הלא דבר הוא
According to Kabbalah, the ברכת האילנות are to be said only in חודש ניסן. In many cities in North America , the trees haven’t started blossoming yet. Some will make the Bracha Iy"h in אייר. According to Halacha, most Poskim hold, it is perfectly acceptable to make the Bracha in the months of אדר or אייר.
In Shas Bavli & Yerushalmi, Zohar, Poskim (Tur Sh. Aruch 233) and all Sidurim printed over 300 years ago, the Nusach of the Bracha ends "Shelo Chisar Bo’olamo כלום". Most Siddurim today have the Nusach is "Shelo Chisar Bo'olamo דבר".
Why the change?