Towards the end of January, an unusual phenomenon occurred in the Sierra foothills - some of the blue oaks began leafing out. While the vast majority of trees remained leafless, one could see occasional light-green canopies interspersed with their bare neighbors. This is unusual in that the earliest leaf-out most people recall observing doesn’t start until late February or early March.

So what is causing this? Clearly the weather pattern this past winter has been very unusual in terms of precipitation. There was abundant early rainfall in October and November, followed by a December and January that were some of the driest on record. However, dormancy and its subsequent breaking are much more controlled by temperature than by rainfall. That is, a significant period of cold is necessary before most temperate plants resume growth in the spring. Photoperiod – or the relative daily lengths of light and darkness - also often plays an important role but this obviously doesn’t vary from year to year.

Has the temperature pattern been abnormal? The CIMIS (California Irrigation Management Information System) long-term data was compared with this past winter’s averages and nothing stood out as particularly different, although there is apparent, large variability from year to year. There was a day or two of somewhat colder-than-average temperatures in mid-January, but below-freezing temperatures in the foothills occur almost every year. Therefore, at this point, the cause of early leaf-out remains a mystery.

                                      Example of an oak tree leafing-out

What about the impacts? It is likely that some of these “early leafers” will suffer frost damage. This occurred several years ago in mid-spring when there was an unusually late freeze and many blue oaks had their foliage killed back.  Most of this occurred at mid-elevations, presumably because trees at higher elevations hadn’t leafed out yet, and those at lower elevations were so far advanced that their foliage was hardier. While this certainly wasn’t good for the trees, they were able to recover and produce a new crop of leaves within a month or 6 weeks and no increase in mortality was noted. It seems likely that, as a species, blue oaks have evolved individuals that leaf out at different times of the year so that at least a portion of their population can take advantage of different weather conditions. The “risk takers” might get hammered now and then, but under the right conditions, they can take better advantage of unusual weather patterns than their more conservative colleagues. In the event of significant warming in California as a result of climate change, these may even be better adapted to survive and prosper in a changing environment.

This year’s delayed “rainy season” in much of California has left many seasonal water sources for wildlife and livestock dry and kept many of the state’s water reservoirs low. If the “rainy season” progresses without rain we may find ourselves thinking about how we capture as much rainfall as possible not only in our soils but also in our ponds and reservoirs.  In other words, how do we manage our watersheds for maximum water yield? 

Vegetation affects the hydrologic cycle through evapotranspiration and the interception of water. Both processes are a direct function of the type and density of vegetation present in the watershed. On one hand, natural vegetation in California is continually being lost to housing development, conversion to agricultural crops, sudden oak death syndrome and wildfire. On the other hand, undistributed rangelands in some parts of the state are reverting to woody vegetation.

A study conducted at Hopland Research and Extension Center (HREC) in the 1950’s sheds some light on vegetation effects on water yield, at least for north coast watersheds in California (Dahlgren et. al. 2001).  Beginning in the early 1950’s, a series of watershed studies was undertaken on experimental watersheds at the HREC in Mendocino County. The watersheds ranged from 30 to 210 acres. All have relatively steep slopes, from 20 to 60%. The climate at Hopland is Mediterranean, with a mean annual precipitation of 37 inches and a mean annual temperature of 57 F. Soils in the watersheds are moderately developed and shallow, rarely exceeding 3 to 4 feet deep.

        Hopland Research and Extension Center watershed landscape and native vegetation

In 1952, Watershed I (63 acres) and Watershed II (210 acres) were fitted with instruments, including precipitation gauges, stream runoff measuring stations and debris basins for sediment transport measurements. Both watersheds were located a lower elevations (500 to 1,000 ft) with typical oak woodland vegetation. Baseline data was collected for several years. In 1956 vegetation from Watershed I was mechanically removed, followed by burning of woody materials, treatment of stumps with herbicide, and seeding with a grass-legume mixture.  Between 1960 and 1965, vegetation in Watershed II was killed with herbicide. Dead trees were left in place. In 1965, Watershed II was burned and reseeded with a grass-legume mixture. Vegetation, stream flow and sediment data were collected from Watershed I and II for over a decade following vegetation conversion on each watershed.

Vegetation and Water Yield Findings

The researchers found that converting woodlands to grass vegetation retarded runoff during storms, and resulted in nearly a doubling in the length of storm hydrographs from both watersheds (Hydrographs plot the flow or discharge of a waterway through time). After conversion to grass vegetation, peak runoff rates were reduced by about 25% compared to pretreatment storms.  This result is different from that realized in other studies conducted in other woodland and forest systems elsewhere in the world. 

The longer hydrograph responses indicated a longer, slower period of runoff with greater contribution of water from subsurface flows.  These changes resulted from an increase in grass cover that retarded overland flow and permitted more opportunities for infiltration. The removal of the deep-rooted trees also resulted in a long-term increase in runoff and an extension of base flow through the dry season. After vegetation was converted, intermittent streams became perennial in both Watershed I and II.

After conversion to grassland in these watersheds, stream discharge increased by an average of 60%.  However, in pre and post treatment condition, there was a high correlation between runoff and total precipitation. There was also a season affect that should be considered. March was the critical month in the runoff process. During the rainy period leading up to March, the increase of water yield in the converted watersheds was definite. During March, the effect of conversion was variable, sometime positive and sometimes negative.  This behavior may be explained by examining the growth patterns of grasses and oak vegetation. At the experimental site in Mendocino County, warm temperatures in March promote the growth of grasses, resulting in increased evapotranspiration. In contrast, deciduous oak trees are not in full leaf in March, resulting in less water loss to interception and evaportranspiration. Rainfall in April and May often produces no runoff due to high evapotranspiration demands, especially after deciduous trees leaf out.

                        Stream alteration to improve and direct streamflow to prevent
                                              erosion during rainy seasons

These experimental results have important ramifications for vegetation and land use throughout the California Coastal Range. Decreased peak flows during storms and reduced flood hazards may be among the benefits of maintaining grasslands and preventing the encroachment of woody species. The increase annual water yield including the increase in summer and fall base flows may have important benefits for anadramous fish species and the health and integrity of the aquatic ecosystem. Similarly, the change in ephemeral streams to perennial streams may improve wildlife habitat by providing a summer source of water.

It should be noted that with these increased stream flows in the converted watersheds came significant erosion problems.  Although a lot of the mass-wasting events observed after the conversion treatment were associated with tree and shrub removal, the loss of root systems in providing reinforcement and the increase in soil-moisture were also factors.  In any case, given needs for water quality and quantity careful consideration should be given to managing and maintaining the type of vegetation that produces desired results.

              Stream bed erosion as a result of possible increased stream flow and runoff


Author: Sheila Barry, UCCE  Livestock and Natural Resources Advisor, San Francisco CA 
                                
                                                    Literature Cited
Dahlgren, R.A. et al. 2001. Watershed research examines rangeland management effects on water quality. California Agriculture 55:6:64-71. http://californiaagriculture.ucop.edu/0106ND/pdfs/watershed1771.pdf

Author: Greg Giusti

Throughout northern coastal California, a great deal of information regarding water quality and fish habitat is being amassed that potentially could change how people view and utilize stream corridors. However, it is widely recognized among the scientific community that stream corridors are an important habitat component for a host of vertebrate and invertebrate species other than fish. Unfortunately, the current fish-centric approach to riparian protection and restoration has often resulted in a narrow discussion of stream corridor management that excludes non-fish species. For example, information detailing the use of oak woodland stream corridors by migratory songbirds in California’s oak woodlands is sorely lacking, limiting the ability of landowners and resource managers to make informed decisions regarding land use practices and policies and their effects on birds. It is important that we consider these other species when managing and restoring riparian areas, as their requirements may be different than those of the fish.

Spring 2012 marks the 20th consecutive year of a bird monitoring study on Parson’s Creek, an ephemeral (seasonal) tributary of the Russian River that traverses the UC Hopland Research and Extension Center (HREC). The goal of this ongoing project is to document resident and migratory bird use of stream corridors in mixed oak woodlands.

                     White-breasted nuthatch. A tree dependent species that forages for food among 
                          the bark, limbs, twigs and leaves of trees. The species is a cavity nester.

Study Site and Sampling Methods

Parson’s Creek, like most creeks in the North Coast, has been subject to many land use impacts over the past 100 years, including livestock grazing, gravel extraction, channelization, and road crossings with associated aggravated erosion. To offset many of these impacts, HREC instituted a series of restoration activities in the early 1990’s to serve as demonstrations to landowners who are interested in stream restoration. Since then, recovery of native vegetation in some sections of Parson’s Creek has been dramatic. In areas that have excluded both sheep and deer, alder and willow have regenerated and are now providing extensive vegetative cover. Other sections were left unprotected and remain denuded, demonstrating how the restored sites used to look. Consequently, vegetative cover is not uniformly distributed throughout the stream reach. Other over-story species that exist across the study area include blue oak, Oregon white oak (also known as Garry oak), and valley oak.

Twelve monitoring points are established along the main creek channel at HREC. Birds are surveyed using a standard sampling protocol commonly referred to as the “point count method”. This method is widely used to survey birds in the field and involves an observer recording birds from a single point for a set length of time.

Each monitoring point is surveyed 3 times a year during the morning. Two 20-minute counts are conducted each spring between mid-May and early June to coincide with the arrival of migratory songbirds. In addition, one 20-minute count is conducted each fall in mid-October, after the departure of neo-tropical migrants to wintering grounds in the tropics. Birds were identified using visual and auditory cues. Only those birds active (perching, foraging, singing, etc.) within the riparian corridor were tallied. Birds flying high above or passing through the stream zone were not counted.

                        Yellow-bellied sapsucker. A relatively uncommon woodpecker of oak woodlands  
                                    is regularly observed in the woody portions of Parson’s Creek.

Findings

Thousands of bird observations have been recorded. The total number of observations per year ranged from a high of 254 (1993) to a low of 173 (1999). The average number of recorded observations over time is 198 detections per year. The unusually high number of recorded observations in 1993 is most likely an aberration of sampling, not a trend in bird presence. Following the first year, the observers became more conservative and standardized in their data collection.

The large number of bird detections yielded an impressive number of species—81 species, representing 24 taxonomic families and 9 orders. Both resident and migratory species were detected in the oak woodland stream corridor. Species most commonly observed and the corresponding number of detections during the study period is provided in Table 1.

Table 1. Most commonly observed species in the Parson's Creek riparian corridor, HREC.

                        Ten Most Commonly           Ten Most Commonly Observed
                        Observed Species              Neo-Tropical Migratory Species

Throughout the study period, an average of 29 species (ranging from 27 to 33) have been detected during the Fall. These species are primarily resident birds that utilize the stream corridor throughout the year. Spring counts averaged 43 species (ranging from 38 to 48). The difference in the average total number of species reflects the seasonal influx of neotropical migratory songbirds that arrive in California’s oak woodlands for the breeding season.

Some species may also be selectively utilizing only portions of the riparian corridor that exhibit special habitat features. For instance, one species in particular, the Black-throated Gray Warbler (Dendroica nigrescens), is consistently found only in those portions of the riparian area where the vegetation canopy is densest. This pattern of occurrence has remained consistent during the entire study period, and suggests that this species may have relatively narrow habitat requirements when compared to other neotropical migrants exploiting the stream corridor.

                      Killdeer are often seen nesting on Parson’s Creek in the areas that are devoid of 
                          vegetation. The bird lays its eggs among the barren rocks. The cryptically 
                             colored eggs are virtually invisible. This is one of the few species that
                                      is not dependent on vegetation in oak woodland settings.

Conclusion

There is very little long-term information detailing the use of oak woodland stream corridors by migratory and resident birds in California’s oak woodlands. Our long-term data set demonstrates that migratory songbirds readily utilize the riparian zone, particularly during the spring breeding season. We also observed that some species are more abundant in sections of the creek where more mature vegetation is present.

We plan to continue to monitor the avian assemblage found within this stream corridor. It is our hope that this project, along with the efforts of others, will generate important, long-term, baseline information that will aid in the sustainable management of California’s riparian hardwood communities.

This webinar will present a series of lectures on the concepts in the ANR publication, “A Planner’s Guide for Oak Woodlands” (UC ANR Publication 3491). The goal will be to create an awareness of the ecological, economic and social values of California’s oak woodlands, and some general planning strategies to ensure long-term conservation of this resource. The selected audience includes city, county, regional and statewide planners, environmental consultants, conservation organizations, land trusts, resource professionals, elected officials, and NGO’s. Complete details on the webinar, including on-line registration instructions, can be found here.

The webinar will be held on March 8, 15, 22 and 29, 2012 from 10 AM to 12 noon, and consists of a series of 2-hour lectures, available on-line through a link to Adobe Connect. This program will be of interest to local planners, professional resource managers and general oak interest groups. The series will be taped and a link to the taped webinar series will be provided for those who are unable to participate on the date and time of the live broadcast. There will also be a weekend field trip to Hopland and/or Sierra Research and Extension Centers at the end of the series.

Participants will register for the webinar and pay a nominal fee ($30) to receive a copy of the publication, ”A Planner’s Guide for Oak Woodlands” and to cover incidental production fees. A social network site will be developed to enhance the sharing of information, and to provide follow-up networking opportunities.

The topics per session include:
March 8-Session 1: Overview of Hardwood Rangeland Resource
March 15-Session 2: Land Management Strategies
March 22-Session 3: Planning Strategies
March 29-Session 4: Sources of Assistance, Developing Plans

Session 5 includes an optional field trip to the Hopland Research and Extension Center on April 21,2012 and to the Sierra Foothill Research and Extension Center on May 5, 2012 from 10 am to 3 pm. The trip will discuss oak planting projects, landscape considerations, mitigation approaches, and addressing ecological functionality through the planning process.

(See: http://ucanr.org/sites/oak_range/Planners_Guidelines_for_Oak_Woodlands/)