Final answer:
To determine if a tropical forest is a secondary forest or old-growth forest from field observations, consider the age of the forest, presence of indicator species, and overall biodiversity and complexity.
Step-by-step explanation:
To determine if a tropical forest is a secondary forest or old-growth forest from observations made in the field, several factors can be considered. First, the age of the forest can provide a clue, as old-growth forests are typically much older than secondary forests. Additionally, the presence of specific indicator species, such as certain tree species or rare wildlife, can indicate an old-growth forest. Finally, the overall biodiversity and complexity of the forest can be used as an indicator, as old-growth forests tend to have higher biodiversity and more complex ecological interactions compared to secondary forests.