Crassula helmsii (New Zealand Pigmyweed) is an invasive aquatic plant in the UK

which has caused considerable damage to native aquatic plant communities in ponds

and lakes (Leach & Dawson, 1999). It is notoriously difficult to eradicate this species

and much evidence suggests that success (which is rare) requires very early

detection at the point of colonisation (Dawson, 1996; Willby, 2007)

Robinson, P

Sayer, CD

English

UCL Discovery

 1   Environmental Change Research Centre  Research Report No. 153  Crassula invasion levels and success of recent eradication attempts at the Thompson Common pingo ponds  Final Report to the Norfolk Non-native Species Initiative   Carl Sayer & Pete Robinson  November 2012   ISSN:  1366-7300 Environmental Change Research Centre Department of Geography, University College London, Pearson Building, Gower Street London, WC1E 6BT  2 List of contributors  Carl Sayer  Environmental Change Research Centre / ENSIS Ltd.  Department of Geography University College London Pearson Building Gower Street London WC1E 6BT  Pete Robinson  Flat 5 58 Tressillian Road Brockley London SE4 1YB                         Acknowledgements Thanks are due to Darrell Stevens for access to Thompson Common and many useful conversations. We also thank the owners of College Farm and Butters Lodge for site access and support and Nick Stewart for charophyte confirmations/ identifications. Finally we thank the Norfolk Non-native Species Initiative for funding this work.  Cover photograph: Pingo pond 37 (photo: Jo Atherton 14th August, 2012)   3 Table of Contents Page  List of Contributors          2 Acknowledgements          2 Table of Contents            3 List of Figures           3  BACKGROUND AND AIMS         4 SITES AND METHODS          4  RESULTS            5 Surveyed ponds          5 Invasive species          5 Plant communities in the pingos        5  DISCUSSION AND RECOMMENDATIONS       6 Eradication work          6 Future invasive species surveys        6 Minimising C. helmsii spread         6 Aquatic plant surveys         7  REFERENCES           7  List of Figures            Figure 1. Map of the Thompson Common pingo ponds    8  List of Tables  Table 1. Pond locations and Crassula helmsii data       9 Table 2. Aquatic plants in the surveyed pingo ponds      10                         4 Background and Aims  Crassula helmsii (New Zealand Pigmyweed) is an invasive aquatic plant in the UK which has caused considerable damage to native aquatic plant communities in ponds and lakes (Leach & Dawson, 1999). It is notoriously difficult to eradicate this species and much evidence suggests that success (which is rare) requires very early detection at the point of colonisation (Dawson, 1996; Willby, 2007).  Recently (2011) C. helmsii was found in two neighbouring pingos at Thompson Common SSSI in the Brecklands of Norfolk (ponds at TL 93373 96310 and TL 93370 96368). Site manager Darrell Stevens located the plants and applied herbicide in an attempt to eradicate C. helmsii. Due to the important and distinctive macrophyte flora of the Thompson Common pingos there are rightly-held concerns regarding possible future impacts of C. helmsii invasion.  The current study sought to determine the success of attempted C. helmsii eradication from the two aforementioned pingos at Thompson Common, whilst ascertaining whether the species had colonised other ponds at the reserve. An opportunity was also taken to record aquatic macrophyte communities in the surveyed pingos.   In summary the aims of the current study were:  1. To identify whether C. helmsii eradication was successful 2. To identify the presence/absence of C. helmsii in Thompson Common pingos that surround the invasion sites 3. To determine possible conduits of C. helmsii to the site (in the future) to help guard against future invasion.  4. To gain more data on aquatic macrophyte occurrence in the ponds.   Sites and Methods  The pingos were visited over the 13th and 14th August, 2012. The survey area was centred around the north-west section of the Thompson Common site (encompassing compartments 1, 2, 3 and 4) close to the two pingos where C. helmsii was found in 2011. Additionally an attempt was made to determine the source of  C. helmsii invasion by searching ponds associated with houses and gardens close to the two affected pingos.  The perimeter of each pond was subjected to a visual survey. In addition Carl Sayer searched the interior of the pingos and any open water areas as far as was safely possible by wading. A double-headed rake was used to assist plant searches in open water regions. All submerged and floating-leaved aquatic plants were recorded as present or absent. It should be recognised that some aquatic plant species may have been missed using this approach as the priority was (i) finding C. helmsii and (ii) covering as many ponds as possible over the two day period.  A map of the surveyed ponds showing the location of C. helmsii was produced using ArcGIS version 10.0.    5 Results  Surveyed ponds  A total of 42 ponds were surveyed including seven ponds associated with private properties and gardens close to the Thompson Common reserve (Fig. 1). The latter included six pingos (pingos 25-30 in Table 1) and one medieval fish pond (pond 24 in Table 1).    Invasive species  C. helmsii was found in one of the original invaded pingo ponds in compartment 3c (pond 22 at TL 93373 96310), but not in the other (pond 23 at TL 93370 96368). This suggests that eradication was likely successful in the latter. In pond 22 C. helmsii covered around one third to half of the pond.  C. helmsii was not found in any of the 33 other surveyed Thompson Common pingos suggesting that it may not, as yet, have invaded the wider nature reserve. Nonetheless caution should be applied to this statement given that it was not possible to visit all of the pingos.  The source of C. helmsii invasion was likely found this being a pingo pond (pond 30 TL 93304 96228, Fig. 1) incorporated into the garden of a private house (Butters Lodge) close to the invaded site. This pond had been subjected to management in 2011, but given its dominance in the pond (it was even growing in the lawn around the pond), it seems likely that C. helmsii was present prior to this time, with the probably origin being a garden centre.  During the survey two small stands of Himalayan balsam (Impatiens glandulifera) was also found in the College Farm area close to a stream that drains into Thompson Common (TL 93258 96784 and TL 93196, 96712). Clearance was not possible at the time of the survey, however, as it was already setting seed.  Plant communities in the pingos  Some 29 aquatic plants were recorded in the survey (Table 2). The most common plants were Common duckweed (Lemna minor in 22 ponds), Ivy-leaved duckweed (Lemna trisulca in 17 ponds), Amphibious bistort (Persicaria amphibia in 12 ponds), Water violet (Hottonia palustris in 12 ponds), Broad-leaved pondweed (Potamogeton natans in 11 ponds), American duckweed (Lemna minuta in 8 ponds) Greater bladderwort (Utricularia vulgaris in 9 ponds) and the floating liverwort Crystalwort (Riccia fluitans in 7 ponds). Gibbons (2004) stated that U. vulgaris “may be extinct” in the Thompson Common ponds so we can clearly show this not to be the case.   Notable species found during the survey were Least bur-reed (Sparganium natans), Frogbit (Hydrocharis morsus-ranae), Tubular water-dropwort (Oenanthe fistulosa), Fen pondweed (Potamogeton coloratus), Water-violet (Hottonia palustris) and the floating liverwort Ricciocarpus natans. Both S. natans and H. palustris are classified as local in the British Isles, with P. coloratus classified as Nationally Scarce and H. morsus-ranae  and O. fistulosa listed as Vulnerable (Cheffings & Farrell, 2005; Palmer et al., 2010). In addition, Dark stonewort (Nitella opaca), although relatively common in Northern Britain is rare in Norfolk (C. Sayer pers. obs.).  6  Discussion and Recommendations  The Thompson Common pingos are of exceptional ecological importance. Currently, as demonstrated by this brief study, they hold populations of several nationally scarce and notable aquatic plants (see above).  The important plant communities at Thompson Common are potentially threatened by C. helmsii invasion, so all possible efforts should be made to prevent this from occurring. We recommend the following courses of action:  Eradication work:  1. Eradication of C. helmsii should be repeatedly attempted at the two invaded pingos. Note that Darrel Stevens of Norfolk Wildlife Trust is already working on this and should be given the full support of the Norfolk Non-native Species Initiative (NNNSI).  2. Clearance of I. glandulifera from the invaded area close to College Farm (Fig. 1) should be undertaken over the next three summers (at least) until it is hopefully eradicated. The NNNSI should liaise with Darrel Stevens regarding this work.  Future invasive species surveys:  3. A second C. helmsii survey (of a similar nature) is undertaken in summer 2013 which again focuses on the two invaded pingos and the area surrounding them. This survey should include ponds missed during 2012 (there are so many it was impossible to cover them all in the two survey days) and further garden ponds/pingos around the reserve to further assess potential invasive species threats in the future.  Minimising C. helmsii spread:  4. Compartment 3c (which contains the C. helmsii pingo 22) should not be grazed by animals that are then transferred to another compartment on the reserve so that the potential for spreading C. helmsii is minimized. Indeed mowing may be the most appropriate grassland management method for the time being in 3c. Further, all surveys of the pingos should be planned so that pingo 22 is the last study site.  Aquatic plant surveys:  5. A Thompson Common-wide survey of aquatic plants should be undertaken to record the rare species present and to assess the value of pond management. We suspect that pond management has been tremendously beneficial to macrophyte communities at Thompson Common and it would be good to further quantify and understand the management effect.     7 References  Cheffings, C.M. & Farrell, L. (Eds), Dines, T.D., Jones, R.A., Leach, S.J., McKean, D.R., Pearman, D.A., Preston, C.D., Rumsey, F.J., Taylor, I. 2005. The Vascular Plant Red Data List for Great Britain. Species Status 7: 1-116. Joint Nature Conservation Committee, Peterborough.  Dawson, F.H. (1996) Crassula helmsii: attempts at elimination using herbicides. Hydrobiologia 340, 241-245.  Gibbons, B. (2004) Reserve Focus: Thompson Common Nature Reserve. British Wildlife 4, 240-243.  Leach, J. & Dawson, F.H. (1999) Crassula helmsii in the British Isles – an unwelcome invader. British Wildlife 10, 234-239.  Palmer, M., Drake, M. & Stewart, N. (2010) A manual for the survey and evaluation of the aquatic plant and invertebrate assemblages of grazing marsh ditch systems. Buglife.  Willby, N.J. (2007) Managing invasive aquatic plants: problems and prospects. Aquatic Conservation: Marine and Freshwater Ecosystems, 17, 659-665.    8   Figure 1. Map of the Thompson Common pingo ponds showing ponds searched for Crassula helmsii (red dots) and current location of C. helmsii (red stars). Note that during the C. helmsii search Himalayan balsam (Impatiens glandulifera) was also found (green triangles).       9    No. NGR (TL…..   …..  C. helmsii present Notes 1 93490 96695   2 93514 96639   3 93553 96652   4 93529 96680  Connected to pingo 1? 5 93522 96599   6 93560 96599   7 93628 96525  Large round pingo 8 93695 96560   9 93634 96609  Small dry pingo 10 93653 96596  Small dry pingo 11 93643 96463   12 93610 96425  Could be fish, looks to be permanent 13 93674 96371   14 93635 96370   15 93586 96356  Crescent shaped pingo 16 93552 96359   17 93564 96300  Could be fish, looks to be permanent 18 93752 96515   19 93844 96478  Lemna-covered nearly 100% 20 93863 96481  Lemna-covered nearly 100% 21 93901 96471   22 93367 96307 YES Crassula covers 1/3 to 1/2 pingo area 23 93370 96365  No Crassula but may have been present before. Eradication successful 24 93265 96617  College Farm medieval fish pond. Lemna-covered 100% 25 93245 96635  College Farm pingo 1 26 93280 96648  College Farm pingo 2. Lemna-covered 100% 27 93244 96714  College Farm pingo 3. Fish fry abundant 28 93432 96195  Sylvia's pingo 1. Dry/damp bed 29 93392 96165  Sylvia's pingo 2. Lemna-covered 100% 30 93291 96231 YES Butters Lodge pingo, cleared out autumn 2011. No survey undertaken, quick look 31 93478 96091   32 93505 96125   33 93535 96148   34 93508 96181   35 93611 96197   36 93618 96227   37 93670 96265  Fish seen topping 38 93653 96170   39 93431 96032   40 93621 95981   41 93530 95982   42 93568 95921    Table 1. Pond locations and Crassula helmsii data for the pingo survey 13-14th August, 2012. Ponds with C. helmsii are highlighted (red fill).          10   Pingo number  Alisma plantago-aquatica  Apium inundatum  Berula erecta  Callitriche sp.  Chara globularis  Chara hispida  Chara virgata  Crassula helmsii  Hippurus vulgaris  Hottonia palustris  Hydrocharis morsus-ranae  Lemna minor  Lemna minuta  Lemna trisulca  Nitella opaca  Nymphaea alba  Oenanthe fistulosa  Persicaria amphibia  Potamogeton coloratus  Potamogeton natans  Potamogeton obtusifolius  Potamogeton polygonifolius  Ranunculus aquatilis  Riccia fluitans  Ricciocarpus natans  Rorripa nasturtium-aquaticum  Sparganium natans  Spirodella polyrhiza  Utricularia vulgaris 1          1  1  1               1 2          1        1            3          1  1      1           1 4          1          1         1 5            1                  6          1  1                 1 7 1  1           1   1 1  1     1     8            1  1   1 1            9                  1            10                  1            11          1  1      1           1 12      1            1  1          13            1  1    1           1 14          1  1  1    1  1         1 15     1 1     1                1  1 16     1       1  1        1        17          1 1 1        1 1   1     1 18  1          1  1    1            19             1 1          1    1  20    1         1           1       11 21                          1    22        1 1 1  1  1           1     23             1 1              1  24             1                 25              1                26             1                 27            1 1 1      1          28    1                          29            1 1                 30        1                      31            1  1                32            1                  33          1  1  1          1      34            1                  35       1             1       1   36                  1            37     1       1    1    1    1      38 1        1 1  1  1      1    1 1  1   39             1           1      40       1       1      1     1     41          1  1  1      1          42       1     1   1    1    1       Total 2 1 1 2 3 2 3 2 2 12 2 22 8 17 1 1 2 12 1 11 1 1 1 7 4 1 3 2 9  Table 2. Aquatic plants in the 42 surveyed ponds given as presence-absence. Note that for pond 32 a plant survey was not undertaken and only C. helmsii occurrence was established based on a quick visit. 

Crassula invasion levels and success of recent eradication attempts at the Thompson Common pingo ponds

https://discovery.ucl.ac.uk/10114755/1/ecrc_report_153_Thompson.pdf

Crassula invasion levels and success of recent eradication attempts at the Thompson Common pingo ponds

Abstract

Similar works

Full text

Available Versions

UCL Discovery