Drivers of Pyrola asarifolia and native orchid abundance on a mine tailings wetland in the Northwestern Adirondacks
Grete Bader
SUNY College of Environmental Science and Forestry
Final Report for the Edna Bailey Sussman Foundation 2015
Background
This study took place at Benson Mines, an inactive iron mine in the Adirondacks near Star Lake, NY. A wetland at the base of the mine tailings supports a number of native orchid species, including Pogonia ophioglossoides (rose pogonia) , Calopogon tuberosus (grass pink orchid) , Spiranthes romanzoffiana (hooded ladies’ tresses) , Liparis loeselii (fen twayblade) , Platanthera clavellata (club spur orchid) , and Platanthera aquilonis (northern green orchid) (Figure 1). The populations of P. ophioglossoides , C. tuberosus, and S. romanzoffiana likely surpass 250,000 individuals . Pyrola asarifolia
(pink wintergreen), a threatened species in New York, also thrives at the site. In addition to their impressive populations, these species are of interest because they all exhibit symbiotic germination with mycorrhizal fungi. The wetland is thought to have developed post-mining disturbance within the last 50 years (Choi 1991).
The objectives of this work are to analyze biotic and abiotic drivers of the orchids and P. asarifolia at Benson Mines, including soil properties, plant functional traits, and associations with mycorrhizal fungi. During the 2015 field season, functional traits and vegetation community characteristics of the orchids and P. asarifolia were assessed.
Figure 1. Species of interest at Benson Mines. Clockwise from top left: P. ophioglossoides, C. tuberosus, S. romanzoffiana, L. loeselii, P. clavellata, P. aquilonis, a dense field of C. tuberosus , and P. asarifolia, summer 2015.
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Results and Discussion
The distribution of the orchids and Pyrola across the study area is illustrated in
Figure 2. P. ophioglossoides and S. romanzoffiana are widely dispersed throughout the site, while the other orchids tend to be more clustered. All six orchid species thrive in open areas dominated by variegated scouring-rush ( Equisetum variegatum) . S. romanzoffiana is the only orchid that also occupies the western edge of the wetland, which is dominated by various graminoid species, including Agrostis gigantea , Carex scoparia , and Juncus articulatus .
P. asarifolia is generally restricted to the central portion of the site with sparse to moderate cover of gray birch and willow species. The P. asarifolia population may be the largest in New York State, with patches reaching densities of up to 192 individuals/m
2
. It has been suggested that P. asarifolia associates with mycorrhizal fungi found on birch species (Hashimoto et al. 2012). This idea is supported by observations at Benson Mines—gray birch was present within 1m of most
P. asarifolia plots.
Figure 2. Distribution of P. asarifolia and orchid species at Benson Mines based on presence/absence surveys completed on a transect grid in June and August 2015.
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Table 1. Density and flower/fruit production data collected for each species. Fruiting is reported as both percent of total individuals and percent of flowering individuals.
Mean % fruiting ± SE
Species n
Mean density/m 2
± SE
P. asarifolia
C. tuberosus
L. loeselii
31 43.62 ± 7.95
30 79.80 ± 21.61
20 8.25 ± 1.99
P. aquilonis
P. clavellata
19 3.05 ± 0.59
31 6.61 ± 1.20
P. ophioglossoides 31 111.29 ± 19.51
S. romanzoffiana 30 8.62 ± 2.04
Mean % flowering
± SE
5.98 ± 1.44
26.12 ± 4.78
45.02 ± 6.82
51.59 ± 9.14
53.09 ± 5.71
2.69 ± 0.76
47.79 ± 5.47
%Fruiting/Total %Fruiting/Flowering
5.50 ± 1.40
2.27 ± 1.39
39.27 ± 6.41
48.52 ± 9.58
46.78 ± 5.91
0.62 ± 0.36
34.64 ± 6.59
89.57 ± 4.61
18.11 ± 13.78
93.42 ± 3.68
89.28 ± 7.74
91.51 ± 6.57
17.06 ± 7.42
58.86 ± 8.66 a. b. c. d.
Figure 3. Boxplots showing mature height (a), root depth (b), specific leaf area (c), and water level in relation to root depth (d) for each species. For boxplot d, positive values reflect species rooting below the water table, while negative values reflect species rooting above the water table.
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Results for density, percent flowering, and percent fruiting for each species are shown in Table 1. These data were collected in 20 to 30 1m
2
plots for each species. Plots were randomly chosen based on presence-absence surveys in June and August 2015.
Species were sampled during their peak flowering period, and the same plots were visited several weeks later to count seed capsules. P. ophioglossoides was observed to reproduce clonally as described by Carlson (1938), which contributes to its high density. While P. ophioglossoides and C. tuberosus had the greatest densities, they exhibited the lowest flowering rates (2.69 and 26.12%, respectively). Approximately 17-18% of flowering individuals for both species produced capsules (Table 1). Though C. tuberosus and P. ophioglossoides are able to self-pollinate (Thien and Marcks 1972; Firmage and Cole
1988), their low fruiting rates suggest that they may be more dependent on insect pollinators than the other orchid species at the site. Approximately 89 to 93% of flowering individuals of L. loeselii, P. clavellata, and P. aquilonis produced seed capsules (Table 1). These species commonly self-pollinate, which explains their high fruit set (Catling 1980, Catling 1983, Sheviak 2001). P. asarifolia exhibited a low flowering rate (5.98%), but nearly 90% of flowering individuals developed capsules
(Table 1). About 59% of S. romanzoffiana flowering individuals produced fruit.
Herbivory of flowering stems was especially evident for S. romanzoffiana . Many flowering individuals had been eaten before seed capsule counts were done and perhaps even before capsules developed.
Mature height was similar (15-20cm) for P. asarifolia , P. clavellata, P. ophioglossoides, and S. romanzoffiana (Figure 3a). C. tuberosus was slightly taller on average (25cm). The tallest and most robust orchid, P. aquilonis , has the smallest population size at the site. Its density may be limited by other factors, such as mycorrhizal fungi specificity. Additionally, seed viability may be lower in P. aquilonis compared with other species at the site, which was not accounted for in this study.
Specific leaf area (SLA) is the area of a fresh leaf divided by its dry mass. Lower values indicate that the leaves are longer-lived and more resistant to environmental changes such as drought. SLA was similar among most orchid species, between 20 and
30mm 2 /mg (Figure 3c). The average SLA of L. loeselii was greatest (35mm 2 /mg). The lowest SLA was observed in P. asarifolia (12mm
2
/mg), which makes sense since it has tough, evergreen leaves.
The shallowest rooting depths (2-2.5cm) were observed in P. ophioglossoides, L. loeselii, and S. romanzoffiana . C. tuberosus, P. aquilonis, and P. asarifolia displayed the greatest root depths (5-5.3cm), while P. clavellata roots were in between (Figure 3b).
These results may be explained by habitat and root architecture. C. tuberosus and P. asarifolia were commonly found growing on sphagnum hummocks, which further elevated them from the water table. Roots of P. aquilonis were consistently larger and more robust than those of other species. Figure 3d depicts the difference in water level and root depth for each species. In general, C. tuberosus and P. ophioglossoides roots were within 5cm of the water table, though both exhibited a large amount of variation. L. loeselii and P. aquilonis roots were typically even with the water level, and P. asarifolia,
S. romanzoffiana, and P. clavellata roots were commonly 8-12 cm above the water table.
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Future Directions
Molecular identification of mycorrhizal fungi is expected to be complete by
January 2016. Additionally, I am working on refined population estimates and models of species abundance based on soil and vegetation community characteristics.
Acknowledgements
I would like to thank the New York Natural Heritage Program and my internship supervisor, Greg Edinger. I would also like to thank my major professor, Dr. Donald J.
Leopold, committee members, Drs. Tom Horton, Russ Briggs, and Lee Newman, and my field assistant Kaitlin Breda. This work would not have been possible without the generous financial support from the Edna Bailey Sussman Foundation. I would also like to recognize my other funding sources: the American Orchid Society, the New York State
Wetlands Forum, SUNY ESF’s Ketchledge and Lowe-Wilcox scholarships, the ESF
Graduate Student Association, and the Honor Society of Phi Kappa Phi.
Literature Cited
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Catling PM (1980) Rain-assisted autogamy in Liparis loeselii (L.) L. C. Rich.
(Orchidaceae). Bulletin of the Torrey Botanical Club 107:525–529.
Catling PM (1983) Autogamy in eastern Canadian Orchidaceae: a review of current knowledge and some new observations. Le Naturaliste Canadien 37–53.
Choi YD (1991) Vegetation development on iron mine tailings in Northern New York.
State University of New York College of Environmental Science and Forestry.
Firmage DH, Cole FR (1988) Reproductive Success and Inflorescence Size of Calopogon tuberosus (Orchidaceae). American Journal of Botany 75:1371.
Hashimoto Y, Fukukawa S, Kunishi A, Suga H, Richard F, Sauve M, Selosse MA
(2012) Mycoheterotrophic germination of Pyrola asarifolia dust seeds reveals convergences with germination in orchids. The New Phytologist 195:620–30.
Sheviak CJ (2001) A role for water droplets in the pollination of Platanthera aquilonis
(Orchidaceae). Rhodora 103:380–386.
Thien LB, Marcks BG (1972) The floral biology of Arethusa bulbosa, Calopogon tuberosus, and Pogonia ophioglossoides (Orchidaceae). Canadian Journal of Botany
50:2319–2325.
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