Between April and October 2021, a survey was conducted at the Lake in St Mary Bourne (the “Lake”) and the adjoining Bourne Rivulet. The objective was to establish a baseline for butterfly, dragonfly, and damselfly populations. While ideally conducted in 2020 before habitat management changes, the one-year difference is not expected to impact the findings significantly. The survey also preceded the Watercress & Winterbournes Landscape Partnership Scheme’s work on the Bourne Rivulet, carried out in late 2021.
Baseline surveys like this one are essential for understanding current ecological conditions and evaluating future conservation measures.
Habitats Overview
The area includes several key habitats:
- The Lake – Featuring steep, deep sections as noted on the information board.
- Lake Margins – Sparse marginal vegetation in most areas, with some sedges and trees.
- Wooded Area – Thin strips of woodland with intermittent clearings on the Lake’s western, southwestern, and southeastern sides.
- Wood Pasture – A blend of open ground and scattered trees along the eastern and northeastern edges, near the Bourne Rivulet.
- Bourne Rivulet – A chalk stream supporting a range of aquatic life.
- Rivulet Margins – Habitat for riparian species.
These habitats support a range of species, though future efforts could better characterize their ecological makeup.
Management Changes and Their Impact
Mowing Regime Change:
Prior to 2021, the area around the Lake was regularly mown. In 2021, the mowing was reduced to a few fishing stations and a circular pathway, with the rest left to grow freely until late October. This change aimed to increase biodiversity by promoting diverse plant growth and providing microhabitats for arthropods, which form the base of the food web for higher species such as bats, birds, and amphibians.
While initial results show promise, the biodiversity benefits of such changes may take years to materialize, as seen in the nearby Black Garden Field, where a once-yearly mowing regime over 17 years resulted in high butterfly diversity.
Balancing Ecological Goals and Resident Concerns:
Concerns were raised by some local residents about obstructed views of the Lake and an increase in stinging nettles. Proposed solutions include:
- Cutting selective “vistas” to maintain views while preserving most of the herbaceous vegetation.
- Leaving uncut refuge areas that shift annually to prevent overgrowth of brambles.
- Highlighting the ecological value of nettles, which host larvae for species like Comma and Peacock butterflies.
Bourne Rivulet Management:
The Winterbournes and Watercress Scheme reshaped parts of the Bourne Rivulet to enhance biodiversity, benefitting species such as water voles, white-clawed crayfish, and southern damselflies. Collaboration with local conservation bodies may provide further opportunities for improving the Lake’s ecological value.
Butterfly Findings
Nine butterfly species were recorded, including:
- Common Species: Brimstone, Large White, Small White, Orange Tip, and Red Admiral.
- Grassland Species: Meadow Brown and Ringlet.
- Nettle-Dependent Species: Small Tortoiseshell and Comma.
Butterflies were primarily observed in sunlit areas, highlighting the importance of open habitats. If the non-mowing regime continues, a greater diversity of larval food plants and nectar sources could establish, increasing butterfly diversity over time. Pruning and selective removal of trees in the wood pasture area may also help maintain open conditions favorable to butterflies.
Dragonfly and Damselfly Findings
Approximately six species were identified, though some were difficult to confirm due to identification challenges:
- Damselflies: Common Blue, Banded Demoiselle, Southern/Azure Damselfly.
- Dragonflies: Emperor, Darter species (Common/Ruddy/Red-Veined), and Brown Hawker.
Dragonflies and damselflies generally prefer shallow, vegetated waters, which are limited at the Lake due to its depth. Recommendations include enhancing existing shallow areas with appropriate emergent and submerged plants to support dragonfly and damselfly lifecycles.
