Ecology of the Bald Hills and Little Bald Hills of Redwood National Park: An assessment of vegetation change

Varner, J.; Jules, Erik; Sahara, E.; Sullivan, Caroline; Sarr, Daniel

The open forest, woodlands, and grasslands of the Bald Hills and Little Bald Hills in Redwood National and State Parks are distinctive habitats that support regionally rare plant species and scenic vistas. Although the specific antecedents are not fully understood, the relatively open habitats are believed to be a consequence of unique edaphic conditions and fire regimes that created disclimax conditions. Recently, park managers have noted vegetation changes that suggest these unique systems are changing, primarily through forest encroachment, with important consequences for understory fuel structure and park biodiversity. This study investigated a suite of questions associated with the dynamics of fire, fuels and vegetation change in the Bald Hills and Little Bald Hills, respectively. The chapters of this study describe distinctive outcomes of specific analyses. Overstory structure plays a dominant role in fuels and fire behavior in the Bald Hills of Redwood National Park. Across the structural gradients spanning grassland to invaded conifer forest, fuel mass decreased sharply, fuels were more compact, and these sheltered fuels retained more moisture and were less affected by wind. These combined effects reduced fire behavior during prescribed fires and suggest a mechanism for the persistence of forests in these landscapes. Invading conifers are susceptible to fire-caused mortality following prescribed fires in the Bald Hills. Sapling mortality was tightly linked to crown and stem injuries, factors easily monitored following prescribed fires. Understanding these injury thresholds will enable fire managers to adjust prescriptions to meet the reverse tree encroachment in these historically fire-prone ecosystems. Grassland and the Jeffrey pine savanna vegetation type is rapidly disappearing from the Little Bald Hills. Time-series analysis of the proportional loss of grassland in LBH indicates the savanna-type vegetation will be gone sometime this century, probably within the next 50 years. Low-elevation, north-west facing slopes have been encroached more quickly than flatter, more south-easterly facing areas, which corresponds well to field reconnaissance of the ridgetop areas that remain savanna. Our results also indicate eventual disappearance of grassland areas. We were not able to assess the role, if any, of climate change on tree encroachment, nor could we directly test whether changes in fire regime have led to encroachment. It is possible that LBH is a remnant of an ecosystem managed by the Tolowa peoples who lived in the area before European settlement in 1850. Some evidence for this is illustrated by early tree establishment in the 1850s and 1860s. Variable establishment across the landscape is likely an artifact of spatial correlation; rapid encroachment into the remaining savanna areas seems likely. Douglas-fir forests of the Little Bald Hills track the same increases in tree establishment as the Jeffrey pine savannas. Large increases in all tree species were found ca. 1850 and peaking around 1900-1920. Among tree species, Douglas-fir, Port Orford-cedar, tanoak, bay laurel, and knobcone pine all follow this pattern. As with the Jeffrey pine results, these increases coincide with the extirpation of the native Tolowa.

Ecology of the Bald Hills and Little Bald Hills of Redwood National Park: An assessment of vegetation change

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