UC IPM Home
Develop a model procedure for risk assessment to prioritize eradication and control efforts.
Measure how invasive woody species effect the light environment by relating canopy openness and leaf area index to basal area, density, and age as a measure of their relative effects.
Measure how invasive woody species affect the edaphic environment by comparing soil moisture, nutrient dynamics and nutrient pools in invaded versus comparable uninvaded habitats.
Experimentally separate invasive effects on aboveground versus belowground environment by the use of a native phytometer and rank the species in terms of their relative competitive performance.
Compare plant community composition and structure in invaded versus comparable uninvaded habitats.
Plants propagated as cuttings of the native Mimulus aurantiacus (monkeyflower) were used as a phytometer to assess the impact of exotic woody species with lowest canopy openness—Ailanthus altissima and Ficus carica. All 40 plants under Ficus carica died and only 12% of plants under Ailanthus altissima survived the whole growing season. Surprisingly, both survival and relative growth rate of survivors were significantly higher in a parallel artificial shading experiment where light intensity was similar to Ailanthus understory. Only 5% of control plants in a semiopen natural environment died.
We compiled a list of invasive exotic woody species and their related noninvasive (or much less invasive) exotic woody species commonly planted in California for use in germination trials and the seedling growth study. Germination of untreated seeds of invasive and less invasive woody species in the phylogenetically related pairs exhibited a complex pattern. Only five of eight pairs of invasive species germinated faster consistently under both light and dark conditions. The growth study provided clearer results. Invasive species had significantly higher seedling relative growth rates (RGR) than phylogenetically related less invasive species. Seedling RGR may be used as a predictor of invasive species and also to test horticultural species for promotion as use as alternatives to invasive species.
We finished harvesting the plants from the Acacia RGR study of 11 species (nine of which are naturalized in California) under three watering regimes, but we are still analyzing the data.
After extensive consulting of nursery catalogues and discussions with land managers, master gardeners, and other experts, we compiled a list of invasive exotic woody species and their related non-invasive (or much less invasive) exotic woody species commonly planted in California for use in our seedling growth study and germination trials. All exotic woody species included in our original proposal will be used in this experiment. We completed the first harvest of all plants and will soon analyze the data. These data should help managers choose alternative horticultural species instead of known invasives and potentially invasive species. Interestingly, it is not always the invasive species that has higher germinability.
By comparing the mean canopy openness of tree and shrub species, we have developed a tool to rank them according to their relative impact on the light environment. Additionally, we have found that a useful tool for ranking tree species is to compare the slopes of canopy openness versus total basal area.
The soil environment for the two invasive nitrogen-fixers, Robinia pseudoacacia and Cytisus, indicates there are significant differences between invaded and non-invaded sites. The soil under Cytisus had significantly lower phosphorus, and moderately significantly higher total nitrogen compared with native soil. The soil under Robinia did not differ in phosphorus or total nitrogen, but had significantly higher organic matter and organic carbon compared to native soil.
When stands could not be located, light measurements were taken for smaller groups of individuals, including Arundo donax and Ficus carica. Preliminary results indicate that F. carica and Rubus armeniacus have very high levels of shading, whereas Robinia pseudoacacia and Ailanthus altissma have the lowest levels of shading. The remaining species have intermediate shading.
A good deal of time was spent searching for sites of invasion either from literature that indicated the location, or through correspondence with various organizations and local botanists. For example, Ficus carica was said to be extensively invading the Dye Creek Preserve. However, only a few trees in isolation were located. Additionally, Sapium sebiferum and Sesbania punicea were said to be invading the American River Parkway, but with a local expert we could only locate individuals scattered among the vegetation. Currently, we are researching the use of fisheye photography for tree and shrub canopy light measurements as our data indicate that plant canopy analyzers allow for a very short period of time to take the measurements without error.
Top of page
Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright ©
The Regents of the University of California. All rights reserved.