WSP00036

• File Number: 8200.750
• Description: San Juan River General
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 3/1/1975
• Author: BOR
• Title: San Juan Ecology Project - Interim Progress Report - March 1975
• Water Supply Pro - Doc Type: Report/Study

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0015'74

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4.2.1. Herbaceous PhenoloKY (Dr. Herbert Owen)

4.2 PHENOLOGY (Drs. Herbert Owen and Gilbert Fechner)

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The Herbaceous Phenology sub-project is designed to
correlate the development of various plant species
during the growing season with such environmental
factors as air temperature, soil temperature, and
soil moisture and in turn correlate these with an
increase in snow quantity. The types of developmental
stages which are being observed and recorded are the
beginning of growth in the spring, maturing of the
vegetative growth, and development of the flowers and
fruits. The plant species being observed represent a
cross-section of types to be found in the research
area.

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- Objectives

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The objectives of the Phenology Project of the San
Juan Ecology Project essentially remain the same as
proposed after one season of field work. That is,
to determine the relationship between snow depth,
soil moisture and temperature, air temperature and
the phenologic development of selected plant species.

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- Procedures

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North and south aspect sites were selected at eleva-
tions of 2900 meters, 3200 meters and 3500 meters on
the Missionary Ridge study area. Plots were selected
to include the desirable herbaceous and shrub species.
On the Wolf Creek Pass area, north aspect sites at
3100 and 3200 meters were selected. Eight study sites
were selected, with 71 plots. Over 800 observations
were recorded in the growing season of 1973. Data
were collected according to.the following categories:

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- Inflorescence development as expressed by percentage
of flowers in bud, open, and/or in various stages of
fruit development and seed dispersal. Generally
speaking, the inflorescences are considered to be in
full bloom when they reach 50% open flowers. In like
manner "full fruit" is when the inflorescences contain
50% mature fruit. All data were collected at weekly
intervals at all sites starting approximately 1 April
1973.

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- Results

In general, the data for the 1973 growing season
substantiate previous tentative conclusions; that is,
a continued period of snow cover affects all pheno-
logical events in an almost linear relationship
(Fig. 1, 2, 3, 4,5, 6).

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- Again, plants of the same species on south aspects
reached maximum growth and flowering maturity approx-
imately one to three weeks ahead of north aspect
plants. An exception can be found at the highest
elevation where the plots are located on comparatively
shallow soil. The very dry growing season conditions
this year apparently caused these higher elevation
plants to mature at approximately the same time on
both the north and south slopes.

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- Plants of the same species at the higher elevations
took approximately one week to ten days less time to
reach their full development and complete their
season's growth than plants at lower elevations.

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- Plants of the same species at higher elevations and
on north aspects matured and flowered at a smaller
size than plants at lower elevations and on south
aspects. (Tables 2, 3, and 4).

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- In some cases, the 1973 plants exhibited greater
productivity (Tables 2, 3, and 4) which might reflect
the greater amount of snow melt, though this is
pure supposition.

- The "catch-up factor" alluded to in previous
reports was noticeable in some species, but not in
others. Festuca thurberi seems to particularly have
this ability (Table 1). Other species had their
maturing dates shifted into July and August by the
late lying snow (graphs Acillea, Thlaspi) instead of
in June or July as in previous years.

- An additional experiment was performed this past
year in which three plots, essentially identical in
all respects except one, were compared from both a
phenological and a productivity standpoint (Table 1).
These data typify the affect of snow cover on plant
development very well. They also demonstrate the
"catch-up faetoe' in Festuca. (Fig. 6)

Table 5 demonstrates typical correlation coefficients
of the data to date. Again, this supports the
primary Results statement.

The mass of data obtained defies the imagination and
much more time will have to be spent in analyzing
them and attempting several correlations to "pin
down" phenological phenomena versus enviromnental
factors versus an increase in snow cover relations.

This year's data definitely supports the idea that
the plant's phenological attributes are going to be
affected by an increase in snow cover. We now need
to determine the degree to which they will be
affected.

- Future Plans

Essentially, the future will consist of continuing
the work now started. Techniques have been refined
and changed (as indicated in last yearts report) to
the extent that they are now considered to be quite
satisfactory.

Table 1. Festuca thurberi leaf length at 3200 m.--
south aspect site. Plot B had approximately
1/2 of the snow removed and put on Plot A.
Thus, Plot A had approximately twice as
much snow as Plot B.

DATE CONTROL PLOT ~ PLOT B
6 June, 1973 0.0 em. 0.0 em. 5.5 em.
12 June, 1973 6.8 em. 4.3 em. 18.6 em.
19 June, 1973 11.3 em. 8.8 em. 24.2 em.
26 June, 1973 13.7 em. 17.7 em. 30.2 em.
3 July, 1973 31.2 em. 27.1 em. 36.1 em.
9 July, 1973 39.0 em. 33.5 em. 41.3 em.
18 July, 1973 48.7 em. 38.9 em. 44.8 em.
24 July, 1973 48.6 em. 40.4 em. 44.3 em.
31 July, 1973 52.5 em. 44.7 em. 44.8 em.
7 August, 1973 56.6 em. 46.3 em. 46.3 em.

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