key: cord-0284183-x8s04sx8 authors: Esperon-Rodriguez, Manuel; Baumgartner, John B.; Beaumont, Linda J.; Lenoir, Jonathan; Nipperess, David; Power, Sally A.; Richard, Benoît; Rymer, Paul D.; Tjoelker, Mark G.; Gallagher, Rachael V. title: Climate-change risk analysis for global urban forests date: 2021-05-10 journal: bioRxiv DOI: 10.1101/2021.05.09.443030 sha: 95024e0c84a689249a61e00c2ae50303873732a9 doc_id: 284183 cord_uid: x8s04sx8 Urban forests (i.e. all vegetation present in urban areas), provide environmental and socioeconomic benefits1 to more than half of the global population2. Projected climate change threatens these benefits to society3–5. Here, we assess vulnerability to climate change of 16,006 plant species present in the urban forests of 1,010 cities within 93 countries, using three vulnerability metrics: exposure, safety margin and risk. Exposure expresses the magnitude of projected changes in climate in a given area, safety margin measures species’ sensitivity to climate change, and risk is the difference between exposure and safety margin6. We identified 9,676 (60.5%) and 8,344 (52.1%) species exceeding their current climatic tolerance (i.e. safety margin) for mean annual temperature (MAT) and annual precipitation (AP), respectively. By 2050, 13,479 (84.2%) and 9,960 (62.2%) species are predicted to be at risk from projected changes in MAT and AP, respectively, with risk increasing in cities at lower latitudes. Our results can aid evaluation of the impacts of climate change on urban forests and identify the species most at risk. Considering future climates when selecting species for urban plantings will enhance the long-term societal benefits provided by urban forests, including their contribution to mitigating the magnitude and impacts of climate change. . F o r a s u b s e t o f 3 7 c i t i e s , t h e e x p o s u r e l e v e l i s p r e d i c t e d t o b e s o h i g h u n d e r f u t y 2 0 7 0 , 1 0 , 2 3 3 s p e c i e s ( 6 4 % ) a r e p r e d i c t e d t o b e c o m e a t r i s k o f d e c r e a s e s i n A P , w i t h f i v e a n d 1 5 1 c i t i e s h a v i n g 1 0 0 % a n d > 5 0 % o f t h e i r s p e c i e s a t r i s k , r e s p e c t i v e l y . S e e s u p p l e m e n t a l m a t e r i a l f o r d e t a i l s o n s p e c i e s ' r i s k o f M T W M a o f l o w p r e c i p i t a t i o n b y p r o v i d i n g s u p p l e m e n t a l w a t e r d u r i n g p e r i o d s o f s e v e r e c l i m a t e s t r e s s 3 3 188 a n d p r o m o t i n g e v a p o t r a n s p i r a t i o n ( l o c a l c o o l i n g e f f e c t g e n e r a t e d b y p l a n t s ) , w h e r e r e s o u r c e s t o m i t i g a t e c l i m a t e c h a n g e a r e m o r e l i m i t e d 4 0 . I n t h e s e c i t i e s , M A T e x p o s u r e i s l o w e r ( p a r t i c u l a r l y i n t h e N o r t h e r n h e m i s p h e r e ) c o m p a r e t o c i t i e s a t h i g h e r l a t i t u d e s ; t h e r e f o r e , s p e c i e s ' s a f e t y m a r g i n m i g h t b e d r i v i n g t h e i n c r e a s e i n r i s k . T h i s h i g h l i g h i n c r e a s e s u n c e r t a i n t y a r o u n d d e c i s i o n -m a k i n g 4 2 . T o m a i n t a i n h e a l t h y u r b a n f o r e s t s i n a c h a n g i n g c l i m a t e , i t w i l l b e n e c e s s a r y t o a d d r e s s b u d g e t c o n s i d e r a t i o n s , t h e p r o v i s i o n o f a d e q u a t e t i m e a n d e f f o r t f o r e s t a b l i s h i n g a n d m a i n t a i n i n g u r b a n p l a n t i n g s , a n d f i l l i n g t L i n e a r r e g r e s s i o n s w e r e f i t t e d t o e v a l u a t e t h e r e l a t i o n s h i p b e t w e e n c l i m a t e e x p o s u r e / r i s k a n d c i t i e s ' l a t i t u d e . M o d e l p e r f o r m a n c e w a s e v a l u a t e d t h r o u g h t h e c a l c u l a t i o n o f 359 a n R 2 v a l u e a n d t h e F -S t a t i s t i c a t a s i g n i f i c a n c e l e v e l o f P < 0 . 0 5 . A l l a n a l y s e s w e r e c o n d u c t e H o w e v e r , o u r r e s u l t s s h o w t h a t s o m e c i t i e s c u r r e n t l y h a r b o r m a n y s p e c i e s l i v i n g o u t s i d e o f 200 t h e i r r e a l i s e d c l i m a t i c t o l e r a n c e . W e f o u n d a h i g h n u m b e r o f s p e c i e s c u r r e n t l y e x c e e d i n g t h e i r 201 s a f e t y m a r g i n f o r t h e f o u r c l i m a t e v a r i a b l e s ( M A T = 6 0 . 5 % ; A P = 5 2 . 1 % ; M T W M = 5 6 . 3 % ; P D Q = 202 4 6 . 8 % ) ,( G C M s ) : ( 1 ) b c c - c s m 1 - 1 , C h i n a ; ( 2 ) C C S M 4 , U S A ; ( 3 ) C E S M 1 - C A M 5 , U S A ; ( 4 ) C S I R O - M k 3 - 6 - 0 , 298 A u s t r a l i a ; ( 5 ) G F D L - C M 3 , U S A ; ( 6 ) H a d G E M 2 - A O , K o r e a ;( 7 )‫ܧ‬ ൌ ‫ܥ‬ ݅ ‫ݐ‬ ‫ݕ‬ ୳ ୲ ୳ ୰ ୣ େ ୪ ୧ ୫ ୟ ୲ ୣ െ ‫ܥ‬ ݅ ‫ݐ‬ ‫ݕ‬ ୟ ୱ ୣ ୪ ୧ ୬ ୣ େ ୪ ୧ ୫ ୟ ୲ ୣ A p o s i t i v337 338 ܵ ൌ ቊ S p e c i e s େ ୪ ୧ ୫ ୟ ୲ ୣ ୟ ୰ ୧ ୟ ୠ ୪ ୣ ሾ ሿ െ ‫ܥ‬ ݅ ‫ݐ‬ ‫ݕ‬ ୟ ୱ ୣ ୪ ୧ ୬ ୣ େ ୪ ୧ ୫ ୟ ୲ ୣ ሺ ‫ܯ‬ ‫ܣ‬ ܶ , ‫ܯ‬ ܶ ܹ ‫ܯ‬ ሻ ‫ܥ‬ ݅ ‫ݐ‬ ‫ݕ‬ ୟ ୱ ୣ ୪ ୧ ୬ ୣ େ ୪ ୧ ୫ ୟ ୲ ୣ െ ܵ ‫‬ ݁ ܿ ݅ ݁ ‫ݏ‬ େ ୪ ୧ ୫ ୟ ୲ ୣ ୟ ୰ ୧ ୟ ୠ ୪ ୣ ሾ ሿ ሺ ‫ܣ‬ ܲ , ܲ ‫ܦ‬ ܳ ሻ 339 F o r S , Sampling effort in herbarium collections largely reflects spatial variation, often related to human settlement and infrastructure 1,2 ; hence, the sampling effort across cities is undoubtedly biased. Therefore, we acknowledge that our approach underestimates the number of species occurring within each city. v a r i a b l e t h a t i s s e n s i t i v e t o i n v e n t o r y c o m p l e t e n e s s w o u l d s h o w a " f u n n e l e f f e c t " w i t h h i g h e r v a r i a b i l i t y a t l o w c o m p l e t e n e s s , t h e r e b y i n d i c a t i n g b i a s e d s a m p l e s ( F i g u r e 7 ) . w e r e r e p r e s e n t e d b y a s i n g l e c i t y . T h e a v e r a g e h u m a n p o p u l a t i o n a c r o s s a l l 1 , 0 1 0 c i t e s w a s 8 3 0 , 8 3 4 ( ± 2 , 1 9 3 , 1 3 6 p e o p l e ) , w i t h a m a x i m u m o f 3 5 , 6 7 6 , 0 0 0 i n T o k y o ( J a p a n ) a n d a m i n i m u m o f 2 4 6 p e o p l e i n T h e o d o r e ( A u s t r a l i a ) . First, species realised niches (assessed here) are not equal to their fundamental niche. We used occurrence records to approximate distribution, but biological factors such as competition, abiotic factors (e.g. soil and nutrients) and dispersal limits may mean that our use of occurrence records underestimate species' climate envelopes. W e o b t a i n e d o c c u r r e n c e r e c o r d s f o r a l l t r a c h e o p h y t e s a n d p o l y g o n s d e f i n i n g t h e b o u n d a r i e s o f c i t i e s g l o b a l l y . T h e n , w e i d e n t i f i e d s p e c i e s o c c u r r i n g o n l y w i t h i n c i t i e s ( i . e . 1 6 , 0 0 6 s p e c i e s ) . C l i m a t e d a t a w e r e d o w n l o a d e d f o r f o u r c l i m a t e v a r i a b l e Widespread sampling biases in herbaria revealed from large-scale digitization How well documented is Australia's flora? 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