Nav: Home

Picky pathogens help non-native tree species invade

July 24, 2019

 

Walk into a forest made of only native trees, and you probably notice many different tree species around you, with no one species dominating the ecosystem. Such biodiversity - the variety of life and species in the forest - ensures that each species gets a role to play in the ecosystem, boosting forest health and productivity. However, when non-native trees invade, they form dense groups of a single species of tree. This bucks conventional wisdom because, in theory, pathogens - microscopic disease-causing organisms - should prevent this from happening.

Trees have many natural enemies, such as herbivores and insects that nibble on their leaves. But their main foes are invisible to the naked eye. In older forests especially, fungal pathogens evolve to attack the seedlings of certain tree species and, over time, accumulate in the soils around the adults, hindering the growth of their seeds. Seeds that fall far away from their parent typically survive better. The pathogens thus help dictate where native trees can grow and prevent some species from dominating others.

This effect is part of the Janzen-Connell hypothesis, a widely accepted explanation for the promotion of biodiversity in forests. The theory was developed in the 1970s by ecologists Daniel Janzen and Joseph Connell, who said that species-specific herbivores, pathogens, or other natural enemies make the areas near a tree inhospitable for the survival of its seedlings. If one species becomes too abundant, there will be few safe places for its seedlings to survive, thus promoting the growth of other plant species within one area.

Why, then, do introduced tree species often invade, outcompete, and displace native trees, even those of the same genus? The subject is the focus of a new study published in the Ecological Society of America's journal Ecosphere.

Aleksandra Wróbel, a PhD candidate in the Department of Systematic Zoology at Adam Mickiewicz University in Poland, says that the relationship between native trees and their enemy pathogens is a tightly co-evolved one; so tight, in fact, that pathogens may not be able to recognize or attack even closely-related introduced tree species. "Enemy-release" theory states that because introduced species are new to the ecosystem, they do not have enemies yet in the soil, and their seeds can fall densely and thrive, becoming invasive. This relaxation of the Janzen-Connell effect, says Wróbel, "gives non-native species a big competitive advantage over native species."

To test how the intensity of the effect differs between tree species of a same genus, Wróbel and colleagues use greenhouse and field experiments to study two pairs of invasive and native tree species in Central Europe: boxelder (Acer negundo) vs. Norway maple (Acer platanoides), and Northern red oak (Quercus rubra) vs. pedunculate oak (Quercus robur). They also conduct surveys of natural forests containing populations of all four species to investigate their survival in an uncontrolled environment.

Under controlled conditions, the invasive species of both pairs fare better than their respective native cousins, avoiding attack by soil pathogens; they are released from the Janzen-Connell effect, giving them the survival advantage. However, under natural conditions, one genus pair (Acer) followed the expected pattern, with non-native seedlings escaping pathogen attack, while the other pair (Quercus) did not. Wróbel chalks this up to the complexity of interactions with other plants and animals that tree seedlings experience in the wild.

This study indicates that freedom from disease partially explains why non-native tree species dominate in areas where they are introduced. Improving understanding of the role that plant-soil interactions play in the establishment and spread of invasive plants is critical for developing effective management and control strategies.

"Figuring out why invasive species are able to proliferate so readily in new areas is one of the most important issues in ecology and nature protection," concludes Wróbel, "and the results of our research provide additional insight into the factors responsible for the success of certain non-native species."
-end-
Journal article

Wróbel, Aleksandra, et al. 2019. "Differential impacts of soil microbes on native and co?occurring invasive tree species." Ecosphere. DOI: 10.1002/ecs2.2802

Authors

Aleksandra Wróbel, Rafa Zwolak; Department of Systematic Zoology, Faculty of Biology, Adam Mickiewicz University, Pozna?, Poland

Elizabeth E. Crone , Department of Biology, Tufts University, Medford, Massachusetts, USA

 

Author contact:

Aleksandra Wróbel, wrobel_a1@wp.pl

The Ecological Society of America (ESA), founded in 1915, is the world's largest community of professional ecologists and a trusted source of ecological knowledge, committed to advancing the understanding of life on Earth. The 9,000 member Society publishes fivejournalsand a membership bulletin and broadly shares ecological information through policy, media outreach, and education initiatives. The Society's Annual Meeting attracts 3,000-4,000 attendees and features the most recent advances in ecological science. Visit the ESA website at http://www.esa.org.

Contact: Zoe Gentes, 202-833-8773 ext. 211, zgentes@esa.org">zgentes@esa.org

Ecological Society of America

Related Biodiversity Articles:

About the distribution of biodiversity on our planet
Large open-water fish predators such as tunas or sharks hunt for prey more intensively in the temperate zone than near the equator.
Bargain-hunting for biodiversity
The best bargains for conserving some of the world's most vulnerable salamanders and other vertebrate species can be found in Central Texas and the Appalachians, according to new conservation tools developed at the National Institute for Mathematical and Biological Synthesis (NIMBioS) at the University of Tennessee, Knoxville.
Researchers solve old biodiversity mystery
The underlying cause for why some regions are home to an extremely large number of animal species may be found in the evolutionary adaptations of species, and how they limit their dispersion to specific natural habitats.
Biodiversity offsetting is contentious -- here's an alternative
A new approach to compensate for the impact of development may be an effective alternative to biodiversity offsetting -- and help nations achieve international biodiversity targets.
Biodiversity yields financial returns
Farmers could increase their revenues by increasing biodiversity on their land.
Biodiversity and wind energy
The location and operation of wind energy plants are often in direct conflict with the legal protection of endangered species.
Mapping global biodiversity change
A new study, published in Science, which focuses on mapping biodiversity change in marine and land ecosystems shows that loss of biodiversity is most prevalent in the tropic, with changes in marine ecosystems outpacing those on land.
What if we paid countries to protect biodiversity?
Researchers from Sweden, Germany, Brazil and the USA have developed a financial mechanism to support the protection of the world's natural heritage.
Grassland biodiversity is blowing in the wind
Temperate grasslands are the most endangered but least protected ecosystems on Earth.
The loss of biodiversity comes at a price
A University of Cordoba research team ran the numbers on the impact of forest fires on emblematic species using the fires in Spain's Doñana National Park and Segura mountains in 2017 as examples
More Biodiversity News and Biodiversity Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Teaching For Better Humans 2.0
More than test scores or good grades–what do kids need for the future? This hour, TED speakers explore how to help children grow into better humans, both during and after this time of crisis. Guests include educators Richard Culatta and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

Space
One of the most consistent questions we get at the show is from parents who want to know which episodes are kid-friendly and which aren't. So today, we're releasing a separate feed, Radiolab for Kids. To kick it off, we're rerunning an all-time favorite episode: Space. In the 60's, space exploration was an American obsession. This hour, we chart the path from romance to increasing cynicism. We begin with Ann Druyan, widow of Carl Sagan, with a story about the Voyager expedition, true love, and a golden record that travels through space. And astrophysicist Neil de Grasse Tyson explains the Coepernican Principle, and just how insignificant we are. Support Radiolab today at Radiolab.org/donate.