Research ArticleECOLOGY

Twentieth century redistribution in climatic drivers of global tree growth

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Science Advances  16 Jan 2019:
Vol. 5, no. 1, eaat4313
DOI: 10.1126/sciadv.aat4313
  • Fig. 1 The 2710 sites that constitute the tree-ring network are assigned to four main clusters based on their monthly to seasonal climate response.

    These four clusters consist of 18 subclusters (A) and correspond to cold-humid, hot-dry, cold-dry, and temperate domains (B). GST, growing season temperature; AP, annual precipitation.

  • Fig. 2 Climate response of tree growth across the four main climatic domains between 1930 and 1960 CE.

    For each of the identified domains (see Fig. 1), we present the mean correlations between tree growth and temperature (A), precipitation (B), VPD (C), and the SPEI (D). The correlations for individual months are shown on the diagonal, whereas consecutive seasons starting in a given month extend upward. Corresponding partial correlations that show similar patterns are provided in data S1. Gray shading indicates correlations that were not significant (P > 0.001) after integrating P values from all sites within a cluster using Fisher’s method (23). Small and capital letters refer to the previous and current years. NH, Northern Hemisphere; SH, Southern Hemisphere.

  • Fig. 3 Spatial interpolation of the climate response from 2710 sites between 1930 and 1960 CE.

    One value per site was calculated for each climate parameter by integrating the significant (P < 0.1) monthly correlations (int) (A). This climate response was spatially interpolated within the growing season temperature and annual precipitation envelope of the network (B). The uncertainty of the interpolation, as expressed by the bootstrapped SDs from 1000 random network subsets (see Materials and Methods), is shown in (C). Please note that the color scale for P and the SPEI have been inverted compared with T and VPD, so red colors consistently indicate water limitation. Gray shading indicates nonsignificant (P > 0.1) areas.

  • Fig. 4 Geographic distribution of the climate response of tree growth between 1930 and 1960 CE.

    The maps were produced by projecting the interpolated growth response to (A) temperature (Tint), (B) precipitation (Pint), (C) vapor pressure deficit (VPDint), and (D) standardized precipitation evapotranspiration index (SPEIint) from 2710 sites into geographic space based on the growing season temperature and annual precipitation of each grid cell (see Fig. 3). Red colors indicate stronger water than energy constraints; blue colors indicate the opposite. Gray areas fall outside the climate envelope covered by the tree-ring network.

  • Fig. 5 The probability that precipitation exceeded temperature as the main driver of tree growth has increased throughout the boreal zone between 1930–1960 and 1960–1990 CE.

    The most pronounced changes (orange to red colors) occurred across cold-dry regions in Alaska, Canada, Finland, and Russia. Accordingly, the area where the temperature response (Tint) exceeded the precipitation response (Pint) of tree growth, i.e., the blue area on the map, was reduced to cold-humid Alpine and coastal areas, as well as the northernmost taiga in Siberia.

  • Table 1 The land area where tree growth responded significantly (P < 0.1) to different climate parameters has changed between 1930–1960 and 1960–1990 CE.

    The most pronounced changes occurred for areas that respond positively to temperature (Tint > 0) and negatively to atmospheric water demand (VPDint < 0). By contrast, the responses to precipitation (Pint > 0) and the standardized precipitation evapotranspiration index (SPEIint > 0) remained relatively stable. Δ is the change between 1930–1960 and 1960–1990 CE. The total land area that falls within the climate envelope of the tree-ring network is 80.4 Mio km2.

    TimeAreaTint > 0Pint > 0VPDint < 0SPEIint > 0
    1930–1960Mio km220.8 ± 3.777.5 ± 3.366.0 ± 1.678.0 ± 1.3
    %25.9 ± 4.696.4 ± 4.182.0 ± 2.097.0 ± 1.6
    1960–1990Mio km212.1 ± 3.177.4 ± 0.874.7 ± 1.777.4 ± 0.8
    %15.1 ± 3.996.2 ± 1.092.8 ± 2.196.2 ± 1.0
    ΔMio km2−8.7 ± 0.6−0.1 ± 2.68.7 ± 0.1−0.6 ± 0.5
    %−10.8 ± 0.7−0.2 ± 3.210.8 ± 0.2−0.8 ± 0.6

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/1/eaat4313/DC1

    Fig. S1. Geographic coverage of the tree-ring network.

    Fig. S2. Definition of the growing season across the tree-ring network.

    Fig. S3. Geographic distribution of the uncertainty associated with the spatial interpolation of climate response.

    Fig. S4. Latitudinal changes in the climate response of forest growth during 1930–1960 CE.

    Fig. S5. The climate response of tree growth across the four main climatic domains has changed between 1930–1960 and 1960–1990 CE.

    Fig. S6. Spatiotemporal changes in the climate response of tree growth between 1930–1960 and 1960–1990 CE.

    Fig. S7. Comparison of the summer climate response of three independent tree-ring networks.

    Table S1. Relationships between the climate response of tree growth and mean climatic conditions.

    Table S2. Comparison of the climate sensitivity of three independent tree-ring networks.

    Table S3. Comparison of the interpolated climate response based on the full tree-ring network versus subsets thereof.

    Data S1. Partial_correlations_clusters.xlsx.

    Data S2. Climate_change_monthly.xlsx.

    Data S3. EUR_biomass_network.xlsx.

    Data S4. FLUXNET2015_Sites.xlsx.

    Data S5. Custom_Code.R.

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Geographic coverage of the tree-ring network.
    • Fig. S2. Definition of the growing season across the tree-ring network.
    • Fig. S3. Geographic distribution of the uncertainty associated with the spatial interpolation of climate response.
    • Fig. S4. Latitudinal changes in the climate response of forest growth during 1930–1960 CE.
    • Fig. S5. The climate response of tree growth across the four main climatic domains has changed between 1930–1960 and 1960–1990 CE.
    • Fig. S6. Spatiotemporal changes in the climate response of tree growth between 1930–1960 and 1960–1990 CE.
    • Fig. S7. Comparison of the summer climate response of three independent tree-ring networks.
    • Table S1. Relationships between the climate response of tree growth and mean climatic conditions.
    • Table S2. Comparison of the climate sensitivity of three independent tree-ring networks.
    • Table S3. Comparison of the interpolated climate response based on the full tree-ring network versus subsets thereof.
    • Legends for data S1 to S5

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Data S1. Partial_correlations_clusters.xlsx.
    • Data S2. Climate_change_monthly.xlsx.
    • Data S3. EUR_biomass_network.xlsx.
    • Data S4. FLUXNET2015_Sites.xlsx.
    • Data S5. Custom_Code.R.

    Files in this Data Supplement:

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