Reiner Zimmermann

Effects of elevation and land use on the biomass of trees, shrubs and herbs at Mount Kilimanjaro

The protection and sustainable management of forest carbon stocks, particularly in the tropics, is a key factor in the mitigation of global change effects. However, our knowledge of how land use and elevation affect carbon stocks in tropical ecosystems is very limited. We compared aboveground biomass of trees, shrubs and herbs for eleven natural and human-influenced habitat types occurring over a wide elevation gradient (866–4550 m) at the worlds highest solitary mountain, Mount Kilimanjaro. Thanks to the enormous elevation gradient, we covered important natural habitat types, e.g., savanna woodlands, montane rainforest and afro-alpine vegetation, as well as important land-use types such as maize fields, grasslands, traditional home gardens, coffee plantations and selectively logged forest. To assess tree and shrub biomass with pantropical allometric equations, we measured tree height, diameter at breast height and wood density and to assess herbaceous biomass, we sampled destructively. Among natural habitats, tree biomass was highest at intermediate elevation in the montane zone (340 Mg ha−1), shrub biomass declined linearly from 7 Mg ha−1 at 900 m to zero above 4000 m, and, inverse to tree biomass, herbaceous biomass was lower at mid-elevations (1 Mg ha−1) than in savannas (900 m, 3 Mg ha−1) or alpine vegetation (above 4000 m, 6 Mg ha−1). While the various land-use types dramatically decreased woody biomass at all elevations, though to various degrees, herbaceous biomass was typically increased. Our study highlights tropical montane forest biomass as important aboveground carbon stock and quantifies the extent of the strong aboveground biomass reductions by the major land-use types, common to East Africa. Further, it shows that elevation and land use differently affect different vegetation strata, and thus the matrix for other organisms.

Application of QuikSCAT Backscatter to SMAP Validation Planning: Freeze/Thaw State Over ALECTRA Sites in Alaska From 2000 to 2007

The mapping of the predominant freeze/thaw state of the landscape is one of the main objectives of the National Aeronautics and Space Administrations proposed Soil Moisture Active Passive (SMAP) mission. This study applies Alaska Ecological Transect (ALECTRA) biophysical network temperature measurements and satellite radar scatterometer data from the Quick Scatterometer (QuikSCAT) to evaluate some of the validation issues regarding the planned SMAP freeze/thaw measurements. Although the QuikSCAT data are acquired at Ku-band frequency, rather than at the L-band frequency of the proposed SMAP instrument, QuikSCAT data do provide a high temporal fidelity over the ALECTRA sites, similar to SMAP. The results of this study show that multiple temperature measurements representative of individual landscape components (soil, snow cover, vegetation, and atmosphere) covering different types of terrain within the satellite field of view are important for understanding the freeze/thaw process and the aggregate radar backscatter response to that process. The backscatter temporal dynamics and relative contribution of the freeze/thaw state of these landscape elements to radar signal vary with land cover, seasonal weather, and climate conditions.

Patterns of wood carbon dioxide efflux across a 2,000-m elevation transect in an Andean moist forest.

During a 1-year measurement period, we recorded the CO2 efflux from stems (RS) and coarse woody roots (RR) of 13–20 common tree species at three study sites at 1,050, 1,890 and 3,050xa0m a.s.l. in an Andean moist forest. The objective of this work was to study elevation changes of woody tissue CO2 efflux and the relationship to climate variation, site characteristics and growth. Furthermore, we aim to provide insights into important respiration–productivity relationships of a little studied tropical vegetation type. We expected RS and RR to vary with dry and humid season conditions. We further expected RS to vary more than RR due to a more stable soil than air temperature regime. Seasonal variation in woody tissue CO2 efflux was indeed mainly attributable to stems. At the same time, temperature played only a small role in triggering variations in RS. At stand level, the ratio of C release (g C m−2 ground area year−1) between stems and roots varied from 4:1 at 1,050xa0m to 1:1 at 3,050xa0m, indicating the increasing prevalence of root activity at high elevations. The fraction of growth respiration from total respiration varied between 10 (3,050xa0m) and 14% (1,050xa0m) for stems and between 5 (1,050xa0m) and 30% (3,050xa0m) for roots. Our results show that respiratory activity and hence productivity is not driven by low temperatures towards higher elevations in this tropical montane forest. We suggest that future studies should examine the limitation of carbohydrate supply from leaves as a driver for the changes in respiratory activity with elevation.

Intra-annual stem growth dynamics of Lebanon Cedar along climatic gradients

Key messageOnset of cambial activity in Lebanon Cedar is triggered by stem temperature but may be delayed by high site-LAI. Higher growth rates and tree-ring widths were observed under better water and light availability. Daily stem radius variations were sensitive to humid conditions.AbstractStudies on intra-annual dynamics of stem growth provide useful information on tree growth responses to environmental conditions, but are fragmentary for species from Mediterranean Mountain ranges. Lebanon Cedar is a frost and drought tolerant species, growing between 1000 and 2000xa0m a.s.l in the Taurus Mountains (Turkey). Foresters see it as a potential candidate for plantation in Central European forests facing global warming. To describe the natural variability of Lebanon Cedar growth dynamics, five study sites were established: four along an altitudinal gradient at a natural site in SW-Turkey and one in a Lebanon Cedar plantation in Central Germany. Two stem growth monitoring methods were used: (1) bi-weekly microcoring during 2013 growing season and (2) point dendrometers during 2013 and 2014. Histological analyses were used to calibrate dendrometer records and to describe cambium phenology. Seasonal dynamics of xylem and stem radial increments were modelled by Gompertz functions. Onset of cambial activity was observed 1–2xa0weeks after stem temperatures reached a threshold of 5xa0°C but could be delayed by high site-LAI. Cedars growing under better light and water availability showed higher growth rates and wider tree rings. Daily stem radius variations (dSRV) extracted from dendrometer records were negatively related to vapor pressure deficit and global radiation; multiple linear regressions explained 30–52% of dSRV variance being dominated by relative humidity, precipitation, and soil water content. Best growth performance was observed at the German site, likely for a continuous water supply throughout the year, underlining the potential of Lebanon Cedar for Central European Forestry.

Cedrus libani : A promising tree species for Central European forestry facing climate change?

Considering climate change, the discussion intensifies whether and to what extent exotic tree species should be taken into account for forest cultivation, especially when indigenous species are no longer able to fulfill essential forest functions. In this study, for the first time growth potential of Cedrus libani was evaluated under climatic conditions in Central Europe (Bayreuth, Germany). The sampled trees exhibited extraordinary growth with tree ring widths averaging 4.9xa0mmxa0year−1 during the past 23xa0years. A continuously available soil water supply enhanced radial stem growth. Thus, growth declined during the dry year of 2003, but recovered to average values the following year. Our results confirm that C. libani is a light-demanding species which is sensitive to competition and which shows a typical age trend. In a second study, we compared cambial growth in Bayreuth with a natural stand in Elmali (Turkey) in 2009. Cambial growing season in Bayreuth was 45xa0days longer, and radial growth rates in Bayreuth were four times higher than in Elmali. Interestingly, C. libani maintained a slow but continuous radial growth at Elmali even during the dry summer period, confirming its exceptional drought tolerance. Our results indicate a high adaption of C. libani to current and future climate conditions in Central Europe. It tolerates extreme cold in winter and prolonged droughts during summer. Thus, its promising potential for establishing stable and productive forest stands in Central Europe under a changing climate should be confirmed in further studies.

Cambial activity and xylogenesis in stems of Cedrus libani A. Rich at different altitudes

BackgroundThe dynamics of cambial activity and xylogenesis provide information on how and to what extent wood formation respond to climatic variability. The Lebanon Cedar (Cedrus libani A.Rich) is a montane tree species which is distributed along a wide altitudinal range in the northeastern Mediterranean region, currently considered as a potential forest species for Central Europe with respect to climate change. This study provides first data on intra-annual growth dynamics at cellular level using the microcore technique for a montane Mediterranean tree species at different altitudes within and outside its natural range.ResultsMicrocores were collected fortnightly in the growing season of 2013 in order to study temporal dynamics of cambial activity and xylogenesis in stems of C. libani at different altitudes in the Taurus Mountains (1000 – 2000 m a.s.l.) and at a plantation at Bayreuth (330 m a.s.l.; Germany). The dormant cambium consisted of about 5 cells at the Turkish sites and 7 cells at Bayreuth. Cambial activity set in, when daily minimum temperatures exceeded 0 °C and daily means of air and stem temperature exceeded 5 °C. Xylogenesis started between April and May, ended approximately the end of September to the beginning of October and lasted 134 (at tree line) to 174 days (at the lowest Turkish site). Mean ring widths varied from 0.55 to 3.35 mm, with highest values observed at Bayreuth very likely resulting from a steady water supply during growing season. Means of daily cell production rates varied from 0.73 to 0.12. Samples containing traumatic resin ducts occurred only rarely and where not used for analysis.ConclusionsIn C. libani, onset and dynamics of cambial activity and xylogenesis are triggered by daily means of stem and air temperatures whereas water availability has a higher influence on growth rates and cessation of wood formation. Within sites, duration of xylogenesis does not significantly differ with respect to age and tree size. C. libani grows well outside its natural range and thus may be a promising species for forestation in Central Europe with respect to climate change. We suggest further studies on if/how traumatic resin ducts influence tree ring width.

Africa’s highest mountain harbours Africa’s tallest trees

While world records of tree heights were set by American, Australian and Asian tree species, Africa seemed to play no role here. In our study we show that Entandrophragma excelsum (Meliaceae) found in a remote valley at Kilimanjaro has to be included in the list of the world’s superlative trees. Estimating tree age from growth rates monitored by high resolution dendrometry indicates that tall individuals may reach more than 470xa0years of age. A unique combination of anatomical peculiarities and favorable site conditions might explain their enormous size. The late date of this discovery of Africa’s tallest trees may be due to the comparably low study efforts at Kilimanjaro compared with other biodiversity hotspots. Since only a few square kilometers of this habitat of Entandrophragma are left, Kilimanjaro (and Africa) is about to lose not only a unique biogeographical archive with highly diverse vegetation, but also its tallest trees. The inclusion of these valleys into the immediately neighboring Kilimanjaro National Park would be an excellent and urgent possibility of protection.

Erratum to: Intra-annual stem growth dynamics of Lebanon Cedar along climatic gradients

Data presented in this figure are correct, however, the LAI at site O1 was determined in a different way as described in the methods section for LAI of T1–T4: LAI at O1 was estimated as a measure of above ground competition by assuming the crown form of the cedar individuals being a cone and the curved surface area open to the sky relatively to the ground area. Abbreviations for T1–T4 are not placed correctly. Erroneous Fig. 5a as published in the article

Sap Flow and Stem Respiration

The effects of seasonal flooding on stem xylem flow and carbon release were investigated on common tree species of the Amazonian floodplain forests locally known as Varzea. The annual flooding lasts several months, reaches five to eight meters and drives the phenology of most forest species. Leaf shedding of deciduous trees starts at the onset of flooding and new leaves are produced after the peak of flooding in July. For evergreen species leaf shedding and new leaf production occur simultaneously during flooding. It has been generally assumed that these phenology patterns are associated to physiological stress during flooding. Here the focus is on tree and species functioning during water stress by flooding. Measurements of stem xylem flux and stem carbon release were taken to monitor changes in species ecophysiological behavior during flooding.