Daniele Castagneri

Diachronic analysis of individual-tree mortality in a Norway spruce stand in the eastern Italian Alps

Abstract• Understanding tree mortality processes across time requires long term studies. Spatiotemporal patterns of mortality in a 200 years-old mono-layered Norway spruce stand were evaluated to determine what factors affected individual-tree mortality.• We performed an analysis on two surveys (1993 and 2005) in a 1-ha permanent plot in the Paneveggio forest (Eastern Italian Alps). Tree diameter and age distribution between surveys were compared. We examined spatial patterns of living and dead trees before 1993, in 1993 and in 2005 using univariate and bivariate Ripley’s K(d) function, and a kernel estimator of local crowding. A logistic model was used to assess the effects of diameter, age, recent growth and competitive pressure on tree mortality.• Spatial pattern analysis indicated mortality was associated to tree neighbourhood (neighbour effect at 2–5 m). An increment of regularization of tree spatial pattern occurred due to density-dependent mortality. Logistic regression showed tree diameter and recent growth were determinant on mortality risk during the monitoring period.• Even if the stand is relatively aged, mortality dynamics are those typical of stem exclusion stage. Mortality was related to competitive dynamics, and small suppressed trees with slow growth rate had higher probability to die.Résumé• Comprendre les processus de la mortalité des arbres à travers le temps exige des études à long terme. Les modèles spatio-temporels de la mortalité dans un peuplement d’épicéa âgé de 200 ans monostrate ont été évalués afin de déterminer quels sont les facteurs qui ont un effet sur la mortalité des arbres individuels.• Nous avons pratiqué une analyse sur deux enquêtes (1993 et 2005) dans une parcelle permanente de 1 ha dans la forêt de Paneveggio (Alpes orientales italiennes). Le diamètre des arbres et la distribution des âges ont été comparés entre les enquêtes. Nous avons examiné les modèles spatiaux des arbres vivants et des arbres morts avant 1993, en 1993 et en 2005 en utilisant des fonctions de Ripley K(d) univariées et bivariées, Un modèle logistique a été utilisé pour évaluer les effets du diamètre, de l’âge, de la croissance récente et de la pression concurrentielle sur la mortalité des arbres.• L’analyse du modèle spatial indique que la mortalité a été associée aux arbres voisins (effet du voisin distant de 2 à 5 m). Un incrément de régularisation du modèle spatial de l’arbre s’est produit en raison de la dépendance de la mortalité de la densité. La régression logistique a montré que le diamètre de l’arbre et la croissance récente ont été déterminant pour le risque de mortalité au cours de la période étudiée.• Même si le peuplement est relativement âgé, les dynamiques de la mortalité sont typiques de l’étape d’exclusion des tiges. La mortalité était liée à la dynamique concurrentielle, et de petits arbres dominés avec un faible taux de croissance avaient une probabilité supérieure de mourir.

Stand and coarse woody debris dynamics in subalpine Norway spruce forests withdrawn from regular management

Abstract• We studied structural characteristics, amount and quality of coarse woody debris (CWD), intensity of competition and mortality in two subalpine Norway spruce stands withdrawn from regular management. The stands, that we measured twice (in 1993 and 2005), have similar age and structure, but a different time has elapsed since the last silvicultural treatments (respectively 22 and about 55 y).• The main purposes were to analyze the current stage of development as compared to the old-growth one and to highlight the legacies of past management.• Although relatively old, the first plot (Valbona 1) was at the end of the pole stage. CWD was low in volume and was mainly of man-made origin (stumps). A recent thinning from below has reduced density-dependent competition and delayed the development of old-growth characteristics. The second plot (Valbona 2a) was at the beginning of the transition stage, with density-dependent and allogenic mortality both active at the same time. CWD volume was higher in plot Valbona 2a than in Valbona 1, but neither was comparable yet to the reference old-growth sites from Central Europe, both in quantity and in quality (e.g., decay rate continuity).• The effects of the past management were: (1) reducing the quality and quantity of the CWD, (2) alleviating competition, (3) increasing resistance to minor disturbances and, as a consequence, (4) delaying the development processes.• In mature or overmature subalpine Norway spruce stands withdrawn from regular management many decades are necessary to develop old-growth characteristics and a longer period of time is necessary to reach a true old-growth stage.

Age and growth patterns of old Norway spruce trees in Trillemarka forest, Norway

Abstract Old trees represent key features of old-growth forests and are important elements for maintaining biodiversity. Due to extensive human exploitation of Fennoscandian boreal forests during several centuries, old Norway spruce trees have become exceedingly rare. We analysed 91 spruce trees in Trillemarka Nature Reserve, southern Norway, to investigate (1) the maximum age of living trees, (2) growth rates of different-age trees and (3) growth trends in very old trees. Increment cores were taken from trees in selected old-growth stands located at 700–850 m a.s.l. Twelve spruce trees had an estimated total age of >400 years, the oldest one being 529 years and presumably the oldest known still living Norway spruce in northern Europe. A negative relationship between growth rate (basal area increment) and total age was observed, being most distinct for growth rates at 126–275 years and less marked for early stage growth (26–75 years). Thus, high age apparently was related more to low growth rates at adult and old stages of life rather than at the earlier stage. Among the trees >400 years, many of them did not show growth decrease with advancing age, indicating that ageing did not reduce growth. We conclude that the maximum age of stand-forming Fennoscandian Norway spruce trees would be in the range of 500–600 years.

Host preference and growth patterns of ivy (Hedera helix L.) in a temperate alluvial forest

Recent studies have highlighted the role of lianas in shaping stand dynamics both in tropical and temperate forests. However, English ivy (Hedera helix L.), one of the most widespread lianas in Europe, has received little attention. We conducted a study in the Siro Negri alluvial forest (NW Italy) to determine what factors most affected ivy distribution and investigate its interactions with the trees in the stand. We evaluated the influence of tree size, age, species, and neighborhood crowding on ivy occurrence. In addition, growth ring widths were used to explore the development pattern of climbing stems. Fifty-two percent of trees in our study plots carried ivy, a value comparable to liana incidence found in mature tropical forests. Tree characteristics and their spatial pattern significantly influenced ivy distribution. Preferred hosts were large, isolated trees, while the effect of tree age and species on ivy occurrence was marginal. Growth pattern analysis revealed that radial growth was positively related to the available space on the tree trunk for each ivy stem. We conclude that neighborhood crowding around trees and competition among climbing stems relying on the same trunk may reduce the colonization rate of ivy.