Peer review report 2 on “Forward modeling of tree-ring width improves simulation of forest growth responses to drought”

The climate of Nepal has changed rapidly over the recent decades, but most instrumental records of weather and hydrology only extend back to the 1980s. Tree rings can provide a longer perspective on recent environmental changes, and since the early 2000s, a new round of field initiatives by international researchers and Nepali scientists have more than doubled the size of the country’s tree-ring network. In this paper, we present a comprehensive analysis of the current tree-ring width network for Nepal, and use this network to estimate changes in forest growth nation-wide during the last four centuries. Ring-width chronologies in Nepal have been developed from 11 tree species, and half of the records span at least 290 years. The Nepal tree-ring width network provides a robust estimate of annual forest growth over roughly the last four centuries, but prior to this point, our mean ring-width composite fluctuates wildly due to low sample replication. Over the last four centuries, two major events are prominent in the all-Nepal composite: (i) a prolonged and widespread growth suppression during the early 1800s; and (ii) heightened growth during the most recent decade. The early 19th century decline in tree growth coincides with two major Indonesian eruptions, and suggests that short-term disturbances related to climate extremes can exert a lasting influence on the vigor of Nepal’s forests. Growth increases since AD 2000 are mainly apparent in high-elevation fir, which may be a consequence of the observed trend towards warmer temperatures, particularly during winter. This synthesis effort should be useful to establish baselines for tree-ring data in Nepal and provide a broader context to evaluate the sensitivity or behavior of this proxy in the central Himalayas.

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Subalpine forest dynamics reconstructed throughout the last 700 years in the Central Pyrenees by means of tree rings and pollen

The Holocene ◽

10.1177/0959683618810402 ◽

2018 ◽

Vol 29 (2) ◽

pp. 300-312

Author(s):

Sandra Garcés-Pastor ◽

Emilia Gutiérrez-Merino ◽

Elisabet Martínez-Sancho ◽

Isabel Dorado-Liñán ◽

J Julio Camarero ◽

...

Keyword(s):

Tree Ring ◽

Low Temperatures ◽

Ring Width ◽

Forest Growth ◽

Subalpine Forest ◽

Pollen Record ◽

Tree Ring Width ◽

Growth Variability ◽

The Past ◽

Central Pyrenees

Understanding how climate has modulated forest growth and composition in the past is necessary to predict the influence of the ongoing climate warming on the dynamics of mountain forests. We studied the past dynamics of subalpine Pyrenean forests during the last 700 years by assessing the relationships between sedimentary pollen and tree-ring records, and their link with climatic drivers. We compared the pollen record and the montane pollen ratio, an integrative index obtained from sedimentary pollen that allows inferring past altitudinal variations in the montane–subalpine ecotone, with tree-ring width from mountain pine ( Pinus uncinata) subalpine forests located in Central Pyrenees. To assess climate–growth associations, we related the dendrochronological data with instrumental meteorological records (1901–2010) and temperature reconstructions from the Pyrenees and Northern Hemisphere. Few robust associations were found between arboreal pollen taxa and tree-ring width series of the surrounding forests. However, significant correlations were found between the montane pollen ratio and tree-ring width series from nearby forests (located less than 10 km apart). This relationship could be potentially useful to infer long-term forest growth changes at decadal to centennial scales using the montane pollen ratio. On the contrary, our results show that tree radial growth has mainly been constrained by low temperatures although the growth sensitivity to climate has considerably varied over the last 700 years. Similar results were obtained for the last century as growth variability of these high-elevation forests is still driven by low temperatures, but a relaxation of this constrain in recent decades has been detected.

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Growth response of Abies spectabilis to climate along an elevation gradient of the Manang valley in the central Himalayas

Journal of Forestry Research ◽

10.1007/s11676-019-01011-x ◽

2019 ◽

Vol 31 (6) ◽

pp. 2245-2254 ◽

Cited By ~ 3

Author(s):

Samresh Rai ◽

Binod Dawadi ◽

Yafeng Wang ◽

Xiaoming Lu ◽

Huang Ru ◽

...

Keyword(s):

Tree Ring ◽

Elevation Gradient ◽

Ring Width ◽

Principal Component ◽

Moisture Stress ◽

Severity Index ◽

Forest Growth ◽

Drought Severity ◽

Tree Ring Width ◽

Standard Tree

Abstract The Himalayas are characterized by a broad gradient of bioclimatic zones along their elevation. However, less is known how forest growth responds to climatic change along elevation. In this study, four standard tree-ring width chronologies of Himalayan fir (Abiesspectabilis) were developed, spanning 142–649 years along an elevation gradient of 3076–3900 m a.s.l. Principal component analysis classified the four chronologies into two groups; the ones at lower elevations (M1 and M2) and higher elevations (M3 and M4) show two distinct growth trends. Radial growth is limited by summer (June–August) precipitation at M3, and by precipitation during spring (March–May) and summer at M4. It is limited by spring temperatures and winter precipitation (December–February) at M1. Tree-ring width chronologies also significantly correlate with winter and spring Palmer Drought Severity Index (PDSI) at M1, and with summer PDSI at M3 and M4. Thus, Himalayan fir growth at high elevations is mainly limited by moisture stress rather than by low temperatures. Furthermore, the occurrence of missing rings coincides with dry periods, providing additional evidence for moisture limitation of Himalayan fir growth.

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Tree-ring growth curves as sources of climatic information

Quaternary Research ◽

10.1016/j.yqres.2004.06.005 ◽

2004 ◽

Vol 62 (2) ◽

pp. 126-133 ◽

Cited By ~ 28

Author(s):

Mukhtar M. Naurzbaev ◽

Malcolm K. Hughes ◽

Eugene A. Vaganov

Keyword(s):

Tree Ring ◽

Regional Growth ◽

Ring Width ◽

Growth Curves ◽

Elevational Gradient ◽

Forest Growth ◽

Tree Ring Width ◽

Cambial Age ◽

Tree Ring Data ◽

Subfossil Wood

Regional growth curves (RGCs) have been recently used to provide a new basis for removing nonclimatic trend from tree-ring data. Here we propose a different use for RGCs and explore their properties along two transects, one meridional and the other elevational. RGCs consisting of mean ring width plotted against cambial age were developed for larch samples from 34 sites along a meridional transect (55–72°N) in central Siberia, and for 24 sites on an elevational gradient (1120 and 2350 m a.s.l.) in Tuva and neighboring Mongolia at approximately 51°N. There are systematic gradients of the parameters of the RGCs, such as I0-maximum tree-ring width near pith, and Imin, the asymptotic value of tree-ring width in old trees. They are smaller at higher latitude and elevation. Annual mean temperature and mean May–September temperature are highly correlated with latitude here, and hence RGC parameters are correlated with these climatic variables. Correlations with precipitation are more complex, and contradictory between meridional and elevational transects. The presence of a similar gradient in the elevational transect is consistent with temperature being the causal factor for both gradients, rather than, for example, latitude-dependent patterns of seasonal photoperiod change. Taking ring measurements from collections of relict and subfossil wood, the RGC–latitude and RGC–temperature relationships are used to estimate paleo-temperatures on centennial time scales. These estimates are consistent with earlier "traditional" dendroclimatic approaches, and with independent information on the northern extent of forest growth in the early mid-Holocene. It may be possible to use this same approach to make estimates of century-scale paleo-temperatures in other regions where abundant relict wood is present.

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Drought Sensitiveness on Forest Growth in Peninsular Spain and the Balearic Islands

Forests ◽

10.3390/f9090524 ◽

2018 ◽

Vol 9 (9) ◽

pp. 524 ◽

Cited By ~ 16

Author(s):

Marina Peña-Gallardo ◽

Sergio Vicente-Serrano ◽

J. Camarero ◽

Antonio Gazol ◽

Raúl Sánchez-Salguero ◽

...

Keyword(s):

Tree Ring ◽

Drought Index ◽

Net Primary Production ◽

Ring Width ◽

Forest Growth ◽

Balearic Islands ◽

Drought Indices ◽

Tree Ring Width ◽

Drought Impacts ◽

Peninsular Spain

Drought is one of the key natural hazards impacting net primary production and tree growth in forest ecosystems. Nonetheless, tree species show different responses to drought events, which make it difficult to adopt fixed tools for monitoring drought impacts under contrasting environmental and climatic conditions. In this study, we assess the response of forest growth and a satellite proxy of the net primary production (NPP) to drought in peninsular Spain and the Balearic Islands, a region characterized by complex climatological, topographical, and environmental characteristics. Herein, we employed three different indicators based on in situ measurements and satellite image-derived vegetation information (i.e., tree-ring width, maximum annual greenness, and an indicator of NPP). We used seven different climate drought indices to assess drought impacts on the tree variables analyzed. The selected drought indices include four versions of the Palmer Drought Severity Index (PDSI, Palmer Hydrological Drought Index (PHDI), Z-index, and Palmer Modified Drought Index (PMDI)) and three multi-scalar indices (Standardized Precipitation Evapotranspiration Index (SPEI), Standardized Precipitation Index (SPI), and Standardized Precipitation Drought Index (SPDI)). Our results suggest that—irrespective of drought index and tree species—tree-ring width shows a stronger response to interannual variability of drought, compared to the greenness and the NPP. In comparison to other drought indices (e.g., PDSI), and our results demonstrate that multi-scalar drought indices (e.g., SPI, SPEI) are more advantageous in monitoring drought impacts on tree-ring growth, maximum greenness, and NPP. This finding suggests that multi-scalar indices are more appropriate for monitoring and modelling forest drought in peninsular Spain and the Balearic Islands.

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