Should a forest ranger's travel pace in Chult's jungle be faster?

Question

My players recently started the Tomb of Annihilation adventure. In Chapter 2, under the heading "Tracking Miles" (p. 38), it says:

Instead of tracking movement by hexes, you can keep track of the actual distances covered (10 miles per day at a normal pace, 15 miles per day at a fast pace, or 9 miles per day at a slow pace), [...]

A character with a flying speed of 30 feet can travel 4 miles per hour.

Comparing this to the Travel Pace table in the PHB (p. 182):

Pace	/Hour	/Day(~×8)	The math is always a little wonky (for simplicity?)
Fast	4 miles	30 miles	→ 30 ×.5 = 15 miles (OK)
Normal	3 miles	24 miles	→ 24 ×.5 = 10 miles (-2 miles a day)
Slow	2 miles	18 miles	→ 18 ×.5 = 9 miles (OK)

A player asked: If his ranger chose forest for the Natural Explorer feature, then when in the "jungle" (a terrain common in Chult), could the group travel twice as far? The reasoning was that they felt ToA was halving the travel pace due to the implicit difficult terrain, which would be negated by the ranger's Natural Explorer feature:

Choose one type of favored terrain: arctic, coast, desert, forest, grassland, mountain, swamp, or the Underdark...While traveling for an hour or more in your favored terrain, you gain the following benefits: Difficult terrain doesn’t slow your group’s travel...

Answer 1

If you like; you're the DM

ToA presents its own rules for long-distance travel and doesn't refer back to the Movement rules in the PHB. Why the authors chose to create their own rules is anybody's guess.

So, you have these options:

• you can use the rules in ToA (which is what I did - mainly because I didn't notice the discrepancy), in which case the answer to your headline question is "no", or
• you can use the rules in the PHB, in which case the answer is "yes",
• you can use whatever rules you like because it's your game, in which case the answer is "it's up to you".

Similarly, it's up to you you to decide if:

• forest includes jungle (which is what I did),
• jungle is its own terrain type that a ranger can choose, or
• jungle is not forest and not open for rangers to chose as favoured terrain.

Answer 2

Jungle is not a defined game term, so it defaults to the dictionary meaning:

a tropical forest in which trees and plants grow very closely together

A tropical forest is still a forest, so the Ranger's Natural Explorer feature will apply to it.

Forests, especially dense ones such as jungle, count as difficult terrain per PHB, p. 182:

But adventurers often face dense forests, deep swamps, rubble-filled ruins, steep mountains, and ice-covered ground—all considered difficult terrain.

Using normal travel rules, the jungle would be difficult terrain, and the travel speed would be expected to be halved due to it, so the Ranger's ability would apply, effectively doubling the travel pace.

That being said, the flora, fauna and dangers in a jungle would be considerably different from those in a temperate forest. So it the Ranger is not local, it would not be entirely unjustified if a DM decided to rule differently.

Also, specific beats general, and the rules given in ToA are specific for this adventure, so by default we would expect them to override the general travel rules. They do not say what the source of the lower travel speed is. It again would be up to the DM to rule if a Rangers ability applies to them.

For what it's worth, to me it would seem bad judgment for a DM to nerf the Ranger's feature based on technicalities such as jungle not being explicitly called out or the travel rules in the module deviating slightly from the normal ones. The point of having a Ranger is in part to be great in their chosen environment. The player picked the class for it, and they cannot use it in dungeons or any other environments, so also not allowing it when it could apply seems a bit harsh.