the role of exotic conifer plantations in rehabilitating degraded tropical forest lands a case study...

8/12/2019 The Role of Exotic Conifer Plantations in Rehabilitating Degraded Tropical Forest Lands a Case Study From the Kib

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Fore st Ecologya n dMa n a g e m e n tL S V I R Forest Ecology and Management81 1996) 215-226

T he ro le o f exo t ic con i fer p lantat ions in rehabi l ita ting degradedtropica l forest lands A case s tudy from the K iba le Forest

in U g a n d aRob er t A . F imb e l , Che ry l C . F im be l

Wild li fe Conseruation Society 185th Street and Southe rn Bouleuard Bronx Ne w York NY 10460 USAAccepted 21 July 1995

b s t r a c t

Exotic softwood plantations were introduced into the Kibale Forest of western Uganda in the 1960s and early 1970s toconvert grassland areas into wood fiber producing sites. Following establishment, few silvicultural activities were initiatedwithin these plantings, and today harvesting operations are planned to remove these over-stocked stands to allow for thedevelopment of natural forest communities. During the period May-September, 1994, we inventoried the overstorey andadvanced regeneration in plantations of P i n u s c a r i b e a e and C u p r e s s u s l u s i t a n i c a . Within 92 randomly located 0.01 ha plotsper plantation type, we measured the height and diameter of all stems encountered. The pines supported approximately 1.5times the densi ty and diversity of native woody stems found beneath the cypress 3424 tree and shrub stems ha- l under thepines), while the pines themselves were characterized by stocking levels, mean heights, and canopy closures which werehigher than those of the cypress. We suggest that the greater natural regeneration development observed beneath the pines,when compared with the cypress, is a function of pine development influence upon competition) and stem characteristicsinfluence upon seed dispersal mechanisms).

We then compared our regeneration observations with those reported for unlogged and logged areas of the surroundingnatural forest. Wi thin the sapling class diameter at breast height dbh) less than 5 cm), which accounted for the majority ofthe advanced regeneration under the softwoods, the plantat ions failed to support the same density of tree-species stems asfound in the natural forest 3077 stems ha -l vs. 2177 and 1111 under the pines and cypress, respectively). The number ofstems ha - ~ in the pines approximated those in 25-year-old logged-over areas of the natural forest. Species richness beneaththe conifers appears to approach the number found in the surrounding forest; however, a closer look at the speciescomposition suggest several deficiencies in the composition of the advanced regeneration beneath the plantations especiallywithin the commercial class).Following 25 years of development, the advanced regeneration beneath the plantations especially the cypress stands) isrelat ively impoverished compared to the levels of tree diversity and stocking characteristic of both unlogged and loggednatural forest sites. The conditions beneath the pines however, suggest that a diverse community of native species mayeventual ly exploit this environment through time. The dominance of the fast-growing, light-canopied, N2-fixing A l b i z i a andM i l l e t i a genera, could help to nurture the further development of a well-structured, well-represented secondary forest

* Corresponding author.

Elsevier Science B.V.SSDI 0039-6028 95)03637-7


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2 1 6 R .4 . F i m b e l , C .C. F i m b e l / F o r e s t E c o l o g y a n d M a n a g e m e n t 8 1 1 9 96 ) 2 1 5 - 2 2 6t h r o u g h t i m e . W i t h t h e a p p l i c a t i o n o f s i l v ic u l t u r a l t r e at m e n t s t h e re m a y b e m a n a g e m e n t o p p o r t u n i t i es t o f u r t h e r e n r i c h th eq u a l i ty o f t h e a d v a n c e d r e g e n e r a t i o n b e n e a t h s o f t w o o d p l a n t a t i o ns . W e e x p l o r e f u t u r e a r e a s o f r e s e a rc h t h a t c o u l d c o n t r i b u t eto th i s e n d .Keyw ords: Cupressus lusitanica; Forest management; Pinu s patula; Plantation; Regeneration; Restoration

1 I n t r o d u c t i o n

Re-es tab l i s h ing d ive r s e and p roduc t ive fo r es t s onlands deg raded by p rev ious l and con ver s ion p rac ti cess uch as ag r i cu l tu r e , min ing and logg ing , o r a r easdevas ta t ed by na tu ra l d i s as t e r s , have o f t en p rovedd i f f i cu l t due to de g raded s o i ls and comp e t i t ion f romundes irable species ar res t ing success ional processes(L ie th and Lohmann , 1993) . La rge ene rgy inpu t s inthe fo rm o f f e r t i l i t y amendmen ts , he rb ic ide app l i ca -t ions, w eed ings , and e n r i chme n t p lan tings have o f t enp roved neces s a ry to b r eak th i s s ucces s iona l log jam ,e n c o u ra g i n g th e d e v e l o p m e n t o f e c o n o m i c a l - a n d / o recological- r ich fores ts . Effor ts to es tabl ish nat ives pec ies on to thes e s i t e s have o f t en been abandonedin f avo r o f p lan t ing exo t i c con i f e r s o r f a s t -g row ingN2-f ix ing t rees , in cons iderat ion of thei r adaptabi l i tyto s uch depaupera te cond i t ions (Thomps on e t a l . ,1986; Turnbul l , 1987; Evans , 1992) . In addi t ion tothe i r capac ity to cons e rve and en r i ch d i s tu rbed s o i l s(Yu an d P i, 1985; Jurgen sen e t a l. , 1986; Anderso n,1987; Lu go, 1992a) , exot ic p lanta t ion s provide thea d d e d b e n e f i t o f p r o d u c i n g t i m b e r , p u l p , a n d / o rfue lw ood mate r i a l s in t ime- f r ames cons ide red r e l a -t ive ly s ho r t in compar i s on w i th many na t ive t r eespecies.

In recent years , the potent ia l for p lanta t ions tos e rve a s nu r s e c rops fo r the e s t ab l i s hmen t o f na t ivefo res t s pec ies has been ga in ing r ecogn i t ion ( J o rdanand F am w or th , 1982; H ug hes and S ty les , 1987 ; Lugo ,1992b; Parro tta, 1992, 1993; Lu go et al . , 1993).While the s i lv icul tura l prescr ip t ions required to max-imize b iomas s p roduc t ion w i th in many p lan ta t ionro ta t ion s ys tems have been ex tens ive ly r e s ea rched( s chedu les fo r w eed ing , th inn ings , ha rves t -r egenera -t ion sys tems , e tc . ) , to date , l imi ted work has beendone to exp lo re t r ea tmen t s des igned to max im ize thena t ive fo r es t r ehab i l i t a t ion - r es to r a t ion capab i l i t i e s o fthes e p lan t ings (Lugo , 1992a ; Brow n and Lugo ,1994).

Wi th in the K iba le N a t iona l P a rk in w es te rnU ganda , exo t i c con i f e r p l an ta t ions w ere e s t ab l i s hedon s mal l g r as s l and s i t e s tha t domina te many o f thefo res t r idge tops , The goa l o f thes e p lan t ings w ast imber product ion . Today these p lanta t ions are ap-p roach ing ma tu r i ty , and benea th the i r canop ies theys uppor t dens e and d ive r s e s t ands o f na t ive s ap l ingsand po les . D ur ing the s ummer o f 1994 w e inven to -r i ed th i s advanced r egenera t ion , w i th the ob jec t ivesof : (a) evaluat ing the dens i ty and d ivers i ty of thena tu ra l f o r es t r egenera t ion g row ing benea th 25 -yea r-o ld unmanaged p lan ta t ions o f P i n u s c a r i b e a e a n dC u p re s su s l u s i t a n i c a ; (b ) mak ing genera l compar -i s ons be tw een th i s advanced r egenera t ion and da tar epo r ted by K as enene (1987) and C . Chapman andL. Chapman (unpubl ished data , 1994) for the sur -round ing na tu ra l f o r es t ( un logged and logged ) ; ( c )assess ing the ro le that these p lanta t ion species mightp lay a s nu r s e c rops fo r the r ehab i l i t a t ion - r es to r a t iono f a na tu ra l f o r es t p lan t co mm uni ty . Th i s w ork r ep re -sents the f i r s t s tage in a p lanned long- term s tudydes igned to examine ha rves t ing op t ions , immed ia teimpac t s o f thes e p r ac t i ces on the adv anced r egenera -t ion , and pos t -ha rves t p l an t and an ima l dynam ics .

2 M e t h o d s

2 1 S tudy a r e a

The K iba le N a t iona l P a rk (K N P ) i s 766 km 2 ins i ze , loca ted ju s t eas t o f the Ruw enzor i M o un ta in s inw es te rn U ga nda b e tw een 013 and 041 N and3 0 1 9 - 3 0 3 2 E . T h e n e w l y d e s i gn a t e d K N P e n c o m -pas s es the fo rmer K iba le F o res t Res e rve and a gamecorr idor to the south , serv ing as a br idge to theQ ueen E l i zabe th N a t iona l P a rk . The P a rk r anges inal t i tude f rom 1590 m in the nor th to 1110 m in thes ou th , r ece iv ing an ave rage o f 1470 m m o f p r ec ip i ta -t ion annua l ly , d i s t r ibu ted ove r tw o d i s t inc t r a iny


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R.A . F imbe l , C .C . F imbe l / F ores t Eco logy and Management 81 1996) 21 5-2 26 217s eas ons . Two r i ve r s , t he Mpanga and t he Dura , d ra i nt h e K i b a l e f o r e s t w a t e r s h e d i n t o L a k e G e o r g e .

Ki ba l e Na t i ona l P a rk i s com pr i s ed p r i m ar i l y o fm at u re fo res t , i n t e r s pe r s ed wi t h s e l ec t i ve l y l oggedfo res t , co l on i z i ng fo res t , g ras s l ands , and papy russ wam ps , w i t h exo t i c s o f t wood p l an t a t i ons d i s t r i bu t edam ong t hes e na t u ra l hab i t a t s . The s o f t wood p l an t a -t i o n s w e r e p l a n t e d b y t h e U g a n d a n F o r e s t D e p a r t -m en t i n t he l a t e 1960s and ea r l y 1970s on l ands i nt he p ro t ec t ed fo res t zone t ha t were p rev i ous l y occu -p i e d b y ' u n p r o d u c t i v e ' g r a s s l a n d s . T h e h i s t o r y o ft hes e g ras s lands i s no t we l l docum en t ed , bu t t hey a rebe l i eved t o have b een t he r e s u l t o f long - t e rm ag r i cu l -t u ra l u s e by l oca l peop l e (Ki ngs t on , 1967 ) . A l t houghprog ram s were o r i g i na l l y des i gned fo r t he m a i n t e -nance o f t hes e p l an t a t i ons , t he c i v i l and po l i t i ca lun res t i n Ug anda du r i ng t he 1970s and m uch o f the1 9 8 0 s c a u s e d t h e s e m a i n t e n a n c e p r o g r a m s t o b ea b a n d o n e d . O t h e r t h a n b r u s h i n g f o r w e e d c o n t r o ldu r i ng t he f i r s t 2 -3 yea r s fo l l owi ng t he i r e s t ab l i s h -m en t , no o t he r s i l v i cu l t u ra l p rac t i ces were conduc t edi n t hes e p l an t a t i ons . The cu r ren t po l i cy fo r t he p l an -t a t i ons does no t i nc l ude a m a i n t enance p rog ram , andas s uch , r egenera t i on f rom t he s u r round i ng ' n a t u ra l '

fo res t i s p reva l en t i n t he s ub -canopy and under s t o reylevels .2.2. Vegetation sampling

A t o t a l o f 184 pe rm anen t l y m a rked s am p l e p l o t sf o r m e a s u r i n g o v e r s t o r e y a n d u n d e r s t o r e y v e g e t a t i o nwere e s t ab l i s hed i n s i x s o f t wood p l an t a t i ons ( t h reew e r e Pinus caribeae and t he o t he r t h ree were Cu-pres sus lusitanica . Each s t and r anged f rom 3 t o 5 hai n s i ze , and wi t h i n s pec i es , exh i b i t ed s i m i l a r b i o t i cand e daph i c cha rac t e r is t i c s.2.3. Ove rstorey plots

C i rcu l a r 0 . 01 ha p l o t s (5 . 64 m rad i u s ) were r an -d o m l y c e n t e r e d a t 2 0 - 5 0 m i n t e r v a l s w i t h i n t h es o f t wood p l an t a t i ons , g i v i ng a m ean p l o t i n t e rva l o fone p l o t pe r 1225 m z . The s e p l o t s r ep res en t an 8s am p l i ng i n t ens i t y o f t he s t udy a rea , and n o p l o t wasc l o s e r t han 20 m t o t he s t and edge o r a road . W i t h i neach p l o t t he fo l l owi ng p l an t cha rac t e r i s t i c s wereno t ed fo r a l l s t em s over 1 . 3 m i n he i gh t : s pec i es ,he i gh t , and dbh i n cen t i m e t e r s . In add i t i on , t he pe r -

Table 1Overstorey and understorey vegetation characteristics beneath exotic softwood plantations of Cupressus lusitanica (CL) and Pinus caribaea(PC) in the Kibale National Park, Uganda, Sep tember 1994. The P-value shows the significance level of a one-way ANOVA test fordifferences within and between stands of these two forest types. Values fol lowed by different letters are significantly different at theP ~< 0.05 levelPlant CL l CL2 CL3 PC 1 PC2 PC3 CL PC P-parameter a (n = 37) (n = 24) (n = 31) (n = 37) (n = 24) (n = 31) mean mean value

(n = 92) (n = 92)onifersStems (h a- 1 454 463 417 827 646 620 444a 710b 0.000BA (m 2 ha - 1) 36.6 42.0 55.7 79,8 66.7 64.7 44.4a 71.3b 0.000dbh (cm) 31.6 35 41.3 34.1 35.6 37.6 35.8 35.4 0.664Cover ( ) 79 82 78 86 83 86 80a 85b 0.000Height (m) 24 22 24 35 37 28 23a 33b 0.000LCR ( ) 23 30 27 20 31 31 27 27

Regenera t ionStems (h a- i ) 1535 1545 2780 3089 4709 3019 1958a 3524b 0.000BA (m 2 ha - i) 4.5 0.9 0.8 3.6 8.4 3.6 2.3a 4.8b 0.004dbh (cm) 2.1 1.3 2.1 2.9 2,9 2.3 1.6a 2.7b 0.000Height (m) 3.1 2.3 2.4 3.8 4.2 3.6 2.6 3.9 0.806Species per plot 5.5 6.1 9.4 9.5 12.7 8.1 6.9a 9.9b 0.000Trees spp. per plot 2.9 2.7 5.0 7.3 7.7 4.9 3.9a 6.6b 0.000Shrub spp. per plot 2.3 3.0 3.8 2.8 4.2 3.2 3.0 3.3 0.340Grd. cover ( ) 61 NA NA 70 NA NA 61a 70b 0.018

a BA, basal area; LCR, live crown ratio; grd. cover, ground cover. NA, not available.


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the role of exotic conifer plantations in rehabilitating degraded tropical forest lands a case study...

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