Most users of SDR receivers use active antenna for the frequency range up to 50 MHz.
The choice for a loop antenna (magnetic field sensor) or a small telescope antenna (E-field sensor) depends mainly on the environment. Since you have plenty of room both options are good choice.
When the tree density is high may be the loop is a better choice. When there is interference generated by local electronics, also the loop is a better choice. The disadvantage of the loop is the directivity, specially for ground wave signals: there is a null in the directional sensitivity. This can also be an advantage.
Loop antennas for reception: tuned loop with high sensitivity can be small, circumference 1 meter is sufficient. Amplification is not necessary. Wideband loop needs no tuning but for good sensitivity the circumference must be 2 or 3 meters and a special amplifier is a must.
Do not forget that the coaxial cable between the antenna and the SDR is a conductor that brings, via the screen, interference from computer and power supply to the base of the antenna and that interference will influence the lowest level signals: the noise floor. Use common-mode means in the coax and ground the coax were it is connected to the antenna. Also a loop antenna will benefit from this interference-to-grond path (poor description, yes).
Using an SDR on a Laptop with Noisy Power Supply