Effects of Ponderosa Pine Ecological Restoration on Forest Soils and Understory Vegetation in Northern Arizona

The human exclusion of wildfire and overgrazing by livestock since settlement have caused dramatic changes in ponderosa pine (Pinus ponderosa Dougl ex Laws) forest ecosystems. These changes include increased numbers of tree stems, reduced understory cover and diversity, and the introduction of invasive, non-native understory species. This study evaluated the coverage and species composition of understory vegetation present in the “cool-season” (late spring and early summer) in a ponderosa pine forest on grazed and ungrazed plots that had undergone restoration treatments on three different soil/geologic parent material types near Flagstaff, Arizona, twelve years after tree thinning and grazing exclosure treatments were applied. Several measured soil properties, such as soil respiration and temperature, were also evaluated in this study. Species richness of “cool-season” vegetation was influenced more by grazing practices than restoration treatments. Differences could be less or greater when vegetation that is active later in the season is measured. Vegetative cover was significantly influenced by restoration treatments (9.3% cover under open canopies and 6.5% under dense canopies), probably due to differences in competition for light and other resources (i.e. soil moisture and nutrients). Unlike finding by Abella et al. (2015), who studied “warm-season” vegetation, “cool-season” understory cover was not influenced by soil parent material type in this study, which might suggest that differences in understory cover due to soil properties are only seen shortly after restoration treatments are applied, or the time of year vegetation is evaluated may play a role in the differences seen. Soil respiration was highest on limestone soil parent material type (3.3 g C-CO2 m-2 day-1), and soil temperature was lowest under closed canopy treatments (15°C)

Extractable nitrogen and microbial community structure respond to grassland restoration regardless of historical context and soil composition.

Grasslands have a long history of invasion by exotic annuals, which may alter microbial communities and nutrient cycling through changes in litter quality and biomass turnover rates. We compared plant community composition, soil chemical and microbial community composition, potential soil respiration and nitrogen (N) turnover rates between invaded and restored plots in inland and coastal grasslands. Restoration increased microbial biomass and fungal : bacterial (F : B) ratios, but sampling season had a greater influence on the F : B ratio than did restoration. Microbial community composition assessed by phospholipid fatty acid was altered by restoration, but also varied by season and by site. Total soil carbon (C) and N and potential soil respiration did not differ between treatments, but N mineralization decreased while extractable nitrate and nitrification and N immobilization rate increased in restored compared with unrestored sites. The differences in soil chemistry and microbial community composition between unrestored and restored sites indicate that these soils are responsive, and therefore not resistant to feedbacks caused by changes in vegetation type. The resilience, or recovery, of these soils is difficult to assess in the absence of uninvaded control grasslands. However, the rapid changes in microbial and N cycling characteristics following removal of invasives in both grassland sites suggest that the soils are resilient to invasion. The lack of change in total C and N pools may provide a buffer that promotes resilience of labile pools and microbial community structure

Living Close to Your Neighbors: The Importance of Both Competition and Facilitation in Plant Communities

Recent work has demonstrated that competition and facilitation likely operate jointly in plant communities, but teasing out the relative role of each has proven difficult. Here we address how competition and facilitation vary with seasonal fluctuations in environmental conditions, and how the effects of these fluctuations change with plant ontogeny. We planted three sizes of pine seedlings (Pinus strobus) into an herbaceous diversity experiment and measured pine growth every two weeks for two growing seasons. Both competition and facilitation occurred at different times of year between pines and their neighbors. Facilitation was important for the smallest pines when environmental conditions were severe. This effect decreased as pines got larger. Competition was stronger than facilitation overall and outweighed facilitative effects at annual time scales. Our data suggest that both competition and the counter‐directional effects of facilitation may be more common and more intense than previously considered

Effects of large herbivores on grassland arthropod diversity

Both arthropods and large grazing herbivores are important components and drivers of biodiversity in grassland ecosystems, but a synthesis of how arthropod diversity is affected by large herbivores has been largely missing. To fill this gap, we conducted a literature search, which yielded 141 studies on this topic of which 24 simultaneously investigated plant and arthropod diversity. Using the data from these 24 studies, we compared the responses of plant and arthropod diversity to an increase in grazing intensity. This quantitative assessment showed no overall significant effect of increasing grazing intensity on plant diversity, while arthropod diversity was generally negatively affected. To understand these negative effects, we explored the mechanisms by which large herbivores affect arthropod communities: direct effects, changes in vegetation structure, changes in plant community composition, changes in soil conditions, and cascading effects within the arthropod interaction web. We identify three main factors determining the effects of large herbivores on arthropod diversity: (i) unintentional predation and increased disturbance, (ii) decreases in total resource abundance for arthropods (biomass) and (iii) changes in plant diversity, vegetation structure and abiotic conditions. In general, heterogeneity in vegetation structure and abiotic conditions increases at intermediate grazing intensity, but declines at both low and high grazing intensity. We conclude that large herbivores can only increase arthropod diversity if they cause an increase in (a)biotic heterogeneity, and then only if this increase is large enough to compensate for the loss of total resource abundance and the increased mortality rate. This is expected to occur only at low herbivore densities or with spatio-temporal variation in herbivore densities. As we demonstrate that arthropod diversity is often more negatively affected by grazing than plant diversity, we strongly recommend considering the specific requirements of arthropods when applying grazing management and to include arthropods in monitoring schemes. Conservation strategies aiming at maximizing heterogeneity, including regulation of herbivore densities (through human interventions or top-down control), maintenance of different types of management in close proximity and rotational grazing regimes, are the most promising options to conserve arthropod diversity

Soil biodiversity: functions, threats and tools for policy makers

Human societies rely on the vast diversity of benefits provided by nature, such as food, fibres, construction materials, clean water, clean air and climate regulation. All the elements required for these ecosystem services depend on soil, and soil biodiversity is the driving force behind their regulation. With 2010 being the international year of biodiversity and with the growing attention in Europe on the importance of soils to remain healthy and capable of supporting human activities sustainably, now is the perfect time to raise awareness on preserving soil biodiversity. The objective of this report is to review the state of knowledge of soil biodiversity, its functions, its contribution to ecosystem services and its relevance for the sustainability of human society. In line with the definition of biodiversity given in the 1992 Rio de Janeiro Convention, soil biodiversity can be defined as the variation in soil life, from genes to communities, and the variation in soil habitats, from micro-aggregates to entire landscapes. Bio Intelligence Service, IRD, and NIOO, Report for European Commission (DG Environment

Towards a methodical framework for comprehensively assessing forest multifunctionality

Funded by Deutsche Forschungsgemeinschaft. Grant Number: DFG FOR 891/1-3 National Natural Science Foundation of China. Grant Numbers: 30710103907, 30930005, 31170457, 31210103910 Swiss National Science Foundation (SNSF) Sino-German Centre for Research Promotion in Beijing. Grant Number: GZ 986Peer reviewedPublisher PD

Taimekoosluse ja arbuskulaarmükoriisse seenekoosluse dünaamika rohumaadel muutuva maakasutuse tingimustes

Väitekirja elektrooniline versioon ei sisalda publikatsiooneEnam kui kaks kolmandikku maismaaökosüsteemidest on inimtegevuse poolt tugevasti mõjutatud. Viimaste hulka kuuluvad ka Euroopa pool-looduslikud rohumaad, mis paistavad silma oma taimekoosluste suure mitmekesisusega. Need rohumaad on kujunenud kestva ja mõõduka niitmise ja/või karjatamise tulemusel ning nende säilitamiseks on vaja samasuguse maakasutuse jätkumist. Kuna pool-looduslike rohumaade pindala on drastiliselt vähenenud, on looduskaitseliste eesmärkide täitmiseks tihtipeale vajalik ka nende rohumaade taimekoosluste taastamine. See omakorda nõuab detailset arusaama rohumaade elurikkust mõjutavatest teguritest. Madalakasvulised väheviljakate rohumaade taimeliigid on valguslembesed ja neil on väiksed, tuule või kariloomade kaasabil levivad seemned. Kinnikasvanud rohumaadel ei ole selliste taimeliikide jaoks piisavalt valgust ning puuduvad sobilikud tingimused seemneleviks. Lisaks võib niiduliikide populatsioonide seisundit halvendada ning taastumist takistada sümbiontsete mullamikroobide puudumine. Viimaste hulka kuuluvad ka arbuskulaarmükoriissed (AM) seened. Antud doktoritöö tulemused kinnitasid, et lisaks seemnelevi soodustamisele ja valgustingimuste parandamisele on kinnikasvanud rohumaade taastamisel tähtis roll ka AM seentel. Tüüpilises avatud rohumaa taimekoosluses on tunduvalt rohkem mükoriisa olemasolust oluliselt sõltuvaid taimeliike kui kinnikasvanud rohumaa taimekoosluses. Seetõttu võib AM seente olemasolu või puudumine rohumaade taastamisprotsessi oluliselt mõjutada.Human activities have modified about two thirds of all terrestrial ecosystems. European semi-natural grasslands are among the most diverse ecosystems globally; at the same time, they are among the ecosystems most affected by human activities. Such grasslands develop under extensive land use practices – notably grazing and mowing – and land use change can dramatically decrease the extent and quality of such habitats, posing a considerable threat to grassland biodiversity. Many restoration efforts have been undertaken to mitigate against habitat loss, but re-establishing grassland specialist plants often challenges restoration practitioners. This may be because many typical grassland plant species have small seeds adapted to dispersal by wind or grazing animals. As such, a lack of grazing animals or dense vegetation around restored grassland patches might hinder seed dispersal between grassland patches, and thus maintenance of vital meta-populations. It is also possible that restoration sites lack certain soil organisms found in intact habitats, and their absence impairs the establishment of plants that rely on them (e.g. symbiotic fungi, such as arbuscular mycorrhizal (AM) fungi). The aim of this doctoral thesis was to assess the relevance of these factors for successful grassland restoration. The results of the thesis confirm the importance of facilitating plant species dispersal between grassland patches by re-opening the vegetation to create dispersal corridors and by re-introducing continuous grazing management, with grazing animals able to move between grassland patches. Moreover, the results suggest that a lack of suitable AM fungi in the soil of severely altered and isolated grassland patches might hamper natural re-establishment of typical grassland vegetation. Coordinated re-introduction of target plant and AM fungal communities could increase restoration succession in such cases

Plant-microbial interactions facilitate grassland species coexistence at the community level

Interspecific competition and plant-soil feedbacks are powerful drivers of plant community structure. However, across a range of edaphic conditions the interactive effects of these drivers on complex plant communities remain unclear. For example, plant-soil feedback studies focus on soil trained by a single plant species. We developed a method to assess effects of plant-microbial interactions (PMI) on a complex plant community. We established mesocosms with 13 grassland species, grown individually or together, in overgrazed or restored soil, with or without soil microbial inoculum collected from a productive and diverse native grassland. We assessed biomass production as influenced by edaphic conditions, interspecific competition and PMI. Furthermore, we assessed potential influences of interspecific competition and edaphic conditions on strength and direction of PMI. Our results indicate PMI drives negative growth responses for graminoids while forbs experience positive growth responses. Generally, interspecific competition did not alter the magnitude or direction of PMI-mediated growth responses. Edaphic conditions altered the influence of soil microbial communities on individual plant growth while PMI facilitated plant evenness. In plant community mesocosms, PMI-associated benefits were observed in overgrazed soil. However, interspecific competition overwhelmed plant growth benefits associated with soil microbial communities when plant communities were grown in restored soil. In mesocosms containing dominant grass species, interspecific competition had negative effects on species coexistence, but both positive and negative PMI partially counterbalanced this influence on plant species evenness. Understanding these mechanisms may improve our capacity to manage diverse and productive grasslands by enabling prediction of plant community composition following disturbance and subsequent restoration