WMOD00002

• Applicant: Western Weather Consultants
• Project Name: San Juan
• Date: 11/1/1984
• Weather Modification - Doc Type: Application

FHE~OL\)~,:CAl DE',,-!...()?~::..;;J {,f !iLF.5ACEu;~ l'LAN1<; i.' ;U.!..ATlOr.: TO SNO',.,'MELT DAT6--l/

ABSTRACT

" ,_ r!->r~r t ~. ,r.. cn-=

In 80 8ttecpt to determine the effect ef an incrca~~J
sn~pack on the development ct ccrt~tn herbaceous
plant species. six sites were chosen, (Jne each on
north and south aspects at three elevations. L~UU m.
314U m. and }L/U m. ~'enty-t1ve species of plants
were observed for the var1DUS phenoptwses w1th 1) spec-
imens of each species measured at each site. Over a
per100 or rour grow1ng seasons. about )U,nou observa-
tions were recorded. The' follo....ing ch;;.racteristics
were observed: leaf growth, shoot gro~th, inflores-
cence height, total plant height. inflorescence devel-
opment by percentage of flo~ers in bud, open. or in
various stages of fruit development and seed dispersal.,
Correlation coefficients were determined between the
year day of various phenophases and year day of 100
percent snow disappearance in the plots. An analysis
of variance was done betwe~n Thurber fescue (Festuca
thurberi Vasey) year day of maximum growth and year
day of snow disappearance 1n 1971, 1972. and 1973.
The data produced the following generalizations:

1. In general for every 10 percent increase in snow
above the long term average, the earlier pheno-
'phases are delayed up to H days, dependlng on
otner varlaD~es SUCh as alr temperature. Ih1S
delay 1s not linear tor all pneoopnases or a
species. Generally. the earl~er pnenophases
are delayed more than the later phenophases.
for a given species.

2. plants of the same species on south aspects
reached maximum growth, tlover~ng, trult~ng. and
maturity up to 4 weeks ahead of plants occurring
on equivalent norLh aspects.

3. Plants of the same species at higher elevations
on equivalent aspects reaChed vegetatlve ano re
productive maturity up to 6 weeks later than
plants at lower elevations.

4. The north aspect and higher elevation plants
matured. flowered. and trulted at a smaller size
than the same species on south aspects and at
lower elevations.

5, There was ~reatest correlation between the various
phenoDhases and snow free date in the excessive
snow year and on south aspects.

6. The late blooming species' phenophasEs~(probably
long day plants) were least lntluenced by snow
depth.

7. Certain plant species sho....ed an ability to "catch-
up" in their development despHe a latE I;.tf.r:;:-izi-'
the spnng.

8. The difference in dates of phenophases between
north and south aspects decreased as the alt1~ude
increased.

l/ln ~teinhoff. H.W., and
~ountains, Colorado.
2/Present address: Dept.

:h~ data support
will result in a
and maturation.
month .

the thesis that an increase in snow
delay in herbaceous plant development
This delay could be as long as 1

See +-W...s

D.....7fed -

CONCLUSIONS

An increase in snow fall in the forest ecosystem will
cause the snow tree date to occur later 10 the sprlnR.
In turn. initiation of growth of herbaceous plants
will be later which will "set back" most. if not clll,
phenophases. This will cause "spring" to come later
1n the year on the average. As far as affecting the
~herbaceous plant populations. an increase in snow fall
is unlikel to have an direct effec . 00 s
of these plants allow a high variation in date of
growth initiation and still obtain maturation before
the end af the growing season. The study needs to be
carried on for several more years for a more
definitive conclusIon.

J~D. Ives (Eds). 197~. EcolGgical impacts of snowpack augmentation
San Juan Ecolo~\" ProJect. Fin.<11 Report, Colorado State Univ. Publ..
of llioJog:;. !"o:-t Lr.',:is Colj;;:ge, Durallgo. Colorado, 81301.

in thf:: ~an JU;J~
Fort Collins.

-9-

323

^_Q...::l_'.l