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Protecting our precious places

Promoting native regeneration in gorse

By Charlie Palmer

Ecosystem processes have a remarkable ability to allow even severely degraded habitats to recover.  But, often the slow, measured approach that Mother Nature takes is not fast enough for us in our haste to restore (at least in part) the former glory of natural areas entrusted to us.

It could be that our modern, consumer driven, short attention span, baby boomer or generation X land managers are too impatient to wait for natural processes to achieve results – fair comment. But, I think this is not so much a criticism, but an attribute that we should be utilising.

Once the high priority, necessary and obvious tasks such as fencing and weed and pest control are complete, there is an opportunity to try simple and easy methods of forest management that act as Mother Nature's Little Helpers. 

Most of you will have noticed that gorse is a good nursery environment for native trees and shrubs, which eventually grow through and suppress gorse.  This assists us toward two ends - ridding us of gorse, and allowing native forest regeneration.

It works like this - gorse provides a sheltered environment with just enough space and light to allow native seed to establish and germinate. 

In addition, due in part to its nitrogen fixing qualities, it assists native seedlings to grow.  Most plants remove essential nitrogen from the soil, but a few from the pea family, including gorse and the clovers and small number of select native species including tutu, collect abundant nitrogen from the air and provide it to the soil for other plants to use. As gorse matures, the tall (up to 2m) canopy opens allowing light to reach the seedlings. They grow taller, for longer and with a denser canopy than the gorse, eventually suppressing it by restricting the available light.

A few years ago, I suggested to a covenantor that one way to speed up the process of native species growing through gorse would be to open up the gorse canopy in small areas simulating the natural maturation of gorse.  Since the growth of native species through gorse appears to be determined by light - simulating senescence by cutting the odd gorse bush should speed up native regeneration. The results last time I looked at this little experiment it seemed to be going well.  The natives under the gorse, which were formerly only seedlings, are now decent sized saplings and taller in areas where a gorse bush was removed.

Alan TottyDown in Canterbury, Alan Totty has also been experimenting.  He has a covenant area that includes several copses of beech trees.  Alan wanted to boost regeneration in the open grass areas around the beech trees. Beech trees are notoriously slow to regenerate for a few reasons.

Firstly, seed production is highly variable from year to year which results in almost no seeding for a few years, then a massive seed set for one year (rarely two in a row).  Called 'mast' seeding, it is quite unusual in the plant world, but for widely debated reasons is a common feature in New Zealand flora.

Secondly, the seed has no dispersal mechanism; it simply falls from the tree.

Thirdly, beech seed, when it actually falls, germinates almost immediately into a seedling – but usually only when it falls into a bare patch of soil. In natural beech forests such bare patches are common, as few other species will grow in the deep shade and dry soil of the beech forest. The seedlings grow very slowly and can remain small, though they may get quite old.  Some 600mm high saplings have been measured as being over 60 years old.  Called 'suppressed juveniles', they are waiting for a canopy tree to fall over giving them the light and space to grow.

Because beech seed is only occasionally produced, rarely germinates in dense vegetation, and if it does, it doesn't travel far from the parent tree, forest expansion is very slow. To speed the process up, Alan used a clever technique.  He sprayed grass patches on the forest margins with selective herbicide that killed only the dense grass sward. He timed the spray application to coincide with seed set from the previous summer's 'mast' year.

Two things happened - one, the few suppressed seedlings already present among the grass were released from competition with the grass, and - two, seeds falling had an open site into which they could germinate. As the photograph shows, the trees - now a couple of years old - are doing well.

Broadleaf and beech seedlings

Both these simple techniques show how innovative techniques that draw on a good ecological knowledge of the species involved can simply and cheaply give nature a helping hand.

Open SpaceTM
Magazine No. 51, April 2001 © QEII National Trust

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