Trial Orchid Monitoring at Belair National Park 1993-1997

April 2013 will be 20 years since a trial of orchid monitoring was done at Belair National Park so it seems like a follow up survey this year could be timely.  A five year study was conducted by members of the Native Orchid Society of South Australia (Bickerton et al 1998).  A follow up survey was conducted in 2007, 10 years after the completion of the previous survey (Bridle & Bridle 2009).

Grey Box (Eucalyptus microcarpa) woodland at Belair National Park in the Adelaide Hills.

Grey Box (Eucalyptus microcarpa) woodland at Belair National Park in the Adelaide Hills.

This post is adapted from Bickerton et al (1998) and is compiled with the assistance of Doug Bickerton who currently works in the Department for the Environment, Water and Natural Resources within the South Australian government.  A future post is planned to present the results and conclusions of the study by Bridle & Bridle (2009).

The original survey was focussed on determining the effect on orchids of removing Boneseed (*Chrysanthemoides monilifera), an environmental weed that invades bushland areas.  This post focusses more on what can be learnt about monitoring orchids.

In 1992 Karen Possingham (newly appointed as was Conservation Officer of the Native Orchid Society of South Australia (NOSSA)) and her husband, Professor Hugh Possingham (President of the Nature Conservation Society of South Australia from 1995-1998) encouraged NOSSA members to conduct an orchid survey trial, with the long-term view of developing a consistent survey method.  A secondary purpose was to collect preliminary data in the response of native orchid populations to the removal of Boneseed.  This is one of the few attempts in Australia to collect long-term systematic data on orchids.  While they were interested in seeing the impact of weeding, they were also very interested to see if a volunteer group could consistently collect data over a long period of time.

The group chose an area of bushland in Belair National Park which was overrun by Boneseed.  Over a 12 month period NOSSA removed Boneseed from the area and during the next five years certain NOSSA members returned at regular intervals to monitor the orchid populations.

Diuris orientis (Wallflower Donkey-orchid or Bulldogs) is a common species at Belair National Park.

Diuris orientis (Wallflower Donkey-orchid or Bulldogs) is a common species at Belair National Park.

SITES AND METHODS

The area chosen for the survey is between Kurra Creek and Workanda Creek, in the northern section of Belair National Park.  In April 1993 they chose three locations (Sites A-C), and pegged out a 20 metre transect at each location.  The sites were all within 20 m of a walking track, and about 100 m apart.

Site A was in open low woodland that was weeded before 1993 and free of Boneseed at the time of the survey; a number of orchid species were present.

Site B was also in open low woodland, was previously heavily infested with Boneseed and was weeded in 1993; no flowering orchids were observed prior to weeding.

Site C was slightly elevated and was more wooded; it was weeded in 1994 and few orchids were present prior to weeding.

Each site was monitored regularly between April 1993 and December 1997.  At each visit, an area of 20 m2 immediately adjacent to the transect was monitored.  This was done by placing a 20 metre rope between the two fixed transect pegs; then a square grid measuring 1 m2 was placed at the beginning of the transect, to the left hand side, and the area within the grid was inspected for orchids.  Then the grid was placed on the opposite side of the transect, and one metre further along the rope.  This process was repeated on alternate sides of the rope, and at one metre intervals, to the end of the transect. By following this same process every visit, the group could ensure that exactly the same ground surface was being inspected each time.

A record was made of the number of orchid leaves, buds, flowers, and seed pods present within the grid.  The species of each orchid was also recorded in most cases, although only the genus was recorded if the species could not be identified conclusively (eg. if only a small leaf was present).  The group also made an informal survey of the surrounding area for five metres either side of the rope.  For the purposes of this report, only the data concerning the flowers in the 20 m2 formal survey area has been considered.  Data on leaves is ignored because of the difficulty in identification, or even finding some species, especially when leaves are small.

The total number of orchid flowers found at each site, for each year of the survey.

The total number of orchid flowers found at each site, for each year of the survey.

RESULTS

Total number of flowering orchids per site

At Site A (the previously weeded site) the total number of flowering orchids declined slightly between 1993 and 1995, from 66 to 50, nevertheless, the number had increased to 105 by 1997.

At Site B, no orchids were seen flowering prior to weeding.  A heavy infestation of boneseed was completely removed from this site, and the following year there were 33 flowering orchids. The number continued to increase each year, so that by 1997 the increase was more than five-fold (174 flowers).

The orchids in flower recorded at Site C declined from 8 in 1993 to 4 in 1994, but after weeding was completed, the overall trend was for an almost ten-fold increase in numbers, to 39 in 1997.

Initial perusal of above graph suggests that the flowering rates of the three sites are different.  The data was not tested for a significant difference between sites, because a time series of five points (in this case five years) is too short to expect a statistically significant result.  The survey would need to be run for at least seven years before a trend could be proved.  The results of a linear regression and coefficient of determination at each site are available to anyone interested.

Number of species of orchids per site

The number of orchid species found flowering at Site A declined from 8 in 1993 to 4 in 1995.  However, this trend was reversed in the next two years, and by 1997 there were 10 species flowering at Site A.  At Site B the trend was similar to that of Site A.  At Site C there was no increase in the number of species flowering between 1993 and 1995, however by 1997 twice as many species were recorded.

The number of orchid species found at each site, during each year of the survey.

The number of orchid species found at each site, during each year of the survey.

Genera Found at each site

At Site A there was a notable increase in Thelymitra flower numbers during the survey (see Table below).  Also three new genera (Orthoceras Arachnorchis, and Petalochilus although the last two of these were recorded as Caladenia species in most of the field notes) had been recorded in small numbers by 1997.  However, for all genera except Thelymitra the trend was for either minor or no increase in flowers.

Table 1 – The orchid genera found flowering at Site A, and the number of flowers found each year.

Genus

 1993

 1994

 1995

 1996

 1997

Corunastylis

3

3

1

Diuris

4

5

4

2

10

Glossodia

2

1

Leptoceras

1

Microtis

2

1

8

Orthoceras

1

1

Petalochilus

2

Thelymitra

54

52

43

78

82

In contrast, every genus found at Site B showed an increase in flowers over the five year survey period (see Table 2). Only three genera (Diuris, Microtis, and Thelymitra) were flowering at the site in 1993, but by 1997 another six genera were flowering. By the end of the survey period there were large numbers of Acianthus, Microtis, and Thelymitra at this site.

Table 2 – The orchid genera found flowering at Site B, and the number of flowers found each year. (Note that Arachnorchis and Petalochilus were both recorded as Caladenia sp. in most of the notes, but two flowers of Caladenia tentaculata are clearly indicated on one data sheet)

Genus

 1993

 1994

 1995

 1996

 1997

Arachnorchis

2

Acianthus

6

1

37

Corysanthes

4

Diuris

4

3

5

5

13

Genoplesium

1

1

5

Glossodia

1

Leptoceras

7

Microtis

1

1

34

42

Petalochilus

2

Thelymitra

28

46

44

40

61

Of the four genera found flowering at Site C in 1993 (Diuris, Glossodia, Leptoceras, and Microtis) none had increased appreciably in number by 1997 (see Table 3).  However, four new genera (Caladenia, Corysanthes, Pterostylis, and Thelymitra) had begun flowering here by 1997, and the number of Thelymitra in particular had increased noticeably.

Table 3 –The orchid genera found flowering at Site C, and the number of flowers found each year.

Genus

 1993

 1994

 1995

 1996

 1997

Caladenia

1

Corysanthes

7

Diuris

1

3

2

4

Glossodia

2

1

3

4

Leptoceras

4

1

1

2

Microtis

1

14

3

3

Pterostylis

1

7

Thelymitra

2

6

9

12

The information in Tables 1-3 above is summarised in Table 4 below:

Table 4 – This table shows the sites at which different genera were flowering, and the number of flowers found each year.

GENUS

SITE

1993

1994

1995

1996

1997

Acianthus

A

 

B

6

1

37

 

C

Arachnorchis

A

 

B

2

 

C

1

Petalochilus

A

2

 

B

2

 

C

Corysanthes

A

 

B

4

 

C

7

Diuris

A

4

5

4

2

10

 

B

4

3

5

5

13

 

C

1

3

2

4

Genoplesium

A

3

3

1

 

B

1

1

5

 

C

Glossodia

A

2

1

 

B

1

 

C

2

1

3

4

Leptoceras

A

1

 

B

7

 

C

4

1

1

2

Microtis

A

2

1

8

 

B

1

1

34

42

 

C

1

14

3

3

Orthoceras

A

1

1

 

B

 

C

Pterostylis

A

 

B

 

C

1

7

Thelymitra

A

54

52

43

78

82

 

B

28

46

44

40

61

C

2

6

9

12

DISCUSSION

In this discussion we will explore the value of the survey method used, and the impact of weeding on the orchid populations.

Experimental design

To assess the impact of Boneseed weeding in a more rigorous fashion, we would need to have a much larger number of more carefully chosen sites.  The ideal design would include four or five replicates of each treatment, where the appropriate treatments might be:

  • Previously weeded
  • Weeded at the start of the survey
  • Weeded during the survey
  • Not weeded

In addition to this, an ideal survey would also continue for about 10 years.  If such a survey method were to be used, the logistics of the task would be significant.  However we propose some changes to the method that was used, and these are listed below.

The survey method

If NOSSA were to survey multi-species orchid populations in the future, with a view to looking at the impact of habitat management, then we suggest the following variations in the method:

  1. Attempt to record the total number of individuals, using leaves and flowers at the time the species is flowering. If it is not possible to positively identify leaves for all species, then only record the flowering plants for some species.
  2. Four carefully timed visits per year, at the same time every year, is probably adequate.
  3. The whole 40 m2 should be marked and used to compile a simple species list.

By using this faster method, greater replication could be achieved.

The impact of weeding on the total orchid population

If we look at the total number of orchid flowers found at each site (see Figure 3), it is evident that Sites B and C improved at a much greater rate than Site A (which had been weeded previously).  It is also apparent at first glance that Site B, which was weeded just before observations began, fared better than Site C, which was not completely weeded until 1994.  Admittedly the total Site B population improved by 178 flowers, compared with less than 39 at Site C, but the dominant Eucalypt trees near Site C were larger and they created more shade than at Site B.  Hence the environmental conditions are likely to be a confounding factor in the difference between all sites.

CONCLUSION

Despite the shortcomings of the survey method used, it appears that the removal of Boneseed from open Eucalyptus microcarpa woodland is beneficial to the populations of at least 50% of the orchid species known to occur in such habitats, and is not detrimental to any orchid species.  We urge NOSSA to explore the impact of other habitat management actions, using a revised version of the method described here.

ACKNOWLEDGEMENTS

We wish to thank the National Parks and Wildlife Service for permission to carry out the survey at Belair National Park.  We also thank the volunteers who assisted in the survey, including (in alphabetical order) Roger Bidell, Phil and Thelma Bridle, Gerry Carne, Bill Dear, Cecil and Margaret Hollamby, Malcolm and Cathy Houston, Andrew and Kathryn Lloyd, Greg Miles, Ray Nash, Thelma O’Neil, John and Joan Peace and David Pettifor.  Their enthusiasm, skill, and patience showed that NOSSA is capable of doing repeatable systematic surveys of high quality.

REFERENCES:

Bickerton D, Possingham K & Possingham H (1998). The Effects of Boneseed Weeding on Orchid Populations at Belair National Park (South Australia) and a Trial of an Orchid Survey Method. Report for the Native Orchid Society of South Australia, Adelaide.

Bridle T & Bridle P (2009).  2007 Update on the Effects of Boneseed Weeding on Orchid Populations at Belair National Park 1993-1997.  Journal of the Native Orchid Society of South Australia, Vol. 33 (2): 16-19.

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