-south) transect (along the Ob, Irtysh and Tobol Rivers). 2. Objectives 2.1. Analysis of age-growth curves and their classification; 2.2. Sensitivity of tree-ring chronologies: spatial and temporal changes to climate; 2.3. Analysis of response function and their classification (for two periods: and ) Ratio (portioning) of climate-nonclimatic variability over the territory of pine distribution in Eurasia; 2.5. Temporal changes in ratio: climatic/nonclimatic variability; 2.6. Spatial analysis of growth trends. 3. Growth of coniferous trees on forested area boundaries as an indicator of potential migration of trees (Can and how fast trees will occupied the new habitats?) 3.1. What provenances will be optimally adapted to new habitat? 3.2. Climatic induced variability of growth and mortality (vegetation); 3.3. Spatial analysis of growth trends (climatic effects) thorough boundaries; 3.4. Analysis of climatic response change in last decades (statistical modeling) Spatio-temporal dynamics of forest-tundra ecosystems; 4. Holocene multi-millennial tree-ring chronologies in Northern Eurasia: a potential for long-term and high-frequency climatic analysis and a unique source of multi-proxy data Inter-comparison of Scandinavian, Polar Urals, Yamal, West-Siberian, Taymir and Yakutia millennial chronologies as an indicator of long-term temperature changes; 4.2. Low-frequency climatic signal from chronologies; 4.3. Combined multi-records (TRW, max. density, cell dimension, isotope composition) to indicate and extract the climatic signals; 4.4. Analysis of links between millennial chronologies with other long-term low resolution proxy records (sediments, pollen spectra etc.). Coincidence in values of reconstructed temperature, Can tree-ring data be used to calibrate those proxies on longer time scale. 5. Reconstruction and analysis of extreme climatic events based on wood pathological structures (frost rings, light rings, missing rings, density fluctuations, pathological resin ducts, etc.) Frequency of repetitions of climatic extreme events and their changes during last millennium; Intensity of climatic extremes; Impact of climatic conditions on forming of pathological structures in wood of coniferous trees (tree age and size, TRW, different species and stands, different areas and sites). Coincidence in climatic extremes in study areas. 8

9 9 Fig 1. Transect measurements based on Pinus sylvestris

10 Fig. 2. Transect measurements based on all climatically sensitive Taiga conifer species 10