Pinyon Seedling Distribution 

 Among Soil Surface Microsites 



Richard L. Everett 

 Susan Koniak 

 Jerry D. Budy 



INTRODUCTION 



Pinyon seedlings require a nurse plant for establish- 

 ment. The nurse plant and seedling need not be the 

 same species (Emmerson 1932), but in fully stocked 

 stands this condition is highly probable. The enhance- 

 ment of conifer seedling establishment in a micro- 

 environment that ameliorates temperature and moisture 

 extremes has been well documented (Youngberg 1965; 

 Cochran 1973). In pygmy forests of the Southwest, seed- 

 lings of pinyon {Piniis edulis) and one-seed juniper 

 {Juniperus monosperma) have been observed to occur in 

 greater numbers under the tree crown for this reason 

 (Meagher 1943; Johnsen 1962). Meagher did not measure 

 seedling distribution patterns of pinyon, but he ade- 

 quately demonstrated that shade and water increase rate 

 of germination and survival of planted pinyon seed. 



Little is known about singleleaf pinyon (Pinus 

 monophylla) seedling numbers and their distribution 

 within stands. Such information is important to land 

 managers who must consider tree regeneration in balanc- 

 ing forage and wood product resources of these wood- 

 lands. An extensive preliminary study was, therefore, 

 undertaken to provide baseline data for the number and 

 distribution of singleleaf pinyon seedlings in fully 

 stocked stands within the Great Basin. 



METHODS 



Square study plots, 20 m to a side, were established on 

 10 fully stocked stands in Nevada on various aspects at 

 elevations of 2 030 m to 2 200 m. Fully stocked stands 

 are defined by the Society of American Foresters (1958) 

 as those stands where tree species effectively occupy all 

 growing space. The soil surface within stands is heter- 

 ogeneous and was classified into three general soil sur- 

 face microsites— duff, transition, and interspace— based 

 on percent needle cover and needle depth. Duff was 

 defined as a soil surface microsite covered (at least 90 

 percent) by pinyon needles to a depth greater than 

 0.5 cm. Soil microsites having 20 to 90 percent of the 

 soil surface covered by needles with an average depth 

 less than 0.5 cm were defined as transition. Interspace 

 soil microsites were characterized by less than 20 per- 

 cent needle cover of less than 0.5-cm depth. 



A series of five transects, 20 m in length, were laid out 

 parallel to each other cross-slope at 5-m intervals across 

 each study plot. Tree cover was determined by line inter- 

 cept (Canfield 1941). Understory cover, number of 

 pinyon seedlings (juveniles with a crown area less than 

 25 cm^ and a height less than 30 cm), and the soil sur- 



face microsite were recorded within a 50- by 50-cm frame 

 placed at every meter mark on the transects. 



To determine seedling distribution from the tree bole, 

 five pairs of trees were randomly selected for tree-to-tree 

 transects in each study plot. Paired trees were greater 

 than 20 cm in diameter (at stump height) and had at 

 least 1 m of interspace between them. A series of 50- by 

 50-cm frames were laid down contiguously from tree bole 

 to tree bole and understory cover, pinyon seedling num- 

 bers, and soil surface microsite recorded within each 

 frame. 



Numbers of seedlings found in parallel and tree-to-tree 

 transects were totaled separately on each soil surface 

 microsite for each study site. The percentage of the total 

 seedlings within each soil microsite and the number of 

 seedlings per square meter of soil surface microsite was 

 determined for the 10 study sites and analyzed 

 separately in one-way analysis of variance tests. An arc- 

 sine transformation was used on percentages to give a 

 more normal distribution pattern to the data. Significant 

 differences (P = 0.05) among means were determined 

 using Hartley's sequential methods of testing (Snedecor 

 1956). 



RESULTS AND DISCUSSION 



Sampled stands were dominated by singleleaf pinyon 

 with lesser amounts of Utah juniper (Juniperus 

 osteosperma). Tree cover varied from 26 to 63 percent of 

 the ground surface on the 10 study sites. Understory 

 cover on all study sites was less than 8 percent. A total 

 of 137 singleleaf pinyon seedlings were recorded in the 

 parallel transects and 78 seedlings in the tree-to-tree 

 transects. Mean seedling density across all sites was 

 estimated at 0.5 seedlings/m- but varied from to 2.28 

 among sites. 



The estimated mean number of singleleaf pinyon seed- 

 lings per hectare was large (X = 5,480) but highly varia- 

 ble (CV = 126 percent) among sampled stands. More 

 pinyon seedlings occurred in the duff than in transition 

 or interspace soil surface microsites on all sites. The duff 

 microsite occupied the greatest portion of the soil sur- 

 faces, but the number of seedlings was disproportion- 

 ately higher than would be expected by chance location 

 (table 1). The majority (87±18 percent) of seedlings 

 occurred under or adjacent to the tree crown (table 1) 

 as reported for Juniperus monosperma seedlings (84 per- 

 cent) in Arizona woodlands (Johnsen 1962). The prepon- 

 derance of seedlings near the parent plant suggests that 

 safe sites for seedling establishment are sparse (Horn 



1 



