Insects, maybe?
Are any other trees in the neighbourhood suffering? Gleditsia may be drought-tolerant but there are degrees of drought and it may be that they have tolerated as much as they can!

Or, the other way, they are in a poorly drained site (do such sites exist where you are?), and have suffered as a result. I suspect, as said above, they've struggled in too dry a spot. What were conditions like over the last year?

Sydney had consistent rain up to June but no rain since. The soil is idea for Gleditsias. The site is well drained also.

Two of the trees are fully grown and the third was doing well.

About a year ago about three branches (at the end) died on one of the three and the branches fell to the ground. This was when they were in full leaf foliage. I suspect a bug of some type but thought nothing more of it. It was very strange to happen to a very healthy tree in mid season.

Tks

Well, they might survive but it sounds very much as though they were already suffering and then have been subjected to 4 months of drought. Branches falling off certainly doesn't sound like a happy tree :o(

Gleditsia trees need a deep soaking about every 2 weeks in our climate, Gordon--about equivalent to Newman, West Australia--and about once every 3 weeks in Los Angeles, California, which is closer to Sydney's temps and humidity.

Thanks everyone. These trees are much higher than I thought - over two stories. It cannot possibly be a water issue as the soil is typically clay and the gleditsias had been fine and very robust for up to ten years. I've lopped off some high limbs and many are dead/dying. I say they started dying over a year ago. I have a Chinese pistiachios (?) next to these gleditsias and it is also struggling to show leaves at the top. We have possums extensively in the area, rabbits, and the bird life seems to be very abundant compared to previous years. I'll make enquires at Flower Power and post result when I find out.

Chinese pistache has similar water needs to Gleditsias, so I would still suggest a watering issue, OR a change of grade in the root area. Look for changes in the way the trees are being maintained.

The local nursery believes it is possums.

I will post a photo of the Chinese pistache that is not doing well. I have two and one is thriving.

Possums? My ignorance is probably showing--I thought that possums were small carnivores. :/

For the past year or so I've heard possums running across our roof nightly and under the Gleditseas their droppings have been very evident. I cut back the Gleditsias a little to stop possums from jumping from the roof onto the Gleditseas. They are small carnivores (feeding on flesh & of plants).

Possums are protected in Australia. One has to catch them and deliver them in the cage over a river so that they won't return. Last year I lost all my tomatoes to possums, rabbits or bandicoots. Possums eat flowers also.

On the internet it says Gleditias often reshoot up to a meter from ground level. I have taken the three back to one meter and yes new shoots are appearing.

The Chinese pistache is not showing any new growth and the Rubenia same. The second Chinese pistache looks very healthy.

Regards

I have also sent pictures to Flower Power in

Are there borers that attack these trees in Australia? We occasionally have problems with flat-headed borers here, and they can cause symptoms like you are describing.