Evaluation Sourcebook (.pdf) - School of Natural Resources and ...

THREATSEcological | Management | Social | Understanding or Attitudes | OrganizationalINVASIVE AND OVERABUNDANT SPECIESInvasive species are a major threat to biodiversity. By out-competing or directly preyingupon native species, they can quickly dominate a previously species-rich area. Trackinginvasive species can be a powerful way of assessing progress toward ecological integrity.In addition to tracking the threat of invasives themselves, it is important to assess changesin the sources of invasive species (nurseries, ballast water, etc.) and the conditions (naturaland human disturbances) that make systems more vulnerable to invasion.Invasive = “A species that is non-native (or alien) to the ecosystem under consideration andwhose introduction causes, or is likely to cause, economic or environmental harm or harm tohuman health” (The National Invasive Species Council). Note that native species can also behavelike an invasive, such as over-abundant deer or algae populations.Introduced = A species that is not native (did not evolve there) but intentionally orunintentionally brought there; also called alien, non-indigenous, or exotic. Introduced species arenot always invasive, either because they are not deemed a threat and/or they do not spread well,such as some crops and ornamentals.Weed = A plant growing where it is not wanted. May or may not be introduced. Noxious weed isa term used for weeds that are particularly difficult to manage.Pest = An insect, weed, plant pathogen, bird, mammal or other organism that is deemedproblematic, usually in high numbers. May or may not be introduced.Sample evaluation questions and indicatorsX What is the extent, scope or severity of invasion?Are we minimizing the direct impact of invasive species? Percent of species in a community orguild that are non-nativeRange of the invasive (how large anarea it occurs in)Rate of increase in rangeAbundance (estimate of number ofindividuals or biomass per area)Per-capita or per-biomass effect of theinvasive species in terms ofchanges in:Behavior of native speciesPopulation size or growthrate of native speciesNative species diversityNutrient or water availabilityFrequency or intensity offiresCompared to What?You can assess the scope or intensityof an invasive threat and understandwhat is causing it by comparing thenumber or type of invasives:• In disturbed (near trails,construction, etc.) vs.undisturbed sites• Before vs. after different efforts tocontrol them (fire, mowing, handpruning, etc.)• Over time in the same area• Near vs. far from the assumedsource of invasives (residentialgardens, trails, bait dumpinggrounds, etc.)Overall impact of the invasive species (range x abundance x per-capita effect)Ecosystem Management Initiative 112