The First Results  

In the mild coastal climate, on a year blessed with late spring rains, both native seed and mustard were germinating well into the summer.   

Native bunchgrasses, including Nassella pulchra, 
were quickly established from both seed and small containers.  
Photo copyright 2001 by Rick Riefner.  

The objective of the project was not to make individual plants mycorrhizal, but to establish a dense network of mycorrhizal fungi throughout the root zone.  To do so requires vigorous native mycorrhizal hosts, aggressive enough to compete with the weeds while building the network.  The champion species for this purpose turned out to be the short-lived perennial grass Bromus carinatus.  With some weedy characteristics of its own, it was able to take good advantage of the fertile soil and kept pace with weed growth over most of the project.  At the same time, it is a good mycorrhizal host and helped prepare the soil for slower-growing native species.  

Bromus carinatus is shown here in competition with some of the 
weeds that came up from the soil seed bank.  B. carinatus 
proved an able competitor, as long as there was mycorrhizal 
inoculum available in the soil.  Photo copyright 2001 by Rick Riefner.  

We quickly learned which of the pretreatments worked best.  Herbicide was useful but no better than organic matter used to absorb excess nitrogen.  The best results came from mowing the pre-existing mustard and letting it dry in place before imprinting.  Imprinting over live mustard also worked, and surprisingly, enough seed worked down through the thatch to give good germination through the organic layer.  The worst treatment of all was cutting and drying the mustard, then raking the debris off the soil.  Those plots gave vigorous, dense stands of mustard under which the native seedlings stood little chance. 

Mycorrhizal inoculation proved essential for many of the native plant species, but not all.  Counts of seedlings in adjacent inoculated and uninoculated areas showed that

Native Plant Species Vary Widely in Mycorrhizal Dependence

Text and photos not otherwise noted are copyright 2001 by Ted St. John, Ph.D.