Douglass F. Jacobs

A conceptual framework for restoration of threatened plants: the effective model of American chestnut (Castanea dentata) reintroduction.

We propose a conceptual framework for restoration of threatened plant species that encourages integration of technological, ecological, and social spheres. A sphere encompasses ideas relevant to restoration and the people working within similar areas of influence or expertise. Increased capacity within a sphere and a higher degree of coalescing among spheres predict a greater probability of successful restoration. We illustrate this with Castanea dentata, a foundation forest tree in North America that was annihilated by an introduced pathogen; the species is a model that effectively merges biotechnology, reintroduction biology, and restoration ecology. Because of C. dentatas ecological and social importance, scientists have aggressively pursued blight resistance through various approaches. We summarize recent advancements in tree breeding and biotechnology that have emerged from C. dentata research, and describe their potential to bring new tools to bear on socio-ecological restoration problems. Successful reintroduction of C. dentata will also depend upon an enhanced understanding of its ecology within contemporary forests. We identify a critical need for a deeper understanding of societal influences that may affect setting and achieving realistic restoration goals. Castanea dentata may serve as an important model to inform reintroduction of threatened plant species in general and foundation forest trees in particular.

Mechanical site preparation for forest restoration

Forest restoration projects have become increasingly common around the world and planting trees is almost always a key component. Low seedling survival and growth may result in restoration failures and various mechanical site preparation techniques for treatment of soils and vegetation are important tools used to help counteract this. In this article, we synthesize the current state-of-knowledge concerning mechanical site preparation for improved tree establishment when carried out in different forest restoration situations, point out critical research gaps and provide some recommendations for future directions. Mechanical site preparation often results in improved seedling survival and growth. However, if not intensive methods with much soil disturbance are used, it is a rather ineffective tool for controlling competing vegetation. Methods such as scarification, mounding and subsoiling also lead to multiple interactions among soil physical and chemical properties that affect plant survival and growth, and it may be difficult to determine the actual cause–effect relationship of any positive seedling responses. Most research to date on mechanical site preparation and plantation performance has been conducted using a few conifer tree species. Seedling responses differ among tree species and alternative species are often used during restoration compared to production forestry indicating a need for additional research for improved understanding. Several management objectives such as soil protection and increased biodiversity are many times relevant during forest restoration, and mechanical site preparation methods should be implemented carefully because they can have large impacts on the environment.

Establishment success of conservation tree plantations in relation to silvicultural practices in Indiana, USA

In the Central Hardwood Forest region of the United States, the variable and somewhat unpredictable establishment success of hardwood tree plantations has traditionally been attributed to competing vegetation and damage due to animal browse. We examined operational plantation establishment success (1–5 years following planting) as it relates to use of particular silvicultural practices. Silvicultural histories were obtained for 87 randomly selected plantations throughout Indiana and field data were collected from each to determine tree survival, tree vigor, and abundance of surrounding vegetation. Survival was highest at sites that were treated with herbicide prior to planting and that had been mechanically planted (as opposed to hand planted). The percentage of trees with evidence of dieback was highest on sites at which browse protection measures had been used, likely reflecting a combination of damage due to inherently high white-tailed deer (Odocoileus virginianus Zimmermann) populations at such sites and ineffectiveness of current browse protection measures. Sites planted by a professional forester and those with herbicide applied subsequent to planting had a higher percentage of trees deemed free-to-grow. Subsequent herbicide application did not reduce cover or height of competing vegetation; however, when used in conjunction with mechanical site preparation techniques, overall cover and height of herbaceous vegetation was reduced.

Quality Assessment of Temperate Zone Deciduous Hardwood Seedlings

Research regarding seedling quality issues has been performed for decades and focused primarily on conifer species, which comprise the greatest proportion of nursery production worldwide. Demand for hardwood seedlings, particularly for conservation purposes, has increased steadily in recent years, emphasizing the need for seedling quality assessment protocols specific to these species. Important differences between conifer (gymnosperm) and hardwood (angiosperm) species require the creation of seedling evaluative programs specific to each group. Variation in phenology and ecological adaptability of hardwood species limits the validity of inferences made between and within genera. Annual cycles of leaf emergence followed by abscission in temperate hardwoods necessitate examination of seasonal variation in indicators of physiological condition that do not require leaf tissue (e.g., mineral nutrition, electrolyte leakage). Also, it is crucial to identify appropriate sampling periods and plant tissues for testing such that test results may be accurately compared. Though certain parameters (e.g., morphological) may be readily used in both conifer and hardwood seedling quality testing programs with little modification, additional refinement is needed to improve predictive capacity for hardwoods across a variety of environments. We review the current state of knowledge regarding seedling quality testing of temperate deciduous hardwood species, discuss limitations in incorporating traditional components of quality testing programs, and set priorities for future study.

Forest restoration following surface mining disturbance: challenges and solutions

Many forested landscapes around the world are severely altered during mining for their rich mineral and energy reserves. Herein we provide an overview of the challenges inherent in efforts to restore mined landscapes to functioning forest ecosystems and present a synthesis of recent progress using examples from North America, Europe and Australia. We end with recommendations for further elaboration of the Forestry Reclamation Approach emphasizing: (1) Landform reconstruction modelled on natural systems and creation of topographic heterogeneity at a variety of scales; (2) Use and placement of overburden, capping materials and organic amendments to facilitate soil development processes and create a suitable rooting medium for trees; (3) Alignment of landform, topography, overburden, soil and tree species to create a diversity of target ecosystem types; (4) Combining optimization of stock type and planting techniques with early planting of a diversity of tree species; (5) Encouraging natural regeneration as much as possible; (6) Utilizing direct placement of forest floor material combined with seeding of native species to rapidly re-establish native forest understory vegetation; (7) Selective on-going management to encourage development along the desired successional trajectory. Successful restoration of forest ecosystems after severe mining disturbance will be facilitated by a regulatory framework that acknowledges and accepts variation in objectives and outcomes.

Restoring forests: What constitutes success in the twenty-first century?

Forest loss and degradation is occurring at high rates but humankind is experiencing historical momentum that favors forest restoration. Approaches to restoration may follow various paradigms depending on stakeholder objectives, regional climate, or the degree of site degradation. The vast amount of land requiring restoration implies the need for spatial prioritization of restoration efforts according to cost-benefit analyses that include ecological risks. To design resistant and resilient ecosystems that can adapt to emerging circumstances, an adaptive management approach is needed. Global change, in particular, imparts a high degree of uncertainty about the future ecological and societal conditions of forest ecosystems to be restored, as well as their desired goods and services. We must also reconsider the suite of species incorporated into restoration with the aim of moving toward more stress resistant and competitive combinations in the longer term. Non-native species may serve an important role under some circumstances, e.g., to facilitate reintroduction of native species. Propagation and field establishment techniques must promote survival through seedling stress resistance and site preparation. An improved ability to generalize among plant functional groups in ecological niche adaptations will help to overcome site-limiting factors. The magnitude and velocity of ongoing global change necessitates rapid responses in genetics that cannot be naturally induced at valid temporal and spatial scales. The capacity for new concepts and technologies to be adopted by managers and accepted by society will depend on effective technology transfer and a community-based approach to forest restoration. The many benefits human society gains from forests requires that forest restoration considers multiple objectives and approaches to minimize trade-offs in achieving these objectives.

Restoring forests: advances in techniques and theory

IntroductionMuch of the past science of forest regeneration emphasized reforestation following timberharvest for industrial purposes. These research initiatives fostered groundbreakingadvances in our field. The establishment of a target seedling concept was developed inNorth America during the 1980’s and 1990’s (Rose et al. 1990; Colombo and Noland1997). Genetic improvements in wood quality and productivity of plantations have led tosubstantial gains in profitability (Ahtikoski et al. 2012). A vast amount of literature hasshown the complex interactions between forest vegetation management and seedlingresponses, underlining the need to untangle the multiple factors involved (Ammer et al.2011). Characterization of ecophysiological processes associated with resistance toplanting stress and early establishment in temperate and boreal forests (Duryea andMcClain 1984; Burdett 1990; Margolis and Brand 1990) has also shed light on the basis toimprove reforestation success by managing cultural variables during nursery productionand post-planting. Collectively, these contributions have greatly advanced the science andapplication of forest regeneration.In recent decades, however, a pronounced evolution has occurred whereby the focalpoint of many of today’s forest regeneration scientists has shifted prominently towardrestoration of harsh, degraded environments. Intensive management practices, such assurface mining and road construction, yield extremely harsh sites requiring restoration,demanding new seedling production and planting techniques (Badi´a et al. 2007; Bell andHobbs 2007; Salifu et al. 2008; Josa et al. 2012). Many areas, previously converted toagriculture, have since been afforested in developed countries by overcoming problemsassociated with years of cropping use, such as weed competition or soil compaction.

Modified exponential nitrogen loading to promote morphological quality and nutrient storage of bareroot-cultured Quercus rubra and Quercus alba seedlings

Abstract Exponential nutrient loading has been used to improve nursery fertilizer uptake efficiency of conifer seedlings, but the technique has received little attention in the culture of temperate deciduous hardwoods. This study examined responses of northern red oak (Quercus rubra L.) and white oak (Q. alba L.) seedlings to modified exponential nitrogen loading during bareroot nursery culture using a broad range of nutrient supply from 0 to 3.35 g nitrogen (N) per plant per season for 18 weeks in Indiana, USA. Seedling growth and nutritional parameters followed a curvilinear pattern that ranged from deficiency to toxicity with increased fertilization consistent with trends depicted in the proposed model for nutrient loading. Fertilization increased plant dry mass by 113–260% for red oak and 49–144% for white oak. Severe nutrient deficiency occurred under indigenous soil fertility, and limited phosphorus and potassium uptake were found to inhibit seedling growth at higher N supply. The sufficiency and optimum rates were determined to be 0.84 and 1.68 g N per seedling per season, respectively, under the current cultural conditions. Fertilization at 1.68 g N per plant increased N content by 40% in red oak and 35% in white oak. This approach may be used to help refine nursery fertilization practices in hardwood culture to produce high-quality seedlings for field planting.

Drought susceptibility and recovery of transplanted Quercus rubra seedlings in relation to root system morphology

Abstract• Transplant shock, implicated by depressed seedling physiological status associated with moisture stress immediately following planting, limits early plantation establishment. Large root volume (Rv) has potential to alleviate transplant shock because of higher root growth potential and greater access to soil water.• We investigated impacts of drought and transplant Rv on photosynthetic assimilation (A), transpiration (E), stomatal conductance (gs), predawn leaf xylem water potential (ΨL), and growth of northern red oak (Quercus rubra L.) seedlings to explain mechanisms associated with susceptibility to transplant shock. One year-old barerooot seedlings were graded into four Rv categories and either well watered or subjected to drought consisting of low, medium, or high moisture stress by discontinuing irrigation at 22-day intervals for 3 months. Thereafter, all treatments were re-watered to examine recovery.• Transplant shock was signified by reduced A, E, gs, and ΨL, which generally increased with increasing moisture stress and Rv. Physiological status improved during recovery, though stress was still evident in seedlings exposed to medium or high moisture stress and in larger Rv seedlings. Growth declined with increasing moisture stress but was generally similar among Rv treatments, likely reflecting greater A at the whole plant level and/or reliance upon stored reserves in large Rv seedlings.• The most effective drought avoidance mechanisms were root growth, stomatal regulation, reduced leaf area, and higher growth allocation to roots relative to shoots. Our results suggest that large initial Rv does not enhance drought avoidance during the first season after transplant in northern red oak seedlings.Résumé• Le choc de transplantation, lié à l’état physiologique déprimé des plants associé à un stress hydrique, immédiatement après la plantation, limite le début de l’installation des plants. Un important volume racinaire (Rv) a le potentiel d’atténuer le choc de transplantation en raison du fort potentiel de croissance racinaire et d’un meilleur accès à l’eau du sol. Nous avons étudié les impacts de la sécheresse et des transplants Rv sur l’assimilation photosynthétique (A), la transpiration (E), la conductance stomatique (gs), le potentiel hydrique de base (ΨL), et la croissance des plants de chêne rouge (Quercus rubra L.) pour expliquer les mécanismes associés à la sensibilité à un choc de transplantation. Des plants de un an à racines nues ont été classés en quatre catégories Rv et soit bien arrosés, ou soumis à une sécheresse, consistant à un faible, moyen ou fort stress hydrique en cessant l’irrigation à 22 jours d’intervalle(27, 49 et 72 après la transplantation) pour 3 mois. Par la suite, tous les traitements ont été arrosés afin d’examiner la reprise.• Le choc de transplantation qui généralement a augmenté avec l’augmentation du stress hydrique et Rv, a été significatif par la réduction de A, E, gs, and ΨL. L’état physiologique s’est amélioré lors de la reprise, même si le stress est encore évident chez les plants exposés à un stress hydrique moyen ou élevé et chez les plants à Rv les plus importants. La croissance a diminué avec l’augmentation du stress hydrique, mais elle a été généralement similaire chez les traitements Rv, reflétant probablement une plus grande A au niveau du plant entier et / ou le recours à des réserves stockées dans les plants à Rv important.• Les mécanismes d’évitement de la sécheresse les plus efficaces ont été la croissance des racines, la régulation stomatique, une surface foliaire réduite et une allocation de la croissance plus élevée aux racines par rapport aux pousses. Nos résultats suggèrent que les grandes Rv initiales n’améliorent pas l’évitement de la sécheresse durant la première saison après transplantation chez les plants de chêne rouge.

Fall fertilization of Pinus resinosa seedlings: nutrient uptake, cold hardiness, and morphological development.

Abstract• Fall fertilization may increase plant nutrient reserves, yet associated impacts on seedling cold hardiness are relatively unexplored.• Bareroot red pine (Pinus resinosa Ait.) seedlings in north-central Minnesota, USA were fall fertilized at the end of the first growing season with ammonium nitrate (NH4NO3) at 0, 11, 22, 44, or 89 kg N ha−1. Seedling morphology and cold hardiness [assessed by freeze induced electrolyte leakage (FIEL)] were evaluated six weeks after fertilization and following the second growing season.• Seedling height and number of needle primordia increased with fertilizer rate for both sampling years. Seedlings fertilized with 44 and 89 kg N ha−1 attained target height (15 cm) after the second growing season. Shoot and root N concentration increased after the first growing season in fall fertilized seedlings compared to controls. Fall fertilized seedlings had lower FIEL (i.e., increased cold hardiness) compared to controls when tested at −40 °C after the first growing season, but no significant differences in FIEL of control and fertilized seedlings were observed after the second growing season.• Results suggest that fall fertilization of red pine seedlings can help render desired target height in the nursery, while maintaining or increasing cold hardiness levels.Résumé• La fertilisation automnale peut augmenter les réserves en éléments nutritifs des plants, mais les répercussions sur la rusticité au froid des semis sont encore relativement inexplorées.• Des plants à racines nues de Pinus resinosa Ait.dans le centre-nord du Minnesota (USA) ont été fertilisés à l’automne à la fin de la première saison de croissance avec du nitrate d’ammonium (NH4NO3) à 0, 11, 22, 44, ou 89 kg N ha−1. La morphologie des plants et la rusticité au froid [estimée par la fuite d’électrolyte (FIEL) induite par le gel] ont été évaluées six semaines après la fertilisation et à la suite dans la deuxième saison de croissance.• La hauteur des plants et le nombre de primordiums d’aiguilles ont augmenté avec le taux de fertilisation pour les deux années d’échantillonnage. Les plants fertilisés avec 44 et 89 kg N ha−1 ont atteint l’objectif de hauteur (15 cm) après la deuxième saison de croissance. La concentration en N des tiges et des racines a augmenté après la première saison de croissance chez les plants fertilisés à l’automne par rapport aux témoins. Les plants fertilisés à l’automne ont eu un plus faible FIEL (c’est-à-dire, une augmentation de rusticité), comparativement aux témoins lors du test à −40 °C après la première saison de croissance, mais aucune différence significative de FIEL entre plants fertilisés et témoins n’a été observée après la deuxième saison de croissance.• Les résultats suggèrent que la fertilisation d’automne des plants de Pinus resinosa Ait. peut aider à obtenir l’objectif de hauteur souhaité dans la pépinière, tout en maintenant ou en augmentant les niveaux de rusticité au froid.