ALERT is achieving a new milestone today by hosting its first scientific debate. This focuses on the fate and condition of the world's vast boreal forests.
The debate arose over a recent paper led by Nick Haddad and colleagues (of which ALERT members Tom Lovejoy and Bill Laurance were coauthors). Haddad and colleagues asserted in their paper -- and also conspicuously in their various press coverage -- that the only two remaining areas of large, intact forest on Earth were the Amazon and Congo Basin.
Boreal forest researcher Jeff Wells takes serious issue with this contention. Below is Wells' complaint, followed by a response from Nick Haddad and another of his coauthors, Joe Sexton, who actually conducted the analyses at the heart of this scientific tussle.
All this is then followed by a synopsis of the debate by boreal forest expert Corey Bradshaw, an ALERT member and professor and senior researcher from the University of Adelaide in Australia. Bradshaw was not involved in either study.
THE COMPLAINT BY JEFF WELLS
The paper “Habitat fragmentation and its lasting impact on Earth’s ecosystems” by Nick Haddad and 23 co-authors published in the 20 March, 2015 issue of Science Advances provided an incredibly important documentation of the many and varied negative impacts to biodiversity that result from human-caused large-scale fragmentation of intact forest habitats. Although there are regional differences in the ways in which fragmentation impacts various biodiversity features, the effects are largely generalizable across the world’s forests.
There are a few regions of the globe where there remains large tracts of forest that are not fragmented by human activities—so-called primary forests. These areas have been mapped in a number of ways over recent decades and all show five large areas of remaining primary forest.
The largest are the North American Boreal Forest, the Siberian Boreal Forest, the Amazon Forest followed by the Congo Basin Forest and the forests of New Guinea and other parts of Indonesia. In fact, some analyses indicate that the world’s largest single intact blocks of forest habitat are now found in the Amazon and in Canada’s Boreal Forest.
Given these facts it was astonishing and disappointing to see in the paper, a map purporting to show forested areas of the globe that are most impacted by fragmentation (defined in the paper as “the division of habitat into smaller and more isolated fragments separated by a matrix of human-transformed land cover”) that portrayed the North American boreal forest as heavily fragmented rather than intact as it truly is. In the paper the authors write that they are presenting “a global analysis of the fragmentation of forest ecosystems, quantifying for the first time the global hotspots of intensive historical fragmentation.”
They go on to say that their analysis showed that “nearly 20% of the world’s remaining forest is within 100 m of an edge — in close proximity to agriculture, urban, or other modified environments…”
Clearly the implication in this statements and others in the paper is that the mapping analyses presented in the paper intends to portray the world’s forest ecosystems that are most impacted by anthropogenic fragmentation. In fact, the map in the paper shockingly indicates that the most northern portions of the Boreal Forest region of North America are among the most fragmented in the world.
Anyone with knowledge of northern and Arctic regions would likely be rather astonished by this portrayal given the incredible lack of human industrial fragmentation in this remote and generally inaccessible part of the world. The inaccurate and misleading map and analysis is the result of a mischaracterized data set that labels natural fires, intact peatland and tundra (far from any human industrial footprint) as the same as clearcuts, areas cleared for agriculture or mines, roads, powerlines and other human caused fragmentation.
While as a scientific issue this mischaracterization is serious enough, more troubling is the fact that media stories about the paper included quotes attributed to the first author like this one in a story in The New Yorker:
“There are really only two big patches of intact forest left on Earth — the Amazon and the Congo — and they shine out like eyes from the center of the map.”
Or this statement in Climate Progress:
“Haddad was surprised by the degree that Boreal forest in Canada and Siberia has already been sliced up.”
These statements are fundamentally incorrect and are a serious blow to conservation initiatives in the massively large, truly intact Boreal Forest region of North America where incredible efforts are underway that are succeeding in achieving some of the world’s largest forest conservation gains.
Canada’s Boreal Forest region (an area of approximately 5.6 million square kilometers) is estimated to contain 25% of the world’s remaining primary forest within its Boreal Forest region, storing a minimum of 208 billion tonnes of carbon, supporting some of the world’s largest populations of northern large mammals including some that undertake the world’s last large-scale annual migrations and hosting 1-3 three billion nesting birds, most of which migrate south to populate temperate and tropical forests.
This vast intact forest region continues to be inhabited by to hundreds of indigenous communities that maintain their cultural traditions including harvesting native fish and wildlife for subsistence.
Over 870,000 square kilometers of new protected areas have been established across Canada’s Boreal Forest region in the last 15 years and the governments of Ontario and Quebec are pursuing conservation visions that together would strictly protect (IUCN categories I-IV) an additional 858,000 square kilometers of intact, primary forest.
In the Northwest Territories, over 425,000 square kilometers of new protected areas and interim protected areas are the result of leadership of indigenous governments that have developed sophisticated land-use plans combining traditional knowledge and Western science approaches.
What is particularly tragic is the portrayal of North America's Boreal Forest as one of the parts of the world that is most highly fragmented by human industrial activities. Scientists and conservationists working in the world's last wildernesses should become more familiar with the threats across ecosystems and regions, in order to accurately portray reality on the ground. This will allow us to protect these ecosystems while there is still time to do so.
THE RESPONSE BY NICK HADDAD AND JOE SEXTON
Dr. Wells’ comments regarding the ecological importance of boreal forests are valuable. The boreal forest houses enormous stocks of carbon; is the origin of many major rivers transporting nutrients to and from the Arctic Ocean; and its trophic system provides essential ecosystem services to human communities. Dr. Wells confirms what is shown in our Figure 1 when pointing out that the boreal forest is one of the greatest remaining expanses of forest on Earth.
We agree with Dr. Wells’ assertion of the conservation value of boreal forest, and our global forest analysis in no way contradicts it. Compared to temperate and tropical forests, the boreal forest is much less impacted by human land-use change.
Whereas the forests of temperate and tropical biomes (except the interior forests of the Amazon and Congo Basins) are heavily fragmented by human land use, edges of the boreal forest are primarily natural. Boreal-forest edges arise predominantly from climatological and edaphic features (i.e., the taiga-tundra ecotone), from hydrological features (the prevalence of rivers and small water bodies), and from acute disturbances such as fires and insect outbreaks (see a recent comparison of natural and human created edge effects in boreal forest).
Whereas logging impacts some regions — including much of British Columbia and Scandinavi— these areas are a comparatively small portion of the total area. Yet even this distinction is increasingly eroded by human impacts, as recent fires in the Siberian boreal forest have been found to be largely human in origin.
It is currently impossible to discriminate natural from human-induced edges, and so our global analysis did not attempt to do so. This contrasts with our experimental analyses which comprise the bulk of our paper, and which are focused on effects of human-caused fragmentation.
In retrospect, we should have emphasized this distinction; we regret the confusion it created. Our Figure 1 does not “portray the world’s forest ecosystems that are most impacted by anthropogenic fragmentation,” (Wells’ assertion) but instead simply maps globally the distance of each forest pixel to the forest’s edge. Regardless, Wells’ assertion that the boreal forest is not fragmented raises an important distinction between natural and human-created edges.
Many of the effects of natural and anthropogenic fragmentation are identical — sunlight and wind penetrate a forest edge regardless of its origin. However, many edge effects — including species invasions, especially by species associated with humans — are not.
As is often the case with the conveyance of scientific findings to the public, the popular media focuses on one or two key points and disregards complexities. The primary objective of our paper was to synthesize long-term experiments documenting the effects of habitat fragmentation. The spatial analysis of forests was included to alert our audience to its global footprint, whether natural or anthropogenic.
Given one figure and two short paragraphs, we could only portray this complexity from one aspect — namely habitat edges. The popular media focused on the Amazon and the Congo forests, the two areas with the least areas of edge, but did not cover the distinction between natural and anthropogenic disturbance.
We share Dr. Wells’ eagerness to overcome the current technical inability to discriminate natural from human-induced vegetation change in the satellite record. We and a large community of researchers are working on precisely this problem. We look forward to specifying the agency of habitat fragmentation in the years to come.
To reiterate, we agree with Dr. Wells about the great need to conserve boreal forest. We are at the same time pleased that Dr. Wells recognizes our study’s central finding: that human-induced habitat fragmentation threatens forests across the globe, leading to long-term decline in the diversity and function of ecosystems.
Long-term experiments and global analysis of the extent, pattern, and dynamics of forest change will continue to advance understanding of the impact of and conservation prospects for landscapes fragmented by people.
A PERSPECTIVE FROM AN INDEPENDENT EXPERT, COREY BRADSHAW
Missing the forest despite its trees
Despite its immense size, there is little doubt that the ugly second cousin of forest conservation is the boreal region covering much of Alaska, Canada, Fennoscandia, and Russia. Indeed, extending some 1.4 billion hectares, of which well over 60% is found in Russia alone, the entirety of the boreal forest is more than double the area of the Amazon forest.
Yet despite this massive expanse, the impressive biota it shelters, and its important contribution to the global carbon, nitrogen and oxygen cycles, the boreal is an oft-overlooked region in terms of global conservation priorities and possibilities.
The exchange between Haddad & Sexton and Wells regarding the former researchers’ recent paper highlights this problem, of which even many expert ecologists are often only vaguely aware. Wells takes particular issue with Haddad and colleagues’ assertion that the boreal forest is highly fragmented, claiming to the contrary that the (North America) boreal forest is “… truly intact … ”. While Haddad and Sexton respond that they did not differentiate between ‘natural’ and human-caused fragmentation, my view is that the exchange misses some important concerns about the state of the boreal forest.
Wells correctly points out that the boreal zone in North America is “massive”, but can his other claim -- that it is “truly intact” -- stand up to scrutiny? Citing one of my own papers from 2009 to demonstrate (correctly) that the boreal forest of North America holds a stunning array of species, Wells neglects to highlight that in that same paper we also identified the extensive, artificial fragmentation that has occurred there and in other parts of the boreal zone over the last few decades.
For example, we showed clearly that only 44% of the entire biome is considered to be ‘intact’, defining the term precisely as “areas over 500 square kilometers, internally undivided by infrastructure (e.g., roads) and with linear dimensions greater than 10 kilometers”.
Satellite imagery has also confirmed that between 2000 and 2005, the boreal biome experienced the largest area of gross forest cover loss compared to any other. Despite recent evidence that so-called edge effects (characteristics of a disturbed matrix that penetrate some distance into habitat fragments) are probably of a smaller spatial magnitude in boreal compared to other biomes, it is disingenuous to claim that North America’s boreal forests are “truly intact”.
Wells' perspective also ignores the intense historical and current fragmentation to the largest boreal forest region in Russia. Between 1988 and 1993, Russia lost an average of 1.1 million hectares of forest per year due principally to logging. An increase in fire and insect outbreaks due to direct (fire) and indirect (climate-driven insect outbreaks) human pressures has eroded the area even further.
Add these observations to mounting evidence that the boreal forest has already or is about to become a net carbon source due to direct (logging, fire) and indirect (climate change, insect outbreaks) human influences, and it is counter-productive in any conservation sense to purport that the boreal zone is anything but a highly modified and increasingly disturbed biome.
I can understand that anyone used to the images of forest devastation from South East Asia, the Amazon, or many parts of Central Africa might be convinced that the boreal forest is comparatively intact -- for it is indeed relatively more contiguous. However, the extent of the boreal fracturing can be easily missed if not observed from broader spatial scales.
From my own personal experience in northern Alberta over 20 years ago, the sight of a vast expanses of boreal forest criss-crossed with seismic exploration lines and clearcuts from logging testify viscerally to our capacity to modify even the seemingly infinite spans of remote boreal wilderness. While the boreal forest might not have the same human population densities or experience the same degree of legal and illegal forest conversion as the tropics, it is nonetheless a highly and increasingly stressed ecosystem.
Fortunately, we still do have the opportunity to limit the worst ravages that deforestation, climate change and fire could wreak there, but we have to get a lot more serious about measuring, recognizing, and limiting the damage that we as a society seem so desperate to render.