Global cover of forest is well-known to be decreasing at an alarming rate. Assessing the current situation is always liable to leave the assessors bemoaning their state of out-of-datedness!. On 20th March, however, several prominent ecologists released their research on just how threatened and lacking in biodiversity our native woodland is becoming.
70% of the remaining forests are only 1km from the edge of the forest, meaning they must look mightily skinny. Over 5 continents and many different biomes over 35 years, that creates a crazy image of lost bits of habitat, isolated like sorry islands in a sea of human development. The smallest of these pieces of woodland are not alone, as they biodiversity has been reduced everywhere by between 13 and 75%, with increases in all cases as time passes.
Restoration and reconnection with wildlife corridors is urgent to prevent many extinctions such as tigers in India or much smaller species that rely on a tiny area to provide their needs in a habitat. If we wipe out one plant area or one ant, for example, we lose a butterfly species such as the large blue, Phengaris arion.
Using a brand-new high resolution map of global tree cover, the forest border figures were obtained. The Amazon and Congo Basins remain as the only pieces of contiguous forests in the world, despite their fast disappearance. SE Asia, New Guinea and the northern taiga forests are the only others left. The Brazilian Atlantic Forest is an object lesson, being now largely deforested, reduced from having 90% of the trees more than 1km from the forest edge to only 9%.
As fragmentation has a large role in reducing population sizes below any viable level, corridors have become essential for organisms that can actually use them. The edge of a forest is a very dangerous area for predation of all types, with fledgling birds an obvious example. This means bird species can be reduced in numbers so badly that extinction looms over their obvious lack of future breeding success. Fragmentation was shown in the study to cause species richness of most groups of organisms to decrease by between 20 and 75%. Effects could be immediate, or they could become greater over time. Bird species in some areas declined by 50% over either 5 years or 12 years, depending on the habitat fragment size. Arthropod species richness in another area declined by between 26 and 40 % after only 1 year.
As food webs lose members, they over-simplify and the whole ecosystem loses functions such as nutrient cycling or decomposition rates and actually reduces its biomass. New experiments are being used to determine how many more biotic and abiotic factors influence species under these stresses in their habitats. In France the 2011
Metatron assesses habitat isolation and abiotic factors that affect species, while
SAFE in a Borneo rainforest will assess anthropogenic influences such as poaching around an agricultural plantation.
Fragmentation of habitats like forests produces consistently strong effects on the species within them. We cannot state how important the research here is to maintain the earth as a set of valid ecosystems. Nick M Haddad of North Carolina State University, US, and his many eminent colleagues produced this paper as Habitat fragmentation and its lasting impact on Earth’s ecosystems. From trees to climate change, we also have a library of extensive studies on the topic of rainforest here.