he never-ending war against non-native weeds on the Irvine Ranch Land Reserve is a curious blend of old-fashioned footwork and computer technology.

The footwork is done mostly by Melissa Ervin, a field ecologist with The Nature Conservancy. She spends a great deal of time walking/hiking the reserve, meticulously documenting locations, varieties and densities of problematic weeds. The conservancy monitors more than 40 weed varieties in all, but pays special attention to artichoke thistle and veldt grass because of their pervasiveness and the threat they pose to entire habitats.

Asked how many miles she's logged since she started making her foot patrols in 1998, Melissa laughs, shakes her head and says, "It's a lot of land..."

The data she collects is fed into a computer-based Geographic Information System (GIS) maintained by the County of Orange for the Nature Reserve of Orange County. Using the GIS, county and Nature Conservancy staff produce maps with color-coded overlays that precisely pinpoint where specific weed varieties are growing, which habitat they're invading, and what percent of the area they're consuming. This detailed information enables the conservancy and the Nature Reserve of Orange County to prioritize weed-abatement efforts across the entire Irvine Ranch Land Reserve.

"It's important to control invasive weeds, because it all gets back to preserving what we've got here," Melissa says. Left unchecked, weeds can negatively alter sensitive habitats by "displacing native plants, insects, lizards and small mammals. Our native habitats just can't tolerate some of these weeds."