Habitat Fragmentation

Michael Vandeman, Ph.D.

April 11, 2024

What’s the very first thing that you learn about wild animals, as a child? If you try to approach them, they run (fly, swim, slither, etc.) away: wild animals don’t like being around humans!

Now look at the East Bay Regional Park District’s plans for the future: master_plan_2013_final.pdf (ebparks.org). Look at page 163 – the next-to-the-last page. Every square inch of the map is crisscrossed with existing or planned trails. So where are the wildlife supposed to live?!

Now look at the maps of the parks (Maps | East Bay Parks (ebparks.org)). With only one exception (I forget which park), there is no place in the parks that is more than a quarter mile from a trail (in one park, the figure is one half mile). This is called "habitat fragmentation". So I repeat: Where are the wildlife supposed to live?! We know that wild animals are aware of the presence of humans. Per Ed Grumbine in Ghost Bears, a grizzly can hear a human from a mile away, and smell one from five miles away. And other animals no doubt have similar capabilities.

I’ve been doing habitat restoration in Claremont Canyon Regional Preserve for thousands of hours over the last decade. In all of that time, I have seen one deer -- a fawn that probably wasn’t very familiar with humans. The parks should be full of deer!

Open any textbook on conservation biology (you can find them in the Marian Koshland Bioscience, Natural Resources & Public Health Library on the University of California Berkeley campus; you can read them in the library, even if you don't have a library card and can’t check them out). Read the section on habitat fragmentation. Habitat fragmentation makes the habitat unusable or less usable, even if it isn't entirely destroyed. Building roads or trails (a trail is just a narrow road) fragments habitat. Some animals cannot or don't want to cross a road (or trail), even if they are physically capable of doing so, due to fear of being visible to their predators. This is also why it's important to build wildlife crossings across our roads and highways.

Mountain bikers want to build a "flow trail" in Wildcat Canyon Regional Park, just so they can have a few cheap thrills (which they can already have in any bike park or many existing roads). They don’t think the damage to the park would be significant. But habitat fragmentation is always significant – especially when there is so little habitat left.

The world's wildlife habitat, large as it is, is still finite (you can learn about that in the mathematics library). If we continue endless trail-building, eventually there will be none left, and the wildlife that depended on it will be extinct. So at some point, we need to stop building trails. Why not now? Isn't that what the Half Earth and 30x30 projects are about? Their purpose is to protect more habitat than is already protected. Building trails destroys and fragments habitat, which is the opposite!

And what does "protect" mean? Does designating a piece of land a "park" protect the habitat it contains? Not if the park management -- such as the East Bay Regional Park District -- considers its mission to be filling it with humans. Or allowing invasive non-native plants to take over the park, as is the case with most of the East Bay Regional Parks….