OCLICAi ; 



trolling factor might be soil moisture, 

 in others it might be summer temper- 

 atures, and in still others it might be 

 solar radiation. If too many variables 

 enter the picture, to a point where 

 they cannot be isolated, the growth 

 patterns become "confused"; in the 

 present state of knowledge, they are 

 of little value for this type of study. 



Numerous studies are being con- 

 ducted on tree growth. Those con- 

 cerned with the bristlecone pine 

 (Pinus aristata Engelen) in the White 

 Mountains of eastern California are 

 among the more important. Living 

 bristlecone trees as old as 5,000 years 

 or more have been studied and a good 

 yearly growth chronology for that 

 period of time has been developed. 

 Bristlecone snags and other pieces of 

 deadwood have enabled the chronol- 

 ogy to be extended back for over 

 7,000 years. Similar but shorter 

 chronologies have been developed in 

 other areas throughout many parts 

 of the northern hemisphere. Some 

 work has been done in the southern 

 hemisphere but none has yet attained 

 the length of the bristlecone studies. 



Although numerous studies on 

 these tree-ring series have been made 

 by meteorologists, climatologists, and 

 statisticians, as well as dendrochron- 

 ologists and others, no cyclic pattern 

 has been detected in spite of the 

 annual variation that exists. The non- 

 uniform periods of good and poor 

 growing conditions for the bristlecone 

 show a cycle-like behavior. But be- 

 cause of the wide variation in inten- 

 sity and duration, one can "screen" 

 the data to find almost any cycle 

 length desired, or even none at all. 

 These data appear to be promising 

 from the standpoint of cyclic be- 



havior, but at present they are of lim- 

 ited value. 



Pollen Profiles and Environmental 

 Cyclic Behavior 



The number of pollen and spores 

 recovered from any depositional se- 

 quence is the result of a wide variety 

 of variable factors which are not yet 

 well understood. Climatic factors are 

 involved in the production and dis- 

 persal of pollen of the various wind- 

 pollinated species; in addition, a dif- 

 ferential is caused by preservation and 

 recovery from the sediments. Experi- 

 mental work is being done on almost 

 every aspect of these wide variations, 

 and there is hope that the future will 

 see at least a reasonable solution to 

 many of these problems. 



Profiles represent a random count 

 of various wind-pollinated species re- 

 covered from sediments. Seldom does 

 the palynologist working with recent 

 materials give an absolute pollen 

 count of every grain present on the 

 slide. These counts are treated in a 

 statistical manner in an attempt to 

 overcome bias caused by differential 

 production (plants too close to the 

 depositional area) or differential pres- 

 ervation (oxidation). Such profiles 

 give only a gross representation of the 

 true situation. Furthermore, no an- 

 nual variation in past pollen produc- 

 tion or preservation can be detected 

 from such profiles unless the variation 

 is frozen into annual deposits such as 

 a varved clay sequence. 



Pollen profiles are being interpreted 

 as essentially representing the vegeta- 

 tive cover existing at the time the pol- 

 len was produced. The vegetative 

 cover was, in turn, a response to envi- 



ronmental conditions during 

 periods, and those environmental con- 

 ditions are interpreted as being of 

 climatic significance. 



Present Status 



There is no question that, under cer- 

 tain environmental conditions, plants 

 produce different amounts of growth 

 in the annual layers of wood, and dif- 

 ferent amounts of pollen are produced 

 and dispersed during the pollen- 

 production seasons. Tree-growth and 

 pollen studies are still, however, in 

 what one could call a primitive state. 

 We are only now learning what the 

 problems actually are. As soon as the 

 problems can be better defined, con- 

 centrated effort can be made toward 

 their solution. At the present time, 

 only trends can be detected in the 

 various environmental conditions; no 

 scientific prediction can yet be made 

 from these trends. 



In general, more physiological 

 studies are needed regarding the con- 

 nection between environment and 

 tree-ring growth, especially in quanti- 

 tative amounts. Such studies need to 

 be made on a variety of species grow- 

 ing under a wide variety of condi- 

 tions. Once these measurements are 

 made and understood, considerable 

 statistical work (computer analysis) 

 will be necessary to reduce the data to 

 usable forms. We are still in need of 

 better knowledge on pollen produc- 

 tion and dispersal, on pollen preserva- 

 tion and recovery, and on statistical 

 (or computer) analyses of recovered 

 grains. These studies will be of 

 limited value, however, if we do not 

 also have a much better understand- 

 ing of all aspects of the physical 

 matrix comprising the natural envi- 

 ronment. 



61 



