Page 9 - Wood Plenty, Grass Good, Water None

Wood Plenty, Grass Good, Water None
Vegetation Changes in Arizona's Upper Verde River Watershed From 1850 to 1997
Harley G. Shaw
Introduction
Manyranchersandresourcemanagershavenoted that pifion and juniper invaded large expanses of historic grassland in northern Arizona over the past 150 years (Arnold and others. 1964; Johnsen 1962). Since the time of European arrival in Arizona, woodlands have constantly been cut or cleared for a variety of reasons. Early fuelwooding and post-cutting, associated with ranching, mining, and railroads, eliminated most of the larger trees. Later, chaining, cutting, bulldozing, and burning for the sole purpose of clearing trees to favorgrasseswereattemptedwithvariedsuccess.Few people described juniper forests as they existed prior to the arrival of livestock and railroads. Until recently,
no one systematically monitored the cleared areas after treeswereremoved.
theearliesthumansarrivedinNorthAmericaattheend of the Pleistocene, and it has continued with varying degreesofhumaninfluencebothbeforeandaftermodern settlement. Fire, freezing, drought, floods, along with global climatic variation, modify vegetation patterns. At times, these changes may be drastic and rapid: a flood removes riparian vegetation along a stream or w i l d f i r e e l i m i n a t e s a m a t u r e s t a n d o f t r e e s .B e t w e e n s u c h catastrophic events, the mosaic of vegetation changes shifts subtly with long-term fluctuations in precipitation , temperature, and agents of seed dispersal.
Thus, any perception of "original conditions" at anygivensitearedependentuponthetimeinhistory when a particular observer entered the scene. Early Anglo settlers did not reflect upon landscape ecology, and such subjects as fire history, plant succession, and woodlanddemographicswerenotofconcern.Owning theland,makingaliving,andgrowingrich,dominated theirthoughts.Fewcarriedcameras,andwhenthey did, they mostly photographed other people. If they shot landscapes, they were usually of the grandiose andextreme,orofhumansettlements.Onlyafewkept diaries,mainly noting adventures and difficulties,hence their descriptions of vegetation were rare and brief. For most of them, the wilderness was something to be subdued; they had no reason to think of vegetation as apartofhistory.
O v e r t h e p a s t 2 5 y e a r s ,s t u d i e s o f p r e h i s t o r y o f v e g e t a
tion(Betancourtandothers1990;Anderson,1989)have
providednew understandingofpost-Pleistocenechanges
in plant distribution in the Southwest, which resulted
mainlyfromchangingcontinentalclimate.Studiesof
prehistoric vegetation provide a backdrop for measuring
more recent change, but the tools used do not provide
resolution fine enough to assess changes in limited
areas over the past 150 years, a period concurrent with
AngloexpansionintotheSouthwest.Weknowlittleof
thedensitiesofwoodlandsthatexistedonandaround Manyquestionsthereforeremainunansweredregard theupperVerdeRiverwatershedwhenthefirstsettlers ingvegetationchangeinnorthernArizona.How much arrivedinthe1860s,andmuchoftheearlyclearingof changehasreallyhappenedinthegrassland/pinon-ju- junipershadbeenaccomplishedbeforeanyonebegan nipercommunitiessinceAnglosarrived?Howhavethe
to study the history of plant communities. Most of the existing records represent conditions that developed after the initial clearing of junipers; heavy grazing of grasslands had already occurred as well.
A current philosophy of wildland management en courages foresters to re-create pre-settlement conditions . Yettheseconditionsarenoteasilydefined.We know that change in the environment was happening before
boundaries between woodland and grassland moved? H o w stable are they? H o w pervasive is the change in distribution of trees or shrubs? What were the original densities of woody vegetation? What was the timing of change? Did itoccur rapidly following some single event— either natural or human-caused? Or is this an intrinsicpatternthatmaybeonlypartlyinfluencedby humans? What was the presettlement composition of
USDAForestServiceRMRS-GTR-177. 2006.
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