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Abstract. This paper characterizes the reproducing kernel Hilbert spaces with orthonormal bases of the form {(a n,0 + a n,1 z + · · · + a n,J z J )z n , n ≥ 0}.The primary focus is on the tridiagonal case where J = 1 and how it compares to the diagonal case where J = 0. The question of when multiplication by z is a bounded operator is investigated and aspects of this operator are discussed.In the diagonal case Mz is a weighted unilateral shift. It is shown that in the tridiagonal case this need not be so and an example is given in which the commutant of Mz on a tridiagonal space is strikingly different from that on any diagonal space.

Red spruce (Picea rubens Sarg.) suffers frequent and extensive injury to current-year foliage during the winter. Experimental freezing of red spruce foliage at cooling rates > 10 degrees C min(-1) induced visible symptomatology similar to natural winter injury at the branch, needle and cellular levels. Such damage was associated with a low-temperature exotherm near -10 to -12 degrees C, a loss in needle fluorescence, massive cellular disruption, foliar discoloration, and low needle survival. Susceptibility of individual trees to rapid freezing injury was associated with historical winter injury patterns and alterations in foliar nutrition. We conclude that anthropogenic deposition may alter the sensitivity of trees to winter injury caused by rapid temperature changes.

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