A high incidence of individuals with low seed set was found in two populations of the field elm Ulmus minor, a European tree that reproduces sexually and via vegetative propagation through root sprouting. One population was a seminatural stand, while the other was established by artificial propagation of genotypes sampled widely across Spain. The low seed set in both populations was due to both pre- and post-zygotic factors, the importance of which vary between genotypes. These factors included gynoecial malformations that produced a non-ovulated pistil, early gynoecial necrosis (i.e., necrosis before any opportunities for pollination), and seed abortion. Female sterility gave rise to two classes of individuals: trees that were largely female-sterile but dispersed normal quantities of viable pollen, and trees that dispersed both normal pollen and substantial numbers of seeds. Reduced production of protein-rich seeds may increase the resource availability for clonal propagation, helping to maintain female-sterile individuals with hermaphrodites.

ResumenSe presentan, revisan y discuten los resultados de una serie de trabajos encaminados al estudio de una olmeda situada en el término municipal de Rivas-Vaciamadrid (Comunidad de Madrid). Desde el año 2000, se han analizado la historia, estado sanitario, taxonomía, dendrocronología, y características reproductivas y genéticas de los olmos que la componen. Esta olmeda puede tener un origen parcialmente antrópico, dada la coexistencia en ella de Ulmus minor s.l., de origen ibérico, con Ulmus minor var. vulgaris, de origen italiano. Existen dos categorías reproductivas en la olmeda, con pies cosexuales y pies funcionalmente masculinos, siendo más frecuentes estos últimos, aunque con una variabilidad genética menor. Desde el punto de vista sanitario, se observa un lento pero progresivo decaimiento de la olmeda a lo largo de la segunda mitad del siglo XX, probablemente como consecuencia de la grafiosis. Se proponen una serie de medidas para su mejor conservación.Palabras clave: conservación, historia forestal, biología reproductiva, taxonomía, sanidad forestal, Ulmus minor, Ophiostoma novo-ulmi. Abstract Historical, ecological, taxonomic and health characterization of the relict elm stand of Rivas-Vaciamadrid (Madrid)A series of studies focused on the characterization of an elm stand located at Rivas-Vaciamadrid (Comunidad de Madrid, Central Spain) are presented, revised and discussed. Since 2000, the elm stand history, its health, taxonomy, dendrochronology, and the reproductive and genetic characteristics of the elms have been analysed. The elm stand could have a partially anthropic origin, as indicated by the coexistence of Ulmus minor s.l. of Iberian origin with Ulmus minor var. vulgaris of Italian origin. The presence of cosexual and functionally-male trees indicates the existence of a gender differentiation. Functionally-male trees are numerically more frequent, but they have less genetic variability than the cosexual trees. A low but progressive decline during the second half of 20 th century has been observed, probably as a consequence of Dutch elm disease. In order to help towards the elm stand conservation, some actions are proposed.

Las plántulas obtenidas por cruzamiento Ulmus minor y U. minor × clones U. pumila fueron evaluados para florecer y por su resistencia de corteza a los daños del escarabajo, por su brotación vegetativa, su crecimiento en altura y su resistencia al Ophiostoma novo ulmi. Ramitas de polinización abierta y plántulas obtenidas a partir de los árboles padres fueron evaluados por los mismos rasgos. La mayoría de progenies tenía rasgos similares a sus padres, pero algunas presentan heterosis en el crecimiento anual o resistencia al Ophiostoma novo ulmi. El marchitamiento de hojas fue significativamente menor en progenies con U. minor × U. pumila en lugar de U. minor como progenitor (21,5 y 30,6%, respectivamente; P<0,05). La resistencia a O. novo ulmi aumentó significativamente en función de las mayores cantidades de U. pumila germoplasma del progenitor, sugiriendo que la resistencia a la enfermedad del olmo holandés es principalmente transmitida de la madre. La brotación fue anterior en las plántulas con tasas más bajas de crecimiento (P=0,0007) y el porcentaje de marchitez fue negativo en relación a comienzos de la brotación (P<0,0001). Otras relaciones fenotípicas incluyeron porcentajes de árboles florecientes y el crecimiento anual en altura (RP=0,44; P=0.0042), el porcentaje de árboles florecientes y la brotación vegetativo (RP=-0,53; p=0,0004), así como el porcentaje de escarabajos-árboles afectados y su crecimiento anual en altura (RP=0,60; P<0,0001). Las estimaciones de heredabilidad obtenidos de la regresión y de los métodos de varianza componentes variaron de 0,06 ± 0,04 a 0,64 ± 0,18; 0,10 ± 0,05 a 0,69 ± 0,17 y 0,13 ± 0,32 a 0,71 ± 0,22 para la brotación, crecimiento y tolerancia al O. novo ulmi, respectivamente. Un amplio y estrecho sentido de los valores de heredabilidad fueron superiores cuando se estima que 60 días después de la inoculación (dpi) de 15, 30 o 120 ppp. Estimaciones de heredabilidad y ventajas genéticas notificadas indican un alto grado de control genético aditivo y a demostrar la eficacia de la selección para la resistencia a la enfermedad del olmo holandés y el rápido crecimiento de los árboles.Seedlings obtained by crossing Ulmus minor and U. minor × U. pumila clones were assessed for flowering, bark beetle damage, vegetative budburst, height growth and resistance to Ophiostoma novo ulmi. Ramets and open pollinated seedlings obtained from the parent trees were assessed for the same traits. Most progenies had similar traits to their parents, but some presented heterosis in annual growth or resistance to O. novo-ulmi. Leaf wilting was significantly lower in progenies with U. minor × U. pumila rather than U. minor as female parent (21.5 and 30.6%, respectively; P<0.05). Resistance to O. novo ulmi increased significantly as a function of increased amounts of U. pumila germplasm from the female parent, suggesting that resistance to Dutch elm disease is primarily transmitted from the mother. Budburst occurred earlier in seedlings with low rather than high growth rates (P=0.0007) and percentage o...

Longitudinal structures manipulation can re-activate channel migration and thus restore flood-dependent riparian plant communities in human-constrained floodplains. However, it has been rarely implemented over long restored river segments and has been infrequently assessed while taking into account river conditions prior to restoration. This study describes the morphological and vegetation response to this type of restoration in a project completed in 2012 along a 21.6 km river segment in the Orbigo River (NW Spain). Land cover changes and channel planform evolution in the restored segment were compared with a downstream non-restored (control) segment and to an upstream unregulated (reference) segment before (2011) and shortly after (2014) the restoration implementation. Riparian vegetation was surveyed in 18 gravel bars of the three river segments four years after restoration completion (2016). The restored segment presented the largest increase of active channel area. Rejuvenation of landforms predominated over transition toward mature stages (succession) in the restored and the reference segment, while succession predominated in the control segment. The sinuosity and braiding indexes in the restored segment increased much more than in the reference and, especially, than in the control segment. Riparian plant communities that colonized gravel bars in the restored segment resembled those found in the unregulated segment and slightly differed from that found in the non-restored segment. Withinsegment variability was much higher, indicating the dependence of riparian plant communities on local processes. Although positive, our results showed that the high stability of floodplain areas in the human-constrained rivers of industrialized societies limits the short-term effectiveness of longitudinal structures manipulation as a restoration strategy. We also showed that assessments using relatively simple aerial photointerpretation and vegetation surveys in pioneer habitats can illustrate trajectories in river restoration projects shortly after their completion. Long-term monitoring of the geomorphic trajectory and associated plant communities, however, will help define the timing of future additional interventions to assure the natural resilience of riparian habitats.