Multiple short-range impulse responses aggregated to simulate a long-distance impulse response
if I were to convolve a source signal twice, would that result in a reasonable approximation of what the sound would be at 100m distance?

Yes. For small number of cascades this is a reasonable assumption.
However, you can't cascade the 10 meter response 10 times to get a single 100 meter response. While the general shape and structure of the response from 20m to 30m is the same as that from 30m to 40m, the phase spectra and the fine structures of the reflections are uncorrelatated. If you cascade the same impulse response over and over again, you get spectral thinning and it's starting sound &quot;metallic&quot; and &quot;hollow&quot;.
You can try to decorrelate short repsonses from the original or just to start with a parametric model that has tree density, tree reflectivity, leaf/brush absorption and obvioulsy distance as tweakable parameters.