Felling 伐採（ばっさい）

Felling = felling trees は立木の伐採です。fell には 木を切り倒すという意味がある。0:39 now Tierra del Fuego has around 100,000 beavers and they are endangering the regional virgin forest. their steady gnawing fells trees which they use to build houses and dykes. アルゼンチンのこの地では、70年前にカナダから持ち込んだ25匹のビーバーが繁殖して約10万匹に殖え、家やダムを作るため木をかじり倒してここの森林を食い荒らしている。

Argentina declared war on beavers | DW News

https://www.youtube.com/watch?v=yJjaQExOPPY  0:32 felling trees with your teeth takes great strength, skill and patience.立木をかじり倒すには相当な体力、技術そして根気が必要だ。
How Beavers Build Dams | Leave it to Beavers | PBS

https://www.youtube.com/watch?v=EzCImKVS7Qk  18:57 thousands of years people of Japan have felled trees and made use of the timber.
[Begin Japanology] Season 4 EP08 : Sashimono Woodwork 木工 2011 03 10

https://www.youtube.com/watch?v=CDZ01iPf1-s  8:55 so in the 1950s huge numbers of Japanese cedars were felled and new ones were planted on an unprecedented scale. 沢山の杉が伐採され、そして前例のない規模の植樹が行われた。
[Begin Japanology] Season 4 EP07 : Pollen Allergy 2011-03-03

練習問題解答
a-5262 big name to be felled
b-2602 was felled
b-5112 were felled