One acre isn't enough for a horse or pony- and even if the OP's two acres were adjacent (but I think he's implied they aren't) that still wouldn't be enough. There are - sadly - only too many folks who buy their "Little Princess" (ugh!) a pony without any knowledge or previous experience whatsoever, and I see the results more often than you might think. Buying just single acre plots isn't always a good idea unless you live nearby and can take advantage of that proximity - however, just because you own a piece of land, it doesn't mean you can always do exactly what you want with it, as an earlier thread this month showed.
The Christmas tree idea is one which does work - and there can be some income every year because people don't always want a big Christmas tree! I've noticed that the one or two local growers spend the weekends from mid-November onwards on site and cut the trees as required when a customer turns up - they don't sell to any "middle man" so get the full amount for themselves. This means that not all the trees are removed each year, leading to the need for some replacements of course, but also to a variety of sizes growing on the site & which is what the customer often likes to choose from.