▁However , ▁rec y cling ▁pro ponents ▁point ▁out ▁that ▁a ▁second ▁tim ber ▁or ▁logging ▁tr uck ▁is ▁elimin ated ▁when ▁paper ▁is ▁collected ▁for ▁rec y cling , ▁so ▁the ▁net ▁energy ▁consumption ▁is ▁the ▁same . ▁An ▁emer gy ▁life - cycle ▁analysis ▁on ▁rec y cling ▁revealed ▁that ▁fly ▁ash , ▁al umin um , ▁rec yc led ▁concrete ▁aggregate , ▁rec yc led ▁pl astic , ▁and ▁steel ▁yield ▁higher ▁efficiency ▁r ati os , ▁whereas ▁the ▁rec y cling ▁of ▁l umber ▁generates ▁the ▁lowest ▁rec ycle ▁benefit ▁ratio . ▁Hence , ▁the ▁specific ▁nature ▁of ▁the ▁rec y cling ▁process , ▁the ▁methods ▁used ▁to ▁analy se ▁the ▁process , ▁and ▁the ▁products ▁involved ▁affect ▁the ▁energy ▁sav ings ▁bud gets . ▁ ▁It ▁is ▁difficult ▁to ▁determine ▁the ▁amount ▁of ▁energy ▁consum ed ▁or ▁produced ▁in ▁waste ▁dispos al ▁processes ▁in ▁bro ader ▁e colog ical ▁terms , ▁where ▁caus al ▁relations ▁diss ip ate ▁into ▁complex ▁networks ▁of ▁material ▁and ▁energy ▁flow . ▁For ▁example , ▁" c ities ▁do ▁not ▁follow ▁all ▁the ▁strateg ies ▁of ▁e cos ystem ▁development . ▁Bi oge och em ical ▁paths ▁become ▁fairly ▁straight ▁relative ▁to ▁wild ▁e cos ystem s , ▁with ▁very ▁reduced ▁rec y cling , ▁resulting ▁in ▁large ▁flows ▁of ▁waste ▁and ▁low ▁total ▁energy ▁effic ien cies . ▁By ▁contrast , ▁in ▁wild ▁e cos ystem s , ▁one ▁population ' s ▁was tes ▁are ▁another ▁population ' s ▁resources , ▁and