Longterm effect of temperature and precipitation

Authors: Magdalena Żywiec Elżbieta Muter Tomasz Zielonka Miguel Delibes Gemma Calvo Jose M Fedriani

Publish Date: 2016/10/11

Volume: 31, Issue: 2, Pages: 491-501

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Abstract

The combined effect of climate change and habitat destruction and fragmentation threatens many plant populations and even entire communities in Mediterranean ecosystems The Iberian pear Pyrus bourgaeana Decne a characteristic species of Mediterranean ecosystems is threatened by both habitat and climate changes We ask whether and how the growth of mature P bourgaeana in the thermoMediterranean zone ie altitude 700 m has been affected by longterm climate changes during the last century in a fragmented landscape Dendrochronological methods were used to find growth–climate relationships We made the first dendroclimatological analyses and constructed a first 103year treering chronology 1905–2007 of this species The treering series revealed large growth variability We found a clear strong relationship between tree growth and climate with annual precipitation being the most important climate factor enhancing radial growth Our results also showed that warm autumns and winters positively affect growth There was no temporal stability in the relationship between tree growth and climate The most general trend was in the relationship between annual precipitation and tree growth the decrease of rainfall in the last decades of the twentieth century was associated with a constant increase of the correlation coefficient Water accumulated in the soil in autumn and winter proved to be a key factor augmenting tree growth in the following vegetation period The climate–growth relationship in P bourgaeana has strengthened in recent decades apparently due to decreased precipitation levelsMost models of climate change predict global warming associated with a marked variation of the level and spatiotemporal distribution of precipitation and temperature IPCC 2014 Fischer and Schär 2010 Hoerling et al 2012 Ecosystems of all climate zones are vulnerable to climate change even in environments where water is not considered a limited resource Allen et al 2010 but according to climate models the Mediterranean Basin is one of the world’s climate change hotspots because of increases in the frequency duration and/or severity of droughts and heat stress IPCC 2014 Luterbacher et al 2012 Anderegg et al 2013 Barbeta et al 2013 Moreover landuse change and habitat fragmentation are also important factors rapidly altering the composition of communities in Mediterranean ecosystems Linares et al 2010 Olano et al 2012 Matesanz et al 2015 Therefore a full understanding of the level of tolerance to climate change is particularly needed in such humanized Mediterranean habitats to forecast population trends and distribution of threatened tree speciesChanges in temperature and water availability often have marked effects on tree growth Schweingruber 1996 Because trees are longlived organisms their ring series record longterm yeartoyear changes in climate conditions Schweingruber 1996 Nicault et al 2008 Olano et al 2008 2012 Due to their complex physiology trees may respond to climatic changes in complex ways Drew et al 2013 Olano et al 2014 Zang et al 2014 Moreover changes in the constraining factors may cause temporal instability in the relationship between climate and tree growth that modulates the response patterns of tree growth Briffa et al 1998 2002 D’Arrigo et al 2008 Briffa and Matthews 2002 Leburgeois et al 2012In the thermoMediterranean zone ie altitude below 700 m Olson et al 2001 climate imposes a double adversity for growth and survival of shrubs and trees ie extreme summer droughts and erratic unpredictable rain Valladares et al 2014 Global climate change is generally resulting in higher temperatures and lower precipitation though such changes are not distributed uniformly throughout the year As a consequence the effect of climate change on treering formation can vary depending on the relative importance of the two main limiting climate factors making predictions particularly difficult At higher altitudes eg meso supra and oroMediterrranean zones 700–2700 m Olson et al 2001 where winter cold can be an important stressor no agreedupon trend in the response of tree growth to climate change has been inferred from long treering series Granda et al 2013 2014 Some studies have documented an increase MartinezVilalta et al 2008 Vila et al 2008 Gimeno et al 2012 Tegel et al 2014 and others a decrease in the growth of Mediterranean trees during the second half of the twentieth century Jump et al 2006 Saris et al 2007 Piovesan et al 2008 Di Filippo et al 2010 Changes in climate–growth relationships have also been reported for several Mediterranean tree species Andreu et al 2007 Planells et al 2009 Carrer et al 2010 Leburgeois et al 2012 However the existing data are based mostly on widespread evergreen trees eg Viera et al 2009 Campelo et al 2010 MartinBenito et al 2011 2013 CandelPerez et al 2012 Gimeno et al 2012 and deciduous species have been much less studied in the Mediterranean area eg Tegel et al 2014 GonzálezGonzález et al 2015 Even less is known about the response to climate change of small trees and shrubs at low altitudes in the thermoMediterraneanIn this study we examined longterm changes in the stability of the climate–growth relationship of a thermoMediterranean deciduous small tree to gain a perspective on the future persistence of this species which has been decimated by different components of global change Our model plant the Iberian pear Pyrus bourgaeana Decne is a characteristic species of Mediterranean ecosystems and is considered important to their functioning Cabezudo and Pérez Latorre 2004 Fedriani et al 2010 ArenasCastro et al 2013 In Doñana National Park SW Spain P bourgaeana trees often occur at low density in small scrubland patches among farmland towns and other builtover areas Fedriani et al 2010 Currently P bourgaeana shows a very low level of natural regeneration most likely because of dispersal limitation extreme summer droughts and increased herbivore pressure limiting seedling establishment Fedriani et al 2010 2015 It is unclear whether and how mature P bourgaeana tree growth has been affected by longterm changes in climate through the last century This should be a fundamental step to predict the fate of the species and in general of other deciduous thermo and mesoMediterranean shrubs and small trees under a scenario of global warming Specifically in this study we sought to answer the following two questions 1 what sort of longterm climate–growth relationship is shown by P bourgaeana and 2 is this relationship temporally stable and if not what is the trend of such/these changes if found anyThe study site is located in southwestern Spain in the Doñana World Biosphere Reserve 37°9′N 6°26′W 0–80 m asl on the west bank of the Guadalquivir River estuary The Doñana area comprises three main ecosystems mobile dunes scrubland where P bourgaeana grows and marshes In the tree layer in addition to our focal species there are scattered Quercus suber Olea europaea var sylvestris Fraxinus angustifolia and Pinus pinea In the understory there are Pistacia lentiscus Halimium halimifolium Ulex spp Chamaerops humilis and Erica sp Valverde 1958 Fedriani et al 1998 2010 P bourgaeana trees occur at low densities generally less than one individual per ha Fedriani et al 2010 in patches of Mediterranean scrubland that are isolated from each other by natural or anthropogenic barriers marshes sand dunes or cultivations see also Żywiec et al 2012 for details

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