Road construction can undermine conservation efforts.

Going beyond deforestation statistics in conservation evaluation: How landscape metrics can help us to understand the effects of infrastructure development on habitat integrity.


The impact of roads on protected areas

Figure 1: Road construction in tropical forest areas

Studies show that the construction of new roads is one of the key drivers behind the conversion of natural ecosystems. New roads enable access to formerly inaccessible areas and facilitate the flow of people and goods in and out of previously forested areas. These dynamics can be detrimental to rural development and may pave the way for selective logging and the extraction of rare and valuable wildlife from protected areas. Therefore, the construction of new roads is an established driver of forest degradation, deforestation, and illegal hunting.

There is less consideration, however, to the direct effect that new roads have on the habitats and species in the areas they are built, especially when measuring forest cover loss and/or emission statistics. Because the total surface area of a new road is small compared to other types of land transformations, the construction of a new road might not immediately result in an unusual spike in forest cover loss, even if it cuts through a large forested area. It is, therefore, important to consider that the construction of a road essentially divides a habitat into two different regions, which can have wide-ranging impacts on the socio-environmental wellbeing of a forest and its inhabitants.

Landscape ecology metrics in combination with forest cover loss statistics can capture these types of effects quantitatively, which is what we did in a project evaluation in Vietnam in 2020. Our team utilized tools found in the mapme.forest software Package to account for a wide range of indicators and phenomena occurring with new infrastructure development. This approach allows us to automatically download data from the Global Forest Watch (GFW) datasets and analyze our areas of interest in terms of forest cover loss, CO2 emissions, and most importantly for this evaluation - habitat fragmentation.


Forest fragmentation indicators can uncover the true effect of road construction on habitat integrity

In this evaluation, we analyzed forest cover loss and associated CO2 emissions, as well as habitat fragmentation in three protected areas: Bach Ma National Park, the Sao La Nature Reserve (both in Vietnam), and Xe Sap National Park in Laos. The maps demonstrate the distinctive pattern of forest cover loss in Bach Ma National Park, most of which occurred in 2016.

If our analysis had only looked at gross forest cover loss and its associated CO2 emissions, we would assume that Bach Ma National Park had the least concerning development impacts amongst the three study areas. Interestingly, we are also able to detect a simultaneous spike in forest cover loss related emissions in all three areas in 2016 (see figure below), which might have led us to the (wrong) conclusion, that this phenomenon might be due to an exogenous shock that equally contributed to increased deforestation activities in all three areas.

The landscape division index (shown here on the right) measures whether two randomly selected patches of forest fall within a larger closed forest area. A value of 0 indicates a 100% probability that the selected patch is part of an untouched large forest area. As forest cover loss increases, the landscape division increases towards 1, which indicates a 100% probability the selected patch is in a deforested area. Increased (forest) landscape division has a negative impact on fauna due to habitat encroachment, especially for larger mammals whose habitat often spans over larger areas. Of particular note in this evaluation, was the extreme increase in the landscape division index for Bach Ma in 2016. This rate of increase was difficult to explain given the established local land-use change dynamics in the region (i.e. conversion of natural forest for Acacia plantations). The only reasonable explanation was the division of a larger forest area due to the construction of a major roadway, which we were able to confirm via local newspaper articles. Although these details are technically unrelated to our project activities, we think it is important to identify all stakeholders present in the region to create more policy coherence.

Given the challenges inherent to visiting project sites during a normal evaluation appraisal (and more so during Corona times), relying on a wider range of tools and indicators can help us to understand different parts of a larger story and point us to urgent developments that should be discussed and addressed in the future.


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