SCIENTIST’S VIEW ON BRIAR

Press, Volume CVI, Issue 31119, 23 July 1966, Page 8

SCIENTIST’S VIEW ON BRIAR

It is the view of Dr. B. P. Molloy, of the research division of the Department of Agriculture, that sweet briar is not now spreading at an alarm* ing rate in most parts of the South Island.

“It appears that there is some confusion among runholders on this point,” said Dr. Molloy this week when he was asked to comment on discussions on the briar problem at the recent conference of South Island high country sub-sections of Federated Farmers, “but a good deal of this confusion can be dispelled by considering the whole problem of briar introduction in retrospect.”

“It is an historical fact that sweet briar entered this country with the early settlers and reached many parts of the South Island very rapidly. As an aggressive opportunist plant, it quickly took advantage of a wide variety of open habitats, which were largely brought about by the then traditional practice of frequent burning, followed by set stocking with sheep, often in large numbers. “There is little doubt that many populations of briar plants of all ages and stages of growth were present long before the rabbit reached appreciable numbers in this country. Rabbit Effect “In its heyday, the rabbit helped to degrade our native grassland to its lowest form, but it also exercised considerable control over the further spread and establishment of i sweet briar by preventing the' growth of seedlings and ’ checking the regrowth of! small, established plants. iThus the main effect of the ! rabbit was to cause a gap in the regeneration of briar in existing infestations, and to

produce a habitat which was inimical to seedling establish, ment in non-infested areas. "This rather static situation took a dramatic turn with the marked reduction in rabbit numbers which, incidentally, broadly coincided with less frequent burning and much lower stock numbers. Re-

leased from these pressures, much of our depleted grassland slowly began to recover, but in the time between its final depletion and its full or partial recovery, a distinct; plant vacuum existed. Sweet briar and other shrubs briefly j exploited this vacuum, in- } creasing their distribution ] and abundance in spectacular '

fashion. However, the gradual increase in cover provided by grasses and other herbs has brought the wheel almost full circle by slowing down the spread of briar into non-in-fested areas and preventing its regeneration in existing ones.

“In most populations that I have examined the mortality of first-year seedlings is high and there is a significant reduction in the number of two-year-old and older seedlings. Those that are present are weak and single-stemmed and their mortality is also very high. Experimental evidence has shown that sweet briar seedlings are weak competitors where growing with grasses and/or clovers whether under conditions of high or low soil fertility. Many mature plants are also declining in vigour because of increasing competition from grasses and other herbs.

“It appears then that much of what is called current sweet briar invasion of pasture land represents the growth to maturity of seedlings which pre-date natural revegetation since the rabbit was eliminated or burning ceased to be a common practice. Seedlings invaded these areas in the past solely because they were maintained in an open condition. They continue to maintain themselves on these areas as mature j plants, but do not appear to be invading the surrounding grasslands, thus confirming the observation that a wellmanaged pasture is generally hostile to establishment of woody plants.”