Do Eucalyptus trees engage in unfair competetion?

We've already discussed at length the controversy about extrmely successful exotics like Eucalyptus trees. But if you're committed to living with these down-under vegetables, or if you just have no real choice in the matter (they're on the neighbor's property, removal would cost too much, you need the shade as the climate shifts, you actually like them, etc.), what can you do to landscape under them.

A 2007 conversation over at GardenWeb does a pretty good job with the problem. Starting with a post that ponders the widely-held belief that "something" exuded into the soil by Eucalypti kills off competing plants, respondents weigh in with varying degrees of civility (ah, the Internets!) to arrive at some convincing approaches to the problem.
 
First off, that the Eucalyptus is in fact significantly allelopathic seems well-documented. See below for a sampling of papers on the subject.

In addition to engaging in chemical warfare, many species of Eucalyptus have other bad habits.  

While not necessarily phreatophytic, these trees can suck lots of water and nutrients from the surrounding soil ... so much so that new plants have a hard time competing.

Some species (notably Eucalpytus globulus) cast dense shade that can be troublesome for many popular ornamentals and food-bearing plants.

Finally, the shear biomass of a large Euc can mean great quantities of dropped leaves, lost branches, and bark peels that can bury or overwhelm lesser organisms.

What all this suggests is that under Eucs tough, drought-resistant, and shade-resistant plants and shrubs are probably your best best.  In addition, keeping the area clear of Euc droppings may help.

While your results may vary, some folks clam the following choices may fare well under and around Eucs.  Those marked "+" are California natives.  Many of the others listed here are moderately to highly invasive ... which may only make matters worse.  Choose wisely!

Large Shrubs, Small Trees —

Acacia longifolia SYDNEY WATTLE

+Arctostaphylos sp. MANZANITA

Callistemon citrinus LEMON BOTTLEBRUSH

Cotoneaster COTONEASTER

Escallonia ESCALLONIA

+Heteromeles arbutifolia TOYON

Melaleuca nesophila PINK MELALEUCA

Myoporum laetum COAST SANDALWOOD

+Myrica californica PACIFIC WAX MYRTLE

Nerium oleander OLEANDER

Pittosporum undulatum VICTORIAN BOX

+Rhamnus californica COFFEEBERRY

Xylosma congestum SHINEY XYOLOSMA

Medium Shrubs —

Abelia x grandiflora ABELIA

+Arctostaphylos MANZANITA 

Cistus ROCKROSES

Correa AUSTRALIAN FUCHSIAS

Cotoneaster COTONEASTER

Escallonia ESCALLONIA

Fatsia japonica JAPANESE ARALIA

Galvesia speciosa ISLAND SNAPDRAGON

Juniperus JUNIPERS

+Mahonia aquifolium OREGON GRAPE

+Mahonia nevinii NEVIN'S BARBERRY

+Mahonia pinnata Shinyleaf Mahonia/ California Barberry 

Nandina domestica HEAVENLY BAMBOO

Nerium oleander OLEANDER

Pittosporum tobira TOBIRA

Rhaphiolepis umbellata INDIAN HAWTHORNE

Ribes sanguineum glutinosum PINK-FLOWERING CURRANT

Rosmarinus officinalis ROSEMARY

Viburnum tinus LAURUSTINUS

Westringia COAST ROSEMARY

Small Shrubs —

Cistus ROCKROSE

Correa AUSTRALIAN FUCHSIA

Escallonia ESCALLONIA

+Mimulus aurantiacus and hybrids BUSH MONKYFLOWER

Nandina domestica HEAVENLY BAMBOO

Pittosporum tobira sp. Wheeler's Dwarf DWARF TOBIRA

Rhaphiolepis umbellata INDIAN HAWTHORNE

Sollya heterophylla AUSTRALIAN BLUEBELL CREEPER

Large Perennials —

Acanthus mollis BEAR'S BREECH

Dietes vegeta FORTNIGHT LILY

Elymus condensatus BLUE WILDRYE

Phormium tenax NEW ZEALAND FLAX

Small to Medium Perennials —

Agapanthus LILY-OF-THE-NILE

Aristea ecklonii BLUE STAR IRIS

Asparagus (many) ASPARAGUS "FERN"

Bergenia cordifolia PIG'S SQUEAK

Clivia miniata KAFFIR LILY

Dianella tasmanica FLAX LILY

Helleborus lividus corsicus CORSICAN HELLEBORE

Hemerocallis DAYLILIES

Heuchera maxima CORAL BELLS

Liriope LILY TURF

Muhlenbergia rigens DEER GRASS

Nephrolepis cordifolia SOUTHERN SWORD FERN

Pelargonium GERANIUMS

Penstemon BEARDTONGUES

Phormium tenax (dwarf cultivars) NEW ZEALAND FLAX

Ground Covers —

Aptenia cordifolia RED APPLE

+Arctostaphylos TRAILING MANZANITA

Coprosma kirkii TRAILING COPROSMA

Cotoneaster TRAILING COTONEASTERS

Duchesnea indica MOCK STRAWBERRY

Hedera IVIES

Juniperus TRAILING JUNIPERS

+Mahonia repens CREEPING BARBERRY

Myoporum parvifolium TRAILING SANDALWOOD

Ophiopogon japonicus MONDO GRASS

Vinca major TRAILING PERIWINKLE

Vines —

Distictis TRUMPET VINES

x Fatshedera lizei BOTANICAL WONDER

Hardenbergia violacea WINTER WISTERIA

Hedges/Screens —

Acacia longifolia SYDNEY WATTLE

Callistemon citrinus LEMON BOTTLEBRUSH

Hakea suaveolens SWEET HAKEA

Juniperus JUNIPER

Ligustrum japonicum JAPANESE PRIVET

Myoporum laetum COAST SANDALWOOD

+Myrica californica PACIFIC WAX MYRTLE

Nerium oleander OLEANDER

Pittosporum eugenioides WAVY-LEAF PITTOSPORUM

Pittosporum tobira TOBIRA

Prunus ilicifolia HOLLYLEAF CHERRY

Rosmarinus officinalis ROSEMARY

Viburnum tinus LAURUSTINUS

Westringia COAST ROSEMARY

Xylosma congestum SHINEY XYLOSMA

Well, there you have it.  We'll update this post as we experiment with these ideas.  Good luck, and good botonizing.

 
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Papers supporting the proposition that the Eucalyptus is significantly allelopathic: Allelopathy: How Plants Suppress Other Plants by James J. Ferguson, professor, Bala Rathinasabapathi, associate professor, Horticultural Sciences Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida at Gainesville.

Pulmonate gastropod species composition inside and outside eucalyptus forests by Michael J. WalGren and Lisa E. Andreano, California Department of Parks and Recreation, Morro Bay State Park, 1 Lower State Park Road, Morro Bay, CA.

FINAL LAND MANAGEMENTPLAN BURTON MESA ECOLOGICAL RESERVE, State of California, DEPARTMENT OF FISH AND GAME.