Learning Lessons from Invaded Forests

In 1946, North American beavers were introduced to the archipelago of Tierra del Fuego at the tip of South America in an attempt to start an industry based on beaver fur. Although this industry has not thrived, beavers have multiplied enormously. By cutting trees and building dams, they have transformed forests into meadows and also fostered the spread of introduced ground cover plants. Now numbering in the tens of thousands in both Chilean and Argentinian parts of the archipelago, beavers are the target of a binational campaign to prevent them from spreading to the mainland of these two nations. — Invasive Species: What Everyone Should Know by Daniel Simberloff

Beavers in South America are just one example of the series of effects a species can have when it is placed in a new environment. Prior to the arrival of beavers, there were no species in the area that were functionally equivalent. Thus, through their felling of trees and damning of streams, the beavers introduced novel disturbances that have, among other things, aided the spread of non-native plant species. Ecologists call this an invasional meltdown, wherein invasion by one organism aids the invasion of another, making restoration that much more difficult.

Complicated interactions like this are explored by David Wardle and Duane Peltzer in a paper published last month in Biological Invasions. Organisms from all walks of life have been introduced to forests around the world, and while many introductions have had no discernable impact, others have had significant effects both above and below ground.

The authors selected forest ecosystems for their investigation because “the imprint of different invaders on long-lived tree species can often be observed directly,” even when the invading organisms are doing their work below ground. Moreover, a greater understanding of “the causes and consequences of invasions is essential for reliably predicting large-scale and long-term changes” in forest ecosystems. Forests do not regenerate quickly, so protecting them from major disturbances is important. Learning how forests respond to invasions can teach us how best to address the situation when it occurs.

The authors begin by introducing the various groups of organisms that invade forests and the potential impacts they can have. This is summarized in the graphic below. One main takeaway is that the effects of introduced species vary dramatically depending on their specific attributes or traits and where they fall within the food chain. If, like the beaver, a novel trait is introduced, “interactions between the various aboveground and belowground components, and ultimately the functioning of the ecosystem” can be significantly altered.

Wardle, D.A., and D.A. Peltzer. Impacts of invasive biota in forest ecosystems in an aboveground-belowground context. Biological Invasions (2017).  doi:10.1007/s10530-017-1372-x

After highlighting some of the impacts that invasive species can have above and below ground, the authors discuss basic tenets of invasion biology as they relate to forest ecosystems. Certain ecosystems are more vulnerable to invasions than others, and it is important to understand why. One hypothesis is that ecosystems with a high level of species diversity are more resistant to invasion than those with low species diversity. This is called biotic resistance.  When it comes to introduced plants, soil properties and other environmental factors come in to play. One species of plant may be highly invasive in one forested ecosystem, but completely unsuccessful in another. The combination of factors that help determine this are worth further exploration.

When it comes to restoring invaded forests, simply eliminating invasive species is not always enough. Because of the ecological impacts they can have above and below ground, “invader legacy effects” may persist. As the authors write, this requires “additional interventions to reduce or remove [an invader’s] legacy.” Care also has to be taken to avoid secondary invasions, because as one invasive species is removed another can take its place.

Nitrogen-fixing plants (which, as the authors explain, “feature disproportionately in invasive floras”) offer a prime example of invader legacy effects. Introducing them to forest ecosystems that lack plants with nitrogen fixing capabilities “leads to substantially greater inputs of nitrogen … and enhanced soil fertility.” Native organisms – decomposer and producer alike – are affected. Simply removing the nitrogen fixing plants does not at once remove the legacy they have left. Examples include Morella faya invasions of forest understories in Hawaii and invasions by Acacia species in South Africa and beyond.

“It has been shown that co-invasion by earthworms enhances the effects that the invasive nitrogen fixing shrub Morella faya has on nitrogen accretion and cycling in a Hawaiian forest, by enhancing burial of nitrogen-rich litter.” – D.A. Wardle and D.A. Peltzer (2017) – photo credit: wikimedia commons

The authors conclude with a list of “unresolved issues” for future research. A common theme among at least a couple of their issues is the need for observing invasive species and invaded environments over a long period. Impacts of invasive species tend to “vary across both time and space,” and it is important to be able to predict “whether impacts are likely to amplify or dampen over time.” In short, “focus should shift from resolving the effects of individual invasive species to a broader consideration of their longer term ecosystem effects.”

This paper does not introduce new findings, but it is a decent overview of invasion biology and is worth reading if you are interested in familiarizing yourself with some of the general concepts and hypotheses. It’s also open access, which is a plus. One thing that is clear after reading this is that despite our growing awareness of the impacts of invasive species, there is still much to be learned, particularly regarding how best to respond to them.


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Dethroning Industrial Argiculture: The Rise of Agroecology

This is the third in a series of posts reviewing the 17 articles found in the October 2014 Special Issue of American Journal of Botany, Speaking of Food: Connecting Basic and Applied Science.

Think Globally, Research Locally: Paradigms and Place in Agroecological Research by Heather L. Reynolds, Alex A. Smith, and James R. Farmer

Before I get into the review, I have to say that it is too bad this article was not selected as one of the open access articles. For me, it really sums up the reasons why this special issue exists at all, and it reads like a clarion call for more research, promotion, and implementation of science-based sustainable agriculture. If I could reprint the whole thing here I would, because my poor excuse for a review will not suffice. Unfortunately, in order to read this article (and most of the other articles I am reviewing here), you will have to pay, unless you otherwise have access through a personal or institutional subscription.  The open access debate is a can of worms that I won’t open here…just saying I wish more people could read this.

In their introduction, the authors discuss the “basic to applied science continuum.” Scientists who choose to do research that is more on the applied side of the spectrum may find it easier to secure funding (due to “convincing social benefits”), but will also find themselves directly confronted with social issues and values. There can be some discomfort involved in this, and so scientists must carefully determine their level of engagement. However, “neither social nor ecological systems can be understood in isolation,” and instead “must be studied as an integrated social ecological system.” Applied science must be carried out in order to address pressing socio-ecological issues, and so scientists interested in this type of research should know what they’re getting into and must “consider what societal values and paradigms they are supporting with their research.”

Applied science research involving agriculture finds itself intertwined with an economic paradigm that is focused on growth – “increased production and consumption of goods and services as indicated by increasing gross domestic product.” The authors argue that this is not sustainable and that agricultural research should be guided in directions that are more place-based and that keep the finite nature of the planet in mind.

“Since the 1940’s, agriculture has evolved toward an increasingly industrial, corporate, and globalized model, involving large-scale, centralized monoculture production requiring inputs of highly concentrated (fossil) fuel, machinery, water, and synthetic pesticides and fertilizers.” The Green Revolution brought new crop varieties and inputs that helped increase yields significantly, but also had the result of increasing irrigated land by 97%, “the use of nitrogen by 638%, phosphorous fertilizer by 203%, and pesticides by 845% during the latter half of the 20th century.” Industrial agriculture, while highly productive, is a juggernaut that requires incredible amounts of energy, petrochemicals, and water, and despite it’s best efforts, still doesn’t feed the world. Social and political issues are to blame for the food distribution problem; however, in the meantime, industrial agriculture is having profound effects on the environment, “including soil erosion and degradation, biodiversity loss, and water and air pollution on local and global scales.” Coupled with all of the environmnental costs of industrial agriculture are the social costs: “local agroecological knowledge has…been displaced by the  knowledge embodied in industrial inputs and sophisticated farming equipment and techniques,” and widespread industrial agriculture has been linked to increases in cancer, obesity and other human health issues.

photo credit: wikimedia commons

photo credit: wikimedia commons

The expansion of industrial agriculture has largely been driven by the economic paradigm of the United States and other industrialized nations that is focused on growth above all else. This paradigm neglects to acknowledge the “biophysical limits” of planet Earth – “an inescapably finite place, with a constant rate of net solar income and zero inputs of matter beyond the occasional asteroid.” Growth has its limits, and unless those limits are respected, we will find ourselves in dire straits. A warming climate and an increasing level of extinctions are major signs that we have approached the limit. It is time to rethink things.

The question of how to address this dilemma is incredibly complex. The authors of this study offer two broad solutions: reform our economic system and rethink our scientific research efforts. First, the economic problem. A finite planet cannot abide a growth above all else economic approach. The authors propose evolving towards a steady-state economy, in which “the product of population and per capita consumption mildly fluctuates at a scale for which energy and material throughput at current technological capabilities does not strain or exceed the regenerative and assimilative capacity of Earth’s natural capital.” In this economic system, “overdeveloped” countries like the United States will need to find ways to “strategically degrow.”

Strategic degrowth will require dismantling the behemoth that is industrial agriculture. Rethinking applied scientific research will assist in this. Rather than a “one-size-fits-all” approach (an approach that has fueled industrial agriculture for decades), research must evolve towards a “custom-fit” approach in order to address the environmental and social conditions of each individual area. Scientists will have to “go local,” collaborating with farmers, land-owners, and other local experts in order to do “place-based” research that will result in “location-specific expertise.”

Urban Farm in Chicago, Illinois (photo credit: wikimedia commons)

 An urban farm in Chicago, Illinois (photo credit: wikimedia commons)

The authors argue for “community-based participatory research,” which relies on scientists and other professionals collaborating to develop research projects, collect data, and arrive at solutions that will address problems particular to local areas. They offer an example of working with farmers in Indiana to research the use of wild bees for agricultural pollination. The data they collected, while helpful for farmers in other areas, was specific to their area of study and “lent credibility to [their] conclusions” when presented to local audiences.

This is a short but dense article that should be read in its entirety if you have access to it. I will end by offering the authors’ description of sustainable agriculture: “the application of ecological and cultural knowledge to local, decentralized, biodiversity-promoting, closed loop food production for a steady-state economy…the farm system is viewed as an agroecological system….wherein traditional and scientific knowledge of ecological interactions are employed to build system fertility, productivity, and resilience from within, thus promoting food sovereignty and autonomy.”