Tag: natural history

When the concept of conservation biology was first introduced in the 1970s, it applied to the species that were disappearing due to deforestation in the tropics. Biologists began to realize that species were going extinct as a direct result of human activity. As conservation science evolved over the decades it has become a multidisciplinary melding of population biology and ecology, economics, and sociology. Quite often the decisions about which species and/or habitats should be conserved are based on human exploitation of some resource. Conservation biology, like every other form of science, costs money, and often funding agencies have an implicit or explicit expectation of economic gain from conservation efforts.

There may also be direct conflicts between conservation activities within a habitat or ecosystem. Take, for example, the beaver and the kokanee salmon, two iconic animals of Taylor Creek. I was up at Lake Tahoe this past weekend, finally able to visit Taylor Creek during the spawning season for the salmon.

As I wrote about earlier, the kokanee is a land-locked sockeye salmon (Onchorhynchus nerka) that migrates from Lake Tahoe into Taylor Creek to spawn; it was introduced as a game fish to the Tahoe basin in the 1940s. It has since become a favorite denizen of Taylor Creek and has spawned a festival all of its own.

The kokanee, like other Pacific salmonids, requires cold, clear water to reproduce successfully. This brings it into direct conflict with Taylor Creek’s other iconic animal, the beaver (Castor canadensis). The beaver’s range historically extended into the Sierra Nevada; however, from the late 19th century into the first decades of the 20th century beavers were viewed as pests and systematically exterminated. As biologists began to understand how beavers affect overall riparian ecosystem health, state and federal agencies re-introduced beavers to the Tahoe basin in the 1930s and 1940s. Whether or not you consider beavers to be native to Taylor Creek, there is no disputing that they are there now.

Beavers, of course, are known for the logging and damming activities. They fell trees, strip off the branches, and use the logs to build dams across rivers. This forms a pond of still water above the dam, where the access to the beavers’ lodge is located. Beavers are herbivores, eating the bark and wood of trees in addition to some aquatic plants. They are nocturnal, but although we returned to Taylor Creek at dusk we did not see any. Evidence of their activities was all around. The phrase “busy as a beaver” is very apt; the dam in the photo above is about twice as tall as it was when I was here in August.

The conflict between the kokanee salmon and the beavers arises because these animals live in the same place but have different requirements for water flow. As I mentioned above, the salmon need cold, clear water. Their eggs will suffocate and die if water temperature is too high, because warm water holds less dissolved oxygen than cold water. Flowing water also helps guide the returning adults to their spawning grounds. Beavers, on the other hand, take active measures to stop or severely restrict flow in the creek. The pond that forms above a beaver dam is very calm and the bottom becomes silty or muddy, the exact opposite of what the salmon need.

Balancing the conservation needs of these popular animals has been a challenge at Taylor Creek. Do you promote the non-native salmon by destroying beaver dams? Or let the beavers do their thing, at the probable expense of the salmon? How much of the decision is due to the fact that beavers are probably native to the Tahoe basin, while the kokanee are undeniably not? And what do Tahoe’s human residents and visitors want more, salmon or beavers?

This year, the strategy has been to leave the dams, but install pipes running through them so that water continues to flow. However, you can see from the photo above that the dam is still holding back about half a vertical meter of water. Plus, as of now no salmon have made it up past the dam; rangers have been seining adult salmon from the creek below the dam and putting them into the stream profile chamber so visitors can see them. Perhaps the salmon are able to spawn in the creek below the dam.

The ecosystem of the Tahoe watershed has been severely affected by the introduction of non-native species. Lake trout, brook trout, rainbow trout, largemouth bass, bluegills, and even goldfish have been released (deliberately or inadvertently) into the lake, and have extirpated the Lahontan cutthroat trout (Oncorhynchus clarki henshawi), the only native salmonid in either Lake Tahoe or Fallen Leaf Lake. The kokanee salmon also falls into this category, and likely competes with the Lahontan cutthroats for food. Recent attempts to re-introduce the Lahontan cutthroat trout have had mixed success. Very interestingly, it appears that the Lahontan cutthroat can move back and forth across beaver dams while the kokanee cannot. Co-evolution, anyone? It seems clear to me that the Lahontan cutthroat trout, which after all shares a long ecological relationship with beavers, is the salmonid that is best adapted for the Taylor Creek ecosystem. As charismatic as the kokanee salmon is, from a biological perspective it really doesn’t belong in Taylor Creek. Perhaps one easy way to restore this ecosystem to a more natural state is to stop removing and damaging beaver dams, and let the kokanee go extinct.

Remember how I said that economics plays a part in conservation? There are several charter fishing companies at Lake Tahoe, all of which have an economic interest in the maintenance of several introduced species in the lake. So in addition to balancing the ecological needs of kokanee and beavers in Taylor Creek, conservation efforts must also address the economic needs of local businesses. These are challenges that we will continue to face all over the planet if we want to live more harmoniously with the natural world.

Mediterranean climates, such as the one that much of California experiences, are characterized by two distinct seasons: a mild, moderately wet season and a warm/hot dry season. In most of the state the majority of precipitation falls between Thanksgiving and Memorial Day, with very little in the other months. At this time of year the dry season is in full swing. I’ve heard of a few reasons why California is called the Golden State: (1) the Gold Rush that began in 1848; (2) the carpets of California poppies that blanket the state in the spring; and (3) the drying up of the summer grasses, which covers much of the state in a golden mantle dotted with oak trees.

We are definitely in the golden season now. We had a good, colorful spring with a banner crop of wildflowers, thanks to the El Niño rains, and it was green well into July. Given the drought, we hadn’t seen that much green in years. But now the annual vegetation has dried out and most of the state is on high alert for wildfire. Fire is a seasonal event in the arid west, and every year several thousand acres burn in California. July and August are the worst months.

This year the most devastating fire in my region of the state is the so-called Soberanes fire burning near Big Sur. As of today the fire has blazed for 23 days, scorched over 71,000 acres, and is 60% contained. Almost 60 homes have been lost and over 400 other structures are threatened, all because some idiot lit an illegal campfire. Up here in Santa Cruz we are over 60 miles away from the fire, but the entire region has been affected by the smoke. Until recently the typical summer onshore winds have blown most of the smoke eastward and while we’ve smelled smoke here we have been spared the worst of it. This satellite photo was taken two days after the fire started:

This morning when I woke up the smell of smoke seemed stronger. It was foggy, enough so that water had condensed on the ground and cars, but instead of smelling like ocean the fog smelled like fire. The sun came out for about an hour in the mid-afternoon, showing a sky that wasn’t as blue as it is when ordinary fog recedes. Air quality is pretty bad so I’ve been staying indoors with windows and doors closed.

Last week I was in the Lake Tahoe region, on a short vacation with my family in South Lake Tahoe. On our first day there we went on a short hike in the Angora Lakes area. Let me tell you, being at altitude makes a concussion headache worse–I had been weaning myself off the ibuprofen, but had to go back on the full doses for the handful of days we were at altitude.

On 27 June 2007 an illegal campfire ignited a wildfire that eventually burned 3100 acres and destroyed more than 300 homes and commercial structures in a populated area near South Lake Tahoe. The Angora fire was fully contained on 2 July and 100% controlled on 10 July.

On the hike out to Angora Lakes you see a few burnt trees off the trail, but don’t really get a feel for the scope of the area affected by the fire. So on our way out of the Tahoe basin we drove through one of the neighborhoods that had burnt. Almost 10 years after the fire now, all of the burnt homes have been either rebuilt or completely torn down. It was interesting to see that the fire’s damage had been spotty: in a neighborhood of mostly older houses there would be a couple scattered here and there that were obviously new construction, likely post-fire rebuilds.

In the years since the fire there has been a lot of restoration work in the Angora region:

It is quite easy to see exactly what the fire did and did not burn.

But even a burnt tree possesses a stark beauty that living trees do not have:

Fire is, or used to be, a significant part of the ecology of much of the western United States. Some plants’ seeds require the heat of fire to germinate, and fire opens up the canopy to allow low-growing plants access to sunlight. When a fire burns through a wilderness region the clock is reset on ecological succession, allowing different species of plants to take their turn thriving in the habitat. We humans experience ecology as a snapshot in time, the duration of our own lifetimes. In the aftermath of a wildfire we have the opportunity to observe the early stages of succession that will likely result, decades down the road, in a mature forest. Even now, only nine years after the fire, it is clear that plants, especially grasses, have been thriving in areas that had been burnt down to charred soil. It will be interesting to watch how succession proceeds over the next several years.