| Abstrakt: |
Relevé data (n = 216) from two-pairs of study areas located in the boreal forest of central and northern Alberta (Canada), with their centroids separated by 3.7° of latitude, were analyzed to determine if latitude-related species richness, composition, and abundance differences occurred in the understories of Populus tremuloidesforest stands. No difference in study area species richness (P =0.248) occurred, which included 78 to 105 species (average 94). North compared to south areas had reduced relevé, forb, and graminoid richness; greater dominance concentration; and less total, vascular understory, herb, forb, and graminoid canopy cover (P<0.001). Nine herbs (Calamagrostis canadensis, Cornus canadensis, Eurybia conspicua, Fragaria virginiana, Galium boreale, Lathyrus ochroleucus, Mertensia paniculata, Pedicularis labradorica, and Sym-phyotrichum ciliolatum) and two shrubs (Lonicera involucrataand Vaccinium caespitosum) decreased in abundance (total ~25% cover) from the south to north areas (P<0.001), and were associated ecologically with more open-growing forests and nontreed sites. Latitudinal differences were interpreted to be a response to cooler and slightly drier climatic conditions, and to reduced PAR availability caused by lower angles of solar incidence and the resulting more intensive shading by trees in northern areas. These factors in combination were estimated to reduce PAR to understory plants by at least 20%. Eight vegetation-types were recognized; each mostly limited to one study area. However, a P. tremuloides/Rosatype occurred in both south and north areas. The northern variant contained less Rosa acicularis(21%) and more (~6%) Leymus innovatus, Linnaea borealis, and Cornus canadensiscover than southern stands. |
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