Full opinion text
Opinion MORENO, J. This case arises from the “Headwaters Agreement” consummated by the Pacific Lumber Company and the state and federal governments. The agreement was intended to settle matters of litigation and public controversy surrounding the intensive logging of old growth redwoods and other trees on Pacific Lumber’s property in Humboldt County. In addition to the state and federal governments’ purchase of a relatively small portion of Pacific Lumber’s property for conservation purposes, it was agreed that Pacific Lumber could log the rest of its property, provided that it obtain certain regulatory approvals from state and federal agencies. The deadline for obtaining these approvals was March 1, 1999. The approvals were timely obtained, in some cases right at the March 1 deadline. Shortly thereafter, various environmental and labor groups challenged the validity of the regulatory approvals on numerous grounds. The trial court resolved the issues mostly in favor of the environmental and labor groups in 2003, and the Court of Appeal, at the end of 2005, reversed the trial court on almost every point and upheld each of the regulatory approvals at issue. We granted review in February 2006 to consider a number of issues, many of them of first impression, in this important case. The case was put on hold due to a stay resulting from Pacific Lumber’s filing for chapter 11 bankruptcy in February 2007. The stay was lifted in August 2007. We conclude that one of the challenges to Pacific Lumber’s Sustained Yield Plan (SYP), which, as explained below, is a kind of master plan for logging a large area, is valid, inasmuch as an identifiable plan was never approved. We also conclude, as explained below, that any resubmitted SYP should have an adequate analysis of individual planning watersheds, which the plan as originally approved did not contain. We further conclude that the state Incidental Take Permit, authorizing the capturing and killing of endangered and threatened species incidental to lawful activity, was deficient because it included overly broad “no surprises” clauses limiting in advance Pacific Lumber’s obligation to mitigate the impacts of its logging operations. In all other respects, we affirm the Court of Appeal opinion, and remand the matter for further proceedings consistent with this opinion. I. Statutory and Regulatory Framework One of the obstacles to the proper understanding of this complex case is that it concerns a myriad of regulatory approvals, each approval supported by a document or documents that are to some degree interrelated with the others. Before discussing the facts of this case, an overview of the regulatory approvals required and the governing statutes is in order. A Sustained Yield Plan is a kind of master plan for logging a large area, authorized by statute (Pub. Resources Code, § 4551.3) and regulation (Cal. Code Regs., tit. 14, §§ 1091.1-1091.14), designed to achieve the Forest Practice Act’s objective of obtaining the maximum timber harvest consistent with various short- and long-term environmental and economic objectives. (Z’berg-Nejedly Forest Practice Act of 1973; Pub. Resources Code, § 4511 et seq.) As explained below, the SYP does not replace the more specific timber harvest plan (THP), but inasmuch as the SYP adequately analyzes pertinent issues, a THP may rely on that analysis. Although SYP’s are usually voluntary at the option of the landowner, in this case the SYP was required by the Headwaters Agreement. Also required in this case under federal law was a Habitat Conservation Plan. Although the “taking” of a federally listed endangered species, i.e., the killing, capturing or harming of such species (16 U.S.C. § 1532(19)), is generally unlawful (id., § 1538), a permit for the taking of a species incidental to an otherwise lawful activity, known as an Incidental Take Permit, may be issued when an applicant submits to the Secretary of the Interior a Habitat Conservation Plan. (16 U.S.C. § 1539(a)(2)(A).) The plan is to specify, among other things, the impacts that will likely result from the taking and the steps the applicant intends to employ to minimize and mitigate those impacts. (Ibid.) Although the federal Incidental Take Permit is not challenged in this appeal, the Habitat Conservation Plan (HCP) was combined with the SYP for purposes of environmental review, and is critical to supporting various other approvals at issue in this case. In addition to a federal Incidental Take Permit, Pacific Lumber in this case was required to obtain a state Incidental Take Permit for species listed as endangered or threatened under the California Endangered Species Act (Fish & G. Code, § 2050 et seq.). In conjunction with approval of the HCP, the United States Fish and Wildlife Service, Pacific Lumber, and various state agencies entered into an Implementation Agreement for the HCP, defining the obligations of each party under the HCP. Because the state SYP and federal HCP contained overlapping and interrelated analyses and provisions, a decision was made to prepare for both of these documents a single joint environmental impact report (EIR) under the California Environmental Quality Act (CEQA) (Pub. Resources Code, § 21000 et seq.) and an environmental impact statement (EIS) under the National Environmental Policy Act of 1969 (42 U.S.C. § 4321 et seq.). Thus, the EIS/EIR also overlaps and is interrelated with the SYP and the HCP, each of these documents considering among other things the impact of proposed logging activities on wildlife and wildlife habitat. In fact, as explained below, substantial portions of the draft and final EIS/EIR were incorporated into and became part of the SYP. Finally, Pacific Lumber was required to apply for a Streambed Alteration Agreement, pursuant to Fish and Game Code former section 1603. As will be further explained, that statute imposed on Pacific Lumber and the Department of Fish and Game (DFG) the obligation to negotiate an agreement that would mitigate impacts on fish and wildlife caused by the obstruction or diversion of streams and other watercourses. With this framework in mind, we turn to the facts of this case. II. Factual and Procedural Background Real parties in interest Pacific Lumber Company, Scotia Pacific Company, LLC, and Salmon Creek Corporation (hereinafter collectively referred to as Pacific Lumber) own approximately 211,000 acres of timberland in Humboldt County that have been used for commercial timber production for some 120 years. In 1986 Pacific Lumber was acquired by Maxxam Incorporated, and in order to pay off Maxxam’s debt for the buyout, Pacific Lumber began cutting down old growth redwoods at a faster rate than ever before. The deforestation led to litigation and considerable local protest. In the 1990’s, as a result of federal and state litigation, Pacific Lumber was enjoined from harvesting a particular stand of old growth timber that served as the habitat for the marbled murrelet, an endangered bird. Pacific Lumber, in turn, filed lawsuits alleging an unlawful taking by the state and federal governments of the land declared unusable for timber production and harvesting. To resolve the existing controversies, Pacific Lumber entered into the Headwaters Agreement of 1996 with the State of California and the United States. The agreement provided for the sale of some 7,000 acres of Pacific Lumber’s timberland to the federal government and the State of California, and for Pacific Lumber to obtain the various regulatory approvals discussed above for its remaining 211,000 acres. What follows is a brief history of Pacific Lumber’s process of gaining these approvals—a history necessary to understanding the issues in this case. Pacific Lumber submitted a draft of the SYP to California’s Department of Forestry and Fire Protection (CDF) for its consideration in December 1996. The CDF forwarded the draft SYP to numerous state and federal agencies seeking their comments on February 20, 1997. As will be elaborated on below, the agencies’ comments were critical of, among other things, the draft SYP’s decision to employ large watershed assessment areas that would not accurately register the impacts of logging on individual watersheds and the fish and wildlife they contained. Pacific Lumber provided responses to those comments on April 1, 1997. The state and federal governments and Pacific Lumber entered into a “Pre-permit Application Agreement in Principle” on February 27, 1998, setting forth the regulatory framework governing the approval of further logging on Pacific Lumber’s property. Under the terms of the agreement, Pacific Lumber agreed that its Incidental Take Permit and HCP would be for a term of 50 years. The agreement set forth various specifications for the Implementation Agreement for the Incidental Take Permit and the HCP and agreed to incorporate various conservation measures. The agreement also provided that Pacific Lumber would submit an SYP to CDF and that “[u]pon receipt from Pacific Lumber of an SYP incorporating CDF’s request for timber growth estimates, CDF will find the SYP sufficient for public review.” The agreement further provided that “[t]he SYP will be evaluated by the [DFG] and CDF” under the California Endangered Species Act (CESA; Fish & G. Code, § 2050 et seq.), the Forest Practice Act, “and other applicable state statutes to ensure that it satisfies applicable statutory requirements.” In June 1998, Pacific Lumber submitted a draft combined SYP/HCP, referred to in the litigation as the Public Review Draft. The draft contained descriptions of existing or “baseline” forest conditions, projections of long-term sustained yield, impacts of anticipated logging on habitat and wildlife, and proposed mitigation measures and management practices to minimize those impacts. The draft was released to the public on July 14, 1998. The HCP proposed three primary conservation strategies to protect endangered and threatened species. The first is the establishment of a series of reserves, i.e., contiguous areas of second growth and old growth redwoods called marbled murrelet conservation areas, after the endangered sea bird whose habitat is partly within Pacific Lumber’s land. These conservation areas are to total approximately 8,446 of the 211,000 acres, including 1,522 acres of uncut old growth redwoods and 3,174 acres of second growth redwoods. These reserves would be for the most part, though not entirely, protected from timber harvesting. The second strategy was the establishment of a series of riparian management zones around streams, establishing no-cut buffers around the streams varying in size depending on the extent to which wildlife was found in the stream, and taking various measures to reduce the amount of sediment that accumulates in the streams. The third strategy would include various timber harvesting or “silvicultural” practices that would protect wildlife, including use of “best management practices” to monitor the forest fish and wildlife and ensure that their populations do not fall below baseline levels. At about the same time, Pacific Lumber officially submitted an application for an Incidental Take Permit to the United States Fish and Wildlife Service and the National Marine Fisheries Service. In order for the Headwaters Agreement to become a reality, Congress and the Legislature were required to approve funding for the purchase of the Headwaters Forest. Congress authorized $250 million in October 1997, conditioned on the approval of all required regulatory permits on or before March 1, 1999. On September 1, 1998, the Legislature passed Assembly Bill No. 1986 (1997-1998 Reg. Sess.) (Stats. 1998, ch. 615 (hereafter Assembly Bill 1986)), which approved expenditures of $245.5 million. Assembly Bill 1986 conditioned the appropriation of funds on modification of the HCP to provide additional measures to mitigate the impacts of Pacific Lumber’s logging on threatened and endangered species. {Ibid.) In October 1998, a draft EIS/EIR was released analyzing the Headwaters acquisition and the Public Review Draft SYP/HCP. The EIS/EIR evaluated five separate alternative harvest levels ranging from 86.9 million board feet (mmbf) to 233.5 mmbf per year on average for the first decade. Pacific Lumber’s proposal for timber operations (alternative 2) had the highest projected harvest volume of 233.5 mmbf per year on average in the first decade. With each of these alternatives, projections were made over a 120-year period and harvest levels were projected to decline in the middle decades and rise again in the later decades. The public draft EIS/EIR also noted that Pacific Lumber’s SYP/HCP application had not been modified in response to the restricting provisions of Assembly Bill 1986, but that the draft EIS/EIR would include assessments of the environmental effects of implementing the legislation. On January 22, 1999, the final EIS/EIR was issued, after an intensive period of public comment. Additional mitigation measures, which were added to the final HCP, reduced the land available for harvest and therefore reduced the estimated long-term sustained yield. The final HCP also called for the analysis of the impacts of logging on individual planning watersheds within five years of the SYP/HCP’s approval. The EIS/EIR was critical of the high harvest levels contemplated by Pacific Lumber and the methodology it used. As the EIS/EIR states, the harvest level projections were based on intensive management methods, “such as site preparation, planting improved stock, herbicide application to control competing vegetation, and thinning to concentrate growth,” which were expected to increase harvest yields. The EIS/EIR commented that Pacific Lumber “has not managed its land using these intensive management practices until recently. Therefore, there is no record to judge [Pacific Lumber’s] likely success at achieving the projected growth increases. If the higher harvest during the first two decades are not followed by a continuing and successful intensive management program, there will be a considerable decrease in timber available for harvest in the following decades.” As a result of this skepticism, as well as the recognition that the restrictions imposed by Assembly Bill 1986 and the final HCP would mean reduced harvest levels, the EIS/EIR proposed to reduce harvest levels from the 233.5 mmbf per year on average in the first decade. Appendix Q to the EIS/EIR, which purported to set forth the contents of the final SYP, proposed a new long-term sustained yield of about 196.5 mmbf per year, with an estimated harvest volume for maximum sustained production of 176.1 mmbf per year on average for the first decade. Appendix Q also contained a “crosswalk,” or index, that purported to identify where all the components of a final SYP were to be found. The EIS/EIR also included a listing of changes to the draft EIS/EIR in response to public comments. On October 29, 1998, Pacific Lumber officially applied for a state Incidental Take Permit and notified DFG that it would be seeking a Streambed Alteration Agreement pursuant to Fish and Game Code former section 1603. The United States Fish and Wildlife Service, in approving the federal Incidental Take Permit and HCP on February 26, 1999, acknowledged that the necessary watershed analysis had not yet occurred but would be done within the next five years, and that various protective measures would be taken in the interim. CDF requested, and Pacific Lumber supplied, additional information regarding the SYP in February 1999. On February 25, 1999, DFG made the required CEQA findings and approved the final EIS/EIR. The CDF director (Director) also approved the SYP, specifically approving the long-term sustained yield estimate identified as alternative 25a, set at 196.1 mmbf per year with a projected conifer harvest level of 136.6 mmbf per year for the first decade. The Director stated that “the Department has determined that alternative 25 a is the only alternative with constraints and timber harvesting that are consistent with the interim mitigations required by the [HCP] and the EIS/EIR.” On February 27, 1999, Pacific Lumber wrote to the Director, disagreeing with some assumptions and advocating alternative 25. Under alternative 25, the long-term sustained yield was set at 190 mmbf per year, and the projected conifer harvest level in the first decade was 178.8 mmbf per year—similar to the projections found in appendix Q to the final EIS/EIR. Both alternatives 25 and 25a proposed to implement the mitigation measures found in the final HCP, but the former was based on assumptions about results of the required watershed analysis that were more optimistic than the latter, i.e., that future watershed analysis would result in fewer restrictions on logging than was assumed under alternative 25a. Officials of the United States Fish and Wildlife Service, the National Marine Fisheries Service, and the DFG also wrote to express their support for alternative 25. They argued that the HCP provided for an “adaptive management” approach that would allow for greater flexibility as conditions in the field were evaluated, which would lead to a relaxation of some of the interim restrictions contained in the HCP, and that therefore the higher harvest level estimate was more likely to be accurate. On March 1, 1999, right at the deadline imposed by federal legislation for obtaining the necessary regulatory approvals, the Director of CDF approved the SYP, selecting alternative 25, allowing for the higher harvest levels. The approved harvest level was substantially lower than Pacific Lumber’s harvest levels for 1987-1997, after Maxxam Corporation had taken over the company, of 250 mmbf per year on average, but was substantially higher than the historic level of logging prior to that time of approximately 120 mmbf per year. On February 26, 1999, DFG executed a Streambed Alteration Agreement pursuant to Fish and Game Code former section 1603. On March 1, 1999, the DFG approved a state Incidental Take Permit authorizing the take of various species incidental to Pacific Lumber’s timber harvesting. On March 31, 1999, an administrative mandamus action was filed by the Environmental Protection Information Center and the Sierra Club (hereafter collectively EPIC). The lawsuit challenged (1) the approval of the SYP by CDF, (2) the issuance of the state Incidental Take Permit by DFG, (3) the approval of the Streambed Alteration Agreement by DFG, and (4) the findings issued by both state agencies under CEQA concerning the Headwaters Forest project. Simultaneously, the United Steelworkers of America (Steelworkers) also petitioned for administrative mandamus to challenge only the SYP on similar but not identical grounds. The trial court proceedings involved an extensive preliminary dispute over the contents of the administrative record. The court then held several days of evidentiary hearings on whether certain materials had been excluded from the administrative record—i.e., whether documents existed that should have been considered by the agencies. EPIC and the Steelworkers were granted leave to amend their complaints to allege a failure by the state agencies to provide an accurate administrative record. The trial court ruled on EPIC’s and the Steelworkers’s petitions in two separate statements of decision, issued June 22, 2003. The trial court ruled that petitioners had failed to sufficiently demonstrate that any of the challenged agency decisions were not based on substantial evidence, because they had not sufficiently identified the evidence claimed to be insufficient. In virtually all other respects, the trial court agreed with petitioners that the public agencies had not proceeded according to law. Specifically, the trial court held that the SYP was deficient on a number of grounds, and that the state Incidental Take Permit, Streambed Alteration Agreement and CEQA findings were all inadequate and represented a failure to comply with the law on the part of CDF and DFG. The trial court then held a further hearing to decide whether Pacific Lumber’s timber operations should be enjoined. The court, weighing the balance of harms, concluded that although Pacific Lumber’s past and current timber operations had resulted in water quality degradation and reduction in fish population, enjoining all of Pacific Lumber’s timber operations would cause excessive hardship to the company, its employees, and the community. The court concluded that timber operations being conducted pursuant to THP’s approved prior to the court’s July 22, 2003 statement of decision would not be enjoined but that logging under any THP approved after that date that relied upon the now-vacated Sustained Yield Plan would be enjoined. Separate judgments were entered in the lawsuits filed by the environmental plaintiffs and by the Steelworkers, and the trial court issued a peremptory writ of mandate in each case. Pacific Lumber and both state agencies appealed from each judgment. The Court of Appeal consolidated the appeals. For reasons discussed at greater length below, the Court of Appeal reversed the trial court on every point that had been decided adverse to the state agencies and Pacific Lumber, upholding the validity of each of the regulatory approvals and reversing the granting of a peremptory writ of mandate. EPIC and the Steelworkers separately petitioned for review and we granted both petitions. The Steelworkers’s petition raises several issues related to the SYP. EPIC raises some of these same issues and, in addition, raises issues with respect to the Incidental Take Permit, the Streambed Alteration Agreement, and the adequacy of CEQA findings. The issues raised by the parties before this court, while numerous, are somewhat fewer than were raised below. III. Discussion A. Standard of Review The standard of review, and the related question of what constitutes prejudicial error, will be discussed in more detail below. For now, we state these general principles. First, the standard for review of agency decisions in connection with regulatory approvals is generally one of abuse of discretion. “ ‘Abuse of discretion is established if the respondent [agency] has not proceeded in the manner required by law, the order or decision is not supported by the findings, or the findings are not supported by the evidence.’ [Citations.]” (Sierra Club v. State Bd. of Forestry (1994) 7 Cal.4th 1215, 1236 [32 Cal.Rptr.2d 19, 876 P.2d 505] (Sierra Club).) In this case, we are reviewing for errors of law, and will not engage in substantial evidence review. As the Court of Appeal correctly stated: “In the present case, the trial court rejected the allegations in [EPIC’s] writ petition that the administrative findings were unsupported by the evidence. The trial court found that [EPIC] failed to present a summary of the material evidence or any argument on the sufficiency of the evidence. In essence, the trial court found that [EPIC] waived or abandoned [its] challenges to the factual bases for the administrative decisions. [EPIC has] not cross-appealed, nor [does it] dispute that the focus of our review is whether the state agencies committed legal, not factual, error. Hence, for purposes of our review, we will accept that the administrative findings were supported by the evidence and we will confine our review to determining whether the state agencies failed to proceed in a manner required by law.” In determining whether the agency complied with the required procedures and whether the agency’s findings are supported by substantial evidence, the trial court and the appellate courts essentially perform identical roles. We review the record de novo and are not bound by the trial court’s conclusions. (Bixby v. Pierno (1971) 4 Cal.3d 130, 149, fn. 22 [93 Cal.Rptr. 234, 481 P.2d 242]; Sierra Club v. California Coastal Com. (1993) 19 Cal.App.4th 547, 557 [23 Cal.Rptr.2d 534].) B. Challenges to the Sustained Yield Plan 1. Standing of the Steelworkers As a threshold matter, Pacific Lumber contends that the Steelworkers have no standing to bring this writ of mandate action to challenge the SYP. We disagree. Generally speaking, in order to have standing to sue, “a party must be ‘beneficially interested’ (Code Civ. Proc., § 1086), i.e., have ‘some special interest to be served or some particular right to be preserved or protected over and above the interest held in common with the public at large.’ ” (Associated Builders & Contractors, Inc. v. San Francisco Airports Com. (1999) 21 Cal.4th 352, 361-362 [87 Cal.Rptr.2d 654, 981 P.2d 499].) There is nonetheless a well-established exception to the beneficial interest rule for citizen suits. “ ‘ “ ‘[W]here the question is one of public right and the object of the mandamus is to procure the enforcement of a public duty, the relator need not show that he has any legal or special interest in the result, since it is sufficient that he is interested as a citizen in having the laws executed and the duty in question enforced (Common Cause v. Board of Supervisors (1989) 49 Cal.3d 432, 439 [261 Cal.Rptr. 574, 777 P.2d 610].) The trial court found that in this case, which involves the proper enforcement of administrative regulations governing a plan for logging over 200,000 acres of timberland highly valued both for environmental and economic reasons, a public right and a public duty were at stake. Pacific Lumber did not contest that finding on appeal. Pacific Lumber argues rather that an exception to the rule of citizen standing should be recognized for labor unions like the Steelworkers, along the lines of the exception recognized for corporations in Waste Management of Alameda County, Inc. v. County of Alameda (2000) 79 Cal.App.4th 1223 [94 Cal.Rptr.2d 740] (Waste Management). In that case, in considering whether a corporation had standing to bring a CEQA action under the citizen suit doctrine, the court reasoned that “where a corporation attempts to maintain a citizen suit, it is appropriate to require the corporation to demonstrate it should be accorded the attributes of a citizen litigant, since it generally is to be expected that a corporation will act out of a concern for what is expedient for the attainment of corporate purposes . . . .” (79 Cal.App.4th at p. 1238.) In giving effect to this principle, the court articulated a number of factors that may be considered, including “whether the corporation has demonstrated a continuing interest in or commitment to the subject matter of the public right being asserted [citations]; whether the entity is comprised of or represents individuals who would be beneficially interested in the action [citations]; whether individual persons who are beneficially interested in the action would find it difficult or impossible to seek vindication of their own rights [citations]; and whether prosecution of the action as a citizen’s suit by a corporation would conflict with other competing legislative policies [citation].” (Ibid.) We need not decide whether the corporate exception to citizen suits articulated by the Waste Management court is a correct statement of the law, nor whether and to what extent that exception applies to labor unions. In this case, the trial court found that the Steelworkers qualified as a citizen litigant under Waste Management. The court concluded that the Steelworkers had shown a continuing interest in and commitment to issues related to this case, including that of sustainable economic development and environmental quality and specifically issues regarding timber harvesting. The court also found that the union had over 12,000 members in California who had sufficient interest in the proper enforcement of timber harvest laws, that interested individuals would have trouble participating in the litigation due to its size and complexity, and that the Steelworkers’ participation presented no conflict with competing legislative policies. Pacific Lumber did not contest those findings on appeal and does not discuss the findings before this court. It does quote a statement in the record that the Steelworkers’ participation was motivated by a labor dispute with Pacific Lumber’s parent company, Maxxam Incorporated. But the record also contains ample evidence the Steelworkers have long-standing involvement in environmental and economic sustainability issues. We will review the trial court’s factual determinations that bear upon the issue of standing under a substantial evidence standard. (Daro v. Superior Court (2007) 151 Cal.App.4th 1079, 1092 [61 Cal.Rptr.3d 716].) We conclude that substantial evidence supports the trial court’s conclusion that the Steelworkers have standing in this case. 2. What Are Sustained Yield Plans? A proper understanding of the nature and purpose of Sustained Yield Plans for timber harvesting begins by placing them in the context of the Forest Practice Act (Pub. Resources Code, § 4511 et seq.). “The Act’s provisions, together with implementing rules and regulations promulgated by the State Board of Forestry (board) ([Pub. Resources Code,] §§ 4521.3, 4551), provide a comprehensive scheme regulating timber operations in a way which promotes the legislative ‘goal of [achieving] maximum sustained production of high-quality timber products . . . while giving consideration to values relating to recreation, watershed, wildlife, range and forage, fisheries, regional economic vitality, employment, and aesthetic enjoyment’ ([Pub. Resources Code,] §§4513, subd. (b), 4512, subd. (c)). The heart of the scheme is its requirement that logging be carried out only in conformance with a timber harvesting plan (THP or plan) submitted by the timber owner or operator and approved by the department after determining, with an opportunity for input from state and county agencies and the general public, that the proposed operations conform to the Act and rules and regulations. ([Pub. Resources Code,] §§ 4581-4582.75, 4583; [citations].) [f] Since 1976, the THP preparation and approval process developed under the Act has been certified as the functional equivalent to, and hence an adequate substitute for, the full environmental impact report (EIR) process required by CEQA. [Citations.]” (T.R.E.E.S. v. Department of Forestry & Fire Protection (1991) 233 Cal.App.3d 1175, 1180 [285 Cal.Rptr. 26].) As part of fulfilling the Forest Practice Act’s goals, the Legislature has authorized the Board of Forestry and Fire Protection to create rules and regulations for the development of Sustained Yield Plans. (Pub. Resources Code, § 4551.3, subd. (a).) The SYP is intended to serve as a kind of master plan for timber harvesting a large geographic area. The board’s regulations, adopted as article 6.75 of title 14 of the California Code of Regulations, declares: “This Article carries out the Legislature’s direction that the Board adopt regulations to assure the continuous growing and harvesting of commercial forest tree species and to protect the soil, air, fish and wildlife, and water resources in accordance with the policies of the . . . Act .... Those policies include creating and maintaining a system of timberland regulations and use which ensures that timberland productivity is maintained, enhanced and restored where feasible and the goal of maximum sustained production of high-quality timber products ... is achieved while giving consideration to environmental and economic values. The Sustained Yield Plan (SYP) may be submitted at the option of the landowner and is intended to supplement the THP process by providing a means for addressing long-term issues of sustained timber production, and cumulative effects analysis which includes issues of fish and wildlife and watershed impacts on a large landscape basis.” (FP Rules, § 1091.1, subd. (b).) Under the Forest Practice Rules, an SYP “shall not replace a THP. However, to the extent that sustained timber production, watershed impacts and fish and wildlife issues are addressed in the approved SYP, these issues shall be considered to be addressed in the THP; that is the THP may rely upon the SYP.” (FP Rules, § 1091.2, italics added.) Forest Practice Rules section 1091.45, subdivision (a) further elaborates on the SYP requirements: “Consistent with the protection of soil, water, air, fish and wildlife resources a SYP shall clearly demonstrate how the submitter will achieve maximum sustained production of high quality timber products while giving consideration to regional economic vitality and employment at planned harvest levels during the planning horizon. The average annual projected harvest over any rolling 10-year period, or over appropriately longer time periods for ownerships which project harvesting at intervals less frequently than once every 10 years, shall not exceed the long-term sustained yield estimate for a SYP submitter’s ownership.” Forest Practice Rules section 1091.3 defines “Planning Horizon” as the “100 year period over which sustained timber production, watershed, and fish and wildlife effects shall be evaluated.” The Forest Practice Rules also require “[a]n estimate of the long-term sustained yield.” (FP Rules, § 1091.45, subd. (c)(2).) Thus, the SYP is a kind of master plan for timber harvesting over a long time period that supplements but does not replace the THP process, and individual THP’s may rely on the SYP to the extent it analyzes the pertinent issues. 3. Omitted Public Comments The Steelworkers contend that certain comments submitted by the public regarding the draft SYP were not taken into account by CDF, which amounts to prejudicial error. It is first undisputed that none of the comments in question were placed in the administrative record. CDF certified the administrative record. A certified record in an action challenging the sufficiency of an EIS/EIR under CEQA is supposed to include all public comments and supporting documentation. (Pub. Resources Code, § 21167.6, subd. (e)(6)-(8), (10)—(11).) Moreover, as the Court of Appeal stated: “The record does suggest that the missing documents were not taken into account. The trial court explained that the order for preparation of the administrative record required the Department of Forestry to prepare a record of all documents that were before the agency and taken into account—not just the documents from the agency’s file compiled post hoc. Trial counsel for the Department (the Attorney General) conceded at trial that what was not in the certified administrative record was not taken into account. The question, then, is whether the failure of the Department of Forestry to consider the missing documents rendered the Sustained Yield Plan invalid.” The trial court found that three types of public comments were not considered by CDF. First, there were documents submitted prior to the November 16, 1998 deadline for receiving public comments on the SYP. Second, there were written documents submitted by members of the public at public hearings. Third, there were a number of letters and public comments submitted after November 16, 1998, which, for reasons discussed below, the Steelworkers contend and the trial court found were timely submitted. Each of these categories will be discussed in turn. As to the first category of comments, CDF characterizes them as “cover memos written on behalf of [EPIC], which transmitted reference materials such as scientific articles cited by other members of the public in their comment letters.” CDF asserts that these materials “contain no substantive comments.” An examination of the record reveals that the exhibits in question consist of scholarly articles about various subjects generally related to the kind of subjects addressed in an SYP; for example, an article entitled “Forest Vegetation Removal and Slope Stability in the Idaho Batholith.” One of the omitted exhibits in this category, submitted by Cynthia Elkins, contains documents pertaining to Pacific Lumber’s previous THP’s. As the Court of Appeal observed: “The articles themselves are not comments on the Sustained Yield Plan but are reference materials that were cited in comment letters that had been previously submitted. Those comment letters are in the certified administrative record and were responded to in the final EIS/EIR.” We agree with the implicit distinction drawn by the Court of Appeal. Although CDF has a duty to consider comments by members of the public under the Forest Practice Rules, that duty does not necessarily extend to considering all of the non-project-specific secondary materials submitted in support of the comments. Whether and to what extent CDF reviews such material cited in the comments is a matter to be left to its sound discretion and professional judgment. This deferential standard does not change when scholarly articles are not only cited in the comments but reproduced and submitted along with the comments. There is no indication CDF did not consider the comments themselves. The second category of excluded documents is written comments apparently submitted at public hearings, in conjunction with oral comments, some opposing and some supporting the SYP. CDF contends that this material was not included in the administrative record because it was duplicative. The third category of documents is comments submitted after CDF’s comment period closed on November 16, 1998, up to February 22, 1999, comments mainly critical of the SYP. The trial court concluded that the public comment period had been extended and that whether or not it had been extended, CDF should have considered these documents. The Court of Appeal did not dispute this factual conclusion, but held that the failure to consider these documents was nonprejudicial. The record discloses that CDF announced that the public comment period would end on November 16, 1998, “unless the public review period is extended by mutual consent of the SYP submitter and the [CDF].” The United States Fish and Wildlife Service posted a notice in the Federal Register on January 22, 1999, announcing that public comments would be received on the SYP/HCP and the EIS/EIR until February 22, 1999. The notice included the address of the United States Fish and Wildlife Service persons who would be receiving the comments, and also stated that “comments on the SYP may be mailed to John Munn” of CDF. The notice further explained that during the initial comment period, CDF and other government agencies had received approximately 18,000 comments on the SYP/HCP and draft EIS/EIR and that numerous changes had been made in response to those comments and to the enactment of Assembly Bill 1986. The new public comment period was intended to address these changes. We therefore agree with the trial court and Court of Appeal that the Federal Register notice effectively reopened the public comment period for the SYP until February 22, 1999. The question, then, is whether the error in failing to consider the second and third category of comments is prejudicial. In order to address this question, we first consider what constitutes prejudicial error in cases involving environmental review. As previously noted, “Only if the manner in which an agency failed to follow the law is shown to be prejudicial, or is presumptively prejudicial, as when the department or the board fails to comply with mandatory procedures, must the decision be set aside . . . .” (Sierra Club, supra, 7 Cal.4th at p. 1236.) In Sierra Club, we found prejudicial abuse of discretion when the Board of Forestry and Fire Protection approved a THP notwithstanding the fact that real party in interest Pacific Lumber had failed to provide information requested by CDF and DFG. “The failure of the board to proceed as required by law was prejudicial. The absence of any information regarding the presence of the four old-growth-dependent species on the site frustrated the purpose of the public comment provisions of the Forest Practice Act. ([Pub. Resources Code,] §§ 4582.6, 4582.7.) It also made any meaningful assessment of the potentially significant environmental impacts of timber harvesting and the development of site-specific mitigation measures impossible. In these circumstances prejudice is presumed.” (Sierra Club, supra, 7 Cal.4th at pp. 1236-1237.) In coming to this conclusion, we cited with approval Rural Landowners Assn. v. City Council (1983) 143 Cal.App.3d 1013 [192 Cal.Rptr. 325] (Rural Landowners Assn.). (Sierra Club, supra, 7 Cal.4th at p. 1237.) That case considered the approval of an FIR for the annexation and development of certain agricultural land by the Lodi City Council, when the draft FIR had not been timely submitted to the Governor’s Office of Planning and Research, as required by law. The city council had therefore failed to consider that agency’s substantive comments before approving the FIR. (Rural Landowners Assn., supra, at pp. 1017-1018.) The trial court found that because the state agency’s comments were incorporated into an addendum after the approval, and the city council had not changed its decision, failure to include the comments in the FIR was harmless error. (Id. at p. 1019.) The Court of Appeal in Rural Landowners Assn, disagreed with this line of reasoning: “Were we to accept respondent’s position that a clear abuse of discretion is only prejudicial where it can be shown the result would have been different in the absence of the error, we would allow ... a subversion of the purposes of CEQA. Agencies could avoid compliance with various provisions of the law and argue that compliance would not have changed their decision. Trial courts would be obliged to evaluate the omitted information and independently determine its value. . . . We conclude that where that failure to comply with the law results in a subversion of the purposes of CEQA by omitting information from the environmental review process, the error is prejudicial. The trial court may not exercise its independent judgment on the omitted material by determining whether the ultimate decision of the lead agency would have been affected had the law been followed. The decision is for the discretion of the agency, and not the courts.” (Rural Landowners Assn., supra, 143 Cal.App.3d at pp. 1022-1023.) The remedy for this deficiency was for the trial court to have issued a writ of mandate compelling the city to prepare a supplemental FIR. (Id. at p. 1025.) The above rule emerges out of the difficulty courts have in assessing the effects of the omitted information, much of it generally highly technical, on the ultimate decision. A trial court’s “independent judgment that the information was of ‘no legal significance’ amounts to a ‘post hoc rationalization’ of a decision already made, a practice which the courts have roundly condemned.” (Rural Landowners Assn., supra, 143 Cal.App.3d at p. 1021.) On the other hand, errors in the CEQA or THP process which are insubstantial or de minimis are not prejudicial. (Environmental Protection Information Center, Inc. v. Johnson (1985) 170 Cal.App.3d 604, 623, fn. 11 [216 Cal.Rptr. 502],) The Forest Practice Rules require the director to “review public input” at the close of a public comment period prior to approval of an SYP. (FP Rules, § 1091.10, subd. (e).) Public comments are therefore an integral part of the SYP approval process, as they are in the FIR approval process, and such comments, like the comments from state agencies at issue in Rural Landowners Assn., may contain information critical to that process. “Public review is essential to CEQA. The purpose of requiring public review is ‘ “ ‘to demonstrate to an apprehensive citizenry that the agency has, in fact, analyzed and considered the ecological implications of its action.’ ‘[P]ublic review and comment . . . ensures that appropriate alternatives and mitigation measures are considered, and permits input from agencies with expertise in timber resources and conservation.’ [Citation.] Thus public review provides the dual purpose of bolstering the public’s confidence in the agency’s decision and providing the agency with information from a variety of experts and sources.” (Schoen v. Department of Forestry & Fire Protection (1997) 58 Cal.App.4th 556, 573-574 [68 Cal.Rptr.2d 343].) If it is established that a state agency’s failure to consider some public comments has frustrated the purpose of the public comment requirements of the environmental review process, then the error is prejudicial. (See Sierra Club, supra, 7 Cal.4th at pp. 1236-1237; Rural Landowners Assn., supra, 143 Cal.App.3d at pp. 1022-1023.) As the case law establishes, courts are generally not in a position to assess the importance of the omitted information to determine whether it would have altered the agency decision, nor may they accept the post hoc declarations of the agencies themselves. (Rural Landowners Assn., supra, 143 Cal.App.3d at p. 1021.) On the other hand, an agency’s failure to consider public comments is not necessarily prejudicial. For example, when the material not considered was, on its face, demonstrably repetitive of material already considered, or so patently irrelevant that no reasonable person could suppose the failure to consider the material was prejudicial, or when the omitted material supports the agency action that was taken, then such omissions do not subvert the purpose of the public comment provisions and are nothing more than technical error. Short of these showings, which the agency that failed to consider the comments would have the burden to make, the omission of the information must be deemed prejudicial. With these principles in mind, we turn to the present case. The Court of Appeal stated that “[t]he Steelworkers do not dispute that the missing comments were duplicative, raising objections to the Sustained Yield Plan that were covered by over 16,000 written comments made by others during the public comment period and responded to in the final EIS/EIR.” The Steelworkers did not contest the accuracy of that statement in its rehearing petition to the Court of Appeal nor in its briefing before this court. Rather, the Steelworkers argue only that under Rural Landowners Assn., the question whether the comments are duplicative is irrelevant, because a court “may not exercise its independent judgment on the omitted material by determining whether the ultimate decision of the lead agency would have been affected had the law been followed.” (Rural Landowners Assn., supra, 143 Cal.App.3d at p. 1023.) But a determination of whether omitted information would have affected an agency’s decision is significantly different from a determination of whether the omitted material is duplicative of information already considered. The former determination is highly speculative, an inquiry that takes the court beyond the realm of its competence. The latter determination—whether omitted evidence is duplicative or cumulative—is an inquiry courts commonly make. (See, e.g., People v. Keehley (1987) 193 Cal.App.3d 1381, 1386-1387 [239 Cal.Rptr. 5].) To be sure, the question whether public comments were duplicative, particularly when these comments involve, as they do here, highly technical material, may not be obvious to a reviewing court. As stated above, when an SYP or FIR is challenged for failing to consider comments alleged to contain significant new information, it is the burden of the agency that erroneously omitted the comments to establish they are merely duplicative. When, however, their duplicative nature essentially is not contested, as in the present case, no further inquiry is necessary. We conclude CDF’s failure to consider these comments was not prejudicial. 4. Consideration in Sustained Yield Plan of Long-term Regional Economic Vitality and Employment The Steelworkers contend that the SYP failed to consider issues of regional economic vitality and employment over a 100-year period, as required in the Forest Practice Rules. As Forest Practice Rules section 1091.45, subdivision (a) states: “Consistent with the protection of soil, water, air, fish and wildlife resources a SYP shall clearly demonstrate how the submitter will achieve maximum sustained production of high quality timber products while giving consideration to regional economic vitality and employment at planned harvest levels during the planning horizon.” (Italics added.) As noted ante, Forest Practice Rules section 1091.3 defines “Planning Horizon” to mean “the 100 year period over which sustained timber production, watershed, and fish and wildlife effects shall be evaluated”—although in the present case a 120-year planning horizon was chosen. Thus, the Forest Practice Rules require “consideration” of regional employment and economic vitality over a 100-year period in the SYP’s demonstration of how Pacific Lumber will achieve “maximum sustained production of high quality timber products.” This is consistent with the primary objective of the SYP regulations: to address “long-term issues of sustained timber production,” such that the “goal of maximum sustained production of high-quality timber products ... is achieved while giving consideration to environmental and economic values.” (FP Rules, § 1091.1, subd. (b).) The Steelworkers point to the statement in the SYP that the first decade of the 120-year planning period “is the only period appropriate for [analysis of] economic and social effects. Too many variables, including economic diversity of the local economy, strain of the local timber industry, and timber-related tax revenue, would not be constant over a longer-term analysis period. Thus, a discussion of social and/or economic effects beyond 2012 would be very uncertain, if not speculative, and would not be appropriate in either an FIS or FIR.” It contends that this limitation of economic analysis to the first decade contravenes the injunction of section 1091.45 of the Forest Practice Rules that the SYP consider economic and employment effects for the entire planning horizon. In rejecting the Steelworkers’ claim, the Court of Appeal relied on a brief portion of the Public Review Draft of the SYP/HCP that in fact assessed the employment impacts of logging over a 120-year period. In that section, Pacific Lumber estimated jobs per decade in relation to millions of board feet of timber per year, using a multiplier of six jobs per year for every million board feet harvested. On this basis, Pacific Lumber projected a decline in employment as timber harvesting tapered off, going from a high of 1,401 jobs in the first decade to a low of 844 jobs in the fifth decade and then steadily rising thereafter as newer growth timber matured and was harvested. As the Steelworkers point out, however, although there is some confusion about the contents of the final SYP (as discussed below), the above draft section was superseded and was not incorporated in the final SYP. CDF does not dispute that the employment portion of the Public Review Draft of the SYP was superseded. Rather, it states that “the evolution of the discussion of jobs and economic vitality from draft to final indicates that the issue is analyzed over twelve decades but ultimately CDF found any discussion beyond ten years to be speculative. This represents evidence of the consideration of the issue, not a failure to consider.” Moreover, the final SYP does contain projections of harvest levels for each decade for a 120-year period that would be the basis for further economic analysis of the effects of timber harvesting. The SYP projects a conifer harvest level of 178.8 mmbf per year for the first decade, declining in each subsequent decade to a low of 113.8 mmbf per year on average for the fifth decade, and then gradually increasing to 166.2 mmbf per year on average for the final decade. The projections also specify the kind of timber to be harvested, with old growth timber making up a large portion of the harvest in the first decade and giving way increasingly to younger growth timber in subsequent decades. It is unclear from the Forest Practice Rules how much detail is required in “giving consideration” to economic issues over the planning horizon. The rules do state that in an SYP, “the accuracy of, and therefore the need for, detailed future projections becomes less as the time horizon lengthens” and that “[i]t is not the intent of this Article that speculation shall be promoted such that analyses shall be undertaken which would produce only marginally reliable results or that unneeded data would be gathered. ... It is the intent of this Article that the requirements for informational or analytical support for a SYP shall be guided by the principles of practicality and reasonableness; no information or analysis shall be required which in the light of all applicable factors is not feasible. However, it is the intent of this Article that all potential adverse environmental impacts resulting from proposed harvesting be described, discussed and analyzed before such operations are allowed. Should such analysis not be included in the SYP, it must be contained in those THPs which rely on the SYP, including any impact discovered after the SYP is approved.” (FP Rules, § 1091.1, subd. (b).) As a general matter, courts will be deferential to government agency interpretations of their own regulations, particularly when the interpretation involves matters within the agency’s expertise and does not plainly conflict with a statutory mandate. (See Yamaha Corp. of America v. State Bd. of Equalization (1998) 19 Cal.4th 1, 12-13 [78 Cal.Rptr.2d 1, 960 P.2d 1031].) In the present case, the question of how much economic and employment analysis over how long a period of time is feasible, and at what point it becomes speculative, is a judgment call, and we will not disturb the agency’s determination without a demonstration that it is clearly unreasonable. Here, the SYP contains information regarding (1) projected harvest levels for 12 decades; (2) a credible estimate of the employment effects of such harvesting and projection of timber-related employment over 12 decades in the draft SYP; (3) a detailed analysis of economic and employment impacts of timber harvesting in the first decade; and (4) a reasoned decision to omit detailed analysis of the effects of timber harvesting on employment and the economy over the subsequent decades of the planning horizon. Under these circumstances, we conclude that CDF did not abuse its discretion in determining that the SYP had adequately followed the Forest Practice Rules by “giving consideration” to the economic and employment consequences of timber harvesting during the period of the planning horizon (EP Rules, § 1091.45), while at the same time not engaging in overly speculative analysis (FP Rules, § 1091.1). 5. Is There a Valid Sustained Yield Plan Document? Petitioners contend there was no single, agreed-upon SYP that has been approved, and that the CDF director’s approval of the SYP must therefore be invalid. We agree. As discussed, various federal and state agencies approved several interrelated documents: an EIS/EIR, an HCP and an SYP. The final EIS/EIR was circulated in January 1999, and contained an appendix Q, which purported to identify the final SYP. Appendix Q states: “This [f]inal EIS/EIR constitutes the final HCP/SYP. To reduce the volume of paper associated with finalizing the six-volume proposed HCP/SYP, it is incorporated here by reference. To ensure that all requirements of the SYP are met, and that key components can be located easily, the following crosswalk is provided. It indicates the primary location where information may be found; it is not all-inclusive, and relevant information may be found in other sections. Except as noted, volume and part references refer to [Pacific Lumber’s] July 1998 draft SYP/HCP.” The crosswalk then references the topics that are required to be addressed in the SYP together with the volume and section in which the topic is addressed in the draft SYP/HCP. For example, “[sustained timber production assessment” is found in “Volume I, Part C, . . . and Part E,” and “Fish and wildlife assessment” is found in Volumes I, II, and IV. Pacific Lumber argues that appendix Q and the documents to which it refers constitute the final SYP. As petitioners point out, however, there are several problems with relying on appendix Q to definitively set forth the contents of the final SYP. First, by its own terms, it “is not all-inclusive, and relevant information may be found in other sections.” Second, appendix Q purports to incorporate the six-volume draft SYP circulated for public review. Yet in a document that was prepared for the trial court below, CDF made clear that substantial portions of the Public Review Draft SYP had been superseded, noting in the margins of the table of contents of the Public Review Draft SYP those portions that had been replaced by the final EIS/EIR. Thus, the appendix Q crosswalk, in referencing a Public Review Draft SYP that had been substantially superseded, failed to give an accurate picture of the document’s contents at the time the SYP was approved by the CDF director on March 1, 1999. Third, appendix Q is included in a January 1999 document. Additional information was provided by Pacific Lumber in February 1999 that the CDF Director relied on for his March 1, 1999 approval of the SYP. On February 16, 1999, Pacific Lumber presented CDF with a lengthy document entitled “Updated Sustained Yield Planning Information,” with extensive supplemental information pertaining to the long-term sustained yield estimate. Pacific Lumber on February 23, 1999, provided further extensive information on alternative 25A, which contemplated a conifer harvest of approximately 136.6 mmbf per year for the first decade in response to a CDF request. Along with providing that information, Pacific Lumber made clear it believed that this alternative was infeasible inasmuch as it contemplated a lower harvest than Pacific Lumber found economically viable. On February 25, 1999, the Director approved the SYP with alternative 25A. On February 28, 1999, Pacific Lumber again supplied extensive additional information, this time targeted to alternative 25, which contemplated the higher conifer harvest of 178.8 mmbf per year for the first decade. The Director eventually chose alternative 25. None of the voluminous supplemental information on which the Director partly based his decision is included in appendix Q. CDF, in contrast to Pacific Lumber, does not contend that appendix Q represents the definitive SYP. Rather, it claims that the CDF Director’s March 1, 1999 and February 25, 1999 letters approving the SYP contain “a description of the location of the substantive information which comprises the various components of the Sustained Yield Plan required by the Forest Practice Rules.” As the CDF Director stated in the March 1, 1999 letter, his determination that the SYP was in conformance with Forest Practice Rules was “[b]ased upon analysis of the revised draft of [the SYP] submitted by [Pacific Lumber] in July of 1998 in combination with provisions of the HCP, EIS/EIR, supplemental information received from [Pacific Lumber] on February 16, 1999, responses from Pacific Lumber to watershed questions received on February 23, 1999, and with additional information provided by the National Marine Fisheries Service, the U.S. Fish and Wildlife Service, and the California Department of Fish and Game . . . .” Yet the Director’s terse statement in this approval letter cannot be regarded as setting forth a definitive SYP. First, the letter refers to the Public Review Draft SYP, a substantial portion of which, as discussed above, had been superseded. The Director’s approval does not specify which portions of the draft SYP are