Drivers of plant species assemblages in forest patches among contrasted dynamic agricultural landscapes

Summary1. Al th o ug h h ab itat frag me n tatio n is reco gn ized as a ma jor th reat to bio dive rsity, few stu dies h av eex am ined th e relative imp o rtan ce o f loca l, land scap e an d histo rica l facto rs in co nt ro lling loca lsp ec ies as semb lage s, an d h o w th ese facto rs intera ct,in pa tchy ec o sy stem s. We q ua n tiÞe d th e directan d ind irec t effects o f pa tch size ,p atch h etero ge n eity,ag ricu ltu ra linten sity an d p atch ag e o n plan tsp ec ies rich n ess an d co mp o sitio n o ffo rest pa tche s em b ed d ed in ag ricu ltu ra lland scap es.2. In six 5 a 5 k m- sa mp ling lan ds ca pe wi n do ws , we su rv ey ed ea ch fo rest p atch fo r va scular p lantsp ec ies an d co llec ted th ree sets of ind ep en d en t va riab les, d escribing p atch size an d h etero ge n eity,lan ds ca pe co mp o sition an d h isto ry .T he six wi n do ws w ere ar ra ng ed alon g a gr ad ien t o f ag ricu ltu reint en sity in ru ra llan ds ca pe s of th e P icar d y region (N Fr an ce ).3. We u sed n on -m etric mu ltidim en sion al scaling (N MS ) to d etec t ma jor en viro n me n tal gr ad ient su n de rlying va riation in sp ec ies co mp o sition am on g pa tche s. We th en co n stru cted stru ctu ra l eq u a-tion mo de ls (S E M) to q ua nt ify th e direct an d ind irec t effects of th e th ree sets of va riab les o n loca lp lant d iversity,wh ich wa s su cc essive ly inco rp or ated as pa tch scor es alon g th e Þ rst th ree NM S ax es,w oo dy sp ec ies rich ne ss,fo rest he rb sp ec ies rich ne ss,an d no n- fo rest h erb sp ec ies rich ne ss.4. A ma jor insu en ce o f th e lan ds ca pe ma trix on loca l sp ec ies co mp os ition wa s reve aled b y NM San d su bs eq ue nt S EM ,ma inly th ro u gh no n -for esthe rb sp ec ies, w hich ex plain ed mo st of th e be tw ee np atch s or istic d issimi larity.S pe cies rich ne ss increa sed wi th pa tch he tero ge n eity,wh erea s pa tch ar ean ev er h ad a direct effect. Fo rest he rb s we re mo re resp o ns ive to pa tch ag e an d co nn ec tivity tha no th er sp ec ies, wh erea s n on -for est an d wo o d y sp ec ies we re mo re insu en ce d by ag ricu ltu re inten sityin th e su rro u nd ing ma trix.5. S ynthesis.We us ed o ne o f th e larg est da ta sets ev er co llec ted in temp erate frag me n ted fo rests tob u ild, fo r th e Þ rsttime ,a stru ctur al mo de linco rp or ating allsu sp ec ted dr ivers of loca lplan t co mm u -n ities. We sh o we d th at th e n u mb er an d iden tity of loca lsp ec ies co ex istin g in su cc essio na lfrag me n tso f a fo rest me taco mm un ity at a give n time is co nt ro lled by a u n iqu e co mb ination o f int erac tin gloc al, lan ds ca pe an d histo rica l factor s. Pr eservin g the larg est, old est frag me n ts an d fav o ur ing sp e-cies mo ve me n ts in th e su rro un d ing ma trix is th e be st wa y to co ns erve fo rest sp ec ialists in ch an gingru ra llan ds ca pe s.Key-wor ds: agricu ltural intens ity, disper sal lim itation, habita t fragm entat ion, he dgerow net-work, metacommun ity, plant communi ty divers ity, specie sÐarea relationshi p, specie sÐtimerelationshi p, struc tural equati on modellingIntroduc tion