While this is interesting, it is also a very wide-ranging topic. We could devote an entire week to discussing just one of the listed issues.
A point if I may; in asking those questions, one must consider the locale. What may have applied in Texas may not apply in Nebraska for instance, or vice-versa.
Texas has a varied environment. The only things you will find in any other state that you will not find in Texas are rockbound coasts & year-round snow-covered mountains. In the eastern part of the state you could as easily be in Mississippi or Alabama as in Texas. I live a little southeast of Austin, in the south-central part of Texas. Less than 40 miles to the east of me is a palmetto swamp much like those you'd find in southern Georgia. Less than 100 miles to the west of me the land is semi-desert.
In Texas you can drive your car to a point higher than the highest point east of the Mississippi River. The highest point in the state is in Hudspeth County, in the Guadalupe Mountains. It's Guadalupe Peak, which is over 8000 feet tall. The highest point east of the Mississippi is Clingman's Dome in eastern Tennessee, which is about 6600 feet high. Mt. Locke, in the Davis Mountains, is the location of McDonald Observatory, which is nearly 7000 feet high--& you can drive on a paved road up to the gates of McDonald Observatory.
In the panhandle, the most northerly part of the state, there's a division in the land. The western half of the panhandle is the llano estacado--the staked plains. This land is so flat, if you dropped a marble it'd lose its mind trying to figure out which way to roll. The only changes in elevation are 'blowouts,' which are old, abandoned buffalo wallows. On the east side of the panhandle are the canyonlands--one of the most broken landscapes in the US.
Just to the northwest of me is the hill country. This is a granitic uplift--one of the oldest surviving granitic uplifts on the earth. Pink granite--& all around it limestone--hills & valleys abound. Where I live there is a blackland prairie. The soil is so rich that the saying is, if you wet your finger & stick it in the ground, if you don't pull it out immediately it'll take root. However, less than 2 miles south of me, across the Guadalupe river, the land is sandy. It'll grow peanuts & watermelons, but not much else.
Outside the cities & their immediate environs, about the only parts of Texas that have changed significantly over the last century & a half are the western half of the Panhandle & parts of the area beyond the Pecos River. The western half of the panhandle was farmed extensively, mostly for grain crops & cotton, for most of the 20th century. However, the farms were irrigated from a vast, but not inexhaustible, supply of underground water, the Ogalala Aquifer. That aquifer has almost been exhausted, so that area is returning to dryland ranching. Parts of the Trans-Pecos were formerly extensive grasslands, but using them to raise horses--horses are destructive grazers--for the US Cavalry has turned the area into semi-desert.