Seedling defoliation may enhance survival of dominant wheatgrasses but not Poa secunda seeded for restoration in the sagebrush steppe of the Northern Great Basin

Restoration of dryland ecosystems is often limited by low seedling establishment and survival. Defoliation caused by insects and small mammals could be an overlooked cause of seedling mortality. In the sagebrush steppe, we examined the effect of seedling defoliation on the survival of perennial grasses commonly used as restoration materials. Under field conditions, seedlings of three perennial bunchgrass species [non-native Agropyron cristatum (L.) Gaertn., and native grasses Poa secunda J. Presl, Pseudoroegneria spicata (Pursh) Á. Löve] were defoliated at two intensities (30% and 70% leaf length removal) and frequencies (1 or 2 clippings) and compared to a non-defoliated control. Following emergence the first year, clippings occurred at the 2-leaf stage; a second clipping occurred one month later for repeated defoliation treatments. We monitored seedling survival and tillering for 2 years. We expected higher defoliation intensity and frequency to reduce survival for all species, but only a few treatments reduced P. secunda survival. Conversely, larger-statured Triticeae (wheatgrasses) benefited from some defoliation treatments. In both years, A. cristatum survival increased with repeated defoliation at both intensities. Defoliation did not affect P. spicata survival in the first year, but a single defoliation in the second year resulted in increased survival. In both A. cristatum and P. spicata, higher intensity defoliation reduced the boost to survival resulting from defoliation frequency. Seedlings with more tillers had greater survival probabilities, but tiller number was unaffected by defoliation. Further research may elucidate mechanisms seedlings use to compensate for or benefit from defoliation. In the meantime, managers should aim to select defoliation-tolerant species if they anticipate herbivory will be problematic for restoration sites.

Poa secunda J. Presl (Poaceae): a modern summary of infraspecific taxonomy, chromosome numbers, related species and infrageneric placement based on DNA

Poasecunda J. Presl. s.l. is a morphologically highly variable bunchgrass that is a valuable forage species in western North America. There has been much controversy as to whether multiple taxa should be recognised and at what rank in this taxonomically challenging apomictic complex. Here we propose an infraspecific classification for Poasecunda of six varieties within two subspecies, juncifolia and secunda. New combinations are P.secunda vars. ampla, gracillima, juncifolia, nevadensis and scabrella. Conflicting plastid and nrDNA phylogenies show that P.sect.Secundae is of ancient hybrid origin. Based on this and its distinct morphology, the section is raised to the rank of subgenus. A key is presented for P.secunda infraspecies and closely related non-arctic species. Suppl. materials are provided of chromosome counts for Secundae taxa and D.D. Keck specimen annotations of taxa here included in P.secunda.

Bromus tectorum cover mapping and fire risk

Fire risk in western North America has increased with increasing cover of Bromus tectorum, an invasive alien annual grass. The relationship between B. tectorum cover and fire risk was determined in a historically burned Artemisia tridentata-Poa secunda shrub–steppe community where B. tectorum cover ranged from 5 to 75%. Fire risk ranged from ~46% with an average of 12% B. tectorum cover to 100% when B. tectorum cover was greater than 45% based on prediction confidence limits. Reflectance of the green and red bands of aerial photographs were related to senescent B. tectorum cover to create fine resolution B. tectorum cover and fire risk maps. This assessment technique will allow land managers to prioritize lands for restoration to reduce fire risk in the shrub-steppe.

Hybridization and the origin of the arctic grass Poa hartzii (Poaceae): evidence from morphology and chloroplast DNA restriction site data

The hypothesized hybrid origin of Poa hartzii Gand. (Poaceae) was investigated by analysis of morphological and molecular data. This endemic nearctic caespitose grass has been considered to be a hybrid between two of the three sympatric arctic species, Poa glauca M. Vahl, Poa arctica R. Br., and Poa abbreviata R. Br. Field observations and morphological studies indicate that Poa hartzii is a morphologically distinct apomictic species that reproduces and disperses by seed. Restriction enzyme analysis of polymerase chain reaction amplified chloroplast DNA revealed the presence in Poa hartzii of two very different haplotypes. One haplotype is identical to the dominant type found in Poa glauca, while the second is identical to the haplotype of Poa secunda J. Presl., located south of the arctic region. These results are consistent with an hypothesis of ancient hybrid origin involving Poa glauca and Poa secunda, but not Poa arclica nor Poa abbreviata. They are also consistent with an hypothesis of cytoplasmic transfer via hybridization and introgression from Poa glauca to an ancestral Poa hartzii in the Poa secunda complex. Direction of transfer is suggested by the widespread occurrence of the Poa secunda haplotype in Poa hartzii and by closer morphological similarity with Poa secunda than Poa glauca. The origin of Poa hartzii provides an excellent example of reticulate evolution and the importance of hybridization in the speciation of arctic grasses. Key words: Poa hartzii, arctic Poa, chloroplast DNA, restriction enzyme analysis, hybridization, introgression.