Influence of biotic and abiotic factors on health status of pine forests in northern spain

Resumen

Forest health can be considered "a condition where biotic and abiotic influences on forests (e.g., pests, pollution, silvicultural treatments, harvesting) do not threaten management objectives now or in the future". This thesis deals with the influence of abiotic and biotic factors on the health status of pine forests in northern Spain, focusing on factors under which pines are growing habitually, including climate, soil and stand characteristics, and as biotic component, the previously established endophytic community, which inhabits plant tissues, and their relationship to the host, i.e pines. The objectives were: 1) To indentify biotic and abiotic factors which are influencing forest health status of pine forests in northern Spain. 2) To assess the more representative damages and their comparison among Pinus nigra, P. sylvestris and P. pinaster, and to find out if the use of this information can help to decide species suitability for future reforestations in the area. 3) To find relationships between canopy condition and some climatic parameters and to contribute to the understanding of how these climatic parameters will affect under future climate change scenarios. 4) To identify the stand characteristics affecting canopy condition in declining Pinus halepensis stands. 5) To characterize the endophytic community of Pinus sylvestris twigs, and to find out if the structure of this community is related to the growth rate of Scots pine. 6) To identify associations between the fungal endophytic communities of Pinus sylvestris twigs with various site factors, including climate, soil and stand characteristics. Our results indicate that the main observed damages were canopy defoliation and discoloration, and stem forking, sinuosity and cankers. However, only defoliation and discoloration were evaluable in all sites and species, so they appear as the most suitable indicators of canopy condition and health status of pine forests. On the other hand, long term precipitations and temperatures do influence the health status, which is a result of past and present climatic conditions. Under future climate change scenarios, an increment of mean temperature by 2ºC would cause a 30% increment in defoliation, representing a remarkable reduction of canopy and tree vigour. Stand characteristics influencing health status of declining Aleppo pine stands were age, basal area, canopy depth and elevation, factors that if not well managed may predispose tree into decline. Additionally, decline is incited by frosts and the loss of canopy and favored by the presence of primary and secondary pathogens. Finally, 43 endophytic fungi were isolated from internal tissues, being three of them reported for the first time in the Pinaceae, and additionally six species were first reported in Pinus sylvestris. Some of these endophytes could be promoting tree growth, as is suggested for Phoma herbarum, while other species, such as Hormonema dematioides, might be protecting the tree against pathogens. The endophyte distribution is determined by climatic factors, such as precipitation and temperatures, and by soil conditions in a way that locations with favorable conditions for tree development showed a higher abundance of beneficial endophytes, while those under stressful conditions enhance the proliferation of other pathogens and opportunistic fungi.