Habitat fragmentation is an important environmental problem that affects wildlife habitats. It can be caused by natural processes such as flooding or lava flows, or by human activity such as agriculture and mining.
The effects of habitat fragmentation on biodiversity are varied and complicated. Some studies focus on direct or population-level welfare effects, while others focus on evolutionary impacts.
While the relationship between biodiversity and ecosystem functioning (BEF) has been a central topic in ecology for more than 20 years, it is poorly understood how habitat fragmentation alters the BEF relationship. To better understand the link between biodiversity and BEF, we conducted a review of the literature and developed a framework to analyze how habitat fragmentation affects BEF from a landscape perspective.
Long-term experimental studies spanning multiple biomes and scales on five continents reveal that habitat fragmentation reduces biodiversity by 13 to 75% and impairs key ecosystem functions by decreasing biomass and altering nutrient cycles. These results suggest that the need for conservation and restoration measures is urgent to preserve and maintain biodiversity.
Our results also highlight the importance of examining how different levels and types of fragmentation influence ecosystems, ecological flows among fragments, and local ecosystem function. This research should combine experiments, observational studies, air- and space-borne imaging, and modeling to identify locally optimal levels and arrangements of habitat for ecosystems at all spatial scales and to guide conservation actions to mitigate the negative impacts of fragmentation.
The effect of fragmentation on species richness and biodiversity depends on the size of the fragment, its isolation, and its connectivity with other landscape patches. We tested the effect of these three factors on BEF through a pattern-process-scale approach in landscape ecology, which enables us to consider the relationships between biodiversity, environmental conditions, and both.
We used a set of terrestrial long-term experiments, each designed to manipulate specific components of fragmentation–habitat size, isolation, and connectivity–while controlling for confounding factors such as the amount of habitat lost across a landscape. These experiments were performed in several biomes and spanned 35 years.
Initially, experiments were designed to manipulate fragment size and isolate habitat within the same patch (e.g., reducing fragment area or increasing edge isolation). Subsequent experiments manipulated both fragment size and isolation and tested the effects of habitat connectivity through structural corridors.
In these experiments, fragments ranged in size from 0.2 to 3.5 km2, matching the average distance to the forest edge found in more than half of forests worldwide. Fragment sizes were chosen to mimic the effects of fragments that result from anthropogenic activities, such as road construction, forest management, and harvesting.
The experiments were designed to test how changing fragment size, isolation, and connectivity affected ecosystem functions such as nutrient cycling and biomass growth. They also tested the effect of edge influences on vegetation and the effects of changes in the size of the fragments on species persistence, immigration, and migration patterns.
The effects of fragmentation were strongest in the smallest and most isolated patches. These effects increased with time, as the patch size decreased and habitat isolation increased. Our findings suggest that the need for landscape conservation and restoration is urgent to protect biodiversity, maintain ecosystem functions, and reduce extinction rates.