When scenic spots are being built and expanded(时间状语从句), //（主句）the ecosystem is destroyed as the result of the following actions: （并列分句1)trees are cut down for buildings and transportation, //(并列分句2)indigenous species are deprived of their habitats, //(并列分句3)and the lack of vegetation may bring about landslides and other natural disasters.

参考译文：当景点正在建设和扩大时，生态系统由于下列行动而遭到破坏：砍伐树木用于建筑和交通；土著物种被剥夺其栖息地；缺乏植被可能导致山体滑坡和其他自然灾害。

逗号相当于连词起连接作用，但是当列举内容结束必须使用“连词and”

when引导时间状语从句语法结构分析如下

从句：：When scenic spots are being built and expanded 

连词：when

主语：scenic spots

谓语：are being built and expanded

主句：the ecosystem is destroyed as the result of the following actions:

主语：the ecosystem

谓语：is destroyed

状语：as the result of the following actions

冒号后面的三个并列分句语法结构分析如下(冒号是来解释actions所体现3个方面信息内容。）

分句(1)trees are cut down for buildings and transportation, 

主语：trees

谓语：are cut down

状语：for buildings and transportation

分句(2)indigenous species are deprived of their habitats, 

主语：indigenous species

谓语：are deprived of their habitats

分句(3)and the lack of vegetation may bring about landslides and other natural disasters.

主语：the lack of vegetation 

谓语：may bring about

状语：landslides and other natural disasters

备注：分句1和分句2用逗号，分句2和分句3用连词and连接表示列举内容结束了。