Here Is One of the More Remarkable Boundary Complexes in Coniferous Growth, Whose Study Might Well Cast New Light on Certain Problems in Plant Physiology

Dendrochronology in Big Bend National Park, Texas

Item Type Article

Authors Schulman, Edmund

Citation Schulman, E. 1952. Dendrochronology in Big Bend National Park, Texas. Tree-Ring Bulletin 18(2-3):18-27.

Publisher Tree-Ring Society

Journal Tree-Ring Bulletin

Download date 29/09/2021 07:01:19

Link to Item http://hdl.handle.net/10150/255375 18 TREE -RING BULLETIN of the northern Rockies in recent years. Particularly hard -hit by low rainfall were some sub -areas in Arizona and New Mexico which have suffered drought with only an occasional wet year since 1920. Since the growth records suggest no strong secular trend in climate during the past millenium, the conclusion is inescapable that a series of generally wet years, as in the past, will again occur in such areas. Though the statistical chance of early occurrence is high, it will be obvious that in the absence of a physical ex- planation for such fluctuations no precise forecast is possible. It is perhaps widely realized, too, that even at best a wet interval can only result in tem- porary alleviation of the increasingly critical problem of water shortage in these regions of rapidly growing population.

DENDROCHRONOLOGY IN BIG BEND NATIONAL PARK, TEXAS EDMUND SCHULMAN Rocky Mountain Douglas -fir (Pseudotsuga taxifolia), an excellent source of climatic chronology throughout its great range southward from middle British Columbia and Jasper National Park in Alberta, is represented by only a few scattered trees in the Chisos Mountains of southwestern Texas. Nevertheless, these trees provide a significant base for estimating the march of winter rainfall and of river flow during the last three hundred years in the Big Bend region of the Rio Grande. Ring analysis suggests also that here is one of the more remarkable boundary complexes in coniferous growth, whose study might well cast new light on certain problems in plant physiology. COLLECTIONS Park headquarters at Chisos Basin, 29° 16' N, 103° 18' W, elev. 5,100 feet, is reached by road south from Marathon, Texas. In late November, 1945, a horseback trip was made to the Boot Spring -Channing Rock area a few miles south of the headquarters in order to sample the groves there.* The sparse stand of Douglas -firs, stunted, slow -growing, and seldom reaching 20 inches in stem diameter, which has developed on the Tertiary lavas in this locality, is truly of an outlier character, some 200 miles s.s.w. of the general limit for this species in the Lincoln National Forest near the New Mexico border. Apparently, the Chisos Mountains, maximum elevation 7,835 feet, reach just high enough to provide the minimum moisture -tem- perature conditions for the presence of Douglas -fir.It is curious that Ari- zona cypress (Cupressus arizonica), usually found on lower, drier sites than Douglas -fir everywhere else within their joint range in the Southwest, here grows interspersed with the latter. "A few canyons of the Chisos Moun- tains are phenomenal in that they harbor trees which are nonexistent in other canyons of the area. "1 *The fine cooperation in the field work of Dr. Ross A. Maxwell, Superintendent, and Mr. Harry Linder, guide, is gratefully acknowledged. Study of the collections beyond the dating stage had to be postponed for some years. Measurement and analysis have now been completed as part of a project in the tree -ring hydrology of the Rio Grande, under contract between the Office of Naval Research, Navy Department, and the University of Arizona (NR089 -020). 'O. E. Sperry and B. H. Warnock, Plants of Brewster County, Texas, Sul Ross State Teachers College Bulletin, v. 22, no. 1, 1941, p. 21. Alpine, Texas. TREE -RING BULLETIN 19 Almost all of the mature Douglas -firs and a few young trees in the area were sampled, yielding 19 cores. Two pinyon pines (P. cembroides) were also sampled, but since examination of the ring records indicated doubtful datability no effort was made to obtain an extensive group. The only other conifer here, Arizona cypress, was disregarded, for repeated testing had shown that species to be entirely unreliable for chronology studies, even in its most favorable environments. Before the superiority of Douglas -fir for chronology had been generally established, Dr. C. T. Elvey of the McDonald Observatory, during an eclipse expedition to the Chisos Mountains in April, 1940, secured a number of increment borings in pinyon, yellow pine (P. ponderosa), and weeping juni- per (Juniperus flaccida), in Pine and Blue Canyons, and kindly forwarded them for analysis. The sequences proved undatable, owing to very difficult false rings and erratic growth characteristics already familiar in many species and stands in southern Arizona.

DATING On first examination the group of Douglas -fir cores seemed undatable, for it was at once evident that an extraordinary number of false rings was present and the lack of agreement in chronology suggested either numerous locally absent rings or erratic growth. Of the hundreds of groups of tree borings collected and analysed by the writer which have yielded significant chronologies this was perhaps the most difficult; yet when the dating problems were all solved and analysis completed, this group was found to be the most sensitive set in our collections. The analysis of the false rings in the Big Bend Douglas -firs is treated in a separate section below. Locally absent rings were very common. An unusual problem was presented by the absence, in a number of specimens, of the outside ring, that for 1945 -a source of much confusion at first.In the six longest records (245 -300 years) an average of 6.5 missing rings was noted for the outer seventy -five years, one core showing eleven such cases. Such high incidence of ring disturbances would be fatal for potential climatic chronologies in the absence of a high degree of consistency among the ring records.For- tunately, such consistency is present, as the diagrams below will show. All of the nineteen sampled Douglas -firs proved to be datable. Fivecores were not measured because of breaks in the ring record, due to rotted sec- tions or to intervals too difficult to date with sureness because of absent rings. Only the inner century of tree2138, the longest record, with inner ring at A.D. 1645, was measured. It was datable throughout except for the interval 1830 -1870, which indicated eight absent rings whose precise identi- fication could not be made. The remaining thirteen were measured and grouped in sets, as follows: Set No. 1.250 -ring class.Center dates 1676,1678,1682,1690,1700. Set No. 2.200 -ring class.Center dates 1720,1733,1741,1748,1748. Set No. 3.125 -ring class.Center dates 1793,1820,1845. 20 TREE -RING BULLETIN A concentration of tree ages near the upper limit for the stand may be noted. The range in center dates for the five trees not measured is 1685 to 1720. Since all samples were taken at breast height, since all but the three shortest series of Set No. 2 show central rings at or near the pith, and since differing rates of height growth to the boring level would account for some of the age differences, it appears likely that all but three of the nineteen trees have true ages near the range 250 -300 years.It may also be noted that the relatively low upper limit of age in this stand as compared with the 700- and 800 -year limits in many areas of Utah and Colorado is consistent with what has been observed in series from southern Arizona and New Mexico. CROSSDATING AND CLIMATIC CHRONOLOGY The extraordinarily high quality of crossdating and sensitivity in the Big Bend Douglas -firs is illustrated in the growth curves in Figure 1.It may be recalled here that, as standard procedure, which long experience has shown to be desirable, the dating of ring records from living trees always precedes their measurement. Growth fluctuations since 1850 in the five longest unbroken series (Set No. 1) show very near perfect parallelism. The three series representing relatively young trees are, on the whole, only slightly less consistent, but show occasional deviations of climatic signifi- cance, which will be examined in some detail; they are plotted in Figure 1 in order to aid in checking, as they did during the dating process, the placement of locally absent rings. Year -by -year mass review of the plotted

1850 60 70 80 90 1900 10 20 30 40 MM. 1.0 -

_ 2119 0.5

0.0 - 0 0 _ 2123 o.s

0.0 - 0 _ 2124 as - - 00 a0.0- _ 2126 05 o.o- 0 0 0 2127 0.5 - 0.0-

_ 2(33 1.0 -

o.o -

_ 2118 1.0 -

- o.o -

_ 2131 0.5 - oo 0.0- Figure 1.Nearly parallel fluctuations in ring- widths of five old Douglas -firs (upper) and three young Douglas -firs (lower) at Big Bend National Park. The co- ordinate grid may be readily completed by connecting the marginal divisions; zeros below the curves represent locally absent rings. TREE -RING BULLETIN 21 growth curves will show that such placement -always a great responsibility, since it is in essence a forecast -is in almost all cases quite secure on the basis of ring -width alone; in actual practice, of course, other evidence is brought to bear:additional specimens, late -wood characteristicsinrings neighboring the suspected locally absent one, etc.

Table 1. Mean Ring -Widths of Douglas -firs at Big Bend National Park, Texas. Unit .01 mm.

A.D. 0 1 2 3 4 5 6 7 8 9 1700 150 98 132 18 73 106 113 36 71 134 1710 31 104 44 29 71 46 21 114 72 50 1720 214 140 221 190 84 226 99 84 84 58 1730 00 46 110 86 151 296 222 273 202 64 1740 175 127 48 77 89 69 150 208 109 63 1750 60 84 41 23 39 34 68 35 67 88 1760 56 138 160 72 74 52 86 86 134 185 1770 174 127 70 80 44 103 63 78 33 36 1780 80 21 59 51 83 22 32 25 78 01 1790 17 57 62 111 79 102 98 63 30 100 1800 65 01 67 84 42 08 61 37 15 52 1810 55 45 11 19 72 29 102 56 45 11 ].820 58 92 61 14 108 68 132 137 106 98 1830 81 39 43 71 64 94 89 106 80 84 1840 09 19 45 80 90 107 124 30 94 59 1850 67 32 22 79 12 51 75 40 102 21 1860 21 50 08 28 32 40 44 16 32 80 1870 40 35 03 42 33 20 54 48 40 11 1880 19 82 64 43 15 63 00 36 81 47 1890 10 65 11 28 11 11 59 10 22 20 1900 36 75 09 91 18 65 70 54 112 18 1910 00 61 45 16 32 64 07 54 39 48 1920 56 43 08 57 55 04 60 33 09 45 1930 10 52 06 47 20 19 52 43 30 39 1940 46 48 33 25 48 05

The mean growth for the five trees of Set No. 1 is given in Table 1 and is compared in Figure 2 with the longest nearby rainfall records. Unfor- tunately, gage records for the Park itself are as yet very short, the nearest unbroken record of length being at El Paso, over 250 miles n.w.; however, this supports the Fort Davis series, which is only some 90 milesn.n.w. 22 TREE -RING BULLETIN

1870 80 90 r 1900 I0 20 30 40 IN NOV.-APRIL RAIN: 5 EL PASO IN. ^ A - 5 i \ A 11 IA A I\ .0- ` 1, y1 n FT. DAVIS `,N -.,r1\\ . . k _

- IO- OCT.-JUNE RAIN: I; - EL PASO I 5- , 1 1 IO' 11 A ,....4 1I 1 ' I ' p- - 1 1 re I Y 1^v 11 I ,. 1 1 / 1 FT. DAVIS i i '. y i r ' 1 5- 1 f 1 ,1/ 1y`' - v 0 -Y , --- - MM. - I.0- ANNUAL RING: as - - BIG BEND 5 - 0.0 - -N. - IO- MAY-JULY RAIN: 5 - EL PASO II - IN. ¡ I h 10- II 0- i 1 A NI / 11I .i , ri r r FT. DAVIS j , r.,¡ - .''I ` - v - 0 - Figure 2. Ring growth in Douglas -fir at Big Bend tends to parallel the march of winter rainfall in west Texas as indicated by two relatively distant stations. Inspection of the diagram indicates only a modest growth -rainfall relation at best, the interval October -June, as elsewhere, proving superior to shorter intervals. It is perhaps obvious, however, that the Big Bend trees provide a better index of local rainfall than is evident in Figure 2, for the distance factor acts strongly in this region of variable and spotty rainfall. It is possible, also, that the assumed October -June rainfall interval as that of maximum effect on tree growth should be extended, particularly to in- clude the rains of the preceding summer, as is suggested by a recent survey reported in the first paper in this Bulletin. Only a Park weather record some decades in length, however, would permit a significant study ofthis, in view of the particularly local nature of summer storms in the Southwest. Mean growth curves representing all three age classes in the Big Bend Douglas -firs are plotted in Figure 3.Careful visual inspection of such mutually independent series enables one to form a secure judgment as to the reliability of the growth records in terms of climatic history, insofar as this is possible for trees from only one locality and of one species. The isolated position of the Big Bend Douglas -firs precludes the develop- ment of a regional growth index. However, the relatively distant compar- ative series plotted at the top of Figure 3 offers some evidence for general- ity in the chronology at Big Bend. The excellent index for the Guadalupe Mts.2, 200 miles n.n.w. of Big Bend, closely parallels the latter record in most decades and thus strongly suggests that the same climatic element is operating in both sequences. Figure 4, from an unpublished report in 1944, Tree -Ring Bulletin, v. 8, p. 27, 1942, group no. 10. 1700 10 20 30 40 1750 80 90 10 20 30 40 60 70 80 90 10 20 30 40 -Average Ring-width: GUADALUPE MTS.,N.ME%-TE%AS 5I ( J1]. 1 0 1850 1900 MM.Lo 1950 r I1 3 r` ^I P , I I _.M /1 1A.1, 0.00.5 . BIG BEND, SET ,, 3 1 / . . . / / z:o0 ° 5 , 11 1 . .I,,,1 1'I(1' Lo . , BIG BEND, SET 2 i 1 I AA _ o.o05 BIG BENO. SET I Irfi , pf,,Ii".l'' Y , I . . I 1 1 IÌI ,, 1 í\IrJl,11, , 1 . I os 0° EL SALTO, MEXICO 2I . W'i , !, I u . A , . ,'rA r y1 a a . A , \ A1" .. 0U05 . . ' ,°A,I\ I 23 ' 27 -'Standardized Means: 3 IL 1 / l'. ' \ n - o a ' pp, S0. ARIZONA 14 r . ' ' r- 14111 \`1 .IV1 .. . . V i J' - 1, ' i a 150 BIG BEND. TEXAS ( 1 1 1 ' 1 , I 1 . I , Sa I 1 ., .1.`!i ' I . ' i ' Jt1A1 150 f. 1 I ,A , PECOS, N.MEX. mil i I 1 17' M. 1r 1 ' I N ' l I I 1 III'1 ! r:, y n I 1 iI11 I I r I / , I - II P' r 1700 I .1 20 30 40 II,,1750 I 60 70 Wir 80 9O ' 1800 10 20 30 40 .1 1850 60 70 60 9p 1900 , 10 ' , 20 1 .30 IIr 40 1 19$0 panel;distant.Figure the3. The The mean number chronology line, ofat component100%, in Douglas is drawn trees -fir on is at notedthe Big standardized Bend above is thesignificantly curve. Eye related -fitted to trend the recordslines I1W/ curves in the lower panel. 'r are superposed on the curvesin inthis ''II'the species upper i',Ir', in areas 200 to 450 miles Al ' miii .-.I' 'I1' . NC0 24 TREE -RING BULLETIN

/n Qt -Tune Precipfation 20- CLOUD CROFT elev. 8650 Ft. ./ 0 -

CARLSBAD ° elev. 3,IZ0 Ft. iOa.E 0- 0.75 River Pencil, v./color-yea!: 050

PECOS.R.nr. Artesia, N.M. US mm. 000 Tree Growth"0 aso- ,/l, GUA 000850 00 70 80 90 /900 /0 20 30 40 Figure 4. Douglas -fir growth in the Guadalupe Mts., New Mexico -Texas, varies in close parallelism with the recorded river flow and winter rainfall in nearby areas. shows this element to be very largely winter rainfall; the Guadalupe trees also provide a fair index of the water -year runoff of the Pecos, though the plotted flow represents a drainage basin well north of the tree sites and uncorrected for considerable depletions above the gaging station. Returning to Figure 3, we note in the lower panel a strong tendency for the Big Bend chronology to parallel that for southern Arizona, nearly 400 miles to the w.n.w.This is perhaps not surprising, despite the distance and the separation by the Continental Divide, for the latter is low in these latitudes, the paths of many winter storms are aligned approximately west - east, and the spotty summer storms of a given year on the whole seem to affect only slightly the ring of that year inmaturetrees (see below) . Another comparison with the Big Bend record is afforded by the long Pecos chronology, from an area some 450 miles n.n.w., discussed in Table 1 of the companion paper in this issue. The outer half of the Pecos record, plotted in the lower panel of Figure 3, parallels the Big Bend chronology only faintly in many decades, and as a whole shows decidedly lower agreement with it in the trend of year -to -year fluctuations than does the southern Arizona series. It is decidedly a surprise to find the tendency, evident in Figure 3, for the chronology in the Big Bend Douglas -firs to parallel that in the high Sierra at El Salto, Durango State in Mexico,' some 300 miles s.s.w.The relation is weak, but too persistent to be disregarded. The march of rainfall in the coniferous forests near El Salto, 8,000 feet or more in elevation, is not available but would appear to have only a slightly greater winter component than that at Mazatlán, about 60 miles west and at sea level, where about 80jó of the annual rainfall occurs in July- August -September. If one judges by the longer records in western Texas, the comparable proportion at the main Douglas -fir grove in Big Bend Park is little if any over 50 %. Although no final conclusions may be made pending a solution of the Mexican chronologies in terms of climate, in light of the above -noted tendency for crossdating between the two areas it would appear probable that (1) a substantial effect of the summer rains is present in the Douglas- fir chronologies and (2) specially strong tendencies for south -north orienta- tion of storm tracks through the two areas exist in many years. Tree -Ring Bulletin, 10: 18 -24, 1944. TREE -RING BULLETIN 25 FALSE RINGS AND LATE WOOD It has long been recognized that false annual rings in trees tend to occur more frequently in the lower latitudes.' With respect to Douglas -fir, such rings are quite uncommon and readily identifiable in chronology groups from southern Colorado and Utah, and, for all practical purposes, are nonexistent farther north. In Arizona and New Mexico, however, false rings become more frequent, though usually offering far less difficulty in recog- nition than similar ring details in pines of these latitudes. Despite the numerous and occasionally quite annual -like form of the false rings in the Big Bend Douglas -firs, it was found that all, without exception, could be recognized under proper surface lighting conditions.' In the case of the three younger and relatively fast -growing trees, averaging about 150 yeas in age, a very high proportion of the annual rings were doublets or triplets; the oldest trees had, characteristically, only occasional, weak extra rings. Since the transition from early -wood to late -wood growth in the annual rings of the three youngest trees was in most cases quite abrupt, it was possible to measure each component separately. A somewhat arbitrary criterion had to be set up for the amount of late wood in the numerous rings which included false bands. Since experience elsewhere in the South- west had indicated that false rings were related to the July and, to a lesser extent, the August rains, and since the onset of normal late -wood growth in the timber conifers is in July, all growth following the first late -wood cells was classed as late wood, no matter how apparently complete the return to early -wood type before the final cells of the season were laid down. In occasional rings the transition from early wood to late wood was very gradual or irregular and the estimated division into the two categories quite unreliable. Such rings, of importance in judging the plotted curves below, occurred as follows: BBN 2118: 1853,1858,1861,1882,1888,1903. BBN 2131: 1851,1862,1926,1930,1931. BBN 2133: 1853,1861,1864,1869,1872,1882,1888,1903,1926,1928. The degree of tree -to -tree crossdating in both early wood and late wood is shown in the upper panel of Figure 5 to approch in quality, though it does not equal, that for the total annual ring -growth. When, however, the mean partial -ring growth for the three young trees* is compared, in panel B, with the total ring- growth of the five old trees of Set 1, it is evident that the chronology in late wood departs widely in many years from that of total annual growth in the old trees; in contrast, the early wood tends to crossdate closely with the old -tree chronology. Since the average late wood is only 30% of the corresponding early wood in thickness, the difference in crossdating is, of course, largely a result of the dominating effect of the latter in total ring -width. There does not appear to be any tendency for compensating changes in early -wood thickness for such years of extreme variance in late -wood chronology as 1852, 1862, 1881, 1895, 1896, 1914, 1915, 1917, 1919, 1929, 1933, 1935, and 1943.Thus the extra late wood of the young trees appears to be additive, and presumably represents some favoring con- dition to which older trees could not fully respond. "In order to allow each curve to enter the means with approximately equal weight, a factor of 1/2 was applied to the BBN 2133 early -wood series and a factor of 2 to the BBN 2131 late -wood series; thus the mm. scales for the two partial -ring mean curves do not represent average growth. 'D. P. Penhallow, The Relation of the Annual Rings of Exogens to Age, Canadian Rec. of Science 1: 162 -175, 1885. 'Cf. Douglass, Tree -Ring Bulletin, v. 6, 1940, p. 24. 1850 s0 70 80 90 1900 io 20 30 40 M M. A. 1.5- -EARLY WOOD: 2133 1.0-

05-

1.0-

2118 0.5 -

1.0-

2131 0.5-

1.5 -

1.0- -LATE WOOD: 2133 05 -

1.0-

0.5- 2118

0.0-

0.5- 2131 00 0.0 -B. 1.0- EARLY WOOD 0.5- 3 TREES 0.0-

- LATE WOOD: 05 - 3 TREES 0.0 -

_ ANNUAL RING: 0.5- 5 OLD TREES 0.0 -

-C.

_ RATIO, 150 - LW /EW: j-- loo - 2131 50 - 00-

150 -

2133 100 - 50 -

00 - 1850 80 70 80 90 1900 10 20 30 40 Figure 5. The parallelism in partial -ring chronology from tree to tree in the Big Bend Douglas -firs is marked (panel A) ; early -wood shows better crossdating with total ring -growth than late -wood (panel B) ; the ratio of late -wood to early -wood emphasizes occasional major disagreements from tree to tree in partial -ring chronology (panel C) . TREE -RING BULLETIN 27 The ratio of late wood to early wood in the Big Bend Douglas -firs (panel C) does not provide an improved crossdating tool, as it does in the pines of Arkansas.6 'To test the probability that the factor which stimulates extra late -wood production in young trees is a favorable summer rainfall, late wood is plotted in Figure 6 against July and July- August rainfall for Ft. Davis and

- 1870' 80 90 1900 10 20 30 40 -

JULY RAIN: 11 - EL PASO I i 5- IN. i l A 5'`V1 I i r' I O- , e° FT. DAVIS L^¡'V^r`! ,y/ ,e"°"'^1¡. i 0- -

MM. LATE WOOD: 3 ^I /, /i 0.5 - BIG BEND IIV WNV, oo_ - IN 10 - JULY-AUG. RAIN:1 _ EL PASO ¡ 5- IN. i1 I1 10 y; i ¡ f 0- FT. DAVIS I , 1 il 11 I , IA I1 o. I Ir, a r,... i v I , 5 - 1 / \1\1 / , e^.r ' - , V V V / J ;, - - Figure 6. The absence of a clear -cut relation between late -wood growth at Big Bend and summer rainfall in west Texas may be related in part to the distance between the growth and rainfall stations. Pecos. On the whole, a very slight suggestion of late -wood dependence on July rain and no effect of August rain may be noted; the problem deserves further study when local rain -data become available. SOME CLIMATIC CHARACTERISTICS If we may assume that the direct and indirect evidence presented above permits us to interpret the Big Bend growth- records as fairly representa- tive of fluctuations in local rainfall, some properties of the 246 -year indices in addition to the history they provide of water -supply at Big Bend Park, are: 1.The growth index is primarily that of winter rainfall, some effect of the July rains of the year of growth and the entire summer rains of the year preceding the growth being probable but not presently prov- able. 2. No single, regular recurrence tendency exists in the succession of wet and dry winters. 3. The median interval between general maxima falls between five and six years. 4. There is a tendency, in some decades strong but in others non -existent, for rainfall at Big Bend Park to fluctuate in parallel with that at El Salto, Mexico, some 300 miles s.s.w., during the two and one -half cen- turies of record; since the rain season for ring growth at El Salto is unknown but may well have a strong if not dominant summer component and in light of (1) above, there is evidence, which deserves further study, for systematic long -period changes in the general cir- culation of the atmosphere in this little documented border zone. `Dendrochronology in Pines of Arkansas, Ecology, 23:309 -318, 1942.