Habitat change

HABITAT CHANGE: WHAT DOES THAT MEAN?

HABITAT CHANGE INCLUDES:

           * Degradation (Overall suitability/quality of habitat is reduced)
           * Partial Loss (A section of habitat is destroyed )
           * Full Loss (An entire habitat is destroyed)
           * Fragmentation (The habitat is broken up , severely reducing the connectivity between populations)  

COMMON HABITAT CHANGE THREATS:

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 habitat. 

Agricultural Practices:

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Agricultural practices are the single largest component of land use. Currently, approximately 36% of the worlds land surface is 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. Some of these changes include altering grazing and mowing practices, encouraging a properly managed burning protocol, and introducing pesticide alternatives for pest management. 

Grazing and Mowing:

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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 a diverse range of pollinators. 
Grazing during the spring, though, may negatively impact pollinator communities. During this time, butterfly larvae are active on host plants and grazing can either eliminate the larvae or reduce the host plants available for those that do survive. 
Other potential negative impacts include the destruction of potential and existing bee nests and the trampling of adult bees by the grazers. Some positive effects include the previously mentioned 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 area. When grazing periods occur, it is generally advised to leave ungrazed areas within or close 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 also 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 non-bloom seasons is recommended. in addition, it is important to cut at higher heights, create less uniform heights across the area, as well as mowing in mosaics. 

Urban Development:

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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. 

Fire:

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Fire is an important role in many native ecosystems, and controlled burns can actually 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, however, burning is highly discouraged. For example, if the area is a small fragmented(broken-up) habitat with little to no adjacent green space available. During a burn in an area such as these, pollinator species run the risk of local extinction 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 burns of any kind would be detrimental. 

Pest Management:

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Pesticide use in green spaces has the most easy to understand ramifications for our native pollinators. Serious impacts are discussed HERE

CASE STUDY

The Rise and Fall of Green-Space in Atlanta

Atlanta 1974

Dark Pink = High Intensity Urban infrastructure

Light Pink = Low Intensity Urban Infrastructure

Atlanta 2005

Dark Pink = High Intensity Urban infrastructure

Light Pink = Low Intensity Urban Infrastructure

Case Overview:

Between 1990 and 2010, the United States census data indicated that 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 every day. 

Direct Effect:

Over a 10 year period, the drastic increase in impervious surfaces 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 supports the habitat, shelter, and food that pollinators need. 

Indirect Effect:

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 a possible local extinction 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. In turn, it is our hope to increase the pathways for pollinators in and across the metro area. This would increase foraging connections and links from one pollinator garden to another!