The Lake & Rivulet Survey

The Lake & Bourne Rivulet, St Mary Bourne – Butterfly, Dragonfly & Damselfly 2021 Survey Report – 12.11.21

Introduction

The Lake, St Mary Bourne (the “Lake”), including the Bourne Rivulet which adjoins the Lake on its eastern side, were surveyed for butterflies, dragonflies and damselflies between April and October 2021.

The above set out surveying work is in essence a baseline survey, albeit that ideally it should have been carried out in 2020 before the below set out management change was implemented to the Lake area (see below) but in practice it is not thought that one year’s difference will have made much practical difference. Additionally, this surveying was undertaken prior to the Watercress & Winterbournes Landscape Partnership Scheme work to the section of the Bourne Rivulet that is adjacent to the Lake area that has been carried out in October & November 2021. It is not known whether the Watercress & Winterbournes Landscape Partnership Scheme carried out any baseline surveys with relation to butterflies, dragonflies & damselflies prior to the Bourne Rivulet work.

For the record a baseline survey is a preliminary ecological assessment against which subsequent ecological survey results can be measured and assessed.

Habitats

The Lake and the area around it are made up essentially of the following different macro habitats (all directional references below are based on Google Maps):

1. The Lake – Itself, which it is noted that the information board on the Lake’s south-western side states that “In places the bottom of the Lake shelves steeply and is very deep”;
2. ​The Lake Margin – There are both some tress and some marginal plants, such as sedges etc, on the Lake’s margin but there are large stretches that are completely devoid of any such species;
3. A Wooded Area – On thin the strip running between the Lake and a footpath on the shortish western, reasonably long south-western and shortish south eastern sides of the Lake, albeit that it has some open areas;
4. Wood Pasture – A mixture of trees and open ground on the shortish eastern and longer north eastern sides between the Lake and the Bourne Rivulet;
5. The Bourne Rivulet and
6. The Bourne Rivulet Margins

 

There may well be other ways of describing these habitats and other habitats present, but it has not been the purpose of the above set out work to assess exactly what habitats are present and what all of the habitats are.

Management Change

3.1 Mowing Regime Change

Prior to 2021 the area around the Lake was regularly mown during the Spring, Summer and Late Summer months. Then in 2021, only some fishing stations and a path around the Lake were regularly mown and the rest of the area was left to grow unabated until it was cut in late October 2021.

It is believed that this mowing regime change was enacted in order to try and boost the Lake area’s biodiversity by increasing its spatial heterogeneity, ie its spatial variety, in this instance by providing an increase in the number of different herbaceous based micro habitats and so associated niches, which over time will lead to a greater number and diversity of arthropods (ie insects etc) which are an important and often overlooked part of an ecosystem, which will in turn provide food for species higher up the food web, such as dragonflies, damselflies, bats, birds, amphibians and mammals.

However, such a conservation management change will take some time to produce a noticeable increase in biodiversity. By way of an example, the significant butterfly biodiversity in Black Garden Field, St Mary Bourne (as set out in the Black Garden, St Mary Bourne - 2020 Records report of 22 February 2021) will have come about as a result of the grassland area of Black Garden only being cut once a year in about September or October for it is believed at least the last 17 years and possibly for longer.

It is believed that the above set out conservation management change was implemented in order to protect and enhance the Lake’s ecology on the basis that the Schedule of Personal Covenants of the Lake’s HM Land Registry Title Number HP445184 of 15 December 2009 states the following:

“2. (a) The Property shall be managed by a Committee of Management (“the Committee”) which shall consist of not less than three members of whom one shall represent the interests of the local residents one of those of ecology and one of those of fishery management …”

It is believed that this conservation management change will have helped protect the Lake’s ecology and will over time result in a more biodiverse and resilient Lake ecology. However, it is proposed that not all of the area around the Lake is cut in late October every year, ie that most of it is cut but that some reasonable sized areas spaced out around the Lake are left uncut as wildlife refuges (and the location of any such refuge areas can be varied year to year to avoid brambles etc taking hold in these areas).

It is understood that there have been some objections to the above set out management change on the basis that the local residents’ interests have been impinged, as they could no longer see the Lake itself once the herbaceous vegetation had grown up. One way of addressing this concern would be to cut some vistas through the herbaceous vegetation so that the local residents were able to see the Lake and yet there remained significant areas of uncut herbaceous vegetation in order to protect and enhance the Lake’s ecology.

3.2 Stinging Nettles

It is also understood that there have been some objections to the number of stinging nettles (Urtica dioica) that have grown up as a result of the mowing regime change. Stinging nettles are a native plant and as such are a valuable part of the area’s ecosystem, for instance they are the larval host plant for Comma, Peacock, Red Admiral and Small Tortoiseshell butterflies.

3.3 Bourne Rivulet

The Winterbournes and Watercress Landscape Partnership Scheme have then also made some changes to the section of the Bourne Rivulet that runs to the east of the Lake area, including shoring up some bank sides and some reshaping of the rivulet in order to increase its biodiversity, in particular with regards to “water voles, brown trout, southern damselfly, water crowfoot, and endangered white-clawed crayfish” (ref. the Hampshire & Isle of Wight Wildlife Trust’s Watercress and Winterbournes’ webpage accessed on 12.11.21).

Butterflies

The following 9 butterfly species were recorded in the in the area surrounding the Lake:

Brimstone
Large White
Small White
Orange Tip
Red Admiral
Small Tortoiseshell
Comma
Meadow Brown
Ringlet

For the record, 2021 was not a good year for butterflies as a result of a significant amount of cold and wet weather between April and September 2021 (the main butterfly flight period).

Not surprisingly all of these species were recorded in the more open wood pasture section of the area around the Lake rather than the wooded section, as butterflies are ectothermic, ie they are cold-blooded and so rely on heat absorbed from the sun either directly or indirectly in order to fly. For the record it needs to be ≥ 12 °C in full sunlight or ≥ 17 °C in the shade or cloudy conditions for butterflies to be on the wing in Britain.

If the non-mowing regime is continued with over time a greater diversity of plant species should colonise the open areas of the wood pasture part of the area around the Lake, some of which will possibly be butterfly larval food and nectar plants and if so, butterfly numbers should increase both in terms of numbers and diversity. However, over time there would need to be some pruning, possibly some delimbing and possibly the taking out of some of the trees in the wood pasture section in order to prevent that area reverting to woodland.

It is believed that the Green Veined White butterfly has also previously been seen around the Bourne Rivulet, which is not surprising as it likes damper conditions. Additionally, Gatekeepers, Holly Blues, Peacocks and Speckled Woods have been seen in a garden adjoining the Lake area / Bourne Rivulet and so are likely to be seen in the Lake area in the near future if the present non-mowing regime is continued with.

With regards to the wooded area on the western and south-western sides of the Lake it is thought that it provides a shelter belt for the Lake (and for that matter for that part of the village) with regards to the prevailing south westerly wind, which will be of benefit certainly to all winged species present in the Lake area, ie butterflies, dragonflies, damselflies and birds. It is also worth pointing out that trees in themselves are habitats (for instance willow species support 266 insect & 160 lichen species and beech trees support 64 insect & 206 lichen species both of which look to be present in the area around the Lake, ref. the countrysideinfo.co.uk’s Value of Different Tree Species for Invertebrates and Lichens web page of 10.11.21).

It is not known if a botanical survey of the Lake area has been undertaken, but if one has been completed it would give some indication of what butterflies might be attracted into this area based on the presence or not of butterfly larval and nectar plants.

1. Dragonflies and Damselflies

The following about 6 dragonfly and damselfly species were recorded in the Lake area and the Bourne Rivulet (the recorder’s dragonfly and damselfly identification skills are not particularly advanced and as a result precise identification was not always possible):

Common Blue Damselfly or White Legged Damselfly
Banded Demoiselle Damselfly – In and around the Bourne Rivulet (but will breed in lakes adjacent to rivers and streams)
Southern Damselfly or Common Blue Damselfly or Azure Damselfly
Emperor Dragonfly
Common Darter or Ruddy Darter or Red-Veined Darter (Dragonflies)
Brown Hawker (Dragonfly)

The exact depth profile of the lake is not known, but is it thought that it is reasonably deep in places (as set out above) which is not the best profile for dragonflies and damselflies which generally prefer much shallower zones.

It would be worth obtaining some advice on how the Lake could be better structured for dragonflies and damselflies, albeit that creating shallower areas by for instance depositing natural materials in and around the margins of the lake is probably best avoided as the Lake is mostly non-natural and so unless managed over time will fill up with sediment and so will develop into marsh and eventually return to woodland. Planting up the shallower areas that do exist with a greater number of appropriate species is one possible way to protect and enhance the Lake’s dragonfly and damselfly biodiversity as the “larvae of many dragonfly species prefer waters with an abundant growth of water plants in which the larvae can hide from predators and ambush their prey … Many require emergent water plants up which a larva, in its last stage, can climb in order to emerge as an adult” (ref. British Dragonfly Society’s Managing Habitats for Dragonflies pdf of 1993). For the record, damselflies are close cousins of dragonflies and so it is presumed that the same applies to damselflies. It is thought that the Hampshire & Isle of Wight Wildlife Trust, the British Dragonfly Society and/or the Wessex Rivers Trust (the latter who it is believed headed up the recent work to the Bourne Rivulet) could all potentially provide such advice.

Conclusion

Not a great number of species of butterflies, dragonflies and damselflies were recorded in the Lake and Bourne Rivulet areas but given that this work amounted to a baseline survey, ie as the area around the Lake has only just begun to be managed for its ecology, that is perhaps not surprising.

A significant number of bird species have been observed in and around the Lake & the Bourne Rivulet and bats have been frequently seen on the wing at dusk also in and around the Lake & the Bourne Rivulet, both of which will benefit from the non-mowing regime for the food chain reason set out above.

Anecdotally, there seemed to be a significant increase in bird activity and birdsong in the Lake area as a result of the non-mowing regime and it was noted about 50 to 60 wild mallard ducks (ie not the semi-tame ducks that are seen in and around the Lake & the Bourne Rivulet) were regularly seen coming into the Lake in about 2 flocks in ‘formation’ in the summer and early autumn evenings presumably to roost there, which was not observed prior to the introduction of the non-mowing regime.

We have become used ‘tidy’ landscapes, but ‘tidy’ landscapes are ecologically poor landscapes as Gerard Manley Hopkins said in his poem Inversnaid (1881):

What would the world be, once bereft
Of wet and wildness? Let them be left,
O let them be left, wilderness and wet;
Long live the weeds and the wilderness yet.