Teachers Guide
Sheldon Forest

Beautiful tall eucalyptus forest preserved in precious few sites

The most obvious first impression of Sheldon Forest is multiple tall trees with smooth trunks – very different to the bushland, heath and woodland of the often steep and rocky Hawkesbury Sandstone terrain like much of Ku-ring-gai Chase National Park. So what’s going on here? What’s special are these trees? Sheldon Forest is one of roughly 15 remnants of the same type of tall forest scattered around the watersheds of Sydney’s North Shore. Others include Dalrymple Hay Nature Reserve in St Ives and there’s another large remnant over in West Pennant Hills. It’s open to the public and is a great place to visit.

What do we mean by “remnants”? Remnants of what?

We all know the meaning of the word remnant, it’s what remains after a greater part of it has been removed. Sheldon Forest is surrounded by houses and truncated by a railway line. Did the same forest once grow where the houses now are? And how big an area did this forest once cover? A few local tens of hectares or tens of square kilometres?

So what’s special about this forest?

Sheldon Forest belongs to a critically endangered plant community that has been named Blue Gum High Forest. It was named after its key tall tree species, the Sydney blue gum (Eucalyptus saligna) which can grow to more than 40 metres and two metre trunk diameter in good conditions. “High Forest” because it is an upland area. Other tall tree species are scattered through, notably blackbutt (Eucalyptus pilularis). You may also spot the odd grey ironbark (Eucalyptus paniculata) and turpentine (Syncarpia glomulifera) but what will strike you is a shorter, medium-sized, slender-trunked tree with a high, dense crown of dark green leaves. It’s a NSW native but some experts think it’s an interloper growing outside its normal range: Can you name it and where it’s normally found growing naturally?

Why is this forest and terrain so different to local sandstone country?

The host country of Blue Gum High Forest remnants like Sheldon Forest is gentle, rolling upland watersheds which are underlain by the relatively soft shales of the Ashfield Shale Formation of the Triassic Wianamatta Group. The city end of Warrawee station platform is a good place to see this rock. The shale sits above the low-nutrient Hawkesbury Sandstone separated by a layer of alternating thin shales and sandstones called the Mittagong Formation. Helped by a high average rainfall, the Ashfield Shale of Sheldon Forest has generated deeper, richer soils than has the Hawkesbury Sandstone of the adjoining valley downstream.

What’s special about Ashfield Shale and why does it form rich deep soils?

Think about what a plant needs to grow tall and strong: the soil structure and chemistry, and what about the annual rainfall? What does altitude above sea level and proximity to the coast do for this? Do tall trees need deep soil to survive long term?

In closing

Sheldon Forest is a beautiful, irreplaceable and a priceless reminder of how the local landscape looked before European settlement and urbanisation.