White Pine Decline in Maine

Transcription

1 White Pine Decline in Maine M. Fries, W.H. Livingston Department of Forest Ecosystem Science University of Maine C. Granger, H. Trial, D. Struble Forest Health and Monitoring Division Maine Forest Service S. Howell S.W. Cole Engineering, Inc. Bangor, ME December 2002

2 Background Tree decline and mortality from Southern Maine Scattered locations Simultaneous appearance Dense, pole-size stands

3 BACKGOUND CON T Field abandonment By 1940 total number of farms in Maine declined by 80 % From over 7 million acres converted back to forest Consequences Plow pans Soil compaction Rooting restrictions

4 Rooting Habits of White Pine White pine rooting depth inhibited by: Plow pans Lithological discontinuity (abrupt texture change from fine to course) Shallow water table or bedrock Steve Howell, 2000 Brown and Lacate, 1961 White pine roots will grow deep if soil-structure inhibitors not present

5 White Pine Decline: Hypotheses Predisposition to drought stress Shallow rooting depth potential High stand densities Poor prior growth Drought prior to 1997 initiated decline

6 Methods: Sampling Oxford Nobleboro Casco Limington New Gloucester Hollis Portland Lebanon Massabesic Wells Paired sites in nine locations High mortality Low mortality

7 Methods: Sampling Site Design Modified Forest Health Monitoring (FHM) - 4 adjacent circles - Each 48 in diameter 48 ft

8 Summary of Methods for Evaluating Hypotheses Hypothesis - Shallow soil restrictions predisposed white pine to drought - Measure and characterize soil restrictions Hypothesis High stand density and poor prior growth also predispose white pine to drought damage - Compute stand density - Measure prior growth using tree ring analysis Hypothesis - Drought prior to 1997 initiated decline - Examine climate data - Ascertain year of last growth on dead trees using tree ring analysis

9 Mortality High mortality = 31% of stems Low mortality =2% of stems Significantly different Depth to rooting restriction High mortality = 24.6 cm Low mortality = 44.8 cm Significantly different Results

10 Decline Associated with Shallow Soil Restrictions (<30cm) Plow pan (2 sites) Water table (1 site) Bedrock (1 site) Lithological discontinuity (5 sites, 3 with plow layer) Harvard Forest Diorama

11 High Mortality Plots Compared to Low Mortality Plots Before mortality Smaller DBH More stems Initial BA similar After mortality understocked for size class density similar to low mortality plots (Philbrook et al 1979)

12 Growth of Surviving Trees Number of years of declining growth, in surviving trees did not differ between plot types High mortality sites: 2.8 Low mortality sites: 2.4 Growth trends in surviving trees in high and low mortality plots did not differ

13 Prior Growth of Dead White Pine Period of reduced growth >24 yrs (7 of 8 sites) Ages similar (43 vs 45 yrs) Smaller DBH (19 vs 25 cm) Increment growth of dead vs. surviving trees at Limington Legend O Dead trees (n=29) - Surviving Trees (n=13) I Standard Error

14 Year of Last Last year of growth % dead trees high mortality % dead trees low mortality Growth % Increment Percent of dead trees sampled Peaked in % 9% 31% 33% 19% 67% 33% % % %

15 Prior to 1997, 1995 Worst Drought Year Standardized Stream Flow Standardized Stream Flows for Little Androscogin (Number of standard deviations from 89 yr mean) May June July Aug. Sept. Oct. Month

16 Drought Prior to 1997 Standardized Stream Flows Indicate Severe Regional Drought in 1995 Year Little Androscoggin Oyster Sheepscot AUG SEPT AUG SEPT AUG SEPT

17 1995 Standardized Stream Flows Drought localized to southern Maine and far northern Maine Station Yr. of Record May June July Aug. Sept. Oct. St. John (north) Mattawamkeag (north) Narraguagus (east) Saco (NH mt.) Carrabassett (mt.) Sandy (mt.) Little Androscoggin Sheepscot Oyster

18 Climate Data Location of stream gauge stations and weather stations

19 Other Considerations Biotic Stress 88 trees sampled at DBH and roots Dominant Few needles, red needles, no needles % of trees with pests 63.6% Cerambycidae 60.2% Ips spp. 56.8% Armillaria spp. All secondary in nature Ips bark beetle Armillaria root rot

20 Plowing changed soil characteristics that predispose pine to decline Plow layer Lithological discontinuity Pine regenerated on sites to which it is not adapted High water table Conclusions: Field Abandonment Created Conditions Leading to White Pine Decline Shallow bedrock Mortality present where field abandoment was highest in south but not in north Harvard Forest Diorama

21 Density might be an additional predisposing factor Mortality thinned-out poorly growing trees Surviving trees growing normally Drought is the likely inciting stress in white pine decline 1995 year of severe drought in southern Maine period for years of last growth period of visual mortality Conclusions Steve Howell, 2000