Restoration treatments in ponderosa pine forests may not promote understory recovery where residual understory plant abundance or propagule availability is insufficient for natural re-establishment. The value of the seed bank for understory recovery in Pacific Northwest ponderosa pine forests is not fully understood, therefore, we designed this study to evaluate the potential of the seed bank as a source of desired herbaceous understory species recruitment. Seed bank samples were collected from 14 ponderosa pine stands, seven with a perennial bunchgrass dominated understory (intact) and seven with little or no understory (depauperate). Seedling emergence methods were used to estimate the germinable seed bank; seedling density and diversity comparisons were made using non-parametric Wilcoxon rank-sum tests; and seedling species composition compared using multiple response permutation procedures. Comparisons were also made between seed bank and understory vegetation species composition. No statistical differences were observed in seedling density or diversity, but the intact group appeared higher in both. Seedling species composition differed between the two groups and in both groups several species present in the seed bank were also present in the corresponding understory vegetation. However, species that germinated from the seed bank of the depauperate understory group did not include any of the predominant species in the standing vegetation of the intact group indicating that a suitable propagule source for understory recovery is not available in dense ponderosa pine forests with severely degraded understories. Direct seeding of desired understory vegetation should be considered in ponderosa pine restoration activities.
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Vol. 86 • No. 3