Changes in key drivers (e.g., climate, disturbance regimes and land use) may affect the sustainability of forest landscapes and set the stage for increased tension among competing ecosystem services. ...We addressed two questions about a suite of supporting, regulating and provisioning ecosystem services in each of two well-studied forest landscapes in the western US: (1) How might the provision of ecosystem services change in the future given anticipated trajectories of climate, disturbance regimes, and land use? (2) What is the role of spatial heterogeneity in sustaining future ecosystem services? We determined that future changes in each region are likely to be distinct, but spatial heterogeneity (e.g., the amount and arrangement of surviving forest patches or legacy trees after disturbance) will be important in both landscapes for sustaining forest regeneration, primary production, carbon storage, natural hazard regulation, insect and pathogen regulation, timber production and wildlife habitat. The paper closes by highlighting five general priorities for future research. The science of landscape ecology has much to contribute toward understanding ecosystem services and how land management can enhance—or threaten—the sustainability of ecosystem services in changing landscapes.
•Douglas-fir comprised 80% of seedlings and 88% of ingrowth in the clearcut regime.•Stand edge competition in the patches and groups regimes limited seedling size 30–39%.•Clearcut vs. non-treated ...control: higher blackberry cover but lower shrub height.•Ingrowth in non-clearcut regimes was a Douglas-fir and western hemlock mixture.•Overstory tree growth in the two-age regime compensated for reduced ingrowth.
In the Pacific Northwestern USA, concerns regarding impacts of forest harvesting on visual quality, wildlife habitat, and carbon management have prompted evaluations of alternative silvicultural regimes for coast Douglas-fir (Pseudotsuga menziesii var. menziesii). Research was initiated in 1998 near Olympia WA USA to conduct long-term comparisons among six silvicultural regimes: clearcut (harvest all trees), two age (harvest all except 38 mature trees ha−1), patches (harvest 20% of the area in 0.6–2.0 ha tracts), groups (harvest 20% of the area in 0.1–0.5 ha tracts), thinning (reduce stand density to 45% of the biological maximum for Douglas-fir), and a non-treated control. Harvested areas in the first four regimes were planted with Douglas-fir seedlings. This report focuses on tree regeneration and stand productivity during the first decade of the study. Fifth year height of planted Douglas-fir was greater in the clearcut regime (1.8 m) than in the patches and groups regimes (1.1–1.2 m). Fifth year tree regeneration in the clearcut and two-age regimes was dominated by Douglas-fir (80–86% of seedlings), but regeneration in the patches and groups regimes was composed of a mixture of conifer and hardwood species. Ten-year periodic annual increment (PAI) in Douglas-fir ingrowth volume was greater in the clearcut regime (1.4 m3 ha−1 yr−1) than in the control (0.1 m3 ha−1 yr−1), whereas ingrowth volume PAI of other conifer species was greater in the two-age regime (0.4 m3 ha−1 yr−1) than in the control (0.0 m3 ha−1 yr−1). Tree regeneration responses indicated increasing abundance of shade tolerant species in the non-clearcut regimes, especially western hemlock (Tsuga heterophylla). Fifth year cover of the vine, California blackberry (Rubus ursinus), in the clearcut regime (21%) was over four times that in the control (5%). Ground disturbance in the clearcut regime reduced 5th-year height of the shrubs, salal (Gaultheria shallon) and red huckleberry (Vaccinium parvifolium), by 40–50% compared to the control. Ten-year volume PAI of Douglas-fir was linearly related to post-harvest stand basal area (r2 = 0.94), and the relationship did not vary significantly among the three replicate sites. During the first decade of the study, Douglas-fir regeneration and stand productivity differed among silvicultural regimes because of post-harvest variation in stand edge competition, species composition of tree seedlings and ingrowth, and residual stand density.
Microorganisms play a central role in litter decomposition and partitioning C between CO sub(2) evolution and sequestration of C into semi- permanent pools in soils. At the ecosystem level, forest ...stand age influences rates of litter accumulation and quality, and micro-climatology which could affect the microbial community structure and C sequestration processes. Although numerous laboratory experiments have studied the decomposition of model super(13)C-labeled compounds, few studies have verified these findings under field conditions. The objective of this study was to track decomposition of super(13)C-labeled Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) materials into the soil microbial community using super(13)C- phospholipids fatty acid (PLFA) analysis in three different aged forest stands. A field experiment was conducted that had three forest stand age treatments: old-growth (>500 yrs); 8-year-old clear-cut (CC8); and 25-year- old clear-cut (CC25) (landscape reps of n = 2). Each stand age had in situ microcosms that were amended with either super(13)C-labeled surface litter or root material. Microcosms were destructively sampled seven times over a 22-month period and the soil was analyzed for the relative amounts of super(13)C incorporated ( super(13)C% sub(INCORP)) into PLFAs and the proportional distribution of super(13)C incorporated into PLFAs. The super(13)C% sub(INCORP) was affected by stand age and super(13)C source with greater super(13)C% sub(INCORP) in samples from CC8 than OG or CC25. Also, the level of super(13)C% sub(INCORP) was greater for labeled litter than root material in five out of the seven sample dates. In general, 18:1Omega9 and 18:2Omega6,9 (common fungal biomarkers) had the greatest amount of super(13)C incorporation throughout the study period in both clear-cut and old-growth sites, especially in plots with super(13)C- labeled litter. Our data showed a low fungal super(13)C-PLFA: bacterial super(13)C- PLFA ratio (0.45) 1 month after incubation was initiated compared to 5, 7 and 9 months after incubation (two of these dates were >1.0). This suggests that initially bacteria played a greater role in the decomposition of the added needles with fungi playing a more important role in subsequent sample dates. Our results illustrate that the use of super(13)C-labeled materials in field studies coupled with super(13)C-PLFA profiling is a powerful tool for determining microbial dynamics during decomposition - enabling statistically significant detection of land management treatment effects on C acquisition by microbial functional groups.
•Pacific Northwest growth-climate-disease relations vary by site and climate regimes.•Douglas-fir growth is limited by dewpoint deficit and temperature regionally.•Growth response to temperature is ...modified by soil moisture and Swiss needle cast.•Swiss needle cast impacts on Douglas-fir growth are spatially extensive in the PNW.•PNW tree growth rates have changed in recent decades due to increasing temperature.
Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) growth in the Pacific Northwest is affected by climatic, edaphic factors and Swiss needle cast (SNC) disease. We examine Douglas-fir growth responses to temperature, dewpoint deficit (DPD), soil moisture, and SNC using time series intervention analysis of intra-annual tree-ring width data collected at nine forest stands in western Oregon, USA. Air temperature, previous-year DPD and SNC and their interactions were the primary factors influencing tree growth at all sites, whereas other key seasonal climatic factors limiting growth varied by site. Winter temperature was more important at high elevation cool sites, whereas summer temperature was more important at warm and dry sites. Growth rate increased with summer temperature to an optimum (Topt) then decreased at higher temperatures. At drier sites, temperature and water affected growth interactively such that Topt decreased with decreasing summer soil moisture. With increasing temperature due to climate change, growth rates increased at high elevation sites and declined at mid-elevation inland sites since ∼1990. Growth response to climate and SNC are confounded at all sites. We conclude that as temperature rises and precipitation patterns shift toward wetter winters and drier summers, Douglas-fir will experience greater temperature and water stress and an increase in severity of SNC.
Thinning is believed to accelerate the development of late-successional attributes, thereby enhancing stand structural heterogeneity in young, secondary forests. By making use of a large-scale ...experiment implemented in 40- to 60-year-old coastal Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) forests, we addressed the following objectives: (i) determine the effect of three thinning treatments on the temporal dynamics (first 11 years after thinning) of key forest structure measures, (ii) evaluate the relationships between spatially explicit structural diversity measures and spatially nonexplicit stand metrics, and (iii) test the relationships between stand structure and observed periodic stand volume growth, ingrowth, and mortality. Treatments consisted of high-density, moderate-density, and variable-density thinnings-from-below, as well as a control. Differences in stand structural heterogeneity between treatments were mostly nonsignificant. However, our results suggest that variable-density stands displayed structural enrichment as tree size and tree species diversity increased throughout the study period as a result of continuous ingrowth of species other than Douglas-fir. Simple spatially nonexplicit metrics could not be used to reliably model spatially explicit structural diversity measures. The inclusion of structural and species diversity measures only rarely improved accuracy of sample plot level growth, ingrowth, and mortality prediction models. Despite the short-term nature of this study, we conclude that variable-density thinning shows promise in increasing structural heterogeneity in young even-aged stands. The inclusion of structural diversity measures in growth and mortality models may be beneficial, but further work is needed to clarify the underlying relationships, particularly at the individual-tree level.
•N-fertilization of a 24-yr-old Douglas-fir stand enhanced basal area increment.•Earlywood Δ13C declined and iWUE increased for two years after fertilization.•Increased iWUE was the key response ...mechanism over LAI or carbon re-allocation.•Key fertilization response mechanisms may vary with inherent site quality.
Many hectares of intensively managed Douglas-fir (Pseudotsuga menziesii Mirb. Franco) stands in western North America are fertilized with nitrogen (N) to increase growth rates, but only about ⅔ of all stands respond. Understanding the mechanisms of response facilitates prioritization of stands for treatment. The primary objective of this study was to test the hypothesis that the short-term basal area growth response to a single application of 224kgNha−1 as urea was associated with reduced stable carbon isotope discrimination (Δ13C) and increased intrinsic water use efficiency (iWUE) in a 20-yr-old plantation of Douglas-fir in the Oregon Coast Range, USA. Increment cores were measured to estimate earlywood, latewood, and total basal area increment over a time series from 1997 to 2015. Stable carbon isotope discrimination and iWUE were estimated using earlywood and latewood stable carbon isotope concentrations in tree-ring holocellulose starting seven years before fertilization in early 2009 and ending seven years after treatment. A highly significant (p<0.01) interaction effect between fertilization treatment and year was found for total basal area growth and earlywood basal area increment. Specifically, fertilized trees showed significant responses (p<0.05) in total basal area growth and earlywood basal area increment in the first (2009) and second (2010) growing seasons after fertilization in 2009. A marginally significant (p<0.10) fertilization effect was found for latewood basal area increment only in the first growing season after treatment. A significant treatment×year interaction was also found for Δ13C and iWUE in earlywood and latewood. Fertilization significantly reduced earlywood Δ13C and increased earlywood iWUE in the first and second growing seasons after fertilization. Only a marginally significant fertilization effect was detected for latewood Δ13C and iWUE in the second growing season after treatment. Previous studies of N fertilization of Douglas-fir forests have reported consistently increased growth and iWUE on low productivity sites treated with relatively high fertilization rates. This study suggested that these responses can also be observed on highly productive sites despite their lower frequency and apparently shorter duration. Other key mechanisms driving growth responses appear less important than iWUE, including an increase in LAI and shift from belowground to aboveground carbon allocation.
1. From the phytocentric perspective, a mycorrhizal network (MN) is formed when the roots of two or more plants are colonized by the same fungal genet. MNs can be modelled as interaction networks ...with plants as nodes and fungal genets as links. The potential effects of MNs on facilitation or competition between plants are increasingly recognized, but their network topologies remain largely unknown. This information is needed to understand the ecological significance of MN functional traits. 2. The objectives of this study were to describe the interaction network topologies of MNs formed between two ectomycorrhizal fungal species, Rhizopogon vesiculosus and R. vinicolor, and interior Douglas-fir trees at the forest stand scale, identify factors leading to this structure and to contrast MN structures between forest plots with xeric versus mesic soil moisture regimes. 3. Tuberculate mycorrhizas were sampled in six 10 × 10 m plots with either xeric or mesic soil moisture regimes. Microsatellite DNA markers were used to identify tree and fungal genotypes isolated from mycorrhizas and for comparison with reference tree boles above-ground. 4. In all six plots, trees and fungal genets were highly interconnected. Size asymmetries between different tree cohorts led to non-random MN topologies, while differences in size and connectivity between Rhizopogon species-specific subnetwork components contributed towards MN nestedness. Large mature trees acted as network hubs with a significantly higher node degree compared to smaller trees. MNs representing trees linked by R. vinicolor genets were mostly nested within larger, more highly connected R. vesiculosus-linked MNs. 5. Attributes of network nodes showed that hub trees were more important to MN topology on xeric than mesic sites, but the emergent structures of MNs were similar in the two soil moisture regimes. 6. Synthesis. This study suggests MNs formed between interior Douglas-fir trees and R. vesiculosus and R. vinicolor genets are resilient to the random loss of participants, and to soil water stress, but may be susceptible to the loss of large trees or fungal genets. Our results regarding the topology of MNs contribute to the understanding of forest stand dynamics and the resilience of forests to stress or disturbance.
•401 trees were sampled for tree-ring analysis, and their neighborhood was measured.•The growth sensitivity to drought was higher for larch than for the two other species.•No effect of species ...diversity on tree radial growth over the period 2000–2020.•The drought resilience of Douglas fir was increased in a more diverse neighborhood.•Competition did not always have an effect on tree growth and drought resilience.
With climate change, the frequency and duration of droughts are increasing, strongly impacting forest ecosystems. Therefore, a thorough understanding of the factors influencing tree response to drought is needed. Particularly, it remains unclear how competition and species diversity influence the drought sensitivity of tree species. Thinning (i.e., lowering competition) and mixing species (i.e., increasing diversity) are two common forest management practices that are thought to help forests to cope with droughts. However, their actual effects are still controversial. We sampled and measured tree-ring widths of 401 conifer trees with a wide range of competition and species diversity in their neighborhood across a bioclimatic gradient in Switzerland. Based on mixed-effects models and correlations, we examined the climate sensitivity of silver fir, European larch and Douglas fir and analyzed how competition and species diversity affect their radial growth and drought sensitivity. Silver fir was the least sensitive species to temperature, precipitation, and climatic water balance. When we analyzed the combined effects of the climatic water balance, competition and species diversity on tree radial growth over the past 20 years, we found that competition usually had a negative effect on radial growth of the three species, while species diversity had no effect. However, when focusing on drought resilience, competition had a negative effect for silver fir only, and a more mixed neighborhood enhanced the drought resilience of Douglas fir. Larch showed a higher drought sensitivity than silver fir and Douglas fir. At most sites, radial growth of all species recovered within two years after the severe droughts of 2003 and 2018. Overall, our results suggest that competition and species diversity have minor effects on the drought resilience of silver fir, larch and Douglas fir in Switzerland.
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Severe drought events negatively affect tree growth and often cause legacy effects, expressed by smaller tree rings in the post-drought recovery years. While the pattern of reduced tree-ring widths ...is frequently described the processes underlying such legacy effects, i.e., whether it is due to shorter growth periods or lower growth rates, remains unclear and is investigated in this study. To elucidate these post-drought effects, we examined radial stem growth dynamics monitored with precision band-dendrometers on 144 Douglas fir, Norway spruce and silver fir sample trees distributed along four elevational gradients in the Black Forest (Southwest Germany) during the post-drought years 2019 and 2020. Growth onset of all investigated species occurred between 11 and 24 days significantly earlier in 2020 compared to 2019. Modelling growth onset based on chilling and forcing units and taking the study year into account explained 88–98 % of the variance in the growth onset data. The highly significant effect of the study year (p < 0.001) led to the conclusion, that other factors than the prevailing site conditions (chilling and forcing units) must have triggered the earlier growth onset in 2020. On the other hand, for Douglas fir growth rates were significantly higher in 2020 compared to 2019 (2.9 μm d−1) and marginally significantly higher for silver fir (1.3 μm d−1), underlining the explanatory power of growth rate on recovery processes in general and suggesting that Douglas fir copes better with droughts, as it recovered faster. Growth dynamics at the beginning of the year showed limited growth for earlier growth onsets, which, however, could not explain the difference between the investigated years. Our results provide evidence that legacy effects of drought events are expressed by a delayed growth onset and a reduced growth rate in the post-drought year and that Douglas fir has a superior recovery potential.
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•Earlier growth onsets caused lower growth rates at the start of the growing season.•Legacy-effects are characterised by later growth onsets and reduced growth rates.•The closer the drought year, the more intense was the legacy effect.•Douglas fir showed superior recovery performance after drought compared to others.
•We examined California black oak response following a 12 year reburn.•Black oaks are resilient to repeated high-severity wildfire.•Oaks gained in relative canopy dominance over conifers at higher ...reburn severities.•Oak regeneration resulting from first fire was topkilled at low reburn severities.•Mature oak woodlands are unlikely to develop in frequent high-severity fire regimes.
Oak woodlands are dependent on frequent fire to maintain the low stem density and diverse understories that typify these ecosystems. Without this recurrent disturbance, fire-sensitive conifer competitors encroach on oaks, reducing their vigor, and diminishing habitat quality. In fire-excluded oak woodlands, stand-replacing wildfire can trigger shifts in canopy dominance from seed-generated conifers to oaks, which are capable of vigorous sprouting following topkill. We examined the occurrence and sprouting dynamics of California black oak (Quercus kelloggii Newb.) following repeated wildfires in the Lassen National Forest, California. We found that following reburn, changes in oak relative stand dominance, as well as oak sprout basal area and height, were each positively related to fire severity (P < 0.0001 for each analysis). While conifer regeneration suffered complete mortality at moderate and high reburn severities, 97% of topkilled oaks resprouted from surviving rootstocks, reinforcing oak dominance. Black oak resprouts that originated following topkill in the first wildfire were frequently topkilled in the second fire, including at lower burn severities survived by advance conifer regeneration. The results of this study indicate that while as individuals, black oaks are resilient to recurring wildfire, restoration of historic woodland structure and function is an unlikely outcome of these repeated disturbances. Management of post-wildfire regenerating oak stands in this region will require supplemental fuel reduction treatments, including prescribed burning.
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