5 
 
 
'b prdation.  (It has recently a.valato& In huge reo*TY      o5 a 
 
kept do.rles. by bunting). 
 
     ftah imoundes appoach instable equilibriua In respect of door, 
 
Jast as alluvitag waersheds approach iutable equilibrium in respet 
 
of eroslon. The first accdental relamtion of pw.4datz'-presvure brings 
 
*a the irruption: exhaustinms ioff sequence recently illustrated on 
 
the Laibab. Just so combinatonas of drouth an ramnfall precipitated the 
 
erosion cycle In vuln. able          S of soil. 
 
     In preosttlemnut times such behavior was sporadic, i.s*, at any on*

 
 time a  glllibU fration of the potantial irruptions were active. Just 
 
 so a negligble fraction of the watersheds were active. In both. aetlv 
 
 periods wer .elf-tormnatizg. both *e*apo detectioan i hiestouial 
 
 2Wort.. Soe. soil i   u    ad e had sufferel no activity since gtlaIa 
 
 tines (Utah Canons). Soms browse Io        ts may have continued indef-

 
 $.itoly. All such bees.. increasiaglyw lnerable. 
 
      Some browse ipudets were increased (male more vulnerable) by 
 
 lumbering an fire, which left uitform and favorable sub-climax stages of

 
 the plant succession over large     (Pennsylvania, Lake Statez). 
 
      Then came oyerpaslug by livestock (in the West) followed by removal

 
 of prdators, oroatton. of reftges, and better law enforcement. These 
 
 act*  in various combinations as the ltri.er'pII' to activate all ,ul- 
 
 amble deer ra.s almost aimaltaueusly. Hence the present "rashO of 
 
 irraptive her  from Oregon to Caroaa, ?Pensylvals to Oaliforaia. 
 
      The same overgraing palled the trier on the vulnerable watershe 
 
 of the West. BI apimlture d±1 the same in the 1aet and Soth. 
 
      These man-idueet cycles are not self-terminating, either In &eer
or