Weeds

Just a few days without downloading my mail and there are dozens of posts 
on the subject of weeds.

Here in New Zealand, European settlers burnt the tussock grassland in the 
high country so they could sow grass that sheep could graze on, and cleared 
forest on the lower areas so they could sow grass for sheep there as well. 
I suppose this means that the introduced grasses are all weeds, but on 
farms they are obviously not regarded as such. Early settlers also 
introduced many familiar plants from their hedgerows, such as gorse, broom 
and blackberry. In the New Zealand climate these plants rapidly became weed 
species, especially gorse and blackberry.

Gorse spreads very easily into grassland, as the sheep do not like to eat 
it, due to the prickles. It only takes a few years for a previously grassy 
hillside to become completely covered with gorse and the grass, starved of 
light, dies. However, as gorse matures it forms a dense canopy, but leaves 
large empty spaces under this canopy, as new gorse seedlings must have 
light to germinate. However, the New Zealand forest tree species all 
germinate in deep shade conditions, so the gorse canopy then gets a huge 
array of native forest tree seedlings growing under it, from seeds 
deposited mainly by birds (which like to nest in gorse). These seedlings 
benefit from the leaf litter left by the gorse as it grows, and also the 
nitrogen fixing properties of the gorse root system. The native trees grow 
a straight leading shoot that rapidly penetrates the gorse canopy. Once 
they get above the canopy they form their own, higher, canopy, and before 
long the gorse, unable to grow taller and starved of light, dies. Once dead 
it rots rapidly in the damp conditions. After around 30-40 years the cycle 
has been completed, and where there was once grassland there is a fresh new 
native forest with dozens of local species, but not a grass or gorse plant 
to be seen.

As a case in point, there is an area of marginal farmland near here that is 
owned by the Regional Council. They have stopped farming it and are 
intentionally letting the gorse grow back as the first step to the area 
reverting to native forest. In a few years the hillsides will be a blaze of 
yellow in the spring, as the gorse flowers, but eventually they will be 
back the way they were, only without the mature forest giant trees.

Obviously not all weed species can be treated this way, and a number of 
climbing plants that can smother the native tree canopy are real long term 
problems. Put simply, gorse is not a problem weed in the natural forest 
environment, but rather in the unnatural environment of farms and gardens, 
with their open spaces, and there it is a BIG problem.

Tim Dutton
"Raindrops", Main Road North, Kaitoke, Upper Hutt, New Zealand
(Latitude 41? 5' South, Longitude 175? 10' East)
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