Whitebark pine (Pinus albicaulis) forest ecosystems in California are diverse and unique, yet their current status and condition are uncertain. Using a combination of geospatial and field plot data, ...we assessed patterns in the structure, composition, and health of whitebark pine ecosystems on national forests throughout the state of California to evaluate potential signs of declining ecosystem integrity. We found whitebark pine ecosystems to be structurally, compositionally, and functionally distinct among subregions of California, and all subregions displayed some evidence of declining ecological integrity. Whitebark pine forests in northern California exhibited signs of greater stand densification (Cascade-Klamath), potential encroachment by shade-tolerant conifer species (Cascade-Klamath and Warner Mountains), and increased tree mortality associated with mountain pine beetle outbreaks (Warner Mountains) than elsewhere in California. Whitebark pine stands in the Sierra Nevada showed signs of stand densification (central Sierra) and localized mountain pine beetle outbreaks (southern Sierra east). Notwithstanding these negative signs, much of the state's whitebark pine ecosystems on national forestlands appear to be relatively healthy and intact compared to more northern latitudes. Active management may be required to restore whitebark pine ecosystems on national forests in California with declining integrity, including stands experiencing substantial stand densification, encroachment by shade-tolerant conifers, and mountain pine beetle outbreaks.
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Climate warming in recent decades has negatively impacted forest health in the western United States. Here, we report on potential early warning signals (EWS) for drought‐related mortality derived ...from measurements of tree‐ring growth (ring width index; RWI) and carbon isotope discrimination (∆13C), primarily focused on ponderosa pine (Pinus ponderosa). Sampling was conducted in the southern Sierra Nevada Mountains, near the epicenter of drought severity and mortality associated with the 2012–2015 California drought and concurrent outbreak of western pine beetle (Dendroctonus brevicomis). At this site, we found that widespread mortality was presaged by five decades of increasing sensitivity (i.e., increased explained variation) of both tree growth and ∆13C to Palmer Drought Severity Index (PDSI). We hypothesized that increasing sensitivity of tree growth and ∆13C to hydroclimate constitute EWS that indicate an increased likelihood of widespread forest mortality caused by direct and indirect effects of drought. We then tested these EWS in additional ponderosa pine‐dominated forests that experienced varying mortality rates associated with the same California drought event. In general, drier sites showed increasing sensitivity of RWI to PDSI over the last century, as well as higher mortality following the California drought event compared to wetter sites. Two sites displayed evidence that thinning or fire events that reduced stand basal area effectively reversed the trend of increasing hydroclimate sensitivity. These comparisons indicate that reducing competition for soil water and/or decreasing bark beetle host tree density via forest management—particularly in drier regions—may buffer these forests against drought stress and associated mortality risk. EWS such as these could provide land managers more time to mitigate the extent or severity of forest mortality in advance of droughts. Substantial efforts at deploying additional dendrochronological research in concert with remote sensing and forest modeling will aid in forecasting of forest responses to continued climate warming.
Widespread forest mortality in the Sierra Nevada Mountains following the 2012–2015 California drought event was preceded by five decades of increasing sensitivity of both tree growth and tree‐ring carbon isotope discrimination (∆13C) to drought variability, as recorded by the Palmer Drought Severity Index (PDSI). We propose that increasing sensitivity of growth and ∆13C to drought‐related variables like PDSI can be complementary early warning signals (EWS) for widespread drought‐related forest mortality. EWS derived from tree‐rings could provide land managers with a decade or more to mitigate the extent or severity of forest mortality in advance of future droughts.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Seedlings of lodgepole pine (Pinus contorta var. latifolia), jack pine (P. banksiana), and their hybrid were infected by Dothistroma septosporum under natural conditions in Alberta, Canada, after ...planting these taxa within a heavily infected stand of lodgepole pine. This experiment has further proven that all three of these taxa are hosts for the pathogen. This information is necessary for assessing the risk of eastward movement of the pathogen from Alberta through populations of P. banksiana in the boreal forest.
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In addition to breeding for genetic resistance, lower branch pruning is a management strategy to mitigate adverse effects of Cronartium ribicola on young western white pine (Pinus monticola; WWP) in ...portions of the Interior Northwest, USA (INW). However, only data on heights of white pine blister rust (WPBR) cankers and post‐treatment effects from outside the Oregon East Cascades (OEC) have previously informed INW pruning guidelines. To evaluate the appropriateness of these guidelines for WWP in the OEC, heights to cankers on young WWP (<30 years old) were measured in 120 plots within 12 stands throughout the OEC. Canker heights were analysed for live WWP ≥2.54 cm in diameter at 1.37 m. Incidence and severity of WPBR on live WWP, in addition to heights to cankers, varied among stands. Increased severity of WPBR (number of cankers on live‐infected trees and percent mortality by WPBR) was observed in stands with the alternate host Ribes more frequently occurring in plots. Of all cankers, approximately 97% were found in the lower half of the total tree height, and only 10% of cankers on young WWP were found above the first third of the total tree height. When evaluating canker heights in all stands, mean heights to branch and bole cankers were <2.2 m. Bole cankers were lower than branch cankers (p = .01), reaffirming that potentially lethal cankers in the INW often originate from infections lower in the crown. In stands, the number of plots with Ribes present was positively correlated with the number of cankers on live‐infected WWP and percent mortality of WWP due to WPBR (p < .04). As the incidence of WPBR on live WWP increased in stands, heights to the highest cankers also increased (p = .002). The number of cankers on live‐infected trees was positively correlated with the mean and highest heights to cankers (p < .002). Given that the vast majority of cankers were prunable and occurred in the lower crown of young WWP, pruning lower branches to increase survival of WWP is a management option in the OEC, and prioritization of stands for treatment is recommended.
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Pine straw, the uppermost forest floor layer of undecayed, reddish-brown pine needles, is raked, baled, and sold as a landscaping mulch throughout the southeastern United States. Loblolly (Pinus ...taeda, L.), longleaf (P. palustris, Mill.), and slash (P. elliottii Engelm. var. elliottii) pine are the three southern pine species commonly raked for pine straw. The value of pine straw as a forest product is large. Private landowner pine straw revenues have steadily increased throughout the southeastern United States over the past two decades and now total more than USD 200 million. Information is limited on the short- or long-term effects of pine straw removal on foliage production or stand growth in southern pine stands. Results from most published studies suggest that annual pine straw raking without fertilization on non-old-field sites reduces straw yields compared to no raking. Old-field sites often do not benefit from fertilization with increased pine straw or wood volume yields. Though fertilization may be beneficial for pine straw production on some sites, understory vegetation presence and disease prevalence may increase following fertilization. This review addresses pine straw removal effects on pine straw production and stand growth parameters based on recent studies and provides fertilization recommendations to maintain or improve pine straw production and stand growth and yield.
Climate change exposes ecosystems to strong and rapid changes in their environmental boundary conditions mainly due to the altered temperature and precipitation patterns. It is still poorly ...understood how fast interlinked ecosystem processes respond to altered environmental conditions, if these responses occur gradually or suddenly when thresholds are exceeded, and if the patterns of the responses will reach a stable state. We conducted an irrigation experiment in the Pfynwald, Switzerland from 2003–2018. A naturally dry Scots pine (Pinus sylvestris L.) forest was irrigated with amounts that doubled natural precipitation, thus releasing the forest stand from water limitation. The aim of this study was to provide a quantitative understanding on how different traits and functions of individual trees and the whole ecosystem responded to increased water availability, and how the patterns and magnitudes of these responses developed over time. We found that the response magnitude, the temporal trajectory of responses, and the length of initial lag period prior to significant response largely varied across traits. We detected rapid and stronger responses from aboveground tree traits (e.g., tree‐ring width, needle length, and crown transparency) compared to belowground tree traits (e.g., fine‐root biomass). The altered aboveground traits during the initial years of irrigation increased the water demand and trees adjusted by increasing root biomass during the later years of irrigation, resulting in an increased survival rate of Scots pine trees in irrigated plots. The irrigation also stimulated ecosystem‐level foliar decomposition rate, fungal fruit body biomass, and regeneration abundances of broadleaved tree species. However, irrigation did not promote the regeneration of Scots pine trees, which are reported to be vulnerable to extreme droughts. Our results provide extensive evidence that tree‐ and ecosystem‐level responses were pervasive across a number of traits on long‐term temporal scales. However, after reaching a peak, the magnitude of these responses either decreased or reached a new stable state, providing important insights into how resource alterations could change the system functioning and its boundary conditions.
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Bark beetle outbreaks are an important cause of tree death, but the process by which trees die remains poorly understood. The effect of beetle attack on whole‐tree nonstructural carbohydrate (NSC) ...dynamics is particularly unclear, despite the potential role of carbohydrates in plant defense and survival. We monitored NSC dynamics of all organs in attacked and protected lodgepole pines (Pinus contorta) during a mountain pine beetle (Dendroctonus ponderosae) outbreak in British Columbia, starting before beetle flight in June 2011 through October 2012, when most attacked trees had died. Following attack, NSC concentrations were first reduced in the attacked region of the bole. The first NSC reduction in a distant organ appeared in the needles at the end of 2011, while branch and root NSC did not decline until much later in 2012. Attacked trees that were still alive in October 2012 had less beetle damage, which was negatively correlated with initial bark sugar concentrations in the attack region. The NSC dynamics of dying trees indicate that trees were killed by a loss of water conduction and not girdling. Further, our results identify locally reduced carbohydrate availability as an important mechanism by which stressors like drought may increase tree susceptibility to biotic attack.
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The pine wood nematode (PWN),
Bursaphelenchus xylophilus
, is a destructive invasive species that exerts devastating effects on most native pines in invaded regions, while many of the non-native ...pines have resistance to PWN. Recently, increasingly more research is focused on how microbial communities can improve host resistance against pathogens. However, the relationship between the microbial community structures and varying levels of pathogen resistance observed in different pine tree species remains unclear. Here, the bacterial and fungal communities of introduced resistant pines
Pinus elliottii
,
P. caribaea
, and
P. taeda
and native susceptible pines healthy and wilted
P. massoniana
infected by PWN were analyzed. The results showed that 6057 bacterial and 3931 fungal OTUs were annotated. The pine samples shared 944 bacterial OTUs primarily in the phyla Proteobacteria, Acidobacteria, Firmicutes, Bacteroidetes, and Chloroflexi and 111 fungal OTUs primarily in phyla Ascomycota and Basidiomycota, though different pines had unique OTUs. There were significant differences in microbial community diversity between different pines, especially between the bacterial communities of resistant and susceptible pines, and fungal communities between healthy pines (resistant pines included) and the wilted
P. massoniana
. Resistant pines had a greater abundance of bacteria in the genera
Acidothermus
(class unidentified_Actinobacteria) and
Prevotellaceae
(class Alphaproteobacteria), but a lower abundance of
Erwinia
(class Gammaproteobacteria). Healthy pines had a higher fungal abundance of
Cladosporium
(class Dothideomycetes) and class Eurotiomycetes, but a lower abundance of
Graphilbum
,
Sporothrix
,
Geosmithia
(class Sordariomycetes), and
Cryptoporus
(classes Agaricomycetes and Saccharomycetes). These differences in microbial abundance between resistant and healthy pines might be associated with pathogen resistance of the pines, and the results of this study contribute to the studies exploring microbial-based control of PWN.
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EMUNI, FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OILJ, PNG, SAZU, SBCE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Severe drought may increase physiological stress on long-lived woody vegetation, occasionally leading to mortality of overstory trees. Little is known about the factors determining tree survival and ...subsequent recovery after drought. We used structural equation modeling to analyse the recovery of Scots pine (Pinus sylvestris) trees 4 yr after an extreme drought episode occurred in 2004-2005 in north-east Spain. Measured variables included the amount of green foliage, carbon reserves in the stem, mistletoe (Viscum album) infection, needle physiological performance and stem radial growth before, during and after the drought event. The amount of green leaves and the levels of carbon reserves were related to the impact of drought on radial growth, and mutually correlated. However, our most likely path model indicated that current depletion of carbon reserves was a result of reduced photosynthetic tissue. This relationship potentially constitutes a feedback limiting tree recovery. In addition, mistletoe infection reduced leaf nitrogen content, negatively affecting growth. Finally, successive surveys in 2009-2010 showed a direct association between carbon reserves depletion and drought-induced mortality. Severe drought events may induce long-term physiological disorders associated with canopy defoliation and depletion of carbon reserves, leading to prolonged recovery of surviving individuals and, eventually, to delayed tree death.
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In Portugal, dozens of bark and wood‐boring beetle species have been recorded colonizing Pinus pinaster Aiton (Pinaceae), the main conifer species affected by pine wilt disease (PWD). However, its ...causal agent, the pinewood nematode (PWN), Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle (Parasitaphelenchidae), has been recovered only from the black pine sawyer, Monochamus galloprovincialis (Olivier) (Coleoptera: Cerambycidae). To understand the mechanisms underlying this specific relationship, our goal was to characterize the cuticular compounds (CCs) of three of the most abundant wood‐boring cerambycids, M. galloprovincialis, Arhopalus syriacus (Reiter), and Pogonocherus perroudi (Mulsant) Villiers, colonizing infested P. pinaster. Three methods of extracting CCs were assessed: (1) headspace solid phase microextraction (SPME), (2) extraction with organic solvent (pentane or ethanol), and (3) hydrodistillation. Pentane extraction was most effective, using pooled samples of each of the insects’ developmental stages. Extracts were analysed by gas chromatography‐mass spectrometry (GC‐MS) to identify compounds, and by GC for quantification. The pentane extracts contained predominantly straight‐chain (n‐C) and methyl‐branched hydrocarbons (meC). Cluster analysis defined two main clusters, with cluster A comprising A. syriacus samples dominated by n‐C23 (7‐39%), n‐C25 (9‐31%), and n‐C27 (5‐11%). Pogonocherus perroudi and the larvae from M. galloprovincialis grouped in sub‐cluster B1, characterized by high proportions of n‐C27 (20‐52%), n‐C29 (4‐18%), and 3‐meC27 (8‐18%). Sub‐cluster B2 included the remaining M. galloprovincialis samples, dominated by n‐C27 (10‐14%), n‐C25 (8‐10%), 5‐meC25 (9‐16%), 2‐meC26 (6‐12%), and 3‐meC27 (6‐10%). The CC profiles of the various species may play a key role in triggering the movement of PWN from the tree to callow adults of the specific insect vector, among all insects colonizing infested host trees. Identification of key components would potentially allow the development of valuable tools to manage PWD, for example, in a lure to quickly detect PWN in a tree, or conversely, by treatment of felled wood with PWN repellents to disrupt PWN transfer to its insect vector, breaking the transmission cycle.
To understand the mechanisms underlying the specific relationship between the pinewood nematode (PWN), Bursaphelenchus xylophilus (Parasitaphelenchidae), and its host, the black pine sawyer, Monochamus galloprovincialis (Coleoptera: Cerambycidae), our goal was to characterize the cuticular compounds (CCs) of the three most abundant wood‐boring cerambycids that colonize Pinus pinaster (Pinaceae), the main conifer species affected by pine wilt disease in Portugal. The CC profiles may play a key role in triggering the movement of PWN from the tree to specific insect vectors.
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