Bussotti, Filippo

Filomena, Maggino

Iacopetti, Giovanni

Pollastrini, Martina

Selvi, Federico

English

Florence Research

Forest diversity and tree health relationships in Italian forests depend on environmental contextGiovanni Iacopetti1, Filippo Bussotti1, Federico Selvi1, Filomena Maggino2, Martina Pollastrini11Department of Agri-Food Production and Environmental Sciences, University of Firenze, Piazzale delle Cascine 28, 50144, Firenze, Italy2 Department of Statistical Sciences, University La Sapienza, Piazzale Aldo Moro 5, Roma, ItalyIntroductionTree diversity is accredited to enhance ecosystem functions in forests and toimprove resistance and resilience of trees subjected to environmental stress,including climate change. This effect, however, can be different for treespecies and ecological context. The pan-european programme for monitoringtree health (ICP-Forests) assumes crown defoliation as indicator of treevitality. Some few studies analyzed the role tree diversity as factor affectingcrown defoliation, with contrasting results. This paper analyzes therelationships between defoliation and diversity in a country (Italy)characterized by very different ecological features, from Mediterranean toAlpine-Boreal, and with a wide range of tree species and functional groups.MethodsThe Italian Level I - ICP Forests monitoring network consists of 245 plots (year2014), with 4,967 trees subdivided into 1,310 conifers and 3,656 broad-leavedtrees. Main tree species are Fagus sylvatica (beech), Quercus pubescens(downy oak), Quercus cerris (Turkey oak), Quercus ilex (holm oak), Castaneasativa (chestnut) among broadleaves, and Picea abies (spruce) and Larixdecidua (larch) among conifers. Conifers are distributed mostly in the Alpinebelt.To reduce the environmental variability, a Cluster Analysis was carried outtacking in account geographical, ecological and vegetational variables. Thisanalysis allowed us to identify 4 clusters oh more homogeneous plots (Fig. 1).General resultsBroadleaved tree species were more defoliated than conifers (Fig. 2). Conifersshowed a peak of defoliation in the period 2008-2012, followed by a recovery.Broadleaved showed an increase of defoliation (specially for Def>60%) in theyears 2016-2017.Among singular tree species (Figs. 3A – 3D), chestnut was the most defoliatedspecies, suffering for the Asian wasp Dryocosmus kuriphilus. Recent partialrecovery can be attributed to the biological treatments with Torymus sinensisand to the improvement of management (Fig. 3A).Environmental causes for recent increase of defoliation were the late frost in2016 and 2017 springs (beech, Fig. 3B) and the extreme heath and droughtwave of the 2017 summer.The analysis of the distribution of defoliation, Fig. 4, evidenced a critical areain the north-western regions, including Piedmont, Liguria, part of Lombardyand northern Tuscany.Cluster 1. Mixed forests on the sub-mountain (Alpine and Apennine) belt, with a prevailing composition on deciduousbroadleaved trees. Main species are: Castanea sativa, Fagussylvatica, Ostrya carpinifolia, Quercus pubescensCluster 2. Forest with similar distribution respect to the Cluster 1, but at lower altitude and with lower degree of diversity. Main species are: Quercus pubescens, Picea abies, Quercus cerris, Fagus sylvatica, Larix decidua-Cluster 3. Monospecific or low diversity forests (broadleavesand/or conifers) at the highest elevations in Alps and Apennine. Main species are: Fagus sylvatica, Picea abies, Larix decidua.Cluster 4. Mediterranean and supra-Mediterraneanbroadleaved forests (evergreen and deciduous), in xero-thermic conditions and with low levels of diversity. Mainspecies are: Quercus ilex, Quercus pubescens, Quercus cerris, Castanea sativa. Relationships of defoliation with tree diversityThe country-wide analysis for the main tree species revealed a general trend of increaseof defoliation in the more diverse stands (positive correlations). This behavior can beconsidered as the effect of the interaction between different ecological and vegetationalconditions.Relationships between defoliation and tree diversity, however, may vary in differentclusters of plots. Whereas no special behaviors was observed for beech, spruce and holmoak showed significant negative correlations respectively in the clusters 3 and 4, betweenthe years 2008 and 2013 (Fig. 4).Crown conditions worsened in spruce monospecific plots in the 2008-2012 period,whereas remained relatively stable in mixed plots (Fig. 5). This behavior suggests that inthis species tree diversity at plot level exerts a stabilizing role.In holm oak the correlation between tree diversity and defoliation was always negativebut became significant in some specific years depending on the relative fluctuation ofdefoliation in monospecific and mixed plots. Tree diversity, therefore, is more beneficial inMediterranean stressful conditions.ConclusionsIn a heterogeneous context forest tree assemblage and diversity are strictly dependentfrom the varying ecological conditions, consequently any analysis at country scale may beseverely biased. It was therefore necessary to limit the analyses to more homogeneousconditions. The results of the Italian survey indicate that forest diversity can modify theresponses of trees subjected to fluctuating environmental pressures, but correlationsbetween crown conditions and tree diversity may change in relation to tree species andecological context.12A2B43D3C3B3A54

Forest diversity and tree health relationships in Italian forests depend on environmental context

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Forest diversity and tree health relationships in Italian forests depend on environmental context

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