Habitat changes include degradation, partial loss, full loss, or fragmentation. These threats are the direct result of human interactions and although the damage can never be reversed, human action and intervention is the only remedy to begin restoring pollinator habitats.
Agricultural practices are the single largest component of land use, with approximately 36% of the worlds land surface devoted to it. In rural areas harsh agricultural practices have become a target for change, with a focus on minimizing the impacts on native pollinators. This includes changes to grazing and mowing practices, encouraging a properly managed burning protocol, and introducing pesticide alternatives for pest management.
Grazing and mowing
Grazing has both a positive and negative effect on pollinators. Overgrazing during periods when flowers are blooming will decrease forage available for pollinators. However, controlled, light, and rotational grazing can help maintain an open herbaceous plant community that supports wide diverse populations of pollinators.
Grazing during springtime may negatively impact pollinator communities by eliminating butterfly larvae that are active on host plants, and also by reducing available host plants for the larvae that might survive the grazing.
Other potential negative impacts include destruction of potential and existing bee nests and adult bee trampling from the grazers. Some positive effects include the aforementioned habitat clearing and the removal of invasive plant species.
Pollinator friendly grazing involves low to moderate rotational grazing whilst being attentive to historical and species specific characteristics of your site. When grazing periods occur it is generally advised to leave ungrazed areas within or adjacent to the grazing area so that a reservoir refuge is available to pollinators.
Mowing is similar to grazing and often occurs on smaller sites and is prevalent in the urban landscape. Mowing creates uniformity in plant species height which decreases habitat diversity and also removes possible nesting areas. It is known that butterflies vary in their ability to pollinate at different heights, with some preferring ground growing plants and others preferring trees or high shrub bushes. Creating height uniformity would directly decrease the diversity of your butterfly populations.
As an alternative, trimming during non bloom seasons is recommended, as is cutting at a higher height, less uniform heights across areas, and mowing in mosaics.
Correctly managed fire schedules
Fire is an important role in many native ecosystems, and controlled burns aid pollinators by restoration and maintenance of the natural environment. However, considerations need to be made when prescribing burns in any areas with pollinator visitors. In general, a good practice is to follow a program of rotational burning which leaves portions of the habitat free to provide refuge.
In some cases burning is highly discouraged. For example,if the area is a small fragmented habitat with little to no adjacent green space available. During a burn in an area such as these, pollinator species run the risk of extirpation because there is little adjoining refuge space and potential for recolonization would be low. Also some species of butterfly overwinter as pupa or larva attached to the base of native grasses. In this case prescribed burning of any kind would be detrimental.
Pesticide use in green spaces has the most easy to understand ramifications for our native pollinators. Serious impacts are discussed here.
Next to agricultural practices, urban development is the most frequent cause of habitat loss and the one that we here at GAPP are most interested in understanding.
Case study: The rise and fall of green-space in Atlanta
Between 1990 and 2010 the US census data indicated the population in the metro Atlanta area increased by 2.4 million people. This resulted in an average loss of 54 acres per day of tree canopy/green space and an increase in impervious surfaces that averaged 28 acres a day.
Over a ten year period this resulted in the loss of nearly 200,000 acres of potential pollinator habitat. The direct effect on pollinator communities is simple. There is now less green space that support habitat, shelter, and food for pollinators.
The indirect effect is: how does this loss impact pollinator corridors? The pathways and by-ways on which pollinators travel are very important for both the pollinator and the plant species it visits. If these pathways are altered, you can imagine that it will alter the entire pollination mechanism and the pollination system. The pollinator can no longer navigate on the same “map” when the links between green-spaces are lost and so therefore needs to navigate a new map or is forced to shorten foraging distances.
Loosing pollinator corridors can often lead to areas of isolation where infrastructure has been built up so much that the small remaining patches of green are now almost unreachable. This often leads to to a possible extirpation of pollinators in an area and will certainly have an effect on its biodiversity.
Part of the reason GAPP exists is not only to increase the total area of green spaces as discussed above but to reclaim important pollinator corridors, increasing the pathways for pollinators in and across the metro area. This would increase foraging connections and links from one pollinator garden to another!