Drought: An insidious stress on wildlife
The University of California’s Agriculture and Natural Resources (UCANR) has developed a series of webinars titled Insights: Water and Drought which feature timely, relevant expertise on water and drought from experts around the University of California system. In this webinar, Greg Giusti, a Cooperative Extension Advisor in Forest and Wildland Ecology in Mendocino County discusses the impact of the drought on wildlife.
“Part of living in California is enjoying the diversity of wildlife that we get to see on a daily basis in urban environments as well as wildland environments,” he said. “The drought and the lack of water affects all organisms, just like it does people, so today is a chance to share some thoughts and give you an opportunity to think about what’s happening out in the natural environment here in the state.”
Not all species respond identically to various stresses, and drought is an insidious stress, he said. “It is somewhat treacherous; it’s somewhat hidden,” he said. “We’re not going to go out and find animals just dying on the street. However, it is a stress factor on these animals that are already in some cases living in a stressful environment.”
Some species, like migratory waterfowl, can be acutely impacted by the drought, he said. He noted that in a couple of months, there will be literally a million birds, waterfowl, shorebirds and the like, coming into California and moving into the Central Valley to spend the winter. “In a normal winter when there’s a lot of water and a lot of flooded fields, those birds are able to disperse over a large area,” he said. “In a drought, all of those birds are going to be crowded into smaller areas … they are susceptible to disease. 100,000-200,000 birds all living in the same water, feeding and disposing of their wastes in that water, and over time, the loss of dilution from rain can cause problems, particularly with avian botulism and avian cholera. In those kinds of situations, we can have acute responses where literally hundreds if not thousands of organisms can die in a very short period of time – a matter of weeks.”
But such dramatic events won’t be what we will see as a result of the drought in most cases, he said. Some species, such as frogs and newts, need water to complete their life cycle, and the longer that the drought continues, the more stress and the more inability that these organisms have on reproducing, he explained. “So what happens is that over time, as nature calls, animals will die, but there will be a lack of recruitment of new animals coming into the population, and over time, 2-3 years, the additive impacts of lack of reproduction can cause local populations to go extinct.”
- Food and water: Different animals and access water in different ways: Large animals like deer need to be able to go drink water like a dog or a cat, while other organisms like mice, can find a dew drop in the morning which will meet their water needs. Oftentimes, many rodents can get the moisture they need from the grasses or the seeds that they are eating.
- Cover: Especially in the middle of the summer where it’s hot and dry, animals simply have to get out of the elements – the sun, the wind, or whatever, he said. Cover is the component that allows animals to stay in the environment 12 months of the year, every day of the week.
- Space: Space refers to how much room an individual species might need, he said, noting that a little deer mouse is going to need less space to find food, water, and cover a mountain lion.
“The behavior of how these animals respond to meeting their basic needs is directly tied to the quality and availability of their habitat,” he said. “It’s a word we hear a lot about and it’s really the basis of what allows animals to live in a particular area.”
The integrity and diversity of the forest are a function of time and space. “The habitat has to work in a certain way to allow a number of animals to live together and to share space,” he said. “The ability of these animals to sustain themselves throughout the year is based on the functions and flows of the habitat.” He explained that there are functions such as soil and water interactions or migratory pathways that allow the animals to live in a particular area or over the course of a landscape. There are flows of water, nutrients, and energy through the system – how the grass gets converted to food and the food gets converted to waste and the waste gets converted back into the soil and the system starts over again. “Functions and flows are very important in how habitat works,” he said.
The structure and composition of the habitat are other important considerations with habitat, he said, explaining that structure refers to the bushes, shrubs, trees, rocks, cliffs, and the different nooks and crannies necessary for different animals to exploit a particular area. “The composition of the habitat – do some trees produce acorns, do some bushes produce berries – these are other elements that an animal can exploit throughout different times of the year,” he said. “For example, deer and squirrels like to eat acorns, but acorns are a seasonal food item. They become available September and October, and by March and April, they are gone. So there has to be other things in the system that allows these animals to find nutrients and to sustain themselves until the next acorn crop.”
All of these things come into play and it allows for what we call a carrying capacity, which is how many kinds of one particular kind of animal can live in one place at one time, and that carrying capacity can change with the concept of succession, he said. “With plant communities, it’s like living in a video, it’s not a snapshot,” he said. “After a fire, for example, the trees are burned, the brush is burned, all the vegetation is close to the ground. It’s called an early seral stage. There are certain animals, many little birds and sparrows that will readily utilize those early seral stages. Deer will because they can reach the food as it’s on the ground. Over time, as that habitat grows and matures, the trees come back, and different kinds of birds are using the tops of the trees, so the different stages of the habitat also describe what wildlife species can exploit it.”
He then presented a picture of a wildland habitat, but noted that habitat can look like anything. “I often joke that suitable habitat for Brewer’s blackbirds is the parking lot of your local supermarket,” said Mr. Giusti. “How many times have you seen blackbirds standing under cars on a hot summer day in the shade (cover); what do they do when they want food, they walk out from underneath the car and they jump up and pick the bugs off of your radiator grill (food); and if they need water, maybe somebody spilled a coke and there are some ice cubes melting or something, so anything can be habitat.”
Some animals have more restrictive habitat requirements, he said. “Certain animals are very narrow in their requirements while other animals, like Brewer’s blackbirds, are very opportunistic. Crows are very opportunistic. They can adapt to any type of habitat.”
A wildland habitat is a mix of different bits and pieces, different nooks and crannies, he said, noting the different elements in the picture: the rock and cliff out cropping, the oaks on the bottom, the conifers on top, and the riparian corridor along the stream. “All of these components, all of these elements are working together to allow an organism to sustain itself throughout the year.”
“When we talk about drought, we’re really talking about weather, but climate is what shaped the vegetation communities in California,” said Mr. Giusti. “When we talk about climate, we’re talking about long term patterns of weather.”
California has a Mediterranean climate which is characterized by dry summers and relatively wet winters, and over the last five and a half million years, it has shaped where both giant sequoias and coastal redwoods are found in California, he explained. He presented a map showing the distribution of coastal redwoods as a narrow band along the coast. “If we look at the distribution of coast redwoods, these organisms are literally hanging on to the edge of the continent. They’ve been pushed to that based on the climate regime that they require. They are an organism that needs fog; they need moisture.”
There are about 70 groves of giant sequoias in the southern Sierras which are found in dark, cool places, he said. “Five and a half million years ago, a different species of sequoia was found in Montana and Wyoming,” he said. “Over the course of millions of years and with the changing climates, and as climate as become warmer and drier, these organisms have retreated back to the only part of the continent that will allow their survival – those areas that are relatively cool and damp.”
Climate has shaped the distribution of oaks in California, he said. Oaks are much newer to California, arriving about 10,000 years ago at the end of the last Ice Age; prior to that, the pollen record was heavily dominated by conifers. As the climate warmed, our Mediterranean climate evolved, and oaks became the dominant tree form over much of the interior part of California. “This Mediterranean pattern of dry hot summers and relatively wet winters has really shaped the kinds of major vegetation types and plant communities that we have here in California,” he said.
“Drought is a phenomenon of weather,” Mr. Giusti said. “It’s sporadic; it can be geographically limited. We’re in the midst of a crushing drought while other parts of the country are suffering from torrential rainfall, so even though it’s sporadic, it can be very intense in localized areas.”
“Droughts can affect wildlife species disproportionately,” he said. “Some species can have slow lingering impacts while other species, like the waterfowl, can be subject to catastrophic disease outbreaks that can decimate populations.”
Drought can also affect wildlife behavior as animals have to go in search of water, changing their behavior and going out of areas that they are normally comfortable with and know, he said. “Drought is an additive factor on an already stressed environment,” he said. “With thirty-eight million people living in California, wildlife are coming in conflict in a number of ways with people in the state, and drought is just another stress factor that’s impacting our native species.”
Redwoods are a unique organism, he said. Climate has caused them to retreat back and hold onto the very edge of the North American continent, existing in the narrow band of the state where historically there has been lingering summer fog. He explained how as the fog comes up and moves across the redwoods, the trees intercept the moisture, and the fog drip falls to the ground, noting that if you’re under the trees on a foggy day, it’s literally raining under the trees.
Coast redwoods are unique in that they can’t close their stomata, the valves on the undersides of leaves that open and close to regulate water transpiration in trees, he said. “Redwoods can’t do that but they don’t have to do that because they are enshrouded in fog and their moisture and water needs are met during the summer because of the fog. They haven’t evolved to have to conserve a lot of summer water, but they are reliant on summer fog. What we are seeing in California, particularly during these drought years, is that the number of fog days has decreased along the coast. Long term, the climate is changing and the number of fog days is decreasing. … Drought is insidious; we’re not going to go out and find dead redwood trees, but these trees are under prolonged stress in the absence of fog, and if this cycle should persist for a decade or longer, I would suspect we would see collapse of some of these redwood stands, particularly in the southern part of the range down by Santa Cruz and Monterey counties.”
He then presented a graph depicting how different parts of the forest are used by different species, such as amphibians, reptiles, mammals, and birds. “The riparian areas, the streams, the rock pile, fallen logs, and just the amount of accumulated duff on the forest floor,” he said. “The birds are highly dependent on snags, which are standing dead trees – there’s a number of species of birds that live in dead trees. … but if you look at the riparian area, across all four of the taxa, those stream corridors are incredibly important for a howl host of organisms.” He noted that these were just the vertebrates, but there are plenty of invertebrates that live in the water, and are dependent on it as well.
“Arguably, the riparian areas are the most biologically diverse and most biologically rich component of a forest,” said Mr. Giusti. “So when those stream corridors dry up or the water flows are depleted or the water temperature is increased, it puts a stress on a whole host of different organisms that are reliant on that one part of the habitat throughout the year.”
Salamanders, frogs, newts, and other amphibians are reliant on surface water to complete their life cycles, he said. “No water, no reproduction, no amphibians. It’s really that simple. Sure they could put it off for a year, but the longer they have to put it off, the more stress is put on their population and eventually those populations will begin to decline.”
Different plant communities respond differently to drought, he said. “Oak woodlands are very different than redwoods,” he said. “They essentially live in a drought condition every summer. They’ve evolved in the Mediterranean climate and they have adaptive abilities to conserve water throughout those extremely dry months. They can close their stomata and they can hold on to water. Their leaves get very leathery; they get very tight, and if things get bad enough, they can drop leaves prematurely and just get rid of any abilities to transpire water. All of this is an adaptation to a Mediterranean climate. They know that hot dry droughty summer is coming, and so over time, evolution has prepared them to address and adjust to the seasonality of California’s interior valleys and mountains.”
He then presented a slide of how different species in oak woodlands use different parts of the forest. “When we think of oak woodlands, we think of acorns and the importance of acorns, and certainly acorns are important for deer and mice … but if you look at the riparian area, across the board, it is the most highly utilized part of the oak woodland forest habitat, that supports the highest number of taxa,” he said. “It’s that water thing. Water is an incredibly important source for all organisms in California.”
“Pines are incredibly susceptible to water stress, particularly those up in the Sierras where they should have lots of snow and lots of time released water,” he said. “In the presence of drought, usually what happens is as the trees become more and more stressed, there’s a whole host of different bark beetles that can attack these trees. These beetles are always attacking the trees, but under normal conditions, when a pine tree is vigorous and it has good sap flows, when the pine beetle tries to bore into the tree, the sap from the tree pushes the beetle out and it thwarts the attack. As water flows subside in the trees, there’s less sap. Beetles are not pushed back, beetles can make an entry into the tree; they develop their galleries, those beetles come out, lay more eggs, have more beetles, and so on and so on, and it’s an exponential increase in beetle numbers in a very short time.”
“Over the last three years, this beetle population explosion has been building,” he said, presenting a slide showing a map of conifer mortality in the Sierras. “We’re starting to see significant pockets of mortality caused from beetles, so even though the beetles are killing the trees, the drought is what started the process that allows the beetles to get started and move forward. This cycle will persist even if the drought was to be broken in the next couple of years, simply because there are so many beetles out there, there are so many stressed trees in the Sierra, so this is something we can expect to expand throughout the coming years.”
Vernal pools are temporary, ephemeral pools of water that provide habitat for distinctive plants and animals that pop up in certain geographic parts of the state. “These are short term pools that fill up with water,” he said. “They often have unique species such as fairy shrimp, which live in these little pockets of water, as well as a whole host of botanical rarities that live only within these small, seasonal pools. These fairy shrimp erupt when the pools fill with water; they lay their eggs. The adults then die and the eggs can sit in the soil for decades and wait for that pool to refill and start the life cycle again.”
California has many variable habitats, all different from one another, and many of them dependent on water, he said. “Vernal pools are very different from a pine forest which is different from an oak forest which is different from a redwood forest, but the common denominator in all of these plant communities and all of these ecological systems is water,” he said. “They all need water to complete their life cycles.”
“There are a number of stress factors that affect water in California,” he said, presenting a slide of a rather complex-looking graph labeled, ‘Simplified cumulative watershed effects schematic. “What we’re talking about there is bank erosion and fine sediments getting into a stream and vegetation being removed along the side corridors, pollutants getting into the water, water getting too warm because there’s not enough shade, temperature is actually considered a pollutant – all of these things are working together and as you add them up, they may have a cumulative impact on how a watershed functions and how those functions and flows are able to provide the necessary ecological services to support wildlife species. All of these impacts are going on all the time, whether from road building, timber harvests, agriculture, or urbanization, all of these cumulative impacts are in place, and added on top of that is the drought.”
“The way California water works is that the system has to be recharged every winter,” he said. “The rains in the wintertime recharge that system and allow those life cycles to go forward in the spring when the creeks are full. And even though many of these species have reproductive cycle time frames are very, very short, and they get into the creeks and they get out fast because they know the creeks are going to dry out eventually. Even though they are very good and quick at what they do, they still need water. In the absence of water, no matter how quick these amphibians or many of these fish can get in and out of the creeks to reproduce, lay their eggs and allow their young to hatch and move downstream and get to a main body of water, they still need water to do that.”
Not only do some animals live in water, many animals are reliant on water to migrate through it to get to one part of their life cycle to another, such as steelhead and salmon. “Not only do the adults have to have free access and move upstream in order to lay their eggs; the juveniles need water long enough in the stream where they can get strong enough to swim out of the stream and get back to the mainstem and eventually grow larger and swim out to the ocean,” said Mr. Giusti. “Migration coming in is just as important as escapement, or downward migration, of juveniles as they get out to the ocean, so they can get big, come out and complete their life cycle.”
The ability to move in water is also a function of water quantity; how much water is there and how long is the water in the system, he said. “Even though these magnificent animals can spawn in mainstem rivers and streams, the predation rates and mortality rates are higher of the juveniles because the mainstem streams have more predators and there are more risk factors, whereas many of the small little seasonal streams lack these predators and other stress factors, so there’s a much better chance of survival in these smaller streams. The streams do dry up, but as long as they dry up after the cycle is completed, it doesn’t matter.”
Water quantity equals water quality and good clean cold water is important for aquatic organisms because cold water oxygen better than warm water, he said. “As water heats up, the oxygen molecules become agitated and literally evaporate out of the water, so the warmer the water gets, the less oxygen it has in that water. Catfish and largemouth bass can tolerate warm water because their oxygen demand is less than things like trout or steelhead or salmon. So one of the concerns in a drought is how reduced water flows are leading to increased temperatures which affect water quality for many of these organisms.”
“Warm water or lack of water will affect the basis of the food web,” he said, presenting a slide depicting a food web. “All of those organisms are part of the nutrient flow of a system that are priming the system that are feeding the system, everything from leaves that are able to decay and rot in water to the organisms that rip them apart and who are consumed by top level predators, so all of these components are connected,” he said. “They are not only connected by the physical presence of water, but of the condition of that water, the temperature of that water, and what is the function of that water in driving these various systems.”
He then presented a slide of a food pyramid, with the Western grebe being the top predator in the diagram. “The primary producers are the algaes and small singular cell plants, and at any one of those levels, if water conditions or water quality negatively affect the producers or the primary consumers, those organisms that live higher up on the food chain will ultimately be affected.”
Most times, these changes don’t happen overnight – these aren’t catastrophic events, but it can be very insidious, year after year, he said. “If primary productivity is reduced, then primary consumerism is reduced and it goes up the food chain until eventually, animals either have to leave. In the case of Western grebes, they can get up and move and go somewhere else, but other species like amphibians don’t have that ability and they simply fall out of the equation on a localized level.”
Drought is just another additive stress factor; the animals that live in California are dealing with altered wildlife habitats for a number of reasons, he said. “Even our strong program of fire suppression has altered habitats by inhibiting the ability of decadent stands of brush to be rejuvenated and started at a seral stage starting that process over again, so there are a lot of ways that we affect how habitat functions and how these functions and flows are affected.”
He then presented a slide of a California landscape. “There is heavy dense urbanization on the left with some intermediate agriculture in between, and then the wildlands going up through the hills,” he said. “The animals that are living in this area, in order for them to live in these kinds of juxtapositioned habitats with different competing factors and different stress factors in close proximity to one another. They’ve migrated, they’ve figured out how to get through life and meet their basic needs. However, in a severe drought like we have now, it could cause animals to change their normal behavior and to have to go beyond the boundaries of what they are comfortable with in search of water or in search of suitable food.”
“The nature of a drought and its impacts on wildlife can be very insidious; it’s very subtle,” he said. “Mortality happens. Every day animals die. That’s part of how the system is intended to work, but without the ability to recruit, without the ability of new juveniles to come into the population, eventually that local population could be lost.”
“So what does the future hold? I wish I knew,” said Mr. Giusti. “I know if the future doesn’t change as it relates to wildlife, it’s not going to get any better. Certainly the demands of water in California and the conflicts between various user groups will only intensify, and the needs for animals for water will remain constant. Certainly there’s concern that a prolonged drought could have lasting implications for a number of species.”
“So one of my take home messages to you is this drought is just one more stress on an already stressed system,” he said. “It has an insidious impact on animals that are trying to live and share space with 38 million Californians.”
For more information …
- To view this webinar, click here.
- To view all the webinars in the series, Insights: Water and Drought, click here.
- For more presentations from UCANR’s Water and Drought series posted on Maven’s Notebook, click here.