Questions: How do canopy–understorey interactions respond to variation in disturbance severity over extended periods of time? For forests with different disturbance histories, do light availability ...and understorey cohort densities converge towards a common old-growth structure, or do historical legacies influence populations indefinitely? Locations: Remnants of primary spruce (Picea abies (L.) Karst.) forests throughout Germany, Slovakia, Ukraine and Romania. Methods: A disturbance history of >200 yr was reconstructed from 11 278 tree cores collected from forest plots (n = 520). Understorey tree densities of two size classes and hemispherical photo-based light availabilities were inventoried and modelled as functions of the severity of the main disturbance and time since the event. Results: Variation in understorey tree densities had a hump-shaped distribution through time. Stem densities were approximately static in the least disturbed sites, and declined in relation to disturbance severity over approx. 100 yr. Similar to patterns of stem densities, initially high understorey light availability also reached a minimum at 100 yr, which indicated crown closure. Following this, light availability and stem densities both increased as stands transitioned from stem exclusion to understorey re-initiation. The effect of disturbance severity on understorey densities and patchiness in light availability persisted for >200 yr. Conclusions: Long-term trends in canopy–understorey interactions validate current conceptual models of forest development. Furthermore, we empirically validate that these conceptual models generalized over gradients in disturbance severity. Higher disturbance sites exhibited a more even-aged character with more pronounced periods of stem exclusion, canopy closure and understorey re-initiation; forests with low-severity disturbance histories yielded a more stationary uneven-aged structure. The model identified the extent of variation in disturbance severity within which these P. abies forests are able to regenerate and retain their monospecific character, which is increasingly relevant as disturbance regimes continue to shift under global climate change.
Abstract
Questions
How have the historical frequency and severity of natural disturbances in primary
P
icea abies
forests varied at the forest stand and landscape level during recent centuries? Is ...there a relationship between physiographic attributes and historical patterns of disturbance severity in this system?
Location
Primary
P
. abies
forests of the
E
astern
C
arpathian
M
ountains,
R
omania; a region thought to hold the largest concentration of primary
P
. abies
forests in
E
urope's temperate zone.
Methods
We used dendrochronological methods applied to many plots over a large area (132 plots representing six stands in two landscapes), thereby providing information at both stand and landscape levels. Evidence of past canopy disturbance was derived from two patterns of radial growth: (1) abrupt, sustained increases in growth (releases) and (2) rapid early growth rates (gap recruitment). These methods were augmented with non‐metric multidimensional scaling to facilitate the interpretation of factors influencing past disturbance.
Results
Of the two growth pattern criteria used to assess past disturbance, gap recruitment was the most common, representing 80% of disturbance evidence overall. Disturbance severities varied over the landscape, including stand‐replacing events, as well as low‐ and intermediate‐severity disturbances. More than half of the study plots experienced extreme‐severity disturbances at the plot level, although they were not always synchronized across stands and landscapes. Plots indicating high‐severity disturbances were often spatially clustered (indicating disturbances up to 20 ha), while this tendency was less clear for low‐ and moderate‐severity disturbances. Physiographic attributes such as altitude and land form were only weakly correlated with disturbance severity. Historical documents suggest windstorms as the primary disturbance agent, while the role of bark beetles (
I
ps typographus
) remains unclear.
Conclusions
The historical disturbance regime revealed in this multi‐scale study is characterized by considerable spatial and temporal heterogeneity, which could be seen among plots within stands, among stands within landscapes and between the two landscapes. When the disturbance regime was evaluated at these larger scales, the entire range of disturbance severity was revealed within this landscape.
Natural disturbances change forest habitat quality for many species. As the extent and intensity of natural disturbances may increase under climate change, it is unclear how this increase can affect ...habitat quality on different spatial scales. To support management tools and policies aiming to prevent habitat loss, we studied how habitat quality develops in the long run depending on the disturbance severity using a space‐for‐time substitution approach.
We explored the effects of time since disturbance (0–250 years) and disturbance severity (20%–100% canopy removal) on structure‐based habitat quality indicators in European primary Norway spruce Picea abies forests using 1000 m2 circular plots in hierarchical design (a total of 407 plots in 35 stands). Disturbance history was reconstructed from tree cores. Habitat quality indicators were modelled as a function of the severity of the most severe disturbance and the time since this disturbance. We hypothesised that high within‐stand habitat heterogeneity is formed by different successional stages after disturbances of various intensities.
The results showed a U‐shaped response of habitat quality to post‐disturbance habitat succession on the plot scale. The decline deepened with disturbance severity. The U‐shape response occurred in: large tree occurrence, amount of standing and lying deadwood, diversity of understory and understory openness. The spatial diversity in disturbance parameters increased spatial diversity of habitat quality on a stand level as expected. This high within‐stand habitat heterogeneity also decreased with increasing age of the most recent disturbance. This suggests that the absence of young successional stages results in the absence of some important elements for biodiversity, for example sun‐exposed snags.
Synthesis and applications. Our results demonstrate that currently intensifying natural disturbance regime can consequently result in a lower habitat heterogeneity. In managed spruce forests after natural disturbances, we recommend at least the partial retention of biological legacies to preserve habitat heterogeneity and to avoid uniform and dense plantations resulting in a greater homogenisation. To emulate the natural disturbances pattern, spruce forests should be managed with a wide range of harvested patches of the size limited by a local natural disturbance regime creating spatial heterogeneity.
Abstraktní
Přírodní disturbance mění kvalitu habitatů lesa. Vzhledem k tomu, že rozsah a intenzita přírodních narušení se výrazně zvyšují v důsledku změn klimatu, není jasné, jak tím bude ovlivněna kvalita stanovišť na různých prostorových měřítcích. Abychom podpořili lesnické hospodaření zaměřené na zachování biodiverzity, zjišťovali jsme, jak se kvalita habitatů lesa dlouhodobě vyvíjí v závislosti na severitě disturbance.
Zkoumali jsme vliv doby od disturbance (0–250 let) a její severity (20–100% odstranění zápoje) na kvalitu habitatů v evropských primárních smrkových lesích (Picea abies) pomocí kruhových ploch (1000 m2), umístěných v hierarchickém designu (celkem 407 ploch v 35 porostech). Historie disturbancí byla rekonstruována pomocí letokruhových vývrtů. Indikátory kvality habitatů byly modelovány jako funkce severity nejzávažnějšího narušení a doby od tohoto narušení. Předpokládali jsme, že vysoká heterogenita v rámci porostu je tvořena různými sukcesními stádii po disturbancích různé intenzity.
Výsledky ukázaly odezvu kvality stanoviště po narušení ve tvaru písmene „U“. Dočasný pokles kvality stanoviště se prohluboval s rostoucí severitou disturbance. Průběh ve tvaru „U “se vyskytl u následujících faktorů: výskyt tlustých stromů, množství stojícího a ležícího mrtvého dřeva, rozmanitost podrostu a světla v podrostu. Prostorová diverzita v parametrech disturbancí podle očekávání zvýšila prostorovou diverzitu kvality habitatů na úrovni porostu. Tato vysoká heterogenita habitatů v rámci porostu se také snižovala s rostoucím dobou od poslední disturbance. To naznačuje, že absence raných vývojových stádií má za následek nedostatek některých důležitých prvků pro biodiverzitu, jakými jsou např. osluněné stojící mrtvé stromy.
Syntéza a aplikace. Výsledky ukazují, že současný zintenzivňující se režim disturbancí může vést k nižší heterogenitě stanovišť. Ve smrkových hospodářských porostech po přírodních disturbancích proto doporučujeme alespoň částečné zachování biologického dědictví pro podporu heterogenity stanoviště. Doporučujeme také omezení uniformních a hustých výsadeb, vedoucích k ještě větší homogenizaci lesního prostředí. Aby se napodobil prostorový vzor přírodních disturbancí, měly bychom využívat širokou škálou velikostí obnovovaných ploch, s maximální velikostí danou lokálním přirozeným režimem disturbancí.
Our results demonstrate that currently intensifying natural disturbance regime can consequently result in a lower habitat heterogeneity. In managed spruce forests after natural disturbances, we recommend at least the partial retention of biological legacies to preserve habitat heterogeneity and to avoid uniform and dense plantations resulting in a greater homogenisation. To emulate the natural disturbances pattern, spruce forests should be managed with a wide range of harvested patches of the size limited by a local natural disturbance regime creating spatial heterogeneity.
Structure and origin of mountain Norway spruce in the Bohemian Forest Cada, V., Ceska Zemedelska Univ., Prague (Czech Republic). Katedra Pestovani Lesu; Svoboda, M., Ceska Zemedelska Univ., Prague (Czech Republic). Katedra Pestovani Lesu
Journal of forest science (Praha),
(Dec 2011), Letnik:
57, Številka:
12
Journal Article
Recenzirano
Odprti dostop
This paper compares the present break-up of mountain spruce stands in the Bohemian Forest (in the Sumava Protected Landscape Area, Czech Republic) with conditions during their initiation using ...dendrochronological techniques. On three selected localities we established two study plots within relatively old stands of unknown origin. Stands were recently broken up by a windstorm. The present situation was described by diameter and decay class distribution. To describe the situation at the stand initiation, we cored at least 40 stems on each plot to get the age structure and growth series of trees. Disturbances were marked by discovering synchronous releases on tree-ring series. Main population waves were initiated in association with severe disturbances during a relatively short period, leading to the establishment of relatively even-aged, homogeneously looking stands. The disturbances were synchronized between plots and accounted for by historically known windstorms or bark beetle outbreaks; notwithstanding, logging as a disturbance factor is also particularly possible.
The future performance of the widely abundant European beech (Fagus sylvatica L.) across its ecological amplitude is uncertain. Although beech is considered drought-sensitive and thus negatively ...affected by drought events, scientific evidence indicating increasing drought vulnerability under climate change on a cross-regional scale remains elusive. While evaluating changes in climate sensitivity of secondary growth offers a promising avenue, studies from productive, closed-canopy forests suffer from knowledge gaps, especially regarding the natural variability of climate sensitivity and how it relates to radial growth as an indicator of tree vitality. Since beech is sensitive to drought, we in this study use a drought index as a climate variable to account for the combined effects of temperature and water availability and explore how the drought sensitivity of secondary growth varies temporally in dependence on growth variability, growth trends, and climatic water availability across the species' ecological amplitude.
Our results show that drought sensitivity is highly variable and non-stationary, though consistently higher at dry sites compared to moist sites. Increasing drought sensitivity can largely be explained by increasing climatic aridity, especially as it is exacerbated by climate change and trees' rank progression within forest communities, as (co-)dominant trees are more sensitive to extra-canopy climatic conditions than trees embedded in understories. However, during the driest periods of the 20th century, growth showed clear signs of being decoupled from climate. This may indicate fundamental changes in system behavior and be early-warning signals of decreasing drought tolerance. The multiple significant interaction terms in our model elucidate the complexity of European beech's drought sensitivity, which needs to be taken into consideration when assessing this species' response to climate change.
Growth variability, growth trends, and climatic water availability interact and significantly influence climate-growth relationships of growth in European beech. Display omitted
•Linear mixed-effects model used to derive individual and interactive effects.•Growth variability and trends are more influential during wet conditions.•Growth variables are decoupled and replaced by climate during dry conditions.•Climate sensitivity decouples at driest conditions, indicating early-warning signal.
Restoring the structural characteristics of secondary old-growth forests that were previously managed is increasingly debated to help increase the area of more complex forests which provide a broader ...array of forest services and functions. The paucity of long-term data sets in Central Europe has limited our ability to understand the ongoing ecological processes required for effective restoration programs for old-growth forests. To address this, we used repeated census data from eight permanent plots to evaluate forest structural dynamics over a 12-year period in the largest complex of European beech (Fagus sylvatica L.) forests in the Czech Highlands without intensive forestry intervention for almost 50 years. Our results showed that previously managed forests can exhibit structural qualities typically associated with old-growth forests after management has ceased for a period. The stand structural characteristics (e.g., density of large and old trees) is comparable with protected reserves of old-growth European beech-dominated forests. The average stand age was 196 years, but the oldest tree was 289 years old. The annual mortality rate was 0.43% for all species, and the U-shaped distribution indicating size-dependent mortality is likely an important process that is balanced by the turnover of new tree recruitment. During the study period, we detected that the diameter distribution tended towards a rotated sigmoid distribution. The lasting effects of the most recent forest management are evident in the scarcity of dead wood, and a prolonged process of dead wood accumulation has begun. Thus, the abandonment of all management activities in near-natural forest reserves, including dead wood removal, will ensure that the forests will develop characteristics typical of old-growth forests.
Background Severe canopy-removing disturbances are native to many temperate forests and radically alter stand structure, but biotic legacies (surviving elements or patterns) can lend continuity to ...ecosystem function after such events. Poorly understood is the degree to which the structural complexity of an old-growth forest carries over to the next stand. We asked how pre-disturbance spatial pattern acts as a legacy to influence post-disturbance stand structure, and how this legacy influences the structural diversity within the early-seral stand. Methods Two stem-mapped one-hectare forest plots in the Czech Republic experienced a severe bark beetle outbreak, thus providing before-and-after data on spatial patterns in live and dead trees, crown projections, down logs, and herb cover. Results Post-disturbance stands were dominated by an advanced regeneration layer present before the disturbance. Both major species, Norway spruce (Picea abies) and rowan (Sorbus aucuparia), were strongly self-aggregated and also clustered to former canopy trees, pre-disturbance snags, stumps and logs, suggesting positive overstory to understory neighbourhood effects. Thus, although the disturbance dramatically reduced the stand's height profile with ~100% mortality of the canopy layer, the spatial structure of post-disturbance stands still closely reflected the pre-disturbance structure. The former upper tree layer influenced advanced regeneration through microsite and light limitation. Under formerly dense canopies, regeneration density was high but relatively homogeneous in height; while in former small gaps with greater herb cover, regeneration density was lower but with greater heterogeneity in heights. Conclusion These findings suggest that pre-disturbance spatial patterns of forests can persist through severe canopy-removing disturbance, and determine the spatial structure of the succeeding stand. Such patterns constitute a subtle but key legacy effect, promoting structural complexity in early-seral forests as well as variable successional pathways and rates. This influence suggests a continuity in spatial ecosystem structure that may well persist through multiple forest generations.
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