By Alastair Macdonald and Gabriela Baczynska BRUSSELS (Reuters) - The European Union hopes Turkey will prevent as many migrants reaching Greece as last year but is readying "contingency" plans to shelter large numbers who may arrive but can no longer trek north toward Germany. Migration Commissioner Dimitris Avramopoulos told Reuters on Thursday that it was unclear how far Turkey could reduce numbers once the weather improves and, with efforts under way to prevent a repeat of last summer's chaotic treks through the Balkans, the EU was working with Athens to shelter refugees in Greece. "As long as our cooperation agreement we made with Turkey doesn't start giving results, the situation will not be easy at all.