Search

Canopy defoliation is an important source of disturbance in forest ecosystems that has rarely been represented in large-scale manipulation experiments. Scalable crown to canopy level experimental defoliation is needed to disentangle the effects of variable intensity, timing, and frequency on forest structure, function, and mortality. We present a novel pressurewashing-based defoliation method that can be implemented at the canopy-scale, throughout the canopy volume, targeted to individual leaves or trees, and completed within a timeframe of hours or days. Pressure washing proved successful at producing consistent leaf-level and whole-canopy defoliation, with 10%-20% reduction in leaf area index and consistent leaf surface area removal across branches and species. This method allows for stand-scale experimentation on defoliation disturbance in forested ecosystems and has the potential for broad application. Studies utilizing this standardized method could promote mechanistic understanding of defoliation effects on ecosystem structure and function and development of synthetic understanding across forest types, ecoregions, and defoliation sources. Key words: defoliation, experiment, herbivory, canopy, disturbance. La defoliation du couvert forestier est une source importante de perturbation dans les ecosystemes forestiers qui a rarement ete etudiee dans des experiences de manipulation a grande echelle. Une defoliation experimentale transposable de l'echelle de la cime a celle du couvert forestier est necessaire pour distinguer les effets de la variation de l'intensite, du moment et de la frequence sur la structure, la fonction et la mortalite de la foret. Nous presentons une nouvelle methode de defoliation fondee sur le lavage a la pression qui peut etre : appliquee a l'echelle du couvert forestier, a tout le volume du couvert forestier, appliquee a des arbres ou des feuilles individuellement et realisee a l'interieur d'une periode de quelques heures a quelques jours. Le lavage a la pression a reussi a produire une defoliation constante a l'echelle des feuilles et de l'ensemble du couvert forestier avec une reduction de 10-20 % de l'indice de surface foliaire et l'elimination d'une surface foliaire constante parmi les branches et les especes. Cette methode permet d'experimenter a l'echelle du peuplement avec les perturbations causees par une defoliation dans les ecosystemes forestiers et pourrait avoir un vaste champ d'application. Des etudes utilisant cette methode standardisee pourraient faciliter la comprehension mecaniste des effets de la defoliation sur les fonctions et la structure des ecosystemes ainsi que la comprehension synthetique des types forestiers, des ecoregions et des sources de defoliation. [Traduit par la Redaction] Mots-cles: defoliation, experimentation, broutage, couvert forestier, perturbation., 1. Introduction Large-scale experimental manipulations have been essential to advancing knowledge about ecosystem processes (e.g., Ainsworth and Long 2005; Templer et al. 2017). For example, experiments emulating variable disturbance severity, [...]

Intermediate disturbances are an important component of many forest disturbance regimes, with effects on canopy structure and related functions that are highly dependent on the nature and intensity of the perturbation. Ice storms are an important disturbance mechanism in temperate forests that often result in moderate-severity, diffuse canopy damage. However, it has not previously been possible to distinguish the specific effect of ice storm intensity (as ice accretion) from predisturbance stand characteristics and physiographic factors. In this study, we utilized a novel experimental ice storm treatment to evaluate the effects of variable ice accretion levels on forest canopy structure. Our results verified significant impacts of ice storm disturbance on near-term canopy structural reorganization. Canopy openness, light transmission, and complexity increased significantly relative to predisturbance baselines and undisturbed controls. We documented variable impacts with disturbance intensity, as significant canopy changes largely occurred with ice accretion levels of [greater than or equal to]12.7 mm. Repeated ice storm disturbance (two consecutive years) had marginal, rather than compounding, effects on forest canopy structure. Our findings are relevant to understanding how ice storms can affect near-term forest canopy structural reorganization and ecosystem processes and add to a growing base of knowledge on the effects of intermediate disturbances on canopy structure. Key words: intermediate disturbance, canopy structure, complexity, ecosystem function. Les perturbations intermediaires sont une composante importante de plusieurs regimes de perturbation des forets qui ont des effets sur la structure du couvert forestier et les fonctions qui y sont reliees lesquels dependent fortement de la nature et de l'intensite de la perturbation. Les tempetes de verglas qui causent des dommages diffus et moderement severes dans le couvert forestier constituent un mecanisme important de perturbation dans les forets temperees. Cependant, il n'a pas precedemment ete possible de distinguer l'effet specifique de l'intensite d'une tempete de verglas (sous forme d'accumulation de glace) des facteurs physiographiques et des caracteristiques du peuplement avant d'etre perturbe. Dans cette etude, nous avons utilise un nouveau traitement experimental qui reproduit une tempete de verglas pour evaluer les effets de differents niveaux d'accumulation de verglas sur la structure du couvert forestier. Nos resultats ont permis de constater les impacts importants de la perturbation due a une tempete de verglas sur la reorganisation structurale a court terme du couvert forestier. L'ouverture, la transmission de la lumiere et la complexite du couvert forestier ont significativement augmente par rapport a la situation anterieure a la perturbation et aux temoins non perturbes. Nous avons observe des impacts variables selon l'intensite de la perturbation alors que des changements importants dans le couvert forestier sont surtout survenus avec des niveaux d'accumulation de verglas [greater than or equal to] 12,7 mm. Des perturbations repetees (deux annees consecutives) dues a une tempete de verglas ont eu des effets marginaux plutot que conjugues sur la structure du couvert forestier. Nos resultats sont pertinents pour comprendre de quelle facon les tempetes de verglas peuvent avoir un impact a court terme sur la reorganisation structurale du couvert forestier et alterer les processus de l'ecosysteme. Ils contribuent au developpement de la base de connaissances sur la structure du couvert forestier. [Traduit par la Redaction] Mots-cles : perturbation intermediaire, structure du couvert forestier, complexite, fonction de l'ecosysteme., Introduction Moderate-severity disturbances are an important driver of ecosystem functioning, structural development, and successional change in forest ecosystems (Frelich 2002; Cohen et al. 2016). Disturbances that result in damage to [...]

Moderate severity disturbances, those that do not result in stand replacement, play an essential role in ecosystem dynamics. Despite the prevalence of moderate severity disturbances and the significant impacts they impose on forest functioning, little is known about their effects on forest canopy structure and how these effects differ over time across a range of disturbance severities and disturbance types.Using longitudinal data from the National Ecological Observatory Network project, we assessed the effects of three moderate severity press disturbances (beech bark disease, hemlock woolly adelgid and emerald ash borer, which are characterized by continuous disturbance and sustained mortality) and three moderate severity pulse disturbances (spring cankerworm moth, spongy moth and ground fire, which are associated with discrete and relatively short mortalities) on temperate forest canopy structure in eastern US. We studied (1) how light detection and ranging (LiDAR)‐derived metrics of canopy structure change in response to disturbance and (2) whether initial canopy complexity offsets impact of disturbances on canopy structure over time. We used a mixed‐effects modelling framework which included a non‐linear term for time to represent changes in canopy structure caused by disturbance, and interactions between time and both disturbance intensity and initial canopy complexity.We discovered that high intensity of both press and pulse disturbances inhibited canopy height growth while low intensity pulse disturbances facilitated it. In addition, high intensity pulse disturbances facilitated increases in the complexity of the canopy over time. Concerning the impact of initial canopy complexity, we found that the initial canopy complexity of disturbed plots altered the effects of moderate disturbances, indicating potential resilience effects.Synthesis. This study used repeated measurements of LiDAR data to examine the effects of moderate disturbances on various dimensions of forest canopy structure, including height, openness, density and complexity. Our study indicates that both press and pulse disturbances can inhibit canopy height growth over time. However, while the impact of press disturbances on other dimensions of canopy structure could not be clearly detected, likely because of compensatory growth, the impact of pulse disturbances over time was more readily apparent using multi‐temporal LiDAR data. Furthermore, our findings suggest that canopy complexity might help to mitigate the impact of moderate disturbances on canopy structures over time. Overall, our research highlights the usefulness of multi‐temporal LiDAR data for assessing the structural changes in forest canopies caused by moderate severity disturbances. [ABSTRACT FROM AUTHOR]

Forest canopy structural complexity (CSC), an emergent ecosystem property, plays a critical role in controlling ecosystem productivity, resource acquisition and resource use‐efficiency; yet is poorly characterized across broad geographic scales and is difficult to upscale from the plot to the landscape.Here, we show that the relationship between canopy height and CSC can be explained using power laws by analysing lidar‐derived CSC data from 17 temperate forest sites spanning over 17 degrees of latitude. Across three plant functional types (deciduous broadleaf, evergreen needleleaf and mixed forests), CSC increases as an approximate power law of forest height. In evergreen needleleaf forests, increases in canopy height do not result in increases in complexity to the same magnitude as in other forest types.We attribute differences in the slope of height:complexity relationships among forest types to: (a) the limited diversity of crown architectures among evergreen conifer trees relative to broadleaf species; (b) differences in how vertical forest layering develops with height; and (c) competitive exclusion by needleleaf species. We show support for these potential mechanisms with an analysis of 4,324 individual trees from across 18 National Ecological Observatory Network sites showing that crown geometry‐to‐tree height relationships differ consistently between broadleaf and needleleaf species.Power law relationships between forest height and CSC have broad implications for modelling, scaling and mapping forest structural attributes. Our results suggest that forest research and management should consider the nonlinearity in scaling between forest height and CSC and that the nature of these relationships may differ by forest type. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]