2002-07-08_GENERAL DOCUMENTS - M2002004 (4)

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r . / ; .. Ip ;, , , • C F H C O P A P O C B A O • E K C G A P L A S M I L E A , n$ d r h a d n t r u t h u o a a p P a y t • a• n r 1 h a t•• h a 1 • t • 1 r• 1 ul :r :cowls C0 s • m r o• a u p s d • d f,s o e • c mt as u ct 1 1 r r ",m y•p 1 p o o • Is a e a a I f S a m a l o • S b i s r p u o n t p I a o o e r u u I r 1 a P s 0 m S s u u u a • ohm, p.cpmaaaa -ppn" _ ortrm = n c i b au - t p d n d at s b s o p s a 9 f s s y , ,s • s •. • f P a e l l r a i t p a p n a s f 1 a n ide P- s• 1 a• P s o a h d a t n I i m 1 r p l nn i t y I• r a s I d d 1 I a a e u d +: s a p swain . a r n i s o at s • o d i n 1 1 d a • r i s e u 1 1 - 0 ul m 1 / - m . 1 • • • t m NMI GRAZED SITE Emerged May - August 1979 Emerged September - December 1979 Emerged January-April 1980 • Emerged May - September 1980 e SPECIES Fig. 1. Numbers of seedlings emergingfrom grazed site samples for each of 26 species types over 4 time periods. (Mc Rill and Sagar 1973, Mortimer 1974). About 94% of the seeds at the grazed site were in the top 7.5 cm compared with 74% seeds in the same layer on the ungrazed site (Figs. 3, 4). The paucity of seeds found in the deeper layer (7.5 -15 cm) at the grazed site may be the result of increased compaction of soils from trampling and the consequent decrease in the number of fissures for seed transport. Major and Pyott (1966) also found a higher proportion of seeds at the surface of a grazed site in California. Again, decreasing seed diversity with depth may be due to compaction with only the small seeded species (i.e., yellow sweetclover, six -weeks fescue, horse - weed) penetrating to the 7.5 -15 cm depth. Time of Emergence Most seedlings emerged during the first 4 months of the experi- 650 YIY V riMGCU ai 1 G ® Em.r•.d May•August 1979 En,. pd Spr/emb.r- D.$.mb.r 197 Eorarvd J.nuary•April 1990 V4_24 Em.N•d May•September 1990 A' 'PAC E 8 A i% P. P i E' LA , j1 c t d y' • 1 h t •'i' -i t ,� t , 11.r. •,• -,m b c c u u m ,o a l ' r r r , I 1 1 0909 t "t • t % Pt -b 0.t_d m m a a s ' -a uv 1 _ bpi a • 'a <� • 9 "1 0 "• Fria "'a o • d r a P r i u a I -I' d a o a m t m <. 1.o • , " ,:1 r - n'_a - d SPECIES tr+8i .therging front ungrazed site sompr'esforeac er4 went. 6! %froth the ,gtaie , • - - r grazed, samples, 71% from the ungrazed (Fig •This = s Could be expected since most seeds have donnaitc• periods of less - than'4 months when conditions are favorable fo germination: The 2 species that germinated most frequently afte - the first 4 months were horseweed and six -weeks fescue (Fig.1, 2) both of which Were found most frequently in the lowest depth. Thi: suggests that seeds with long'dormancy periods have greater pro- pensity for survival at greater depths than do seeds with short dormancy periods. Comparison with Previous Studies Our data fall well within the range reported by other workers - (Table _1): ,Dwyer and, Aguirre (1978) reported a seed density of only 285 seeds, m ..on good condition Desert Grassland range in New Mexico whereas Jensen (1969) found up to 19,240 seeds m in a Denmark cultivated field. Differences among sites may be attrib- uted to differences in community types, field conditions, sampling methodologies, and duration of the experiments. In general, culti- JOURNAL OF RANGE MANAGEMENT 35(5), September 1982