PWS CSE GunflintRD.pdf

PERFORMANCE WORK STATEMENT

SUPERIOR NATIONAL FOREST

GUNFLINT RANGER DISTRICT, GRAND MARAIS, MN

Common Stand Exam (CSE) Project

July 1, 2020

PWS.1.0 INTRODUCTION

PWS.1.1 SCOPE OF WORK

Perform common stand exams for the Gunflint Ranger District, Superior National Forest located in USFS Region 9. The Contractor shall furnish the necessary personnel, material, equipment, services and facilities (except as otherwise specified), to perform this Performance Work Statement

PWS.1.2 DESCRIPTION AND LOCATIONS

This project is located on the Superior National Forest. Work will be done on the Gunflint Ranger District.

The District Office is located in Grand Marais, MN. Government housing is not available.

General location and vicinity map is available (see attached map).

PWS.1.3 ACCESSIBILITY

The Contractor shall be responsible for obtaining all necessary permission to gain access to sample locations. If the Contractor cannot obtain permission to access a sample location, the Contractor must notify the Government in writing.

Vehicle access may be difficult or restricted. Stand locations may necessitate that the Contractor walk to the stand or acquire some other means of travel. Government will not plow or otherwise keep roads open.

PWS.1.4 PROGRAM OF WORK

Contractor shall complete work on a given stand to the Government’s satisfaction before moving to the next line item.

The Government will, as much as possible, groups stands in close geographical proximity.

Upon request by Contractor, the Government will provide a “courtesy” demonstration on data collection protocol and procedures.

PWS.1.5 CONTRACTOR QUALITY CONTROL

Prior to work commencing a Quality Control Plan will be submitted by the Contractor. The general Quality Control Plan must demonstrate how the Contractor will assure quality to meet the requirements and specifications of the contract. The Quality Control Plan shall describe how quality will be monitored to assure the performance standards are met, the supervision of crew and work, and personnel that will be performing the quality control. Quality control shall include monitoring quality during and after CSE work is being completed.

PWS.1.6 PROJECT MANAGEMENT PLAN

Provide a project management plan that describes your ability to organize, schedule (production rate), and staff (crew size) this project to completion and on schedule.

Performance Work Statement Gunflint Ranger District - Common Stand Exam Project

PWS.2.0 CONTRACTOR WORK REQUIREMENTS AND STANDARDS/TECHNICAL SPECIFICATIONS

PWS.2.1 STAND EXAM INSTRUCTIONS

PWS.2.1.1

A list of sample plot locations (latitude and longitude coordinates) within each stand will be provided by the Government at the pre-work conference. Plots may be allocated as following:

PWS.2.1.1: Table of Stand Size and Estimated Number of Allocated Plots

Stand size (acres)

Estimated Nbr of Plots

Stand size (acres)

Estimated Nbr of Plots

Stand size (acres)

Estimated Nbr of Plots

0-15 3 45-54 8 85-94 12 16-20 4 55-64 9 95-104 13 21-24 5 65-74 10 105-114 14 25-34 6 75-84 11 115+ 15 35-44 7

PWS.2.1.2 Survey Technique:

A global positioning system (GPS) shall be used to locate plot centers.

Acceptable error is +/- 10 meters (30 feet) from plot center.

Recurring errors in plot location that are greater than the acceptable error will make the plot data unsatisfactory, and the Contractor shall re-locate and re-measure the unsatisfactory plots.

PWS.2.1.3 Flagging: To facilitate inspection, the Contractor shall:

Mark all plot centers with a fluorescent pink wire flag. This wire flag will have the compartment, stand and plot identification written on it with black permanent marker. The point at which the wire flag intersects the ground shall be used as plot center.

Sufficient fluorescent pink flagging will be hung on surrounding vegetation, at eye level, to facilitate visual identification of the plot from a distance.

Borderline “In” trees will be marked with fluorescent pink flagging. The flagging will have compartment, stand, plot and “Borderline In” written on it with black permanent marker.

PWS.2.1.4 During field examination, the Contractor should note if originally delineated stand boundaries are incorrect. If so, stand boundaries will be corrected to reflect actual site conditions.

NOTE: A paper map, with current stand boundaries/background image will be provided to Contractor for this purpose. Changes to stand boundaries will be made with permanent ink on the map and turned into the Government at the completion of contract. All maps should be returned to Government at completion of contract.

In the event that plot center falls outside a corrected stand boundary:

Proceed using reciprocal of previous heading, back into the original stand 4 chains (264 feet).

Re-establish the plot and document actual latitude and longitude in Plot Remarks.

Reference Plot Number and reason for re-establishment in Plot Remarks.

In the event that plot center falls within either: 1) A linear opening (road, right-of-way, etc) that is 33 feet or greater in width (includes maintenance clearing on both sides of a road); or 2) An opening greater than 2 acres, use the following procedure to re-establish the plot within the original stand:

Proceed 2 chains (132 feet) into the original stand using previous heading or reciprocal heading.

Re-establish the plot and document actual latitude and longitude in Plot Remarks.

Reference Plot Number and reason for re-establishment in Plot Remarks.

PWS.2.2 RECORDING INSTRUCTIONS

Plot data and location data shall be entered directly into a handheld personal data recorder (PDR) provided by the Contractor. The PDR software used for data entry must be the “ExamsPC” software designed for collecting common stand exam data. The version in effect as of the date of this solicitation will be required. A .cse “template” file with the Superior National Forest’s CSE protocols for this contract will be available from the Forest to enable successful completion of this contract. This template file is available, if requested, prior to award. Plot and location data will be submitted electronically.

ExamsPC can be downloaded at https://www.fs.fed.us/nrm/fsveg/ and loaded onto any PDRs used for data collection prior to start of contract, PWS.2.3 QUALIFICATIONS

The success of this field inventory is dependent primarily on the Contractor’s professionalism and expertise. It is necessary that Contractor’s staff meet certain standards. A crew can consist of one or more individuals. Specific technical experience may be substituted for a given educational requirement.

Minimum qualifications are specifically defined as follows:

Each crew must have a crew leader with undergraduate courses in mensuration, tree identification, plant (shrub/forb) identification, silviculture, and ecology, or adequate prior experience collecting data for accurate Forest inventory or vegetation classification.

Each crew member must be able to use GPS technology.

Each crew member must be able to satisfactorily interpret aerial photographs.

The Contract shall designate crew leaders for each crew. The crew leader shall be the individual responsible for ensuring plot measurements are taken in accordance with the accuracy standards. The Contractor agrees to use only personnel meeting those qualifications for performance of the work specified herein.

PWS.2.4 DATA COLLECTION SPECIFICATIONS

Specific protocols for the collection of data are found in the current CSE User Guide. Current is defined as of date of a resulting contract. The examination level is considered “1000”. This indicates “quick plots” for the Tree data. Refer to the Contract Inspection and Criteria section (PWS.3.0) for data collection specifications.

This work will not require data collection for Vegetation Composition, Surface Data and Down Woody Material.

PWS.2.4.1 Format Data is to be Provided:

The Contractor shall provide data to the Government in a file format created by ExamsPC software (*.cse) No adjustments will be made due to personnel or program errors that result in data errors or loss of data.

File names should correspond to the data blocks being submitted.

PWS.3.0 INSPECTIONS

Inspections will be conducted by the Government on five (5%) percent of the plots. The Contractor shall submit data to the Government every seven (7) days as stands are completed. This data will be used for random inspections of up to 10% of sampled plots. Immediately upon downloading, inspection reports will be generated and sent to inspectors.

PWS.3.1 Compliance Inspections

The COR will, by formal review, determine if the specified progress and methods of work are being carried out. Failure to comply with specified work standards may be cause for termination of the Contractor’s right to proceed.

PWS.3.2 Inspections of Work

The Government will inspect the stand examinations to determine compliance with contract specifications and to provide a basis for payment. The Contractor shall submit completed stand information every seven

(7) days during the contract period or other time period the COR agrees to. The work completed in each period will constitute a “block”. Electronic files (*.cse) should be named to correspond to these blocks.

Completed work, consisting of required electronic data will be turned in for inspection. Inspection will only be made on completed stands. This will constitute the minimum sample plot inspection for determining satisfactory performance. Each block of work will be judged acceptable or unacceptable based on each inspection.

The Government will make the initial inspection of each block of completed stands without cost to the Contractor. No charge will be made for the first rework inspections on the Contractor’s first work block.

Thereafter, any re-inspections required due to the Contractor reworking a block will be at the Contractor’s expense. Re-inspection charges may include, but are not limited to: inspector’s wages for travel to and from work site; inspector’s wages to re-inspect; per diem cost (meals, lodging, field costs); COR wages; and vehicle use rate and mileage.

PWS.3.3 Block Examinations

Examinations deficient in the following specifications are unacceptable on a “pass-fail” basis and will be returned to the Contractor with the entire block for rework. The determination of noncompliance with these items may be made during the office edit or during field inspection.

(a) Electronic data not submitted to the Government in a timely manner after Contractor completion.

(b) Electronic data that cannot be read by Government computers.

(c) Stands where plots have reoccurring latitude and longitude location error of more than 10 meters.

(d) Stands having less than the prescribed number of sample plots examined.

(e) Any sample plot center which cannot be located because of improper plot center labeling, or for any other reason attributable to noncompliance with specifications.

(f) Stands submitted with incomplete information.

(g) Stands submitted with inaccurate information.

PWS.3.4 Rework of Unacceptable Work

The Government reserves the right to require unacceptable blocks. Determination of Acceptable Work, to be reworked. Upon written notification by the Contracting Officer that a block is unacceptable, the Contractor may be required to complete and submit rework before beginning work on another block. The Government will specify rework requirements for each unacceptable block. In the case of data errors, the Government can require that they be corrected. In the case of plot location errors, the Government may require that the plots be relocated and measured.

PWS.3.4.1 Correction of Data Errors:

NOTE: “Forms” refers to electronic forms in ExamsPC. Only “TREE FORM” and “SETTING FORM” are being used in this contract.

For failure of data on the Form: Correct individual items or measurements in the Form that failed. For example, if “TREE FORM” fails, then only that Form would need to be reworked. Corrections may require revisiting all stands and sample plots on the block.

For failure of data across the Forms: Correct all items and measurements on all forms. Corrections may require revisiting all stands and sample plots on the block.

PWS.3.4.2 Correction of Plot Location Errors”

Incorrectly located plot: Relocate and sample all incorrectly located plots.

The Government may re-inspect blocks of data that have been reworked to determine compliance.

If reworked and re-inspected blocks fail during the first re-inspection, additional rework may be allowed at the discretion of the Contracting Officer. Failure to pass inspection may result in contract default.

PWS.3.5 Demonstration of Inspection Procedures

Upon written request from the Contractor, the Government will perform one re-inspection of one sample plot at no cost to the Contractor as an example of inspection procedures and demonstration of potential problems. The Contractor shall accompany the Government inspector on the re-inspection.

PWS.3.6 Re-inspection Upon Contractor Request

If the original inspection results are not acceptable to the Contractor, a re-inspection may be requested, in writing, up to seven (7) days after receiving notification of unacceptable work. If the re-inspection confirms the results of the original inspection, the Contractor shall reimburse the Government for actual costs incurred for performing re-inspection. If re-inspection indicates that work does meet acceptable standards, the Government assumes the cost of re-inspection.

PWS.3.7 Inspection Criteria

PWS.3.7.1 Setting Data Fields that must be completed on the SETTING FORM include the following:

NAME Comments

Project Name Use appropriate name based on line item awarded Administrative Region Use code (09) Administrative Forest Use code (09) Proclaimed Region Use code (09) Proclaimed Forest Use code (09) District Use code (02) Gunflint Ranger District Location (compartment, 5 digits) Stand (stand number, 4 digits) Owner (USFS) State (MN) County (Cook County) Date (Date of actual field data collection) Exam level (1000) Exam purpose (SE) Existing Vegetation Note: Code 12 (black spruce) and

Code 14 (northern white cedar) are lowlands Examiner (Name of person conducting the exam) Precision Protocol (CSE_Q) Setting Remarks General Stand Remarks:

Note things about the stand that wouldn’t be reflected in the data such as:

Presence of tree species not counted on plots Uniformity of overstory, brush and balsam fir understory Unique features such as vernal pools, wildlife activity, etc.

Supplemental Wildlife Data: Stick Nests Document nests made of twigs or sticks (“stick nests”) whenever encountered within settings.

A “stick nest” is defined as: Nests constructed of twigs or sticks, 12 inches or more in diameter and at least 20 feet high in a tree.

Documentation Requirements:

Record tree species, Diameter of nest (to nearest foot), Height in tree (+/- 5 feet) Latitude/Longitude (identify datum used)

NOTE: Contractor will be paid a bonus of $50.00 for each documented stick nest verified by a District Biologist or COR.

Damage Category Damage Category, Damage Agent, Damage Severity are recorded by selecting codes with definitions from dropdown menus.

See Figure 1 Damage Recording at the Setting Level.

The lists are limited to general groups with the purpose of being able to key in on stands with problems rather than using CSE as a means of diagnosis.

Record after plot data has been collected and before leaving setting.

Document top three significant damage categories in the Setting (See Figure 1), if affecting greater than 30% of the stand.

Damage Agent

Damage Severity

Figure 1 Damage Recording at the Setting Level

PWS.3.7.2 Plot Data Predetermined plot locations with corresponding latitude/longitude coordinates will be provided to the contractor at the pre-work conference.

Fields that must be completed on the PLOT FORM include the following:

Plot Number Plot Latitude Plot Longitude Plot Remarks NOTE: For “null” plots contractor must document in Plot

Remarks. Use the following format: Plot xx-Null plot.

“Null” plot = plots with no “large” or “small” tree present.

PWS.3.7.3 Sample Design Large tree data is collected on the variable radius plot.

Large trees are live trees with a diameter breast height of 5”+, and dead trees with a diameter breast height of 9”+ and greater than 30’ tall.

Contractor shall use a basal area factor (BAF) of 10 for the variable plot in each setting unless otherwise agreed to by the COR.

Variable plots within a stand must average at least 5 trees.

Sapling, seedlings, and certain shrub species are also recorded using a fixed radius (6.8’) plot.

PWS.3.7.4 Tree Data The intent of this contract is to collect information on all tree species which are defined as “trees” in the R9 Appendices (Glossary section) and ExamsPC http://fsweb.nrm.fs.fed.us/applications/fsveg/fieldguides.shtml).

Fields that must be completed on the TREE FORMS include the following:

Plot Number Tag ID Tree Status – Large tree plot

Record as Live (L) or Dead (D)

Tree (Large & Small) and Shrub species

Using the first tree 5”+dbh encountered from the North bearing as tree #1.

All trees 5”+dhb should be recorded in order, heading in a clockwise direction.

Tree and Shrub count DBH Record for trees with a dbh of 0.5 inches or greater.

Diameters for similar tree species, 5” or greater may be grouped in 2-inch diameter classes. For example, trees in the 5.0-6.9” diameter class will be recorded as 6.0”.

Saplings and brush above 4.5’ tall require a dbh, and may be grouped into 0.5” and 1” diameter classes, up to 5”.

Height Record total height to nearest foot Live Crown Ratio Estimate the crown ratio, in percent, as the length of the live crown divided by tree height. Live crown length is assessed from the uppermost live leader or branch to the lowest live branch.

Visually adjust large openings in the crown or lopsided crowns by transferring lower branches to fill in the holes.

Compressing the live crown length because the crown appears “sparse” or contains “unhealthy” foliage is not appropriate.

For live trees only.

See Figure 2

Figure 2: How to estimate live crown ratio

PWS.4.0 INSPECTION FORMS

PWS.4.1 Common Stand Exam Inspection Form (2 sides) side 1

PROJECT NAME --- CONTRACT NUMBER

Gunflint Ranger District CSE Project

FOREST / UNIT

Superior/Gunflint

DATE BLOCK RECEIVED

DATE BLOCK INSPECTED

INSPECTORS

NUMBER OF STANDS:

NUMBER OF STANDS INSPECTED:

L.T. TREE RECORDS INSPECTED:

S.T. TREE RECORDS INSPECTED:

NUMBER OF PLOTS NUMBER OF PLOTS INSPECTED:

OFFICE INSPECTION

ACCEPTABLE UNACCEPTABLE N/A

ALL REQUIRED MATERIALS RETURNED IN GOOD CONDITION

CORRECT NUMBER OF PLOTS COMPLETED IN EACH STAND

ALL REQUIRED FORMS AND FIELDS COMPLETED AND LEGIBLE

ALL SETTINGS MEET MINIMUM TREE PER PLOT AVERAGES

ELECTRONIC DATA COMPLETE AND ACCEPTABLE

FIELD INSPECTION

ACCEPTABLE UNACCEPTABLE N/A

ALL REFERENCE POINTS AND PLOT CENTERS RELOCATABLE

ALL PLOT LOCATIONS CORRECT AND UNBIASED

ALL STANDS HAVE A PLOT DISTRIBUTION THAT EQUALLY SAMPLES ALL

SUFFICIENT ERRORS ACCUMULATE TO INDICATE A DISCREPANCY TREND

ALL INFORMATION ON SAMPLE DESIGN FORMS COMPLETE AND CORRECT

ALL SETTINGS AND PLOTS HAVE CORRECT SETTING ID

TOTAL FORM SCORE CALCULATION

Setting Form Score

Sample Design Form Score

Plot Form Score Total Tree Form Score Walk-thru Form Score

TOTAL SCORE (sum of all scores)

OFFICE AND FIELD INSPECTION

-- ANY UNACCEPTABLE ITEM FAILS INSPECTION BLOCK

INSPECTION BLOCK

TOTAL FORM SCORE CALCULATION

All form scores < 5.0 and Total Score < 10.0 = pass (full payment) PASS Any Form >= 5.0 = rework forms that fail for entire inspection unit Total Score >= 10.0 = rework entire inspection unit FAIL Errors in any field that has a Point Value of "unacceptable" will fail the block

INSPECTION CREW SIGNATURES:

DATE

COMMENTS AND FOLLOW-UP ACTION on side 2 side 2

POINTS INSPECTED:

COMPARTMENT STAND PLOT NUMBERS

COMMENTS -- OFFICE:

COMMENTS -- FIELD INSPECTIONS:

FOLLOW-UP ACTION:

PWS.4.2 Setting Inspection Form

A B C

FIELD

NUM

NAME ACCURACY

STANDARD

POINT

VALUE

# OF

ERRORS

DEDUCTIO

N (A X B)

1 Project Name no errors unacceptable 2 Administrative Region (09) no errors unacceptable 3 Administrative Forest (09) no errors unacceptable 4 Proclaimed Region (09) no errors unacceptable 5 Proclaimed Forest (09) no errors unacceptable 6 District – Gunflint RD (02) no errors unacceptable 7 Location - (compartment) 5 no errors unacceptable 8 Stand – (#) 4 digits no errors unacceptable 9 Owner (USFS) no errors unacceptable 10 State (MN) no errors unacceptable 11 County (Lake) no errors unacceptable 12 Date (of actual data collection) no errors unacceptable 13 Exam Level (1000) no errors unacceptable 14 Exam Purpose (SE) no errors unacceptable 15 Existing Veg no errors 2 16 Potential Veg Reference no errors na 17 Potential Veg +/- phase na 18 Examiner no errors unacceptable 19 Precision Protocol (CSE_Q) no errors unacceptable 20 Setting Remarks no errors unacceptable 21 Damage Category no errors 2 22 Damage Agent no errors 2 23 Damage Severity no errors 2

Total Deductions (sum of Col ‘C’)

D

Number of Stands Inspected E

Setting Form Score (D / E) F

PWS.4.3 Sample Design Inspection Form

FIELD

NUM

NAME - Tree ACCURACY STANDARD

POINT

VALUE

# OF

ERRORS

DEDUCTIO

N (A X B)

1 Selection Method Type no errors unacceptable

2 Sample Expansion Factor no errors unacceptable

3 Starting Azimuth no errors unacceptable

4 Condition no errors unacceptable

5 Subpop Filter no errors unacceptable

6 Subpop Variable no errors unacceptable

7 Subpop Min Value no errors unacceptable

8 Subpop Max Value no errors unacceptable

9 Sample/Select Remarks no errors unacceptable

(sum of column 'C')

Number of Stands Inspected E

Sample Design Form Score (D / E)

F

PWS.4.4 Plot Inspection Form

FIELD

NUM

NAME

ACCURACY

STANDARD

POINT

VALUE

# OF

ERRORS

DEDUCTIO

N (A X B)

1 Plot Number no errors unacceptable

2 Plot Latitude no errors unacceptable

3 Plot Longitude no errors unacceptable

4 Remarks no errors unacceptable

Number of Plots Inspected E

Plot Form Score (D / E) F

PWS.4.5 Tree Inspection Form: Large Trees – Variable Radius

No tolerance for recording a tree when none are actually present in the 2-inch diameter class. The recording of a variable plot tree when none are present will result in an unacceptable error.

SAMPLE PLOT for LARGE TREES (L.T.) -- Variable Radius

A B C

FIELD

NUM NAME

ACCURACY

STANDARD

POINT

VALUE

# OF ERRORS

DEDUCTION

(A X B)

1 Plot Number no errors unacceptable 2 Tag ID Number no errors 10 3 Tree Status no errors 50 4 Tree Species no errors 50 5 Tree Count (live/dead) no errors* 75 6 DBH 1) See NOTE 17 7 Tree Height +/- 10% 10 8 Live Crown Ratio +/- 10 % 10 9 Damage Category no errors 10 10 Damage Agent no errors 2 11 Damage Part no errors 2 12 Damage Severity no errors 5 13 Tree Remarks no errors unacceptable

L.T. Deductions

L.T. Tree Records Inspected E

L.T. Sample Score (D / E) F 7

1) NOTE: DBH Accuracy Standards – Quick Plot

(a) All trees +/- 0.1 inch (for purpose of determining trees in or out)

(b) All other within correct 2” dbh class

6” = 5.0-6.9” 8” = 7.0-8.9” 10” = 9.0-10.9” Etc.

PWS.4.6 Tree Inspection Form: Small Trees and Shrubs – Fixed Area Plot

No tolerance for recording a tree when none are actually present in the 2-inch diameter class. The recording of a variable plot tree when none are present will result in an unacceptable error.

SAMPLE PLOT for SMALL TREES and SHRUBS (S.T.) -- Fixed Area Plot

FIELD

NUM

NAME

ACCURACY

STANDARD

POINT

VALUE

# OF

ERRORS

DEDUCTION

(A X B)

1 Plot Number no errors unacceptable 2 Tag ID Number no errors 10 3 Tree Species (and Shrub) no errors 10 4 Tree Count (and Shrub) 1) See NOTE 20 5 DBH 2) See NOTE 10 6 Tree Height (and Shrub) +/- 10 % 10 7 Tree Remarks no errors unacceptable

S.T. Deductions

S.T. Tree Records Inspected

E

S.T. Sample Score (D / E)

F

Total Tree Form Score (Sum of L.T. score and S.T. score)

(ST) + (LT)

1) NOTE: Tree Count (and Shrub) Accuracy Standards: All Exam Levels Height Range/Grouping

Diameter Range/Grouping

Actual Trees on Plot

Accuracy Standard

All All 0 0 trees <= 4.5 feet 1-5 +/- 2 trees <= 4.5 feet >= 6 +/- 50% > 4.5 feet < 1 inch 1-5 +/- 1 trees > 4.5 feet < 1 inch >= 6 +/- 20 %

All 0.1”-4.9” dbh 1-5 +/- 1 trees All 0.1”-4.9” dbh >= 6 +/- 10 trees

2) NOTE: DBH Accuracy Standards – Quick Plot

(a) <0.5 inch: NO ERRORS

(b) 0.5 inch to 4.9”: +/- 0.1 inch

PWS.5.0 CONTRACT ADMINISTRATION DATA

PWS.5.1 Government Furnished Property

The Government will provide the following item(s) of Government Property to the Contractor for use in the performance of this contract.

Item Description Where, When, How

Stand (setting) information Map of project boundary with vicinity inset. Plots will be located with this project boundary on Gunflint Ranger District.

Majority of plot locations will be in mature upland stands.

General project map and vicinity provided as part of this solicitation.

UTM coordinates for plots Predetermined latitude/longitude coordinates for plot locations

Provided at pre-work conference

Superior National Forest maps

Maps for corrected stand boundaries

Two copies Provided at pre-work conference

ExamsPC software and instructions

Data entry software for handheld personal data recorders https://www.fs.fed.us/nr m/fsveg/ Note: Version in effect as of date of solicitation will be used for the contract.

Common Stand Exam Field Guide with Region 9 appendices

Field user’s guide for CSE protocol https://www.fs.fed.us/nr m/fsveg/ Note: Version in effect as of date of solicitation will be used for the contract.

.cse template file with Superior National Forest information

Allows preloading of data specific to this contract

Provided at pre-work conference

Plot locations Spatial data Provided at pre-work conference