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Home , Birch, Kamchatka (river), Larch, Picea jezoensis, Subarctic climate

Article Response of and across an Elevational Transect and Hemisphere-Wide Comparisons, ,

Clara Deck 1,*, Gregory Wiles 1,2, Sarah Frederick 1, Vladimir Matsovsky 3, Tatiana Kuderina 3, Rosanna D’Arrigo 2, Olga Solomina 2,3 and Nicholas Wiesenberg 1

1 Department of Geology, The College of Wooster, Wooster, OH 44691, USA; [email protected] (G.W.); [email protected] (S.F.); [email protected] (N.W.) 2 Lamont-Doherty Ring Lab, Columbia University, Palisades, NY 10964, USA; [email protected] (R.D.); [email protected] (O.S.) 3 Institute of Geography, Russian Academy of Sciences, Moscow, 119991, ; [email protected] (V.M.); [email protected] (T.K.) * Correspondence: [email protected]; Tel.: +1-(708)-207-5038

Academic Editor: Timothy A. Martin Received: 14 July 2017; Accepted: 21 August 2017; Published: 27 August 2017

Abstract: Kamchatka’s forests span across the peninsula’s diverse topography and provide a wide range of physiographic and elevational settings that can be used to investigate how forests are responding to climate change and to anticipate future response. Birch ( Cham.) and larch ( (Rupr.) Kuzen) were sampled at eight new sites and together with previous collections were compared with monthly temperature and records to identify their climate response. Comparisons show that tree-ring widths in both species are primarily influenced by May through August temperatures of the current growth , and that there is a general increase in temperature sensitivity with altitude. The ring-width data for each species were also combined into regional chronologies. The resulting composite larch chronology shows a strong resemblance to a Northern Hemisphere (NH) tree-ring based temperature reconstruction with the larch series tracking NH temperatures closely through the past 300 . The composite birch ring-width series more closely reflects the Pacific regional coastal late temperatures. These new data improve our understanding of the response of forests to climate and show the low frequency warming noted in other, more continental records from high latitudes of the Northern Hemisphere. Also evident in the ring-width record is that the larch and birch forests continue to track the strong warming of interior Kamchatka.

Keywords: dendrochronology; dendroclimatology; Kamchatka; tree rings; Betula ermanii; Larix gmelinii

1. Introduction The future of the forests in and eastern with a changing climate remains uncertain. Some modeling studies suggest an increase in productivity in the coming decades with a warming climate [1], whereas other models point to a large-scale change in the composition of the ecosystems from coniferous to and [2]. Given that larch (Larix spp.) forests are important and extensive global coniferous forests, and birch (Betula spp.) are significant along the eastern margin of Asia and in the Northern Hemisphere as a whole, we have undertaken a tree-ring investigation of the climatic controls in Kamchatka of past and recent changes in tree growth of these important species. Since larch forests in Siberia and the Far East are being managed in different way, they are susceptible to illegal logging and fire, and are underlain by discontinuous melting

Forests 2017, 8, 315; doi:10.3390/f8090315 www.mdpi.com/journal/forests Forests 2017, 8, 315 2 of 11 northForests of 57 2017 degrees,, 8, 315 the future of the forests remains uncertain [1,2]. Tree rings can be used to assess past changes in forest productivity and climate, and also can be used to assess recent changes in they are susceptible to illegal logging and fire, and are underlain by discontinuous melting forest growth with changing climate conditions. Interior regions of Kamchatka can be considered a permafrost north of 57 degrees, the future of the forests remains uncertain [1,2]. Tree rings can be microcosmused to of assess the larger past changes Siberian in forest forest ecosystem,productivity although and climate, with and heavier also can precipitation be used to assess due torecent moist air from thechanges Pacific in forest Ocean growth and the with Sea changing of Okhotsk climate and conditions. a milder Interior regions climate of than Kamchatka interior can Siberia be [3]. The interiorconsidered Kamchatkan a microcosm larch of the forest larger can Siberian also forest serve ecosystem, as a case studyalthough for with general heavier forest precipitation change with increaseddue to warming. moist air Kamchatkanfrom the Pacific forests Ocean have and the undergone Sea of Okhotsk logging and and a milder disturbance, subarctic but climate they than are more pristineinterior than Siberia many other [3]. The boreal interior forests Kamchatkan and thus larch provide forest a good can also study serve site as to a drawcase study distinctions for general between moreforest human change impacted with areas increased [4]. warming. Kamchatkan forests have undergone logging and Thedisturbance, Kamchatka but they Peninsula are more (Russian pristine than Federation) many other is boreal located forests in the and western thus provide North a good Pacific, study on the site to draw distinctions between more human impacted areas [4]. eastern margin of Asia where the prevailing climate is determined in large part by its complex The Kamchatka Peninsula (Russian Federation) is located in the western North Pacific, on the geography,eastern with margin a continental of Asia where interior the prevailing valley surrounded climate is bydetermined the cool andin large more part maritime by its complex ocean-facing flanksgeography, of the Sredinny with a continental and Eastern interior Ranges valley (Figure surrounded1). The Northby the cool Pacific and liesmore to maritime the east ocean of the‐facing peninsula and theflanks Sea of of the Okhotsk Sredinny to theand west.Eastern Generally, Ranges (Figure it is considered 1). The North to Pacific have a lies subarctic to the east climate of the with peninsula an annual precipitationand the Sea between of Okhotsk 600–1100 to the mm west. in theGenerally, high mountains it is considered and upto have to 2500 a subarctic mm along climate the coasts.with an Mean annualannual temperature precipitation is about between 0 ◦C 600–1100 in the coastal mm in south the high at the mountains capital Petropavlovsk-Kamchatsky and up to 2500 mm along the and in the interiorcoasts. theMean rural annual locality temperature of Klyuchi is about to the 0 °C north in the experiences coastal south an at extreme the capital range Petropavlovsk of temperatures‐ from 19Kamchatsky◦C in summer and in to the− interior41 ◦C in the . rural locality The climate of Klyuchi of the to the region north is experiences sensitive toan the extreme intensity range of the of temperatures from 19 °C in summer to −41 °C in winter. The climate of the region is sensitive to summer North Pacific High and the winter, Aleutian Low. In winter the brings cold, dry the intensity of the summer North Pacific High and the winter, Aleutian Low. In winter the Siberian weatherHigh to brings the region cold, [dry5]. weather Early summer to the region sea ice [5]. in Early the Sea summer of Okhotsk sea ice in brings the Sea cold of airOkhotsk to the brings peninsula and competescold air to with the thepeninsula summer and monsoonal competes with influence the summer and the monsoonal Pacific subtropical influence and high, the which Pacific brings warm,subtropical moist air high, masses which in from brings the warm, south moist and air east. masses in from the south and east.

159° E

Sea of Okhot sk

UstUst‐‐KamchatskyKamchatsky

Esso

Paci f i c Ocean 54° N

Figure 1. Locations of tree‐ring chronology sites on the Kamchatka Peninsula, Russia. Also shown are Figure 1. Locations of tree-ring chronology sites on the Kamchatka Peninsula, Russia. Also shown are Klyuchi, Ust Kamchatsky and Petropavlovsk‐Kamchtasky meteorological stations that were used in Klyuchi, Ust Kamchatsky and Petropavlovsk-Kamchtasky meteorological stations that were used comparisons with ring‐width series. NR: North Road; LTB: Lower Tobalchik Volcano; TBT: Tobalchik in comparisons with ring-width series. NR: North Road; LTB: Lower Tobalchik Volcano; TBT: Tobalchik Volcano; MTB: Mid-Tobalchik Volcano; MK: Malkee; UG: Garchche Sopa; VV: Viluchi Volcano; PRT: Paratunka. 2 Forests 2017, 8, 315 3 of 11

The two dominant mountain ranges, 29 active volcanoes and over 300 extinct volcanoes (Figure1)[ 6] provide a complex terrain in which grow in a wide range of settings and the differences in tree growth with altitude and location can be investigated. This information is important in identifying how trees are responding to changes in climate, and to improve sampling strategies for optimal climate sensitivity for dendroclimatology. Recently, there has been increased attention focused on the dendroclimatic potential of tree species on the Kamchatka Peninsula in the Russian Far East [3]. The region has experienced almost 2 ◦C warming of annual temperatures over the last 100 years. Several tree-ring chronologies have been generated on Island, and the Asian mainland during a 2013–2014 field campaign [7,8]. These new data build on previous tree-ring based temperature reconstructions for the Peninsula [9–11]. The bulk of the previous work has been conducted with larch (Larix gmelinii (Rupr.) Kuzen) due to its long-life span and wide distribution across Kamchatka, especially in the central lowlands where it can be found at altitudes as high as 1000 m in the bordering mountains [3,12]. This interior forest is often referred to as a Island, which occurs with Japanese white birch ( Sukaczev), poplar ( tremula L.), Manchurian (Alnus hirsute Turcz), larch (Larix gmelinii (Rupr.) Kuzen, syn. Larix cajanderi Mayr.), Siberian dwarf (Pinus pumila Pall.) and Ajan (Picea ajanensis Fisch., syn. Picea jezoensis Sieb. et Zucc.) [13]. Of Kamchatka’s coniferous forests, only 2.1 percent (350,000 ha) remain undisturbed by logging or fire [14] and assembling tree-ring chronologies from undisturbed old-growth sites is a challenge. Gostev et al. [9] conducted one of the first dendroclimatic studies for Kamchatka, and generated a larch based tree-ring reconstruction that explained 38% of the variance in May-June temperatures back to AD 1670. Other studies have also reported that larch ring widths are positively related to early summer temperature [12,15,16] and that in general larch growth has been responding favorably (increased growth) to recent warming [16]. In addition, interior Siberian studies have found that larch in the northern region has responded positively to summer warming [17,18], but that there is a negative tree growth response with environmental warming in continental dry regions [19]. Stone birch (Betula ermanii Cham.) is the most extensive tree found in lower elevation forests, and its abundance is a distinctive feature of Kamchatka’s [3,4]. These trees dominate the lowlands and middle zone of the peninsula’s mountainous regions and coastal margins [14]. Due to complex ring boundaries and its shorter life span, birch has not been used as extensively in tree-ring research [13]. However, some studies have noted that this widespread species shows promise for dendroclimatic studies [9,11–13]. In particular, Sano et al. [10] developed a 247-year ring-width chronology at Paratunka (Figure1) for Betula ermanii. They determined that ring width was primarily controlled by July–August temperature and developed a well-verified temperature reconstruction using meteorological records from Petropavlovsk-Kamchatsky. Herein, we determine how birch and larch trees respond to climate along elevational gradients of the Kamchatka Peninsula, and compare the climate response of the two species. We now have ring-width data from an additional eight new, well replicated sites in two areas of Kamchatka (Figure1), the northeast region, near Klyuchi, and in the south, near Petropavlovsk-Kamchatsky. Besides examining the elevational climate response, we study the low frequency response of the larch series as a record of regional summer temperature and compare it with a Northern Hemisphere tree-ring based temperature reconstruction [20].

2. Materials and Methods Tree-ring samples of birch and larch were collected from nine sites during the summer of 2014 (Table1). Five sites are located in the northeastern region of the peninsula, near Klyuchi, and four birch sites are from the Petropavlovsk area in the southeast (Figure1). Eight of the chronologies are unpublished and one, the Paratunka birch site (PRT; Figure1) was sampled previously [ 11] and has been updated here (Table1). Forests 2017, 8, 315 4 of 11

Table 1. Chronology descriptions.

Altitude Number of Site Location Species Period of Record (m) Cores/Trees 56.52759◦ N, 54 km from Ust (50 km) 112 Betula ermanii 1814–2014 (200 years) 21/14 161.97069◦ E 56.70416◦ N, North Road (NR) 95–150 Betula ermanii 1823–2014 (191 years) 21/16 160.95035◦ E 55.97215◦ N, Lower Tobalchik Volcano (LTB) 486 Larix gmelinii 1675–2014 (339 years) 34/17 160.13524◦ E 55.94931◦ N, Mid-Tobalchik Volcano (MTB) 743 Larix gmelinii 1674–2014 (340 years) 41/20 160.19910◦ E 55.9567◦ N, Tobalchik Volcano (TBT) 944 Larix gmelinii 1653–2014 (361 years) 63/31 160.23132◦ E 52.8243◦ N, Garchche Sopa (UG) 68 Betula ermanii 1763–2014 (252 years) 28/17 158.1664◦ E 52.68926◦ N, Viluchi Volcano (VV) 410 Betula ermanii 1792–2014 (223 years) 22/13 158.16354◦ E 53.32233◦ N, Malkee (MK) 278 Betula ermanii 1841–2014 (173 years) 23/13 157.54709◦ E 52.50◦ N, Paratunka * (PRT) 864 Betula ermanii 1755–2014 (259 years) 73/41 158.10◦ E Tree-ring width chronologies from this study; * Chronology PRT was updated from Sano et al. [11] using collections in this study.

Two to three cores were extracted from each tree for at least twenty trees per stand (Table1). Cores were sanded and prepared for tree-ring analysis. Rings were counted, cross dated and measured to a precision of ±0.001 mm using a Velmex measuring system ( Velmex, Inc., Bloomfield, NY, USA) and the program Measure J2X (Version 4, VoorTech Consulting, Holderness, NH, USA). We used the COFECHA computer program [21] to verify cross dating and as a to assess the quality of the dating [22]. Individual ring-width series were standardized using ARSTAN software, initially using a negative exponential curve fit for the individual series [23]. The resulting ring-width chronologies were then correlated with mean monthly temperature and precipitation data from weather stations in Klyuchi and Petropavlovsk-Kamchatsky. These station data were obtained from the KNMI Climate Explorer [24,25]. The Klyuchi mean temperature record spans the years 1908–2015, with incomplete data from 1991 to 2004. These missing values were supplemented with other data [26]. There were also missing years in the Petropavlovsk temperature and precipitation records, however, no suitable supplemental data was available. Our tree-ring sites are located 40–70 km from the meteorological stations and reflect similar environments, elevations and vegetation, and thus are appropriate for our comparisons. Two composite chronologies, one for larch and one for birch, were combined from our new sites together with those of the previous studies within each region (the south for birch and the interior for larch). The composite larch series were standardized using signal-free Regional Curve Standardization (RCS) [27,28]. This technique aligns the tree ring width series by their biological age, and then fits a regional curve to the composite series that is used in standardization [29]. We used signal-free RCS because of the relatively large sample size of the combined ring-width series and the relatively uniform negative exponential fit for detrending. The resulting chronology maintains low frequency variability [29] and the signal-free aspect also minimizes problems associated with RCS performed on contemporarily growing trees [28]. The combined 331 ring width series for larch date back to the late-, which consists of our new collections from the Tobalchik Volcano (TBT Figure2) with those of Gostev et al. [ 9], Sano et al. [16] and Solomina et al. [12]. For the birch collection, we chose conservative detrending using negative exponential curve fits in standardization using ARSTAN [20]. The relatively smaller sample size (n = 113) compared with larch (n = 331) and the shorter series length and relatively weaker climate signal and less uniform growth curves did not merit the use of RCS in this case. The composite of 113 birch series extends to the mid-18th century and includes our new records and Forests 2017, 8, 315 ForestsForests2017 2017, 8,, 315 8, 315 5 of 11 signal and less uniform growth curves did not merit the use of RCS in this case. The composite of 113 signalbirch series and less extends uniform to thegrowth mid ‐curves18th century did not and merit includes the use our of RCS new in records this case. and The those composite of Sano of et 113 al. those of Sano et al. [11] (Table1, Figures2 and3). For both composite series, we used the expressed birch[11] (Table series 1,extends Figure to2 andthe midFigure‐18th 3). century For both and composite includes series,our new we records used the and expressed those of populationSano et al. population[11]signal (Table (EPS) signal 1, [30,31] Figure (EPS) to 2 assessand [30, 31Figure the] to signal assess 3). For strength the both signal composite of the strength chronology series, of thewe back used chronology in timethe expressed and back to indicate in population time when and to indicatesignala critical when (EPS) EPS a[30,31] of critical 0.85 to is EPSassess exceeded of the 0.85 signal(Figure is exceeded strength 2). (Figure of the chronology2). back in time and to indicate when a critical EPS of 0.85 is exceeded (Figure 2).

FigureFigure 2. 2.Left, Left, larch larch chronologies starting starting from from 1800, 1800, ordered ordered with withrespect respect to increasing to increasing altitude altitude(over Figure 2. Left, larch chronologies starting from 1800, ordered with respect to increasing altitude (over (overa 500 a 500 meter meter difference) difference) from from bottom bottom to top. to top. EPS EPS statistic statistic is greater is greater than than 0.85 0.85 for for the the entire entire interval interval ashown. 500 meter Thick difference) line shows from values bottom smoothed to top. with EPS a 6% statistic weighted is greater curve. thanRight, 0.85 correlations for the entire with Klyuchiinterval shown. Thick line shows values smoothed with a 6% weighted curve. Right, correlations with Klyuchi shown.mean temperature Thick line shows for a values 19 month smoothed dendroclimatic with a 6% weighted year, March–December curve. Right, correlations of the previous with Klyuchi year mean temperature for a 19 month dendroclimatic year, March–December of the previous year through meanthrough temperature September offor the a current19 month growth dendroclimatic year. ° denotes year, a correlation March–December significant of atthe a 90%previous confidence year September of the current growth year. ◦ denotes a correlation significant at a 90% confidence level, throughlevel, whereas September * a correlation of the current significant growth at year. the 99% ° denotes confidence a correlation level. significant at a 90% confidence whereas * a correlation significant at the 99% confidence level. level, whereas * a correlation significant at the 99% confidence level.

Figure 3. Left, Birch chronologies starting from 1800, ordered in increasing altitude from bottom to Figuretop Label 3. Left, elevations. Birch chronologies Red vertical starting lines indicate from 1800, when ordered EPS exceeds in increasing 0.85. Thick altitude line from shows bottom values to Figure 3. Left, Birch chronologies starting from 1800, ordered in increasing altitude from bottom to top topsmoothed Label elevations.with a 6% Redweighted vertical curve. lines Right,indicate correlations when EPS with exceeds Petropavlovsk 0.85. Thick andline Klyuchishows values mean Label elevations. Red vertical lines indicate when EPS exceeds 0.85. Thick line shows values smoothed smoothedtemperature with of 19a 6%months, weighted from curve.prior March–DecemberRight, correlations through with Petropavlovsk September of andthe currentKlyuchi growth mean with a 6% weighted curve. Right, correlations with Petropavlovsk and Klyuchi mean temperature of temperatureyear are shown of 19on months,the right. from ° denotes prior March–Decembera correlation significant through at aSeptember 90% confidence of the level,current whereas growth * 19 months, from prior March–December through September of the current growth year are shown on yeardenotes are ashown correlation on the significant right. ° denotes at the 99%a correlation confidence significant level. at a 90% confidence level, whereas * ◦ thedenotes right. adenotes correlation a correlation significant significant at the 99% atconfidence a 90% confidence level. level, whereas * denotes a correlation significant at the 99% confidence level.

5 5 ForestsForests2017 2017, 8, 315, 8, 315 6 of 11

3. Results 3. Results 3.1. Stand Level Climate Signal 3.1. Stand Level Climate Signal For the individual ring‐width chronology, a strong positive correlation with mean monthly temperaturesFor the individual during summer ring-width (May chronology, or June through a strong August) positive of the correlationcurrent growth with year mean is observed monthly temperaturesin all the chronologies during summer of both (May species or June (Figure through 2 and August) Figure of3). the The current three new growth larch year records is observed from an in all theelevational chronologies transect of bothon the species Tobalchik (Figures Volcano2 and show3). The a generally three new improved larch records correlation from anwith elevational summer transecttemperature on the Tobalchik with increasing Volcano elevation show a (Figure generally 2). improvedLower and correlation middle elevation with summer UG and temperature MK birch withchronologies increasing elevationcorrelate (Figurenegatively2). Lowerwith May and temperature middle elevation (although UG andnot significant MK birch chronologiesat the 90% correlateconfidence negatively level; Figure with May3). The temperature northeastern (although birch, 50 km not and significant NR sites at (Table the 90%1), have confidence a consistent level; Figurepositive3). The correlation northeastern with birch, July 50temperature. km and NR In sites both (Table regions,1), have lower a consistent elevation positivebirch chronologies correlation withgenerally July temperature. show a weaker In both correlation regions, to lower temperatures elevation than birch the chronologies larch, as has generally been found show elsewhere a weaker correlation(Table 1, to [11]). temperatures than the larch, as has been found elsewhere (Table1,[11]). CorrelationsCorrelations with with monthly monthly precipitation precipitation records records are are not not consistentconsistent at at the the northern northern sites sites for for either either larchlarch or birch. or birch. However, However, in in the the south, south, positive positive correlation correlation withwith March and and May May precipitation precipitation were were foundfound at all at fourall four birch birch sites sites (PRT, (PRT, VV, VV, UG UG and and MK; MK; Figure Figure4 ).4). In In general, general, thethe higher elevation elevation birch birch sites show a stronger relationship with spring precipitation than those at lower elevations. sites show a stronger relationship with spring precipitation than those at lower elevations.

FigureFigure 4. Correlations 4. Correlations of of the the four four southern southern Kamchatka Kamchatka birchbirch ringring width chronologies chronologies with with monthly monthly precipitationprecipitation from from Petropavlovsk-Kamchatsky. Petropavlovsk‐Kamchatsky. The The circles circles denote denote those months that that are are significant significant at at the 90%the 90% confidence confidence level. level. In In all all cases, cases, the the period period of of overlap overlap is is 1941–20051941–2005 common era era (CE). (CE).

To further analyze the temperature sensitivity and build on previous temperature To further analyze the temperature sensitivity and build on previous temperature reconstructions, reconstructions, we assembled the larch and birch series from our new collections with those of past we assembled the larch and birch series from our new collections with those of past studies for studies for Kamchatka. For the Northeast sector, the 331 ring‐width based larch chronology spans Kamchatka. For the Northeast sector, the 331 ring-width based larch chronology spans 1580 to 2014; 1580 to 2014; the series has an EPS of 0.85 beginning in 1650 CE. This larch dataset is remarkably the seriescoherent has given an EPS the of diverse 0.85 beginning topography in across 1650 CE. Kamchatka, This larch with dataset a mean is remarkably series intercorrelation coherent given of 0.62 the diverseand topographya mean sensitivity across of Kamchatka, 0.32 (a measure with of a meaninterannual series intercorrelationvariability) (Figure of 0.625a). For and the a mean birch, sensitivity the 113 of 0.32ring (a‐width measure series of from interannual the four variability)southern sites (Figure (including5a). For the the Paratunka birch, the site 113 [10]) ring-width were combined. series The from the fourseries southern intercorrelation sites (including is 0.53 with the a Paratunka mean sensitivity site [10 of]) 0.35 were over combined. the 1755–2014 The series CE common intercorrelation interval is 0.53(Figure with a 6a). mean sensitivity of 0.35 over the 1755–2014 CE common interval (Figure6a).

6 Forests 2017, 8, 315 7 of 11 Forests 2017, 8, 315

(a)

R

()

R

(c)

Figure 5. (a) Larch composite chronology (, blue thick line shows values smoothed with a 6% Figure 5. (a) Larch composite chronology (green, blue thick line shows values smoothed with a 6% weighted curve with Kaleidagraph) standardized using signal free regional curve standardization weighted curve with Kaleidagraph) standardized using signal free regional curve standardization (RCS) and changing sample size over time (lower blue curve); (b) Larch composite chronology (green) (RCS) and changing sample size over time (lower blue curve); (b) Larch composite chronology (green) compared with NTREND series (blue), which is composed of 54 Northern Hemispheric tree ring compared with NTREND series (blue), which is composed of 54 Northern Hemispheric tree ring chronologies [20]. The correlation of larch with NTREND is 0.41 for 1670–2014. Major NH volcanic chronologies [20]. The correlation of larch with NTREND is 0.41 for 1670–2014. Major NH volcanic events are labeled on the NH record and note that the NH series deviates from the Kamchatka series; events are labeled on the NH record and note that the NH series deviates from the Kamchatka series; (c) Comparison of the larch ring‐width series (green) with the Northern Hemisphere meteorological (c)summer Comparison temperatures of the larch [20]. ring-width The two NH series series (green) are coherent with the with Northern the larch Hemisphere ring‐width meteorological series with summerrespect temperatures to the low frequency [20]. The variability. two NH The series records are do coherent diverge within the thedecades larch of ring-width the 1950s and series 1960s, with respect to the low frequency variability. The records do diverge in the decades of the 1950s and 1960s, possibly due to wide scale disturbance and logging at the varied sites and a growth release during this time. 7 Forests 2017, 8, 315

possibly due to wide scale disturbance and logging at the varied sites and a growth release during this time.

3.2. Regional and Hemispheric Climate Signals To further explore the regional climatic significance and dendroclimatic potential for forests in Kamchatka, we compared our regional larch RCS series and birch ring‐widths with monthly climate records and with a tree‐ring based Northern Hemisphere summer temperature reconstruction (NTREND) [20]. The larch composite, which is strongly correlated to local (Petropavlovsk‐ Kamchatsky) May–August temperatures over the 1909–2014 CE interval (R = 0.46; N = 105 years; not shown) is also strongly correlated with the May–August Northern Hemisphere instrumental temperature record ([20]; R = 0.56; N = 164 years; Figure 5c). Comparison of the larch series with the tree‐ring based NTREND [20] reconstructed temperature series shows good agreement (R = 0.43; 1670–2011CE; N = 344 years; Figure 5a and Figure 5b) with the Kamchatka series, capturing the broad‐scale features of low frequency summer warming for the Northern Hemisphere. Taken together, these results indicate that the Kamchatka larch is reflecting larger scale hemispheric temperature trends and is tracking the overall increase in summer temperature in the region that is well documented in the instrumental records and changes in the cryosphere [9]. Disagreement with the NTREND series primarily occurs during multi‐year cooling forced by large‐scale volcanic events (Figure 5b, [32]) that do not appear to have influenced summer temperatures in the interior of Kamchatka, but are well‐expressed in the NTREND record (i.e., 1697, 1783, 1810–1816 and 1835 [32]; Figure 5b). The continual increase in ring‐width in recent decades is commensurate with warming in the Northern Hemisphere and in Kamchatka ([9], Figure 5) and is not noticeably diverging from the warm conditions. The temperature‐sensitive composite birch chronology (Figure 6a) is also compared here with the coastal stations at nearby Petropavlovsk and Ust‐Kamchatsky 450 km north of Petropavlovsk on the Pacific coast. A correlation of 0.48 with July/August temperatures (n = 59 years of observations from Ust‐Kamchatky) is the strongest regional signal detected in the birch. Like the larch, the birch composite records the recent low frequency warming as seen in the more interior areas of Kamchatka and the NTREND series. Although the more coastal summer signal in the birch is not characterized by as strong of a low frequency rise as birch, the decades since the mid‐1980s suggest the strongest summer warming for the past 200 years (Figure 6a). As noted above, some of the individual birch chronologies show a possible decline in ring‐widths (Figure 3), however, the composite overall shows Forests 2017, 8, 315 8 of 11 this sustained increase.

Forests 2017, 8, 315 (a)

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FigureFigure 6. (6.a) ( Compositea) Composite Kamchatka Kamchatka birch birch ring-width ring‐width chronology. Blue Blue line line shows shows changing changing sample sample size; (b) Kamchatka birch chronology (green) plotted with July/August average temperatures from size; (b) Kamchatka birch chronology (green) plotted with July/August average temperatures from Ust‐Kamchatsky (R = 0.46; p > 0.001). Ust-Kamchatsky (R = 0.46; p > 0.001). 4. Discussion 3.2. Regional and Hemispheric Climate Signals All the tree‐ring chronologies developed herein show positive correlations with current mean summerTo further temperatures explore the (Figures regional 2 and climatic 3), indicating significance that temperatures and dendroclimatic during this potential for (May– forests in Kamchatka,August) have we the compared strongest ourinfluence regional on radial larch RCSgrowth series of birch and birchand larch ring-widths trees in withKamchatka. monthly climateGenerally, records correlations and with aof tree-ring mean monthly based Northerntemperatures Hemisphere increase with summer increasing temperature altitude reconstruction in both the (NTREND)larch and [ 20birch]. The series. larch These composite, findings which also isfollow strongly the trends correlated found to localin the (Petropavlovsk-Kamchatsky) northern interior Siberian May–Augustlarch studies temperatures that overincreased the 1909–2014 tree growth CE interval with warming (R = 0.46; summerN = 105 years;temperatures not shown) [17,18]. is also stronglyPrecipitation correlated is not with a significant the May–August influence Northern on the Hemispherenorthern study instrumental sites, but has temperature significant record positive ([20 ]; R =correlations 0.56; N = 164 in March years; Figureand May5c). of the current growth year for southern sites. ComparisonThe negative of thecorrelation larch series of spring with thetemperature tree-ring with based growth NTREND at the [20 lower] reconstructed elevation sites temperature in the seriessouthern shows birch good series agreement (UG, MK) (R = suggests 0.43; 1670–2011CE; that warmer NMarch–May= 344 years; temperatures Figure5a,b) may with be the unfavorable Kamchatka series,to growth capturing as May the and broad-scale March are features the driest of months low frequency in southern summer Kamchatka warming and over for the the past Northern 100 years, May has also warmed over 3.0 °C. This tendency may eventually negatively impact growth if Hemisphere. Taken together, these results indicate that the Kamchatka larch is reflecting larger continue to warm. Sano et al. [12] noted that their inland and coastal tree‐ring scale hemispheric temperature trends and is tracking the overall increase in summer temperature in reconstructions were out of phase with one another. We show that in more recent decades, our the region that is well documented in the instrumental records and changes in the cryosphere [9]. updated composite birch series is in step with birch growth and warming although further Disagreement with the NTREND series primarily occurs during multi-year cooling forced by investigation is needed (Figure 6). large-scaleFor volcanic the northeastern events (Figure larch, the5b, highest [ 32]) that elevation do not chronology, appear to have TBT, influenced is less strongly summer correlated temperatures with in theMay interior temperature of Kamchatka, than the but lower are well-expressedelevation MTB insite the (Figure NTREND 2). This record pattern (i.e., 1697,is also 1783, seen 1810–1816 in the andsouthern 1835 [32 region]; Figure where5b). The mean continual temperature increase at the in VV ring-width birch site in has recent the decadesstrongest is correlation, commensurate instead with warmingof the highest in the Northern elevation Hemisphereand better replicated and in Kamchatka PRT site in each ([9], Figuresummer5) month and is not(Figure noticeably 3). This divergingfinding fromsuggests the warm that conditions. there may be an elevation where growth response to temperature is optimized somewhere between these elevations. Additional factors that could influence the varying climate response include differences in geography and climate at our sites compared with meteorological stations. Klyuchi is more inland compared with coastal Petropavlovsk‐Kamchatsky and Ust‐ Kamchatsy (Figure 1), where the Pacific Ocean has a strong influence on temperature and precipitation. Both sites are at similar elevations with the coastal Petropavlovsk‐Kamchatsky at 84 m and Klyuchi at 29 m a.s.l. The low frequency climate signal in the larch record is broadly similar to that identified for the extratropical Northern Hemisphere (NTREND) [17] except for an interval in the late 1950s and 1960s. A possible explanation for this difference is that some of the series within our composite are from the area around Esso, a region impacted by forest fires in the late 1940s [33,34] and extensive construction of logging roads in the early 1960s. One or both of these factors may have forced a release in tree growth that may explain the disagreement in the larch series and the meteorological data. The larger deviations on the order of a year to several years occur during times when volcanic events [29] have

9 Forests 2017, 8, 315 9 of 11

The temperature-sensitive composite birch chronology (Figure6a) is also compared here with the coastal stations at nearby Petropavlovsk and Ust-Kamchatsky 450 km north of Petropavlovsk on the Pacific coast. A correlation of 0.48 with July/August temperatures (n = 59 years of observations from Ust-Kamchatky) is the strongest regional signal detected in the birch. Like the larch, the birch composite records the recent low frequency warming as seen in the more interior areas of Kamchatka and the NTREND series. Although the more coastal summer signal in the birch is not characterized by as strong of a low frequency rise as birch, the decades since the mid-1980s suggest the strongest summer warming for the past 200 years (Figure6a). As noted above, some of the individual birch chronologies show a possible decline in ring-widths (Figure3), however, the composite overall shows this sustained increase.

4. Discussion All the tree-ring chronologies developed herein show positive correlations with current mean summer temperatures (Figures2 and3), indicating that temperatures during this season (May–August) have the strongest influence on radial growth of birch and larch trees in Kamchatka. Generally, correlations of mean monthly temperatures increase with increasing altitude in both the larch and birch series. These findings also follow the trends found in the northern interior Siberian larch studies that saw increased tree growth with warming summer temperatures [17,18]. Precipitation is not a significant influence on the northern study sites, but has significant positive correlations in March and May of the current growth year for southern sites. The negative correlation of spring temperature with growth at the lower elevation sites in the southern birch series (UG, MK) suggests that warmer March–May temperatures may be unfavorable to growth as May and March are the driest months in southern Kamchatka and over the past 100 years, May has also warmed over 3.0 ◦C. This tendency may eventually negatively impact growth if summers continue to warm. Sano et al. [12] noted that their inland and coastal tree-ring reconstructions were out of phase with one another. We show that in more recent decades, our updated composite birch series is in step with birch growth and warming although further investigation is needed (Figure6). For the northeastern larch, the highest elevation chronology, TBT, is less strongly correlated with May temperature than the lower elevation MTB site (Figure2). This pattern is also seen in the southern region where mean temperature at the VV birch site has the strongest correlation, instead of the highest elevation and better replicated PRT site in each summer month (Figure3). This finding suggests that there may be an elevation where growth response to temperature is optimized somewhere between these elevations. Additional factors that could influence the varying climate response include differences in geography and climate at our sites compared with meteorological stations. Klyuchi is more inland compared with coastal Petropavlovsk-Kamchatsky and Ust-Kamchatsy (Figure1), where the Pacific Ocean has a strong influence on temperature and precipitation. Both sites are at similar elevations with the coastal Petropavlovsk-Kamchatsky at 84 m and Klyuchi at 29 m a.s.l. The low frequency climate signal in the larch record is broadly similar to that identified for the extratropical Northern Hemisphere (NTREND) [17] except for an interval in the late 1950s and 1960s. A possible explanation for this difference is that some of the series within our composite are from the area around Esso, a region impacted by forest fires in the late 1940s [33,34] and extensive construction of logging roads in the early 1960s. One or both of these factors may have forced a release in tree growth that may explain the disagreement in the larch series and the meteorological data. The larger deviations on the order of a year to several years occur during times when volcanic events [29] have forced cooling as exhibited in the NTREND record, but these events are not expressed in our composite larch series. Our updated larch ring-width series together with those from previous studies show that larch forests appear to be maintaining their growth in accordance with the strong climatic warming in the region, at least for the study sites. The birch record shows increased growth in response to the strong summer warming, however, it is unclear of the role that precipitation changes may have in controlling birch growth in southern Kamchatka. Forests 2017, 8, 315 10 of 11

5. Conclusions In summary, trees from both the northeastern and southern regions have comparable responses to temperature. The tree ring chronologies described herein that May–August summer temperatures are the main climatic influence on both birch and larch growth in Kamchatka, and that precipitation is important in March and May (Figure4) for the southern birch chronologies. Sensitivity to climate increases with altitude and reveals a similar pattern to that seen at other northern sites [35] although trees lose their sensitivity at the very highest elevations [36]. In response to strong summer warming, both birch and larch are responding in phase. Despite inconsistencies between the larch composite chronology and the NTREND record, there is a strong low frequency warming signal in the larch series that reflects broad Northern Hemispheric trends. Future compilations of Northern Hemisphere temperature reconstructions of temperature should consider including this Kamchatka series to improve the coverage in the Asian Fareast.

Acknowledgments: This study was supported by NSF-ATM 115430, 1202218 and NSF-AGS-1502186. We thank Amanda Young for valuable feedback in this manuscript. LDEO contribution No. 8139. Author Contributions: G.W., S.F., O.S., V.M. T.K. and R.D. designed and sampled for this study. C.D. and G.W. performed the analysis, and C.D., G.W., R.D. wrote the . Conflicts of Interest: The authors declare no conflict of interest.

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