Ecological Survey of the Royal Canal 1989
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sws R I AA NI T I!P n R 1f 1 ' Ir'l Iii^ pop 'a'll' 1! l!'wAlll 'r,l I I I 1 10141 dR1IN' o l One' poll1' .I + 6N r1n., IUM Ollill, 1, lei 1 ff a y ' I 11 r"-1 01.)CO F- 1 r.r r-Owl I s. I w{ I ap 3 r - I R I u 1 0 1. Part 1 contains the report of an ecological survey ofthe entire length of the Royal Canal, carried out over two years,1989 and 1991. The min objectives were to assess the values of thecanal 0 corridor for nature conservation and to make recommendations for restoration and management of the canal taking these values into aooouat. For the purposes of this survey the waterway was divided 0 into three management units which were: Unit I. Recently dredgedand navigable channel; Unit II. Watered channel but not recently dredged; and Unit III. Dry channel. There are 10 listedAreas of u Scientific Interest (ASI) along the length of the Royal Canal. 2. The habitats of the canal corridor were divided, in arose- u section, into four zones - boundary, towpath, bank and channel. Hedgerows are the dominant habitats of the boundary but inplaces there are small areas of native woodland and scrub whichhave developed due to lack of grazing. Wetland habitats on theboundary include small areas of fen, oarr woodland and raised bogswith a number of drains and ditches. The towpath is generally a grassy 0 track dominated by trample-resistant species but there are some 1 areas of meadow and nutrient-poor limestone grassland. The canal bank includes transitional habitats between dry grassland at the top u and the emergent fringe at the base.The channel habitats are arranged in a series of parallel bands from the emergentvegetation in the shallow water to the submerged and floating-leaved plantsin 0 the centre of the channel. The stonework of looks, bridges and harbours provides a range of wall habitats. 1 3. The vascular flora was surveyed in detail on every sectionof the canal. A total of 398 species was recorded with the greatest diversity in the boundary and bank zones. The frequency of 0 occurrence of each species along the canal and its preferencefor particular zones was calculated in order to provide an indexof occurrence within the canal system. The boundary zone of Unit II u contains many more of the rarer species than the otherunits. The greatest diversity in the towpath zone occurs where there are adjacent harbours, looks, woodland or nutrient-poor grassland. The u greatest diversity in the bank zone occurs where the slopeis gradual and incorporates a range of habitat types. Lowest bank diversity is found in urban areas and sections which haverecently 0 been dredged. In the channel the greatest diversity occurs in the .semi-aquatic sections of Units II and III which may includeopen water, muddy bed, grassland and scrub. The looks, bridges and u harbours along the canal support a range of plants typicalof wall habitats and are especially diverse in the derelict sections. A number of nationally rare species were found in the canalcorridor a mainly in habitats such as fens which are themselves scarce. Two species, Groenlandia denser and Orohia morio. which are protected under the Wildlife Act, 1976, were recorded.A number of plant species are confined to the Dublin pity sections of thecanal because of their proximity to gardens, waste ground and thecoast'. 0 0 a 1 4. The revegetation of dumped spoil one year after dredging vas recorded in 12 sample sections along Unit I of thecanal. The resulting vegetation vas more diverse on the bank than inthe other zones. The rate of revegetation on the towpath and boundary was negatively correlated with spoil depth and compaction caused by heavy machines travelling on drying spoil. The revegetation with species present prior to dredging was most rapid where spoilwas shallow or where it was mixed with topsoil. Vegetation vas slower 0 to reoolonise the boundary zone when this was damaged bymachinery during dredging operations. i 5. The breeding bird communities of the canal were surveyed. A complete census of riparian species was undertaken in May andJune 1990 and a mapping census of non-riparian species vas carriedout-on M a sample of 25km of canal boundary. Overall, the canal had a very 1 low density of breeding riparian birds by comparison with other waterways. This is due to the recent disruption of the channeland _ 0 banks by dredging in Unit I and the lank ofwater in Unit III. Unit II held the highest density of water birds, especially inthe sections vest of Mullingar where there was a combination ofopen 0 water, think marginal vegetation and undisturbed banks with overhanging trees. Moorhens were especially sensitive to dredging. The density of non-riparian breeding birds in the canal boundaries was similar to that found in mature hedgerows in otherparts of Ireland. The community was dominated by five species, Robin, Blackbird, Wren, Willow Warbler and Chaffinch, which together accounted for about 80% of all breeding territories. The community structure and species diversity were very similar to those foundin hedgerows on farmland. 6. A sample survey of dragonflies and damselflies (Odonata) vas carried out in five study areas chosen to represent thefull range M of habitat types and management regimes on the canal. Previous records from the canal have also been reviewed. A total of 13 species has been recorded, representing over half of the Irish Odonata, although none of those found is nationally rare. The species composition was similar to that found in still-eater habitats (including canals) in lowland Britain. A significant difference in species richness was found between the study areasand this was related to the intensity of management with theremoval of emergent vegetation and bankside trees having the moat drastic M effects. Recovery of the Odonata one year after dredging at 1 Clonsilla, Co. Dublin was only partial with the absence ofshelter and emergent vegetation limiting the return of some species. 1 7. Previous surveys of freshwater molluscs and water beetles in the canal system have been reviewed. A total of 28 mollusc species has 0 been recorded from the canal between 1975 and 1983 representingover half the Irish freshwater gastropod and bivalve fauna. The continuous vaterbody of the canal has enabled many species toexpand r beyond their normal range and several are unknown outside thecanal systems of south-east Ireland. The rare snail nyxc glutinosa has 1 been recorded from one locality only on the canal. Water beetle 1 1 1 assemblages in six localities on the Co.Weataeath section of the - canal were sampled in.1986. A total of 49 aquatic and semi-aquatic species was recorded including several which are scarce in similar habitats in Britain. One species, ZWzyohiua velutua, has not been recorded elsewhere in Ireland in recent years. The water beetle I fauna in most of the sites sampled was dominated bythose species which live in deep open water among vegetation. It was impoverished because of eutrophication (water pollution) and the absence of well- I vegetated and structurally complex banks to the canal. An exception was found along the canal feeder supply from Lough Ovelwhich held u over twice as many species as the other localities. 8. -The impacts of management on nature conservation throughout the canal system have been reviewed. These were considered under the a general headings of restoration, maintenance and recreational use. I Dredging and dumping of spoil can have significant impacts onflora and fauna as can tree-cutting and scrub clearance. Changing the u grazing regime may reduce species diversity on the towpath and 1 boundary habitats. Maintenance of high water quality is essential for nature conservation and fisheries while the use of aquatic 0 herbicides has reduced species diversity in the channel. Fisheries management is limited at present but is likely to increasein 1 future. The most significant potential impacts of angling are disturbance to nesting birds and contamination with lead weights. Increased boat traffic is likely to reduce the abundance ofsome aquatic and semi-aquatic plant species but this is preferable to chemical means of keeping the channel clear. 9: Part 2 of this report contains general guidelines for conservation management on the Royal Canal and recommendation.for each auction of the entire system. This should allow nature conservation to be given equal priority with other values ofthe u canal, to maximise diversity and to allow flexibility in management- to take account of the variability of nature. u 0 1 1 u 1 0 __+MyKi W LIST OF FIGURES ii LIST OF TABLES LIST OF APPENDICES V 1 E ACKNOWLEDGE ENTS Vi E SOME DEFINITIONS ANDABBREVIATIONS GENERALRECOPOUMCDATIONS E PHOTOGRAPHS I CHAPTER 1. E 1 1.1 General Description 43 1.2 Canal Restoration 43 1.3 Ecological Survey 46 1.4 Study Area E CHAPTER 2. HABITATS 2.1 Introduction 52 0 2.2 Habitats of the Boundary 2.3 Towpath Habitats 59 2.4 Bank Habitats 60. E 2.5 Channel Habitats 60 2.6 Stonework Structured Habitats61 2.7 Summary. CHAPTER 3. FLORA OF THE ROYAL CANAL 3.1 Introduction 63 3.2 Methodology 63 3.3 Results 64 E 3.4 Discussion 82 3.5 Plants Generally confined to the Dublin City Stretch of the RoyalCanal. 86 i 3.6 Revegetation of Dredged Areas 87 CHAPTER 4. FAUNA E 1 4.1 Mammals 4.2 Birds 100 E 4.3 Invertebrates 111 1 0 CHAPTER 5. IMPACTS OF MANAGEMENT 5.1 Restoration 132 5.2 Maintenance 141 5.3 Recreational Use 154 BIBLIOGRAPHY 160 APPENDICES 1 E FIGURE NO 1.1 Royal Canal - Management Units and Areas of Scientific Interest 44 2.1 Limestone Grassland and Woodland 1 E alongthe Royal Canal 57 2.2 Bogs, Fens and Drains along the 1 E Royal Canal 58 4.1 Study Areas for the Census of Non-Riparian Breeding Birds 106 4.2 Study Areas for Survey of E Dragonfliesand Damselflies 113 1 E 5.1 Channel Design 139 5.2 Channel orientation and planting 1 0 for shade 147 5.3 Manipulation of Shading 148 E 0 ., E 0 M 1 E 1 E 1 t I 1 ii 1 a LIST OF TABLES f N TABLE NO.