I would say, in the examples above the both options are possible. But there are some subtle differences.
Using "там" with the verbs like "класть, ставить, сажать etc." conveys a more generic idea of location: it specifies "where you perform the action", "where the action takes place":
Я сажаю дерево в парке. (or) Я там сажаю дерево. - It means you are in a park now (or you are "there") and being located in the specified place, you perform planting a tree.
Using "туда" is more specific, it specifies a direction, i.e. to where you put something.
E.g., you cannot say "Я сажаю дерево в парк". But you can say: "Я сажаю дерево в землю" (into the ground).
"Я кладу мясо туда" specifies a place to where you put the meat.
"Я кладу мясо там" I think is also valid, but it is more generic (where you are used to put the meat everytime, not only for this specific occasion), so "там" denotes a static location, not a direction. And it may mean a more generic location: a room, a storage etc. where you KEEP meat.
If you specifically mean a bag or a can, then you cannot say "Я кладу мясо там". Only "туда" would be valid.
Exactly the same way as you use "там" and "туда"
Accusative means direction (corresponds to "туда"). Prepostitional means location (corresponds to "там").
I would prefer "Я сажаю дерево в землю" because you insert it to inside the ground, not just onto the surface.
It can be used when you want to specify that "You are planting a tree when you are (yourself) on the ground" or "on the earth".
Compare: Он сажает дерево на Марсе. - He is performing this being on the Mars
It should be "я кладу мясо в кастрюлю" - I am putting meat to inside the saucepan. Note that "кастрюля" is not any kind of pan. It is usually deep and intended for boiling (not for frying!): http://ru.wikipedia.org/wiki/%D0%9A%...8E%D0%BB%D1%8F. If you mean a pan for frying or roasting, it is "сковорода": http://ru.wikipedia.org/wiki/%D0%A1%...BE%D0%B4%D0%B0, which is shallow.
That is why, you say "в кастрюлю" (to inside, since it is deep) but "на сковороду" (onto the surface), depending on how you are going to cook the meat. The same is with static location:
"мясо сейчас в кастрюле" but "мясо сейчас на сковороде".
If you say "я кладу мясо на кастрюлю" it would be strange, as if the saucepan were covered, and you were putting meat onto the cover.
It sounds extremely odd. There are two possible options I can imagine:
1) you are on the covered soucepan yourselfand you perform the action when being there
2) or you do it regularly, so as if it were a normal place where you keep meat (on the cover of the saucepan).
Normally, we would never use this phrase.
No, "где" uses prepositional, not accusative. It is used for STATIC LOCATIONS.
But "куда" uses accusative, and it is used for DIRECTIONS.