Should tropical rainforests begin with capital letters when used in a sentence?

Whether you capitalize "tropical rainforests" depends on context. Here's a breakdown:

When to Capitalize:

* As a Proper Noun: If you are referring to a specific rainforest with a unique name, like the Amazon Rainforest, then "tropical rainforests" should be capitalized because it acts as a proper noun.

* As a Title: If "Tropical Rainforests" is part of a book title, article title, or other formal heading, it should be capitalized.

When Not to Capitalize:

* As a General Term: When referring to rainforests in general, "tropical rainforests" is a common noun and should not be capitalized. For example: "Tropical rainforests are important for biodiversity."

Examples:

* Capitalized: "The Amazon Rainforest is the largest rainforest in the world."

* Capitalized: "The book, 'Tropical Rainforests: A Global Perspective', explores the ecological importance of these ecosystems."

* Not Capitalized: "Tropical rainforests are crucial for regulating climate."

In summary: Capitalize "tropical rainforests" only when it refers to a specific named rainforest or when it's part of a title. Otherwise, use lowercase.