March 7, 2014 By Joe Schwartz

ITHACA, N.Y. – By literally looking below the surface and digging up the dirt, Cornell researchers have discovered that a burgeoning deer population forever alters the progression of a forest’s natural future by creating environmental havoc in the soil and disrupting the soil’s natural seed banks.

The study, “Deer Browsing Delays Succession by Altering Aboveground Vegetation and Below g ound Seed Banks,” was published online March 7 in PLOS ONE.

“Deer are slowing down forest succession or natural establishment. In fact, the deer are preventing forests from establishing,” says Anurag Agrawal, Cornell professor of ecology and evolutionary biology, a co-author on the paper.

Deer typically prefer to eat native, woody plants and rebuff invasive species. The study showed that when deer consume native plants, the non-native species are left to flourish, dropping their seeds in the soil.

As forests normally mature, their grasses give way to herbs and shrubs, and then new trees eventually take root. Expanding deer populations in the Northeast, however, stall forest development and promote the growth of thorny thickets of buckthorn, viburnum and multiflora rose bushes. If deer leave the forests alone, such trees as cottonwood, locust and sumac can sprout and grow unimpeded.

The researchers found that the impacts of deer grazing on vegetation were severe and resulted in bare soil and reduced plant biomass, less recruitment of woody species and relatively fewer native species. And the deer’s negative impact on seed banks resulted in significantly decreased overall species richness and relatively more short-lived species of both annual and biennial plants.

Co-author Antonio DiTommaso, Cornell associate professor of weed ecology and management, and research technician Scott Morris gathered soil cores – from both within and outside of fenced “deer exclosures” – and germinated the seed. They found the soil cores from outside of the exclosures contained many more seeds from non-native species.

Deer select forests for their trees but in doing so disrupt forest system growth trajectories, concludes the study.

“It’s obvious that the deer are affecting the above-ground species, but it’s like an iceberg. There are major effects below the soil surface. We are seeing a divergence of seeds contained within the soil from what should be there,” says DiTommaso. “We are not seeing the seeds of woody plants. Instead, we’re seeing an escalation of non-native seed and the virtual elimination of woody plant seeds.”

The multiyear study was conducted on Cornell land near Freese Road in Ithaca, where the deer density is about 39 animals per square kilometer – about 10 times greater than it was before European settlement in the late 1700s.

Theme of the photo contest:
The Tree Timeline
Past-The Storyteller
Present-Here and Now
Future- The Oracle

Check out this photo from Simon Bell.

“I would never have noticed them myself, but Martin Bosch was staring intently up into a maple tree in St. Georges Park in Guelph yesterday. What was he looking at? A mother Eastern screech owl and five babies! Quite amazing.”

To enjoy some more os Simon’s great photography, visit

Photo: Simon Bell

Mycorrhizal partnerships are symbiotic, or, mutually beneficial, relationships between plants and fungi, that take place around plant roots.

Mycorrhrizae  in the soil have been shown to be essential to plant growth by facilitating the uptake of minerals and nutrients by breaking them down into available forms for the trees to use  as well as stimulating fine root development that lengthen the life of the roots.

They can also protect plants from drought, predators (such as nematode worms), and pathogens (micro-organisms that cause disease). Furthermore, in areas polluted by toxic heavy metals, fungi can buffer their plant partners against harm.

A diversity of fungi is desirable, as different fungi specialize in different functions, as mentioned above. One fungal species may be good at taking up particular nutrients, while another will be better at producing enzymes.

Threats to Mycorrhizae
Mycorrhizae can be damaged by soil compaction and disturbance, as well as by the use of certain chemicals, all of which occur in intensive agriculture and landscape maintenance.

Applying large amounts of inorganic fertilizers to young trees, can suppress the development of mycorrhizae. Excess nitrogen, whether from fertilizer use or atmospheric pollution, affects the reproductive parts of the fungus, and so could have long term effects on fungal populations.

Development practices have greatly affected the life in the soil.  Adding a handful of decaying leaves into a hole that a new tree is planted in can inoculate the soil and help bring back the organisms that the trees need so much!

Research into the interactions between old trees and their moss that harbours cyanobacteria, produces a combination that contributes to the long-term health of surrounding trees. They are somehow fertilizing the ecosystems around them.

Without the presence of these old trees, the health of the surrounding younger trees is degraded.

Read more about this  interesting research HERE.


Diana Beresford Kroeger

Diana Beresford-Kroeger, botanist and medical biochemist,  was the keynote speaker at the Ontario Urban Forest Council Conference held in St Catherine’s in autumn 2010.

In her presentation Diane talked of trees as extraordinary, complex species. In our earth system the trees connect us to the sun as they oxygenate the planet. She spoke of the vast tonnage of tri-terpenes that are liberated by the boreal forest like a detergent cleaning the air with natural fungicides and natural antibiotics. They hang onto cloud droplets and regulate the weather of the world.

Diane talked about democracy of the land and how we need a land agreement between the species for care and sharing. And then she detailed specific trees that give massive carbon sequestration and can help us withstand the huge flow of severe weather and UV exposure that climate change is bringing .

If you want to learn more, there are a few copies of her latest book, The Global Forest at the Guelph Public Library. It is a fascinating read. You won’t be disappointed.


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