Rising synchrony controls western North American ecosystems

Abstract

Along the western margin of North America, the winter expression of the North Pacific High (NPH) strongly influences interannual variability in coastal upwelling, storm track position, precipitation, and river discharge. Coherence among these factors induces covariance among physical and biological processes across adjacent marine and terrestrial ecosystems. Here, we show that over the past century the degree and spatial extent of this covariance (synchrony) has substantially increased, and is coincident with rising variance in the winter NPH. Furthermore, centuries-long blue oak (Quercus douglasii) growth chronologies sensitive to the winter NPH provide robust evidence that modern levels of synchrony are among the highest observed in the context of the last 250 years. These trends may ultimately be linked to changing impacts of the El Niño Southern Oscillation on midlatitude ecosystems of North America. Such a rise in synchrony may destabilize ecosystems, expose populations to higher risks of extinction, and is thus a concern given the broad biological relevance of winter climate to biological systems.

Predator‐mediated effects of severe drought associated with poor reproductive success of a seabird in a cross‐ecosystem cascade

“…Drought conditions in this area are also linked to regional oceanographic indices (McCabe‐Glynn et al, ), so this long ecological cascade ultimately begins with ocean‐atmosphere interactions and ends up looping back onto the marine food web via murrelets. Similar synchronous effects between marine and terrestrial ecosystems have been increasingly recognized through the effects of rainfall (Black et al, ; Ong et al, ; Thomsen et al, ), but our study is unique for the California Current system in that long‐term data revealed a stronger connection between terrestrial productivity and the reproductive dynamics of a marine predator. In 2013, much of California was in an exceptional drought of a magnitude that had not been experienced for perhaps over ~1,200 years (Griffin & Anchukaitis, ; Diffenbaugh, Swain, & Touma, ).…”

Increased Drought Sensitivity Results in a Declining Tree Growth of Pinus latteri in Northeastern Thailand

“…The temporal variation in ring-width synchrony among trees showed an increasing trend of synchrony since 1980s for the two low elevation sites (KJ and NK) ( Figure 6), which implies an intensification of shared climatic constraints on tree growths [28]. An increasing growth synchrony has also been detected in Mediterranean Spain [28], boreal Siberia [37], Pinus pinea in South Iberia [63], in western North American ecosystems [64] and in high-elevation sites of the Southeast Tibetan Plateau [65]. An increasing in temperature and decreasing moisture availability at the lowland area in Thailand would likely brings more severe drought stresses for Tenasserim pine and thus triggers more synchrony among trees.…”

Tail associations in ecological variables and their impact on extinction risk

“…Let X i ( t ) and X j ( t ) denote the values of some weather variable as measured in fixed locations i and j at time t . Although changes in the correlation, through time, between X i ( t ) and X j ( t ) are increasingly documented, and may also be a consequence of climate change (Black et al 2018), we are unaware of any studies examining the extent to which tail associations between X i ( t ) and X j ( t ), and asymmetries of tail association, may be changing. If ECEs are becoming more spatially extensive, as seems likely given that they are becoming more intense (Ummenhofer and Meehl 2017), then the conditional probability that both of X i ( t ) and X j ( t ) are influenced by an ECE, given that one of them is so influenced, should be increasing.…”

“…Perhaps unfortunately, the Pearson correlation, which is the most commonly used measure of association of two variables, depends not only on association information, but also on the marginals. For this reason, it is possible that recently observed changes in environmental (Black et al 2018) and biological (Koenig and Liebhold 2016) synchrony are, at least in part, just another feature of already‐studied changes in distributional characteristics of variables, rather than reflecting true changes in association as would be measured using rank‐based correlation methods.…”