Vegetation monitoring at Homestead National Monument of America, Nebraska: 1998–2017

Leis, Sherry

The Heartland Inventory and Monitoring Network has sampled permanent monitoring sites in three vegetation community types (restored prairie, successional forest, and bur oak forest) at Homestead National Monument of America since 1998 (includes nine sample years). Network scientists record each specie, aerial cover estimates of ground flora, diameter at breast height of midstory and overstory trees, and tree regeneration frequency (tree seedlings and saplings) within these permanent sites. The park has experienced similar periods of drought and wetness through the monitoring record. Ground cover estimates indicate that prairie litter and bare ground are negatively related; prescribed fire cycles in the prairie are likely related to these trends in litter and bare ground. In the forests, bare ground is very low because deciduous leaf litter is high and variable. Ground flora vegetation is also sparse in the forests. Basal area for the park forests appears to be very stable through time. The successional forest is dominated by hackberry (Celtis occidentalis) with prominent bur oaks (Quercus macrocarpa), but the bur oak forest is domi-nated by a small number of large bur oak trees, although there are more hackberry trees overall in both forest types. Both forest types have a developed midstory layer (class 1 trees). Canopy closure continues to be high in both forest types. This closed canopy forest structure may limit oak regeneration because light is required on the forest floor for germination and recruitment. The most common species in the regeneration layer (seedlings and saplings) is hackberry. Bur oak regeneration was uncommon. Tree regeneration in the prairie was greatest in 2017 and domi-nated by elms (Ulmus spp.). The prairie ground flora was most diverse (109 native species found in 2017), meeting prairie management goals. Composition within the prairie monitoring sites may be becoming more distinct over time. Diversity measures were variable across the successional forest sites in most years. Forbs were the primary plant guild in the ground flora layer of both forest communities. Grass and forb guilds appeared to decline over time in the prairie, but we attribute that in part to sampling error. The woody species guild remained similar through time; this guild is better understood through focused thicket monitoring. Exotic species are most common in the prairie, but two target species, Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis), were below management thresholds. Plant communities at the park have remained relatively stable through the monitoring record. Trends in total plant cover and prairie forbs and grasses are unclear and likely due to sampling errors. Management actions that affect canopy cover have the potential to affect forest composition.

Vegetation monitoring at Homestead National Monument of America, Nebraska: 1998–2017

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