Are out-of-cull-distance objects being kept in memory?

I mean, if I have, for instance, tons of trees, but only 1/4 of them are being shown in my cull distance. Are the 3/4 of trees kept in memory so they can be shown in no time when I move towards them? Are there a performance/ram/cpu usage difference when I have, for example, 1/4 of that tree amount placed as objects and that’s all, or 1/4 of that tree amount being in the cull distance and with another 3/4 tree amount being hidden?