Introduction

Mixed conifer forests on the east side of the Oregon Cascade Range and in the Blue Mountains of northeastern Oregon contain a variety of species growing in diverse environments. During the 1950's and early 1960's, clearcutting was the primary method of harvesting timber in these forests. More recently, the shelterwood system has been used to increase the probability of obtaining natural regeneration by moderating harsh microclimates found on many high elevation sites or improving the esthetic quality of harvest cuttings.

Success of regeneration on these clearcuts has been mixed, ranging from poor to good in various locations, but there has been no broadscale attempt to evaluate the regeneration or to relate it to environmental factors. Clearcuts in eastern Oregon mixed conifer' forests are now old enough for regeneration to be established. Therefore, in 1976, I began a survey of regeneration on these clearcuts and a study of the factors affecting its establishment. paper reports the results of the field survey conducted during 1976 and 1977 on the Deschutes, Winema, Umatilla, and Wallowa - Whitman National Forests.

Objectives

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The purpose of this study was twofold: (1) to quantify regeneration found on the clearcuts and (2) to identify environmental factors associated with the presence or absence of regeneration.

Specific study objectives were:

1. To determine success of regeneration in terms of stocking percentage and density (number per acre);

2. To determine species composition of regeneration;

3. To determine origin of regeneration as preharvest (advance) or postharvest (natural and planted); and

4. To determine the relationship between regeneration and some measurable environmental factors such as elevation, aspect, slope, and time since harvest.

Study Areas

Stand structure and species composition of mixed conifer forests in eastern Oregon are extremely variable, depending upon site, logging history, insect and disease attacks, and wildfire. Within the broad, general area classified as mixed conifer forests, a number of forest zones are recognized based on the single species which is the major climax dominant. These forest zones are described by Franklin and Dyrness (1973). Major tree species found in these zones are ponderosa pine (Pinus ponderosa Laws.), lodgepole pine (Pinus contorta Dougl.) Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), grand fir (Abies grandis (Dougl.) Lindl.), Shasta red fir (Abies magnifica var. shastensis Lemm.), Pacific silver fir (Abies amabilis (Dougl.) Forbes), western white pine (Pinus monticola Dougl.), western larch (Larix occidentalis Nutt.), Engelmann spruce (Picea engelmannii Parry ex. Engelm.), and mountain hemlock (Tsuga mertensiana (Bong.) Carr.).

EASTERN CASCADES

A number of plant communities have been identified within mixed conifer forests on the east side of the Oregon Cascades by Volland (1976). Identification was based on the dominant overstory tree along with the dominant understory shrub, forb, or grass. Study areas (plots) were located in two of these plant communities: (1) a high elevation mountain hemlock/grouse huckleberry community and (2) a lower elevation mixed conifer/snowbrush-chinkapin community (table 1). Understory vegetation in the mountain hemlock/ grouse huckleberry community is generally sparse, consisting primarily of grouse huckleberry (Vaccinium scoparium), Prince's pine (Chimaphila umbellata), and pinemat manzanita (Arctostaphylos nevadensis). Major

understory vegetation in the mixed. conifer/snowbrush-chinkapin community consists of snowbrush. (Ceanothus velutinus), golden chinkapin (Castanopsis chrysophylla), pinemat manzanita, dogbane (Apocynum pumilum), and fireweed (Epilobium angustifolium).

Study areas are within the pumice plateau region of south-central Oregon (fig. 1). Soils in this region are immature Regosols (Vitrandepts) developed from aerially deposited dacite and rhyolitic pumice ejected from Mount Mazama (Crater Lake) about 6,500 years ago. These well-drained, coarse-textured soils have thin A horizons low in fertility which grade into unweathered sand and gravel. A finer textured buried soil is found at a depth of 2 to 6 feet (Larsen 1976).

BLUE MOUNTAINS

Plant communities of the Blue Mountains of eastern Oregon have been described by Hall (1973). All of the clearcuts examined in this study were located in the grand fir/big huckleberry community in the Umatilla and Wallowa - Whitman National Forests (fig. 1). Understory vegetation in mixed conifer forests of the Blue Mountains is much more diverse than in the Cascade Range, especially the forb component which averaged 41.5-percent cover compared to only 1.1 percent in the Cascade mountain hemlock forest (table 1). Principal understory species are big huckleberry (Vaccinium membranaceum) heartleaf arnica (Arnica cordifolia), sideflower mitrewort (Mitella stauropetala), piper anemone (Anemone piperi), yarrow (Achillea millefolium), strawberry (Fragaria virginiana), prickly currant (Ribes lacustre),

It is more accurate to refer to the harvesting method in these units as an overstory removal or the final cut in a shelterwood system rather than a clearcut. For the purpose of this study, however, units were considered clearcuts if all of the mature overstory was cut.

DATA COLLECTION

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A grid of 25 sample point locations (subplots) was centrally located on each 10-acre plot. cular subplots were systematically spaced at 1-chain intervals on five parallel lines 1 chain apart containing five subplots each. At each of 25 sample point locations in the plot, two concentric subplots (1- and 4-milacre) were examined for regeneration and associated environmental variables. Individual sample points were rejected if conditions such as streambeds, marshs, swamps, active roads, gravel, cinder pits, solid rock, or erosion occurred on more than one-half of the subplot thus making it unsuitable for regeneration. (Only 0.3 percent of the subplots were rejected for these reasons.)

Information about the clearcut unit and the timber stand in which it was located was obtained from Ranger District records and from field observations. Information obtained was the plant community in which the plot was located, average elevation, timber type, date of harvest, slash treatment method and year of treatment, species planted and year of planting, subsequent cultural treatments, and general notes on regeneration size, growth, distribution, or damage. The plant community was identified. by observing adjacent uncut stands.

On each 1-milacre subplot the total number of trees of each species was counted and recorded by class (origin). Regeneration was classified as being of preharvest (advance) origin or of postharvest (subsequent) origin. Trees of subsequent origin were further subdivided into 1- and 2-year-old seedlings from natural seedfall, seedlings 3 years and older from natural seedfall, and

planted trees. On each 4-milacre subplot, the species and origin (advance, natural subsequent, or planted) of the tree most likely to dominate the subplot because of its size and vigor was recorded.

Identification of planted trees was accomplished by using information on species planted, date of planting, and spacing. In clearcuts where plantation survival was high, regular rows of planted trees were clearly visible. Planted tree identification was less certain when survival was low, but counting whorls to check tree age helped to determine the planted trees.

On each 1-milacre subplot, the following environmental factors were observed and recorded: 1/ aspect, slope, seed bed condition (mineral soil, litter, slash), degree of burn, understcry vegetation (forbs, woody, grass), distance from subplot to timber edge, and presence or absence of animal damage.

DATA ANALYSIS

To illustrate the present degree of reforestation, data were summarized in a number of tables showing tree numbers and stocking percentage by species and origin for the plant communities. To determine the relationship between regeneration and environmental variables, stepwise multiple regression procedures were used to fit linear equations of the form Y = bo+b1x1 + b2X2 + ....bnXn to the data. Dependent (Y) variables used were stocking percentage of the various species and origins, and independent (X) variables were the environmental factors given in the appendix.