Scientific Literature Review of Forest Management Effects on Riparian Functions for Anadromous Salmonids

Transcription

1 Scientific Literature Review of Forest Management Effects on Riparian Functions for Anadromous Salmonids Presentation to: The California State Board of Forestry and Fire Protection Prepared by: Mike Liquori Dr. Doug Martin Dr. Lee Benda Dr. Robert Coats Dr. David Ganz

2 Scientific Literature Review of Forest Management Effects on Riparian Functions for Anadromous Salmonids Mike Liquori Dr. Doug Martin Dr. Robert Coats Dr. Lee Benda Dr. David Ganz Outline Project Approach Key Findings Synthesis Policy Inferences Process Critique Next Steps 1

3 Our Team Mike Liquori Dr. Doug Martin Dr. Robert Coats Dr. Lee Benda Dr. David Ganz Ms. Shelby Sheehan Project Approach Reviewed Assigned Literature TAC Primer Peer Reviewed Literature Addressed Key Questions Collaborative & Integrated 2 Day Synthesis Workshop TAC Review Responded to extensive comments 2

4 General Themes General Themes 1. Spatial context is important, as it influences functional response patterns. 2. Longitudinal controls on exchange functions AND lateral controls are important in maintaining the watershed scale ecosystem structure that maintains aquatic habitats. 3

5 General Themes 3. Disturbances are an important mechanism for establishing conditions that support riparian functions Stand structure Vegetative succession Wood recruitment Nutrient exchange Thermal regulation General Themes 4. Riparian zones can buffer a stream from direct management impacts, and they alter the disturbance regimes in ways that can affect both short term and long term evolution of riparian areas. 5. There are dynamic interactions among and between riparian exchange functions that alter the importance of exchange functions for any particular setting. 4

6 General Themes 6. Active and strategic riparian management can limit risks and benefit salmonids temperature regimes ecological productivity woody debris recruitment fuel loads and other disturbance risks etc General Themes 7. There are variations in the buffer width necessary to meet each function, and these variations depend on several factors 8. The reviewed literature offers many opinions, but limited hard data to evaluate the scientific effectiveness of any approach 5

7 9. Risks and benefits are inherently value judgments best determined by policy General Themes Science can only provide the context 10. The geographic and watershed scale variables for buffers requires a policy framework Information in the literature is available, but inconclusive in the absence of a framework Biotic & Nutrient Exchange 6

8 Key Findings Biotic & Nutrient Riparian leaf litter is an important food source Key Findings Biotic & Nutrient Litter quantity & quality is important Highest: alder Moderate: maple, willow and cottonwood Low: conifers and oaks 7

9 Key Findings Biotic & Nutrient Opening the canopy cover over some streams increases ecological productivity Key Findings Biotic & Nutrient Tradeoffs between nutrient exchange and other functions Heat regulation Water response to flooding Wood recruitment potential 8

10 A 100 foot wide no cut buffer on both sides of a stream provides conditions similar to a no harvest level Key Findings Biotic & Nutrient No cut buffers may forego opportunities to: Key Findings Biotic & Nutrient increase fish growth rate and biomass manage other functions 9

11 Heat Exchange Functions Key Findings Heat Stream temperatures affect the growth and mortality of salmonids Too COOL: insufficient growth & lower ocean survival Too HOT: lower abundance & risk of mortality 10

12 Key Findings Heat Riparian shade helps to control heat input to streams Other factors important too Key Findings Heat No single, fixed width buffer or canopy closure prescription can regulate heat objectives for salmon in all cases. Effective shading can be provided by: Lateral: buffer widths ranging from 30 to 100 ft Longitudinal: generally within 500 to 650 ft upstream 11

13 Key Findings Heat Water temperature protection could be provided by varying the riparian shade requirements in relation to stream temperature sensitivity. Key Findings Heat The relative importance and sensitivity of riparian vegetation to influence stream temperature varies by: Geographic province At least 11 site specific factors Stream temperature targets can be helpful in managing to desired shade conditions 12

14 Key Findings Heat Timber harvest in or adjacent to riparian areas can influence microclimate, HOWEVER microclimate changes have not been demonstrated to translate to changes in water temperature. Key Findings Heat Shade conditions inversely influence biotic and nutrient exchange functions. Similarly, the canopy that provides shade also influences: Water exchange functions Wood exchange functions 13

15 Water Exchange Functions Key Findings Water Forest management activities in riparian areas might affect stream functions effect is likely to be small highly variable strongly influenced by the watershed context impacts are mixed 14

16 Key Findings Water Management affects the riparian canopy canopy interception evapotranspiration Key Findings Water There is little direct evidence of riparian effects: studied for entire watersheds riparian zones alone have not been studied The most sensitive hydrologic areas may be steep, zero order basins (hollows) This was not a focus of this review 15

17 Key Findings Water Soil compaction in riparian areas can negatively affect hydrologic processes. Suggests limits for heavy equipment near streams Key Findings Water Hyporheic flows are important ecologically forest management effects are unclear 16

18 There is very little in the reviewed literature that can used to directly address the issue of buffer strip delineation relevant to the water function Key Findings Water Key Findings Water There are probably regional differences Casper Creek (coastal Mendocino County) 17

19 Regional differences are likely to reflect: Key Findings Water Geology topographic variation dominant runoff mechanisms Wood Exchange Functions 18

20 Wood functions vary by stream type and geomorphic context Key Findings Wood There are three dominant sources of instream wood in California second growth forests bank erosion: ~40 60% streamside landslides: ~30% treefall: ~10 30% 19

21 Bank Treefall Landslides Erosion Windthrow Key Findings Wood The zone that can contribute 90% of observed wood recruitment varies depending on the dominant processes Bank erosion: < 30 feet Streamside landsliding: ?? feet Wind: ?? feet Treefall: <100 feet 20

22 Key Findings Wood The major factors that are reported to influence wood recruitment conditions include: Existing Stand Density, Composition And Structure Stream Type, Order and Watershed Context Vegetation Type and Soil/ Site Index Regional Context Disturbance Context 21

23 Key Findings Wood Instream wood can move downstream through: Flood: in larger streams Debris flow: in steep, low. order streams 22

24 Key Findings Wood Wood recruitment potential depends upon: Existing stand conditions Successional pathway Disturbance Regime Key Findings Wood Forest management appears to influence natural disturbance regimes by affecting How often disturbances occur How large the disturbances are Which type of disturbances are likely 23

25 Key Findings Wood Active forest management can manipulate riparian stand structure in ways that: a) affect the growth and mortality dynamics for the stand and b) influence the types, qualities and risks of disturbances and thus influence wood functions Sediment Exchange Functions 24

26 Key Findings Sediment Sediment Best Management Practices (BMPs) typically address sediment primarily in three general ways: Source controls Runoff Controls Treatment Controls Key Findings Sediment Sediment sources from forest management include: surface erosion processes (rills and sheetwash) skid trails yarding ruts gullies soil piping roads fire mass wasting processes bank erosion windthrow legacy forest management practices 25

27 Key Findings Sediment Riparian buffers are mostly effective at limiting sediment delivery In the absence of buffers, ground disturbances that are near streams have the potential to deliver sediment Relevant Report Section Erosion Mechanism Effectiveness of Buffers Surface Erosion Effective Skid Trails and Yarding Ruts Effective Bank Erosion Effective Windthrow Varies Gullies Somewhat Effective Road-Related Sediment Somewhat Ineffective Fire Insufficient Information Mass Wasting Insufficient Information Soil Piping 1 Insufficient Information 26

28 Key Findings Sediment Selective forest management within buffers does not appear to substantially increase sediment production or delivery The extent that riparian buffers along headwater streams are necessary to prevent sediment delivery is not clear from the reviewed literature. Key Findings Sediment Despite the lack of evidence for direct sediment delivery, instream sediment yields tend to increase following logging Sources of such sediment are not clear 27

29 Key Findings Sediment Source distance relationships for sediment also appear to vary with the dominant processes and site conditions Sediment filtration effectiveness 100% 80% 60% 40% 20% 0% Buffer width (ft) Castelle (1996) Ketcheson (1996) King (1979) Megahan (1996) Benoit (1978) Key Findings Sediment The reviewed literature did not provide a sufficient guidance for the various landscape situations in California, although a more detailed analysis of data may lead to more definitive specifications for buffer width. 28

30 Key Findings Sediment Riparian sediment management objectives include mitigating for: Harvest Related Sediment Hydrologic Link to Sediment Delivery Road Sediment Mass Wasting Impacts Synthesis 29

31 The scientific basis for defining buffer widths in fish bearing streams is based on source distance relationships Challenges with Source Distances 1. The instream biological response to source distance relationships has not been established. 2. Source distance relationships ignore the trade offs between functions. 3. Source distance relationships downplay the importance of the quality of contributed inputs. 4. Source distance relationships only capture the effects of some disturbances. 30

32 Challenges with Source Distances 5. Source distance relationships describe the relative contribution, but not the total contribution. 6. Source distance relationships ignore changes over time. 7. Source distance relationships ignore the longitudinal context. River Continuum v. Network Dynamics Longitudinal Variation Geomorphic Context is Important Biological Hotspots 31

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34 Longitudinal Variation Managing for longitudinal variation requires an understanding of how different ecosystem processes act to form and maintain habitats throughout the channel network. Key Findings Synthesis The concept of disturbance cascades may provide an ecologically and geomorphically integrated framework for developing management practices guidelines in these landscapes. 33

35 Key Findings Synthesis Such a framework might benefit by considering practices at larger spatial scales and longer time scales that recognize the recovery rates associated with various functional processes 34

36 Policy Inferences 35

37 Typical Forest Buffer Widths Typical Forest Buffer Widths Selective v. No cut 36

38 Policy Approaches to Riparian Management Advanced Recovery & Enhancement Riparian Reserves Resource Optimization Riparian Reserves Large, often uniform & continuous buffers Driven by buffer width Minimize management effects within riparian areas GOAL: return late seral characteristics to riparian areas over a period of centuries 37

39 Resource Optimization Actively design the characteristics of riparian forests Driven by buffer width, often varied by stream type Allows flexibility Minimize management effects on stream functions GOAL: maximize benefits while supporting other resource objectives Advance Recovery & Enhancement Actively design the characteristics of riparian forests Driven by landscape context Requires detailed site specific tools & skills Maximize benefits to salmonids GOAL: expedite recovery of functional aquatic ecosystem dynamics 38

40 Policy Sets the Framework Riparian reserves low risk, long recovery period (centuries) Active Management higher risk, faster rates of recovery & function Careful design can mitigate increased risk Scientific Basis for Management BMPs Decision Support Tools Regulatory Framework Design Approaches 39

41 Scientific Basis for Management Process Critique 40

42 Process Critique Level of effort greatly exceeded budget Very strong steering too focused on details Limited ability to focus on policy implications Many of the assigned papers were not relevant Several topics were not well addressed by assigned literature TAC steering well intended but cumbersome Process Critique Challenges with the Key Questions Too many questions (64) Too many sub questions within questions Lots of redundancy Many fringe issues Too broadly framed Often ambiguous Often did not capture the real issue 41

43 Example Key Question Have forest management activities in riparian zones for higher order channels with floodplains and adjacent to small headwater first and second order channels been shown to alter water transfer to stream channels, affecting near stream and flood prone area functions (e.g., source area contributions to stormflow, bank instability, lateral and vertical channel migration, flow obstruction or diversion of flow)? Example Key Question Have forest management activities in riparian zones for higher order channels with floodplains and adjacent to small headwater first and second order channels been shown to alter water transfer to stream channels, affecting near stream and flood prone area functions (e.g., source area contributions to stormflow, bank instability, lateral and vertical channel migration, flow obstruction or diversion of flow)? 42

44 Process Recommendations Better focus in developing Key Questions Less redundancy Less ambiguity More clarity & focus Allow the consultant team more opportunity to influence the scope of work More clear focus on desired outcomes Recommended Next Steps 43

45 Recommended Next Steps Lot s of good detail available from literature Supports specific rule making elements Support for management decision support tools that incorporate science Requires a policy framework to provide direction Recommended Next Steps Establishes value positions regarding various management approaches Advanced Recovery & Enhancement Riparian Reserves Resource Optimization 44

46 Recommended Next Steps Identify clear functional goals and performance measures that define the decision space for science based management Outline a planning approach that provides a policy oriented framework (i.e. based in regulations, planning processes, etc) Recommended Next Steps Identify supporting science based management and policy infrastructure (e.g. science resources, adaptive management framework, etc) 45

47 Recommended Next Steps With a policy framework in place, revisit the literature to identify specific details Decision support tools Models & mapping capabilities Resource targets Riparian management specifications Design tools etc 46