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a r. ties oa anti ao: co rrsn atu ccu aYaa 1 ' 352 M. L. Scott and otll~rs acos.i attb,b • E V V UTtansea a c 0 tJ6 f ~ _ ~ ~ Trmtsect 1 ~ 0 `_.~ ~~... LlJ `_.~~ -~ Tcerrsnct 2 ,~` H I N _1 ~ J ty TranaeR 3 Deep Mining Beg/ns -2 1990 7991 1992 Time transect 2 (T = 0.90, dJ= 26, P = 0.38) and the pooled controls. Mining Effects on Alluvial Water Table Dynamics Surfaces within transecss exhibited consisunt changes in water table levels over the mining interval from 1991 to 1994 (Figure 2). Control transect 4 had a 0.01-m rise in water table level, while individual surfatts ranged from a rise of 0.04 m to a decline of 0.01 m. The water table at control transec[ 1 declined an average of 0.12 m, while declines on individual surfaces ranged from 0.11 to 0.14 m. Transecss affttted by mining (2 and 3) had greater water table declines. Average declines were 0.47 m (surface ranges = 0.45-0.49 m) for tran- xct 2 and 1.12 m (surface ranges = 1.08-1.21 m) for transect 3. Changes in water table elevation were signifi- cantly different from the pooled controls for both transect 2 (T= 25.2, dJ= 21.1, P=.0.0001) and tran- sect 3 (T = 31.8, dJ= 22, P < 0.0001). Quantitative Response of Measured Variables to Changes in Water Table Tree survival rates and stand structure were signifi- candyaffected by sustained declines in the alluvial water table surface >_1 m. In transect 3, average survival over the interval 1991-1994 was 12% (surface range 39'0-769'0) and was signifi~ndy lower (T = 5.6, dJ= 4, P = 0.0049) than the pooled coavols (trarrseco 1 and 4). In contrast, tranxc[ 2, which experienced a water rabic decline of 50.5 m, survival averaged 94% (surface 7993 1994 Flgare 2. Change in water table elevation relative to inr rial, prcmining elevation mea- surtd on 14 August 1990 for selected wells at each transecc Control tratueca are repre- sented by solid lines and min- ing effected transecrs are rep- rexnted by dashed line. range 7596-10096) and was not significantly different from the pooled controls (T = 1.9, df= 9.8, P= 0.086). Average survival was 98% in control [ransect 1 (surface range 92%-100%) and 100% in control transect 4 (Figure 3). Tree morphological and growth variables responded differentially to water table declines. Average changes in Gve gown volume, from September 1991 to November 1994, declined significantly at transect 3 (T= 6.87, df= 4.4, P= 0.0025) but not at transect 2 (T= 0.53, dj= 11.4, P = 0.60) compared with the pooled controls (nansects 1 and 4) (Figure 3). Similarity, stem growth was significantly reduced in transect 3 (T= 3.9, df= 12.5, P= 0.002) but not in transect 2 (T= 0.85, df = 27, P = 0.405) in comparison to the pooled con- trols (Figure 3). On the other hand, normalized branch increments decreased significantly in transect 2 (T=5.05, dj=25, P<O.D001) but not in transett 3 (T=1.2, df=20, P=0.24) (Figure 3). Water table declines had no significant effect on leaf siu (P = 0.38, Table 2) or average specific leaf mass (P = 0.28, Table 2). Temporal Patterns of Tree Responses to Water Table Declines At the end of three years (1994), 88% of the trees had died at the site with the greatest and most rapid water mble declines (transect 3, Figtue 3). The greatest mortality was observed in the second year following initiation of mining (1993). Mortality was p[esaged by declines in live crown volume (Figure 4A and B). A IQI 008