Oecologia DOI 10.1007/s00442-013-2846-x
Global change ecology - Original research
Temperature and rainfall strongly drive temporal growth variation in Asian tropical forest trees Mart Vlam · Patrick J. Baker · Sarayudh Bunyavejchewin · Pieter A. Zuidema
Received: 23 July 2013 / Accepted: 16 November 2013 © Springer-Verlag Berlin Heidelberg 2013
Abstract Climate change effects on growth rates of tropical trees may lead to alterations in carbon cycling of carbon-rich tropical forests. However, climate sensitivity of broad-leaved lowland tropical trees is poorly understood. Dendrochronology (tree-ring analysis) provides a powerful tool to study the relationship between tropical tree growth and annual climate variability. We aimed to establish climate–growth relationships for five annual-ring forming tree species, using ring-width data from 459 canopy and understory trees from a seasonal tropical forest in western Thailand. Based on 183/459 trees, chronologies with total lengths between 29 and 62 years were produced for four out of five species. Bootstrapped correlation analysis revealed that climate–growth responses were similar among these four species. Growth was significantly negatively correlated with current-year maximum and minimum temperatures, and positively correlated with dry-season precipitation levels. Negative correlations between growth and temperature may be attributed to a positive relationship between Communicated by Jeremy Lichstein. Electronic supplementary material The online version of this article (doi:10.1007/s00442-013-2846-x) contains supplementary material, which is available to authorized users. M. Vlam (*) · P. A. Zuidema Forest Ecology and Forest Management Group, Wageningen University, P.O. Box 47, 6700 AA Wageningen, The Netherlands e-mail: [email protected] P. J. Baker Department of Forest and Ecosystem Science, University of Melbourne, Victoria 3010, Australia S. Bunyavejchewin Department of National Parks, Wildlife and Plant Conservation, Chatuchak, Bangkok 10900, Thailand
temperature and autotrophic respiration rates. The positive relationship between growth and dry-season precipitation levels likely reflects the strong water demand during leaf flush. Mixed-effect models yielded results that were consistent across species: a negative effect of current wet-season maximum temperatures on growth, but also additive positive effects of, for example, prior dry-season maximum temperatures. Our analyses showed that annual growth variability in tropical trees is determined by a combination of both temperature and precipitation variability. With rising temperature, the predominantly negative relationship between temperature and growth may imply decreasing growth rates of tropical trees as a result of global warming. Keywords Climate–growth relationship · Global change · Thailand · Tree rings · Tropical tree
Introduction Tropical forests are currently experiencing some of the most rapid rates of warming in recent geological times (Marcott et al. 2013). And not only are temperatures rising around the world but there are indications that temperature anomalies are becoming more frequent (Hansen et al. 2012). The response of tropical forests to global warming may potentially have large impacts on global carbon cycling (Corlett 2011). Warming may reduce leaflevel photosynthesis (Doughty 2011), increase autotrophic respiration rates (Lloyd and Farquhar 2008), and increase evaporative demand (Galbraith et al. 2010), resulting in reduced tree growth. As tropical forests contain one of the largest terrestrial carbon pools (Dixon et al. 1994; Malhi and Grace 2000), it is crucial to understand their response to warming (Clark et al. 2003).
13
Oecologia
In the absence of in situ tree-level warming experiments in the tropics, analysis of temporal tree growth variability in relation to annual climatic variation can be the next best source of information on global warming effects on tropical trees (Brienen et al. 2010; Clark et al. 2010; Pumijumnong 2012). Repeated diameter measurements of tropical trees has shown that temporal variation in diameter growth was negatively correlated with temperature (Clark et al. 2003, 2013; Dong et al. 2012). However, due to the multi-year census interval of most permanent plot studies (e.g., Dong et al. 2012), the power of correlation analyses is generally low and the multi-year census interval requires an integration of yearly climate parameters over the census interval. Tropical dendrochronology (tree-ring analysis) can provide long-term, high-resolution tropical tree growth data to complement plot-based repeated diameter measurements (Worbes 1995; Zuidema et al. 2013). Tropical tree species that form reliable annual growth rings provide annual-resolution growth data at multi-decadal to centennial scales, which enhance the detectability of climatic influences on growth variation in tropical trees (Zuidema et al. 2012). Multi-species tree-ring studies on climate–growth relationships of broad-leaved trees from moist lowland tropical forests are rare, but studies in the Amazon (Dünisch et al. 2003; Brienen and Zuidema 2005) and West Africa (Schöngart et al. 2006) have shown that temporal variation in growth was positively correlated with total annual precipitation. In lowland tropical forests in Southeast Asia, analysis of the relationship between climate and ring width has mainly focused on teak (Tectona grandis) (Pumijumnong et al. 1995; Buckley et al. 2007), and only a few examples of other species exist (e.g., Zuidema et al. 2011). Besides the generally low representation of lowland moist tropical forest trees species in climate–growth studies, the focus has traditionally been on precipitation correlations (Jacoby 1989; Rozendaal and Zuidema 2011; Pumijumnong 2012), and effects of temperature anomalies on annual growth variability were often not evaluated (Dünisch et al. 2003; Brienen and Zuidema 2005; Schöngart et al. 2006) or determined non-significant (Couralet et al. 2010). However, whereas there is large uncertainty regarding predicted rainfall changes for the tropics, a clear warming trend across most of the tropics is undisputed (IPCC 2007; Wright et al. 2009). Here, we use tree-ring analyses to evaluate tree growth sensitivity to climatic variation in Southeast Asia. We took tree ring samples from over 450 individuals belonging to five species known to form annual rings (Baker and Bunyavejchewin 2006). These species represent three different families, vary in leaf phenology, and represent several ecological guilds. The availability of >60 years of high quality climate data from a nearby meteorological station allowed us to address questions and hypotheses on the relationship
13
between climate variability and tree growth. Specifically, we addressed the following questions. (1) Is tree growth correlated with minimum and maximum temperature? And (2) is tree growth correlated with precipitation? Furthermore, we used linear mixed-effects models to assess the relative importance of various seasonal climate indices on standardized diameter growth rates.
Materials and methods Study area and species The study area was situated in the Huai Kha Khaeng Wildlife Sanctuary (HKK), Uthai Thani province, western Thailand (15.60°N, 99.20°E), approximately 550 m above sea-level. Climate in Huai Kha Khaeng is strictly seasonal with a marked dry season from November to April (Fig. 1a). Mean annual rainfall in HKK is 1,473 mm and mean annual temperature is 23.5 ºC (Bunyavejchewin et al. 2009). Soils are highly weathered, slightly acidic ultisols, and soil textures are sandy loam at the surface and sandy clay-loam in the subsurface horizons (Bunyavejchewin et al. 2009). The vegetation in the area is classified as seasonal dry evergreen and mixed deciduous forest (Bunyavejchewin et al. 2009). Canopy height in the forest is around 30 m, with occasional emergent trees reaching 50 m. Members of the family Dipterocarpaceae dominate the area in total basal area; other well-represented families include Annonaceae, Euphorbiaceae, and Meliaceae (Bunyavejchewin et al. 2001). We sampled five tree species: Afzelia xylocarpa (Kurz) Craib (Fabaceae), Chukrasia tabularis A. Juss. (Meliaceae), Melia azedarach L. (Meliaceae), Neolitsea obtusifolia Merr. (Lauraceae), and Toona ciliata M. Roem. (Meliaceae). See Table 1 for a summary of the species’ characteristics. All five species were known to form annual rings following a cambial wounding experiment over the period 1988–1998 (Baker et al. 2005). Afzelia, Melia, and Toona have a distinctly deciduous leaf phenology, whereas Chukrasia is classified as brevi-deciduous and Neolitsea is evergreen (Williams et al. 2008). All five species are canopy trees, reaching maximum heights of 30–45 m. Sampling and measurements Wood samples for tree-ring analysis were collected from 459 trees during the period between December 2010 and December 2011. All samples were collected within a ~300ha area of mixed deciduous and seasonal dry evergreen forest. Samples from the locally more abundant species, Neolitsea and Chukrasia, were mainly collected following a clustered sampling design. These trees were sampled
Oecologia Nakhon Sawan (35 m) 1951−2010
28.6C
1147 mm 300
(a) 50
100
40
80
30
60
20
40
18.5 10
20
0
0 J
35
30
F
M
A
M
J
J
A
S
O
N
D
(b)
Precipitation (mm)
Temperature ° C
38.0
2000
Tmax (0.011**)
1500 Rainfall 1000
25 500
Tmin (0.025***) 20
1920
1940
1960
1980
2000
0
Year
Fig. 1 a Climate diagram for the Nakhon Sawan meteorological station, ~100 km east of the study site. b Annual precipitation and temperature observations from the Nakhon Sawan meteorological station. Upper line (Tmax, filled circles) represents the mean daily maximum temperature, middle line rainfall (triangles) and lower line (Tmin, open circles) is the mean daily minimum temperature. Linear regression models were fit to the temperature data and regression coefficients are indicated (*,**,*** for P 5 cm dbh, irrespective of, for example, canopy position. At a height of approximately 1 m on the stem, we manually extracted wood cores with a 5.0-mm-diameter Suunto (Vantaa, Finland) or a 5.15-mm-diameter Haglöf (Långsele, Sweden) increment borer. Depending on the diameter of the tree, we used borers with lengths varying between 40 and 70 cm. Two cores were taken from trees 60 %) from their respective species-specific chronologies (Table 2). Because of high dating uncertainty remaining after attempting to cross-date the Neolitsea ring-width series, we excluded this species from all further analyses. For the other four species, a species-specific chronology was produced (Fig. 2e–h). Of the total sample size, the proportion of trees included in the chronology was 38 % for Afzelia, 27 % for Chukrasia,
Tree ring data quality was checked by visually cross-dating tree-ring series in WinDENDRO. For trees sampled during the growing season of 2011, this year was excluded from analysis because this ring did not represent a full growing season. After visually cross-dating the tree-ring series, we checked for dating errors using the computer program COFECHA (Holmes 1983). This iterative process of crossdating greatly reduces the number of false and missing rings, both of which are known to occur in tropical species (Worbes 1995). Ring-width series that correlated poorly with the master chronology—for example, due to prolonged growth suppressions—were removed from the dataset prior to chronology development (Pederson et al. 2004). We used the dendrochronology program library in R (dplR; Bunn 2008) to produce species-specific chronologies from the previously selected tree-ring series. Ring-width indices were obtained by detrending the raw ring-width series using a 20-year cubic spline. A 20-year cubic spline was chosen because it showed the best result in removing
13
Oecologia Table 2 Descriptive statistics of the ring-width series Species
n sampled (trees/radii)
n chronology (trees/radii)
Time span
n years
r
ms
Rbar.wt
Rbar.bt
EPS
Afzelia
100/341
38/133
1976–2011
36
0.38
0.42
0.45
0.13
0.90
Chukrasia
104/330
28/70
1982–2010
29
0.46
0.57
0.46
0.18
0.88
Melia
90/330
71/252
1970–2011
42
0.48
0.42
0.51
0.20
0.96
Toona
61/220
46/168
1950–2011
62
0.50
0.65
0.64
0.26
0.95
All the statistics displayed concern only those series that were used for the chronology production r mean series intercorrelation of every series with the master chronology as produced by the program COFECHA (Holmes 1983), ms mean sensitivity, which is a measurement of the year-to-year variability in tree-ring, width as produced by the program COFECHA (Holmes 1983), Rbar. wt mean of the correlations between series from the same tree, Rbar.bt mean interseries correlation between all series from different trees, EPS expressed population signal
89 % for Melia, and 79 % for Toona (see Fig. S2 for diameter distributions of trees included in the chronologies). In Afzelia and Chukrasia, false, wedging, and generally indistinct rings were frequently observed, especially in periods when growth was suppressed, resulting in higher rejection rates. The resulting chronologies were cut off when the running expressed population signal (EPS) was
Global change ecology - Original research
Temperature and rainfall strongly drive temporal growth variation in Asian tropical forest trees Mart Vlam · Patrick J. Baker · Sarayudh Bunyavejchewin · Pieter A. Zuidema
Received: 23 July 2013 / Accepted: 16 November 2013 © Springer-Verlag Berlin Heidelberg 2013
Abstract Climate change effects on growth rates of tropical trees may lead to alterations in carbon cycling of carbon-rich tropical forests. However, climate sensitivity of broad-leaved lowland tropical trees is poorly understood. Dendrochronology (tree-ring analysis) provides a powerful tool to study the relationship between tropical tree growth and annual climate variability. We aimed to establish climate–growth relationships for five annual-ring forming tree species, using ring-width data from 459 canopy and understory trees from a seasonal tropical forest in western Thailand. Based on 183/459 trees, chronologies with total lengths between 29 and 62 years were produced for four out of five species. Bootstrapped correlation analysis revealed that climate–growth responses were similar among these four species. Growth was significantly negatively correlated with current-year maximum and minimum temperatures, and positively correlated with dry-season precipitation levels. Negative correlations between growth and temperature may be attributed to a positive relationship between Communicated by Jeremy Lichstein. Electronic supplementary material The online version of this article (doi:10.1007/s00442-013-2846-x) contains supplementary material, which is available to authorized users. M. Vlam (*) · P. A. Zuidema Forest Ecology and Forest Management Group, Wageningen University, P.O. Box 47, 6700 AA Wageningen, The Netherlands e-mail: [email protected] P. J. Baker Department of Forest and Ecosystem Science, University of Melbourne, Victoria 3010, Australia S. Bunyavejchewin Department of National Parks, Wildlife and Plant Conservation, Chatuchak, Bangkok 10900, Thailand
temperature and autotrophic respiration rates. The positive relationship between growth and dry-season precipitation levels likely reflects the strong water demand during leaf flush. Mixed-effect models yielded results that were consistent across species: a negative effect of current wet-season maximum temperatures on growth, but also additive positive effects of, for example, prior dry-season maximum temperatures. Our analyses showed that annual growth variability in tropical trees is determined by a combination of both temperature and precipitation variability. With rising temperature, the predominantly negative relationship between temperature and growth may imply decreasing growth rates of tropical trees as a result of global warming. Keywords Climate–growth relationship · Global change · Thailand · Tree rings · Tropical tree
Introduction Tropical forests are currently experiencing some of the most rapid rates of warming in recent geological times (Marcott et al. 2013). And not only are temperatures rising around the world but there are indications that temperature anomalies are becoming more frequent (Hansen et al. 2012). The response of tropical forests to global warming may potentially have large impacts on global carbon cycling (Corlett 2011). Warming may reduce leaflevel photosynthesis (Doughty 2011), increase autotrophic respiration rates (Lloyd and Farquhar 2008), and increase evaporative demand (Galbraith et al. 2010), resulting in reduced tree growth. As tropical forests contain one of the largest terrestrial carbon pools (Dixon et al. 1994; Malhi and Grace 2000), it is crucial to understand their response to warming (Clark et al. 2003).
13
Oecologia
In the absence of in situ tree-level warming experiments in the tropics, analysis of temporal tree growth variability in relation to annual climatic variation can be the next best source of information on global warming effects on tropical trees (Brienen et al. 2010; Clark et al. 2010; Pumijumnong 2012). Repeated diameter measurements of tropical trees has shown that temporal variation in diameter growth was negatively correlated with temperature (Clark et al. 2003, 2013; Dong et al. 2012). However, due to the multi-year census interval of most permanent plot studies (e.g., Dong et al. 2012), the power of correlation analyses is generally low and the multi-year census interval requires an integration of yearly climate parameters over the census interval. Tropical dendrochronology (tree-ring analysis) can provide long-term, high-resolution tropical tree growth data to complement plot-based repeated diameter measurements (Worbes 1995; Zuidema et al. 2013). Tropical tree species that form reliable annual growth rings provide annual-resolution growth data at multi-decadal to centennial scales, which enhance the detectability of climatic influences on growth variation in tropical trees (Zuidema et al. 2012). Multi-species tree-ring studies on climate–growth relationships of broad-leaved trees from moist lowland tropical forests are rare, but studies in the Amazon (Dünisch et al. 2003; Brienen and Zuidema 2005) and West Africa (Schöngart et al. 2006) have shown that temporal variation in growth was positively correlated with total annual precipitation. In lowland tropical forests in Southeast Asia, analysis of the relationship between climate and ring width has mainly focused on teak (Tectona grandis) (Pumijumnong et al. 1995; Buckley et al. 2007), and only a few examples of other species exist (e.g., Zuidema et al. 2011). Besides the generally low representation of lowland moist tropical forest trees species in climate–growth studies, the focus has traditionally been on precipitation correlations (Jacoby 1989; Rozendaal and Zuidema 2011; Pumijumnong 2012), and effects of temperature anomalies on annual growth variability were often not evaluated (Dünisch et al. 2003; Brienen and Zuidema 2005; Schöngart et al. 2006) or determined non-significant (Couralet et al. 2010). However, whereas there is large uncertainty regarding predicted rainfall changes for the tropics, a clear warming trend across most of the tropics is undisputed (IPCC 2007; Wright et al. 2009). Here, we use tree-ring analyses to evaluate tree growth sensitivity to climatic variation in Southeast Asia. We took tree ring samples from over 450 individuals belonging to five species known to form annual rings (Baker and Bunyavejchewin 2006). These species represent three different families, vary in leaf phenology, and represent several ecological guilds. The availability of >60 years of high quality climate data from a nearby meteorological station allowed us to address questions and hypotheses on the relationship
13
between climate variability and tree growth. Specifically, we addressed the following questions. (1) Is tree growth correlated with minimum and maximum temperature? And (2) is tree growth correlated with precipitation? Furthermore, we used linear mixed-effects models to assess the relative importance of various seasonal climate indices on standardized diameter growth rates.
Materials and methods Study area and species The study area was situated in the Huai Kha Khaeng Wildlife Sanctuary (HKK), Uthai Thani province, western Thailand (15.60°N, 99.20°E), approximately 550 m above sea-level. Climate in Huai Kha Khaeng is strictly seasonal with a marked dry season from November to April (Fig. 1a). Mean annual rainfall in HKK is 1,473 mm and mean annual temperature is 23.5 ºC (Bunyavejchewin et al. 2009). Soils are highly weathered, slightly acidic ultisols, and soil textures are sandy loam at the surface and sandy clay-loam in the subsurface horizons (Bunyavejchewin et al. 2009). The vegetation in the area is classified as seasonal dry evergreen and mixed deciduous forest (Bunyavejchewin et al. 2009). Canopy height in the forest is around 30 m, with occasional emergent trees reaching 50 m. Members of the family Dipterocarpaceae dominate the area in total basal area; other well-represented families include Annonaceae, Euphorbiaceae, and Meliaceae (Bunyavejchewin et al. 2001). We sampled five tree species: Afzelia xylocarpa (Kurz) Craib (Fabaceae), Chukrasia tabularis A. Juss. (Meliaceae), Melia azedarach L. (Meliaceae), Neolitsea obtusifolia Merr. (Lauraceae), and Toona ciliata M. Roem. (Meliaceae). See Table 1 for a summary of the species’ characteristics. All five species were known to form annual rings following a cambial wounding experiment over the period 1988–1998 (Baker et al. 2005). Afzelia, Melia, and Toona have a distinctly deciduous leaf phenology, whereas Chukrasia is classified as brevi-deciduous and Neolitsea is evergreen (Williams et al. 2008). All five species are canopy trees, reaching maximum heights of 30–45 m. Sampling and measurements Wood samples for tree-ring analysis were collected from 459 trees during the period between December 2010 and December 2011. All samples were collected within a ~300ha area of mixed deciduous and seasonal dry evergreen forest. Samples from the locally more abundant species, Neolitsea and Chukrasia, were mainly collected following a clustered sampling design. These trees were sampled
Oecologia Nakhon Sawan (35 m) 1951−2010
28.6C
1147 mm 300
(a) 50
100
40
80
30
60
20
40
18.5 10
20
0
0 J
35
30
F
M
A
M
J
J
A
S
O
N
D
(b)
Precipitation (mm)
Temperature ° C
38.0
2000
Tmax (0.011**)
1500 Rainfall 1000
25 500
Tmin (0.025***) 20
1920
1940
1960
1980
2000
0
Year
Fig. 1 a Climate diagram for the Nakhon Sawan meteorological station, ~100 km east of the study site. b Annual precipitation and temperature observations from the Nakhon Sawan meteorological station. Upper line (Tmax, filled circles) represents the mean daily maximum temperature, middle line rainfall (triangles) and lower line (Tmin, open circles) is the mean daily minimum temperature. Linear regression models were fit to the temperature data and regression coefficients are indicated (*,**,*** for P 5 cm dbh, irrespective of, for example, canopy position. At a height of approximately 1 m on the stem, we manually extracted wood cores with a 5.0-mm-diameter Suunto (Vantaa, Finland) or a 5.15-mm-diameter Haglöf (Långsele, Sweden) increment borer. Depending on the diameter of the tree, we used borers with lengths varying between 40 and 70 cm. Two cores were taken from trees 60 %) from their respective species-specific chronologies (Table 2). Because of high dating uncertainty remaining after attempting to cross-date the Neolitsea ring-width series, we excluded this species from all further analyses. For the other four species, a species-specific chronology was produced (Fig. 2e–h). Of the total sample size, the proportion of trees included in the chronology was 38 % for Afzelia, 27 % for Chukrasia,
Tree ring data quality was checked by visually cross-dating tree-ring series in WinDENDRO. For trees sampled during the growing season of 2011, this year was excluded from analysis because this ring did not represent a full growing season. After visually cross-dating the tree-ring series, we checked for dating errors using the computer program COFECHA (Holmes 1983). This iterative process of crossdating greatly reduces the number of false and missing rings, both of which are known to occur in tropical species (Worbes 1995). Ring-width series that correlated poorly with the master chronology—for example, due to prolonged growth suppressions—were removed from the dataset prior to chronology development (Pederson et al. 2004). We used the dendrochronology program library in R (dplR; Bunn 2008) to produce species-specific chronologies from the previously selected tree-ring series. Ring-width indices were obtained by detrending the raw ring-width series using a 20-year cubic spline. A 20-year cubic spline was chosen because it showed the best result in removing
13
Oecologia Table 2 Descriptive statistics of the ring-width series Species
n sampled (trees/radii)
n chronology (trees/radii)
Time span
n years
r
ms
Rbar.wt
Rbar.bt
EPS
Afzelia
100/341
38/133
1976–2011
36
0.38
0.42
0.45
0.13
0.90
Chukrasia
104/330
28/70
1982–2010
29
0.46
0.57
0.46
0.18
0.88
Melia
90/330
71/252
1970–2011
42
0.48
0.42
0.51
0.20
0.96
Toona
61/220
46/168
1950–2011
62
0.50
0.65
0.64
0.26
0.95
All the statistics displayed concern only those series that were used for the chronology production r mean series intercorrelation of every series with the master chronology as produced by the program COFECHA (Holmes 1983), ms mean sensitivity, which is a measurement of the year-to-year variability in tree-ring, width as produced by the program COFECHA (Holmes 1983), Rbar. wt mean of the correlations between series from the same tree, Rbar.bt mean interseries correlation between all series from different trees, EPS expressed population signal
89 % for Melia, and 79 % for Toona (see Fig. S2 for diameter distributions of trees included in the chronologies). In Afzelia and Chukrasia, false, wedging, and generally indistinct rings were frequently observed, especially in periods when growth was suppressed, resulting in higher rejection rates. The resulting chronologies were cut off when the running expressed population signal (EPS) was
