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Different methods employed
Different methods were used to collect data in order to assess (a) trampling impact and risk; and (b) patterns of eutrophication (increased nutrient) impacts on the site’s vegetation.
TRAMPLING - Aligning with the Footprint study of 2010 and the 2019 botanical survey, the site was split into 25m x 25m grids via a computer Geographic Information System (GIS) and thereafter a 5-point scale was defined to estimate trampling intensity and erosion risk. This scale ranged from (1) Slight risk/impact areas to (5) Very high risk/impact areas.
NUTRIENT - Cells from the 25m x 25m grid were selected for vegetation assessment based on the location of quadrats used in previous assessments. This selection was then expanded to provide a wider and representative coverage of the site.
"Ground truthing"
The assessment of 573 cells was initially carried out by interpretation of high resolution, recent aerial photography. Seasonal variation in aerial imagery and the impacts of drought in the summer of 2022 meant that certain cells were considered ambiguous or determined with low levels of certainty. These areas were therefore included in the list of squares to be assessed in the field.
To “ground truth” the assessment, a sample of 183 cells were assessed onsite by the surveyors, with an independent re-assessment of the 5-point scale in the field. Of the ground-trothed cells, 39 were changed from the initial desk-based scoring, giving it an accuracy of around 79%.
The report states that sand dune systems are, by their nature, dynamic and there is a complex interaction between natural processes which cause erosion and changes caused by human activity. The independent reassessment of the situation on the ground was aimed at minimising this effect, which could result if only a desk-based study of aerial imagery was undertaken.
Results
As found in the 2019 survey, the pattern of trampling and erosion risk throughout the site remains complex. The majority of hotspots are centred around access points to the reserve, path nodes and corridors between the amenity beach and the interior of the site.
There has been significant coastal erosion around the edge of Warren Point. A large number of squares assessed in the previous survey no longer contain vegetation. The 2019 pattern of linear pressure from walkers that follow the edge of the beach and dunes around the point has simply been replicated along the newly eroded edges of established vegetation
The results of the indicative soil fertility mapping show higher levels of fertility:
1. in and around the southern end of the site near the entrance gates and in a corridor between the entrance and the visitor centre.
2. in the dune slack to the west of the main trackway.
3. at the narrowing west of groynes 8 to 10.
4. in some diffuse areas within the Marram grassland on Warren Point.
Conclusion
The significant areas of risk from erosion from recreational trampling pressure are mostly associated with the frontal dune ridge. These are often in areas which technically belong to mobile dune vegetation types but are partially stabilised. Specifically for fixed dune and dune slack habitats the risk areas in order of decreasing severity are:
1. A small area of dune grassland at the extreme south end of the reserve next to the pedestrian entrance and adjacent to the buffer zone.
2. A particularly high density of path nodes and desire lines concentrates pressure on a relatively small area where the site narrows to the dune ridge level with groyne 8. Here there are a mixture of grassland types including dry and damp communities with the dune slack habitat reaching its northern limit flanked by areas of both fixed and semi-fixed turf.
3. The turf in a corridor on both sides of the main access track and footpath from the south end of the reserve to the visitor centre. Abrasion is frequent in these areas and is necessary to maintain the habitat suitable for some notable species present but risk of abrasion turning to net erosion and habitat loss is still significant.
4. The turf along the back path and in a corridor linking the back path and main trackway between the visitor centre and pond (i.e., along south edge of flood bank). Impacts are more diffuse in these areas but moderately high locally.
Areas subject to high and moderate risk from dog fouling have been identified and recorded. An area of dune grassland approximately 0.25ha in size in the SE corner of the reserve is most prone to nutrient enrichment. The level of enrichment here is comparable with that in the buffer zone (towards the resort), immediately to the SE of this area.
Trampling - comparisons
71% of the area has not changed in terms of its trampling assessment (319 of 447 squares). Approximately 20% of the area is assessed as experiencing higher trampling pressure and risk than in 2019 and 9% with some relaxation of trampling.
93 squares (21% of the area) changed to a minor degree of one scale increment (for example the assessment score altered from 2 to 3 or 5 to 4 between 2019 and 2023). Only 8% of the area (35 squares) changed by 2 or more increments.
The net increase in trampling risk and pressure over the whole site (the sum of all changes to individually assessed squares) equates to a mean increase in the trampling index of 16%. This figure is derived from the qualitative 5-point scale used in the assessment and it is not suggested to demonstrate an absolute index of recreational pressure.
Nevertheless, it suggests a small but significant increase since the previous assessment. The assessment finds that the overall spatial pattern of trampling risk has, unsurprisingly, not changed since 2019 and the heatmaps produced for 2019 and 2023 are very similar.
Nutrient (fouling) - comparisons
The broad scale pattern shown on indicative fertility maps produced in 2019 and 2023 is very similar. Small differences are as likely to stem from differences in the way the data were collected (derived from vegetation data collected for other purposes in 2019 and the result of a more limited but purposely collected dataset in 2023) as change.
The only significant discrepancy between these maps is that in 2019 the reedbeds are shown as a fertility hotspot but show as a neutral area in 2023. This is because they were sampled for NVC work in 2012 and 2019 but not prioritised under the objectives of the present survey.
The best judgement from the available data in the current survey is that the spatial distribution of nutrient enrichment effects from dog fouling is substantially the same as in 2019. These data do not allow an assessment of whether there have been any significant changes in severity, either at individual locations or for the whole site.