ALPINE PLANT SPECIES COMPOSITION, ABUNDANCE AND Β-DIVERSITY ALONG AN ALTITUDINAL
GRADIENT IN THE SAN JUAN MOUNTAINS GLORIA TARGET REGION (COLORADO, USA)
Gandini M1., Crawford J.A.2, Rossi G.3, Nydick K.4
1. MUSE - Museo delle Scienze, Trento , Italy 2.U.S. Fish and Wildlife Service Tucson, AZ , USA
3. University of Pavia, Italy 4. National Park Service, Three Rivers, California, USA
GLORIA - Global Observation Research Initiative in Alpine environments
• Long-term monitoring network for the comparative study of climate change impacts
on mountain biodiversity, focusing on plants;
• Multi-summit approach and standardized low-impact monitoring methodology;
116 active Target Regions
22 in North America
Target Region and Sampling scheme
 1 Target Region = 4 summits along an altitudinal gradient;
 1 summit = 8 summit area sections (SAS), subdivided along compass
direction and down to 10 m vertical elevation below the highest point
(4 at -5m and 4 at -10m).
Study area
Methods
Located in San Juan Mountains (Colorado, USA), which represents the southern
extent of the Rocky Mountains. The four summits fall within the Lake City Caldera –
BLM Public Land. The selected peaks are characterized by volcanic rock substratum.
• Sampling of plant species composition and relative
abundance in 4 SAS at -5m, in each summit;
• Estimation of biotic and abiotic % cover;
• Plant species classified in life-forms: forbs, graminoids
and ferns;
• SAS S1-N5 was excluded from analysis because of
missing data.
S4 – 4234.9 m
Nival/subnival ecotone
S3
S4
S2
S3 – 3974.6 m
Subnival/upper alpine ecotone
S1
S2 – 3804.8 m
Upper/lower alpine ecotone
Aims
Since 1970 some areas of the San Juan Mountains experienced a rise in temperatures
of over 1°C in summer and 4°C in winter. Thus it’s crucial to understand how Global
Warming affects alpine tundra and treeline vegetation in this region. This study shows
the results of the first survey, in summer 2006.
Results
Species richness - summit
S1 – 3717 m
Lower alpine/subalpine ecotone
Species richness - aspect
Species richness & Diversity
• SJM Target Region displays 97 species, 71 in
-5m SAS;
• Richness increases with elevation, but it
drops in S4;
• Life-forms % cover: forbs range between
68% and 77%, graminoids between 23% and
32%, mantaining the proportion 1/3 in all
summits;
• S3 has the highest richness and diversity,
but most species have very low or trace
cover;
• S4 and North aspect show the lowest
richness and diversity;
• Neither richness nor diversity was
significantly different by summit or aspect.
S1
S2
S3
S4
S1
0.000 0.370 0.575 0.547
S2
0.370 0.000 0.412 0.586
S3
0.575 0.412 0.000 0.569
S4
0.547 0.586 0.569 0.000
% Cover
• Biotic=vascular plants; Abiotic = rock, scree, bare ground, litter;
Crypto = cryptogams on soil not covered by vascular plants;
• Abiotic predominant in highest peaks S3 and S4, while nearly
60% biotic cover in S2.
% rel. abundance - summit
Shannon diversity - summit
β – Diversity between summits:
Whittaker Bw index
Diversity increase along the altitudinal
gradients, showing the highest values for
the highest peaks.
Whittaker pairwise comparisons matrix
% rel. abundance- aspect
Shannon diversity - aspect
Looking forward…
The great biodiversity found in SJM
summits will be further investigated
by comparison with resurvey
datasets and in relation to
temperatures, to evaluate changes in
the mid-term.
22-25 SEPTEMBER 2013 – BERGÜN (SWITZERLAND)
% Relative abundance
• S2 greatly surpass the other peaks for plants cover, showing
higher value for graminoids;
• % relative cover does not significantly differ by aspect.