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Archive Document Historic, Do not assume content reflects current scientific knowledge, policies, or practices. 1 P 7C 31 U ?2?>\ UUnniitteedd SSttaatteess Mixed Conifer and Aspen UL£j) DDeeipartment of AAggrriculture Regeneration in Small Clearcuts Forest Service Within a Partially Harvested Rocky Mountain Arizona Mixed Conifer forest Forest and Range — Experiment Station r 22rr J—>- i ? . Fort Collins, Colorado 80526 :0 — Research Paper £2 > '- a RM-294 Abstract Small patch clearcutting hasbeen recommended as a method ofob- taining satisfactory regeneration ofmixed conifer species and aspen within southwestern mixed coniferforests. Uneven-aged silvicultural systems are also favored in many southwesternforesttypes. Regener- ation density, composition, and stocking were studied in nine representative clearcuts and surrounding partially harvested stands during four surveys over an 11-year period following harvesting. Conifer seedling and aspen sucker densities initially increased over pretreatment levelsbut declined a year laterand remained stable after- wards. In 1989, 11 years afterharvesting, the openings contained an average of 1,014 trees per acre and adjacent forested areas contained 3,092 trees per acre, a significant difference. The partially harvested forest and eight of the nine openings had satisfactory regeneration densities. White fir was the only species to have significant density differencesbetweencovertypes. Average stocking in 1989 was similar, with 45% inthe openings and 61% intheforest; ideally, the dis- tribution of regeneration on both areas could have been improved. Patch clearcuts have resulted in satisfactory regeneration as well as meeting other multiresource goals of increased water yields and increased herbaceous production for livestock and wildlife. USDA Forest Service February 1991 Research Paper RM-294 Mixed Conifer and Aspen Regeneration in Small Clearcuts Within a Partially Harvested Arizona Mixed Conifer Forest Peter F. Ffolliott, Professor School of Renewable Natural Resources University of Arizona, Tucson and Gerald J. Gottfried, Research Forester Rocky Mountain Forest and Range Experiment Station1 ^GottfriedisassignedtotheStation'sResearch WorkUnitinFlagstaff, incooperation withNorthern Arizona University. Headquarters is in Fort Collins, in cooperation with Colorado State University. Mixed Conifer and Aspen Regeneration in Small Clearcuts Within a Partially Harvested Arizona Mixed Conifer Forest Peter F. Ffolliott and Gerald J. Gottfried Introduction A prescriptionthatincludedcreating small, dispersed openings by patch clearcutting and group-selection Southwesternmixed coniferforests are found onhigh- methods, inconjunctionwithsingle-tree selectioninthe elevation sites, generally above 8,000 feet, throughout adjacent stand, is currently being evaluated at Thomas Arizona, New Mexico, and southwesternColorado. The Creek, in the White Mountains ofeast-central Arizona. forests are an important source ofwood products forthe A resource allocation evaluation (Brown 1976) indicat- Southwest and also provide a wide range of commer- ed thatthis prescriptionwouldbenefit the greatest mix cial and noncommercial resources. Natural regeneration of mixed conifer resources, such as water yields, her- appears to be satisfactory in most undisturbed stands. bage production, many wildlife populations, and tree These contain adequate numbers and stocking of ad- and stand growth. Successful tree regeneration was an vance regeneration to replace trees lostby natural mor- important factor; the lack ofadequate natural regenera- tality or by moderate harvesting. However, natural tion in the clearings would limit the usefulness of the regeneration is poorwhen large openings arecreatedby prescriptionformultiresource management. The objec- harvesting or natural disturbances. Jones (1967) found tive of the present study, which is a part of the multi- little natural or successful artificial regeneration in the resource studyatThomas Creek, was to determine ifthe clearcut blocks on Burro Creek, in eastern Arizona, 7 small mixed coniferclearcuts have regenerated satisfac- years after harvesting. He also found that most natural torily in the 11 years since harvesting. The specific regeneration ina 10-acre clearcutoccurredwithin 66feet objective was to evaluate the amount, composition, and ofthe timber margin, and recommended that openings stocking of natural mixed conifer and aspen regenera- be no wider than 198 feet to enhance natural regeneration in small clearcuts, and to compare it to regeneration. Ronco et al. (1984) supported this observation by tion in the surrounding partially harvested forest. The reporting that most conifer seed falls within 198 feet of results from this study should also be applicable to the windward timber edge. Many large mixed conifer group-selection openings ofsimilar sizes, although this openings only regenerate rapidly because of abundant was not specifically evaluated. aspen suckering, although conifer numbers and stocking will gradually increase (Gottfried 1983). The harvesting ofmixed coniferforests to create small Study Area patch clearcut openings of 1 to 2 acres has been advo- cated as a method ofincreasing wateryields from these The study was conducted on the South Fork of relatively moist areas (Hibbert 1979, Rich and Thomp- Thomas Creek, a 562-acre watershed in the Apache- son 1974), as well as enhancing other resource values. Sitgreaves National Forests, about 15 miles south of Such a prescription is consistent with the silvicultural Alpine, Ariz. Elevations on SouthForkrange from 8,350 recommendations ofAlexander (1974) andJones (1974) to 9,150 feet. Soils inthe study area, which are primari- for southwestern mixed conifer forests. Under this op- ly sandy loams derived from basaltic parent materials, tion, a portion of the watershed would be patch clear- have been classified as Mollic Eutroboralfs loamy- cut periodically throughout the stand rotation. Once skeletal mixed (Sexton 1976). Average annual precipi- harvested, the openingswould regenerate naturally, and tation is over 30 inches (fig. 1), approximately 56% of eventually contain sufficient timber to be harvested which occurs from October through May, mostly as again atthe end ofa 120-yearrotation. Abasic hypothe- snow. July and Augustreceivethe mostmonthlyprecipi- sis associated with such a prescription is that natural tation, with means of 4.5 and 4.4 inches, respectively. regeneration inthese small clearingswouldbe adequate Precipitationduring the first 8 years ofthe posttreatment to sustainforestproductivity. Inadditionto greateravail- period was significantly higherthanthe average forthe ability ofseed from the surrounding stand, small open- previous 14-year pretreatment period (fig. 1). ings should have amore moderate microclimate, as well The South Fork ofThomas Creekoriginally supported as better moisture conditions than larger openings be- an old-growth, uneven-aged, mixed conifer forest con- cause of increased snow accumulations and reduced sisting of eight main tree species: Engelmann spruce evapotranspiration. It is assumed that these conditions (Picea engelmannii), blue spruce (P. pungens), Douglas- should benefit the major species, including the more fir (Pseudotsuga menziesii var. glauca), white fir (Abies shade-intolerantpines (Pinus spp.) and aspen (Populus concolor), corkbark fir (A. lasiocarpa var. arizonica), tremuloides). The hypothesis concerning regeneration ponderosa pine (Pinus ponderosa), southwesternwhite success insmall clearcuts has neverbeenevaluatedfully pine (P. strobi/ormis), and quaking aspen. Preharvest in the Southwest. forest conditions for the South Fork sale area are given 1 50 - Q'j Summer Year Figure 1.—Annual precipitationattheThomasCreekrecordingprecipitationgagecanbedivided into winter and summer seasons. — Table 1. ForestchangesintheThomasCreekSouth Fork harvesting unitfortrees >1 inchdiameter breast high (on a per acre basis). The 1979 values reflect growth of survivor trees and the reduc- tions associated with harvesting and natural mortality. Pretreatment (1974) Posttreatment (1979) Total Total Basal tree Basal tree Species Trees area volume Trees area volume no. ft2 e/w1 no. ft2 e/w1 Engelmann spruce 19.04 12.50 1,631 15.26 9.58 1,188 Blue spruce 7.90 6.91 1,020 6.22 4.52 584 Douglas-fir 122.85 66.22 7,876 94.42 42.82 4,536 White fir 51.75 40.16 6,375 27.66 23.40 3,387 Corkbark fir 7.55 3.72 427 7.01 3.19 307 Ponderosa pine 40.56 30.59 5,931 34.23 16.75 2,934 Southwestern white pine 64.49 19.68 2,260 47.08 13.83 1,441 Quaking aspen 47.46 19.68 1,752 40.93 17.55 1,509 Total 361.60 199.47 27,272 272.81 131.64 15,886 Percent change 25 34 42 1S/W = Board feet. in table 1. Douglas-fir was the most common species, (Gottfried 1987). White and corkbark fir were the most while ponderosa pine was the mostcommercially valu- common species observed. able species. The stand consisted ofa mosaic ofgroups The multiresource prescription was prepared for the and patches ofvarious sizes and species compositions. 422 acres intheupperpart ofthe South Forkwatershed; Although Fitzhugh et al. (1987) classified the Thomas the lowerareaswerewithdrawnfromthetimbersalebe- Creek stand as belonging to the Picea engelmannii/ cause oflocally steep slopes. The prescriptioncalledfor Senecio cardamine habitattype (PIEN/SECA), Abies con- group selection and single-tree selection on 233 acres, colorphase, the study sites containsome characteristics patch clearcutting and single-tree selection on 159 acres, of the Abies concolor/Muhlenbergia virescens habitat and single-tree selection on 28 acres adjacent to the type (Moir 1990, pers. comm.). An intensive survey of stream channel. Two acres of meadow were left un- advance regenerationpriorto harvesting indicated 1,928 disturbed. Harvesting operations were primarily con- trees per acre between 3 inches and 0.9 feet in height ducted in 1978, removing approximately 3.4 million 2 board feet ofvolume (ScribnerDecimal C), afterdeduct- Seedling measurements, including number ofstems, ing for defect, and reducing stand basal area in the sale species, and percentstocking, were made in 1982, 1983, area by 34% (table 1). The harvest created 63 dispersed 1986, and 1989, representing 4, 5, 8, and 11 years fol- patch clearcut and group-selection openings throughout lowing treatment. Because it often was difficult to dis- the entire sale area. Openings covered 13% of the tinguish between small seedlings of the same genus, watershed. Engelmann spruce andblue spruce were combined into one class, as were white fir and corkbark fir. The combined groups retain the name ofthe more common spe- Methods cies; blue spruce and corkbark fir were not commonly found in the sample. It is recognized that the two spe- Priorto harvesting in 1978, established mixed conifer cies within a class have different regeneration require- seedlings and aspen suckers were measured in nine ments. The original survey in 1982 only considered trees forested areas that had been marked for patch clearcut- less than 1 foot tall to avoid trees that had become es- ting. Regenerationineach areawas measured alongtwo tablished prior to harvesting. Subsequent surveys re- transects that intersected at right angles. Circular movedthisrestrictionas long asthetree appearedto date 1-milacre plots were established at 50-foot intervals fromthe logging period. Individual trees were not iden- along thetransects, whichextended approximately 150 tified, so tallies included trees that had been present feet intotheforestadjacenttothe markedopening. Trees since 1978 as well as younger trees. Some trees tallied tallied in the milacre plots were classified as seedlings in one surveymaynothave survived until a subsequent or suckers ifthey were less than 1 foot in height, or as visit. Seedling heights were only measured in 1989. In advanceregeneration iftheywerebetween 1 and 4.5 feet line withthe Forest Service's requirements forhigh-site in height. A plotwas considered stocked with a species mixed conifer stands (Bassett 1990, pers. comm.), we if at least one healthy tree was present. The initial sur- considered an opening to be satisfactorily regenerated vey did not include a complete tree count for all spe- if it contained at least 325 trees per acre. cies. Number of stems and percent stocking were Comparisons betweenregeneration density and stock- recorded by tree species. These data provided an indi- ing in the nine openings and under the surrounding cation of pretreatment conditions on the study area. forested areas, for each measurement date, were evalu- Following the harvest, 9 ofthe 63 harvested clearings ated by paired t-tests (values are given as means and were selected for intensive study. Permanently located standard errors). Changes over time, as well as time x transects and milacre sampling plots were established type (opening orforest) andtime x site interactions, were in the clearings and in the adjacent partially harvested analyzedby repeated measures procedures. Height data forested areas. The characteristics of the nine sites, in- for all regeneration were pooled for analysis because of cluding the surrounding stands, are shown in table 2. the varying sample sizes among plots; forexample, not The overstory basal areas were measured in 1989 by all species were presentonall plots orwithin eachcover point sampling procedures using a 25 basal area factor group. Density data also were grouped by five height wedge. The openings were in areas that generally were categories (0-3 inches, 4-6 inches, 7-12 inches, 13-24 level, with some slope to the north. Slash disposal ac- inches, and greater than 25 inches) for comparison be- tivities hadbeen conducted in all sites. Five ofthe nine tween forest and clearcuts by paired t-test analysis. In sites hadbeen sampled priorto harvesting. The current addition, an attempt was made to relate the density of analysis isbased onmeasurements ofregenerationinthe reproduction inthe opentovarious opening, forest, and nine sites from 1982 through 1989. These areas also have herbage production-utilization characteristics using beenused to studysnowaccumulationpatterns (Plasen- regression techniques. A similar attempt was made to cia 1988) and the production and utilization of herba- relateregenerationintheforestto residualoverstory den- ceous plants (Ffolliott and Gottfried 1989). sity. Datawere nottransformedforthese analyses. State- Table 2.—Characteristics of the nine clearings and adjacent partially harvested stands. Opening Area Basal area Mean tree Most common species number (acres) (ft2/acre) height (ft) (percent by basal area per acre) X±SE X±SE 1 1.2 146+29 64+7 White fir (26%), ponderosa pine (23%) 2 0.8 156+20 94±6 Douglas-fir (40%), white fir (15%) 3 1.1 148+22 90±5 Douglas-fir (44%), white fir (13%) 4 1.1 158+22 59±6 Douglas-fir (54%), ponderosa pine (22%) 5 0.8 158±21 62+7 Douglas-fir (59%), aspen (21%) 6 0.3 169+26 72±7 Douglas-fir (51%), Engelmann spruce (12%) 7 1.1 123+23 57±4 Engelmann spruce (32%), Douglas-fir (27%) 8 1.0 208±31 56±5 Aspen (34%), Douglas-fir (26%) 9 1.6 191 ±22 85±6 Douglas-fir (45%), white fir (45%) Total study area 1.0±0.1 162± 8 71 ±5 3 766 ments referringto increases ordecreases, and greateror openings (table 3). White fir and Douglas-fir were the lesser, indicatethatthe differenceswere statistically sig- mostcommonspecies, comprising 75% ofthe seedlings nificant at the 5% level. intheforestand 80% inthe clearings (fig. 2). Therewere more white fir than Douglas-fir seedlings in the forest but their densities were similar in the clearings. This Results relationship betweenwhite firand Douglas-firwas true for all of the surveys except 1986. Density and Composition In 1983, a year later, regeneration densities declined sharply inboth forested and open sites (table 3); differ- The 1978 preharvest survey measured approximately ences between 1982 and 1983 were highly significant. 1,746 seedlings and suckers per acre less than 1 foot in The 1983 inventory indicated that only six ofthe open- height (table 3). Douglas-fir and white firaccounted for ings contained satisfactory numbers of seedlings and 67% ofthesetrees, while aspen accountedfor 25% (fig. suckers. One opening, which had over 1,000 trees per 2). The numbers ofDouglas-firandwhite firwere statis- acre in 1982, contained no regeneration in 1983. All of tically similar. Although the study was concerned the forested areas contained at least 325 seedlings or primarily with seedlings, larger advance regeneration suckers peracre. Theaverageclearcutopening stillcon- alsowastallied duringthissurvey. Douglas-firandwhite tained 1,082 trees per acre, while the forest averaged firpredominated inthis size classtoo, contributing 52% 2,272 trees per acre; these values were not statistically of the density of 651 ± 116 trees per acre. Aspen made different. Conifer and aspen numbers were also similar up 34% of the advance regeneration. between the two cover types; only white fir showed a In 1982, the year of the first postharvest survey, all significant difference between cleared and forest sites ofthe nine openings and all ofthe adjacentpartiallyhar- (table 3). All nine sites respondedthe samewithrespect vested areas were satisfactorilyregenerated, containing to total tree numbers; however, in two sites increases atleast 325 seedlings orsuckers peracre. The difference were noted inthe numberofconifers inthe forest, while betweenthe meanforopenings and forthe forestedareas density decreased inthe open. Aspenregeneration den- was not statistically significant (table 3). Aspen made sities between 1982 and 1983 did not followthe general up 12% ofthe trees in the forest and 8% ofthe trees in trend; they increased in the openings (table 3), making the clearings (fig. 2). This species was found in most up about 46% of the average density (fig. 2), and forested areas but was concentrated in three openings. declined slightly in the forest, making up 14% of the The aspen comparison, as well as those for all conifers regeneration. However, most aspen regeneration was except white fir, did not indicate statistically significant again concentrated in three clearings; this is reflected differences between the two cover conditions. There in the high standard error. Aspen regeneration was were more white fir seedlings in the forest than in the found inboth the largest and smallest clearings. White Table 3.—Total, total conifer, and individual species regeneration density per acre (mean standard error) by survey date.1 Species 1978 1982 1983 1986 1989 Douglas-fir Forest 611 ± 51 919+297 324± 116 712±270 376± 126 Open 998±592 189± 116 440± 169 335± 155 White fir Forest 555± 88 2234±51 1239+303 1015+245 1275±348 Open 1081 ±823 273±111 118± 57 141 ± 65 Engelmann spruce Forest 44+ 28 448+151 296±203 932+389 974+322 Open 224± 76 54± 28 133± 64 247± 173 Ponderosa pine Forest 32± 20 18± 12 69+ 33 28+ 20 28± 14 Open 57± 29 63± 46 126± 63 144± 73 Southwestern white pine Forest 68± 31 63± 18 18± 12 0 56± 20 Open 41 ± 28 0 0 47± 31 Total conifers Forest 1311 ± 102 3682±71 1947±414 2687±698 2709±559 Open 2400±91 579+158 817±226 913±280 Aspen Forest 435± 86 502± 153 324± 89 321 ± 100 384± 135 Open 205± 164 503±382 281 ± 97 100± 69 TOTAL STUDY AREA Forest 1746±123 4184±817 2272±453 3008±701 3092±623 Open 2605±902 1082±466 1098±298 1014±266 1Columns may notadd up exactly because ofrounding to integer values. 4