Ecology is a science that studies the interaction between inorganic environment and biological groups (energy, matter and information flow).
First of all, soil research is an important part of ecology. Material circulation and energy flow, water circulation and microbial metabolism, global temperature change and CO2 concentration, local pollution and nitrogen deposition are all very important in these processes. In addition, the development of plant roots, animal predation model, global climate simulation, and even Mars exploration to find water sources all have the role of considering soil. This direction can be said to be very hard core.
So there are many directions that don't need to consider soil, deep-sea ecosystems need to be considered less, and the dynamics of large mammals. Evolutionary biology, especially the systematic development direction, can be very specialized. I can think of these for the time being.
The popularity of wetlands in recent years is due to the support of national policies (the wetland retention rate is 8%).
Industrial ecology and green circular economy are certainly a promising direction, but the foundation of anything with "broad prospects" is generally weak. Considering plug and play, I think you should take a series of related majors with the word "management" such as environmental engineering, agriculture, tobacco, plant protection, forest and resource management. The direction of social science can consider planning, regional economy and the like.
If there is no soul in the direction of plants, then go to the direction of animals, soil, or turn to the direction of environmental protection. This is all the same, as well as microbial direction, molecular biochemistry and ecological information. If you know more, you may be interested.