Oak-Pine-Hemlock Silviculture: Some Preliminaries

Transcription

1 Oak-Pine-Hemlock Silviculture: Some Preliminaries Mark Ducey, University of New Hampshire Preliminary Topics Natural and Human Disturbance Regimes Single-Tree Selection what it is, what it isn t Quantitative Stocking Control do we need it? what would it look like? 1

2 Preliminary Topics Natural and Human Disturbance Regimes Single-Tree Selection what it is, what it isn t Quantitative Stocking Control do we need it? what would it look like? Cogbill et al

3 Pine Oak Hemlock Silviculture Institute 7/18/2017 The New Thing (?) The New Thing (?) 3

4 The New Thing (?) Toumey, The Foundations of Silviculture Upon an Ecological Basis,

5 Evidence demonstrates convincingly that such forests were dominated by relatively frequent, partial disturbances that produced a finely patterned, diverse mosaic dominated by late-successional species and structures. In contrast, large-scale, catastrophic standreplacing disturbances were rare (Seymour et al. 2002) 5

6 Let s explore that 1. Northeast in this paper does not include the oak/pine portions of New York and New England. We searched the literature for studies of disturbance regimes in the northeastern quarter of North America. The region, which we will call the northeast, extends from Nova Scotia through New Brunswick, southern Quebec and southeastern Ontario, and from northern New England westward through New York, north-eastern Pennsylvania, and the upper Lake States. The forest types emphasized lie within the temperate forest zone or transitional to the boreal zone, and include northern hardwoods and mixed-species forests in the Acadian region (Seymour, 1995). Studies from the boreal zone, and fire-dependent communities such as Populus spp. and various Pinus spp. common in the Lake States, were excluded. Let s explore that 2. A large body of evidence indicates frequent, catastrophic wind disturbance in southern and coastal New England. F2: Significant damage. Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; highrise windows broken and blown in; lightobject missiles generated. Boose et al. 2001, redrawn in Lorimer and White

7 Boose et al Let s explore that 3. How is natural defined? Here, we adopt Hunter s (1996) definition of natural as meaning without human influence Russell 1980 Human-associated disturbance is not included in the study. 7

8 The preponderance of evidence suggests that Native Americans land-use practices promoted the distribution and importance of mast and fruit trees prior to European settlement. This occurred through direct and indirect means, such as land clearing for agriculture, broadcast burning of vegetation, the abandonment of villages and agricultural fields, and the planting, transport and cultivation of favoured tree species. Native Americans lived throughout the eastern biome at reasonably high population levels, and it is difficult to discern any large tracts of land that were not directly or indirectly impacted by them. -- Abrams and Nowacki (2008) The American land was more like a widow than a virgin. Europeans did not find a wilderness here; rather, however involuntarily, they made one. Francis Jennings Let s explore that 4. How is stand-replacing defined and how should we interpret it in action? At the other end of the spectrum are catastrophic fires and windstorms Although often considered stand-replacing, they can create gaps as small as 2 ha or less or as large as 80,000 ha The larger recorded sizes [of fires] might not have included total destruction of the canopy throughout the burn, however. 8

9 Donald Davis, for NASA; released into public domain. What Do We Know? Pre-European Variable patchwork created by wind and fire Frequent individual-tree disturbance; messy and less frequent stand-replacing disturbance Scale, frequency, and pattern modulated by regional location and human landuse (settlement, agriculture, fire) Many exceptions to rules Modern Coarser, more uniform patchwork Frequent individual-tree disturbance; handful of historic regional standreplacing disturbances Scale, frequency, and pattern heavily influenced by 19 th -century agriculture, abandonment, subsequent harvesting Fewer large (16 +) trees, probably fewer young forests Many early-successional areas converted to other land uses 9

10 Preliminary Topics Natural and Human Disturbance Regimes Single-Tree Selection what it is, what it isn t Quantitative Stocking Control do we need it? what would it look like? History of Silviculture in the U.S. (Seymour 2005) Custodial Era ( ) Selective Cutting Era ( ) Multiple-Use, Production Forestry Era (1960s-1990s) Balanced Forestry Era (1990s-???) 10

11 A Dilemma Past? By this time, the profession had almost universally embraced selection cutting as a universal panacea. In part, this was a strong reaction against clearcutting, because this form of logging had become so closely associated with exploitation that any support of its legitimate applications would have threatened the profession s growing public support and mandate. By the 1950s, the negative legacy of the selective cutting era was becoming increasingly apparent... Poor markets and limited logging technology had too often led to high grading via diameter-limit cutting; smaller d.b.h. classes had not been tended, and regeneration had often been ignored. Oliver-Larson Stand Dynamics Model I. Stand Initiation II. Stem Exclusion (single-cohort stratified mixtures) III.Understory Reinitiation (two-cohort stands) IV. Old-Growth (multi-cohort stands) What is an appropriate balance between stages? What silvicultural approaches can create and maintain that balance? 11

12 Single-Tree Selection Uses small gaps (one to a few canopy trees) Regeneration and harvest continuous in space and time Intimate, multicohort mixture Use of diameterbased control common Trees/acre Basal Area, ft 2 /acre DBH DBH Some Challenges Not all reverse-j stands are uneven-aged or multi-cohort Having, or achieving, a desired reverse-j is not the same as attaining the desired dynamics Success of a selection system requires success in regeneration and maintenance of growth in smaller trees This is harder than making a bar chart Even if natural stands were intimate, multicohort structures, single-tree selection may not mimic dynamics 12

13 Tree Diameter and Crown Size Pre-European Dominant Tree: 36 DBH Eastern White Pine Crown radius approx. 23 feet Canopy gap nearly 0.04 acres Selection-System Dominant Tree: 18 DBH Eastern White Pine Crown radius approx. 12 feet Canopy gap about 0.01 acres The Evidence Openings should be 0.3 ac or larger to encourage mixedspecies regeneration Use patches (remove small trees), not just groups Diameter distribution not particularly helpful as a guide; focus on area 13

14 Preliminary Topics Natural and Human Disturbance Regimes Single-Tree Selection what it is, what it isn t Quantitative Stocking Control do we need it? what would it look like? Langsaeter s Hypothesis The total production of cubic volume by a stand of given age and composition on a given site is, for all practical purposes, constant and optimum for a wide range of density and stocking. It can be decreased, but not increased, by altering the amount of growing stock to levels outside this range. 14

15 Open Growing Self Thinning Per Tree Closing Up Stagnation Fully Stocked Whole Stand? Goals of Density Indices/Graphs Provide a general indication of where in Langsaeter Space a stand is or will be Combine number and size of trees Potential uses: Description Prescription Projection and Planning HOW DO WE MEASURE DENSITY? 15

16 How? Trees/ac pretty lousy! Basal Area/ac easy to measure, no good comparing between species/types, not much good between size classes If we had a good normal yield table, we could use volume as a fraction of normal volume (for a given species or species mixture, age or age distribution, site quality) Maybe we could use basal area as a fraction of normal basal area in the same way Bickford et al. (1957) SAF Committee on Stocking One unfamiliar with the problems of measuring stocking might marvel that a committee could exist for 8 years and do anything without producing a definitive report. 16

17 The Next Few Decades Practioners focus on basal area Researchers emphasize translation of Reineke, TAR, and CCF concepts into graphical guides Links to -3/2 law recognized Theoretical bases explored Emphasis remains on single species or well-defined types usually assumed even-aged Adding Functional Traits to SDI SDI=N(D g /25) 1.6 Reineke (1933) ASDI= TF i (D i /25) 1.6 Curtis (1971) RD= TF ij (a+bsg j )(D i ) 1.6 Ducey & Knapp (2010) Coefficients a and b are chosen so RD=1 at A-line or normal stocking, irrespective of species composition 17

18 RD= TF ij ( SG j )(D i ) 1.6 Equation fit to regional FIA data 0.85 quantile matches Pinus strobus guide, and gives good match to other widely-used regional guides as well Fairly close match to guides for exotic species (larch, Norway spruce) Consistent guidance with Stout et al. when restricted to same species mix But does it help? Improved prediction of ingrowth and mortality in NB forests (McGarrigle et al. 2012) Remeasured old-growth plots show trend toward RD=0.8 except with heavy beech-bark disease (Ducey et al. 2013, Gunn et al. 2014) RD of larger trees is a good predictor of individual growth for many species Still exploring dynamics with longterm thinning and uneven-age study data 18

19 OK, but do we need that? Perfectly good silvicultural decisions can be made without any quantitative data (and bad data can make them worse) Quantitative data and models are useful for Imagining alternatives Communicating and convincing Comparing diagnoses and prescriptions Projecting future outcomes Basal area is just fine in well-defined situations 19