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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001586

on Missionary Ridge?

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- Hypotheses

1) Spring movement of elk back into the high sunnner-
ing areas 1s directly correlated to the receding
snow line.

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2) Elk calving areas are favorable sites below the
zone of partial snow cover (ZPSC), and there is no
shortage of calving areas below the ZPSC each year
on Missionary Ridge.

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- Findings

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Spring MOvements -

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Through the spring of 1973, 1080 elk sightings (25
calves) were recorded during 21.75 hra. of flight
time. These observations, along with the 1129 sight-
lugs from the first two springs, indicate that spring
movement of elk back into the high summering areas is
associated more strongly with the greening up of the
open fescue parks, than directly with a receding snow
line.

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The first spring of study (1971) followed a mild
winter. As a result. at the beginning of the spring
elk were found at relatively high elevations (3050
meters). With the onset of new growth at lowere1eva-
tions, the elk were observed to migrate down slope
into the newly green meadows (Fig.. 4). Movement back
into the high country generally followed the initia-
tion of growth in the higher meadows. In 1973, elk
were again high (2900 meters) in early spring. How-
ever, they were not observed to move down slope as
, they did in 1971. The spring (1972) was unseasonably
warm, and green up of the higher meadows had occurred
at an earlier date, negating the need for elk to
migrate to obtain new growth. The receding snow line
for both of these springs was well above the eleva-
tion of elk and new growth. and was not considered a
direct influence on movement patterns.

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The spring of 1973 was quite different from the
previous two springs. Following a severe winter, the
elk were concentrated in the valley (2100 meters).
Movement back into the high country was again associ-
ated with greening up of the higher meadows even
though the initiation of growth was later than
previous springs (Fig. 5). Because of the heavy
accumulation of snow during the winter and the late
spring, the advancing green line was closely associ-
ated with the lower limit of the receding zone of
partial snow cover (ZPSC). In this instance. the
receding ZPSC may have limited to some degree the
movement of elk, particularly those animals which
exhibit the tendency to migrate higher and earlier
than the average herd. However, the majority of
animals were located an average of 150 meters below
the ZPSC and green line throughout the spring.

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Calving -

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Data collected to date indicate that calving on
Missionary Ridge follows the general pattern reported
in the literature. Compilation of aerial and ground
observations indicates that calving on the study area
occurs between mid-May and mid-June at an elevation
of 2900 to 3200 meters.

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For the three calving seasons studied, there appeared
to be ample habitat available for calving below the
snow line. The prime calving areas were open each
spring. The receding snow line for 1971 and 1972 was

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well above the calving areas, but in 1973 the lower
portion of the ZPSC was still within the upper
calving areas. The lower border of the ZPSC, however.
is characterized by having snow cover only in protect-
ed areas on north facing slopes. As such, the reced-
ing snowpack probably presented little if any physical
limitation to the location of calving.

These data indicate that snow probably does not limit
the actual location of calving on Missionary Ridge.
Perhaps of greater importance is the possible deleter~
10us influence of late spring snow storms on calving
success, through the creation of a cold. wet environ-
ment for the newborn calf.

4.6.3 Job 3. Oak (John R. Sweeney)

- Objective

To answer the following questions:

1) What is the present structure of typical oak
stands at the upper elevational limits of oak?

2) How'are significant phenologic events. which are
related to growth and browse production of oak.
related to varying snowpacks?

3) How do varying snowpacks affect annual productiv-
ity of oak on the target area?

4) How will varying snowpack affect the survival of
oak on Missionary Ridge?

- Hypotheses

1) Annual productivity of oak will be increased in
the first few years of consistently greater annual
snowfall.

2) Oak survival will be decreased in the long term
by increased snow because of superior competition
from aspen or ponderosa pine.

- Findings

Community Structure-

The phytosociology of oak stands at their upper limits
was described in the 1973 Interim Progress Report.

Phenology-

The amount of winter precipitation does not appear to
affect initiation of growth in oak. Even though the
snowfall of 1972-73 (61.34 cm of water) was more than
twice that of 70-71 (24.64 cm of water), soil mois-
tures at -50 cm and -90 cm depth were near a water
potential of ~2 bars after snow melt each year. The
seasonal pattern of snowfall, however. probably does
affect growth initiation in that the frequency and
amounts of snow storms influence the date of final
snow melt. In 1970-71 only one decimeter of snow was
detected on the plots in late February (Fig. 6) but
three late season storms deposited a total of 1 dm on
the plots in mid-May and final snow melt did not occur
until May 13. The winter of 1972-73 was a heavy snow
year and at least 2 dm of snow were recorded on the
plots each month. Five dm were recorded in late
March. As a result of the large snowpack final melt
did not occur until May S. Seventy-five percent bud
burst in the oak was recorded on June 9 for both 1971
and 1973 (Table 3). The only snowfall in 1971-72
came in the early part of the season and the plots
were clear of snow by as early as March Initiation

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