The areas of specialization fall into three groupings: Regions, Biomes, and Elements.
Region -- pick a specific natural (not political) region of the Wold, like the Culverwood or the Cursed Swamp. All spells you cast while in that region gain the benefit of the feat; but all spells you cast outside the region suffer the feat's penalty. You gain the benefit even in cities, indoors, and underground in your region.
Biome -- pick a biome, or type of environment, like jungle, plains, ocean, wetlands, desert, or forest. All spells you cast while outdoors in that biome gain the benefit of the feat; but all spells you cast outside the biome suffer the feat's penalty. You do not generally gain the benefit in cities, indoors, or underground.
Elements -- pick an element: air, earth, fire, or water. The spells listed below (and only those spells) are arranged in elemental groups. Spells you cast in your elemental group gain the benefits of the feat; but all spells you cast outside the group suffer the feat's penalty.
Air
Lvl .... Spell
0 .... Know Direction
1 .... Endure Elements
1 .... Jump
1 .... Obscuring Mist
2 .... Fog Cloud
2 .... Gust of Wind
2 .... Resist Energy (elec, cold)
2 .... Summon Nature's Ally II (Elemental, Small)
3 .... Call Lightning
3 .... Protection from Energy (elec, cold)
3 .... Wind Wall
3 .... Summon Nature's Ally III (Elementals, Small)
4 .... Air Walk
4 .... Ice Storm
4 .... Summon Nature's Ally IV (Elemental, Medium; Arrowhawk, juvenile)
5 .... Call Lightning Storm
5 .... Control Winds
5 .... Summon Nature's Ally V (Elemental, Large; Arrowhawk, adult)
6 .... Transport via Plants
6 .... Summon Nature's Ally VI (Elemental, Huge)
7 .... Control Weather
7 .... Wind Walk
7 .... Summon Nature's Ally VII (Elemental, greater; Arrowhawk, elder)
8 .... Whirlwind
8 .... Summon Nature's Ally VIII (Elementals, greater)
9 .... Elemental Swarm (Air)
9 .... Summon Nature's Ally IX (Elemental, elder
Earth
Lvl .... Spell
0 .... Know Direction
1 .... Endure Elements
1 .... Longstrider
1 .... Magic Stone
2 .... Heat Metal
2 .... Resist Energy (elec)
2 .... Soften Earth and Stone
2 .... Summon Nature's Ally II (Elemental, Small)
3 .... Meld into Stone
3 .... Protection from Energy (elec)
3 .... Stone Shape
3 .... Summon Nature's Ally III (Elementals, Small; Thoqqua)
4 .... Spike Stones
4 .... Summon Nature's Ally IV (Elemental, Medium; Xorn, minor)
5 .... Commune with Nature (underground)
5 .... Transmute Mud to Rock
5 .... Summon Nature's Ally V (Elemental, Large)
6 .... Move Earth
6 .... Stone Tell
6 .... Wall of Stone
6 .... Summon Nature's Ally VI (Elemental, Huge; Xorn, average)
7 .... Summon Nature's Ally VII (Elemental, greater; Xorn, elder)
8 .... Earthquake
8 .... Repel Metal or Stone
8 .... Summon Nature's Ally VIII (Elementals, greater)
9 .... Elemental Swarm (Earth)
9 .... Summon Nature's Ally IX (Elemental, elde
Fire
Lvl .... Spell
0 .... Light
1 .... Endure Elements
1 .... Faerie Fire
1 .... Produce Flame
2 .... Fire Trap
2 .... Flame Blade
2 .... Flaming Sphere
2 .... Resist Energy (fire)
2 .... Summon Nature's Ally II (Elemental, Small)
3 .... Call Lightning
3 .... Protection from Energy (fire)
3 .... Quench
3 .... Summon Nature's Ally III (Elementals, Small; Thoqqua)
4 .... Flame Strike
4 .... Summon Nature's Ally IV (Elemental, Medium)
5 .... Call Lightning Storm
5 .... Wall of Fire
5 .... Summon Nature's Ally V (Elemental, Large)
6 .... Fire Seeds
6 .... Summon Nature's Ally VI (Elemental, Huge)
7 .... Fire Storm
7 .... Sunbeam
7 .... Summon Nature's Ally VII (Elemental, greater)
8 .... Summon Nature's Ally VIII (Elementals, greater)
9 .... Elemental Swarm (Fire)
9 .... Summon Nature's Ally IX (Elemental, elder)
Water
Lvl .... Spell
0 .... Create Water
1 .... Endure Elements
1 .... Goodberry
1 .... Obscuring Mist
2 .... Chill Metal
2 .... Fog Cloud
2 .... Resist Energy (acid, cold)
2 .... Summon Nature's Ally II (Elemental, Small)
3 .... Protection from Energy (acid, cold)
3 .... Sleet Storm
3 .... Water Breathing
3 .... Summon Nature's Ally III (Elementals, Small)
4 .... Blight
4 .... Control Water
4 .... Ice Storm
4 .... Summon Nature's Ally IV (Elemental, Medium; Tojanida, juvenile)
5 .... Commune with Nature (at sea / small isles)
5 .... Transmute Rock to Mud
5 .... Summon Nature's Ally V (Elemental, Large; Tojanida, adult)
6 .... Summon Nature's Ally VI (Elemental, Huge)
7 .... Control Weather
7 .... Summon Nature's Ally VII (Elemental, greater)
8 .... Summon Nature's Ally VIII (Elementals, greater; Tojanida, elder)
9 .... Elemental Swarm (Water)
9 .... Storm of Vengeance
9 .... Summon Nature's Ally IX (Elemental, elder)