Hidden Habitat Implications of California’s Drought

Fall 2014 Ecesis, Volume 24, Issue 3

Plant and animal species surveys may also be affected by drought. Dormant plants can cause loss of local habitat or food shortages which in turn can affect populations of sensitive species like the California gnatcatcher.

Plant and animal species surveys may also be affected by drought. Dormant plants can cause loss of local habitat or food shortages which in turn can affect populations of sensitive species like the California gnatcatcher.

California had its worst drought conditions in 90 years between January and May last year, and the first seasonal snow survey in early January of 2014 showed the state’s water content at about 20% of average. It was made official on Jan. 17, 2014, when Governor Edmund Brown Jr. declared a drought emergency. 

The effects of an ongoing drought may result in plant diseases and insect infestations along with increased erosion, a decrease in air quality and degradation of landscape and habitat, along with an increased risk of fire due to drier vegetation. While the environments can quickly bounce back from short-term droughts, it’s the long-term droughts that cause the most damage to not only animal life but plant life too.  

Plant/Tree Diseases and Insect Infestations —  Quercus Agrifolia

While California’s oak trees are well adapted to survive the state’s drought, the right approach to supplemental irrigation is critical in preventing pests from taking advantage of drought-stressed oaks. In a drought, oaks conserve water by reallocating resources to sustain basic physiological functions. Unfortunately, this can lower a tree’s defenses against disease and insects, including borer colonization. Trees showing foliage discoloration, leaf loss, and burned leaves need supplemental irrigation to mimic the rain associated with winter storms. Slowly soaking the ground beyond the tree’s dripline in the late spring and early fall —  for several days every few weeks — allows the water to saturate the root zone. Keeping the ground immediately around the trunk dry —moist, warm soil increases the risk of root, crown, and collar rots caused by fungal pathogens — can be achieved by building a 12-inch-high, firmly-packed soil berm, 2 to 3 feet out from the trunk.

Fuel Modification for Fire Protection

With California fire officials concerned about a more dangerous fire season, performing fuel modification maintenance is a key part of effective fire protection planning, particularly as vegetation dries out. Fuel maintenance should focus on dead and dying plants, highly flammable species, thick vegetation, and ‘ladder’ fuels that reach tree canopies.

Each site’s environment determines the fire risk and how wide a defensible space needs to extend from structures. Although 100 feet is the norm, very hazardous sites may require more than 200 feet of defensible space, and flat, predominantly grass-covered landscapes with an ignition-resistant structure may justify reduced space.

Where 100 feet of defensible space isn’t possible, a fire protection plan can justify use of alternative materials and methods that will allow a fire authority to make a finding that equivalent protection is achieved.

While many ordinances refer to clearing vegetation, effective fuel modification does not necessarily mean clearing/cutting the defensible space. Proper fuel modification strategies include selective thinning of vegetation to reduce fuel load and planting fire-resistant species to reduce fire risk while maintaining vegetative cover for erosion control.

Fuel modification plans to implement include:

  • Removing, thin, or replace combustible vegetation,
  • Planting adequately-spaced, drought-tolerant, and fire-resistant plants
  • Complying with U.S. Fish & Wildlife regulations when working in sensitive habitat areas
  • Being aware of bird nesting and breeding seasons
  • Understanding the role of irrigation in vegetation management for defensible space
  • Being knowledgeable of seasonal erosion issues and the effect on vegetation management.

Degradation of Landscape and Native Habitat

Exotic species compete with native vegetation and this is even more pronounced during a drought. Exotics, such as tamarisk, consume large quantities of water, an already limited resource. Exotics also establish and spread more quickly than natives, reducing the quality and quantity of indigenous plant populations. Many California cities and counties are removing banned species from their properties to promote all the benefits of native vegetation with the added benefit of water conservation. 

Delays to Habitat Mitigation Projects

Project owners with pending permits and habitat mitigation programs will need to plan for potential setbacks if California’s extended dry weather continues. A seed shortage for native plant species will likely occur that could delay the implementation of habitat mitigation requirements on construction projects.

Although native species flower year-round, the largest number of native species flower in the Spring. In typical seasons, seeds are collected by experts and then sold for use in mitigation projects. Plant species can still flower in the dry conditions but it would be deceptive — it’s likely these plants won’t form seeds without greater rainfall. Without adequate water resources, viable seeds may not form even though the plant flowers.

As part of mitigation, resource agencies often require that seeds come from within 5 to 20 miles of the mitigation site in order to be consistent with local genetic populations. This limits the source vegetation where seed can be collected. It pays to collect seed during wet rain years, even if the project is years away. Also, many seed collection sites in coastal California are located in the wildland-urban interface (WUI) so the local seed supply would be at risk if the extreme drought brings on catastrophic fires.

High Risk to Non-irrigated Mitigation Projects

Non-irrigated mitigation projects are challenging in normal rain years; during consecutive dry seasons it is virtually impossible for them to succeed because seeds may not germinate. If non-irrigated, project owners should anticipate losing a year on their mitigation program and expect to pay for adaptive remedial actions such as hand-watering container plants, and/or replanting or reseeding when wet weather returns.

In addition, there is increased risk of plant loss due to browsing by local herbivores such as deer and rabbits. As the quality of surrounding “browse” diminishes due to drought, these species are more likely to impact typically more succulent mitigation sites.

Permitting Implications for Biology Surveys

Sensitive and rare plant species may not come up in these dry years, so vegetation surveys may not detect the presence or the full extent of the plant population. A drought year can leave open questions about potentially significant constraints on land use such as the presence of a rare or endangered plant or animal species.

Required focused surveys for some species may not even be possible or only partially possible. For example, fairy shrimp surveys might be compromised because few to none of the vernal depressions might support standing water for a long enough period to support a shrimp life-cycle. If this occurs during a low-rainfall year, then the wildlife agencies usually question the negative survey results.

As an example of the dry spell’s domino effect, dormant coastal sage scrub could threaten the California gnatcatcher (Polioptila californica) population. Coastal sage scrub supports the gnatcatchers’ food supply of insects and spiders. Dormant vegetation will reduce the insect population, and the resulting stress will trickle up the food chain. Native vegetation also hides the gnatcatchers’ nests and protects them from rain, dew, and too intense direct sunlight. Drought-stressed vegetation makes the nests more exposed and susceptible to failure.

Although it is frustrating that no short-term action can be taken to counter these problems — except to monitor the extent of the impact and be prepared to adjust plans when the situation changes — awareness of these hidden ramifications allows for recommended mitigation strategies that inoculate clients and their projects from the climate-driven delays. Such recommendations might seem strange at the time, but these are the years that demonstrate the wisdom of forward thinking.

With proper planning and implementation, we can help native flora and fauna survive the drought. — by Mark Girard (HRS), Mike Sweesy (Dudek), Mike Huff (Dudek), and Bob Mackie (HRS)