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1.
Compared to lowland trees and forests, evidence on water relations at mountainous and sub-alpine sites with their climatic and topographic peculiarities is scarce. On such limited grounds, the outcome of three pilot studies is reviewed, intended to launch working hypotheses for initiating integrative research across the altitudinal gradient of the European Alps. Highlighted are tree transpiration and structural differentiation as well as stand water balance of mono-specific and/or mixed forests with Picea abies, Pinus cembra, Larix decidua and Fagus sylvatica at sub-alpine (timberline ecotone), mountainous and colline elevation. Given the preliminary evidence, tree-allometric structures of relevancy for water transport appeared to be independent of elevation and forest type, although timberline trees under open-canopy conditions did not buffer transpiration by internal water storage and had enhanced foliage/sapwood area ratios. Transpiration appeared to depend on site conditions rather than site-dependent adaptation. Canopy transpiration approached 20% of the high seasonal precipitation at the mountainous site, with about 60% being ascribed to run-off, whereas the water budget of the colline site was balanced during summer. The water balance of the subalpine site resembled, at lower precipitation, that of the mountainous site. The derived hypotheses focus on mixed-stand transpiration under altitude-specific topography and moisture regimes, hydraulic adaptation and water demand versus uptake capacity, as this latter ratio is crucial at high altitude in view of expected warming. The clarification of consistencies relative to contrasts indicated by the pilot studies will be challenging across altitudes in view of tree species, forest types and topography.  相似文献   

2.
There is increasing pressure to manage forests for multiple objectives, including ecosystem services and biodiversity, alongside timber production. However, few forests are currently co-managed for timber and wildlife, despite potential economic and conservation benefits. We present empirical data from a commercial Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) production system in southern Norway in which moose (Alces alces) are an important secondary product. Combining long-term hunting and forestry records, we identified temporal variation in clear-felling over the past five decades, peaking in the 1970s. Herbicide treatment of regenerating stands and a fivefold increase in moose harvest has lead to a reduction in availability of successional forest per moose of >90 % since the 1960s. Field estimates showed that spraying with the herbicide glyphosate reduced forage availability by 60 and 96 % in summer and winter, respectively, 4 years after treatment. It also reduced moose use and habitat selection of young spruce stands compared with unsprayed stands. Together these lines of evidence suggest that forest management led to an increase in moose carrying capacity during the 1970s and a subsequent decline thereafter. This is likely to have contributed to observed reductions in moose population productivity in southern Norway and is counter to sustainable resource management. We therefore call for better integration and long-term planning between forestry and wildlife management to minimise forest damage and the development of large fluctuations in ungulate populations.  相似文献   

3.
Managed forest stands are typically younger and structurally less diverse than natural forests. Introduction of non-native tree species might increase the structural changes to managed forest stands, but detailed analyses of tree- and stand-structures of native and non-native managed forests are often lacking. Improved knowledge of non-native forest structure could help clarify their multiple values (e.g. habitat for native biodiversity, bioenergy opportunities). We studied the structural differences between the introduced, non-native Pinus contorta and the native Pinus sylvestris and Picea abies over young forest stand ages (13–34 years old) in managed forests in northern Sweden. We found that P. contorta stands had greater mean basal areas, tree heights, diameters at breast height, and surface area of living branches than the two native species in young stands. The surface area of dead attached branches was also greater in P. contorta than P. abies. Although this indicates greater habitat availability for branch-living organisms, it also contributes to the overall more shaded conditions in stands of P. contorta. Only one older 87 years old P. contorta stand was available, and future studies will tell how structural differences between P. contorta and native tree species develop over the full forestry cycle.  相似文献   

4.
This study investigated characteristics of riparian forests on managed forest land in Sweden. Forest and site characteristics were inventoried at three sites, located along a south to north gradient, in 139 transects placed perpendicular to 38 stream reaches (<10?m wide), in forests representing the age classes 0–25, 26–75 and >75 years. Starting from the stream edge, the 30?m long transects were divided into three zones: 0–5, 5–15 and 15–30?m. The stem volumes of Pinus sylvestris L., Picea abies (L.) H. Karst, Betula spp. and broadleaved trees, the basal area share of Alnus spp., the stem density, and Sphagnum spp. coverage all showed an effect of zone (p?P. sylvestris and the highest volumes of P. abies, Betula spp. and broadleaved trees as well as the highest total stem density and basal area share of Alnus spp. Some characteristics of the northernmost site tended to differ from the two sites located in south-central Sweden. Knowledge of the characteristics of riparian forests as found in this study could aid long-term forestry planning and improve precision in the preservation and development of riparian forests with certain qualities.  相似文献   

5.
Canopy transpiration (E c) of a 50-year-old Pinus canariensis Chr. Sm. Ex DC. stand at tree line in Tenerife, Canary Islands, was estimated continuously throughout a year from March 1, 2008, to February 28, 2009, by means of xylem sap flow measurements. E c varied markedly throughout the entire year generally following the seasonal trends in soil water availability and varied between 0.89 mm day?1 under the conditions of non-limiting soil water availability and close to zero under soil drought. This is because canopy conductance declined significantly with increasing evaporative demand and thus significantly reduced tree water loss, and this decrease was more pronounced during the soil drought. Total annual E c was 79.6 mm, which is significantly below the values estimated for other Mediterranean forest ecosystems and even 70 % lower than the value estimated for a P. canariensis forest at 1,650 m a.s.l. where the soil water content was higher than at the tree line site. Therefore, these results highlighted the importance of drought stress in tree line ecotone and should be taken more into account in semiarid tree lines.  相似文献   

6.
Hydrology-oriented silviculture might adapt Mediterranean forests to climatic changes, although its implementation demands a better understanding and quantification on the water fluxes. The influence of thinning intensity (high, medium, low and a control) and its effect on the mid-term (thinned plots in 1998 and 2008) on the water cycle (transpiration, soil water and interception) and growth [basal area increment (BAI)] were investigated in 55-year-old Aleppo pine trees. Thinning enhanced a lower dependence of growth on climate fluctuations. The high-intensity treatment showed significant increases in the mean annual BAI (from 4.1 to 17.3 cm2) that was maintained in the mid-term. Thinning intensity progressively increased the sap flow velocity (v s) in all cases with respect to the control. In the mid-term, an increased functionality of the inner sapwood was also observed. Mean daily tree water use ranged from 5 (control) to 18 (high intensity) l tree?1. However, when expressed on an area basis, daily transpiration ranged from 0.18 (medium) to 0.30 mm (control), meaning that in spite of the higher transpiration rates in the remaining trees, stand transpiration was reduced with thinning. Deep infiltration of water was also enhanced with thinning (about 30 % of rainfall) and did not compete with transpiration, as both presented opposite seasonal patterns. The changes in the stand water relationships after 10 years were well explained by the forest cover metric. The blue to green water ratio changed from 0.15 in the control to 0.72 in the high-intensity treatment, with the remaining treatments in the 0.34–0.48 range.  相似文献   

7.
Average population growth in the African Sudanian belt is 3 % per year. This leads to a significant increase in cultivated areas at the expense of fallows and forests. For centuries, rural populations have been practicing agroforestry dominated by Vitellaria paradoxa parklands. We wanted to know whether agroforestry can improve local rainfall recycling as well as forest. We compared transpiration and its seasonal variations between Vitellaria paradoxa, the dominant species in fallows, and Isoberlinia doka, the dominant species in dry forests in the Sudanian belt. The fallow and dry forest we studied are located in northwestern Benin, where average annual rainfall is 1200 mm. Sap flow density (SFD) was measured by transient thermal dissipation, from which tree transpiration was deduced. Transpiration of five trees per species was estimated by taking into account the radial profile of SFD. The effect of the species and of the season on transpiration was tested with a generalized linear mixed model. Over the three-year study period, daily transpiration of the agroforestry trees, V. paradoxa (diameters 8–38 cm) ranged between 4.4 and 26.8 L day?1 while that of the forest trees, I. doka, (diameters 20–38 cm) ranged from 9.8 to 92.6 L day?1. Daily transpiration of V. paradoxa was significantly lower (15 %) in the dry season than in the rainy season, whereas daily transpiration by I. doka was significantly higher (13 %) in the dry season than in the rainy season. Our results indicate that the woody cover of agroforestry systems is less efficient in recycling local rainfall than forest cover, not only due to lower tree density but also to species composition.  相似文献   

8.
Cacao trees under different shade tree shelter: effects on water use   总被引：1，自引：1，他引：0  
We asked how shade tree admixture affects cacao water use in agroforests. In Central Sulawesi, Indonesia, cacao and shade tree sap flux was monitored in a monoculture, in a stand with admixed Gliricidia trees and in a mixture with a multi-species tree assemblage, with both mixtures having similar canopy openness. A Jarvis type sap flux model suggested a distinct difference in sap flux response to changes in vapor pressure deficit and radiation among cacao trees in the individual cultivation systems. We argue that differences originate from stomatal control of transpiration in the monoculture and altered radiation conditions and a different degree of uncoupling of the VPD from the bulk atmosphere inside shaded stands. Probably due to high sap flux variability among trees, these differences however did not result in significantly altered average daily cacao water use rates which were 16 L day?1 in the multi-species assemblage and 22 L day?1 in the other plots. In shaded stands, water use of single cacao trees increased with decreasing canopy gap fraction in the overstory since shading enhanced vegetative growth of cacao fostering transpiration per unit ground area. Estimated transpiration rates of the cacao tree layer were further controlled by stem density and amounted to 1.2 mm day?1 in the monoculture, 2.2 mm day?1 for cacao in the cacao/Gliricidia stand, and 1.1 mm day?1 in the cacao/multi-species stand. The additional transpiration by the shade trees is estimated at 0.5 mm day?1 for the Gliricidia and 1 mm day?1 for the mixed-species cultivation system.  相似文献   

9.
Interception loss is related to the nature of the rain. Thespatial variability of rainfall on the forest floor and thevariability between stemflow of trees are examined in an attemptto discover their relationships. Comparison between rainfallon the forest floor and stemflow with rainfall over the canopyshows that leaf fall produces very little effect on interceptionloss in the deciduous species. Relative to precipitation outsidethe forest, there is concentration of rainfall on certain partsof the forest floor. This is most evident in beech (Fagus sylvatica);spruce (Picea abies) concentrates water to a lesser extent,and in larch (Larix decidua) a negligible area of the floorreceives more than gross rainfall. The implications of thiscomparison with respect to water conservation are discussed.  相似文献   

10.

? Key message

Natural regeneration of P. abies (L.) H. Karst. may reach high densities in lower mountain elevations. The highest densities were found in sites with moderate light availability, with low pH, and not near the riverbank. However, age-height classes differed in the predicted magnitude of response, but were consistent in response directions. Mosses and understory species typical of coniferous forests were positively correlated with regeneration density.

? Context

Norway spruce Picea abies (L.) H. Karst. in Central Europe is at risk under climate change scenarios, particularly in mountain regions. Little is known about the impact of environmental factors on the natural regeneration of P. abies in low-elevation mountain forests.

? Aims

We aimed to assess impacts of distance from the riverbank, soil pH, and light availability on natural P. abies regeneration. We hypothesized that (1) natural P. abies regeneration would depend on light availability and soil pH and (2) there are understory plant species which may indicate the microsites suitable for natural regeneration of P. abies.

? Methods

The study was conducted in the Sto?owe Mountains National Park (SW Poland, 600–800 m a.s.l.). We established 160 study plots (25 m2) for natural regeneration, light availability, soil pH, and understory vegetation assessment.

? Results

The highest densities of natural regeneration of P. abies were observed in sites with moderate light availability (0.1–0.2 of open sky) and low pH (3.5–4.5), and located relatively far from the riverbank. Cover of 22 understory plant species were correlated with natural P. abies regeneration densities, mostly positively.

? Conclusion

Different stages of natural regeneration of P. abies revealed different regeneration niches. Most understory plant species (bryophytes and herbs typical of coniferous forests) do not compete with natural regeneration of P. abies.
  相似文献   

11.
Chronic decline and Sudden death are two syndromes of cork oak (Quercus suber) dieback. Mortality is associated with water stress, but underlying physiological mechanisms are poorly understood. Here, we investigated the physiological performance of declining trees during the summer drought. Leaf water potential, gas-exchange, fluorescence of photosystem II and leaf and root starch concentration were compared in healthy (asymptomatic) and declining trees. Low annual cork increment in declining trees indicated tree decline for several years. All trees showed similar water status in spring. In summer, declining trees showed lower predawn leaf water potential (?2.0 vs. ?0.8 MPa), but unexpectedly higher midday leaf water potential than healthy trees (?2.8 vs. ?3.3 MPa). The higher midday water potential was linked to by means of strongly reduced stomatal conductance and, consequently, transpiration. This study is pioneer showing that declining trees had high midday water potential. A tendency for lower sap flow driving force (the difference between predawn and midday water potential) in declining trees was also associated with reduced photosynthesis, suggesting that chronic dieback may be associated with low carbon uptake. However, starch in roots and leaves was very low and not correlated to the health status of trees. Declining trees showed lower water-use efficiency and non-photochemical quenching in summer, indicating less resistance to drought. Contrarily to chronic decline, one tree that underwent sudden death presented predawn leaf water potential below the cavitation threshold.  相似文献   

12.
A field experiment was established in two Picea abies (L.) Karst. plantations in southern Sweden to study yield and effects of competition on growth in beeted stands. Beeting was carried out in gaps where originally planted seedlings had been removed. Tree species used for beeting were P. abies, Pinus sylvestris L., Pinus contorta Dougl. and Larix decidua Mill × L. leptolepis Gord. The plantations were beeted when mean heights were 95 cm (Ullasjo) and 40 cm (Knäred). Effects of competition on diameter growth of P. abies were found when originally planted stands were 2.5 and 3.5 m in height. On both sites, diameter growth in stump height was significantly lower for seedlings beeted in small gaps (approx. 20 m2) than for seedlings beeted in the middle of large gaps (approx. 155 m2). This difference was larger at Ullasjo than at Knared. About 50 % of the P. sylvestris 70 % of the P. contorta and 80% of the L. decidua x L. leptolepis were dead or severely damaged six years after beeting. The main causes of damage were fraying and browsing by moose and roe‐deer.  相似文献   

13.
Physiological reactions of 25-year-old Norway spruce (Picea abies (L.) Karst.) trees to drought were examined during 2009 vegetation period. During the second half of summer, the decrease in soil water content was observed and irrigation was applied to a group of spruce trees, while the second group was treated under natural soil drought. The response to water deficit was recorded at the level of leaf water potential (ΨL). However, it appears that ΨL plays minor role in early stomata regulation of Norway spruce as CO2 assimilation rate (P N) and stomatal conductance (g S) were reduced already before water potential decrease. Leaf water potential decreased significantly only in case when soil water content was low in the long run and when transpiration losses were simultaneously relatively high. Almost complete stomatal closure even of the irrigated trees was caused by the increase in the vapour pressure deficit of the air (D) above the value of approximately 1.5?kPa. Low values of D were accompanied by partial stomata opening of drought-treated trees. In non-irrigated spruce trees, the values of P N decreased by 35–55% in comparison with irrigated trees. No drought-induced significant changes were found either in chlorophyll and carotenoid concentration (chl a?+?b, car) or in maximal photochemical efficiency of photosystem II (F v/F m). High rates of sap flow (F) did not always lead to stomatal closure during midday. It?appears that high transpiration rates do not control stomatal response to D.  相似文献   

14.
Previous studies have demonstrated a clear relationship between diameter at breast height (DBH) and tree transpiration (Q T) in multi-specific broadleaved forests. However, these studies were conducted with a limited range of tree sizes and species, and thus many multi-specific broadleaved forests fall outside these conditions. Therefore, this study examined the relationship between DBH and Q T in a warm-temperate multi-specific broadleaved forest (n = 12 species) with a wide range of tree sizes (5.0–70.0 cm DBH) using the Granier-type heat dissipation method. The results showed that, although sap flow density varied between individual trees and species, there was a significant relationship between log Q T and log DBH (r 2 = 0.66, P < 0.001) because of the strong dependence of sapwood area on DBH. This study confirmed the applicability of the relationship for the stand transpiration (E C) estimates even in a multi-specific broadleaved forest with a wide variation in DBH. Our results also revealed that selecting the sample trees in descending order of DBH effectively reduced potential errors in E C estimates for a specific sample size, as larger trees contribute more to E C. This information should be useful for future studies investigating the transpiration of multi-specific broadleaved forests, reducing errors during the scaling-up procedure.  相似文献   

15.
The assessment of forest transpiration rates is crucial for determining plant-available soil water consumption and drought risk of trees. Xylem sap flux measurements have been used increasingly to quantify stand transpiration in forest ecosystems. Here, we compare this empirical approach with hydrological modeling on the basis of a stand transpiration dataset of adult beech (Fagus sylvatica), which was acquired across Bavaria, Germany, at eight forest sites. Xylem sap flux sensors were installed in five dominant trees each. Two tree to stand upscaling approaches, related to site-specific (1) sapwood area or (2) to leaf area index, were compared. The outcome was examined each in relation to process-based stand hydrological modeling, using LWF-BROOK90. Distinct relationships between tree diameter at breast height (1.30 m) and sapwood area-weighted sap flux along the radial profile became apparent across the study sites, confirming a generic allometric basis for stand-level upscaling of transpiration. The two upscaling approaches did not differ in outcome, representatively covering stand structure for comparison with modeling. Differential analysis yielded high agreement between the empirical and modeling approaches throughout most of the study period, although LWF-BROOK90 tended to overestimate sap flux measurements under low soil moisture. The two empirical approaches proved reliable for even-aged beech stands, as performance under high stand-structural heterogeneity awaits clarification. Findings advance stand-level hydrological modeling regarding coverage of stomatal behavior during temporary limitation in water availability.  相似文献   

16.
Dendroclimatological studies in a dry inner Alpine environment (750 m a.s.l.) revealed different growth response of co-occurring coniferous species to climate, which is assumed to be caused by a temporal shift in wood formation among species. The main focus of this study therefore was to monitor intra-annual dynamics of radial increment growth of mature deciduous and evergreen coniferous species (Pinus sylvestris, Larix decidua and Picea abies) during two consecutive years with contrasting climatic conditions. Radial stem growth was continuously followed by band dendrometers and modelled using Gompertz functions to determine time of maximum growth. Histological analyses of tree ring formation allowed determination of temporal dynamics of cambial activity and xylem cell development. Daily fluctuations in stem radius and radial stem increments were extracted from dendrometer traces, and correlations with environmental variables were performed. While a shift in temporal dynamics of radial growth onset and cessation was detected among co-occurring species, intra-annual radial growth peaked synchronously in late May 2011 and early June 2012. Moist atmospheric conditions, i.e. high relative air humidity, low vapour pressure deficit and low air temperature during the main growing period, favoured radial stem increment of all species. Soil water content and soil temperature were not significantly related to radial growth. Although a temporal shift in onset and cessation of wood formation was detected among species, synchronous culmination of radial growth indicates homogenous exogenous and/or endogenous control. The close coupling of radial growth to atmospheric conditions points to the importance of stem water status for intra-annual growth of drought-prone conifers.  相似文献   

17.
Increased climatic variability, including extended periods of drought stress, may compromise on the health of forest ecosystems. The effects of defoliating pests on plantations may also impact on forest productivity. Interactions between climate signals and pest activity are poorly understood. In this study, we examined the combined effects of reduced water availability and defoliation on maximum photosynthetic rate (A(sat)), stomatal conductance (g(s)), plant water status and growth of Eucalyptus globulus Labill. Field-grown plants were subjected to two water-availability regimes, rain-fed (W-) and irrigated (W+). In the summer of the second year of growth, leaves from 75% of crown length removed from trees in both watering treatments and physiological responses within the canopies were examined. We hypothesized that defoliation would result in improved plant water status providing a mechanistic insight into leaf- and canopy-scale gas-exchange responses. Defoliated trees in the W+ treatment exhibited higher A(sat) and g(s) compared with non-defoliated trees, but these responses were not observed in the W- treatment. In contrast, at the whole-plant scale, maximum rates of transpiration (E(max)) and canopy conductance (G(Cmax)) and soil-to-leaf hydraulic conductance (K(P)) increased in both treatments following defoliation. As a result, plant water status was unaffected by defoliation and trees in the defoliated treatments exhibited homeostasis in this respect. Whole-plant soil-to-leaf hydraulic conductance was strongly correlated with leaf scale g(s) and A(sat) following the defoliation, providing a mechanistic insight into compensatory up-regulation of photosynthesis. Above-ground height and diameter growth were unaffected by defoliation in both water availability treatments, suggesting that plants use a range of responses to compensate for the impacts of defoliation.  相似文献   

18.
We investigated the influence of climate on the ring width and xylem anatomy of two co-occurring pines (Pinus nigra Arn. and P. sylvestris L.) in the mountains of east-central Spain in order to test their utility for dendroclimatic reconstructions. We developed chronologies of ring width, mean lumen diameter and mean cell-wall thickness (in the earlywood, latewood, and the total annual ring) and the number of cells between 1960 and 2006. Drought, expressed as the standardized precipitation-evapotranspiration index (SPEI), was the main climatic driver of tree radial growth, although trees were also sensitive to temperature (negative effect in previous autumn and current summer) and precipitation (with a general positive effect). P. sylvestris response was stronger to climate of the current year, whereas the effect of previous-year climate was more important for P. nigra. Warm and dry summers reduced ring width, tracheid lumen, and wall thickness in both species, whereas warm winter-spring temperatures had the opposite effect, primarily for P. sylvestris. Previous-year or early-season conditions mainly affected earlywood features, whereas latewood was more responsive to summer climate. Overall, climate appeared to be a stronger limiting factor for P. sylvestris. During periods of drought, cell-wall thickness was reduced while lumen width increased in the latewood of P. sylvestris. This could compromise its hydraulic safety against drought-induced cavitation as our site was close to the southern and dry edge of the species distribution area. Our results suggest that anatomical variables record different and stronger climate information than ring width variables, especially in P. sylvestris. Reconstruction models for SPEI at the 3-month scale were developed for July–August and September–October using principal components regression. The best models included anatomical and width variables of both pine species suggesting that tracheid chronologies can be useful for drought reconstructions especially at mesic sites or with species that encode a mixed drought and temperature-precipitation signal.  相似文献   

19.
Whole-tree water use of nine Pinus cembra trees was estimated in the treeline ecotone of the Central Austrian Alps. Sap flow density using Granier-type thermal dissipation probes and environmental parameters was monitored along an elevational gradient from the forest limit up to treeline and finally mediating the krummholz limit throughout two growing seasons. Normalized sap flow density (Q s) was significantly correlated with solar radiation (R s) and vapor pressure deficit (D) throughout the treeline ecotone. Multiple regression analysis indicated that at the forest limit and at treeline, D had a similar effect on Q s than R s. At the krummholz limit by contrast, D had a greater effect on Q s than R s due to partially stomatal closure and wind-induced clustering of the needles, which impaired their response to available irradiance. Whole-tree water use scaled to crown surface area estimated for an entire growing (172 days) declined from 449 mm at the forest limit to 274 mm at treeline and was 251 mm at the krummholz limit, which is within the values estimated for other European forest ecosystems. Nevertheless, the observation above the forest limit in the central Tyrolean Alps tree transpiration scaled to crown surface area is comparable to the water use of adjacent low-stature vegetation, which should also be taken into account when forecasting potential effects of global change on the water balance of the treeline ecotone.  相似文献   

20.
In this study, the effect of girdling on the moisture content of small-sized trees for heat energy production was clarified. The moisture content was measured for Scots pine (Pinus sylvestris), Norway spruce (Picea abies), and Downy birch (Betula pubescens) during two growing seasons after girdling. The trees were girdled at breast height for around 30 cm by removing the bark, phloem, and cambium from around the stem. At the beginning of the growing season the mean moisture content of the living Scots pine (P. sylvestris) and Norway spruce (P. abies) was 60%, and for Downy birch (B. pubescens) it was 50%. During the first growing season the effect of girdling on the moisture content was low, but during the second growing season the moisture content decreased significantly. The moisture content of the Norway spruce (P. abies) (23%) and Downy birch (B. pubescens) (33%) was at its lowest point at 14 months after girdling. There were no significant changes in the moisture content of the Scots pine (P. sylvestris) in this study. The results of this study can be used in basic research and in the development of energy wood production.  相似文献   

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