Structural changes and potential vertebrate responses following simulated partial harvesting of boreal mixedwood stands

Partial harvesting, where different numbers and arrangements of live trees are retained in forest stands, has been proposed for maintaining late-successional structure and associated vertebrate species within managed boreal forests. Using the stand dynamics model SORTIE-ND, we examined 80-year patterns of structural change in response to different intensities (30-70% basal area removal) and spatial patterns (22-273 m² mean patch size) of harvesting. We also applied habitat models for seven late-successional vertebrates to the structural conditions present after harvesting to assess potential species responses.Partial harvesting increased understory and downed woody debris (DWD) cover and decreased overstory structure for the first 25 years after harvest, in comparison to unharvested stands, with this effect subsequently reversing as harvest-induced regeneration reached the canopy. Although harvesting enhanced long-term structural development in this regard, large trees, large snags, and large DWD all remained below unharvested levels throughout the simulation period. Harvesting also produced transient increases in early-decay DWD and ground exposure. Most changes in structural attributes increased in proportion to harvest intensity, but structural differences among harvest patterns were generally small. Dispersed harvesting induced somewhat less pronounced decreases in vertical structure, and produced more post-harvest slash, than aggregated harvesting.All seven vertebrate species decreased in abundance as harvest intensity increased from 30 to 70%. In comparison to their pre-harvest abundances in old stands, vertebrates associated with DWD (redback salamander, marten, red-backed vole) showed neutral or positive responses at one or more harvest intensities, whereas those associated with large trees and snags (brown creeper, flying squirrel) consistently exhibited substantial adverse impacts.     

The influence of canopy patch mosaics on understory plant community composition in boreal mixedwood forest

We assessed the composition of understory vascular plant communities in relation to the mosaic of canopy patch types, and their associated structure and environment, within unmanaged, mature boreal mixedwood forests in western Canada. Within a 30 km² area, we sampled patches of four different canopy types: conifer-dominated, broadleaf-dominated, mixed conifer-broadleaf, and canopy gaps (total n = 98). There were significant differences in understory composition among the four patch types (based on multi-response permutation procedure (MRPP)) and these were mainly due to differences in relative abundances of understory species. The understory communities of conifer patches were characterized by low abundances of shade intolerant species while shade-tolerant and evergreen species were indicators (based on an indicator species analysis (ISA)). Understory communities under gap and broadleaf patches were characterized by higher abundances of grasses and shade intolerant species. Gap, broadleaf, and mixed patches had higher abundances of certain shrub species than did conifer patches. The patch types also differed in terms of their environmental conditions. Conifer patches had drier, cooler soils and the lowest understory light. Broadleaf patches had the warmest soils while understory light during the leaf-off period was similar to that of canopy gaps. Gap patches had the lowest litter cover and PO₄⁻ availability and the highest light. Seven environmental variables (soil moisture, soil temperature, total light during the leaf-off period, cover of coarse and fine downed woody material, and availability of NH₄⁺ and Ca²⁺) were significantly related to understory species composition (in a constrained ordination by means of a distance-based redundancy analysis (db-RDA); 16.5% of variation in understory community data explained). Even within a single patch type, there was substantial environmental variation that was related to understory species composition. Our study suggests that the mosaic of canopy patches within mixedwood forests supports coexistence of both early and late successional understory plant species in mixedwood stands. Maintaining the mixture of canopy patch types within mixedwood stands will be important for conserving the natural patterns of understory plant composition in boreal mixedwood forests.     

辽宁冰砬山不同林龄蒙古栎次生林生物量和生产力初探

森林生物量和生产力直接关系到森林生态系统的固碳能力。该文以冰砬山3个年龄阶段的蒙古栎次生林为研究对象,采用标准木收获法建立了生物量与胸径的相对生长方程,推算了各林龄的生物量、生产力及其分配规律。结果表明：幼龄林、中龄林和近熟林的乔木层生物量分别为112.09 t.hm^-2、224.92 t.hm^-2和276.18 t.hm^-2。蒙古栎林分配到其地上生物量的比例,随着林龄的增加而增大,与此同时分配到根系生物量的比例从幼龄林的36%下降到28%。蒙古栎林乔木层的年平均净生产力在中龄林达到最大12.13 t.hm^-2.a^-1,比幼龄林和近熟林分别高3.43 t.hm^-2.a^-1和1.42 t.hm^-2.a^-1。在所有不同年龄阶段,各器官的生产力占总生产力的比例平均为叶（45%）〉树干（30%）〉根（18%）〉枝（7%）。     

基于CASA模型的瓦屋山林场植被净初级生产力估算

在地理信息系统和遥感技术支持下,利用改进的CASA模型,并结合Landsat TM遥感影像、气象数据和林班数据,估算出瓦屋山林场2008—2009年的植被净初级生产力(PNPP),并通过实测植被生物量和生产力的关系,验证CASA模型在研究地区估算结果。结果表明:CASA模型估测植被PNPP与实测结果有较好的一致性,能够适用于瓦屋山林场植被净生产力估算;CASA模型估算结果主要植被类型年均PNPP区别明显,从高到低依次是:中国山杨、麻栎、板栗、马尾松、湿地松、灌木、杉木和池杉;瓦屋山林场植被PNPP季节变化显著,夏季贡献率最大,其次是春季和秋季,冬季最少,主要由于不同季节环境因素不同,其中又以太阳辐射最为重要。     

Understory plant communities of boreal mixedwood forests in western Canada: Natural patterns and response to variable-retention harvesting

We examined patterns of variation in richness, diversity, and composition of understory vascular plant communities in mixedwood boreal forests of varying composition (broadleaf, mixedwood, conifer) in Alberta, Canada, before and for 2 years following variable-retention harvesting (clearcut, 20 and 75% dispersed green tree retention, control). Broadleaf-dominated forests differed from mixedwood or conifer-dominated forests in that they had greater canopy cover, litter depth, soil nitrogen, warmer soils, as well as greater shrub cover, herb and shrub richness and diversity (plot scale). In contrast, conifer, and to a lesser extent mixedwood, forest had greater β diversity than broadleaf forest. Overall, mixedwood and conifer forests were similar to one another, both differed from broadleaf forest. Several species were found to be significant indicators of broadleaf forest but most of these also occurred in the other forest types. Understory composition was related to canopy composition and edaphic conditions. Variable-retention harvesting had little effect on understory cover, richness, or diversity but resulted in reduced richness and β diversity at a larger scale. The clearcut and 20% treatments affected composition in all forest types. Early successional species and those common in disturbed sites were indicators of harvesting while evergreen, shade-tolerant understory herbs were indicators of the control forest and 75% retention harvest. We conclude that it is important to maintain a range of variation in canopy composition of mixedwood forests in order to conserve the associated understory communities. The presence of conifers in these forests has a particularly important influence on understory communities. The threshold for a lifeboat effect of variable-retention harvesting is between 20 and 75% retention. Examination of richness and β diversity at a variety of scales can provide interesting information on effects of harvesting on spatial reorganization and homogenization of understory plant communities.     

Long-term response of planted conifers, natural regeneration, and vegetation to harvesting, scalping, and weeding on a boreal mixedwood site

This study reports 14th-year response of a boreal mixedwood stand to different harvest intensities (uncut, 50% partial cut with and without removal of residuals after 3 years, and clearcut), spot site preparation treatments (none and scalped), and chemical weeding frequencies (none, single, and multiple) in northeastern Ontario. The response variables include the survival and growth of planted white spruce (Picea glauca [Moench] Voss) and jack pine (Pinus banksiana Lamb.), height and density of natural regeneration and shrubs, and cover of shrubs and non-woody vegetation. Harvesting and weeding generally improved survival and growth of planted trees, although white spruce survival did not significantly differ among the three weeding frequencies. Harvesting tended to increase heights of hardwood (mostly trembling aspen (Populus tremuloides Michx.)) and conifer (largely balsam fir (Abies balsamea (L.) Mill.).) natural regeneration, cover and density of shrubs, and cover of herbs, lichens, and ferns. Chemical weeding reduced height, density and cover of shrubs, height and density of hardwood regeneration, and fern cover, but increased moss and lichen cover. Spot scalping did not significantly affect planted seedling, natural regeneration, or the vegetation.Maximum survival and growth of planted white spruce and jack pine were achieved using a combination of clearcutting and multiple weeding. However, partial cutting followed by a single weeding produced acceptable survival and reasonable growth of planted trees, particularly for white spruce. Partial canopy removal alone substantially reduced the amount of hardwood regeneration, relative to clearcutting, but did not adequately suppress understory shrubs. Significant improvement in seedling growth following multiple weedings was evident primarily in the complete canopy removal treatments: 50% partial cut with removal of residuals after 3 years and clearcut. While the effects of harvesting and weeding on planted crop trees found in the 5th-year assessments generally persisted at year 14, survival decreased, likely due to light competition from developing hardwood and shrubs.     

Disturbance history affects lightning fire initiation in the mixedwood boreal forest: Observations and simulations

The emulation of natural disturbances such as fire is a prominent harvest management strategy for ecosystems in Canada's boreal forest region, but the effect of harvesting on subsequent lightning fire occurrence has not been studied systematically in the mixedwood boreal forest. We quantified the relationship between annual patterns of lightning fire initiation, forest composition, lightning, and fire weather conditions over eight years (1994–2001) in a 60,000 km² region of actively harvested mixedwood boreal forest in western Canada. Our analyses illustrated that forest harvesting and burning had opposite effects on subsequent fire initiation, so harvest was not a surrogate for fire. Fire initiation increased in landscapes with more area harvested and decreased with area recently burned. Our data suggested that increased fire initiation was most pronounced in harvested stands up to a decade old, and there was some evidence that the effect might last as long as 30 years. We then used a dynamic fire-succession simulation model to quantify the long-term effects of these fuel-based relationships using two metrics. As expected, the first metric demonstrated that the number of years between disturbances was significantly less in stands that were harvested and then burned, than those that were burned and then burned again. However, the more revealing component of the simulations was an illustration that despite the strong, positive relationship between harvested areas and fire initiation, the area affected over the long-term by a reduced disturbance interval was relatively small. Accordingly, our study shows that spatiotemporal regulation of lightning fire initiation through harvesting activity results in a systematic accelerated frequency of disturbance that is novel to the mixedwood boreal system, but the area affected by these events amount to local peculiarities rather than broad-scaled regularities.     

Effects of pre- and post-harvest spray with glyphosate and partial cutting on growth and quality of aspen regeneration in a boreal mixedwood forest

In the boreal forest, conifer release treatments can leave a low quality hardwood component, which does not contribute to healthy, productive mixedwood forests. In this study, the growth and quality of trembling aspen (Populus tremuloides Michx.) regeneration were examined 5-7 years after spraying with glyphosate herbicide before and after harvesting. Results were compared to those from a partial cut and clearcut treatment without herbicide treatments. The preharvest spray treatment effectively reduced aspen density and height but did not lower regeneration quality—assessed by stem and crown deformation and stem stain—compared to the postharvest spray and clearcut treatments. Increased stem stain in the postharvest spray treatment was largely associated with the stem section that grew prior to herbicide application—post-herbicide growth was not affected. While the effect of stem stain may be restricted to growth that occurred before herbicide use, stem deformation from stem dieback may have longer term effects. In the partial cut treatments both density and stocking of aspen regeneration were lower, but aspen basal diameter growth, height growth, and quality were similar to those in the clearcut treatment. Thus, preharvest spray should promote conifer growth by reducing the density and growth of aspen regeneration without reducing the quality of aspen; this should be considered a preferred treatment to support for management objectives calling for productive and healthy mixtures of fast-growing aspen and slow-growing conifers.     

Quantifying local factors in medium-frequency trends of tree ring records: Case study in Canadian boreal forests

Growth rings of a tree are simultaneously affected by various environmental constraints, including regional factors such as climate fluctuations and also local, gap-scale dynamics such as competition and stochastic mortality of neighbor trees. Although these local effects are often discarded by dendroclimatologists as random variation, the dendroecological trends may provide valuable information on past forest dynamics. Since dendroecological trends arising from local stand dynamics often have medium-term frequencies with persistence of several years to a few decades, it is usually difficult to separate local, gap-scale forcings from regional, medium-frequency forcings such as El Niño Southern Oscillation or North Atlantic Oscillation. Moreover, conventional dendroecological practices have failed to analyze the continuously changing medium frequency trends. In this study, a continuous index of medium-frequency dendrochronological trends was developed, by generalizing previous analytical methods that evaluate relative changes using moving averages. This method was then tested against a tree ring dataset from a site with a known history of release and suppression due to a hurricane disturbance. To quantify the effects of local gap dynamics against the regional, often climatic effects, increments cores of black spruce (Picea mariana) were sampled from boreal forests in Saskatchewan, Canada, using a stratified sampling design. Assuming that regional forcings affect trees in the given stand homogeneously, the relative effect of stochastic heterogeneity within stand was quantified. The results closely agreed with conventional dendrochronological observations. In closed-canopy stands, stochastic local effects explained 12.9–35.4% of the variation in tree ring widths, because interactions between neighbor trees were likely to be intense. In open-canopy stands, on the other hand, the proportion of explained variance was 1.4–10.2%, reflecting the less-intense local tree interactions in low-density stands. These advancements in statistical analysis and study design will help ecologists and paleo-climatologists to objectively evaluate the effects of climate fluctuations, relative to the effects of local, ecological interactions. Moreover, forest managers can apply concepts of filtering medium-frequency trends to assess release and suppression caused by forest management practices, such as selective cutting and forest thinning.     

Influence of fire intensity on structure and composition of jack pine stands in the boreal forest of Quebec: Live trees,understory vegetation and dead wood dynamics

North American jack pine (Pinus banksiana Lamb.) stands are generally characterized by an even-aged structure resulting from high intensity fires (HIF). However, non-lethal fires of moderate intensity (MIF), which leave behind surviving trees, have also been reported. The objectives of this study were two-fold: (1) assess the concurrent dynamics of live trees, understory vegetation and different types of coarse woody debris (CWD) during succession after HIF; and (2) document how MIF affects stand structure component dynamics compared to HIF. Stands affected by both HIF and MIF were selected. Tree characteristics and age structure, understory biomass, and CWD volume were assessed. Our results suggest that the structural succession of jack pine stands following HIF comprises three stages: young stands (<48 years), premature and mature stands (58–100 years) and old stands (>118 years). Canopy openness and jack pine density significantly decreased with time since HIF, while black spruce density and CWD volume significantly increased. The highest structural diversity was measured in the premature and mature stands. Compared to HIF, MIF increased mean jack pine basal area, decreased average stand density, delayed the replacement of jack pine by black spruce replacement in the canopy, decreased CWD volume, and significantly increased bryophytes mass. MIF increased the diversity of live trees and generally decreased CWD structural diversity. The study confirms the diversity of natural disturbance magnitude and successional processes thereby initiated. Thereafter, it appeared to be relevant for adjustment of disturbance emulating forest-management systems.     

南京城市森林生态系统生产力与碳储量的计算

基于遥感数据Landsat TM影像与气象数据,利用温度、水分胁迫系数改进CASA模型,对南京市森林生态系统NPP与碳储量进行估算。结果表明,南京城市森林生态系统植被NPP空间分布较均匀,平均在200～1400g/(m2.a)之间;河流、市城区裸地植被NPP最小,在0～100g/(m2.a)之间;整个南京市植被NPP空间分布由北向南呈现逐渐增加趋势,由于最南部地区为自然森林区,保留了原始的自然环境状态,NPP最大。而分布在南京市的各个森林区,森林植被NPP均在1300～1426g/(m2.a)之间。利用生物量-蓄积量方程计算出南京市针叶林、阔叶林、针阔混交林碳储量分别占全市森林碳储量的24%、59%、17%。全市森林生态系统碳储量为111.73万t,平均森林植被碳密度为17.38t/hm2,郊区和县的森林植被碳储量远远高于市区,但是两者的碳密度并无很大的差异。     

Planning timber harvest of residual forest stands without compromising bird and small mammal communities in boreal landscapes

Numerous efforts have been invested in designing and configuring residual forest stands in Canadian boreal forest to preserve their overall biodiversity. Now that several landscapes have been partially logged, the next issue in forest management involves the planning of residual forest stand harvesting without compromising wildlife populations. Residual stands can be cut when adjacent regeneration reaches 3 m in height according to current regulations in several Canadian provinces (e.g., Québec, Ontario, Alberta, and British-Columbia). However, little is known on whether such regenerating habitat (RE-3m) can maintain wildlife communities similar to those found in unharvested mature forest (CO). We estimated the relative abundance of small mammals and forest birds in RE-3m and CO habitats and characterized landscape and stand structures. These variables were then compared between the two contrasting successional stages and were used to build habitat use models (HUMs) for 21 species. CO and RE-3m differed with regard to several landscape characteristics and stand structure variables as a result of logging. Snowshoe Hare, Northern Flicker, Alder Flycatcher, Ruby-crowned Kinglet, White-throated Sparrow and Magnolia Warbler were more abundant in RE-3m than CO, while Red-backed Vole, Brown Creeper and Golden-crowned Kinglet exhibited lower abundances in RE-3m. No significant differences in abundance were observed for the 12 other species. Species HUMs were highly significant and explained between 64.3 and 99.1% of the total variability in abundance. Following variance partitioning, stand structure variables accounted for most of the explained variability (54.2%) while landscape characteristics accounted for only 28.7%. No difference in species richness was observed but community evenness was greater in CO than RE-3m. Our results suggest that current regulations may threaten the maintenance of 3 out of 21 censused species for which abundances were significantly lower in regenerating 3 m tall stands. As stand structure explained a large amount of variability in abundance, it should be considered during timber harvest planning in both mature and regenerating stands. Until we know more on whether the current regulations are suitable for maintaining overall biodiversity, our results suggest that some mature forest stands should be maintained within managed landscapes for a complete logging rotation period.     

Partitioning of soil respiration into its autotrophic and heterotrophic components by means of tree-girdling in old boreal spruce forest

Forests accumulate much less carbon than the amount fixed through photosynthesis because of an almost equally large opposing flux of CO₂ from the ecosystem. Most of the return flux to the atmosphere is through soil respiration, which has two major sources, one heterotrophic (organisms decomposing organic matter) and one autotrophic (roots, mycorrhizal fungi and other root-associated microbes dependent on recent photosynthate). We used tree-girdling to stop the flow of photosynthate to the belowground system, hence, blocking autotrophic soil activity in a 120-yr-old boreal Picea abies forest. We found that at the end of the summer, two months after girdling, the treatment had reduced soil respiration by up to 53%. This figure adds to a growing body of evidence indicating (t-test, d.f. = 7, p < 0.05) that autotrophic respiration may contribute more to total soil respiration in boreal (mean 53 ± 2%) as compared to temperate forests (mean 44 ± 3%). Our data also suggests that there is a seasonal hysteresis in the response of total soil respiration to changes in temperature. We propose that this reflects seasonality in the tree below-ground carbon allocation.     

A comparison of annual transpiration and productivity in monoculture and mixed-species Douglas-fir and red alder stands

Although much is known about drivers of productivity in Douglas-fir and red alder stands, less is known about how productivity may relate to stand transpiration and water use efficiency. We took advantage of a 15-year-old experiment involving Douglas-fir (Pseudotsuga menziesii) and red alder (Alnus rubra) in the western Cascade Range of western Oregon to test the following hypotheses: (a) more productive stands transpire more water, (b) the relationship between productivity and transpiration differs between species, and (c) the relationship between productivity and transpiration differs between sites varying in soil moisture and fertility. Furthermore, the experimental design included alder, a facultative nitrogen-fixing species, which could also affect fertility. Fixed area plots (20 × 20 m) were planted as monocultures of each species or in mixtures at a common density (1100 trees ha⁻¹) in a randomized-block design. Transpiration of Douglas-fir and red alder was measured using heat dissipation sensors installed in eight trees per plot and scaled to the plot level based on sapwood basal area for each species. Although up to 53% of the variability in tree transpiration was explained by basal area, irrespective of species or site conditions, the two stands with the highest biomass and sapwood basal area did not transpire the most. Instead of more productive stands transpiring more water, the greatest variability in both productivity and transpiration was determined by site conditions and to a lesser degree, species composition. For example, 70% of the variation in tree biomass increment (TBI) was determined by leaf area index, which was much higher at the site with higher fertility and soil moisture (p < 0.05). Despite marked phenological and physiological differences, Douglas-fir and red alder performed similarly. Only 19% of annual water use of Douglas-fir occurred between October and March when alder was leafless. Also, there was no evidence of a fertilization effect of the nitrogen-fixing red alder on the Douglas-fir: the nitrogen concentration and N-isotopic ratio of Douglas-fir needles did not differ whether trees were grown in monoculture or in mixtures with red alder. We conclude that lower soil fertility and contrasting microclimate at one site relative to the other suppressed NPP while maintaining higher transpiration, thus reducing water use efficiency.     

丁营飞播区林分变化及经营管理措施的研究

根据1976年播后出苗率和成苗率调查,1987--1990年油松毛虫灾害对油松林分的影响,及1991年和2003年丁营飞播区森林资源清查资料,通过调查数据对比分析,丁营飞播区播后林分变化规律,符合近自然林业发展规律。面向整个丁营飞播区生态系统,依据近自然林业经营理念,研究丁营飞播区经营管理措施,实现林业经营目标的最大化。     

Simulating the productivity of a subalpine forest at high elevations under representative concentration pathway scenarios in the Qilian Mountains of northwest China

The current work adopted the Biome-BioGeochemical Cycle model to simulate the net primary productivity (NPP) of a subalpine forest (Picea crassifolia forest) under four representative concentration pathway (RCP) scenarios in the Qilian Mountains of northwest China. This study also investigated the responses of forest’s NPP to different combinations of climatic changes and CO₂ concentration increase. Results showed that (1) under the RCP scenarios, greater increases in temperature, precipitation, and CO₂ concentration caused larger increments in forest NPP; (2) the effect of CO₂ concentration (increased NPP from 19.9% to 21.7%) was more significant than that of climate change (increased NPP from 7.5% to 17.1%); (3) the simultaneous increments in climatic change and atmospheric CO₂ concentration led to a remarkable increase in P. crassifolia forest NPP (ranging from 33.1% to 41.3%), with the combination of the two exerting strong interactive effects on forest NPP; and (4) the response of the forest’s NPP to future global change was more intense at high elevations than at low ones, with the temperature being the main factor controlling forest NPP variation at the high-elevation regions. These valuable predictions can help clarify how subalpine forest ecosystems respond to simultaneous or independent changes in climate and CO₂ concentration.     

Carbon sequestration in the growing stock of trees in Finland under different cutting and climate scenarios

In this work the aim was to determine how carbon sequestration in the growing stock of trees in Finland is dependent on the forest management and increased production potential due to climate change. This was analysed for the period 2003–2053 using forest inventory data and the forestry model MELA. Four combinations of two climate change and two management scenarios were studied: current (CU) and gradually warming (CC) climate and forest management strategies corresponding to different rates of utilisation of the cutting potential, namely maximum sustainable removal (Sust) or maximum net present value (NPV) of wood production (Max). In this analysis of Finland, the initial amount of carbon in the growing stock was 765 Mt (2,802 Tg CO₂). At the end of the simulation, the carbon in the growing stock of trees in Finland had increased to 894 Mt (3,275 Tg CO₂) under CUSust, 906 Mt (3,321 Tg CO₂) under CUMax, 1,060 Mt (3,885 Tg CO₂) under CCSust and 1,026 Mt (3,758 Tg CO₂) under CCMax. The results show that future development of carbon in the growing stock is not only dependent on climate change scenarios but also on forest management. For example, maximising the NPV of wood production without sustainability constraints results, over the short term, in a large amount of wood obtained in regeneration cuttings and a consequent decrease in the amount of carbon in growing stock. Over the longer term, this decrease in the carbon of growing stock in regenerated forests is compensated by the subsequent increase in fast-growing young forests. By comparison, no drastic short-term decrease in carbon stock was found in the Sust scenarios; only minor decreases were observed.     

1987年大兴安岭林火碳释放及火后NPP恢复

以大兴安岭地区1985年一类森林资源连续清查资料和1987年林火资料为数据基础,结合GIS技术,进行大兴安岭1987年林火碳释放及火后净初级生产力(NPP,net primary productivity)恢复的研究.通过对1987年火烧迹地林火发生前各树种的生物量的估算,得出在1987年林火中大兴安岭林区森林释放的碳量约为1.97×10~6～2.47×10~6 t;同时分别比较火烧中各树种的碳释放量和不同火烧等级下的碳释放量.结果表明:落叶松在1987年林火中释放碳量约0.96×10~6～1.19×10~6 t,占碳释放总量的49%左右;重度火灾中碳释放量占总碳释放量的99.4%.火后乔木层的NPP恢复在21年间成逐渐增加的趋势,并且恢复趋势表明在火后23～24年的时候中度火灾后的乔木层NPP可达到未过火林地的水平.     

中国东北样带植被净初级生产力时空动态及其对气候变化的响应

根据净初级生产力(NPP)遥感估算模型,重建了中国东北样带(NECT)1982–2000 年间每月的 NPP 时空序列,分析了研究时段内 NPP 的时空格局特征及其与气候因子的关系。结果表明:(1)NECT 样带植被 NPP 的空间变化趋势同降水量的空间变化十分相似,由东到西逐渐降低,二者在空间上的相关性达到了 0.84(P<0.01),说明 NECT 样带的植被 NPP在空间分布上主要受水分趋动;(2)NECT 样带植被 NPP 的年际变化主要是由各年份夏季 NPP 的变化造成的,夏季对NECT 样带植被 NPP 的年际增长贡献率最大(67.6%),二者之间的相关性达到了 0.95(P<0.01);(3)NECT 样带的植被NPP 积累期主要发生在 5–9 月份,这 5 个月的 NPP 占了全年NPP 总量的 89.8%,整个夏季(6–8 月份)的 NPP 占了全年的 65.9%,冬季(12–2 月份)的 NPP 最低,基本为 0;(4)近 19 年来的气候变化促进了 NECT 样带的植被生长,从 1980年代到 1990 年代,NPP 显著增加,年代际相对增长率为 14.3%,平均年际绝对增长趋势为 4.6 gC m-2 a-1,相对增长趋势为 1.17%,这主要是由温度升高引起的。图 6 表 1 参 36。