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Landscape Ecology: the New Forest

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Pollinators provide a key ecosystem service, vital to shaping wild plant communities. Wild bees (Apidae) (including bumblebees (Bombus sp.) and solitary bees) are primary pollinators but are significantly declining in the UK in diversity and abundance.

Apidae exhibit several life habits, necessitating a broad spectrum of habitats. Species-specific foraging and nesting behaviour coupled with finite ranges and available resources define the temporal and spatial extent of critical landscape elements with which Apidae can interact . Such interactions determine pollinator success .

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Referencing the New Forest, this paper will evaluate how critical landscape elements, such as the presence and accessibility of floral resources and nesting sites, are integral to Apidae populations. Significant constraints faced by the New Forest in safeguarding Apidae will also be evaluated.

Floral resources

Apidae are nutritionally dependent on floral resources for pollen and nectar throughout their foraging periods – arguably the most critical landscape element of Apidae. Apidae floral resource use is affected by the quality of floral assemblages, compounded by species-specific foraging behaviour.

The New Forest is considered a vital reserve for UK Apidae species. The semi-natural habitat provides a range of floral resources that are paramount to their success. Within a landscape, plant species flower at different times, resulting in temporal turnover in the floral assemblage which may also vary spatially with different habitat types  – a display of spatial-temporal heterogeneity. The New Forest heathland , produces many flowering heathers  between June and September, increasing the capacity of the landscape to support both social and solitary species which forage mostly on heathers. Prior to heather flowering in June, acid grassland provides important food sources such as gorse (Ulex sp.), Bird’s foot trefoil (Lotus corniculatus) and Cat’s-ear (Hypochaeris radicata) for many pollinators, particularly Bombus queens for whom early season foraging is vital for colony establishment .

Species such as Bombus, are generalists by necessity, ecologically dictated by a long foraging season. Accessing a wide range of floral hosts, they utilise nectar in both the local and broader landscape . Contrastingly, floral specialisation, known as oligolecty, limits the breadth of resources that Apidae species can exploit. Solitary, often ground-nesting species, tend to forage over a short season and some display oligolecty. An example is the nationally scarce Tormentil mining bee (Andrena tarsata), found in the New Forest, whose sole food plant is Tormentil . Such reliance results in populations vulnerable to changes in floral resources. To mitigate this, increasing landscape heterogeneity allows for greater resource abundance and diversity within individual foraging ranges, varying environmental conditions and niche availability for specialists, allowing for more interactions between plants and floral visitors .

However, adequate floral resources are only one of the many landscape elements that serve as critical components to Apidae ecology.

Nesting

Another important aspect of Apidae colonisation success are existing or potential nesting cavities and resources such as bare ground.Nest sites vary between Apidae species; most species prefer dry dark cavities. These can be above ground in plant stems, thick grass or in trees, or underground withspecific nesting requirements.

Apidae in the New Forest are mostly ground nesting, the abundance of which varies but highest numbers have been found in freshly burnt areas. Burning is a common traditional method for heather control and regeneration, implemented in the New Forest. This practice inadvertently supports Apidae populations by clearing vegetation, while generating bare ground, potentially for burrow creation during the foraging season. However, extensive burning could have a negative impact on Apidae spatially by causing fragmentation thus limiting floral resource patches – a critical landscape element.

The quality of bare ground, in terms of soil and aspect, is also significant. The proportion of sandy soil potentially correlates to increased pollinator nests, as ground nesting bees prefer to dig holes in looser soil to make their burrow. However, it should be noted too sandy areas resulted in fewer nests with the soil likely to collapse . The slope of the ground may be a factor. Steep slopes promote erosion and bare soil, increasing radiation (particularly on south-facing slopes) compared to flat areas. Potts and Willmer (1997) showed that the nest density of ground-nesting species, such as sweat bees found in the New Forest, positively correlates with the slope angle of the nesting site.

Essential for supporting Apidae communities, although highly specific in requirements, nesting resources need to be considered when implementing land management practices. Additionally, the provision of floral resources could be considered more critical due to floral specialisation restricting the use of alternative food plants.

Commutability

The vagility of Apidae to access these resources depends on matrix quality and species-specific physiology.

The matrix  provides functional connectivity, facilitating movement between both immediate and further ranging patches of natural or semi-natural habitat . The matrix habitat quality may either prevent or promote Apidae dispersal. Floral and nesting resources within the matrix promotes safer dispersal for individuals between patches. Additionally, higher patch density decreases the size of the matrix while increasing the number of edges and corridors that can act as food and nesting resources thus promoting overall dispersal. However, a matrix devoid of resources will prevent dispersal, isolating populations within habitat patches. Optimal commutability relies on a habitat mosaic, with minimal structural contrast between the patch and the matrix, resulting in a shifting continuum of ecotonal area.

Physiological dispersal capacity through the matrix also affects vagility. Large Apidae and Bombus species, tend to have broader dispersal ranges, able to move further through the matrix utilising a greater number of habitat patches over a larger landscape. However, spatially widespread commutes may be beneficial or injurious, since workers face a trade-off between the increased costs of foraging and potential energetic gains from access to additional resources . Alternatively, smaller predominately solitary species with less foraging range are limited in the number of suitable habitats that can be reached, compounded further by an increased potential of isolation from neighbouring populations in suboptimal matrices.

While some studies have suggested that floral resources are the most critical landscape element for Apidae, the author would argue that the quality of the matrix is of greater significance. The inability of Apidae to utilise high quality floral resources means they are of limited value as a landscape element. The synergy between all elements examined is inherent to successful Apidae populations.

Constraints

The ability of the New Forest National Park Authority (NFNPA) to enhance critical landscape elements of Apidae species are subject to and limited by social, economic and environmental constraints.

Social

Recreational use is the main social constraint in promoting Apidae populations in the New Forest.

The New Forest landscape regularly attracts large numbers of tourists. Causing high levels of disturbance, trampling of floral resources and possible nest sites, particularly in the spring and summer months, they affect commutability and causing isolation of populations. However, Winfree et al.,(2009) found that, while both species abundance and richness were negatively affected by disturbance, the magnitude of the effects was not large. Despite this, studies suggest the footfall could significantly increase, creating an overall negative effect the ability of habitat to support Apidae species.

Economic

Grazing and decreasing budget allocations to the management of the New Forest are resulting in the deterioration of the Apidae habitat.

Commoners maintain the tradition of extensive common grazing across the New Forest, which are protected by law. Under the Verderer’s Grazing Scheme, increased payments to commoners have resulted in higher numbers of animals (particularly ponies) grazing on the New Forest. This has coincided with a loss of habitat for Apidae through the removal of floral resources and reduction of potential nesting sites by soil compaction. Commoners rights are one of the biggest challenges facing NPA managers and their ability to effectively safeguard Apidae populations. However, recent urban migration of younger generations is leading to a steady decline in commoners, resulting in a reduction in grazing.

Decreasing public sector budgets coupled with increasing competition for funding has resulted in minimal staffing and funding resources, increasing the difficulty to enable integrated, landscape-scale methods to enhance and support Apidae conservation and mitigate the negative effects of overgrazing and tourism. In the changing political climate, it is predicted that this economic pressure will only worsen .

Environmental

Climate change is potentially the most damaging constraint, altering the New Forest landscape and biodiversity.

Apidae species are affected according to their specific ecology, causing spatial or temporal disruption of pollination. Decoupling of pollinator phenological responses from their forage plants is a key biodiversity change . Species, such as the bumblebee, for which early and late season foraging is important, might be particularly affected. Alternatively, as an r-selected species, pollinators may adapt quick enough to climatic changes and could colonise new regions. Current research regarding the extent of the effect of climate change on pollinators is still limited; therefore, adapting management practices accordingly is difficult. Ultimately climate change has the potential to decrease abundance, shift plant and insect ranges and increase extinction risk, especially for specialists.

Conclusion

The New Forest is a significant reserve for pollinators, providing critical landscape elements for Apidae that are required reciprocally for successful populations.

The constraints presented indicate potential further damage to critical landscape elements facilitating future declines in pollinator abundance and richness. Multi-faceted management is required by the NFNPA to mitigate constraints and conserve Apidae landscape ecology, preventing further degradation of semi-natural ecosystems while safeguarding the species.  

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