Hi! I’m a fairly new environmentalist and member of iNaturalist and would appreciate and ideas or advice for how to approach this subject. I am trying to find a way to compare which invasive plants most greatly contribute to a loss of bio-diversity in my town. I have documented close to a hundred species of plants in a small area, and am trying to get a sense of which invasive plants hold the greatest influence in the ecosystem I have chosen.
in the US, the worst invasive weeds are usually listed on federal and state noxious weed lists. here’s the Massachusetts Prohibited Plant List: https://www.mass.gov/service-details/massachusetts-prohibited-plant-list.
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Thanks! I’ll definitely look at that. Do you have any suggestions for comparing multiple plants that are on that list?
Interesting and difficult question.
An idea would be to select one expected effect (a variable linked to loss of biodiversity) and measure it along the time. For example: you may want to consider the idea of “competition with native plants”. For that you can select a number o alien species and measure how fast each one “conquer” new area. It involve measure the area of a “spot” of an invasive species and measure it again (directly or by image comparison) after a time (6 months, for instance). That can give you an idea of the “invasive potential” in terms of competitive displacemt of the native flora. Another “effect” could be the competition for polinators. Invasive species frequently have big and colourful flowers that “attract” polinators, which then spend less time with native flora. If possible, a series of cameras recording polinator visits on different species of invasive plants could provide data on the effectiveness of each species to attrac polinators (sit and count visits is also possible, if cameras are not available, I have done it some time ago). There are other methods as direct measure of biodiversity, for instance, you can visit “patches” of different invasive species (ideally of similar size and other enviroment variables) and obtain a measure of the biodiversity (maybe a bioblitz and count total number of species).
All info on the real effect and behaviour of invasive species is of high interest. Sorry for my bad english and too-much writing 
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I am doing research on exactly this topic. I compare the diversity (including its multiple aspects) of grassland patches invaded by different invasive plants and uninvaded patches. This approach is called space-for-time substitution because I suppose that close sites have a similar background and differ only in the invasion process. Unfortunately, I have no quantitative data from the past and no time to wait for the future. Of course, the best is if you can see how invasive plants transform their environment over time.
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usually, noxious weeds are determined based on some sort of risk assessment. here’s an example risk assessment by USDA for Hydrilla: https://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/downloads/wra/hydrilla-verticillata.pdf, and here’s the generic USDA risk assessment framework: https://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/downloads/wra/wra-guidelines.pdf.
i suggest you collect some data! Find some areas infested by each weed and log all other species you find on or directly under them. Use tags or annotations to sort them, and you can really start to see patterns.
For instance, in Vermont i have observed that Glossy Buckthorn usually has way more native plants growing under it compared with other invasive species such as common buckthorn, reed canary grass, common reed, Japanese knotweed, multiflora rose, etc. Most of my data is in another database not iNat but you can start to see things here:
vs
About the same number of observations but glossy buckthorn has way more native species including some neat wetland understory plants (these were all observed in wetlands)
I can’t definitively say glossy buckthorn should be prioritized less than reed canary grass with invasive management based on this non systematic set of annotations, but i am getting closer to finding the right questions i think. More data will make that clearer.
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