Twenty Years Of Post-Fire Vegetation Development In Yellowstone National Park

Don G. Despain (don_despain@usgs.gov) USGS, Northern Rocky Mountain Science Center (406-994-7257

Eric Miller (eric_miller@nps.gov), NPS, Yellowstone National Park (307-344-2474)

Much of what we know of the effects of wildfire on plant community succession comes from plots established prior to low intensity prescribed fires or from plots sampled immediately after high intensity crown fires. There seems to be little information on the effects of crown fire where pre-fire vegetation conditions are well documented. Moreover, little information exists regarding plant community succession in the extensive areas of Yellowstone National Park that burned in 1988. We address these issues by analyzing a set of permanently marked vegetation sampling plots that were established ahead of wildfires in the late seventies and in 1988. Some plots were sampled prior to burning, annually for five years, and every several years thereafter. Others were established post-fire in forest types where we were unable to establish pre-fire plots. It is hoped that these plots can be continually sampled into the future.

We present data on three sites with vegetation records spanning 21 years, two of which re-burned in 1988. Two plots were installed before burning in 1979, one of which re-burned in 1988. One was installed post-fire in 1977. We used Detrended Correspondence Analysis (DCA) to reduce the complexity of the dataset allowing us to analyze trends in plant communities. By using DCA we hope to be able to plot gross trends in community composition with time. We used simple plots of species abundance (cover) and frequency versus time to track changes in individual species. Our preliminary findings indicate an obvious change in community structure. Species associated with older forest ( e.g. Erythronium gradiflorum. Thallictrum occidentale, Pyrola secunda, Pedicularis racemosa) that are present but not common drop out altogether. Other species survive and become more abundant at first then begin to decrease but still dominate during early post-fire succession (e.g. Arnica cordifolia, Epilobium angustifolium, Aster spp., Senecio sp.) Fire sensitive species such as Vaccinium scoparium and Fragaria virginiana) initially decrease in abundance after fire and recover slowly, particularly at the re-burned sites. Some native species appear (e.g., Collinsia parviflora and Collomia linearis). We see invasion by some exotics at all three sites, particularly by Cirsium arvense and Taraxacum spp. After the re-burn in 1988 we see invasion of some new exotic species (e.g. Rumex acetosella) and an increase in cover of existing exotics. We also see increases in post-fire graminoid cover (e.g., Carex geyeri, C. rossii, Poa sp., Bromus sp., Calamagrostis sp.)

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