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What's the situation?
Once upon a time, the military took account of the importance of the view of solstice sunrise from Stonehenge.
When - in 1910 - the British and Colonial Aeroplane Company gained permission to establish their flying school alongside the Army's aerodrome on Larkhill they were compelled to build their hangars so as to leave a gap for the summer solstice sunrise to shine down to Stonehenge.
This became known as the "Sun Gap".
In the intervening years, and long after the army's hangars were torn down (although the BCAC's are still there) a plantation of trees was created along the length of Wood Road and Tombs Road at Larkhill, filling in the Sun Gap.
These are the trees that have now reached such a height as to obscure summer solstice sunrise as seen from Stonehenge.
(Click any image for a larger version in a new window)
 First Gleam 24th June 2013 at 4:03am GMT to the right of the tip of the Heelstone
Now the MoD plans to build many hundreds of houses for personnel returning from Germany and one of the options "held in reserve" is to use the land alongside Wood Road and Tombs Road (referred to as sites L2 and L13b in their plans).
 Google Earth image overlaid with Larkhill 1912 map and the MoD's Army Basing Proposal
If this was to go ahead, any chance of restoring the Sun Gap would be lost forever.
As an exercise I decided to try and determine which of the plantation trees should be removed to restore enough of the original Sun Gap to allow summer solstice sunrise to be seen to the left of the tip of the Heelstone.
In 1902, Sir Norman Lockyer determined the azimuth of the solstice axis from Stonehenge to be 49° 34'. Later researchers have adjusted this value (Atkinson in 1978 suggested 49° 54') but since I have a deep respect for the former Astronomer Royal I've decided to use Lockyer's value.
Here's an image from Google Earth showing Lockyer's azimuth as a purple line extended from Stonehenge in the direction of Larkhill.
 Oblique view Lockyer's Azimuth from Stonehenge
The next image shows this azimuth as it passes over Larkhill.
 Oblique view over Wood Road and Tombs Road in Larkhill with Lockyer's Azimuth
Knowing that I took the Stonehenge summer solstice first gleam picture at 4:03am GMT, I used Google Earth to show me the Sun at that time of day on the summer solstice and drew a line towards it (in white) in order to determine the approximate azimuth of the modern day first gleam position from Stonehenge.
 Oblique view showing modern day first gleam azimuth (approx) in white
Armed with this information I was then able to look down on Wood Road and Tombs Road and see the limiting azimuths between which the trees would need to be removed in order to restore the first gleam to appearing to the left of the tip of the Heelstone.
 Overhead view of Wood Road and Tombs Road plantation (and another nearby one) showing Lockyer's azimuth (purple), modern day first gleam azimuth (white) and which trees to remove
This is the minimal solution, ideally the entire plantation along Wood and Tombs Roads would be removed, along with a larger proportion of the other one to the southwest.
However, I'm also a fan of trees in general so it would be a shame to remove them all when it's not completely necessary.
There is a degree of approximation in these calculations - mainly because:
a) You can't trust Google Earth to be wholly accurate in its aerial photo registration or orthogonality (I have previously discovered)
b) You can't trust Google Earth to show the Sun position entirely accurately
c) A desktop exercise is no substitute for a proper survey on the ground, but sadly I don't have access to a theodolite nor do I have command of the weather on the solstice to cross-check azimuths with a clear sky
All that said, I think there is a strong case for restoring the Sun Gap and I also bear in mind the "CONCORDAT GOVERNING THE LOCATION AND CONSTRUCTION OF BUILDING FOR MINISTRY OF DEFENCE AT LARKHILL (1970)" which states:
The Ministry of Defence have a requirement for a School of Artillery at Larkhill for as long as can be foreseen. In addition to the buildings now being erected, this Army Establishment may require further buildings or structures. However, it is the long term objective of the Ministry of Public Building and Works that no buildings or large tree plantings should be visible from Stonehenge.
The existing plantations are in violation of this concordat.
In view of this and the Army's century-old regard to the importance of preserving the summer solstice sightline to the horizon of Larkhill in conjunction with the forthcoming public consultation on the Army Rebasing Plan, now would seem to be the ideal time to restore the Sun Gap.
Read my submission to the MoD's consultation for more detailed information. Remember, this consultation closes on 1st April 2014.
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simon
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Larkhill Sun Gap (original from 
