Effects on the functioning of Minnamurra's ecosystem
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7A. Boardwalk through subtropical
forest |
Today Minnamurra Rainforest consists of an inner core of 20 hectares of rainforest
that is largely natural, with an ecosystem that has been allowed
unimpeded change. A larger area of the remaining 401 hectares has
been disturbed as a result of clearing for pasture (1930s) in the
north-east section of the park and there has been disturbance from
fires (1939, 1960) and floods (1960) in the other areas. The nature
of the change, as well as the speed or rate of change, can have
varying impacts on the ecosystem. For instance, where disturbance
has occurred on the south-facing shaded slopes they have regenerated
much better than those slopes that face north, which are more likely
not to recover, once strong sunlight dries out the soils. Over time,
the changes that have occurred to Minnamurra have caused some changes
which are reversible, and others which are not.
Traditional uses of the Minnamurra Rainforest area are those
which had minimal impact on the ecosystem of the rainforest, as
discussed at Stop 5.
This allowed the rate of change in Minnamurra to continue at a
natural pace, having little impact on the ecosystem. However,
European arrival in the early 1800s changed this pattern and the,
nature and rate of change began to be altered in ways that did
affect the ecosystem. As we saw at Stop 5, the initial removal
of all the red cedar from the rainforests of the Illawarra had
the immediate impact of allowing more sunlight into the subtropical
areas of the rainforest where the trees had been, changing the
warmth, level of evaporation and therefore growing conditions
for other trees and plants. This would have allowed species that
previously might have struggled in the moist shaded environment
to grow within this part of the rainforest.
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7B. Forest floor and middle
layer
warm temperate forest |
This type of small change to one tiny patch of rainforest was repeated each time
a tree was removed, causing irreversible change to the ecosystem.
As we saw earlier, the rate of this change was very quick, with
all the significant red cedar removed from the area by 1850, with
the most significant damage being done in the first seven years.
This change was followed by the complete removal of up to 75%
of the Illawarra rainforest, to allow farming to take place. This
change began as the cedar ran out, and has continued to the present
day. The change that this represents generally completely destroys
the ecosystem, where removal takes place but also contributes
to the degradation of the other 25% of rainforest that remains.
This occurs because, prior to European arrival, the area we now
call Minnamurra Rainforest would have been deep in the middle
of rainforest, whereas now it is surrounded on all sides by farms
and other human activities. These activities contribute to change
in the ecosystem, albeit at a slower rate than direct action on
the rainforest. For example, stray domestic animals wandering
into the rainforest may graze on rainforest species, kill the
native fauna or just trample the delicate plants that exist on
the forest floor. This contributes to a reduction in the biodiversity
of both plants and animals. In addition, these animals might leave
droppings around which will change the nature of the soil chemistry,
adding more fertiliser in the form of nitrogens and phosphorus
than the forest plants are used to. This gives the opportunity
for weed species, which enjoy the greater fertility, to grow.
This problem is added to when the droppings contain the seeds
of these weed species. Over time, this intrusion into the remaining
areas of rainforest, would have degraded them making it justifiable
to remove them, as well.
Following on from these large changes, there have continued to
be smaller changes. The area of Minnamurra was dedicated as a
reserve in 1898, after the area had been a popular picnic spot
since the 1870s. It was during this period that the first picnic
facilities were constructed, creating change to accommodate recreational
pursuits in the area. This type of activity represented a slow
rate of change that led to significant degradation of the environment
over time. People using an area such as this for picnics and short
walks to the Fall, created tracks through the rainforest, trampling
any forest floor species under foot. In addition, because of the
moist nature of the rainforest, rainfall would make the tracks
wet and people would increase the size of the tracks by walking
around the puddles. Over time this creates a vast area of rainforest
ecosystem which is degraded. The soil involved becomes hard packed
from all those feet; even if left alone for a long period, vegetation
will not regenerate. In addition, where these tracks are running
up slopes they are subject to erosion, especially if the soil
is a podzolic (sedimentary parent rock) rather than a krasnozem
(volcanic parent rock).
Attempts to control this change were first made in 1945, when
Kiama Council, which controlled the reserve, appointed a ranger/caretaker
to the park. This man, Howard Judd, worked for 33 years trying
to conserve and protect the rainforest, as well as educate people
about it. Development in the park whilst he managed it included
the building of a museum, kiosk, picnic shelter and toilets to
cope with upwards of 100,000 people a year who were visiting Minnamurra
Rainforest. By the time Mr. Judd retired, the huge popularity
of the reserve had taken its toll and the ecosystem was severely
degraded, with the impact of trampling and vehicles being most
prominent. In 1980 attempts were made to facilitate Mr. Judd's
vision of education and conservation of the ecosystem, in a way
that did not affect the ecosystem quite so severely. A wooden
decking was built over parts of the track so that visitors no
longer walked on the floor of the rainforest in the worst affected
areas, but above it; rangers began to provide firewood for visitors
so they didn't take it from the forest, and an education program
was started, with talks provided to visitors.
This change, and the recognition of the need to value the site
and spend money conserving it, have helped to slow the rate of
change that was affecting the ecosystem. This was improved even
further when, in 1986, the National Parks and Wildlife Service
of NSW (NPWS) took over management of the park and the State and
Commonwealth Governments supplied $3 million over 7 years, to
continue to improve the park's condition. Importantly, this included
the construction of new facilities, including a centre for the
education of visitors, which has helped to lower the impact visitors
have on the rainforest.
Some of the work which the NPWS has carried out directly on the
ecosystem over time has included arresting vehicle and pedestrian
damage to the rainforest, reducing weed infestations, replanting
rainforest species, disposing of waste so that it does not affect
the park, further repairing the final sections of walking track
so that all the tracks are now either raised boardwalks or bricked
and guttered (the walk to the Falls), and acting to reduce the
numbers of feral species within the park threatening native fauna.
These actions have themselves caused change to the ecosystem;
in most cases this has been positive change because it has allowed
the rainforest ecosystem to recover from past change, as well
as attempting to rehabilitate the rainforest where it has not
been self-repairing. The challenge for the future is to continue
to cause positive change where it is needed, but, at the same
time, allowing unimpeded natural change in the rainforest in an
effort to conserve the rainforest ecosystem.
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