A novel dendroecological method finds a non-linear relationship between elevation and seasonal growth continuity on an island with trade wind-influenced water availability

Abstract

Climatic seasonality drives ecosystem processes (e.g. productivity) and influences plant species distribution. However, it is poorly understood how different aspects of seasonality (especially regarding temperature and precipitation) affect growth continuity of trees in climates with low seasonality because seasonality is often only crudely measured. On islands, exceptionally wide elevational species distribution ranges allow the use of tree rings to identify how growth continuity and climate–growth relationships change with elevation. Here, we present a novel dendroecological method to measure stem growth continuity based on annual density fluctuations (ADFs) in tree rings of Pinus canariensis to indicate low climatic seasonality. The species ranges from 300 to >2000 m a.s.l. on the trade wind-influenced island of La Palma (Canary Islands), where we measured three decades of tree-ring data of 100 individuals distributed over 10 sites along the entire elevational range. The successfully implemented ADF approach revealed a major shift of stem growth continuity across the elevational gradient. In a remarkably clear pattern, stem growth continuity (percentage of ADFs) showed a hump-shaped relationship with elevation reaching a maximum at around 1000 m a.s.l. Low- to mid-elevation tree growth was positively correlated with the Palmer Drought Severity Index (PDSI; indicating aridity) and sea surface temperature (indicating trade wind-influenced moderation of water supply), while high-elevation tree growth was positively correlated with winter temperature (indicating a cold-induced dormancy period). We conclude that ADFs are a useful method to measure stem growth continuity in low-seasonality climates. Growth of P. canariensis on the Canary Islands is more frequently interrupted by winter cold at high elevations and by summer drought at low elevations than in the trade wind-influenced mid elevations, where growth sometimes continues throughout the year. Climate change-associated alterations in trade wind cloud formation might cause non-analogue growth limitations for many unique island species.

Tree-ring distinctness, dating potential and climatic sensitivity of laurel forest tree species in Tenerife Island

“…The statistics of the tree-ring chronologies for the four studied species were within the common range of variation of MS (0.25-0.74), and even surpassed the common variation range of r xy (0.15-0.60) and EPS (0.27-0.94) found in tropical and subtropical tree-ring chronologies (Locoselli et al, 2013;Mendivelso et al, 2014;López and Villalba, 2016;Pagotto et al, 2017;Islam et al, 2018;Blagitz et al, 2019;Fontana et al, 2019;Marcelo-Peña et al, 2019). Statistics of the studied tree-ring chronologies were also similar than those from the conifers Juniperus brevifolia and Pinus canariensis in Azores and the Canaries, respectively (Rozas et al, 2013;Weigel et al, 2018;Pavão et al, 2022). These evidences indicate that ring width series from laurel forests tree species have analogous dendrochronological potential than Macaronesian conifers and tree species from tropical and subtropical forests worldwide.…”

Climate controls plant life‐form patterns on a high‐elevation oceanic island

“…comprise a substantial proportion of species diversity (del Arco‐Aguilar et al., 2010). Under such favourable growing conditions with very little seasonality in temperature and precipitation (Weigel et al., 2018), short‐lived species such as therophytes and low stature species (geophytes and hemicryptophytes but also dwarf shrub chamaephytes) are outcompeted by tall‐growing woody species (trees, large shrubs) that produce a dense and dark canopy (Delgado et al, 2007). Merely as a result of their large structures, phanerophytes have a competitive advantage over other plant life‐forms, indicating a climate‐driven selection of tall‐growing plant life‐forms under humid and mild conditions.…”

Summer drought exposure, stand structure, and soil properties jointly control the growth of European beech along a steep precipitation gradient in northern Germany

“…The latter most likely will affect the response of tree growth to climate variability, but the related evidence is still insufficient and contradictory (Andrews et al, 2020; Steckel et al, 2020). Since inter‐annual growth variation and growth synchrony among co‐occurring trees should theoretically increase toward more stressful and variable environments (Fritts, 1966; Shestakova et al, 2016; Weigel, Irl, et al, 2018), we expected that both growth variation and synchrony are higher at the dry end of the studied precipitation gradient and have increased with the recent warming since about the 1980s. We thus hypothesize that (i) the radial growth rate of beech has declined since about 1980, with more pronounced reductions occurring at drier sites, (ii) inter‐annual growth fluctuation and within‐stand growth synchrony have increased since the 1980s and both are larger at drier sites, and (iii) variables related to climatic drought in summer have a larger impact on growth and drought sensitivity than soil and stand structural factors including competition intensity.…”