Veratrum californicum presence structures Sierra Nevada meadow plant communities

Background/Question/Methods

The subalpine meadows of California’s Sierra Nevada provide an ideal system for the study of plant ecology. Large parts of some meadows are dominated by a vigorous clonal plant, Veratrum californicum (Liliaceae)-commonly called Corn lily. The toxics produced by the plant make it resistant to insect predation—only phloem feeders and a single species of sawfly (Rhadinoceraea aldrichi) feed on it. Sierra Nevada meadows cover less than ten percent of the Sierra, yet their importance in maintaining biodiversity is much greater.  They are hotspots of floristic endemism. Sierra Nevada meadows face the threats of conifer encroachment and climate change.

My hypotheses are: 1. The presence of Veratrum limits species richness and cover. 2. The removal of sawfly larvae from Veratrum will increase species cover and richness. 3. Addition of water will increase species cover and richness.

Five experimental blocks were established, each with a representative of the eight treatments (n=40) in one square meter study quadrats. It was a two by four fully factorial experiment. There were two water treatments: a control with no added water and a water addition. The water added treatment consisted of weekly addition of 2 gallons of water to each quadrat. There were four Corn lily treatments:

1.      No Corn lily present.  Here there was no naturally occurring Corn lily.

2.      Cut Corn lily.  We cut the corn lily off at ground level once.

3.      Corn lily- sawfly.  We manually removed sawfly larvae regularly.

4.      Corn lily+ sawfly.  We allowed the sawfly larvae to predate Veratrum.

Results/Conclusions

We found that the presence or absence of Veratrum had a strong effect upon both species richness and total cover.  When Veratrum was present, species richness and cover were lowered.  Where it was cut or was naturally absent both richness and cover increased.   The sawfly treatment had no effect upon either richness or cover.  The water treatment had highly variable species-specific responses.  The results of this study clearly showed Veratrum californicum regulates plant diversity in Sierra Nevada meadows.