The "Review of the Alameda Creek Habitat Conservation Plan Modeling Strategy" by an independent science review panel highlighted the value of historical ecology (excerpt below).

Link to the full report, released August 2012

(p20-22)

IV: Historical Ecology of Alameda Creek Watershed

Historical ecology is becoming more widely used as a means of informing the construction of

landscape restoration and management plans. The method can indicate what conditions “were

actually like before the changes that restorationists seek to undo or mitigate” (from the

Consultant’s presentation). However, the activity can yield several other products useful for the

goals of HCPs, even in a watershed that has been so radically altered that ecosystem planning is

unlikely to return the landscape anywhere close to original conditions. For example, it can

identify habitat patterns, connectivity, and processes that no longer exist but that be reestablished

even within modern constraints. It can document secular changes in vegetation

patterns, sediment supplies, or channel conditions that have not been sampled in the instrumental

record of environmental change. It can document the relative magnitude and quality of habitat

loss or transformation in various parts of a river system, such as in the two main tributary

watersheds of Alameda Creek, highlighting the potential importance of seeing an HCP in the

context of other positive and negative trends that might influence the effectiveness of the

conservation plan. Combined with modeling, this aspect of historical ecology constitutes one

form of cumulative watershed effects analysis. An example of such analysis occurs when

mapped land cover changes reflect changes in the water balance of groundwater recharge,

leading to desiccation or waterlogging of riparian zones downstream. Observations of this type

might indicate the potential for unwelcome surprises or changes that landowners wish to avoid,

no matter how natural they might be.

The consultant team from the San Francisco Estuary Institute has documented landscape

change since the late-18th century in the entire Alameda Creek Watershed, including the

watershed of the larger tributary, Arroyo de la Laguna. The data sources are diverse in nature and

reliability, and mainly qualitative, but when recorded in consistent ways, compiled by time

period, and geo-referenced, they can reveal patterns and persistent changes, which when

interpreted by people with training in landscape functioning can produce important insights for

conservation planning. Early data sources tend to comprise descriptions and other records at

places or on small areas of land, although early instrumental surveys or even sketched maps are

surprisingly widespread and can be digitally geo-referenced. The record became significantly

enriched beginning in the 1920s with the introduction of aerial photographic surveys of

increasing scale and quality, many of which are now published directly in digital form. The

increasing wealth of data, however, does not diminish the level of interpretive skill required to

convert these subtle spatial records into understanding of landscape patterns and change.

A crucial step in assimilating the diverse data sources is to recognize the fingerprint of

landscape processes, such as how patterns of ground water flow relate to topography, geological

structure, and surface water bodies, and thereby create patterns of water flow and availability that

sustain plant communities and the activities of people. The magnitude and role of flooding and

the density and intricacy of water bodies are other important recognizable landscape features.

Another potential of the method is the documentation of rates of processes, such as the spread of

plants and other aspects of succession. One of the limitations of the reconstructions, however, is

that they often can involve only qualitative identification of processes, habitat potentials, or

ecosystem services. Thus, it is valuable to combine the results with quantitative estimates based

on process models or statistical characterizations from elsewhere.

Although the historical documentation and interpretation of the Alameda Creek watershed is

not yet complete, it has already yielded important insights which suggest both conceptual models

for restoration but also targets for quantitative interpretation through mathematical modeling of

hydrology, hydraulics, and ecosystem functioning. The most widespread and significant targets

of this work have been outside of the parts of Alameda Creek watershed involved in the current

HCP. Relevant features within the HCP domain include natural and anthropogenic influences on

channel morphology and riparian vegetation in the Sunol Valley reach, and channel

simplification and pool eradication in the flood-control reach downstream of Niles. These results

emphasize that the critical ecological role of those two reaches should be closely addressed by

EDT and other habitat modeling exercises involving flow, channel morphology, and water

temperature.

The historical analysis also points to wider issues that would favor aquatic ecosystem

improvements in the longer term, building on the fruits of the HCP. Examples include the former role of extensive marshlands in providing fish habitat and turbidity control along Arroyo de la

Laguna. Another is the original denser and more intricate network of tidal channels with pools

and shade provided by tree-covered natural levees and securely watered channels, sustained by

artesian ground water immediately upstream from them. These channels probably provided

extensive rearing habitat for anadromous fish throughout the year, and the historical

documentation suggests analyzing the potential yield of partial restoration. This larger historical

spatial context provides a strong foundation for SFPUC to play an important role in ecosystem

management by promoting the expansion of its current approach of monitoring and modeling in

support of its HCP.